Experimental study of nonequilibrium ionization in a linear MHD generator.

Abstract

The primary purpose of this study was to obtain, through magnetically induced ionization, a plasma in which the electron temperature was significantly greater than the gas stagnation temperature. The magnetohydrodynamic (MHD) generator was mounted at the downstream end of a shock tuhe. Noble gases were shock-heated to static gas temperatures, corresponding to equilibrium electron densities ne between 108 cm~~3 and 1012 cm~3. The major results were: 1) An initial ne of the order of 1011 cm~3 was required at the generator entrance to obtain significant magnetically induced ionization; if ne was produced by pre-ionization with an applied electric field, the pre-ionization power requirement was 10% of the maximum generator power output. 2) Electrode conduction losses controlled the minimum initial ne requirement, the ionization growth rate in the generator, and the maximum generator power output. 3) The rate of ionization growth in the freestream of the generator was in agreement with the predictions of a one-dimensional theory in which electron collisional ionization and recombination dominated the rate equations. 4) The measured steady-state, electron densities in the generator were up to 1000 times greater than the corresponding values at the gas stagnation temperatures. The measurements were in general agreement with the theoretical predictions obtained from the electron energy equation and the Saha equation at the electron temperature.