Radiative energy loss and the electrical conductivity in nonequilibrium MHD generators

Abstract

THE radiative energy loss and its effect on the electrical conductivity in a nonequilibrium Faraday magnetohydrodynamic generator have been studied. Considering the nonMaxwellian distribution of electrons in a nonequilibrium argon-potassium plasma with significant radiation loss, the calculated electrical conductivity is found to show the experimentally observed peculiar behavior of decreasing conductivity in a certain current density range. Contents The electrical conductivity of a nonequilibrium magnetohydrodynamic (MHD) plasma is often determined by means of the Saha equation at the electron temperature, where the population of the excited states is assumed to be in thermal equilibrium with the electrons having a Maxwellian distribution. This consideration is, however, strictly justified only when the collisional loss due to electron/atom elastic collisions is the dominant electron energy loss. When the radiative energy loss arising from inelastic collisions of electrons with heavy particles in seeded inert gases is significant, the electron distribution function is in general non-Maxwellian. With a view to explaining the observed hump-1'* in the conductivity/current relation as a peculiar behavior, Sakao and Sato1 considered the non-Maxwellian distribution of electrons in the presence of radiative energy loss. Without explicitly considering the radiative energy loss, they considered a parameter characterizing such loss and calculated the electrical conductivity showing the qualitative decrease in a certain range of current density. The present paper deals with the radiative energy loss by following Lutz4 and then calculating the electrical conductivity of a nonequilibrium argon-potassium plasma using a non-Maxwellian electron distribution similar to Sakao and Sato.1 When the radiative loss is negligible, the electrons follow the Maxwellian velocity distribution defined by one electron temperature. Since inelastic collisions giving rise to radiation loss remove electrons from the high-energy tail of the electron velocity distribution, the electrons are redistributed quite differently with tail being depressed below its Maxwellian value. This depressed high-energy tail is represented as if there were a new Maxwellian at lower electron temperature denoted by Teh, which is used in the Saha equation to determine the electron number density ne. As the