Ionization Relaxation in a Closed-Cycle MHD Generator

Abstract

The onset of the nonequilibrium conductivity in a closed-cycle MHD generator is experimentally investigated. Conditions for deviations from a Maxwellian electron energy distribution are realized during an afterglow experiment. Here, values of the electron temperature and electron density correspond with those present at the entrance of an MHD generator working at low stagnation temperatures (TS less than or equal to 2000 K). Minimum currents are measured in MHD experiments. They correspond to the threshold values of the electron density (5 x 10 to the 18th per cu m) for the transition from a non-Maxwellian to a Maxwellian shape of the electron energy distribution. For low inlet electron densities (less than or equal to the threshold value) the onset of the nonequilibrium conductivity becomes difficult and relaxation ionization lengths up to the generator length have been shown to exist by the experiments. At low stagnation temperatures, higher inlet values of electron density and shorter relaxation lengths are realized by means of preionization. 12 references.