ELFIE - Study of anomalous electron heating produced by kinetic saturation processes of LPI's in picosecond time scale (C. Rousseaux)
Among problems issued from the laser-plasma interaction domain, laser parametric instabilities (LPI) are oneof the most complex ones for ICF issues. Besides worrying backward stimulated Raman scattering (SRS) reflectivities from the inner laser cone as well as significant energy transfer between the inner cones and outer cones, as reported from NIF experiments, the hot electron populations generated by stimulated Raman scattering and other instabilities producing electron plasma waves (EPW) are generally pointed out for issues relevant to the preheat of the compressed target. However, we are interested here in additional effects of these hot electron populations that are related to basic properties of plasmas: as the velocity distribution functions (VDF) of the particles are no more Maxwellian, the hot electron populations, even in small proportions, may significantly alter either heating transport coefficients, or damping rates of waves in the plasma, or radiation properties of high Z materials in the indirect drive scheme of ICF. The aim of this proposal is to investigate how far from thermal equilibrium would be the plasmas experiencing strong local, kinetic heating generated during LPI saturation processes (the thermal equilibrium state refers to a plasma where the VDFs of particles (electrons and ions) are Maxwellian). The most suitable diagnostics for this purpose are highly space- and time-resolved Thomson imaging systems that are regularly used on the ELFIE facility. Particular attention will be paid to detect thermal ion acoustic and electron plasma waves that inform on local plasma characteristics, as local electron temperature (and gradients) or macroscopic particle drifts (or currents). As thermal Thomson measurements are challenging in the short pulse interaction context, the driven electrostatic waves of a second, weak laser pulse fired just after the main perturbing laser pulse will be also diagnosed by means of a second 3ω Thomson probe.
ELFIE : S26-30 / 2016
co-PI : S. Baton (LULI)