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The contribution from detailed atomic-physics codes
The contribution from detailed atomic-physics codes

Figure 2: Emission of a xenon 10+ plasma at temperature 30 eV computed with HULLAC code: configuration interaction effect.

To go beyond the atomic formalism of auto-coherent central-field type, we have used the relativistic parametric potential code HULLAC, developed by Bar-Shalom and coworkers [7]. This code allows one to account for configuration interactions, particularly relevant for Dn = 0 transitions (as 4p – 4d or 4d – 4f) and for doubly excited states. It is available as a series of modules and determines for each detailed level its energy, wave-function, bound-bound radiative transition and autoionization probability, and if necessary cross-sections for collisional ionization, excitation and photoionization. A particularly important effect in ionic spectroscopy illustrated by fig. 2 is the configuration interaction (CI). Explicitly, one of the important processes in Xe10+ is associated to the transition between 4s2 4p6 4d6 and 4s2 4d5 4f configurations (the core with closed n = 1, 2, and 3 shells is omitted); but this transition is correctly described only if one considers that the excited state is mixed notably to the configurations 4p5 4d6 et 4p6 4d5 np. Such an effect shifts the levels of the band centered around 120 Å towards 100–110 Å and shrinks this band. In some cases, CI may also make allowed dipolar electric transitions that would be forbidden in a single-configuration one-active-electron description. One will notice however that all lines are not equally affected by CI: the group of 4d–5p lines around 135 Å is weakly shifted when CI is accounted for.

From energies and transition probabilities computed with the HULLAC code it is possible to determine plasma emission: an example is given in Fig. 3 and compared to a direct measurement performed in our laboratory. Several hypotheses were necessary to obtain this spectrum. First, one assumes that all ion populations and, for a given ion, all level populations obey LTE, i.e., Saha-Boltzmann equation. Then, one considers the active medium as homogeneous and one-dimensional, and light-scattering is neglected. With these conditions one may derive that spectral intensity obey a simple lay known as Kirchhoff law which reduces itself to Planck formula in the limit of an optically thick medium. This Planck limit shows up as the envelope of the detailed yellow curve on figure 2.
[7] A. Bar-Shalom, M. Klapisch, and J. Oreg, J. Quant. Spectrosc. Radiat. Transfer 71, 169 (2001).
The contribution from detailed atomic-physics codes

Figure 3: Computation with HULLAC code of the emission of a xenon plasma at density 0,01 g/cm3 and temperature 26 eV compared to an experimental spectrum obtained in Saclay by M. Schmidt and coworkers [6].

#1113 - Last update : 08/01 2011


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