Injected propellant ionization in MPD thrusters

A model is presented for the selfmagnetized, weakly ionized preionization region at the entrance to a magnetoplasmadynamic (MPD) accelerator. The model is steady, one-dimensional and inviscid, and assumes supersonic flow of argon plasma with zero current in the region. Heavy particle temperature is constant, and electron temperature Te is determined by ambipolar diffusion and by photoand electron-impact ionization processes. The plasma continuity, momentum and energy equations are integrated numerically with appropriate boundary conditions, giving a region width Ax ranging from 3 to 17 mm, depending on density, and a degree of ionization a increasin from an initial value of inlet. The electron temperature rises monotonically from Te=lOOOK to Te~18,000'K, a level sufficient to sustain MPD accelerator operation. The total electrostatic potential across Ax is AV=12.5+0.6 V. Reducing the injected particle flux Qo increases Ax, until a critical Qo is reached below which no solutions exist. W a=IO-' to a = 4 f 2 ~ 1 0 3 at the MPD accelerator NOMENCLATURE j IRoss L n no nn Pe qe Qci