Stimulated Raman scattering and Hard x-rays from small scale hohlraums with high power and energy laser beams*

Millimeter-scale, vacuum gold hohlraums illuminated with 200TW of laser power and 400kJ laser energy have small levels of Stimulated Raman scatter. This work concentrates on the SRS spectrum and the hot electrons accelerated by the electron plasma waves(EPW) driven by the beat ponderomotive force of the laser and SRS light. Because of the high electron temperature (T_e > 10 keV)in the underdense plasma, k_epw λ_De is large enough that the EPWs are strongly Landau damped except near the quarter-critical surface. Here, k_epw is the wavenumber of the EPW and λ_De is the electron Debye length. The measured SRS frequency spectrum is consistent with ω ~ ω₀/2. The Vlasov code, LOKI, is used to obtain both the SRS frequency spectrum and, self-consistently, the electron distribution function modified by the high phase velocity (v_ph~ c) electron plasma waves where c is the speed of light. For the high phase velocities, relativistic treatments are important and used in LOKI to obtain the correct EPW frequency and damping rates. The electrons accelerated up to the phase velocity of the EPWs are beamed in velocity along the propagation direction of the EPW in the interaction region. Once they are transported to higher density, collisions with gold ions scatter the electrons in angle and isotropize their distribution. We calculate the hard X-ray bremsstrahlung with the isotropized distribution of electrons.