Measurements of Non-Maxwellian Electron Distribution Functions and Their Effect on Laser Heating

Electron velocity distribution functions driven by inverse bremsstrahlung heating are measured to be non-Maxwellian using a novel angularly resolved Thomson-scattering instrument and the corresponding reduction of electrons at slow velocities results in a similar to 40% measured reduction in inverse bremsstrahlung absorption. The distribution functions are measured to be super-Gaussian in the bulk (v/v(th) < 3) and Maxwellian in the tail (v/v(th) > 3) when the laser heating rate dominates over the electron-electron thermalization rate. Simulations with the particle code QUARTZ show the shape of the tail is dictated by the uniformity of the laser heating.