INJECTED PROPELLANT IONIZATION IN MPD THRUSTERS

A model is presented for the self-magnetized, weakly ionized preioniza tion region at the entrance to a magnetoplasmadynamic (MPD) accelerato r. The model is steady, one-dimensional and inviscid, and assumes supe rsonic flow of argon plasma with zero current in the region. Heavy par ticle temperature is constant, and electron temperature T(e) is determ ined by ambipolar diffusion and by photo- and electron-impact ionizati on processes. The plasma continuity, momentum, and energy equations ar e integrated numerically with appropriate boundary conditions, giving a region width DELTAx ranging from 3 to 17 mm, depending on density, a nd a degree of ionization alpha increasing from an initial value of al pha = 10(-7) to alpha = 4 +/- 2 x 10(-4) at the MPD accelerator inlet. The electron temperature rises monotonically from T(e) = 1000 K to T( e) is-approximately-equal-to 18,000 K, a level sufficient to sustain M PD accelerator operation. The total electrostatic potential across DEL TAx is DELTAV = 12.5 +/- 0.6 V. Reducing the injected particle flux Q0 increases DELTAx, until a critical Q0 is reached below which no solut ions exist.