Picture: Conception and realization of our Thomson Parabola diagnostic. From left to right, the SIMION© model (showing ion flight trajectories), the related CATIA© plan and the final mechanical outcome.
• brief introduction to ion acceleration
For over a decade, high power laser driven ion and proton acceleration has exerted a particular interest in the scientific community. This is due to many possible applications of such particle beams, both in basic research (isochoric heating, material or dense plasmas "probing") as well as in the field of health applications (proton therapy). Today, the research in this area is mainly devoted to the increase of the maximum ion energy, getting a monochromatic beam of particles and tailoring the bunch spatial properties (divergence, emittance, laminarity).
In Saclay, the PHI team has been working on this issue since 2005 by exploiting the ultra high laser facility UHI100 (formerly UHI10). We were the first to show, in the past, that both the target sides, once exposed to ultra high contrast laser beams, are able to produce opposite side particles bunches with similar characteristics, which propagate in opposite directions normally to the target. Today, our research focuses primarily on the study of the influence of properly structured targets on the emission properties of the proton beam.
We dispose of two radio-protected experimental halls, both exploiting the UHI 100 TW Ti-Sa laser, whose main features are the extreme brevity of the pulse (25 fs) and the very good intrinsic contrast (around 108). In each hall, a double plasma mirror device increases the pulse contrast value of four orders of magnitude, meanwhile a deformable mirror improves the quality of focal spot.
These unique features of pulse duration, power and contrast make this laser the ideal device for basic research on ion acceleration.
Finally, a full range of diagnostics are used to fully characterize the accelerated ion beams (Thomson parabola spectrometers, radiochromic films, electron spectrometers, diodes) as well as the laser beam in itself (a third order cross-correlator, a self correlator and a SPIDER system for the direct measurement of the intensity and phase profiles of the fs pulse).
Picture: Radiochromic film profiles for the same laser shot in the forward (top) and in the backward (bottom) direction. Recorded energies (from the left to the right) are comprised between about 0.45 and 2 MeV.
