In ICF plasmas, laser parametric instabilities (LPI) are one of the most complex problems in the laser-plasma interaction domain. We are interested here in characterizing the suprathermal electron population produced by electron parametric instabilities such as stimulated Raman scattering in sub-quarter-critical plasmas. Indeed, these hot electrons, accelerated at velocities around 3-4 vthe, may alter heating transport coefficients, or damping rates of waves in the plasma in the vicinity of Raman active regions. The goal of this proposal is to investigate how far from thermal equilibrium are the plasmas experiencing strong, local, kinetic heating generated during LPI saturation processes (plasmas at thermal equilibrium refer to plasmas having Maxwellian velocity distribution functions (VDF)). The experiment described here proposes to set up three types of diagnostics: (i) the main one, based on Thomson scattering, will analyze thermal electron plasma wave numbers kp according to two crossed directions, and sensitive to these hot electrons, that is to say for kpλD ~ 0.3 (λD is the electron Debye length); (ii) X-ray emission produced by these electrons in the plasma will be quantified and imaged; (iii) time- and space-resolved backward Raman scattering excited by the nanosecond beams will be recorded for cross-correlating Raman data with the two other diagnostics. The goals of this experiment are ambitious; progress and improvements of the diagnostics are expected during these multi-experiments, for which we require a multi-year access, at least over two years. Additional X-ray spectroscopy will provide a significant progress for this prospective experiment devoted to non-Maxwellian electron distribution functions.
LULI2000 - S3-S4-S5/2021