Control of the electric-field profile in the Hall thruster

Control of the electric-field profile in the Hall thruster through the posi tioning of an additional electrode along the channel is shown theoretically to enhance the efficiency. The reduction of the potential drop near the an ode by use of the additional electrode increases the plasma density there, through the increase of the electron and ion transit times, causing the ion ization in the vicinity of the anode to increase. The resulting separation of the ionization and acceleration regions increases the propellant and ene rgy utilizations. An abrupt sonic transition is forced to occur at the axia l location of the additional electrode, accompanied by the generation of a large (theoretically infinite) electric field. This ability to generate a l arge electric field at a specific location along the channel, in addition t o the ability to specify the electric potential there, allows us further co ntrol of the electric-field profile in the thruster. In particular, when th e electron temperature is high, a large abrupt voltage drop is induced at t he vicinity of the additional electrode, a voltage drop that can comprise a significant part of the applied voltage. (C) 2001 American Institute of Ph ysics.