Experimental and numerical investigations of ion acceleration by ultraintense laser pulses in near-critical transparent gas jets *

High-energy ion sources driven by ultra-intense laser pulses are interesting for many applications ranging from medicine to fundamental research. While laser-driven ion acceleration has been extensively investigated in solid targets, much fewer studies have addressed the case of near-critical plasmas (n_e ~ n_c) due to the technical difficulty of achieving controlled high gas densities. Such plasmas are predicted to give rise to new ion acceleration regimes combining TNSA and collisionless shock acceleration (CSA), as well as enhanced hot-electron production, beyond the standard ponderomotive scaling. 

We report on the results of two experimental campaigns conducted at the 200 TW, 30 fs VEGA II and recently at the 1 PW, 30 fs VEGA III laser systems (CLPU, Spain) together with an extensive parametric PIC study performed to explore the physics of the expected interaction. Our first campaign aimed at studying the potential for ion acceleration of a state-of-the-art gas jet coupled with shock nozzles. Preliminary time-of-flight results of our most recent campaign show ~5 MeV/a.m.u. alpha particles accelerated at a moderately high repetition rate with relatively low energy dispersion and divergence. They also validate the strong electron heating predicted by our numerical studies.