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2016
"Free-energy functional of the Debye-Hückel model of simple fluids"
Piron R et Blenski T, Physical Review E., December, 2016. Vol. 94(6), pp. 062128-. American Physical Society, (2016).
Abstract: The Debye-Hückel approximation to the free energy of a simple fluid is written as a functional of the pair correlation function. This functional can be seen as the Debye-Hückel equivalent to the functional derived in the hypernetted chain framework by Morita and Hiroike, as well as by Lado. It allows one to obtain the Debye-Hückel integral equation through a minimization with respect to the pair correlation function, leads to the correct form of the internal energy, and fulfills the virial theorem.
BibTeX:
@article{Piron2016,
  author = {Piron, R. and Blenski, T.},
  title = {Free-energy functional of the Debye-Hückel model of simple fluids},
  journal = {Phys. Rev. E},
  publisher = {American Physical Society},
  year = {2016},
  volume = {94},
  number = {6},
  pages = {062128--},
  url = {http://link.aps.org/doi/10.1103/PhysRevE.94.062128},
  doi = {10.1103/PhysRevE.94.062128}
}
"High-order moments of spin-orbit energy in a multielectron configuration"
Na X et Poirier M, Physical Review E., Jul, 2016. Vol. 94, pp. 013206. American Physical Society, (2016).
Abstract: In order to analyze the energy-level distribution in complex ions such as those found in warm dense plasmas, this paper provides values for high-order moments of the spin-orbit energy in a multielectron configuration. Using second-quantization results and standard angular algebra or fully analytical expressions, explicit values are given for moments up to 10th order for the spin-orbit energy. Two analytical methods are proposed, using the uncoupled or coupled orbital and spin angular momenta. The case of multiple open subshells is considered with the help of cumulants. The proposed expressions for spin-orbit energy moments are compared to numerical computations from Cowan's code and agree with them. The convergence of the Gram-Charlier expansion involving these spin-orbit moments is analyzed. While a spectrum with infinitely thin components cannot be adequately represented by such an expansion, a suitable convolution procedure ensures the convergence of the Gram-Charlier series provided high-order terms are accounted for. A corrected analytical formula for the third-order moment involving both spin-orbit and electron-electron interactions turns out to be in fair agreement with Cowan's numerical computations.
BibTeX:
@article{PhysRevE.94.013206,
  author = {Na, Xieyu and Poirier, M.},
  title = {High-order moments of spin-orbit energy in a multielectron configuration},
  journal = {Phys. Rev. E},
  publisher = {American Physical Society},
  year = {2016},
  volume = {94},
  pages = {013206},
  url = {http://link.aps.org/doi/10.1103/PhysRevE.94.013206},
  doi = {10.1103/PhysRevE.94.013206}
}
"Dynamic linear response of atoms in plasmas and photo-absorption cross-section in the dipole approximation "
Caizergues C, Blenski T et Piron R, High Energy Density Physics. Vol. 18, pp. 7 - 13, (2016),
Abstract: Abstract We report results on the self-consistent linear response theory of quantum average-atoms in plasmas. The approach is based on the two first orders of the cluster expansion of the plasma susceptibility. A change of variable is applied, which allows us to handle the diverging free-free transitions contribution in the self-consistent induced electron density and potential. The method is first tested on the case of rare gas isolated neutral atoms. A test of the Ehrenfest-type sum rule is then performed in a case of an actual average-atom in a plasma. At frequencies much higher than the plasma frequency, the sum rule seems to be fulfilled within the accuracy of the numerical methods. Close to the plasma frequency, the method seems not to account for the cold-plasma dielectric function renormalization in the sum rule, which was correctly reproduced in the case of the Thomas–Fermi–Bloch self-consistent linear response. This suggests the need for a better accounting for the outgoing waves in the asymptotic boundary conditions.
BibTeX:
@article{Caizergues20167,
  author = {C. Caizergues and T. Blenski and R. Piron},
  title = {Dynamic linear response of atoms in plasmas and photo-absorption cross-section in the dipole approximation },
  journal = {High Energy Density Physics },
  year = {2016},
  volume = {18},
  pages = {7 - 13},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181815001032},
  doi = {10.1016/j.hedp.2015.11.001}
}
2015
"Influence of the plasma environment on atomic structure using an ion-sphere model"
Belkhiri M, Fontes CJ et Poirier M , Phys. Rev. A., Sep, 2015. Vol. 92, pp. 032501. American Physical Society, (2015).
Abstract: Plasma environment effects on atomic structure are analyzed using various atomic structure codes. To monitor the effect of high free-electron density or low temperatures, Fermi-Dirac and Maxwell-Boltzmann statistics are compared. After a discussion of the implementation of the Fermi-Dirac approach within the ion-sphere model, several applications are considered. In order to check the consistency of the modifications brought here to extant codes, calculations have been performed using the Los Alamos Cowan Atomic Structure (cats) code in its Hartree-Fock or Hartree-Fock-Slater form and the parametric potential Flexible Atomic Code (fac). The ground-state energy shifts due to the plasma effects for the six most ionized aluminum ions have been calculated using the fac and cats codes and fairly agree. For the intercombination resonance line in Fe22+, the plasma effect within the uniform electron gas model results in a positive shift that agrees with the multiconfiguration Dirac-Fock value of B. Saha and S. Fritzsche [J. Phys. B 40, 259 (2007)]. Last, the present model is compared to experimental data in titanium measured on the terawatt Astra facility and provides values for electron temperature and density in agreement with the maria code.
BibTeX:
@article{Belkhiri2015,
  author = {Belkhiri, Madeny and Fontes, Christopher J. and Poirier, Michel},
  title = {Influence of the plasma environment on atomic structure using an ion-sphere model},
  journal = {Phys. Rev. A},
  publisher = {American Physical Society},
  year = {2015},
  volume = {92},
  pages = {032501},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.92.032501},
  doi = {10.1103/PhysRevA.92.032501}
}
"Detailed computation of hot-plasma atomic spectra"
Pain J-C, Gilleron F et Blenski T, Laser and Particle Beams. Vol. 33, pp. 201-210, (2015).
Abstract: We present recent evolutions of the detailed opacity code SCO-RCG which combines statistical modelings of levels and lines with fine-structure calculations. The code now includes the Partially Resolved Transition Array model, which allows one to replace a complex transition array by a small-scale detailed calculation preserving energy and variance of the genuine transition array and yielding improved higher-order moments. An approximate method for studying the impact of strong magnetic field on opacity and emissivity was also recently implemented. The Zeeman line profile is modeled by fourth-order Gram-Charlier expansion series, which is a Gaussian multiplied by a linear combination of Hermite polynomials. Electron collisional line broadening is often modeled by a Lorentzian function and one has to calculate the convolution of a Lorentzian with Gram-Charlier distribution for a huge number of spectral lines. Since the numerical cost of the direct convolution would be prohibitive, we propose, to obtain the resulting profile, a fast and precise algorithm, relying on a representation of the Gaussian by cubic splines.
BibTeX:
@article{Pain2015,
  author = {Jean-Christophe Pain and Franck Gilleron and Thomas Blenski},
  title = {Detailed computation of hot-plasma atomic spectra},
  journal = {Laser and Particle Beams},
  year = {2015},
  volume = {33},
  pages = {201--210},
  url = {http://journals.cambridge.org/article_S0263034615000257},
  doi = {10.1017/S0263034615000257}
}
"Réponse linéaire dynamique et auto-cohérente des atomes dans les plasmas quantiques : photo-absorption et effets collectifs dans les plasmas denses".
Caizergues C, Thesis at: Université Paris XI - Paris Sud., (2015).
Abstract: Dans la modélisation de la matière dense, et partiellement ionisée, une question importante concerne le traitement des électrons libres. Vis-à-vis des électrons liés, la nature délocalisée et non discrète de ces électrons est responsable d'une différence de traitement, qui est souvent effectuée dans les modélisations des propriétés radiatives des plasmas. Cependant, afin d'éviter les incohérences dans le calcul des spectres d'absorption, tous les électrons devraient, en principe, être décrits dans un même formalisme. Nous utilisons deux modèles variationnels d'atome-moyen : un modèle semi-classique, et un modèle quantique, qui permettent cette égalité de traitement pour tous les électrons. Nous calculons la section-efficace de photo-extinction, en appliquant le cadre de la théorie de la réponse linéaire dynamique à chacun de ces modèles d'atome dans un plasma. Pour cette étude, nous développons et utilisons une approche auto-cohérente, de type random-phase-approximation (RPA), qui, en allant au-delà de la réponse des électrons indépendants, permet d'évaluer les effets collectifs, par l'introduction de la polarisation dynamique. Cette approche s'inscrit dans le formalisme de la théorie de la fonctionnelle de la densité dépendant du temps (TDDFT), appliquée au cas d'un système atomique immergé dans un plasma. Pour les deux modèles, semi-classique et quantique, nous dérivons, et vérifions dans nos calculs, une nouvelle règle de somme, qui permet d'évaluer le dipôle atomique à partir d'un volume fini dans le plasma. Cette règle de somme s'avère être un outil de premier ordre pour le calcul des propriétés radiatives des atomes dans les plasmas denses.
BibTeX:
@phdthesis{Caizergues2015,
  author = {Caizergues, C.},
  title = {Réponse linéaire dynamique et auto-cohérente des atomes dans les plasmas quantiques : photo-absorption et effets collectifs dans les plasmas denses},
  school = {Université Paris XI - Paris Sud},
  year = {2015},
  note = {http://www.theses.fr/2015PA112042},
  url = {https://tel.archives-ouvertes.fr/tel-011540568}
}
"A study of density effects in plasmas using analytical approximations for the self-consistent potential"
Poirier M, High Energy Density Physics. Vol. 15, pp. 12 - 21, (2015).
Abstract: Abstract Density effects in ionized matter require particular attention since they modify energies, wavefunctions and transition rates with respect to the isolated-ion situation. The approach chosen in this paper is based on the ion-sphere model involving a Thomas-Fermi-like description for free electrons, the bound electrons being described by a full quantum mechanical formalism. This permits to deal with plasmas out of thermal local equilibrium, assuming only a Maxwell distribution for free electrons. For H-like ions, such a theory provides simple and rather accurate analytical approximations for the potential created by free electrons. Emphasis is put on the plasma potential rather than on the electron density, since the energies and wavefunctions depend directly on this potential. Beyond the uniform electron gas model, temperature effects may be analyzed. In the case of H-like ions, this formalism provides analytical perturbative expressions for the energies, wavefunctions and transition rates. Explicit expressions are given in the case of maximum orbital quantum number, and compare satisfactorily with results from a direct integration of the radial Schrödinger equation. Some formulas for lower orbital quantum numbers are also proposed.
BibTeX:
@article{Poirier2015,
  author = {M. Poirier},
  title = {A study of density effects in plasmas using analytical approximations for the self-consistent potential},
  journal = {High Energy Density Physics},
  year = {2015},
  volume = {15},
  pages = {12 - 21},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181815000245},
  doi = {10.1016/j.hedp.2015.03.008}
}
2014
"Analysis of density effects in plasmas and their influence on electron-impact cross sections"
Belkhiri M and Poirier M, Phys. Rev. A., Dec, 2014. Vol. 90, pp. 062712. American Physical Society, (2014).
Abstract: Density effects in plasmas are analyzed using a Thomas-Fermi approach for free electrons. First, scaling properties are determined for the free-electron potential and density. For hydrogen-like ions, the first two terms of an analytical expansion of this potential as a function of the plasma coupling parameter are obtained. In such ions, from these properties and numerical calculations, a simple analytical fit is proposed for the plasma potential, which holds for any electron density, temperature, and atomic number, at least assuming that Maxwell-Boltzmann statistics is applicable. This allows one to analyze perturbatively the influence of the plasma potential on energies, wave functions, transition rates, and electron-impact collision rates for single-electron ions. Second, plasmas with an arbitrary charge state are considered, using a modified version of the Flexible Atomic Code (FAC) package with a plasma potential based on a Thomas-Fermi approach. Various methods for the collision cross-section calculations are reviewed. The influence of plasma density on these cross sections is analyzed in detail. Moreover, it is demonstrated that, in a given transition, the radiative and collisional-excitation rates are differently affected by the plasma density. Some analytical expressions are proposed for hydrogen-like ions in the limit where the Born or Lotz approximation applies and are compared to the numerical results from the FAC.
BibTeX:
@article{PhysRevA.90.062712,
  author = {Belkhiri, M. and Poirier, M.},
  title = {Analysis of density effects in plasmas and their influence on electron-impact cross sections},
  journal = {Phys. Rev. A},
  publisher = {American Physical Society},
  year = {2014},
  volume = {90},
  pages = {062712},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.90.062712},
  doi = {10.1103/PhysRevA.90.062712}
}
"Plasma out of thermodynamical equilibrium : influence of the plasma environment on atomic structure and collisional cross sections"
Belkhiri M, Thesis at: Université Paris XI - Paris Sud, (2014).
Abstract: In hot dense plasmas, the interaction of an ion with other ions and free electrons may strongly affect the atomic structure. To account for such effects we have implemented a potential correction based on the uniform electron gas model and on a Thomas-Fermi Approach in the Flexible Atomic Code (FAC). This code has been applied to obtain energies, wave-functions and radiative rates modified by the plasma environment. In hydrogen-like ions, these numerical results have been successfully compared to an analytical calculation based on first-order perturbation theory. In the case of multi-electron ions, we observe level crossings in agreement with another recent model calculation. Various methods for the collision cross-section calculations are reviewed. The influence of plasma environment on these cross-sections is analyzed in detail. Some analytical expressions are proposed for hydrogen-like ions in the limit where Born or Lotz approximations apply and are compared to the numerical results from the FAC code. Finally, we study the influence of the plasma environment by including it in a new collisional-radiative model named Foch. Because of this environment, the mean charge state of the ions increases. The line shift is observed on the bound-bound emission spectra. A good agreement is found between our work and experimental data on a Titanium plasma.
BibTeX:
@phdthesis{Belkhiri2014,
  author = {Belkhiri, M.},
  title = {Plasma out of thermodynamical equilibrium : influence of the plasma environment on atomic structure and collisional cross sections},
  school = {Université Paris XI - Paris Sud},
  year = {2014},
  url = {http://www.theses.fr/2014PA112268}
}
"Linear response of a variational average atom in plasma: Semi-classical model "
Caizergues C, Blenski T and Piron R, High Energy Density Physics. Vol. 12(0), pp. 12 - 20 - (2014).
Abstract: The frequency-dependent linear response of a plasma is studied in the finite-temperature Thoma-Fermi approximation, with electron dynamics described using Bloch hydrodynamics. The variational framework of average-atoms in a plasma is used. Extinction cross-sections are calculated for several plasma conditions. Comparisons with a previously studied Thomas-Fermi Impurity in Jellium model are presented. An Ehrenfest-type sum rule, originally proposed in a full quantum approach is derived in the present formalism and checked numerically. This sum rule is used to define Bremsstrahlung and collective contributions to the extinction cross-section. It is shown that none of these is negligible. Each can constitute the main contribution to the cross-section, depending on the frequency region and plasma conditions. This result obtained in the Thomas-Fermi-Bloch case stresses the importance of the self-consistent approach to the linear response in general. Some of the methods used in this study can be extended to the linear response in the quantum case.
BibTeX:
@article{Caizergues2014,
  author = {C. Caizergues and T. Blenski and R. Piron},
  title = {Linear response of a variational average atom in plasma: Semi-classical model },
  journal = {High Energy Density Physics },
  year = {2014},
  volume = {12},
  number = {0},
  pages = {12 - 20},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181814000299},
  doi = {10.1016/j.hedp.2014.04.004}
}
2013
"Models of atoms in plasmas based on common formalism for bound and free electrons "
Blenski T, Piron R, Caizergues C and Cichocki B, High Energy Density Physics. Vol. 9(4), pp. 687 - 695 - (2013).
Abstract: Atom-in-plasma models: Thomas-Fermi (TF) and INFERNO, AJCI and VAAQP, that use the same formalism for all electrons are briefly described and analyzed from the point of view of their thermodynamic consistence. While the TF and VAAQP models may be derived from variational principle and respect the virial theorem, it appears that two earlier quantum extensions of the quasi-classical TF model, INFERNO and AJCI, are not fully variational. The problems of the two latter approaches are analyzed from the point of view of the VAAQP model. However all quantum models seem to give unrealistic description of atoms in plasma at low temperature and high plasma densities. These difficulties are connected with the Wigner-Seitz cavity approach to non-central ions that is present in all considered models. Comparison of some equation-of-state data from TF, INFERNO and VAAQP models are shown on a chosen example. We report also on the status of our research on the frequency-dependent linear-response theory of atoms in plasma. A new Ehrenfest-type sum rule, originally proposed in the quantum VAAQP model, was proven in the case of the response of the TF atom with the Bloch hydrodynamics (TFB) and checked by numerical example. The TFB case allows one to have a direct insight into the rather involved mathematics of the self-consistent linear response calculations in situations when both the central atom and its plasma vicinity are perturbed by an electric field.
BibTeX:
@article{Blenski2013,
  author = {T. Blenski and R. Piron and C. Caizergues and B. Cichocki},
  title = {Models of atoms in plasmas based on common formalism for bound and free electrons },
  journal = {High Energy Density Physics },
  year = {2013},
  volume = {9},
  number = {4},
  pages = {687 - 695},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181813001493},
  doi = {10.1016/j.hedp.2013.06.003}
}
"Variational Average-Atom in Quantum Plasmas (VAAQP) - Application to radiative properties",
Piron R and Blenski T, High Energy Density Physics. Vol. 9(4), pp. 702 - 710 - (2013).
Abstract: We present an application of the Variational Average-Atom in Quantum Plasmas (VAAQP) model and numerical code to dense plasmas radiative properties. We propose an approximate Detailed Configuration Accounting (DCA) approach starting from the variational model of configurations in jellium. This leads to a simplified model which is qualitatively different from those which usually stem from the atom-in-cell approach. It is also shown that, with some additional approximations, the DCA calculation can be handled by use of the Gaussian approximation to perform a statistical approach to the spectrum. Our purpose here is to show that this model provides a simple way to calculate the radiative properties and is likely to give realistic results.
BibTeX:
@article{Piron2013,
  author = {R. Piron and T. Blenski},
  title = {Variational Average-Atom in Quantum Plasmas (VAAQP) – Application to radiative properties },
  journal = {High Energy Density Physics },
  year = {2013},
  volume = {9},
  number = {4},
  pages = {702 - 710},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181813001626},
  doi = {10.1016/j.hedp.2013.07.002}
}
"Density effects in plasmas: detailed atomic calculations and analytical expressions"
Belkhiri M and Poirier M, High Energy Density Physics. Vol. 9(3), pp. 609-617 - (2013).
Abstract: In warm dense plasmas, the free-electron and ion spatial distribution may strongly affect atomic structure. To account for such effects we have implemented a potential correction based on uniform electron gas model in the Flexible Atomic Code. This code has been applied to get energies, wave-functions and radiative rates modified by the plasma environment. In hydrogen-like ions, these numerical results have been successfully compared to an analytical calculation based on first-order perturbation theory. In the case of multi-electron ions, we observe level crossings in agreement with another recent model calculation.
BibTeX:
@article{Belkhiri2013,
  author = {Belkhiri, M. and Poirier, M.},
  title = {Density effects in plasmas: detailed atomic calculations and analytical expressions},
  journal = {High Energy Density Physics},
  year = {2013},
  volume = {9},
  number = {3},
  pages = {609--617},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181813000773},
  doi = {10.1016/j.hedp.2013.05.016}
}
"Testing the reliability of non-LTE spectroscopic models for complex ions"
Hansen S, Armstrong G, Bastiani-Ceccotti S, Bowen C, H-K C, Colgan J, de Gaufridy de Dortan F, Fontes C, Gilleron F, Marquès J-R, Piron R, Peyrusse O, Poirier M, Ralchenko T, Sasaki A, Stambulchik E and Thais F, High Energy Density Physics. Vol. 9(3), pp. 523-527 - (2013).
Abstract: Collisional-radiative atomic models are widely used to help diagnose experimental plasma conditions through fitting and interpreting measured spectra. Here we present the results of a code comparison in which a variety of models determined plasma temperatures and densities by finding the best fit to an experimental L-shell Kr spectrum from a well characterized, but not benchmarked, laser plasma. While variations in diagnostic strategies and qualities of fit were significant, the results generally confirmed the typically quoted uncertainties for such diagnostics of ±20% in electron temperature and factors of about two in density. The comparison also highlighted some model features important for spectroscopic diagnostics: fine structure was required to match line positions and relative intensities within each charge state and for density diagnostics based on emission from metastable states; an extensive configuration set was required to fit the wings of satellite features and to reliably diagnose the temperature through the inferred charge state distribution; and the inclusion of self-consistent opacity effects was an important factor in the quality of the fit.
BibTeX:
@article{Hansen2013,
  author = {Hansen, S. and Armstrong, G.S.J. and Bastiani-Ceccotti, S. and Bowen, C. and Chung H-K and Colgan, J.P. and de Gaufridy de Dortan, F. and Fontes, C.J. and Gilleron, F. and Marquès, J.-R. and Piron, R. and Peyrusse, O. and Poirier, M. and Ralchenko, Tu. and Sasaki, A. and Stambulchik, E. and Thais, F.},
  title = {Testing the reliability of non-LTE spectroscopic models for complex ions},
  journal = {High Energy Density Physics},
  year = {2013},
  volume = {9},
  number = {3},
  pages = {523--527},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181813000633},
  doi = {10.1016/j.hedp.2013.05.002}
}
"Analytical description of absorption profiles in warm dense plasmas: discussion of the non-overlapping-line limit"
Poirier M, High Energy Density Physics. Vol. 9(3), pp. 618-625 - (2013).
Abstract: This paper is devoted to a theoretical description of the spectral absorption in warm dense plasmas, such as those involved in hohlraum-based opacity measurements. Dealing with complex spectra, when the effect of natural and experimental broadening, optical thickness and line overlap is taken into account, the calculation of plasma transmission becomes quite elaborate. In the hypothesis of large experimental broadening, simple analytical formulas are obtained here for this transmission. They are checked by comparison to the exact convolution of various detailed spectra with a broadening profile. The current numerical method is then applied to the computation of transmission in Fe and Br plasmas, where opacity and line-overlap effects may be substantial.
BibTeX:
@article{Poirier2013,
  author = {Poirier, M.},
  title = {Analytical description of absorption profiles in warm dense plasmas: discussion of the non-overlapping-line limit},
  journal = {High Energy Density Physics},
  year = {2013},
  volume = {9},
  number = {3},
  pages = {618--625},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181813000803},
  doi = {10.1016/j.hedp.2013.05.019}
}
"Radiative properties of stellar envelopes: Comparison of asteroseismic results to opacity calculations and measurements for iron and nickel"
Turck-Chièze S, Gilles D, Le Pennec M, Blenski T, Thais F, Bastiani-Ceccotti S, Blancard C, Busquet M, Caillaud T, Colgan J, Cossé P, Delahaye F, Ducret J-E, Faussurier G, Fontes C, Gilleron F, Guzik J, Harris J, Kilcrease D, Magee N, Pain J, Reverdin C, Silvert V, Villette B and Zeippen C, High Energy Density Physics. Vol. 9(3), pp. 473-479 - (2013).
Abstract: The international OPAC consortium consists of astrophysicists, plasma physicists and experimentalists who examine opacity calculations used in stellar physics that appear questionable and perform new calculations and laser experiments to understand the differences and improve the calculations. We report on iron and nickel opacities for envelopes of stars from 2 to 14MΘ and deliver our first conclusions concerning the reliability of the used calculations by illustrating the importance of the configuration interaction and of the completeness of the calculations for temperatures around 1527 eV.
BibTeX:
@article{Turck-Chieze2013,
  author = {Turck-Chièze, S. and Gilles, D. and Le Pennec, M. and Blenski, T.J. and Thais, F. and Bastiani-Ceccotti, S. and Blancard, C. and Busquet, M. and Caillaud, T. and Colgan, J. and Cossé, P. and Delahaye, F. and Ducret, J.-E. and Faussurier, G. and Fontes, C.J. and Gilleron, F. and Guzik, J. and Harris, J. and Kilcrease, D.P. and Magee, N.H. and Pain, J.C. and Reverdin, C. and Silvert, V. and Villette, B. and Zeippen, C.J.},
  title = {Radiative properties of stellar envelopes: Comparison of asteroseismic results to opacity calculations and measurements for iron and nickel},
  journal = {High Energy Density Physics},
  year = {2013},
  volume = {9},
  number = {3},
  pages = {473--479},
  url = {http://www.sciencedirect.com/science/article/pii/S157418181300044X},
  doi = {10.1016/j.hedp.2013.04.004}
}
"Optically Aligned, Space Resolving, Extreme Ultra-Violet and Soft X-ray Spectrograph"
Busquet M, Thais F, Geoffroy G, Raffestin D and Chièze J, Applied Physics Research. Vol. 5, pp. 25-32 - (2013).
Abstract: We describe in this paper an extreme ultra-violet/soft X-ray (XUV) spectrograph with high sensitivity, high spectral resolution and spatial resolution, which we developed to record XUV emission from a 10 J laser-irradiated gas jet. This spectrograph uses a flat field grazing incidence grating and a grazing incidencecollection and imaging mirror. We designed a system where initial positions of elements can be set with a low accuracy of half a millimeter and where the final alignment is done with a visible light low intensity laser beam. High spectral resolution, good spatial resolution and nominal dispersion function have been achieved. A few illustrative results are presented.
BibTeX:
@article{Busquet2013,
  author = {Busquet, M. and Thais, F. and Geoffroy, G. and Raffestin, D. and Chièze, J.P.},
  title = {Optically Aligned, Space Resolving, Extreme Ultra-Violet and Soft X-ray Spectrograph},
  journal = {Applied Physics Research},
  year = {2013},
  volume = {5},
  pages = {25--32},
  url = {http://dx.doi.org/10.5539/apr.v5n2p25}
}
2012
"Velocity asymmetries in young stellar object jetsIntrinsic and extrinsic mechanisms"
Matsakos T, Vlahakis N, Tsinganos K, Karampelas K, Sauty C, Cayatte V, Matt S, Massaglia S, Trussoni E and Mignone A, Astronomy and Astrophysics. Vol. 545, pp. A53 - (2012).
Abstract: Context. It is well established that some YSO jets (e.g. RW Aur) display different propagation speeds between their blue and redshifted parts, a feature possibly associated with the central engine or the environment in which the jet propagates.Aims. To understand the origin of asymmetric YSO jet velocities, we investigate the efficiency of two candidate mechanisms, onebased on the intrinsic properties of the system and the other on the role of the external medium. In particular, a parallel or anti-parallelconfiguration between the protostellar magnetosphere and the disk magnetic field is considered, and the resulting dynamics examinedboth in an ideal and in a resistive magneto-hydrodynamical (MHD) regime. Moreover, we explore the effects of a potential differencein the pressure of the environment, as a consequence of the nonuniform density distribution of molecular clouds.Methods. Ideal and resistive axisymmetric numerical simulations were carried out for a variety of models, all of which are basedon a combination of two analytical solutions, a disk wind and a stellar outflow. The initial two-component jet is modified by eitherinverting the orientation of its inner magnetic field or imposing a constant surrounding pressure. The velocity profiles are studied byassuming steady flows as well as after strong time variable ejection is incorporated.Results. Discrepancies between the speeds of the two outflows in opposite directions can indeed occur both due to unaligned magneticfields and different outer pressures. In the former case, the asymmetry appears only on the dependence of the velocity on the cylindricaldistance, but the implied observed value is significantly altered when the density distribution is also taken into account. On the otherhand, a nonuniform medium collimates the two jets unevenly, directly affecting their propagation speed. A further interesting featureof the pressure-confined outflow simulations is the formation of static knots whose spacing seems to be associated with the ambientpressure.Conclusions. Jet velocity asymmetries are anticipated both when multipolar magnetic moments are present in the star-disk systemand when nonuniform environments are considered. The latter is an external mechanism that can easily explain the large timescale ofthe phenomenon, whereas the former naturally relates it to the YSO intrinsic properties.
BibTeX:
@article{Matsakos2012,
  author = {Matsakos, T. and Vlahakis, N. and Tsinganos, K. and Karampelas, K. and Sauty, C. and Cayatte, V. and Matt, S.P. and Massaglia, S. and Trussoni, E. and Mignone, A.},
  title = {Velocity asymmetries in young stellar object jetsIntrinsic and extrinsic mechanisms},
  journal = {Astronomy and Astrophysics},
  year = {2012},
  volume = {545},
  pages = {A53},
  url = {http://dx.doi.org/10.1051/0004-6361/201219498},
  doi = {10.1051/0004-6361/201219498}
}
"Equation of State of Dense Plasma Mixtures: Application to the Sun Center"
Pain J, Dejonghe G and Blenski T, Contribution to Plasma Physics. Vol. 52, pp. 23-27 - (2012).
Abstract: We present a self-consistent approach to the modeling of dense plasma mixtures in local thermodynamic equi-librium. In each electron configuration the nucleus is totally screened by electrons in a Wigner-Seitz sphere (ion-sphere model). Bound and free electrons are treated quantum-mechanically. The assumption that all species should have the same electronic environment leads to the equality of the electronic pressure for all ions of all elements having therefore different cell volumes. The variation of the average atomic radii of the different elements with respect to temperature is investigated, and the procedure is applied to the determination of pressure in the Sun center
BibTeX:
@article{Pain2012,
  author = {Pain, J.C. and Dejonghe, G. and Blenski, T.},
  title = {Equation of State of Dense Plasma Mixtures: Application to the Sun Center},
  journal = {Contribution to Plasma Physics},
  year = {2012},
  volume = {52},
  pages = {23--27},
  url = {http://dx.doi.org/10.1002/ctpp.201100069}
}
"X-ray grating spectrometer for opacity measurements in the 50 eV to 250 eV spectral range at the LULI 2000 laser facilit"
Reverdin C, Thais F, Loisel G, Busquet M, Bastiani-Ceccotti S, Blenski T, Caillaud T, Ducret J, Foelsner W, Gilles D, Gilleron F, Pain J, Poirier M, Serres F, Silvert V, Soullie G, Turck-Chièze S and Villette B, Review of Scientific Instruments. Vol. 83, pp. 10E134 - (2012).
Abstract: An x-ray grating spectrometer was built in order to measure opacities in the 50 eV to 250 eV spectral range with an average spectral resolution (E/dE) ~ 50. It has been used at the LULI-2000 laser facility at école Polytechnique (France) to measure the ?n = 0, n = 3 transitions of several elements with neighboring atomic number: Cr, Fe, Ni, and Cu in the same experimental conditions. Hence a spectrometer with a wide spectral range is required. This spectrometer features one line of sight looking through a heated sample at backlighter emission. It is outfitted with one toroidal condensing mirror and several flat mirrors cutting off higher energy photons. The spectral dispersion is obtained with a flatfield grating. Detection consists of a streak camera sensitive to soft x-ray radiation. Some experimental results showing the performance of this spectrometer are presented.
BibTeX:
@article{Reverdin2012,
  author = {Reverdin, C. and Thais, F. and Loisel, G. and Busquet, M. and Bastiani-Ceccotti, S. and Blenski, T. and Caillaud, T. and Ducret, J.E. and Foelsner, W. and Gilles, D. and Gilleron, F. and Pain, J.C. and Poirier, M. and Serres, F. and Silvert, V. and Soullie, G. and Turck-Chièze, S. and Villette, B.},
  title = {X-ray grating spectrometer for opacity measurements in the 50 eV to 250 eV spectral range at the LULI 2000 laser facilit},
  journal = {Review of Scientific Instruments},
  year = {2012},
  volume = {83},
  pages = {10E134},
  url = {http://link.aip.org/link/?RSI/83/10E134},
  doi = {10.1063/1.4740266}
}
"Counterrotation in magnetocentrifugally driven jets and other winds"
Sauty C, Cayatte V, Lima J, Matsakos T and Tsinganos K, Astrophysical Journal Letters, The. Vol. 759, pp. L1 - (2012).
Abstract: Rotationmeasurements in jets from T Tauri stars is a rather difficult task. Some jets seem to be rotating in a direction opposite to that of the underlying disk, although it is not yet clear if this affects the totality or part of the utflows. On the other hand, Ulysses data also suggest that the solar wind may rotate in two opposite ways between the northern and southern hemispheres. We show that this result is not surprising as it may seem and that it emerges naturally from the ideal MHD equations. Specifically, counterrotating jets do not contradict the magnetocentrifugal driving of the flow nor prevent extraction of angular momentum from the disk. The demonstration of this result is shown by combining the ideal MHD equations for steady axisymmetric flows. Provided that the jet is decelerated below some given threshold beyond the Alfv´en surface, the flow will change its direction of rotation locally or globally. Counterrotation is also possible for only some layers of the outflow at specific altitudes along the jet axis. We conclude that the counterrotation of winds or jets with respect to the source, star or disk, is not in contradiction with the magnetocentrifugal driving paradigm. This phenomenon may affect part of the outflow, either in one hemisphere, or only in some of the outflow layers. From a time-dependent simulation, we illustrate this effect and show that it may not be permanent.
BibTeX:
@article{Sauty2012,
  author = {Sauty, C. and Cayatte, V. and Lima, J.J.G. and Matsakos, T. and Tsinganos, K.},
  title = {Counterrotation in magnetocentrifugally driven jets and other winds},
  journal = {Astrophysical Journal Letters, The},
  year = {2012},
  volume = {759},
  pages = {L1},
  url = {http://iopscience.iop.org/2041-8205/759/1/L1/},
  doi = {10.1088/2041-8205/759/1/L1}
}
2011
"Electron-hole dynamics in normal and deuterated KH2PO4 illuminated by intense femtosecond laser pulses"
Duchateau G, Geoffroy G, Dyan A, Piombini H and Guizard S, Physical Review B. Vol. 83(7), pp. 075114\_1-11 - (2011).
Abstract: The dynamics of electrons and holes in potassium dihydrogen phosphate (KH2PO4 or KDP) crystals and its deuterated analog (KD2PO4 or DKDP) induced by femtosecond laser pulses is investigated at λ=800 nm. To do so, experiments based on a femtosecond time-resolved interferometry technique have been carried out. It is shown that two relaxation dynamics exist in KDP and DKDP crystals. Both of them correspond to physical mechanisms for which the multiphoton order required to promote valence electrons to the conduction band is lower than the one of a defect-free crystal. These results suggest the presence of states located in the band gap that may be due to the presence of defects existing before any laser illumination or created in the course of interaction. In order to interpret the experiments, a model based on a kinetic equation system has been developed. Modeling results are in good agreement with the experimental data.
BibTeX:
@article{Duchateau2011,
  author = {Duchateau, G. and Geoffroy, G. and Dyan, A. and Piombini, H. and Guizard, S.},
  title = {Electron-hole dynamics in normal and deuterated KH2PO4 illuminated by intense femtosecond laser pulses},
  journal = {Physical Review B},
  year = {2011},
  volume = {83},
  number = {7},
  pages = {0751141--11},
  url = {http://prb.aps.org/abstract/PRB/v83/i7/e075114},
  doi = {10.1103/PhysRevB.83.075114}
}
"Theoretical interpretation of X-rays photo-absorption in medium-Z elements plasmas measured at LULI2000 facility"
Blenski T, Loisel G, Poirier M, Thais F, Arnault P, Caillaud T, Fariaut J, Gilleron F, Pain J-C, Porcherot Q, Reverdin C, Silvert V, Villette B, Bastiani-Ceccotti S, Turck-Chièze S, Foelsner W and de Gaufridy de Dortan F, High Energy Density Physics. Vol. 7(4), pp. 320-326 - (2011).
Abstract: We analyzed the spectra of X-ray transmission through radiatively heated medium-Z plasma (Fe, Ni, Cu and Ge) measured at LULI2000 facility in the wavelength range of 2p–nd transitions. The analysis was performed using the statistical superconfiguration code SCO, two line-by-line opacity codes based on the HULLAC and FAC packages and a new hybrid statistical-detailed code SCORCG. The temperature and mass density of the samples were estimated from hydrodynamic simulations based on the cavity radiative temperature measurements. The theory–experiment agreement is relatively good in the wavelength range corresponding to the 2p–3d transitions except in the germanium case. In the wavelength range of the 2p–2d, n > 3 transitions a relatively good theory–experiment agreement was found in the copper case. As predicted by calculations the separation of the characteristic spin-orbit-split 2p–3d structures, absent in the iron measured spectrum, appears in the nickel spectrum and is visible in the copper and germanium spectra. Comparisons of the experimental transmission with calculations confirm the importance of the relativistic configuration interaction. The absorption strength of the measured germanium 2p–3d transition is much larger than that obtained from the codes. Spatial temperature and density gradients, relatively high in the germanium sample, may be at the origin of this discrepancy.
BibTeX:
@article{Blenski2011,
  author = {Blenski, T.J. and Loisel, G. and Poirier, M. and Thais, F. and Arnault, P. and Caillaud, T. and Fariaut, J. and Gilleron, F. and Pain, J.-C. and Porcherot, Q. and Reverdin, C. and Silvert, V. and Villette, B. and Bastiani-Ceccotti, S. and Turck-Chièze, S. and Foelsner, W. and de Gaufridy de Dortan, F.},
  title = {Theoretical interpretation of X-rays photo-absorption in medium-Z elements plasmas measured at LULI2000 facility},
  journal = {High Energy Density Physics},
  year = {2011},
  volume = {7},
  number = {4},
  pages = {320--326},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181811000759},
  doi = {10.1016/j.hedp.2011.06.006}
}
"Opacity of iron, nickel and copper plasmas in the x-ray wavelength range: theoretical interpretation of 2p - 3d absorption spectra"
Blenski T, Loisel G, Poirier M, Thais F, Arnault P, Caillaud T, Fariaut J, Gilleron F, Pain J-C, Porcherot Q, Reverdin C, Silvert V, Villette B, Bastiani-Ceccotti S, TurckChieze S, Folsner W and de Gaufridy de Dortan F, Physical Review E - Statistical, Nonlinear and Soft Matter Physics. Vol. 84, pp. 036407_1-17 - (2011).
Abstract: This paper deals with theoretical studies on the 2p-3d absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004–0.01 g/cm3. The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of 2p-3d transitions has been studied with the help of the statistical superconfiguration opacity code sco and with the fine-structure atomic physics codes hullac and fac. A new mixed version of the sco code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code rcg has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by sco. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the 2p-3d transitions have been investigated as a function of the atomic number Z. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code scric. The sensitivity of the 2p-3d structures with respect to temperature and density in medium-Z plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the ?n=0 absorption in medium-Z plasmas for astrophysical applications.
BibTeX:
@article{Blenski2011a,
  author = {Blenski, T.J. and Loisel, G. and Poirier, M. and Thais, F. and Arnault, P. and Caillaud, T. and Fariaut, J. and Gilleron, F. and Pain, J.-C. and Porcherot, Q. and Reverdin, C. and Silvert, V. and Villette, B. and Bastiani-Ceccotti, S. and TurckChieze, S. and Folsner, W. and de Gaufridy de Dortan, F.},
  title = {Opacity of iron, nickel and copper plasmas in the x-ray wavelength range: theoretical interpretation of 2p - 3d absorption spectra},
  journal = {Physical Review E - Statistical, Nonlinear and Soft Matter Physics},
  year = {2011},
  volume = {84},
  pages = {036407_1--17},
  url = {http://dx.doi.org/10.1103/PhysRevE.84.036407},
  doi = {10.1103/PhysRevE.84.036407}
}
"On the influence of opacity variation on spatial structure of radiative shocks"
Busquet M, Klapisch M and Thais F, High Energy Density Physics. Vol. 7(4), pp. 217-223 - (2011).
Abstract: We provide a theoretical analysis of Radiative Shocks, defined as supercritical shocks accompanied by an ionization wave in front of the density jump. In particular, we look at the influence of opacity variation with temperature and photon energy on spatial structure of radiative shocks, with a view to understanding a split precursor feature observed in recent experiments. We show that multigroup processing, a more refined angular description and improved low temperature opacities are needed to explore the radiative precursor structure, at least in some temperature regimes where rapid change of ionization can be found.
BibTeX:
@article{Busquet2011,
  author = {Busquet, M. and Klapisch, M. and Thais, F.},
  title = {On the influence of opacity variation on spatial structure of radiative shocks},
  journal = {High Energy Density Physics},
  year = {2011},
  volume = {7},
  number = {4},
  pages = {217--223},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181811000516},
  doi = {10.1016/j.hedp.2011.04.010}
}
"Comparison of Fe and Ni opacity calculations for a better understanding of pulsating stellar envelopes"
Gilles D, Turck-Chieze S, Loisel G, Piau L, Ducret J-E, Blenski T, Poirier M, Thais F, Blancard C, Cossé P, Faussurier G, Gilleron F, Pain J-C, Porcherot Q, Guzik J, Kilcrease D, Magee N, Harris J, Busquet M, Delahaye F, Zeippen C and Bastiani-Ceccotti S, High Energy Density Physics. Vol. 7(4), pp. 312-319 -(2011).
Abstract: Opacity is an important ingredient of the secular evolution of stars. The calculation of opacity coefficients is complex because the plasma is generally partially ionized for the heavy ions contribution of a mixture dominated by H/He. Up to now, the astrophysical community has greatly benefited from the work of the Los Alamos and OPAL teams and also from the Opacity Project (OP) tables and their corresponding spectra. However unexplained differences in the radiative forces and Rosseland mean values for Fe up to 50% have been noticed for conditions corresponding to stellar envelopes. Such uncertainty has a real impact on the understanding of pulsating stellar envelopes on the excitation of modes and on the identification of the mode frequencies. Temperature and density conditions equivalent to those found in stars can now be produced in laboratory experiments for different atomic species. Recently the photo-absorption spectra of nickel and iron plasmas have been measured during the LULI 2010 campaign, for temperatures between 15 and 40 eV and densities of ~3 mg/cm3. A large theoretical collaboration (consortium "OPAC") has been formed to prepare this experiment. We present here the panel of opacity calculations performed by eight different groups for conditions relevant to the LULI 2010 experiment and to astrophysical stellar envelope conditions.
BibTeX:
@article{Gilles2011,
  author = {Gilles, D. and Turck-Chieze, S. and Loisel, G. and Piau, L. and Ducret, J.-E. and Blenski, T.J. and Poirier, M. and Thais, F. and Blancard, C. and Cossé, P. and Faussurier, G. and Gilleron, F. and Pain, J.-C. and Porcherot, Q. and Guzik, J.A. and Kilcrease, D.P. and Magee, N.H. and Harris, J. and Busquet, M. and Delahaye, F. and Zeippen, C.J. and Bastiani-Ceccotti, S.},
  title = {Comparison of Fe and Ni opacity calculations for a better understanding of pulsating stellar envelopes},
  journal = {High Energy Density Physics},
  year = {2011},
  volume = {7},
  number = {4},
  pages = {312--319},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181811000723},
  doi = {10.1016/j.hedp.2011.06.001}
}
"Variational Average-Atom in Quantum Plasmas (VAAQP) Recent progress, virial theorem and applications to the equation-of-state of warm dense Be"
Piron R and Blenski T, High Energy Density Physics. Vol. 7, pp. 346-352 - (2011).
Abstract: The Variational Average-Atom in Quantum Plasmas (VAAQP) code is based on a fully variational theory of dense plasmas in equilibrium in which the neutrality of the Wigner-Seitz ion sphere is not required, contrary to the Inferno model. We report on some recent progress in the VAAQP model and numerical code. Three important points of the virial theorem derivation are emphasized and explained. The virial theorem is also used as an important tool allowing us to check the formulas and numerical methods used in the code. Applications of the VAAQP code are shown using as an example the equation-of-state of beryllium in the warm dense matter regime. Comparisons with the Inferno model, and with available experimental data on the principal Hugoniot are also presented.
BibTeX:
@article{Piron2011,
  author = {Piron, R. and Blenski, T.},
  title = {Variational Average-Atom in Quantum Plasmas (VAAQP) Recent progress, virial theorem and applications to the equation-of-state of warm dense Be},
  journal = {High Energy Density Physics},
  year = {2011},
  volume = {7},
  pages = {346--352},
  url = {http://dx.doi.org/10.1016/j.hedp.2011.06.006},
  doi = {10.1016/j.hedp.2011.06.006}
}
"Variational-average-atom-in-quantum-plasmas (VAAQP) code and virial theorem: Equation-of-state and shock-Hugoniot calculations for warm dense Al, Fe, Cu, and Pb"
Piron R and Blenski T, Physical Review E - Statistical, Nonlinear and Soft Matter Physics. Vol. 83, pp. 026403_1-22 - (2011).
Abstract: A numerical code: VAAQP (Variational Average-Atom in Quantum Plasmas) which is based on a fully variational model of equilibrium dense plasmas is applied to equation-of-state calculations for aluminum, iron, copper and lead in the warm dense matter regime. VAAQP does not impose the neutrality of the Wigner-Seitz ion sphere, it provides the average-atom structure and the mean ionization self-consistently from the solution of the variational equations. The formula used for the electronic pressure is simple and does not require any numerical differentiation. In this article, the virial theorem is derived in both non-relativistic and relativistic versions of the model. This theorem allows one to express the electron pressure as a combination of the electron kinetic and interaction energies. It is shown that the model fulfills automatically the virial theorem in case of local density approximations to the exchange-correlation free energy. Applications of the model to the equation-of-state and Hugoniot shock adiabat of aluminum, iron, copper and lead in the warm dense matter regime are presented. Comparisons with other approaches, including the INFERNO model, and with available experimental data are given. This work allows one to understand the thermodynamic consistency issues in the existing average-atom models. Starting from the case of aluminum, a comparative study of the thermodynamic consistency of the models is proposed. A preliminary study of the validity domain of the INFERNO model is also included.
BibTeX:
@article{Piron2011a,
  author = {Piron, R. and Blenski, T.J.},
  title = {Variational-average-atom-in-quantum-plasmas (VAAQP) code and virial theorem: Equation-of-state and shock-Hugoniot calculations for warm dense Al, Fe, Cu, and Pb},
  journal = {Physical Review E - Statistical, Nonlinear and Soft Matter Physics},
  year = {2011},
  volume = {83},
  pages = {026403_1--22},
  url = {http://link.aps.org/doi/10.1103/PhysRevE.83.026403},
  doi = {10.1103/PhysRevE.83.026403}
}
"A consistent approach for mixed detailed and statistical calculation of opacities in hot plasmas"
Porcherot Q, Pain J-C, Gilleron F and Blenski T, High Energy Density Physics. Vol. 7(4), pp. 234-239 - (2011).
Abstract: Absorption and emission spectra of plasmas with multicharged-ions contain transition arrays with a huge number of coalescent electric-dipole (E1) lines, which are well suited for treatment by the unresolved transition array and derivative methods. But, some transition arrays show detailed features whose description requires diagonalization of the Hamiltonian matrix. We developed a hybrid opacity code, called SCORCG, which combines statistical approaches with fine-structure calculations consistently. Data required for the computation of detailed transition arrays (atomic configurations and atomic radial integrals) are calculated by the superconfiguration code SCO (Super-Configuration Opacity), which provides an accurate description of the plasma screening effects on the wave-functions. Level energies as well as position and strength of spectral lines are computed by an adapted RCG routine of R. D. Cowan. The resulting code provides opacities for hot plasmas and can handle mid-Z elements. The code is also a powerful tool for the interpretation of recent laser and Z-pinch experimental spectra, as well as for validation of statistical methods.
BibTeX:
@article{Porcherot2011,
  author = {Porcherot, Q. and Pain, J.-C. and Gilleron, F. and Blenski, T.J.},
  title = {A consistent approach for mixed detailed and statistical calculation of opacities in hot plasmas},
  journal = {High Energy Density Physics},
  year = {2011},
  volume = {7},
  number = {4},
  pages = {234--239},
  url = {http://www.sciencedirect.com/science/article/pii/S1574181811000528},
  doi = {10.1016/j.hedp.2011.05.001}
}
"Radiative properties of stellar plasmas and open challenges"
Turck-Chièze S, Loisel G, Gilles D, Piau L, Blancard C, Blenski T, Busquet M, Cosse P, Delahaye F, Faussurier G, Gilleron F, Guzik J, Harris J, Kilcrease D, Magee N, Pain J, Porcherot Q, Poirier M, Zeippen C, Bastiani-Ceccotti S, Reverdin C, Silvert V and Thais F, Astrophysics and Space Science. Vol. 336, pp. 103-109 - (2011).
Abstract: The lifetime of solar-like stars, the envelopof more massive stars and the acoustic frequencieslargely depend on the radiative properties of the stellar plasmas. Up to now, these complex quantities have been estimated only theoretically. With the strong development of helio- and astero- seismology, a real insight on the stellar interiors is becoming a very active astrophysical research. Consequently, an increase pressure is put on the appropriate knowledge of the monochromatic opacity coefficients. In this review, we recall how these ingredients play a role and where the radiative properties are the most important to know. We then specifically concentrate on the envelops of the beta Cephei. We discuss the dispersion of eight different theoretical estimates of the monochromatic opacity spectrum and the challenges we need to face to check these calculations experimentally.
BibTeX:
@article{Turck-Chieze2011a,
  author = {Turck-Chièze, S. and Loisel, G. and Gilles, D. and Piau, L. and Blancard, C. and Blenski, T.J. and Busquet, M. and Cosse, P. and Delahaye, F. and Faussurier, G. and Gilleron, F. and Guzik, J. and Harris, J. and Kilcrease, D.P. and Magee, N.H. and Pain, J.C. and Porcherot, Q. and Poirier, M. and Zeippen, C. and Bastiani-Ceccotti, S. and Reverdin, C. and Silvert, V. and Thais, F.},
  title = {Radiative properties of stellar plasmas and open challenges},
  journal = {Astrophysics and Space Science},
  year = {2011},
  volume = {336},
  pages = {103--109},
  url = {http://dx.doi.org/10.1007/s10509-010-0583-8},
  doi = {10.1007/s10509-010-0583-8}
}
"Theoretical and experimental activities on opacities for a good interpretation of seismic stellar probes"
Turck-Chièze S, Loisel G, Gilles D, Thais F, Bastiani S, Blancard C, Busquet M, Caillaud T, Cossé P, Blenski T, Delahaye F, Ducret J, Faussurier G, Gilleron F, Guzik J, Harris J, Kilcrease D, Magee N, Piau L, Pain J, Poirier M, Porcherot Q, Reverdin C, Silvert V, Villette B and Zeippen C, Journal of Physics Conference Series. Vol. 271, pp. 012035 - (2011).
Abstract: Opacity calculations are basic ingredients of stellar modelling. They play a crucial role in the interpretation of acoustic modes detected by SoHO, COROT and KEPLER. In this review we present our activities on both theoretical and experimental sides. We show new calculations of opacity spectra and comparisons between eight groups who produce opacity spectra calculations in the domain where experiments are scheduled. Real differences are noticed with real astrophysical consequences when one extends helioseismology to cluster studies of different compositions. Two cases are considered presently: (1) the solar radiative zone and (2) the beta Cephei envelops. We describe how our experiments are performed and new preliminary results on nickel obtained in the campaign 2010 at LULI 2000 at Polytechnique.
BibTeX:
@article{Turck-Chieze2011,
  author = {Turck-Chièze, S. and Loisel, G. and Gilles, D. and Thais, F. and Bastiani, S. and Blancard, C. and Busquet, M. and Caillaud, T. and Cossé, P. and Blenski, T.J. and Delahaye, F. and Ducret, J.E. and Faussurier, G. and Gilleron, F. and Guzik, J. and Harris, J.W. and Kilcrease, D.P. and Magee, N.H. and Piau, L. and Pain, J.C. and Poirier, M. and Porcherot, Q. and Reverdin, C. and Silvert, V. and Villette, B. and Zeippen, C.},
  title = {Theoretical and experimental activities on opacities for a good interpretation of seismic stellar probes},
  journal = {Journal of Physics Conference Series},
  year = {2011},
  volume = {271},
  pages = {012035},
  url = {http://dx.doi.org/10.1088/1742-6596/271/1/012035},
  doi = {10.1088/1742-6596/271/1/012035}
}
"Des plasmas stellaires aux plasmas de laboratoire :Application aux mesures d'opacité dans les domainesX et XUV"
Loisel G, In Astrophysique et physique des plasmas. Thesis at: Université Paris XI - Paris Sud, UFR Orsay (2011).
Abstract: Cette thèse s'inscrit dans le contexte général des propriétés radiatives de la matière à haute densité d'énergie (>10^11 J/cm3). Les densités d'énergie de la MHDE font qu'une partie importante des échanges d'énergie passe par l'interaction rayonnement-matière. Mes études portent sur l'opacité spectrale, un paramètre fondamental pour la modélisation des intérieurs stellaires et qui constitue aussi une observable propice aux tests expérimentaux des descriptions théoriques de la physique des plasmas chauds et denses.Mes travaux de thèse sont centrés sur l'étude expérimentale des opacités de plasmas à l'équilibre thermodynamique local pour des températures de quelques dizaines d'eV (soit quelques 100 000 K) et quelques mg/cm3 en densité. Les plasmas sont obtenus dans des conditions aussi homogènes que possible en utilisant le chauffage radiatif d'une cavité irradiée par laser de haute énergie, 100-300 J. Ainsi, nous avons pu mettre à profit pour ce type de mesure la configuration utilisant des lasers nanoseconde et picoseconde du LULI (Laboratoire pour l'Utilisation des Lasers Intenses) pour réaliser le chauffage d'une part et la mesure sur un temps bref d'autre part de la transmission des plasmas, l'utilisation d'impulsions courtes constituant une première pour ce type d'expériences.Dans le domaine des X de l'ordre du keV, les transitions absorbantes 2p-3d ou 3d-4f d'éléments de numéro atomique moyen ou élevé ont été sondées. Elles font apparaitre des structures d'absorption dont la forme résulte principalement de la compétition entre l'éclatement spin-orbite et les effets d'élargissement statistiques. Il a été montré que cette compétition dépendait fortement du numéro atomique Z. Ainsi à paramètres plasma proches nous avons exploré l'opacité des éléments fer, nickel, cuivre et germanium (Z autour de 30) dans une première série de mesures puis celle du baryum, samarium et du gadolinium, dans une seconde expérience (Z autour de 60).L'astrophysique stellaire nécessite aussi de mesurer précisément, et de manière bien caractérisée, les opacités du groupe du fer (Cr, Fe, Ni et Cu) dans le domaine des XUV (50 - 200 eV). Ces opacités sont à l'origine de l'excitation dans les enveloppes radiatives des étoiles pulsantes massives de type spectral B pour une température de l'ordre de 200 000 K. Dans ces conditions, les moyennes de Rosseland présentent des différences nettes entre les calculs utilisés par la communauté astrophysique et ne permettent pas d'interpréter les oscillations et l'ensemble des fréquences observées de manière univoque. Pour permettre des comparaisons avec divers calculs spectraux, j'ai participé à la mise en place d'un nouveau schéma expérimental à deux cavités dont le but était d'améliorer l'homogénéité du chauffage des échantillons. Je montrerai enfin l'analyse des paramètres plasmas pour ce type de schéma. J'ai en particulier analysé le cas du nickel dont la transmission a été mesurée pour la première fois dans cette gamme spectrale.Dans chaque cas je présenterai l'analyse des résultats obtenus.
BibTeX:
@phdthesis{PhdThesisLoisel2011,
  author = {Loisel, G.},
  title = {Des plasmas stellaires aux plasmas de laboratoire :Application aux mesures d'opacité dans les domainesX et XUV},
  booktitle = {Astrophysique et physique des plasmas},
  school = {Université Paris XI - Paris Sud, UFR Orsay},
  year = {2011},
  url = {http://tel.archives-ouvertes.fr/tel-00579800/fr/}
}
2010
"Relaxation dynamics of electronic excitations in CaWO4 and CdWO4 crystals studied by femtosecond interferometry technique"
Nagirnyi V, Geoffroy G, Grigonis R, Guizard S, Kirm M, Kotlov A, Nagornaya L, Nikl M, Sirutkaitis V and Vielhauer S, Radiation Measurements. Vol. 45(3-6), pp. 262-264 - (2010).
Abstract: The relaxation of electronic excitations in CdWO4 and CaWO4 crystals was studied using the method of time-resolved interferometry with 100-fs temporal resolution at temperatures 15295 K. The electronic system was excited in the one-photon and two-photon regime within the excitonic band in CaWO4 and in the electron-hole continuum in CdWO4. Immediate trapping of charge carriers was detected under pumping in the excitonic band of CaWO4. This result is in agreement with decay kinetics measurements with nanosecond time resolution under direct creation of excitons by 100-fs laser pulses. Fast relaxation of charge carriers followed by formation of excitons was observed in CdWO4. The comparison with previous work allows suggesting the formation of bulk excitons and surface-perturbed excitons in the multi-photon and one-photon regime. The corresponding models of self-trapped exciton creation in tungstate crystals are discussed.
BibTeX:
@article{Nagirnyi2010,
  author = {Nagirnyi, V. and Geoffroy, G. and Grigonis, R. and Guizard, S. and Kirm, M. and Kotlov, A. and Nagornaya, L.L. and Nikl, M. and Sirutkaitis, V. and Vielhauer, S.},
  title = {Relaxation dynamics of electronic excitations in CaWO4 and CdWO4 crystals studied by femtosecond interferometry technique},
  journal = {Radiation Measurements},
  year = {2010},
  volume = {45},
  number = {3-6},
  pages = {262--264},
  url = {http://www.sciencedirect.com/science/article/pii/S1350448709003746},
  doi = {10.1016/j.radmeas.2009.12.007}
}
"Electron heating through a set of random levels in the conduction band of insulators induced by femtosecond laser pulses"
Bachau H, Belsky A, Bogatyrev I, Gaudin J, Geoffroy G, Guizard S, Martin P, Popov YV, Vasil'ev A and Yatsenko B, Applied Physics A : Materials Science & Processing. Vol. 98, pp. 679-689 - (2010).
Abstract: We develop a theory describing the heating ofelectrons in crystalline insulators irradiated by high-intensitylaser pulses. In agreement with photoelectron yield versus intensity measurements, we assume that electrons are excited into the conduction band from defect layers and traps.The electron dynamics due to direct inter-branch transitions within the conduction band is simulated by solving of time-dependent Schrodinger equation. The set of levels for this equation is supposed to be random with a distribution function equal to the density of states in the conduction band.The influence of different parameters on the electron heating efficiency is studied. The theory is applied for diamond; the theoretical spectrum is in qualitative agreement with the experimental observations.
BibTeX:
@article{Bachau2010,
  author = {Bachau, H. and Belsky, A. and Bogatyrev, I.B. and Gaudin, J. and Geoffroy, G. and Guizard, S. and Martin, P. and Popov, Yu. V. and Vasil'ev, A.N. and Yatsenko, B.N.},
  title = {Electron heating through a set of random levels in the conduction band of insulators induced by femtosecond laser pulses},
  journal = {Applied Physics A : Materials Science & Processing},
  year = {2010},
  volume = {98},
  pages = {679--689},
  url = {http://link.springer.com/article/10.1007%2Fs00339-009-5465-y},
  doi = {10.1007/s00339-009-5465-y}
}
"Measure of precursor electron density profiles of laser launched radiative shocks"
Busquet M, Thais F, Gonzalez M and Audit E, Journal of Applied Physics. Vol. 107, pp. 083302/1-9 - (2010).
Abstract: We have studied the dynamics of strong radiative shocks generated with the high-energy subnanosecond iodine laser at Prague Asterix Laser System facility (Prague) over long time scales, up to 100 ns. These shock waves are characterized by a developed radiative precursor, a radiation driven ionization wave in front of the density jump of the shock. Electronic density profiles are measured at different times after the laser pulse and at different distances from the axis of the shock tube. A new feature, described as a split precursor, has been observed. Comparisons with two-dimensional computations are shown.
BibTeX:
@article{Busquet2010,
  author = {Busquet, M. and Thais, F. and Gonzalez, M. and Audit, E.},
  title = {Measure of precursor electron density profiles of laser launched radiative shocks},
  journal = {Journal of Applied Physics},
  year = {2010},
  volume = {107},
  pages = {083302/1--9},
  url = {http://dx.doi.org/10.1063/1.3330636},
  doi = {10.1063/1.3330636}
}
"X-ray crystal spectrometer for opacities measurements in the 818 Å spectral range at the LULI laser facility"
Reverdin C, Thais F, Loisel G and Bougeard M, Review of Scientific Instruments. Vol. 81, pp. 10E327_1-5 (2010).
Abstract: An x-ray crystal spectrometer was built in order to measure opacities in the 8–18 Ĺ spectral range with an average spectral resolution of (λ/δλ) - 400. It has been successfully used at the LULI-2000 laser facility ( See C. Sauteret, rapport LULI 2001, 88 (2002) at école Polytechnique (France) to measure in the same experimental conditions the 2p-3d transitions of several elements with the neighboring atomic number Z: Fe, Ni, Cu, and Ge [ G. Loisel et al., High Energy Density Phys. 5, 173 (2009) ]. Hence, a spectrometer with a wide spectral range is needed. This spectrometer features two lines of sight. In this example, one line of sight looks through the sample and the other one is looking directly at the backlighter emission. Both are outfitted with a spherical condensing mirror. A TlAP crystal is used for spectral dispersion. Detection is made with an image plate Fuji BAS TR2025, which is sensitive to x rays. We present some experimental results showing the performances of this spectrometer.
BibTeX:
@article{Reverdin2010,
  author = {Reverdin, C. and Thais, F. and Loisel, G. and Bougeard, M.},
  title = {X-ray crystal spectrometer for opacities measurements in the 818 Ĺ spectral range at the LULI laser facility},
  journal = {Review of Scientific Instruments},
  year = {2010},
  volume = {81},
  pages = {10E327_1--5},
  url = {http://link.aip.org/link/?RSI/81/10E327},
  doi = {10.1063/1.3491285}
}
2009
"Exciton-exciton interactions in CdWO4 irradiated by intense femtosecond vacuum ultraviolet pulses"
Kirm M, Nagirnyi V, Feldbach E, De Grazia M, Carré B, Merdji H, Guizard S, Geoffroy G, Gaudin J, Fedorov N, Martin P, Vasil'ev A and Belsky A, Physical Review - B: Solid State (former title). Vol. 79, pp. 233103\_1-4 - (2009).
Abstract: Exciton-exciton interaction is experimentally revealed and quantitatively analyzed in a wide band-gap scintillator material CdWO4. Under high-intensity femtosecond vacuum ultraviolet excitation, the CdWO4 luminescence is quenched, while its decay becomes essentially nonexponential. We propose an analytical model,which successfully reproduces the decay kinetics recorded in a wide range of excitation densities. The dipoledipole interaction between excitons leading to their nonradiative decay is shown to be the main cause of a nonproportional response common for many scintillators.
BibTeX:
@article{Kirm2009,
  author = {Kirm, M. and Nagirnyi, V. and Feldbach, E. and De Grazia, M. and Carré, B. and Merdji, H. and Guizard, S. and Geoffroy, G. and Gaudin, J. and Fedorov, N. and Martin, P. and Vasil'ev, A. and Belsky, A.},
  title = {Exciton-exciton interactions in CdWO4 irradiated by intense femtosecond vacuum ultraviolet pulses},
  journal = {Physical Review - B: Solid State (former title)},
  year = {2009},
  volume = {79},
  pages = {2331031-4},
  url = {http://prb.aps.org/abstract/PRB/v79/i23/e233103},
  doi = {10.1103/PhysRevB.79.233103}
}
"Absorption spectroscopy of mid and neighboring Z plasmas: iron, nickel, copper and germanium"
Loisel G, Arnault P, Bastiani-Ceccotti S, Blenski T, Caillaud T, Fariaut J, Folsner W, Gilleron F, Pain J-C, Poirier M, Reverdin C, Silvert V, Thais F, Turck-Chièze S and Villette B, High Energy Density Physics. Vol. 5, pp. 173-181 - (2009).
Abstract: Opacities of four medium Z element plasmas (iron, nickel, copper and germanium) have been measured at the LULI-2000 facility in similar conditions: temperatures between 15 and 25 eV and densities between 2 and 10 mg/cm3, in a wavelength range (8–18 Ĺ) including the strong 2p–3d structures.

Two laser beams from the LULI facility were used in the nanosecond-picosecond configuration. The NANO-2000 beam (at λ = 0.53 µm) heated a gold hohlraum with an energy between 30 and 150 J with a duration of 0.6 ns. Samples covering half a hohlraum hole were thus radiatively heated. The picosecond pulse PICO-2000 beam (at λ = 1.053 µm) has been used to produce a short (about 10 ps) X-ray backlighter in order to reduce time variations of temperatures and densities during the measurement. A crystal high-resolution spectrometer was used as the main diagnostic to record at the same time the non-absorbed and the absorbed backlighter spectra. Radiation temperatures were measured using a broadband spectrometer. 1D and 2D simulations have been performed in order to estimate hydrodynamic plasmas parameters.

The measured spectra have been compared with theoretical ones obtained using either the superconfiguration code SCO or the detailed term accounting code HULLAC. These comparisons allow us to check the modeling of the statistical broadening and of the spin-orbit splitting of the 2p–3d transitions and related effects such as the interaction between relativistic subconfigurations belonging to the same non-relativistic configuration.

BibTeX:
@article{Loisel2009,
  author = {Loisel, G. and Arnault, P. and Bastiani-Ceccotti, S. and Blenski, T.J. and Caillaud, T. and Fariaut, J. and Folsner, W. and Gilleron, F. and Pain, J.-C. and Poirier, M. and Reverdin, C. and Silvert, V. and Thais, F. and Turck-Chièze, S. and Villette, B.},
  title = {Absorption spectroscopy of mid and neighboring Z plasmas: iron, nickel, copper and germanium},
  journal = {High Energy Density Physics},
  year = {2009},
  volume = {5},
  pages = {173--181},
  url = {http://dx.doi.org/10.1016/j.hedp.2009.05.015},
  doi = {10.1016/j.hedp.2009.05.015}
}
"Variational Average-Atom in Quantum Plasmas (VAAQP) A check of thermodynamic consistency"
Piron R, Blenski T and Cichocki B, High Energy Density Physics. Vol. 5, pp. 258-262 - (2009).
Abstract: A new code called VAAQP (Variational Average-Atom in Quantum Plasmas) is presented. The conceptual model on which the code is based, as well as the important results of previous studies are briefly discussed. The code is based on a new fully variational model of equilibrium dense plasmas employing a quantal treatment of all electrons. VAAQP can calculate the Average-Atom structure and the mean ionization from the variational equations satisfying the virial theorem and without imposing the neutrality of the WignerSeitz sphere. The formula obtained for the electron pressure is simple and does not require any numerical differentiation. A description of the principal features of the code is given. The thermodynamic consistency of the results obtained with VAAQP is shown by a comparison with another approach for the aluminium 2 eV isotherm. An initial comparison to an Inferno-type model is also presented.
BibTeX:
@article{Piron2009,
  author = {Piron, R. and Blenski, T.J. and Cichocki, B.},
  title = {Variational Average-Atom in Quantum Plasmas (VAAQP) A check of thermodynamic consistency},
  journal = {High Energy Density Physics},
  year = {2009},
  volume = {5},
  pages = {258--262},
  url = {http://dx.doi.org/10.1016/j.hedp.2009.05.013},
  doi = {10.1016/j.hedp.2009.05.013}
}
"Variational Average-Atom in Quantum Plasmas(VAAQP) - first numerical results."
Piron R, Blenski T and Cichocki B, Journal of Physics A-Mathematical and Theoretical. Vol. 42, pp. 214059 - (2009).
Abstract: The work on a new fully variational model of average-atom inquantum plasmas using a numerical code called VAAQP is reported. A briefdescription of the code is given. Application to aluminium at solid densityand temperatures between 0.05 and 12 eV is presented. Comparisons to resultsobtained using other approaches are also shown and discussed. The results provethe feasibility of the variational model in the warm dense matter regime. Effectsof the variational treatment can lead in this region to significant differences withrespect to existing models.
BibTeX:
@article{Piron2009a,
  author = {Piron, R. and Blenski, T.J. and Cichocki, B.},
  title = {Variational Average-Atom in Quantum Plasmas(VAAQP) - first numerical results.},
  journal = {Journal of Physics A-Mathematical and Theoretical},
  year = {2009},
  volume = {42},
  pages = {214059},
  url = {http://dx.doi.org/10.1088/1751-8113/42/21/214059},
  doi = {10.1088/1751-8113/42/21/214059}
}
"Highly efficient sparse-matrix inversion techniques and average procedures applied to collisional-radiative codes"
Poirier M and de Gaufridy de Dortan F, High Energy Density Physics. Vol. 5, pp. 328-336 - (2009).
Abstract: The behavior of non-local thermal-equilibrium (NLTE) plasmas plays a central role in many fields of modern-day physics, such as laser-produced plasmas, astrophysics, inertial or magnetic confinement fusion devices, and X-ray sources. In steady-state cases the proper description of these plasmas may require the solution of thousands of linear rate equations. A possible simplification for this numerical task lies in some form of statistical averaging, such as the averaging over configurations or superconfigurations. However, to assess the validity of such an averaging procedure and to handle cases where isolated lines play an important role, it will be important to treat detailed levels systems. This involves matrices with potentially billions of elements, which are rather sparse but still involve thousands of diagonals above and below the main one. We propose here a numerical algorithm based on the LU decomposition for such linear systems. It will be shown that this method is orders-of-magnitude faster than the traditional Gauss elimination. Moreover, it is found that there are no convergence or accuracy issues, which are found when using methods based on conjugate gradients or minimization. Among cases treated at the last NLTE-kinetics-code meeting, krypton and tungsten plasmas are considered. Furthermore, to assess the validity of configuration averaging, several criteria are discussed. While a criterion based on detailed balance is relevant in cases not too far from LTE, it is found to be insufficient in general. An alternate criterion based on the inspection of the influence of an arbitrary configuration temperature is proposed and tested successfully.
BibTeX:
@article{Poirier2009,
  author = {Poirier, M. and de Gaufridy de Dortan, F.},
  title = {Highly efficient sparse-matrix inversion techniques and average procedures applied to collisional-radiative codes},
  journal = {High Energy Density Physics},
  year = {2009},
  volume = {5},
  pages = {328--336},
  url = {http://dx.doi.org/10.1016/j.hedp.2009.03.012},
  doi = {10.1016/j.hedp.2009.03.012}
}
"On plasma radiative properties in stellar conditions"
Turck-Chieze S, Delahaye F, Gilles D, Loisel G and Piau L, High Energy Density Physics. Vol. 5, pp. 132-138 - (2009).
Abstract: The knowledge of stellar evolution is evolving quickly thanks to an increased number of opportunities to scrutinize the stellar internal plasma properties by stellar seismology and by 1D and 3D simulations. These new tools help us to introduce the internal dynamical phenomena in stellar modeling. A proper inclusion of these processes supposes a real confidence in the microscopic physics used, partly checked by solar or stellar acoustic modes. In the present paper we first recall which fundamental physics has been recently verified by helioseismology. Then we recall that opacity is an important ingredient of the secular evolution of stars and we point out why it is necessary to measure absorption coefficients and degrees of ionization in the laboratory for some well identified astrophysical conditions. We examine two specific experimental conditions which are accessible to large laser facilities and are suitable to solve some interesting questions of the stellar community: are the solar internal radiative interactions properly estimated and what is the proper role of the opacity in the excitation of the non-radial modes in the envelop of the ß Cepheids and the Be stars? At the end of the paper we point out the difficulties of the experimental approach that we need to overcome.
BibTeX:
@article{Turck-Chieze2009,
  author = {Turck-Chieze, S. and Delahaye, F. and Gilles, D. and Loisel, G. and Piau, L.},
  title = {On plasma radiative properties in stellar conditions},
  journal = {High Energy Density Physics},
  year = {2009},
  volume = {5},
  pages = {132--138},
  url = {http://dx.doi.org/10.1016/j.hedp.2009.06.007},
  doi = {10.1016/j.hedp.2009.06.007}
}
"Atome moyen variationnel dans les plasmas quantiques"
Piron R, In Physique.. Thesis at: Ecole Polytechnique. - (2009).
Abstract: Le calcul des propriétés radiatives des plasmas denses fait en général appel au concept d'atome dans un plasma. Parmi les modèles qui définissent un tel concept, les modèles d'atome moyen représentent souvent un point de départ indispensable avant des approches statistiques plus sophistiquées. En outre, ils permettent de calculer les propriétés thermodynamiques ainsi que certains coefficients de transport. Depuis l'application du modèle quasiclassique de Thomas-Fermi aux plasmas denses par Feynman, Metropolis et Teller, toutes ses généralisations quantiques ont conduit à des modèles qui présentent des inconsistances thermodynamiques. Ce travail porte sur un modèle variationnel d'atome moyen pour la description des plasmas denses. Contrairement aux autres modèles, ce dernier donne, par construction, accès à l'équilibre thermodynamique et vérifie le théorème du viriel. Afin de résoudre les équations de ce modèle, un code nommé VAAQP (Variational Average-Atom in Quantum Plasmas) a été réalisé. Il permet notamment le calcul de l'équation d'état des plasmas denses. Après un état de l'art des modèles d'atome moyen, le formalisme du modèle variationnel est décrit dans ses versions Thomas-Fermi, quantique non-relativiste et quantique relativiste. La validité du théorème du viriel pour ce modèle est démontrée et l'inconsistance thermodynamique des autres modèles est expliquée. Les méthodes numériques qui sont appliquées dans VAAQP sont ensuite exposées. Enfin, les résultats obtenus avec le modèle variationnel, concernant les équations d'état, sont commentés et comparés aux résultats d'autres modèles, dont le modèle INFERNO, ainsi qu'à des résultats d'expériences sur les adiabatiques d'Hugoniot.
BibTeX:
@phdthesis{PhdThesisPiron2009,
  author = {Piron, R.},
  title = {Atome moyen variationnel dans les plasmas quantiques},
  booktitle = {Physique},
  school = {Ecole Polytechnique},
  year = {2009},
  url = {http://tel.archives-ouvertes.fr/tel-00446558/fr/}
}
"FEMTOSECOND LASER ABLATION OF DIELECTRICS: EXPERIMENTAL STUDIES OF FUNDAMENTAL PROCESSES."
Guizard S, Fedorov N, Geoffroy G, Belsky A, Martin P, Bachau H and Vasil'ev A, In 10th International Conference on Laser Ablation (COLA - 2009). Singapour - (2009).
Abstract: In the field of laser ablation of wide band gap materials by ultrashort laser pulses, there has been a long debate regarding the excitation and energy deposition mechanism. This is due to the lack of direct experimental investigations, which have been mostly limited to the measurement of ablation threshold. In principle the energy balance of the interaction is completely characterised if one measure the excited carrier's density and their energy distribution. We have used an original time resolved pump-probe interferometry technique [1] to measure in real time the excited carrier density in the solid, at intensities below and above ablation threshold. The evolution of the carrier density as a function of incident intensity for different pulse duration in the range 50fs to 1.2ps suggests that multiphoton ionization is the dominant excitation mechanism. This conclusion is valid for all the materials investigated, namely SiO2 Al2O3 and MgO [2]. This results have been recently been confirmed [3]. Furthermore, we will present unpublished data of recent experiments performed with longer pulse durations (up to 10ps) and also with double pulse excitation, which bring new information on the excitation and propagation mechanisms. To measure the energy distribution of the photo-excited carriers, we used photoelectron spectroscopy. After excitation with a single pulse (Ti-Sa laser, 50fs pulse duration), the kinetic energy spectra of electron emitted at the surface of a quartz sample (α-SiO2) is measured as a function of laser intensity. We have shown that energies up to 30 eV, i.e. more than 20 times the incident the photon energy, can be observed, at intensities of the order of 1013W/cm2, i.e. far below breakdown threshold [4]. To interpret this observation, we have developed a new model, describing the heating of carriers in the conduction band as a succession of multiphoton transition enhanced by resonance with different branches of the conduction band. This mechanism is extremely efficient, at lest 100 times more efficient than in atoms, and should be taken into account in the modeling of laser induced breakdown. Finally, we have observed, with a new MEB providing images with resolution better than 10nm on dielectrics, the surface of craters after ablation under various experimental conditions (number of shots, polarization, wavelength, etc). Unexpectedly, the structures observed very much depends upon the material considered (SiO2, Al2O3, MgO, KDP) showing that ablation is not only a pure plasma process, but that the materials properties play a major role in the final result of ablation. [1] Audebert P., Daguzan Ph., Guizard S., et al. Physical Review Letters 52, p. 1994.[2] Quéré F, Guizard S, Martin P, Europhys. Lett. 56, p. 138-144, 2001. [3] V.V. Temnov, et al., Phys. Rev. Lett. 97, p. 237403, 2006. [4] Belsky A, Martin P, Bachau H, Guizard S. et al.EuroPhysics Letters 67 (2): p.301, 2004.
BibTeX:
@inproceedings{InproGuizard2009,
  author = {Guizard, S. and Fedorov, N. and Geoffroy, G. and Belsky, A. and Martin, P. and Bachau, H. and Vasil'ev, A.},
  title = {FEMTOSECOND LASER ABLATION OF DIELECTRICS: EXPERIMENTAL STUDIES OF FUNDAMENTAL PROCESSES.},
  booktitle = {10th International Conference on Laser Ablation (COLA - 2009)},
  year = {2009}
}
2008
"Les supraconfigurations : un outil pour l'étude des plasmas d'ions multichargés à l'ETL"
Blenski T and Pain J-C, Chocs. Vol. 36, pp. 13-21 - (2008).
Abstract: Afin de modéliser l'absorption et l'émission du rayonnement par les plasmas, il s'avère nécessaire de prendre en compte un très grand nombre de configurations électroniques des ions et de décrire de manière réaliste leurs structures. La méthode des supraconfigurationsa été introduite afin de calculer l'opacité des plasmas à l'équilibre thermodynamique local.Elle constitue une approche statistique de la physique atomique des plasmas denses au-delàdu modèle de l'Atome Moyen. Chaque espèce ionique est décrite par un ensemble de supraconfigurations, chaque supraconfiguration représentant un groupe de configurations électroniques. Dans cet article, nous présentons les principes de la méthode des supraconfigurations ainsi que sa réalisation pratique dans un code de calcul d'opacité (SCO). Une des spécificités de ce code est l'inclusion de l'écrantage statique des ions par le plasma. Ce modèle a été confronté aux résultats d'une série d'expériences de mesure d'opacité dans lesquelles la densité du plasma était de l'ordre de 0.01 g/cm3. En principe, ce modèle permettra également l'étude des effets de densité (notamment de l'ionisation par pression) sur l'opacité et sur l'équation d'état des plasmas plus denses.AbstractIn order to model absorption and emission of radiation by plasmas it is necessary toaccount for a huge number of ion configurations and to use a realistic description of theirelectronic structures. The superconfiguration method has been introduced in order to calculateopacities in plasmas at local thermodynamic equilibrium. This method is a statisticalapproach to ions allowing one to study atomic physics of dense plasmas beyond the AverageAtom model. Each ionic species is described by a group of superconfigurations and each superconfiguration represents in turn a certain number of configurations. In this article we present the basic principles of the superconfiguration method as well as its practicalimplementation in a numerical code (SCO). One of the main features of that code is the inclusion of static screening of ions by plasma. Results of this model have been compared to results of published opacity measurements in which plasma density was of the order of 0.01 g/cm3. In principle the model will allow us to study plasma density effects (for example pressure ionization) on opacity and equation of state in case of higher density plasmas.
BibTeX:
@article{Blenski2008,
  author = {Blenski, T. and Pain, J.-C.},
  title = {Les supraconfigurations : un outil pour l'étude des plasmas d'ions multichargés à l'ETL},
  journal = {Chocs},
  year = {2008},
  volume = {36},
  pages = {13--21}
}
"On various validity criteria for the configuration average in collisional-radiative codes"
Poirier M, Journal of Physics B. Atomic, Molecular and Optical Physics. Vol. 41, pp. 025701 - (2008).
Abstract: The characterization of out-of-local-thermal-equilibrium plasmas requires the use of collisional-radiative kinetic equations. This leads to the solution of large linear systems, for which statistical treatments such as configuration average may bring considerable simplification. In order to check the validity of this procedure, a criterion based on the comparison between a partial-rate systems and the Saha-Boltzmann solution is discussed in detail here. Several forms of this criterion are discussed. The interest of these variants is that they involve each type of relevant transition (collisional or radiative), which allows one to check separately the influence of each of these processes on the configuration-average validity. The method is illustrated by a charge-distribution analysis in carbon and neon plasmas. Finally, it is demonstrated that when the energy dispersion of every populated configuration is smaller than the electron thermal energy, the proposed criterion is fulfilled in each of its forms.
BibTeX:
@article{Poirier2008,
  author = {Poirier, M.},
  title = {On various validity criteria for the configuration average in collisional-radiative codes},
  journal = {Journal of Physics B. Atomic, Molecular and Optical Physics},
  year = {2008},
  volume = {41},
  pages = {025701},
  url = {http://dx.doi.org/10.1088/0953-4075/41/2/025701},
  doi = {10.1088/0953-4075/41/2/025701}
}
"Relaxation of electronic excitations in wide-gap crystals studied by femtosecond interferometry technique"
Nagirnyi V, Geoffroy G, Guizard S, Kirm M and Kotlov A, Physics of the Solid State. Vol. 50(9), pp. 1784-1788 - (2008).
Abstract: Time-resolved interferometry with a 100-fs temporal resolution was applied for the first time to studying the relaxation of electronic excitations in complex oxides, namely, tungstates CDWO4 with a crystal lattice of the wolframite-type and CaWO4 with a scheelite-type lattice. Two stages of charge carrier relaxation, namely, very fast carrier trapping in 200 fs resulting in self-trapped exciton formation and a relatively slow picosecond relaxation process probably due to configurational relaxation within the oxyanion molecule and modification of the surrounding lattice, are revealed in tungstate crystals. Corresponding models of self-trapped exciton creation in tungstate crystals are discussed.
BibTeX:
@article{Nagirnyi2008,
  author = {Nagirnyi, V. and Geoffroy, G. and Guizard, S. and Kirm, M. and Kotlov, A.},
  title = {Relaxation of electronic excitations in wide-gap crystals studied by femtosecond interferometry technique},
  journal = {Physics of the Solid State},
  year = {2008},
  volume = {50},
  number = {9},
  pages = {1784--1788},
  url = {http://link.springer.com/article/10.1134%2FS1063783408090382},
  doi = {10.1134/S1063783408090382}
}
2007
"Interpretation of some X-ray and XUV absorption experiments using SCO"
Arnault P, Blenski T and Dejonghe G, High Energy Density Physics. Vol. 3, pp. 17 - (2007).
Abstract: We review some X-ray and XUV absorption experiments on aluminium and germanium making systematic comparison between theory and experiment with the help of the superconfiguration code SCO. The objective is to identify areas that require further theoretical development. As for the low and medium Z elements considered, the statistical term treatment essential in the superconfiguration method is less physically sound than a detailed line-by-line treatment. Nevertheless, we comment on recent spectroscopic measurements at near solid density that suggest a larger domain of validity for statistical approximation than previously thought. We will also address some specific theoretical issues that affect the absorption structures such as orbital relaxation in the final state of optical transitions and the broadening of spectral lines by collisions with electrons.
BibTeX:
@article{Arnault2007,
  author = {Arnault, P. and Blenski, T.J. and Dejonghe, G.},
  title = {Interpretation of some X-ray and XUV absorption experiments using SCO},
  journal = {High Energy Density Physics},
  year = {2007},
  volume = {3},
  pages = {17},
  url = {http://dx.doi.org/10.1016/j.hedp.2007.01.001},
  doi = {10.1016/j.hedp.2007.01.001}
}
"Analysis of the X-ray and time-resolved XUV emission of laser produced Xe and Kr plasmas"
Bastiani-Ceccotti S, Kontogiannopoulos N, Marquès J-R, Tzortzakis S, Lecherbourg L, Thais F, Matsushima I, Peyrusse O and Chenais-Popovics C, High Energy Density Physics. Vol. 3, pp. 20-27 - (2007).
Abstract: A frequency-doubled laser beam of the Nd:glass kilojoule nanosecond LULI2000 facility (1.5 ns duration, 200–400 J energy, 0.53 µm wavelength) was focused on a Xe or Kr gas jet. The plasma was simultaneously diagnosed with X-ray (in the wavelength range of 6–8 Ĺ for Kr and of 12–15 Ĺ for Xe) and time-resolved XUV (20–200 Ĺ) emission spectroscopy. Electron density and temperature as well as the ionization charge were measured by time-resolved Thomson scattering of the heating laser pulse. The spectra are compared with the calculations performed with the NLTE collisional-radiative code AVERROES/TRANSPEC. Best fits of the X-ray and XUV spectra obtained are presented. The measured charge distribution and dynamics is analyzed using the simultaneous Thomson scattering diagnostic.
BibTeX:
@article{Bastiani-Ceccotti2007,
  author = {Bastiani-Ceccotti, S. and Kontogiannopoulos, N. and Marquès, J.-R. and Tzortzakis, S. and Lecherbourg, L. and Thais, F. and Matsushima, I. and Peyrusse, O. and Chenais-Popovics, C.},
  title = {Analysis of the X-ray and time-resolved XUV emission of laser produced Xe and Kr plasmas},
  journal = {High Energy Density Physics},
  year = {2007},
  volume = {3},
  pages = {20--27},
  url = {http://dx.doi.org/10.1016/j.hedp.2007.01.004},
  doi = {10.1016/j.hedp.2007.01.004}
}
"Variational theory of Average-Atom and superconfigurations in quantum plasmas"
Blenski T and Cichocki B, Physical Review E. Vol. 75, pp. 056402 - (2007).
Abstract: Models of screened ions in equilibrium plasmas with all quantum electrons are important in opacity and equation of state calculations. Although such models have to be derived from variational principles, up to now existing models have not been fully variational. In this paper a fully variational theory respecting virial theorem is proposed -- all variables are variational except the parameters defining the equilibrium, i.e., the temperature T, the ion density ni and the atomic number Z. The theory is applied to the quasiclassical Thomas-Fermi (TF) atom, the quantum average atom (QAA), and the superconfigurations (SC) in plasmas. Both the self-consistent-field (SCF) equations for the electronic structure and the condition for the mean ionization Z* are found from minimization of a thermodynamic potential. This potential is constructed using the cluster expansion of the plasma free energy from which the zero and the first-order terms are retained. In the zero order the free energy per ion is that of the quantum homogeneous plasma of an unknown free-electron density n0=Z*ni occupying the volume 1/ni. In the first order, ions submerged in this plasma are considered and local neutrality is assumed. These ions are considered in the infinite space without imposing the neutrality of the Wigner-Seitz (WS) cell. As in the Inferno model, a central cavity of a radius R is introduced, however, the value of R is unknown a priori. The charge density due to noncentral ions is zero inside the cavity and equals en0 outside. The first-order contribution to free energy per ion is the difference between the free energy of the system central ion + infinite plasma and the free energy of the system infinite plasma. An important part of the approach is an ionization model (IM), which is a relation between the mean ionization charge Z* and the first-order structure variables. Both the IM and the local neutrality are respected in the minimization procedure. The correct IM in the TF case is found to be Z−Z*= Integral d3r [n(vec(r))−n0], where n(vec(r)) is the first-order electron density. It is shown that in the QAA case the same IM has to be used and that other IMs lead to unphysical solutions. With this IM R becomes in both cases (TF and QAA) equal to the WS radius and the variational calculation leads to SCF equations in an infinite plasma while n0 (or equivalently Z*) is to be found from the condition Integral d3r Theta(r−R) Vel(vec(r))=0, where Theta denotes Heaviside function and Vel(vec(r)) is the SCF electrostatic potential. In the SC case results are similar except that averages over all superconfigurations appear. In the TF case the condition for n0 gives the neutrality of the WS sphere and one gets the classical TF ion-in-cell average atom. The situation is different in the QAA and in the SC cases in which the cavity is not neutral and the SCF potential Vel(vec(r)) is not zero outside the cavity. Due to the fully variational character of our approach the expression for the thermodynamic pressure in all cases does not require any numerical differentiation and is consistent with the virial theorem.
BibTeX:
@article{Blenski2007,
  author = {Blenski, T.J. and Cichocki, B.},
  title = {Variational theory of Average-Atom and superconfigurations in quantum plasmas},
  journal = {Physical Review E},
  year = {2007},
  volume = {75},
  pages = {056402},
  url = {http://dx.doi.org/10.1103/PhysRevE.75.056402}
}
"Variational approach to the Average-Atom-in-jellium and superconfigurations-in-jellium models with all electrons treated quantum-mechanically"
Blenski T and Cichocki B, High Energy Density Physics. Vol. 3, pp. 34-47 - (2007).
Abstract: Models of average atom and superconfigurations in plasmas with full quantum description of all electrons are important in opacity and EOS calculations, especially in case of high density plasmas in which pressure ionization phenomena can occur. However variational formulation of models becomes difficult when quantum free electrons are considered.In our approach we use a cluster expansion of the free energy expression from which we retain the sum of the zero and of the first order terms. In the zero order the free energy is that of the homogeneous jellium of an unknown free electron density. In the first order we consider a one self-consistent-field (SCF) average atoms or ions submerged in this jellium. The SCF potential is assumed to be localized. We consider the first-order atoms or ion in the whole space without imposing the neutrality of the Wigner-Seitz cell. The important part of the model is a relation between the average ion charge and the localized part of electron density that is called ionizationmodel.The minimization procedure of the free energy is performed with respect to all variables except these characterizing the plasma equilibrium i.e. except the temperature, the ion density and the atomic number. It is interesting that when the electron density is taken in the Thomas-Fermi (TF) approximation together with a specific choice of the ionization model, our approach correctly leads to the classical TF ion-in-cell average atom. It also appears that the same ionization model has to be used in the quantum case and that other ionization models lead to unphysical solutions. This observation is important with respect to the choice of correct ionization model in the case of superconfigurations in jellium.Due to the fully variational character of our approach the resulting expression for the thermodynamic pressure in all considered cases is simple and does not require any numerical differentiation.
BibTeX:
@article{Blenski2007a,
  author = {Blenski, T.J. and Cichocki, B.},
  title = {Variational approach to the Average-Atom-in-jellium and superconfigurations-in-jellium models with all electrons treated quantum-mechanically},
  journal = {High Energy Density Physics},
  year = {2007},
  volume = {3},
  pages = {34--47},
  url = {http://dx.doi.org/10.1016/j.hedp.2007.01.006}
}
"Effect of lateral radiative losses on radiative shock propagation"
Busquet M, Audit E, Gonzalez M, Stehle C, Thais F, Acef O, Bauduin D, Barroso P, Rus B, Kozlova M, Polan J and Mocek T, High Energy Density Physics. Vol. 3, pp. 8-11 - (2007).
Abstract: Experimental and numerical studies of radiative shocks, of interest as scaled astrophysical objects, have been performed. Experiments were conducted at the PALS facility in Prague with a xenon filled mini-shock tube using a laser accelerated plastic pusher. Numerical simulations of the hydrodynamics including radiation effects have been performed with the 3D code HERACLES. Measurements have been made of the electronic density of the shocked gas and of the time history of the position of the radiative precursor. Simulations and experimental results show good agreement when lateral radiative losses are taken into account, including a wall albedo of 40%.
BibTeX:
@article{Busquet2007,
  author = {Busquet, M. and Audit, E. and Gonzalez, M. and Stehle, C. and Thais, F. and Acef, O. and Bauduin, D. and Barroso, P. and Rus, B. and Kozlova, M. and Polan, J. and Mocek, T.},
  title = {Effect of lateral radiative losses on radiative shock propagation},
  journal = {High Energy Density Physics},
  year = {2007},
  volume = {3},
  pages = {8--11},
  url = {http://dx.doi.org/10.1016/j.hedp.2007.01.002},
  doi = {10.1016/j.hedp.2007.01.002}
}
"High-gain direct-drive inertial confinement fusion for the Laser Mégajoule: recent progress"
Canaud B, Garaude F, Ballereau P, Bourgade J, Clique C, Dureau D, Houry M, Jaouen S, Jourdren H, Lecler N, Masse L, Masson A, Quach R, Piron R, Riz D, Van der Vliet J, Temporal M, Delettrez J and McKenty P, Plasma Physics and Controlled Fusion. Vol. 49, pp. B601-B610 - (2007).
Abstract: Recent progress in high-gain direct-drive inertial confinement fusion with the laser Mégajoule is reviewed. A new baseline direct-drive target design is presented which implodes with a two-cones irradiation pattern of indirect-drive beam configuration and zooming. Perturbation amplitudes and correlated growth rates of hydrodynamic instabilities in the compressed core of a directly driven inertial confinement fusion capsule are analyzed in planar and spherical geometries, with and without heat conduction, in the unsteady state regime of the deceleration. Shock propagation in heterogeneous media is addressed in the context of first shock. The neutron and photon emissions of high-gain direct-drive target are characterized. Numerical interpretations of directly driven homothetic cryogenic D2 target implosion experiments on the Omega facility are presented.
BibTeX:
@article{Canaud2007,
  author = {Canaud, B. and Garaude, F. and Ballereau, P. and Bourgade, J.L. and Clique, C. and Dureau, D. and Houry, M. and Jaouen, S. and Jourdren, H. and Lecler, N. and Masse, L. and Masson, A. and Quach, R. and Piron, R. and Riz, D. and Van der Vliet, J. and Temporal, M. and Delettrez, J.A. and McKenty, P.W.},
  title = {High-gain direct-drive inertial confinement fusion for the Laser Mégajoule: recent progress},
  journal = {Plasma Physics and Controlled Fusion},
  year = {2007},
  volume = {49},
  pages = {B601-B610},
  url = {http://dx.doi.org/10.1088/0741-3335/49/12B/S56},
  doi = {10.1088/0741-3335/49/12B/S56}
}
"Measurement of XUV-absorption spectra of ZnS radiatively heated foils"
Kontogiannopoulos N, Bastiani-Ceccotti S, Thais F, Chenais-Popovics C, Sauvan P, Schott R, Folsner W, Arnault P, Poirier M and Blenski T, High Energy Density Physics. Vol. 3, pp. 149-155 - (2007).
Abstract: Time-resolved absorption of zinc sulfide (ZnS) and aluminum in the XUV-range has been measured. Thin foils in conditions close to local thermodynamic equilibrium were heated by radiation from laser-irradiated gold spherical cavities. Analysis of the aluminum foil radiative hydrodynamic expansion, based on the detailed atomic calculations of its absorption spectra, showed that the cavity emitted flux that heated the absorption foils corresponds to a radiation temperature in the range 55 60 eV. Comparison of the ZnS absorption spectra with calculations based on a superconfiguration approach identified the presence of species Zn6+ - Zn8+ and S5+ - S6+. Based on the validation of the radiative source simulations, experimental spectra were then compared to calculations performed by post-processing the radiative hydrodynamic simulations of ZnS. Satisfying agreement is found when temperature gradients are accounted for.
BibTeX:
@article{Kontogiannopoulos2007,
  author = {Kontogiannopoulos, N. and Bastiani-Ceccotti, S. and Thais, F. and Chenais-Popovics, C. and Sauvan, P. and Schott, R. and Folsner, W. and Arnault, P. and Poirier, M. and Blenski, T.J.},
  title = {Measurement of XUV-absorption spectra of ZnS radiatively heated foils},
  journal = {High Energy Density Physics},
  year = {2007},
  volume = {3},
  pages = {149--155},
  url = {http://dx.doi.org/10.1016/j.hedp.2007.02.011},
  doi = {10.1016/j.hedp.2007.02.011}
}
"A comparison between detailed and configuration-averaged collisional radiative codes applied to non-local-thermal-equilibrium plasmas"
Poirier M and de Gaufridy de Dortan F, Journal of Applied Physics. Vol. 101, pp. 063308 - (2007).
Abstract: A collisional-radiative model describing nonlocal-thermodynamic-equilibrium plasmas is developed. It is based on the HULLAC (Hebrew University Lawrence Livermore Atomic Code) suite for the transitions rates, in the zero-temperature radiation field hypothesis. Two variants of the model are presented: the first one is configuration averaged, while the second one is a detailed level version. Comparisons are made between them in the case of a carbon plasma; they show that the configuration-averaged code gives correct results for an electronic temperature Te = 10eV (or higher) but fails at lower temperatures such as Te = 1eV. The validity of the configuration-averaged approximation is discussed: the intuitive criterion requiring that the average configuration-energy dispersion must be less than the electron thermal energy turns out to be a necessary but far from sufficient condition. Another condition based on the resolution of a modified rate-equation system is proposed. Its efficiency is emphasized in the case of low-temperature plasmas. Finally, it is shown that near-threshold autoionization cascade processes may induce a severe failure of the configuration-average formalism.
BibTeX:
@article{Poirier2007,
  author = {Poirier, M. and de Gaufridy de Dortan, F.},
  title = {A comparison between detailed and configuration-averaged collisional radiative codes applied to non-local-thermal-equilibrium plasmas},
  journal = {Journal of Applied Physics},
  year = {2007},
  volume = {101},
  pages = {063308},
  url = {http://dx.doi.org/10.1063/1.2713085},
  doi = {10.1063/1.2713085}
}
"Revisiting nonlocal electron-energy transport in inertial-fusion conditions"
Schurtz G, Gary S, Hulin S, Chenais-Popovics C, Gauthier J, Thais F, Breil J, Durut J, Feugeas J, Maire P, Nicolaï P, Peyrusse O, Reverdin C, Soullié G, Tikhonchuk V, Villette B and Fourment C, Physical Review Letters. Vol. 98(9), pp. 095002.1-4 - (2007).
Abstract: Correct modeling of the electron-energy transport is essential for inertial confinement fusion target design. Various transport models have been proposed in order to extend the validity of a hydrodynamical description into weakly collisional regimes, taking into account the nonlocality of the electron transport combined with the effects of self-generated magnetic fields. We have carried out new experiments designed to be highly sensitive to the modeling of the heat flow on the Ligne d'Integration Laser facility, the prototype of the Laser Megajoule. We show that two-dimensional hydrodynamic simulations correctly reproduce the experimental results only if they include both the nonlocal transport and magnetic fields.
BibTeX:
@article{Schurtz2007,
  author = {Schurtz, G. and Gary, S. and Hulin, S. and Chenais-Popovics, C. and Gauthier, J.C. and Thais, F. and Breil, J. and Durut, J. and Feugeas, J.L. and Maire, P.H. and Nicolaï, P. and Peyrusse, O. and Reverdin, C. and Soullié, G. and Tikhonchuk, V. and Villette, B. and Fourment, C.},
  title = {Revisiting nonlocal electron-energy transport in inertial-fusion conditions},
  journal = {Physical Review Letters},
  year = {2007},
  volume = {98},
  number = {9},
  pages = {095002.1--4},
  url = {http://dx.doi.org/10.1103/PhysRevLett.98.095002},
  doi = {10.1103/PhysRevLett.98.095002}
}
"Two Collisional-Radiative Codes based on the HULLAC suite: Detailed Levels (CRCHDL5) and Configuration Average (CRCHCA5)"
Poirier M, In 5th Non-LTE Code Comparison Workshop. Etats-Unis - (2007).
BibTeX:
@inproceedings{InproPoirier2007,
  author = {Poirier, M.},
  title = {Two Collisional-Radiative Codes based on the HULLAC suite: Detailed Levels (CRCHDL5) and Configuration Average (CRCHCA5)},
  booktitle = {5th Non-LTE Code Comparison Workshop - 2007},
  year = {2007}
}
"Physique atomique des plasmas hors équilibre : codes détaillés et moyennes en configurations"
Poirier M, de Gaufridy de Dortan F, Blenski T, Piron R and Thais F, In Forum ILP France - (2007).
Abstract: Les plasmas créés en laboratoire, par exemple par interaction laser, ou ceux d'intérêt astrophysique sont souvent hors équilibre thermodynamique local. Les codes collisionnels-radiatifs (CR) permettent alors de caractériser ces plasmas et de décrire notamment leur distribution de charges, de populations, leur émissivité ou leur opacité. Après une brève revue des processus physiques mis en jeu et des modèles disponibles, deux codes CR fondés sur la suite HULLAC sont présentés, l'un détaillé et l'autre moyenné en configurations. Cette moyenne améliore considérablement la rapidité du calcul, cependant il est important de tester sa validité. Aussi un nouveau critère fondé sur le principe de microréversibilité est-il proposé. Il est testé dans le cas d'un plasma de carbone et se révèle préférable au critère intuitif requérant que la moyenne de la dispersion en énergie des configurations soit plus petite que l'énergie thermique des électrons. Les améliorations possibles du modèle numérique et les applications nouvelles sont discutées.
BibTeX:
@inproceedings{InproPoirier22007,
  author = {Poirier, M. and de Gaufridy de Dortan, F. and Blenski, T.J. and Piron, R. and Thais, F.},
  title = {Physique atomique des plasmas hors équilibre : codes détaillés et moyennes en configurations},
  booktitle = {Forum ILP - 2007},
  year = {2007}
}
2006
"Interaction of intense VUV impulsions with luminescent solids."
Belsky A, Carre B, N F, E F, Gaudin J, Guizard S, Geoffroy G, Grazia D, Kirm, Martin P, Merdji H, Nagirnyi, Petite G and Vasil'ev , Journal de Physique IV. Vol. 138, pp. 155-161 - (2006).
Abstract: Nous présentons les résultats d'études de luminescence résolue en temps émise par des cristaux sous excitation par des photons VUV issus de la génération d'harmoniques d'ordre élevé. L'utilisation d'un laser Ti-Sa PLFA à Saclay, qui délivre des impulsions d'une énergie de 13mJ et d'une durée de 35 fs à 1 KHz, pour la génération des harmoniques dans l'Argon et la microfocalisation du faisceau VUV nous ont permis de faire varier la densité du rayonnement sur la cible dans une large gamme. Nous avons étudié l'effet de la densité d'excitation VUV sur la luminescence intrinsèque de cristaux à large bande interdite (CdWO4 et BaF2). En fonction de la densité d'excitation VUV nous avons observé les modifications des spectres d'émission et de la cinétique de la luminescence excitonique. Quand la densité d'excitation VUV croît, le rendement de la luminescence diminue et apparaissent dans la cinétique de luminescence descomposantes rapides. Le profil de la courbe de déclin devient alors complexe avec une forte déviation de la loi exponentielle dans sa partie initiale.
BibTeX:
@article{Belsky2006,
  author = {Belsky, A. and Carre, B. and Fedorov N and Feldbach E and Gaudin, J. and Guizard, S. and Geoffroy, G. and De Grazia and Kirm and Martin, P. and Merdji, H. and Nagirnyi and Petite, G. and Vasil'ev},
  title = {Interaction of intense VUV impulsions with luminescent solids.},
  journal = {Journal de Physique IV},
  year = {2006},
  volume = {138},
  pages = {155--161},
  url = {http://jp4.journaldephysique.org/articles/jp4/abs/2006/07/jp4138018/jp4138018.html},
  doi = {10.1051/jp4:2006138018}
}
"On the linear dynamic response of average atom in plasma"
Blenski T, Journal of Quantitative Spectroscopy and Radiative Transfer. Vol. 99(1-3), pp. 84-101 - (2006).
Abstract: The theory of linear response of an Average Atom (AA) in plasma is considered. It is assumed that the model of the AA is of the Density Functional Theory (DFT) type, i.e., can be characterized by an equilibrium electron density in terms of a complete set of bound and free one-electron wave functions of a screened self-consistent-field (SCF) potential. The starting point in the linear response theory is the cluster expansion of the energy extinction coefficient. This coefficient expresses the rate of extinction of the energy due to an external potential irradiating a plasma composed if ions and electrons. As shown in previous publications the first order term in the cluster expansion correctly gives the linear response of the AA. The first order formula for the extinction coefficient is directly related to the AA photo-absorption cross-section. The cluster expansion technique shows how the homogeneous plasma contribution shall be correctly subtracted from the response of the AA and its surrounding plasma. The linear response is considered in the dipole approximation and in the framework of the RPA approximation which can be viewed as a version of a time-dependent DFT with local density approximation to the exchange-correlation potential. In the paper we discuss a possible practical scheme for calculation of the dipole linear response and obtain some theoretical results that allow one to reduce the theoretical and numerical difficulties of the approach. We show formally how in the dipole approximation the homogeneous plasma contribution to the induced potential results in the appearance of the cold-plasma dielectric function. We also derive a new sum rule which allows one to calculate the induced dipole using the localized density and potential gradients of the AA in equilibrium. We further propose a change of variables that allows us to eliminate the leading dipole divergence in the first order Schrödinger equations. We next discuss some aspects of a simplified case in which the induced potential is neglected. Finally, we present and comment on the radial equations for the SCF frequency-dependent induced density and potential.
BibTeX:
@article{Blenski2006,
  author = {Blenski, T.},
  title = {On the linear dynamic response of average atom in plasma},
  journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
  year = {2006},
  volume = {99},
  number = {1-3},
  pages = {84--101},
  url = {http://dx.doi.org/10.1016/j.jqsrt.2005.05.007},
  doi = {10.1016/j.jqsrt.2005.05.007}
}
"Use of luminescent materials for the metrology of intense UVX bundles of ultrashort impulsions."
Fedorov, Nagirnyi, Vasil'ev, Belsky A, Carre B, Feldbach, Gaudin J, Geoffroy G, Guizard S, De Grazia M, Kirm M, Martin P, Merdji H and Petite G, Journal de Physique IV. Vol. 138, pp. 251-257 - (2006).
Abstract: Récemment nous avons débuté des séries d'expériences sur l'interaction d'impulsions intenses VUV avec les solides luminescents. Le but principal en est l'étude des mécanismes d'interaction et de transfert d'énergie entre les excitations électroniques dans les solides à large bande interdite. L'application directe de ces études sera le développement de matériaux et de méthodes de métrologie pour les faisceauxUVX intenses. Nous présentons les résultats obtenus pour CdWO4 qui montrent que ce cristal pourra servir comme un scintillateur pour le rayonnement VUV intense.
BibTeX:
@article{Fedorov2006,
  author = {Fedorov and Nagirnyi and Vasil'ev and Belsky, A. and Carre, B. and Feldbach and Gaudin, J. and Geoffroy, G. and Guizard, S. and De Grazia, M and Kirm, M.) and Martin, P. and Merdji, H. and Petite, G.},
  title = {Use of luminescent materials for the metrology of intense UVX bundles of ultrashort impulsions.},
  journal = {Journal de Physique IV},
  year = {2006},
  volume = {138},
  pages = {251--257},
  url = {10.1051/jp4:2006138029}
}
"Astrophysical radiative shocks: From modeling to laboratory experiments"
Gonzalez M, Stehlé C, Audit E, Busquet M, Rus B, Thais F, Acef O, Barroso P, Bar-Shalom A, Bauduin D, Kozlova M, Lery T, Madouri A, Mocek T and Polan J, Laser and Particle Beams. Vol. 24, pp. 535-540 - (2006).
Abstract: Radiative shock waves are observed around astronomical objects in a wide variety of environments, for example, they herald the birth of stars and sometimes their death. Such shocks can also be created in the laboratory, for example, by using energetic lasers. In the astronomical case, each observation is unique and almost fixed in time, while shocks produced in the laboratory and by numerical simulations can be reproduced, and investigated in greater detail. The combined study of experimental and computational results, as presented here, becomes a unique and powerful probe to understanding radiative shock physics. Here we show the first experiment on radiative shock performed at the PALS laser facility. The shock is driven by a piston made from plastic and gold in a cell filled with xenon at 0.2 bar. During the first 40 ns of the experiment, we have traced the radiative precursor velocity, that is showing a strong decrease at that stage. Three-dimensional (3D) numerical simulations, including state-of-art opacities, seem to indicate that the slowing down of the precursor is consistent with a radiative loss, induced by a transmission coefficient of about 60% at the walls of the cell. We infer that such 3D radiative effects are governed by the lateral extension of the shock wave, by the value of the opacity, and by the reflection on the walls. Further investigations will be required to quantify the relative importance of each component on the shock properties.
BibTeX:
@article{Gonzalez2006,
  author = {Gonzalez, M. and Stehlé, C. and Audit, E. and Busquet, M. and Rus, B. and Thais, F. and Acef, O. and Barroso, P. and Bar-Shalom, A. and Bauduin, D. and Kozlova, M. and Lery, T. and Madouri, A. and Mocek, T. and Polan, J.},
  title = {Astrophysical radiative shocks: From modeling to laboratory experiments},
  journal = {Laser and Particle Beams},
  year = {2006},
  volume = {24},
  pages = {535--540},
  url = {http://dx.doi.org/10.1017/S026303460606071X},
  doi = {10.1017/S026303460606071X}
}
"Quantum mechanical model for the study of pressure ionization in the superconfiguration approach"
Pain J, Dejonghe G and Blenski T, Journal of Physics A. Mathematical and General Physics. Vol. 39, pp. 4659-4666 - (2006).
Abstract: The knowledge of plasma equation of state and photoabsorption requires suitable and realistic models for the description of ions. The number of relevant electronic configurations of ions in hot dense plasmas can be immense (increasing with atomic number Z). In such cases, calculations relying on the superconfiguration approximation appear to be among the best statistical approaches to photoabsorption in plasmas. The superconfiguration approximation enables one to perform rapid calculation of averages over all possible configurations representing excited states of bound electrons. We present a thermodynamically consistent model involving detailed screened ions (described by superconfigurations) in plasmas. The density effects are introduced via the ion-sphere model. In the usual approaches, bound electrons are treated quantum mechanically while free electrons are described within the framework of semi-classical ThomasFermi theory. Such a hybrid treatment can lead to discontinuities in the thermodynamic quantities when pressure ionization occurs. We propose a model in which all electrons (bound and free) are treated quantum mechanically. Furthermore, resonances are carefully taken into account in the self-consistent calculation of the electronic structure of each superconfiguration. The model provides the contribution of electrons to the main thermodynamic quantities, together with a treatment of pressure ionization, and gives a better insight into the electronic properties of hot dense plasmas.
BibTeX:
@article{Pain2006,
  author = {Pain, J.C. and Dejonghe, G. and Blenski, T.J.},
  title = {Quantum mechanical model for the study of pressure ionization in the superconfiguration approach},
  journal = {Journal of Physics A. Mathematical and General Physics},
  year = {2006},
  volume = {39},
  pages = {4659--4666},
  url = {http://dx.doi.org/10.1088/0305-4470/39/17/S53},
  doi = {10.1088/0305-4470/39/17/S53}
}
"A self-consistent model for the study of electronic properties of hot dense plasmas in the superconfiguration approximation"
Pain J-C, Dejonghe G and Blenski T, Journal of Quantitative Spectroscopy and Radiative Transfer. Vol. 99(1-3), pp. 451-468 - (2006).
Abstract: We propose a thermodynamically consistent model involving detailed screened ion, described by superconfigurations, in plasmas. In the present work, the electrons, bound and free, are treated quantum-mechanically so that resonances are carefully taken into account in the self-consistent calculation of the electronic structure of each superconfiguration. The procedure is in some sense similar to the one used in Inferno code develop by D. Liberman; however, here we perform this calculation in the ion-sphere model for each superconfiguration. The superconfiguration approximation allows rapid calculation of necessary averages over all possible configurations representing excited states of bound electrons. The model enables a fully quantum mechanical self-consistent calculation of the electronic structure of ions and provides the relevant thermodynamic quantities (e.g., internal energy, Helmholtz free energy and pressure), together with an improved treatment of pressure ionization. It should therefore give a better insight into the impact of plasma effects on photo-absorption spectra
BibTeX:
@article{Pain2006a,
  author = {Pain, J.-C. and Dejonghe, G. and Blenski, T.},
  title = {A self-consistent model for the study of electronic properties of hot dense plasmas in the superconfiguration approximation},
  journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
  year = {2006},
  volume = {99},
  number = {1-3},
  pages = {451--468},
  url = {http://dx.doi.org/10.1016/j.jqsrt.2005.05.036},
  doi = {10.1016/j.jqsrt.2005.05.036}
}
"Modeling of EUV emission from xenon and tin plasma sources for nanolithography"
Poirier M, Blenski T, de Gaufridy de Dortan F and Gilleron F, Journal of Quantitative Spectroscopy and Radiative Transfer. Vol. 99(1-3), pp. 482-492 - (2006).
Abstract: Since the last decade a strong effort has been devoted to the development of efficient extreme UV sources designed for nanolithography, operating mainly in the 13.5 nm range. Possible devices involve laser-produced plasmas and discharge-produced plasmas. This paper, devoted to the modeling of such emission, puts emphasis on the atomic physics effects and noticeably on configuration interaction. Mainly two types of theoretical approaches are presented, one involving the detailed computation with the parametric potential code HULLAC, the other based on the supraconfiguration code SCO. Computations of emission spectra in xenon and tin are presented. The possible influence of non-local thermodynamic equilibrium (LTE) effects is investigated using populations given by the simple collisional-radiative formulae from Colombant and Tonon. Convergence to LTE is analyzed in the tin case.
BibTeX:
@article{Poirier2006,
  author = {Poirier, M. and Blenski, T. and de Gaufridy de Dortan, F. and Gilleron, F.},
  title = {Modeling of EUV emission from xenon and tin plasma sources for nanolithography},
  journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
  year = {2006},
  volume = {99},
  number = {1-3},
  pages = {482--492},
  url = {http://dx.doi.org/10.1016/j.jqsrt.2005.05.038},
  doi = {10.1016/j.jqsrt.2005.05.038}
}
"Modeling laser-produced plasma sources"
Al-Rabban M, Richardson M, Scott H, Gilleron F, Poirier M and Blenski T, In EUV Sources for Lithography. Vol. PM149, pp. 299-337 - (2006).
BibTeX:
@incollection{InCollection2006,
  author = {Al-Rabban, M. and Richardson, M. and Scott, H. and Gilleron, F. and Poirier, M. and Blenski, T.J.},
  editor = {V., Bakshi and Press, SPIE},
  title = {Modeling laser-produced plasma sources},
  booktitle = {EUV Sources for Lithography},
  year = {2006},
  volume = {PM149},
  pages = {299--337},
  url = {http://bookstore.spie.org/index.cfm?fuseaction=DetailVolume&productid=613774}
}
"Interpretation of some X and XUV absorption experiments using the superconfiguration code SCO"
Arnault P, Blenski T and Dejonghe G, In 12th International Workshop on Radiative Properties of Hot Dense Matter (RPHDM - 2006). Portugal - (2006).
BibTeX:
@inproceedings{InproArnault2006,
  author = {Arnault, P. and Blenski, T.J. and Dejonghe, G.},
  title = {Interpretation of some X and XUV absorption experiments using the superconfiguration code SCO},
  booktitle = {12th International Workshop on Radiative Properties of Hot Dense Matter (RPHDM - 2006)},
  year = {2006}
}
"Measurement of XUV absorption spectra of ZnS radiatively heated foils"
Bastiani-Ceccotti S, Thais F, Kontogiannopoulos N, Chenais-Popovics C, Sauvan P, Schott R, Folsner W, Arnault P, Poirier M and Blenski T, In 12th International Workshop on Radiative Properties of Hot Dense Matter (RPHDM - 2006). Portugal - (2006).
BibTeX:
@inproceedings{InproCeccotti2006,
  author = {Bastiani-Ceccotti, S. and Thais, F. and Kontogiannopoulos, N. and Chenais-Popovics, C. and Sauvan, P. and Schott, R. and Folsner, W. and Arnault, P. and Poirier, M. and Blenski, T.J.},
  title = {Measurement of XUV absorption spectra of ZnS radiatively heated foils},
  booktitle = {12th International Workshop on Radiative Properties of Hot Dense Matter (RPHDM - 2006)},
  year = {2006}
}
"A variational approach to average atom and superconfigurations in plasmas"
Blenski T and Cichocki B, In 12th International Workshop on Radiative Properties of Hot Dense Matter (RPHDM - 2006). Portugal - (2006).
BibTeX:
@inproceedings{InproBlenski2006,
  author = {Blenski, T.J. and Cichocki, B.},
  title = {A variational approach to average atom and superconfigurations in plasmas},
  booktitle = {12th International Workshop on Radiative Properties of Hot Dense Matter (RPHDM - 2006)},
  year = {2006}
}
2005
"Photoconductivité et photoémission de diamant(s) sous irradiation XUV femtoseconde"
Gaudin J, Geoffroy G, Guizard S, Esnouf S, Olevano V, Petite G, Klimentov S, Pivovarov P, Garnov S, Carre B, Martin P and Belsky A, Journal de Physique IV. Vol. 127, pp. 131-137 - (2005).
Abstract: Notamment à cause de ses applications à la détection rapide de particules, mais aussi parce qu'il représente un modèle de matériau covalent à grande bande interdite, se prêtant bien à la modélisation, l'étude du comportement des porteurs libres dans le diamant est un sujet particulièrement captivant. Nous avons abordé cette question sur le plan expérimental par une étude des propriétés de photoconductivité induite dans différents types de diamants (monocristaux de type IIa et couches CVD) par des impulsions femtosecondes allant du proche IR (800 nm) à l'XUV (jusqu'à l'harmonique 19 du laser titane/saphir). En complément de ces études, les spectres de photoémission de ces échantillons ont aussi été étudiés. La méthode utilisée pour la mesure de la photoconductivité est spécifique dans la mesure ou elle ne nécessite pas la réalisation de contacts ohmiques (mesure « capacitive » du courant de déplacement), et est donc d'une grande simplicité, et aussi d'une grande sensibilité (typiquement 1011 porteurs).Pour l'IR et les harmoniques basses du laser titane/saphir, on observe que la photoconductivité induite est essentiellement pilotée par les défauts du matériau : comportement linéaire en intensité dans la plupart des cas, forte sensibilité au chargement électronique des défauts dans le diamant CVD, au contraire de ce qui se passe dans un diamant pur. Des études en RPE menées sur les différents échantillons n'ont pas permis d'identifier clairement le défaut responsable, mais permettent par contre d'éliminer le centre P1. Une expérience est en cours pour étudier un matériau pur dans lequel des défauts lacunaires sont introduits par irradiation aux électrons de 2.5 MeV. On ne retrouve pas un telle sensibilité aux défauts quand on utilise les harmoniques élevées (7 et plus). Nous avons étudié le comportement du signal de photoconductivité en fonction de l'ordre de l'harmonique. Malgré des difficultés de calibration, on constate que ce signal augmente tout d'abord, avec l'ordre (harmoniques 9 à 13) puis diminue au delà. Si l'augmentation s'interprête aisément comme résultant de phénomènes de multiplication par collisions inélastiques, la diminution ultérieure n'a pas pour le moment d'explication. Les mesures de spectre et de rendement de photoémission permettent en effet d'exclure la compétition en photoconductivité et photoémission (l'excitation étant localisée dans ce cas près de la surface).Enfin, nous avons réalisé le premier calcul ab-initio de la durée de vie des porteurs tenant compte des interactions électron-électron, à l'aide d'une approche de théorie quantique à plusieurs corps de type GW. Au voisinage du gap, on observe un comportement très proche de celui d'un liquide de Fermi (ce qui peut se comprendre ici aussi à l'aide d'arguments du type espace de phase accessible, mais qui néglige l'interaction électron-phonon, importante dans cette gamme d'énergie). A plus haute énergie on observe des déviations à ce comportement, provenant d'effets de structure de bande d'une part, et d'excitations de plasmons d'autre part.Ce travail a été soutenu par le contrat INTAS 01-458, ainsi que par le PAI France-Russie n° 04527 ZM.
BibTeX:
@article{Gaudin2005a,
  author = {Gaudin, J. and Geoffroy, G. and Guizard, S. and Esnouf, S. and Olevano, V. and Petite, G. and Klimentov, S.M. and Pivovarov, P.A. and Garnov, S.V. and Carre, B. and Martin, P. and Belsky, A.},
  title = {Photoconductivité et photoémission de diamant(s) sous irradiation XUV femtoseconde},
  journal = {Journal de Physique IV},
  year = {2005},
  volume = {127},
  pages = {131--137},
  url = {http://dx.doi.org/10.1051/jp4:2005127020}
}
"Plasmon channels in the electronic relaxation of diamond under high-order harmonics femtosecond irradiation."
Gaudin J, Geoffroy G, Guizard S, Olevano V, Esnouf S, Klimentov S, Pivovarov P, Garnov S, Martin P, Belsky A and Petite G, Laser Physics Letters. Vol. 2(6), pp. 292-296 - (2005).
Abstract: We used high order harmonics of a femtosecond titanium-doped sapphire system (pulse duration 25 fs) to realise Ultraviolet Photoelectron Spectroscopy (UPS) measurements on diamond. The UPS spectra were measured for harmonics in the range 13 to 27. We also made ab initio calculations of the electronic lifetime of conduction electrons in the energy range produced in the UPS experiment. Such calculations show that the lifetime suddenly diminishes when the conduction electron energy reaches the plasmon energy, whereas the UPS spectra show evidence in this range of a strong relaxation mechanism with an increased production of low energy secondary electrons. We propose that in this case the electronic relaxation proceeds in two steps : excitation of a plasmon by the high energy electron, the latter decaying into individual electron-hole pairs, as in the case of metals. This process is observed for the first time in an insulator and, on account of its high efficiency, should be introduced in the models of laser breakdown under high intensity.
BibTeX:
@article{Gaudin2005,
  author = {Gaudin, J. and Geoffroy, G. and Guizard, S. and Olevano, V. and Esnouf, S. and Klimentov, S.M. and Pivovarov, P.A. and Garnov, S. and Martin, Pa. and Belsky, A. and Petite, G.},
  title = {Plasmon channels in the electronic relaxation of diamond under high-order harmonics femtosecond irradiation.},
  journal = {Laser Physics Letters},
  year = {2005},
  volume = {2},
  number = {6},
  pages = {292--296},
  url = {http://arxiv.org/abs/cond-mat/0501687},
  doi = {10.1002/lapl.200510001}
}
"Time-resolved two-colour photoemission in wide band gap dielectrics"
Guizard S, Belsky A, Gaudin J, Geoffroy G, Martin P, Petite G, Philippov A and Yatsenko B, Physica Status Solidi C - Current Topics in Solid State Physics. Vol. 2, pp. 223-227 - (2005).
Abstract: We have measured the relaxation of photo-excited carriers in different wide band gap dielectrics by using time resolved two-colour photoemission. Electrons are excited by an ultra-short pulse of VUV photons directly in the conduction band. They are then are re-excited by an IR probe pulse. The evolution of the photoemission spectra as a function of the pump-probe delay gives direct information on the relaxation of the population of excited electron. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
BibTeX:
@article{Guizard2005,
  author = {Guizard, S. and Belsky, A.N. and Gaudin, J. and Geoffroy, G. and Martin, Pa. and Petite, G. and Philippov, A. and Yatsenko, B.},
  title = {Time-resolved two-colour photoemission in wide band gap dielectrics},
  journal = {Physica Status Solidi C - Current Topics in Solid State Physics},
  year = {2005},
  volume = {2},
  pages = {223--227},
  url = {http://www3.interscience.wiley.com/cgi-bin/abstract/109866909/ABSTRACT},
  doi = {10.1002/pssc.200460151}
}
"Mesure de coefficients d'absorption de plasmas créés par laser nanoseconde"
Thais F, Chenais-Popovics C, Eidmann K, Bastiani S, Blenski T and Gilleron F, Journal de Physique IV. Vol. 127, pp. 119-124 - (2005).
Abstract: La mesure des coefficients d'absorption dans les plasmas chauds est particulièrement utile dans le domaine de la fusion par confinement inertiel ainsi que dans divers contextes en astrophysique. Le développement des calculs de physique atomique qui y sont associés repose sur des hypothèses qu'il est nécessaire de vérifier dans la plus large gamme possible de conditions physiques. Nous présentons ici la méthode de mesure et d'analyse employée en nous appuyant sur l'exemple des cibles multicouches nickel/aluminium.
BibTeX:
@article{Thais2005,
  author = {Thais, F. and Chenais-Popovics, C. and Eidmann, K. and Bastiani, S. and Blenski, T. and Gilleron, F.},
  title = {Mesure de coefficients d'absorption de plasmas créés par laser nanoseconde},
  journal = {Journal de Physique IV},
  year = {2005},
  volume = {127},
  pages = {119--124},
  url = {http://dx.doi.org/10.1051/jp4:2005127018},
  doi = {10.1051/jp4:2005127018}
}
"Creation of high energy electronic excitations in inorganic insulators by intense femtosecond laser pulses"
Yatsenko BN, Bachau H, Belsky AN, Gaudin J, Geoffroy G, Guizard S, Martin P, Petite G, Philippov A and Vassil'ev AN, Physica Status Solidi C - Current Topics in Solid State Physics. Vol. 2, pp. 240-243 - (2005).
Abstract: We measured photoemission spectra for a number of insulators (CsI, Diamond, SiO2, CeF3) excited by femtosecond Ti-Sapphire laser pulses at peak intensities, from 0.5 to 6 TW/cm2, which are at least one order of magnitude below the optical breakdown threshold. An intense and pronounced plateau of high energy electrons appears in the photoelectron spectra in this intensity range, which extends up to 30-40 eV at the highest intensities, which we used. The excitation of electrons at high energies is treated in terms of direct interbranch transitions in the conduction band of insulator. These processes are described using calculations based on numerical solution of time dependant Schrödinger equation (TDSE) for Bloch electrons in electric fields. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
BibTeX:
@article{Yatsenko2005,
  author = {Yatsenko, B. N. and Bachau, H. and Belsky, A. N. and Gaudin, J. and Geoffroy, G. and Guizard, S. and Martin, P. and Petite, G. and Philippov, A. and Vassil'ev, A. N.},
  title = {Creation of high energy electronic excitations in inorganic insulators by intense femtosecond laser pulses},
  journal = {Physica Status Solidi C - Current Topics in Solid State Physics},
  year = {2005},
  volume = {2},
  pages = {240--243},
  url = {http://www3.interscience.wiley.com/cgi-bin/abstract/109866894/ABSTRACT},
  doi = {10.1002/pssc.200460155}
}
"Température radiative de cavités chauffées avec le laser NANO 2000"
Chenais-Popovics C, Tzortzakis S, Bastiani S, Radier C, Chiaramonti B, Thais F, Eidmann K and Foelsner W, pp.3 pages - (2005).
Abstract: Absorption coefficients of hot dense matter in local thermodynamic equilibrium can be measured in a foil radiatively heated by the X-ray emission of a laser heated cavity. The present measurements provide the radiative temperature of a 1.2 mm diameter gold cavity. The laser beam isdirectly focused inside the cavity or heats a thin gold foil set on the cavity entrance hole. The radiative temperature is in the range of 90-100 eV for both types of cavities.
BibTeX:
@techreport{Techreport2005,
  author = {Chenais-Popovics, C. and Tzortzakis, S. and Bastiani, S. and Radier, C. and Chiaramonti, B. and Thais, F. and Eidmann, K. and Foelsner, W.},
  title = {Température radiative de cavités chauffées avec le laser NANO 2000},
  year = {2005},
  pages = {3 pages}
}
"Self-consistent statistical approach to electronic properties of hot dense plasmas"
Pain J-C, Dejonghe G and Blenski T, In Conference on "Strongly Coupled Coulomb Systems". Moscou - (2005).
BibTeX:
@inproceedings{InproPain2005,
  author = {Pain, J.-C. and Dejonghe, G. and Blenski, T.},
  title = {Self-consistent statistical approach to electronic properties of hot dense plasmas},
  booktitle = {Conference on "Strongly Coupled Coulomb Systems"},
  year = {2005}
}
2004
"Heating of Conduction Band Electrons by Intense Femtosecond Laser Pulses"
Belsky A, Martin P, Bachau H, Vasil'ev A, Yatsenko B, Guizard S, Geoffroy G and Petite G, Europhysics Letters. Vol. 67, pp. 301-306 - (2004).
Abstract: We present photoelectron spectra for CsI excited by intense femtosecond Ti-Sapphire laser pulses. A high energy plateau is detected in the spectra, at excitation intensities above 0.5 TW/cm˛. This plateau extends up to 24 eV at 3 TW/cm˛ and 90% of the emitted electrons have energy higher than twice the laser photon energy. Such intensive electron heating in solids can not be explained in terms of phonon assisted transitions. A model of conduction band electrons heating, which accounts for direct interbranch transitions in strong laser field, is used for simulation of photoelectron spectra
BibTeX:
@article{Belsky2004b,
  author = {Belsky, A. and Martin, P. and Bachau, H. and Vasil'ev, A.N. and Yatsenko, B. and Guizard, S. and Geoffroy, G. and Petite, G.},
  title = {Heating of Conduction Band Electrons by Intense Femtosecond Laser Pulses},
  journal = {Europhysics Letters},
  year = {2004},
  volume = {67},
  pages = {301--306},
  url = {http://iopscience.iop.org/0295-5075/67/2/301},
  doi = {10.1209/epl/i2004-10058-0}
}
"Observation of high energy photoelectrons from solids at moderate laser intensity"
Belsky A-N, Bachau H, Gaudin J, Geoffroy G, Guizard S, Martin P, Petite G, Philippov A, Vasil'ev A-N and Yatsenko B-N, Applied Physics B : Lasers and Optics. Vol. 78(7-8), pp. 989 - (2004).
Abstract: We investigate the photoemission for a set of wide band-gap crystals irradiated by femtosecond Ti-Sapphire laser pulses at intensities varying from 0.5 to 6 TW/cm2 (below the optical breakdown threshold). The measured total electron yield increases linearly with the laser intensity in this intensity range. An intense and wide plateau of high energy electrons appears in the photoelectron spectra at excitation intensities larger than 1 TW/cm2. The exponential cut-off of this plateau reaches 40 eV at maximal applied intensities. In order to explain such a behavior, we propose a mechanism where the heating is due to a sequence of direct interbranch one- and multi-photon transitions in the conduction band.
BibTeX:
@article{Belsky2004,
  author = {Belsky, A.-N. and Bachau, H. and Gaudin, J. and Geoffroy, G. and Guizard, S. and Martin, Ph. and Petite, G. and Philippov, A. and Vasil'ev, A.-N. and Yatsenko, B.-N.},
  title = {Observation of high energy photoelectrons from solids at moderate laser intensity},
  journal = {Applied Physics B : Lasers and Optics},
  year = {2004},
  volume = {78},
  number = {7-8},
  pages = {989},
  url = {http://link.springer.com/article/10.1007%2Fs00340-004-1438-1#}
}
"Observation of laser driven supercritical radiative shock precursors"
Bouquet S, Stehle C, Koenig M, Chieze J, Benuzzi-Mounaix A, Batani D, Leygnac S, Fleury X, Merdji H, Michaut C, Thais F, Grandjouan N, Hall T, Henry E, Malka V and Lafon J-P, Physical Review Letters. Vol. 92, pp. 225001 - (2004).
Abstract: We present a supercritical radiative shock experiment performed with the LULI nanosecond laser facility. Using targets filled with xenon gas at low pressure, the propagation of a strong shock with a radiative precursor is evidenced. The main measured shock quantities (electronic density and propagation velocity) are shown to be in good agreement with theory and numerical simulations. PACS numbers. 95.30.Jx, 52.72.+v
BibTeX:
@article{Bouquet2004,
  author = {Bouquet, S. and Stehle, C. and Koenig, M. and Chieze, J.P. and Benuzzi-Mounaix, A. and Batani, D. and Leygnac, S. and Fleury, X. and Merdji, H. and Michaut, C. and Thais, F. and Grandjouan, N. and Hall, T. and Henry, E. and Malka, V. and Lafon, J-P.},
  title = {Observation of laser driven supercritical radiative shock precursors},
  journal = {Physical Review Letters},
  year = {2004},
  volume = {92},
  pages = {225001},
  url = {http://dx.doi.org/10.1103/PhysRevLett.92.225001},
  doi = {10.1103/PhysRevLett.92.225001}
}
"Photoconductivity and photoemission studies of diamond irradiated by ultrashort VUV pulses"
Gaudin J, Geoffroy G, Guizard S, Petite G, Klimentov S, Garnov S, Pivovarov P, Carré B, Belsky A and Martin P, Applied Physics B : Lasers and Optics. Vol. 78(7-8), pp. 1001-1004 - (2004).
Abstract: We investigated relaxation of free charge carriers in pure crystalline diamond exposed to VUV irradiation of high order harmonics of femtosecond Ti:Sa laser in the spectral range 17-32 eV.Electron-hole pairs, possessing a significant kinetic energy, are generated in the material via direct interband transitions possessing significant kinetic energy, relaxation of which is monitored by means of induced conductivity in the bulk and photoemission from the surface of the material.The experimental data provided by these complementary techniques are compared and discussed in terms of competition between ionization and conductivity looking for evidences of multiplication of free charge carriers due to impact ionization.
BibTeX:
@article{Gaudin2004a,
  author = {Gaudin, J. and Geoffroy, G. and Guizard, S. and Petite, G. and Klimentov, S.M. and Garnov, S.V. and Pivovarov, P.A. and Carré, B. and Belsky, A. and Martin, P.},
  title = {Photoconductivity and photoemission studies of diamond irradiated by ultrashort VUV pulses},
  journal = {Applied Physics B : Lasers and Optics},
  year = {2004},
  volume = {78},
  number = {7-8},
  pages = {1001--1004},
  url = {http://springerlink.metapress.com/app/home/contribution.asp?wasp=n49byglgxmcvydm38dwg&referrer=parent&backto=searcharticlesresults,1,2;journal,1,1;linkingpublicationresults,1:100502,1},
  doi = {10.1007/s00340-004-1454-1}
}
"Absorption of LTE aluminum and nickel at different densities"
Bastiani-Ceccotti S, Chenais-Popovics C, Pisani F, Thais F, Gauthier J-C, Gilleron F, Blenski T, Poirier M, Folsner W and Eidmann K, In Inertial Fusion Sciences and Applications 2003 (IFSA 2003). , pp. 987 - (2004).
BibTeX:
@incollection{Incollection2004,
  author = {Bastiani-Ceccotti, S. and Chenais-Popovics, C. and Pisani, F. and Thais, F. and Gauthier, J.-C. and Gilleron, F. and Blenski, T. and Poirier, M. and Folsner, W. and Eidmann, K.},
  editor = {Society, American Nuclear and Hammel, B.A. and Meyerhofen, D.D. and Meyer-ter-Vehn, Y. and Azechi, H.},
  title = {Absorption of LTE aluminum and nickel at different densities},
  booktitle = {Inertial Fusion Sciences and Applications 2003 (IFSA 2003)},
  year = {2004},
  pages = {987}
}
"Experimental characterization of electron densities and temperatures in radiative shocks"
Leygnac S, Michaut C, Sthelé C, Vinci T, Koenig M, Benuzzi-Mounaix A, Bouquet S, Thais F and Merdji H, In Third International Conference on Inertial Fusion Sciences and Applications (IFSA-2003). Etats-Unis Vol. (7003), pp. 958 - (2004).
BibTeX:
@inproceedings{InproLeygnac2004,
  author = {Leygnac, S. and Michaut, C. and Sthelé, C. and Vinci, T. and Koenig, M. and Benuzzi-Mounaix, A. and Bouquet, S. and Thais, F. and Merdji, H.},
  title = {Experimental characterization of electron densities and temperatures in radiative shocks},
  booktitle = {Third International Conference on Inertial Fusion Sciences and Applications (IFSA-2003)},
  year = {2004},
  volume = {(7003)},
  pages = {958}
}
2003
"Opacity measurements of tamped NaBr samples heated by z-pinch X-rays"
Bailey JE, Arnault P, Dejonghe G, Peyrusse O, MacFarlane JJ, Mancini RC, Cuneo ME, Nielsen DS, Rochau GA and Blenski T, Journal of Quantitative Spectroscopy and Radiative Transfer. Vol. 81(1-4), pp. 31-45 - (2003).
Abstract: Laboratory measurements provide benchmark data for wavelength-dependent plasma opacities to assist inertial confinement fusion, astrophysics, and atomic physics research. There are several potential benefits to using z-pinch radiation for opacity measurements, including relatively large cm-scale lateral sample sizes and relatively-long 3– experiment durations. These features enhance sample uniformity. The spectrally resolved transmission through a CH-tamped NaBr foil was measured. The z-pinch produced the X-rays for both the heating source and backlight source. The (50±4) eV foil electron temperature and foil electron density were determined by analysis of the Na absorption features. LTE and NLTE opacity model calculations of the n=2 to 3, 4 transitions in bromine ionized into the M-shell are in reasonably good agreement with the data.
BibTeX:
@article{Bailey2003,
  author = {Bailey, J. E. and Arnault, P. and Dejonghe, G. and Peyrusse, O. and MacFarlane, J. J. and Mancini, R. C. and Cuneo, M. E. and Nielsen, D. S. and Rochau, G. A. and Blenski, T.},
  title = {Opacity measurements of tamped NaBr samples heated by z-pinch X-rays},
  journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
  year = {2003},
  volume = {81},
  number = {1-4},
  pages = {31--45},
  url = {http://www.sciencedirect.com/science?_ob=IssueURL&_tockey=%23TOC%235541%232003%23999189998%23435457%23FLA%23Volume_81,_Issues_1-4,_Pages_1-520_(15_September_-_1_November_2003)%2BMRadiative_Properties_of_Hot_Dense_Matter%2BMEdited_by_R._Lee&_auth=y&view=c&},
  doi = {http://www.sciencedirect.com/science/article/pii/S0022407303000505}
}
"Photoémission de CsI induite par une impulsion laser intense femtoseconde"
Belsky A, Vasil'ev A, Yatsenko B, Bachau H, Martin P, Geoffroy G and Guizard S, Journal de Physique IV. Vol. 108, pp. 113-117 - (2003).
Abstract: Nous avons mesuré pour la première fois les spectres de photoélectrons émis par un cristal isolant à large bande interdite, CsI, avec une dynamique de 106 coups/s, excité par la source laser haute cadence du C.E.L.I.A ( 800 nm, 40 fs, I kHz, 1 TW). L'émission d'électrons jusqu'à des énergies de quelques dizaines d'électrons-volts a été observée pour des impulsions d'éclairement compris entre 0.5 et 3 TW/cm2, relativement faible donc par comparaison aux éclairements utilisés pour accélérer les électrons d'un atome aux mêmes énergies. Ces spectres contiennent tous, en particulier, deux bandes dans le domaine des basses énergies d'électrons (<5 eV), également observées lors d'études précédentes. Les électrons les plus énergétiques forment un plateau intense légèrement structuré et limité par une coupure exponentielle. Pour des impulsions de 3 TW/cm2 cette coupure est située à 27 eV. L'insuffisance du mécanisme électron-photon-phonon, considéré jusqu'à présent comme le principal processus d'échauffement des électrons dans les solides en interaction non destructrice avec un champ laser, nous a poussé à proposer un mécanisme alternatif. Ce modèle met en évidence les transitions directes multiphotoniques dans la bande de conduction du solide qui sont incontournables du fait de sa structure électronique multi-branches.
BibTeX:
@article{Belsky2003,
  author = {Belsky, A. and Vasil'ev, A.N. and Yatsenko, B. and Bachau, H. and Martin, P. and Geoffroy, G. and Guizard, S.},
  title = {Photoémission de CsI induite par une impulsion laser intense femtoseconde},
  journal = {Journal de Physique IV},
  year = {2003},
  volume = {108},
  pages = {113--117},
  url = {http://cat.inist.fr/?aModele=afficheN&cpsidt=14859859}
}
"La photoémission VUV résolue en temps sur des solides isolants"
Geoffroy G, Guizard S, Constant E, Mevel E, Belsky A and Martin P, Journal de Physique IV. Vol. 108, pp. 119-122 - (2003) - (2003).
Abstract: L'objectif de ce travail expérimental est l'étude de la dynamique des processus de relaxations électroniques dans les solides, et en particulier dans les diélectriques. La technique la plus couramment employée pour étudier ces phénomènes est la photoémission résolue en temps, à l'aide d'impulsions laser ultra-brèves. Une première impulsion excite les électrons du solide, et une seconde impulsion provoque l'ionisation d'une partie de ces électrons. La mesure de l'énergie cinétique de ces photoélectrons en fonction du retard entre les impulsions pompe et sonde donne une image directe de l'évolution de leur distribution énergétique. Cette technique très puissance a déjà été utilisée pour étudier les cinétiques de relaxation dans les semi-conducteurs et les métaux. En effet, les énergies de photons nécessaires aux excitations électroniques correspondent aux longueurs d'onde d'émission des lasers femtosecondes les plus courants. Les harmoniques d'ordres élevés obtenues à partir de laser femtosecondes intenses permettent d'étendre ces études à des matériaux isolants à grande bande interdite. Les résultats d'une étude systématique de la relaxation d'électrons de grande énergie (~30 eV) dans différents diélectriques (Si02, CeF3), réalisées avec la source d'harmoniques du laboratoire CELIA sont comparés et discutés.
BibTeX:
@article{Geoffroy2003,
  author = {Geoffroy, G. and Guizard, S. and Constant, E. and Mevel, E. and Belsky, A. and Martin, P.},
  title = {La photoémission VUV résolue en temps sur des solides isolants},
  journal = {Journal de Physique IV},
  year = {2003},
  volume = {108},
  pages = {119--122},
  url = {http://jp4.journaldephysique.org/articles/jp4/abs/2003/07/jp4pr6p119/jp4pr6p119.html},
  doi = {10.1051/jp4:20030610}
}
"Emissive Properties of Xenon Ions from a Laser-Produced Plasma in the 100-140 Ĺ Spectral Range: Atomic-Physics Analysis of the Experimental Data"
Gilleron F, Poirier M, Blenski T, Schmidt M and Ceccotti T, Journal of Applied Physics. Vol. 94(3), pp. 2086-2096 - (2003).
Abstract: In order to design extreme ultraviolet sources for nanolithography, xenon EUV emission has been experimentally studied in a plasma generated by the interaction of a high-power laser with a droplet jet. A theoretical model assuming that the resulting plasma is optically thick allows to find the distribution of the relevant ions and transitions involved in the emission process. Atomic physics computations are performed using the HULLAC code to give a detailed account of the transitions involved. The importance of 4p-4d, 4d-4f and 4d-5p transitions is stressed, as well as the need for configuration-interaction treatment of the Delta n=0 transitions. Comparisons of a modeled LTE spectrum with experiment provides qualitative agreement and permits an estimate of the plasma temperature, density, and dimensions.
BibTeX:
@article{Gilleron2003,
  author = {Gilleron, F. and Poirier, M. and Blenski, T. and Schmidt, M. and Ceccotti, T.},
  title = {Emissive Properties of Xenon Ions from a Laser-Produced Plasma in the 100-140 Ĺ Spectral Range: Atomic-Physics Analysis of the Experimental Data},
  journal = {Journal of Applied Physics},
  year = {2003},
  volume = {94},
  number = {3},
  pages = {2086--2096},
  url = {http://dx.doi.org/10.1063/1.1587264},
  doi = {http://jap.aip.org/resource/1/japiau/v94/i3/p2086_s1}
}
"A SANS investigation of the irradiation-enhanced a–a' phases separation in 7–12 Cr martensitic steels"
Mathon M, de Carlan Y, Geoffroy G, Averty X, Alamo A and de Novion C, Journal of Nuclear Materials. Vol. 312, pp. 236-248 -(2003).
Abstract: Five reduced activation (RA) and four conventional martensitic steels, with chromium contents ranging from 7 to 12 wt%, were investigated by small angle neutron scattering (SANS) under magnetic field after neutron irradiation (0.7–2.9 dpa between 250 and 400 °C). It was shown that when the Cr content of the b.c.c. ferritic matrix is larger than a critical threshold value ( ~ 7.2 at.% at 325 °C), the ferrite separates under neutron irradiation into two isomorphous phases, Fe-rich (a) and Cr-rich (a'). The kinetics of phase separation are much faster than under thermal aging. The quantity of precipitated a' phase increases with the Cr content, the irradiation dose, and as the irradiation temperature is reduced. The influence of Ta and W added to the RA steels seems negligible. Cold-work pre-treatment increases slightly the coarsening of irradiation-induced precipitates in the 9Cr–1Mo (EM10) steel. In the case of the low Cr content F82H steel irradiated 2.9 dpa at 325 °C, where a' phase does not form, a small irradiation-induced SANS intensity is detected, which is probably due to point defect clusters. The a' precipitates contribute significantly to the irradiation-induced hardening of 9–12 wt% Cr content steels.
BibTeX:
@article{Mathon2003,
  author = {Mathon, M.H. and de Carlan, Y. and Geoffroy, G. and Averty, X. and Alamo, A. and de Novion, C.H.},
  title = {A SANS investigation of the irradiation-enhanced a–a' phases separation in 7–12 Cr martensitic steels},
  journal = {Journal of Nuclear Materials},
  year = {2003},
  volume = {312},
  pages = {236--248},
  url = {http://www.researchgate.net/publication/229391670_A_SANS_investigation_of_the_irradiation-enhanced__phases_separation_in_712_Cr_martensitic_steels},
  doi = {10.1016/S0022-3115(02)01630-6}
}
"Self-consistent approach for the thermodynamics of ions in dense plasmas in the superconfiguration approximation"
Pain J-C and Blenski T, Journal of Quantitative Spectroscopy and Radiative Transfer. Vol. 81(1-4), pp. 355-369 - (2003).
Abstract: We propose a new thermodynamic approach to ions in dense plasmas taking into account the screening by free electrons. The ions in fundamental and excited states are represented by a group of superconfigurations. Each superconfiguration containing an integer number of bound electrons is totally screened by free electrons in a WignerSeitz (WS) sphere. The minimisation of the plasma free energy with respect to the WS radii of the ions, under the condition that the specific mass of the plasma is preserved, leads to the equality of the electronic pressure for all ions. This pressure, as well as the WS radii and the distribution of ionic probabilities, are calculated by iteration. In this way, our approach not only gives the charge neutrality of the plasma, but also assures that the plasma environment is the same for each ion. In principle, the proposed approach allows one to apply the superconfiguration method to calculate radiative properties of plasmas for higher densities than those encountered in transmission experiments. Numerical examples for nickel, aluminium and samarium plasmas will be given. Comparisons with results from the previous statistical approach using the same WS radius for each ion charge state will also be discussed.
BibTeX:
@article{Pain2003,
  author = {Pain, J.-Ch. and Blenski, T.},
  title = {Self-consistent approach for the thermodynamics of ions in dense plasmas in the superconfiguration approximation},
  journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
  year = {2003},
  volume = {81},
  number = {1-4},
  pages = {355--369},
  url = {http://dx.doi.org/doi:10.1016/S0022-4073(03)00087-6},
  doi = {10.1016/S0022-4073(03)00087-6}
}
"Absorption of local thermodynamic equilibrium aluminum at different densities"
Thais F, Bastiani S, Blenski T, Chenais-Popovics C, Eidmann K, Folsner W, Gauthier J-C, Gilleron F and Poirier M, Journal of Quantitative Spectroscopy and Radiative Transfer. Vol. 81(1-4), pp. 473-485 - (2003).
Abstract: Increasing the range of plasma parameters accessible for laboratory absorption coefficients measurements is of interest for astrophysical applications. Aluminum is of special interest as its 1s-2p inner shell absorption transitions permit one to precisely determine the ionization balance that is strongly dependent on the electron temperature. A method to increase the density of the probed sample was tested on aluminum confined by carbon tampers of different thickness (8 to 70 µg/cm2). This created a density increase in the aluminum of a factor of ~10. Measurements showed that the aluminum ionization decreases substantially with increasing carbon thickness. Radiative hydrodynamic simulations showed that density and temperature gradients could not be neglected and had to be taken into account in calculating the absorption structures with the atomic physics code HULLAC. Very good agreement between theory and experiment was obtained by coupling HULLAC with hydrodynamic simulations.
BibTeX:
@article{Thais2003,
  author = {Thais, F. and Bastiani, S. and Blenski, T. and Chenais-Popovics, C. and Eidmann, K. and Folsner, W. and Gauthier, J.-C. and Gilleron, F. and Poirier, M.},
  title = {Absorption of local thermodynamic equilibrium aluminum at different densities},
  journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
  year = {2003},
  volume = {81},
  number = {1-4},
  pages = {473--485},
  url = {http://dx.doi.org/doi:10.1016/S0022-4073(03)00097-9},
  doi = {10.1016/S0022-4073(03)00097-9}
}
"XUV emission from a xenon plasma: atomic physics models"
Poirier M, Gilleron F, Blenski T, Schmidt M and Ceccotti T, In EUV Source Modeling Workshop. Anvers (Belgique) - (2003).
Abstract: In this talk, various theoretical approaches are proposed in order to analyze the extreme-UV emission from laser-produced xenon plasmas. In a first step, the superconfiguration code allows one to define the relevant ionic stages and the mono-electronic transitions involved. Then, an analysis using the relativistic parametric potential code HULLAC emphasizes the importance of configuration interaction (CI): while CI weakly affects the 4d-5p lines in the 130--140 Ĺ region, it strongly shrinks the 4p-4d and 4d-4f lines which for the relevant ionic stages coalesce in the 100--110 Ĺ band. This analysis confirms the main importance of Xe 10+ ions in the 130--140 Ĺ range, but Xe 4+ appears as a new candidate for nanolithography since it exhibits an isolated line close to the 135 Ĺ wavelength. Since various part of the experimental spectrum are most efficiently reproduced at various temperatures, the possibility of non-LTE effects is mentioned. The influence of doubly-excited states is stressed as well. Possible improvements of the theoretical description are finally reviewed.
BibTeX:
@inproceedings{InproPoirier2003,
  author = {Poirier, M. and Gilleron, F. and Blenski, T. and Schmidt, M. and Ceccotti, T.},
  title = {XUV emission from a xenon plasma: atomic physics models},
  booktitle = {EUV Source Modeling Workshop},
  year = {2003}
}
2002
"Sur la physique atomique des ions dans les plasmas en présence de l'écrantage"
Pain J - (2002).
Abstract: Résumé : L'objectif de ce travail de thèse est d'améliorer la caractérisation des différentes espèces ioniques présentes dans les plasmas. La modélisation de la thermodynamique de ces plasmas est importante, notamment pour décrire leur capacité à absorber le rayonnement électromagnétique. L'écrantage des ions par les électrons libres joue un rôle capital dans cette thermodynamique. Le nombre de configurations électroniques du plasma est considérable, ce qui rend leur traitement détaillé prohibitif. Une approche récente fondée sur l'approximation des ''supraconfigurations'' permet de regrouper les configurations électroniques des ions en quelques centaines ou milliers de supraconfigurations pertinentes. Chaque supraconfiguration est caractérisée par un potentiel ainsi qu'une base d'états quantiques à un électron qui sont calculés de manière auto-cohérente. Ce travail de thèse constitue une amélioration de la méthode des supraconfigurations, prenant en compte l'écrantage des ions par les électrons délocalisés et assurant simultanément que chaque espèce ionique a le même environnement plasma. Ainsi, l'approche proposée assure non seulement la neutralité électrique du plasma, mais aussi, en faisant varier les volumes des sphères ioniques, l'égalité de la pression électronique du plasma autour de chaque ion. Cette égalité est obtenue par un calcul itératif fondé sur la méthode de Newton multi-dimensionnelle. Ce calcul est complexe mais la méthode converge et permet, dans le cas de plasmas de fortes densités (de l'ordre de la densité du solide), de mieux tenir compte de phénomènes d'ionisation par pression. L'impact de cette nouvelle approche thermodynamique sur le calcul de spectres de photo-absorption a été étudié. Des comparaisons avec des spectres expérimentaux obtenus au laboratoire LULI ont été effectuées. Une nouvelle règle de somme concernant la densité dipolaire induite a été obtenue dans le cadre d'une étude de la réponse linéaire prenant en compte l'écrantage dynamique dans les plasmas. This work is an improvement of the characterisation of ionic species in plasmas. It is important to model the thermodynamics of these plasmas, especially in order to describe their ability to absorb radiations. The screening of ions by free electrons plays a crucial role in these thermodynamics. The number of electronic configurations in the plasma is huge, which makes their individual treatment prohibitive. A recently developed approach based on the " superconfiguration " approximation enables to group electronic configurations into several hundreds or thousands of relevant superconfigurations. Each superconfiguration is characterised by a potential and a one-electron-quantum-state basis calculated in a self-consistent way. The present work consists in a improvement of the superconfiguration method, in which the screening of ions by free electrons is taken into account and each ionic specie has the same plasma environment. Therefore, the proposed approach not only assures that the plasma is electrically neutral, by also gives, varying the volume of each ion sphere, the equality of the electronic pressure around each ion. This equality is obtained by a multi-dimensional Newton method. The latter calculation is complex but the method is definitely convergent and allows, in case of high-density plasmas (about density of solids) to take pressure ionisation phenomena into account. The influence of the new thermodynamics on photo-absorption spectra has been studied. Comparisons with experimental spectra obtained in LULI laboratory have been investigated. In the framework of dynamic linear response theory, a new sum rule for the induced dipolar density has been developed.
BibTeX:
@mastersthesis{pain2002,
  author = {Pain, J.},
  title = {Sur la physique atomique des ions dans les plasmas en présence de l'écrantage}
}
"L-band x-ray absorption of radiatively heated nickel"
Chenais-Popovics C, Fajardo M, Gilleron F, Teubner U, Gauthier J-C, Bauche-Arnoult C, Bachelier A, Bauche J, Blenski T, Thais F, Perrot F, Benuzzi A, Turck-Chieze S, Chieze J-P, Dorchies F, Andiel U, Foelsner W and Eidmann K, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics. Vol. 65(1), pp. 016413/1-9 - (2002).
Abstract: Absorption of L-M and L-N transitions of nickel has been measured using point projection spectroscopy. The x-ray radiation from laser-irradiated gold cavities was used to heat volumetrically nickel foils "tamped with carbon" up to 20 eV. Experimental spectra have been analyzed with calculations based on the spin-orbit split arrays statistical approach and performed for each ionic species Ni 5+ to Ni 11+ . Using a least-squares fit, this method provides an ion distribution broader than at local thermodynamic equilibrium, which is explained by spatial and temporal temperature gradients. A major improvement in the simulation of the absolute value of transmission is obtained with a resolved transition array statistical calculation that reproduces the experimental spectrum with the nominal areal mass density by taking into account the saturation of narrow lines.
BibTeX:
@article{Chenais-Popovics2002,
  author = {Chenais-Popovics, C. and Fajardo, M. and Gilleron, F. and Teubner, U. and Gauthier, J.-C. and Bauche-Arnoult, C. and Bachelier, A. and Bauche, J. and Blenski, T. and Thais, F. and Perrot, F. and Benuzzi, A. and Turck-Chieze, S. and Chieze, J.-P. and Dorchies, F. and Andiel, U. and Foelsner, W. and Eidmann, K.},
  title = {L-band x-ray absorption of radiatively heated nickel},
  journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics},
  year = {2002},
  volume = {65},
  number = {1},
  pages = {016413/1--9},
  url = {http://link.aps.org/abstract/PRE/v65/e016413},
  doi = {10.1103/PhysRevE.65.016413}
}
"A laser experiment for studying radiative shocks in astrophysics"
Fleury X, Bouquet S, Stehlé C, Koenig M, Batani D, Benuzzi-Mounaix A, Chièze J-P, Grandjouan N, Grenier J, Hall T, Henry E, Lafon J-P, Leygnac S, Malka V, Marchet B, Merdji H, Michaut C and Thais F, Laser and Particle Beams. Vol. 20(2), pp. 263 - (2002);
Abstract: In this article, we present a laboratory astrophysics experiment on radiative shocks and its interpretation using simple modelization. The experiment is performed with a 100-J laser (pulse duration of about 0.5 ns) which irradiates a 1-mm 3 xenon gas-filled cell. Descriptions of both the experiment and the associated diagnostics are given. The apparition of a radiation precursor in the unshocked material is evidenced from interferometry diagrams. A model including self-similar solutions and numerical ones is derived and fairly good agreements are obtained between the theoretical and the experimental results.
BibTeX:
@article{Fleury2002,
  author = {Fleury, X. and Bouquet, S. and Stehlé, C. and Koenig, M. and Batani, D. and Benuzzi-Mounaix, A. and Chièze, J.-P. and Grandjouan, N. and Grenier, J. and Hall, T. and Henry, E. and Lafon, J.-P. and Leygnac, S. and Malka, V. and Marchet, B. and Merdji, H. and Michaut, C. and Thais, F.},
  title = {A laser experiment for studying radiative shocks in astrophysics},
  journal = {Laser and Particle Beams},
  year = {2002},
  volume = {20},
  number = {2},
  pages = {263},
  url = {http://journals.cambridge.org/bin/bladerunner?REQUNIQ=1065531404&REQSESS=16896055&117000REQEVENT=&REQINT1=130342&REQAUTH=0},
  doi = {10.1017/S0263034602202165}
}
"Des étoiles en laboratoire"
Merdji H and Thais F, Phases Magazine, La lettre du DRECAM et du SPhT. Vol. 119, pp. 1 - (2002).
BibTeX:
@article{Merdji2002,
  author = {Merdji, H. and Thais, F.},
  title = {Des étoiles en laboratoire},
  journal = {Phases Magazine, La lettre du DRECAM et du SPhT},
  year = {2002},
  volume = {119},
  pages = {1}
}
"New approach to dense plasma thermodynamics in the superconfiguration approximation"
Pain J-C and Blenski T, Laser and Particle Beams. Vol. 20(2), pp. 211-216 - (2002).
Abstract: We propose a new approach to the calculation of ion populations in the LTE dense plasmas in the superconfiguration approximation. The screening of plasma ions is obtained using the same free-electron chemical potential for each ion charge. This chemical potential is determined by iteration keeping the total density constant and varying the volume of each ion. In such a way our approach not only gives the charge neutrality of the plasma, but also assures that the free-electron density is equal in the vicinity of each ion. The resulting ion charge distribution is different with respect to the one obtained without imposing the constraint of equal chemical potential. For instance, the effective charge is a little bit higher, which can change the shape of the absorption spectra, especially at higher densities. Examples of absorption spectra of medium-Z plasmas in a temperature and density range close to the present opacity measurements are shown.
BibTeX:
@article{Pain2002,
  author = {Pain, J.-Ch. and Blenski, T.},
  title = {New approach to dense plasma thermodynamics in the superconfiguration approximation},
  journal = {Laser and Particle Beams},
  year = {2002},
  volume = {20},
  number = {2},
  pages = {211--216},
  url = {http://dx.doi.org/10.1017/S0263034602202086},
  doi = {10.1017/S0263034602202086}
}
"Calcium silicate hydrates studied by small-angle neutron scattering (SANS)."
Popova A, Geoffroy G, Gartner E and Lapp A, Journal of the American Ceramic Society. Vol. 85(5), pp. 1303-1305 - (2002).
Abstract: Small-angle neutron scattering (SANS) was used to study calcium silicate hydrate (C-S-H) formed via pozzolanic reaction between calcium oxide and ultrafine silica in water or polymer solutions at a temperature of 20°C. The SANS profile of this product was consistent with a structure that consisted of platelets with maximum diameters of ~ 20 nm (± 5 nm) in the x–y plane, which was similar to a structure that had been deduced in previous work via X-ray diffractometry. The presence of two different types of superplasticizer in solution (at a concentration of 10 g/L) had no significant effect on its formation kinetics or its SANS profile.
BibTeX:
@article{Popova2002,
  author = {Popova, A. and Geoffroy, G. and Gartner, E.M. and Lapp, A.},
  title = {Calcium silicate hydrates studied by small-angle neutron scattering (SANS).},
  journal = {Journal of the American Ceramic Society},
  year = {2002},
  volume = {85},
  number = {5},
  pages = {1303--1305},
  url = {http://onlinelibrary.wiley.com/doi/10.1111/j.1151-2916.2002.tb00264.x/abstract},
  doi = {10.1111/j.1151-2916.2002.tb00264.x}
}
  
"A new approach to the thermodynamics of dense plasmas"
Blenski T , Pologne -(2002).
BibTeX:
@inproceedings{InproBlenski22002,
  author = {Blenski, T.},
  title = {A new approach to the thermodynamics of dense plasmas},
  year = {2002}
}
"The Radiative Shock : Theory, Laser Experiments and Interpretation"
Fleury X, Bouquet S, Koenig M, Benuzzi-Mounaix A, Batani D, Hall T, Grandjouan N, Malka V, Henry E, Leygnac S, Merdji H, Grenier J, Barroso P, Stehlé C, Michaut C, Thais F, Chièze J, Lafon J, Cathala B, Marchet B and Polès L, In Second International Conference on Inertial Fusion Sciences and Applications (IFSA 2001). Kyoto, Japon , pp. 1029-1033 - (2002).
Abstract: In this paper, a « Laser Laboratory Astrophysics » study concerning the radiative shock is presented. This kind of shock plays a major role in several astrophysical phenomena (star formation, supernovae explosion, stellar winds ) and the main effects produced by the full radiative contributions (radiative pressure and energy density, in addition to the radiation flux) are reminded from a recent analytical work carried out by us [S. Bouquet, et al., ApJ. Supp. 127, 245 (2000)]. One of the most important effect is the apparition of a radiative precursor. It has been simulated experimentally by using the nanosecond LULI laser. The targets consisted in xenon cells and the physical quantities have been adapted in order to recover the radiative shock conditions. As expected from the theory, the formation and the propagation of a precursor arose. Its velocity and the velocity of the shock have been measured. Comparisons between, on one hand, analytical calculations (self-similar solutions) and numerical simulations and, on the other hand, experimental results have been performed and pretty good agreements have been obtained.
BibTeX:
@inproceedings{InproFleury2002,
  author = {Fleury, X. and Bouquet, S. and Koenig, M. and Benuzzi-Mounaix, A. and Batani, D. and Hall, T. and Grandjouan, N. and Malka, V. and Henry, E. and Leygnac, S. and Merdji, H. and Grenier, J. and Barroso, P. and Stehlé, C. and Michaut, C. and Thais, F. and Chièze, J.P. and Lafon, J.P. and Cathala, B. and Marchet, B. and Polès, L.},
  title = {The Radiative Shock : Theory, Laser Experiments and Interpretation},
  booktitle = {Second International Conference on Inertial Fusion Sciences and Applications (IFSA 2001)},
  year = {2002},
  pages = {1029--1033}
}
"Rare gas cluster explosion in an intense laser field"
Ishikawa K and Blenski T, In 7th Int. Symp. of the Graduate Univ. for Adv. Studies on Science of Superstrong Field Interactions. Shonan Village, Hayama (Japan) Vol. 634(), pp. 211-216 - (2002).
Abstract: We study rare gas cluster explosion in an intense, femtosecond laser pulse using Monte Carlo particle dynamics simulations. The obtained dependence of ion energy on ion charge is approximately quadratic for lower charge states and linear for higher ones. This behavior, also observed in experiments, can be entirely explained on the basis of the Coulomb explosion mechanism. Our results also show that electron impact ionization plays only a minor role in ionization.
BibTeX:
@inproceedings{InproIshikawa2002,
  author = {Ishikawa, K. and Blenski, T.},
  title = {Rare gas cluster explosion in an intense laser field},
  booktitle = {7th Int. Symp. of the Graduate Univ. for Adv. Studies on Science of Superstrong Field Interactions},
  year = {2002},
  volume = {634()},
  pages = {211--216}
}
"New Radiative Shocks Experiments"
Leygnac S, Bouquet S, Stehlé C, Benuzzi-Mounaix A, Boireau L, Chièze J-P, Grandjouan N, Huser G, Koenig M, Malka V, Merdji H, Michaut C, Thais F and Vinci T, In Semaine de l'astrophysique française. Paris Vol. (), pp. 531 - (2002).
Abstract: An experimental study of shocks with astrophysical relevance is performedwith the high energy density laser of the LULI, at the école Polytechnique(France). The peculiarity of these shocks is the strong coupling betweenradiation and hydrodynamics which leads to a structure governed by a radiative precursor. A new experiment has been performed this year wherewe have observed shocks identified as radiative shocks. From the measurements, it is possible to infer several features of the shock such as the speed and the electronic density. New diagnostics have been implemented to study the geometrical shape of the shock and obtain spectroscopic informations.
BibTeX:
@inproceedings{InproLeygnac2002,
  author = {Leygnac, S. and Bouquet, S. and Stehlé, C. and Benuzzi-Mounaix, A. and Boireau, L. and Chièze, J.-P. and Grandjouan, N. and Huser, G. and Koenig, M. and Malka, V. and Merdji, H. and Michaut, C. and Thais, F. and Vinci, T.},
  title = {New Radiative Shocks Experiments},
  booktitle = {Semaine de l'astrophysique française},
  year = {2002},
  volume = {()},
  pages = {531}
}
"X-ray absorption of radiatively heated Al/Ni multi-layered foils"
Thais F, Chenais-Popovics C, Fajardo M, Gauthier J-C, Blenski T, Gilleron F, Pain J-C, Poirier M, Eidmann K and Folsner W , In IFSA-2001. Japon , pp. 451-455 - (2002).
Abstract: Mixtures of light and mid-Z elements have been used in order to measure the absorption of the mid-Z element (Ni), the temperature being inferred from the K-shell absorption of the light element (Al). We test here this method by comparing the temperatures deduced from Al K-transitions and nickel L-shell absorption spectra in Al/Ni bi- and multi-layers. The temperatures obtained from the experimental spectra using a new version of the opacity code SCO are compared with tempera-tures predicted by standard hydrodynamic simulations.
BibTeX:
@inproceedings{InproThais2002,
  author = {Thais, F. and Chenais-Popovics, C. and Fajardo, M. and Gauthier, J.-C. and Blenski, Th. and Gilleron, F. and Pain, J.-Ch. and Poirier, M. and Eidmann, K. and Folsner, W.},
  title = {X-ray absorption of radiatively heated Al/Ni multi-layered foils},
  booktitle = {IFSA-2001},
  year = {2002},
  pages = {451--455}
}
2001
"Supernovae Rayleigh-Taylor instability experiments on the CEA-Phebus laser facility"
Benuzzi-Mounaix A, Bouquet S, Chieze J-P, Mucchielli F, Teyssier R and Thais F, Astrophysics and Space Science. Vol. 277(1-2), pp. 143-146 - (2001).
Abstract: Hydrodynamic instabilities play a key role in several astrophysical phenomena. We present a laser experiment related to the evolution of Rayleigh-Taylor instabilities (RTI) due to the passage of the shock wave through the He/H interface in a type II supernova. The experiment is performed on the CEA-Phébus laser facility and the RTI are studied using a bi-layer Cu/CH2 target with sinusoidal ripple at the interface.
BibTeX:
@article{Benuzzi-Mounaix2001,
  author = {Benuzzi-Mounaix, A. and Bouquet, S. and Chieze, J.-P. and Mucchielli, F. and Teyssier, R. and Thais, F.},
  title = {Supernovae Rayleigh-Taylor instability experiments on the CEA-Phebus laser facility},
  journal = {Astrophysics and Space Science},
  year = {2001},
  volume = {277},
  number = {1-2},
  pages = {143--146},
  url = {http://link.springer.com/article/10.1023%2FA%3A1012256801365#}
}
"Absorption measurements of radiatively heated multi-layered Al/Ni foils"
Chenais-Popovics C, Fajardo M, Thais F, Gilleron F, Gauthier J-C, Eidmann K, Folsner W, Blenski T, Perrot F, Bauche-Arnoult C, Bachelier A and Bauche J, Journal of Quantitative Spectroscopy and Radiative Transfer. Vol. 71(2-6), pp. 249-256 - (2001).
Abstract: Mixtures of light and mid-Z elements have been used to measure the absorption of the mid-Z element Ni, the temperature is inferred from the K-shell absorption of the light element Al. Here we test this method by comparing the temperatures deduced from Al Ka transitions and nickel L-shell absorption spectra in Al/Ni multilayers and bilayers. The ionisation state is obtained by comparison of the Al and Ni spectra with calculations assuming local thermodynamic equilibrium. The temperatures obtained from the experiment are compared with hydrodynamic simulations predictions. Simulation code results show that the density differs by a factor of 2 in the two elements. This has to be taken into account in the determination of the temperature.
BibTeX:
@article{Chenais-Popovics2001,
  author = {Chenais-Popovics, C. and Fajardo, M. and Thais, F. and Gilleron, F. and Gauthier, J.-C. and Eidmann, K. and Folsner, W. and Blenski, T. and Perrot, F. and Bauche-Arnoult, C. and Bachelier, A. and Bauche, J.},
  title = {Absorption measurements of radiatively heated multi-layered Al/Ni foils},
  journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
  year = {2001},
  volume = {71},
  number = {2-6},
  pages = {249--256},
  url = {http://www.sciencedirect.com/science/article/pii/S0022407301000723},
  doi = {10.1016/S0022-4073(01)00072-3}
}
"Rare gas cluster explosion in a strong laser field"
Ishikawa K and Blenski T, Laser Physics. Vol. 11(2), pp. 269-277 - (2001).
Abstract: We study rare gas cluster explosion in an intense, femtosecond laser pulse using Monte Carlo particle dynamics
simulations. The obtained dependence of ion energy on ion charge is approximately quadratic for lower charge states
and linear for higher ones. This behavior, also observed in experiments, can be entirely explained on the basis of
the Coulomb explosion mechanism. Our results also show that electron impact ionization plays only a minor role in
ionization.
BibTeX:
@article{Ishikawa2001,
  author = {Ishikawa, K. and Blenski, T.},
  title = {Rare gas cluster explosion in a strong laser field},
  journal = {Laser Physics},
  year = {2001},
  volume = {11},
  number = {2},
  pages = {269--277},
  url = {http://ishiken.free.fr/Publication/ECLIM2000.pdf}
}
"Series interaction and polarization effects in large-angular momentum two-electron atoms"
Poirier M, Physical Review A. Vol. 63, pp. 052513/1-14 - (2001).
Abstract: Doubly excited atoms with an outer large-l electron are expected to exhibit moderate series interaction. However, accidental or systematic degeneracies may lead to strong configuration mixing. To describe such phenomena, the present formalism uses a partial diagonalization of the dielectronic interaction plus a second-order correction based on Coulomb Green's function. It makes it possible to determine the eigenfunction composition, level positions, and autoionization widths. While series interaction turns out to be weak for almost degenerate high members of the 4djng series in strontium, a significant configuration mixing is observed on 6pjnl series of barium. A generally fair agreement is observed with 6pjng experimental data. The 6pjnh levels are accurately predicted, too, and new assignations are reported for some of them; however, the computed linewidths are about twice as small as the measured ones. The method also applies to helium and multiply charged ions, where the relevance of collective quantum numbers is analyzed. Some level positions and widths are detailed.
BibTeX:
@article{Poirier2001,
  author = {Poirier, M.},
  title = {Series interaction and polarization effects in large-angular momentum two-electron atoms},
  journal = {Physical Review A},
  year = {2001},
  volume = {63},
  pages = {052513/1--14},
  url = {http://dx.doi.org/10.1103/PhysRevA.63.052513},
  doi = {10.1103/PhysRevA.63.052513}
}
"Absorption d'une feuille d'aluminum à l'équilibre thermodynamique local, pour différentes densités"
Chenais-Popovics C, Gilleron F, Thais F, Eidmann K, Folsner W, Gauthier J and Blenski T - (2001).
BibTeX:
@techreport{Techreport2001,
  author = {Chenais-Popovics, C. and Gilleron, F. and Thais, F. and Eidmann, K. and Folsner, W. and Gauthier, J.C. and Blenski, T.},
  title = {Absorption d'une feuille d'aluminum à l'équilibre thermodynamique local, pour différentes densités},
  year = {2001}
}
2000
"Radiative heating of B, Al and Ni thin foils at 15 - 25 eV temperatures"
Chenais-Popovics C, Gilleron F, Fajardo M, Merdji H, Mißalla T, Gauthier J, Renaudin P, Gary S, Bruneau J, Perrot F, Blenski T, Folsner W and Eidmann K, Journal of Quantitative Spectroscopy and Radiative Transfer. Vol. 65, pp. 117 - (2000).
Abstract: Several thin foils have been heated by X-ray radiation emitted by a small gold cavity irradiated with the LULI facility Nd glass laser. The foils were heated to moderate temperatures (1025 eV) in conditions near local thermodynamic equilibrium. Measurements of the absorption of K transitions of aluminum, of the K-shell transitions of boron, and of the n=23 and 4 transitions of nickel are reported. A 5000 l/mm transmission grating spectrograph recorded the boron data, and a flat thallium hydrogen phthalate (TlAP) crystal was used for aluminum and nickel absorption measurements. The nickel and aluminum spectra indicate a higher temperature (2225 eV) than the boron case (14 eV), explained by a difference in the absorption spectra of these elements. In the Ni case the measured 2p-3d spinorbitsplit absorption structures compared well with theoretical spectra obtained with the SCO superconfiguration code using the spin orbit split transition arrays formalism (SOSA). The heating of the foils as calculated with radiative hydrodynamic simulations is very similar to the experimental data.
BibTeX:
@article{Chenais-Popovics2000a,
  author = {Chenais-Popovics, C. and Gilleron, F. and Fajardo, M. and Merdji, H. and Mißalla, T. and Gauthier, J.C. and Renaudin, P. and Gary, S. and Bruneau, J. and Perrot, F. and Blenski, T. and Folsner, W. and Eidmann, K.},
  title = {Radiative heating of B, Al and Ni thin foils at 15 - 25 eV temperatures},
  journal = {Journal of Quantitative Spectroscopy and Radiative Transfer},
  year = {2000},
  volume = {65},
  pages = {117},
  url = {http://dx.doi.org/10.1016/S0022-4073(99)00061-8},
  doi = {0.1016/S0022-4073(99)00061-8}
}
"Opacity studies of iron in the 15-30eV temperature range"
Chenais-Popovics C, Merdji H, Mißalla T, Gilleron F, Gauthier JC, Blenski T, Perrot F, Klapisch M, Bauche-Arnoult C, Bauche J, Bachelier A and Eidmann K, Astrophysical Journal. Supplement series. Vol. 127(2), pp. 275-281 - (2000).
Abstract: Absorption of the 2p-3d transitions of iron has been measured using point projection spectroscopy. Thin C tamped Fe foils were heated around 20 eV by X-rays generated in gold spherical hohlraums irradiated by the high-power laser ASTERIX IV. Absorption of Fe V to Fe X has been observed in the spectral vicinity of 730 eV (17 Ĺ). The Ag backlighter source and absorbed spectra were recorded on the same shot by a TlAP crystal spectrograph. The experimental spectra have been reproduced by the two superconfiguration local thermodynamic equilibrium codes SCO and STA. Detailed statistical calculations of the different ionic structures have also been performed with the Spin Orbit Split Arrays method, allowing the determination of ion populations. The electron temperature and average ionization obtained by fitting the experiment with the different calculations were compared with radiative hydrodynamic simulations.
BibTeX:
@article{Chenais-Popovics2000,
  author = {Chenais-Popovics, C. and Merdji, H. and Mißalla, T. and Gilleron, F. and Gauthier, J. C. and Blenski, T. and Perrot, F. and Klapisch, M. and Bauche-Arnoult, C. and Bauche, J. and Bachelier, A. and Eidmann, K.},
  title = {Opacity studies of iron in the 15-30eV temperature range},
  journal = {Astrophysical Journal. Supplement series},
  year = {2000},
  volume = {127},
  number = {2},
  pages = {275--281},
  url = {http://dx.doi.org/10.1086/313354}
}
"Explosion dynamics of rare gas clusters in an intense laser field"
Ishikawa K and Blenski T, Physical Review A. Vol. 62(6), pp. 063204/1-11 - (2000).
Abstract: We study the explosion dynamics of rare-gas clusters (Ar55, Ar147, Xe55, and Xe147) in an intense, femtosecond laser pulse via Monte Carlo classical particle-dynamics simulations. Our method includes tunnel and impact ionization as well as ion-electron recombination, and allows us to follow the motion of both ions and free electrons during laser-cluster interaction. Our simulation results show that ionization proceeds mainly through tunnel ionization by the combined fields from ions, electrons, and laser while the contribution of electron-impact ionization is secondary. The ions are ejected in a stepwise manner from outer shells and accelerated mainly through their mutual Coulomb repulsion. Taking a spatial laser intensity profile into account, we show that the Coulomb explosion scenario leads to the same charge dependence of ion energy, i.e., quadratic for lower charge states and linear for higher ones, as that observed in experiments with larger clusters. This indicates that Coulomb explosion may be a dominant cluster explosion mechanism even in the case of large clusters. We also find that the ion energy is higher in the direction parallel to laser polarization than in the direction perpendicular to it. When ions are emitted along the direction of laser polarization, their charge changes in phase with the laser field, and this leads to an efficient acceleration.
BibTeX:
@article{Ishikawa2000,
  author = {Ishikawa, K. and Blenski, T.},
  title = {Explosion dynamics of rare gas clusters in an intense laser field},
  journal = {Physical Review A},
  year = {2000},
  volume = {62},
  number = {6},
  pages = {063204/1--11},
  url = {http://dx.doi.org/10.1103/PhysRevA.62.063204},
  doi = {0.1103/PhysRevA}
}
"Simulations "Particle-in-cell" d'ionisations multiples de petites molécules dans un champ de laser intense.Particle-in-cell simulations of multiple ionization of small molecules in a strong laser field."
Ishikawa K and Blenski T, Physical Review A. Vol. 61, pp. 063408 - (2000).
Abstract: Nous présentons des simulations "Particle-in-cell" (PIC) à une dimension appliquées à l'ionisation multiple et à la fragmentation de molécules di- et tri-atomiques soumises à un cham laser intense ultracourt. Notre méthode permet de traiter tous les électrons et tous les noyaux explicitement et de suivre l'évolution temporaire de l'ionisation. Les résultats des simulations confirment que la probabilité d'ionisation est fortement augmentée à une certaine distance critique internucléaire (enhanced ionization). Ce phénomène a lieu quand les barrières internes du potentiel sont plus hautes que celle externe. Le mécanisme de "enhanced ionization" dans une molécule triatomique se comprend de manière similaire au cas diatomique, bien que les trois puits de potentiel y participent dans le cas triatomique. Malgré le phénomène, l'ionization n'est pas nécessairement localisée à la distance critique. D'ailleurs nos simulations montrent qu'il n'y a pas de différences significatives en ce qui concerne l'état de charge des fragments ioniques entre le cas des molécules di- et tri-atomique. La faible valeur de la distance critique dans nos résultats peut impliquer que le défaut de l'énergie cinétique observé expérimentalement soit causé non seulement par "enhanced ionization" autour de cette distance mais aussi par la nature non-couloumbienne du potentiel moléculaire.
BibTeX:
@article{Ishikawa2000a,
  author = {Ishikawa, K. and Blenski, T.J.},
  title = {Simulations "Particle-in-cell" d'ionisations multiples de petites molécules dans un champ de laser intense.Particle-in-cell simulations of multiple ionization of small molecules in a strong laser field.},
  journal = {Physical Review A},
  year = {2000},
  volume = {61},
  pages = {063408},
  url = {http://dx.doi.org/10.1103/PhysRevA.61.063408},
  doi = {0.1103/PhysRevA.61.063408}
}
"SANS study of the microstructural evolution of martensitic steels under thermal ageing and neutron irradiation."
Mathon M, Geoffroy G, De Carlan Y, Alamo A and De novion C, Physica B. Vol. 276-77, pp. 939-940 - (2000).
Abstract: SANS technique has been used to study the microstructural evolution of martensitic steels containing 7-12% Cr, under thermal ageing and neutron irradiation. Some of the investigated alloys are industrial low activation martensitic (LAM) materials, where alloying elements have been substituted by elements with low radiological impact. For materials quenched from the austenitic phase, a direct correlation was found between the hardening and the number density of M2C precipitates induced by thermal ageing at 500 °C. Irradiation-accelerated spinodal decomposition of the B.C.C. ferrite was observed in alloys containing large (= 11%) chromium content.
BibTeX:
@article{Mathon2000,
  author = {Mathon, M. and Geoffroy, G. and De Carlan, Y. and Alamo, A. and De novion, C.},
  title = {SANS study of the microstructural evolution of martensitic steels under thermal ageing and neutron irradiation.},
  journal = {Physica B},
  year = {2000},
  volume = {276-77},
  pages = {939--940},
  url = {http://hal.archives-ouvertes.fr/hal-00725142/},
  doi = {10.1016/S0921-4526(99)01299-5}
}
"Absorption X de feuilles multicouches d'aluminium-nickel chauffées radiativement"
Chenais-Popovics C, Fajardo M, Gilleron F, Gauthier J-C, Thais F, Folsner W, Eidmann K, Perrot F and Blenski T - (2000).
BibTeX:
@techreport{Techreport2000,
  author = {Chenais-Popovics, C. and Fajardo, M. and Gilleron, F. and Gauthier, J.-C. and Thais, F. and Folsner, W. and Eidmann, K. and Perrot, F. and Blenski, T.},
  title = {Absorption X de feuilles multicouches d'aluminium-nickel chauffées radiativement},
  year = {2000}
}
"Absorption of X-rays in dense plasmas"
Blenski T, Pologne - (2000).
BibTeX:
@inproceedings{InproBlenski32000,
  author = {Blenski, T.},
  title = {Absorption of X-rays in dense plasmas},
  year = {2000}
}
"X-Ray Absorption In Dense Plasmas Theory vs. Experiment"
Blenski T, Perrot F, Renaudin P, Chenais-Popovics C, Fajardo M, Merdji H, Gilleron F, Gauthier J-C, Eidmann K and Andiel U, In IFSA-1999. France , pp. 1111-1114 - (2000).
BibTeX:
@inproceedings{0InproBlenski22000,
  author = {Blenski, T. and Perrot, F. and Renaudin, P. and Chenais-Popovics, C. and Fajardo, M. and Merdji, H. and Gilleron, F. and Gauthier, J-C. and Eidmann, K. and Andiel, U.},
  title = {X-Ray Absorption In Dense Plasmas Theory vs. Experiment},
  booktitle = {IFSA-1999},
  year = {2000},
  pages = {1111--1114}
}
"The Astrolab experiment : Rayleigh-Taylor instabilities in supernova"
Thais F, Chièze J, Baclet P, Benuzzi A, Bouquet S, Cherfils C, Mucchielli F, Polès L, Reverdin C, Teyssier R, Thébault J and Troussel P, In IFSA 1999. Bordeaux (France) Vol. (), pp. 1083-1086 - (2000).
Abstract: Hydrodynamic instabilities play a key role in several astrophysical phenomena. Here we present a laser experiment related to the evolution of Rayleigh-Taylor instabilities at the passage of the shock wave through the He/H interface in a type II supernova. The growth rate of the instabilities is studied for different initial conditions using a bi-layer Cu/CH2 target with sinusoidal ripple at the interface. The experiment is performed on the PHéBUS laser facility, in an indirect drive configuration.
BibTeX:
@inproceedings{InproThais2000,
  author = {Thais, F. and Chièze, J.P. and Baclet, P. and Benuzzi, A. and Bouquet, S. and Cherfils, C. and Mucchielli, F. and Polès, L. and Reverdin, C. and Teyssier, R. and Thébault, J.P. and Troussel, P.},
  title = {The Astrolab experiment : Rayleigh-Taylor instabilities in supernova},
  booktitle = {IFSA 1999},
  year = {2000},
  volume = {()},
  pages = {1083--1086}
}
1999
"Observation of ions with energies above 100 keV produced by the interaction of a 60-fs laser pulse with clusters"
Dobosz S, Schmidt M, Perdrix M, Meynadier P, Gobert O, Normand D, Ellert C, Blenski T, Faenov AY, Magunov IA, Pikuz T, Skobelev IY and Andreev NE, Journal of Experimental and Theoretical Physics. Vol. 88(6), pp. 1122-1129 - (1999).
Abstract: The x-ray spectra of a plasma generated by heating CO2 and Ar clusters with high-intensity femtosecond laser pulses with qlas ~ 1018 W/cm2 are investigated. Spatially resolved x-ray spectra of a cluster plasma are obtained for the first time. Photoionization absorption is observed to influence the spectral line profiles. The recorded features of the x-ray emission spectra definitely indicate the existence of a large relative number of excited ions (=~10-2–10-3) with energies of 0.1–1 MeV in such a plasma. Possible mechanisms underlying the acceleration of ions to high energies are discussed. It is shown that the experimental results can be attributed to the influence of ponderomotive forces in standing waves generated by the reflection of laser radiation from the clusters.
BibTeX:
@article{Dobosz1999,
  author = {Dobosz, S. and Schmidt, M. and Perdrix, M. and Meynadier, P. and Gobert, O. and Normand, D. and Ellert, C. and Blenski, T. and Faenov, A. Ya. and Magunov, I. A. and Pikuz, T.A. and Skobelev, I. Yu. and Andreev, N. E.},
  title = {Observation of ions with energies above 100 keV produced by the interaction of a 60-fs laser pulse with clusters},
  journal = {Journal of Experimental and Theoretical Physics},
  year = {1999},
  volume = {88},
  number = {6},
  pages = {1122--1129},
  url = {http://dx.doi.org/10.1134/1.558900},
  doi = {10.1134/1.558900}
}
"Effets de polarisation lors des processus d'autoionisation des atomes alcalino-terreux : analyse par la fonction de Green Coulombienne.Polarization effects in autoionisation processes of alkaline-earth atoms : Coulomb Green's function analysis."
Poirier M and Semaoune R, Physical Review A. Vol. 59(5), pp. 3471-3479 - (1999).
Abstract: Dans les systèmes multiélectroniques, la corrélation électronique qui est la manifestation du comportement non-indépendant des électrons joue un rôle important à plus d'un titre : la classification des états doublement excités doit la prendre en compte, les positions de ces mêmes états en dépendent fortement et, récemment divers travaux ont souligné le lien entre l'apparition du chaos et la présence des corrélations. A priori les atomes doublement excités de grand moment cinétique, dans lesquels l'orbitale de l'électron le plus excité (de grand moment l) ne recouvre pratiquement pas celle de l'électron moins excité ni le coeur atomique, ne sont pas les candidats idéaux pour étudier de tels effets ; une description par la théorie de perturbations à l'ordre le plus bas qui ignore les corrélations devrait alors suffire. Or un précédent travail portant sur les premiers états doublement excités de grand l des alcalino-terreux (3dng du calcium, 4dng du strontium, 5dng du baryum, donc avec l égal à 4) a établi que leurs positions sont décrites de manière très insuffisante par la théorie des perturbations à l'ordre le plus bas. Il en est de même pour le calcul des probabilités d'autoionisation, processus caractéristique des états doublement excités et principalement responsable de la largeur de ces états. Le présent travail, en développant le calcul en perturbation jusqu'à l'ordre 2 à l'aide de la technique de la fonction de Green Coulombienne, permet d'obtenir pour les largeurs des états 5d5g du baryum un accord tout à fait satisfaisant avec les données expérimentales existantes. Cette description théorique correspond physiquement à la prise en compte de la polarisation (déformation à distance) de l'orbitale de l'électron interne par l'électron externe. Plus généralement, il est montré ici que ce phénomène se manifeste sur chacun des états doublement excités des alcalino-terreux mentionnés plus haut. A la différence des positions de niveaux qui peuvent être comparées à un vaste ensemble de données expérimentales, les largeurs calculées ici constituent dans leur grande majorité des déterminations originales et leur confirmation expérimentale est vivement souhaitée. Toutefois, dans le cas des niveaux 5d5/2nh J=5 du baryum, pour lesquels la description théorique devrait à fortiori être pertinente puisque le moment l est encore plus grand (5 au lieu de 4), l'accord avec une mesure réalisée à l'Université d'Amsterdam s'avère excellent.
BibTeX:
@article{Poirier1999,
  author = {Poirier, M. and Semaoune, R.},
  title = {Effets de polarisation lors des processus d'autoionisation des atomes alcalino-terreux : analyse par la fonction de Green Coulombienne.Polarization effects in autoionisation processes of alkaline-earth atoms : Coulomb Green's function analysis.},
  journal = {Physical Review A},
  year = {1999},
  volume = {59},
  number = {5},
  pages = {3471--3479},
  url = {http://prola.aps.org/abstract/PRA/v59/i5/p3471_1},
  doi = {10.1103/PhysRevA.59.3471}
}
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