ELECTRON HEAT-TRANSPORT WITH NON-MAXWELLIAN DISTRIBUTIONS

Measurements are presented of electron heat transport with non-Maxwell ian (flattopped) distributions due to inverse bremsstrahlung absorptio n of intense microwaves in the University of California at Davis Auror a II device [Rogers et al., Phys. Fluids B 1, 741 (1989)]. The plasma is created by pulsed discharge in a cylindrical vacuum chamber with su rface magnets arranged to create a density gradient. The ionization fr action (approximately 1%) is high enough that charged particle collisi ons are strongly dominant in the afterglow plasma. A short microwave p ulse (approximately 2 mus) heats a region of the afterglow plasma (n(e )/n(cr) less-than-or-equal-to 0.5) creating a steep axial (L(T) approx imately 1 - 10lambda(ei)) temperature gradient. Langmuir probes are us ed to measure the relaxation of the heat front after the microwave pul se. Time and space resolved measurements show that the isotropic compo nent of the electron velocity distribution is flat topped (approximate ly exp[-(nu/nu(m))m], m >2) in agreement with Fokker-Planck calculatio ns using the measured density profile. Classical heat transport theory is not valid both because the isotropic component of the electron vel ocity distribution is flattopped and the temperature gradients are ver y steep.