MEASUREMENTS OF INVERSE BREMSSTRAHLUNG ABSORPTION AND NON-MAXWELLIAN ELECTRON VELOCITY DISTRIBUTIONS

Non-Maxwellian (flattopped) electron velocity distributions resulting from inverse bremsstrahlung of intense microwaves are measured directly for the first time in experiments performed on the UCD AURORA II device. The experiments are performed in the afterglow of a pulsed discharge plasma that is moderately collisional and sufficiently ionized (approximately 1%) that Coulomb collisions are dominant. Langmuir probe measurements indicate that the isotropic component of the electron velocity distribution is non-Maxwellian in very good agreement with electron kinetic (Fokker-Planck) simulations.