Ionizational and Electron Thermal Nonequilibrium in MHD Boundary Layers

Abstract

The effects of thermal nonequilibrium (elevated electron temperatures), and ionizational nonequilibrium (finite-rate recombination) are studied in the insulator boundary layer of a potassium-seeded nitrogen MHD accelerator. The nonsimilar, compressible boundary layer is assumed steady, laminar, and two-dimensional. A collisionless sheath is assumed and matched with the continuum boundary-layer equations through a transition region, the physics of which is dominated by ambipolar diffusion. Numerical results are presented for a typical core flow Hall-neutralized Faraday accelerator. Profiles are presented demonstrating the gradual development of severe #-wall shorting with the best available values of energyloss factor and recombination rate coefficient. The relative importance of the various terms in the electron energy equation is assessed, and the need for more accurate energy exchange cross sections is pointed out by the high sensitivity of the solutions to energy-loss factor. An unexpected result is that finite-rate recombination is not particularly important for the class of accelerators under study, although it could well be important for other applications, such as noble gas generators.