The role of Alfven's critical ionization velocity in the performance of the self-field MPD thruster has been investigated. The existence of a well defined characteristic velocity can be attributed to an ionization process involving the production of a population of suprathermal electrons by an electrostatic instability. It is shown that for the MPD thruster plasma, suprathermalization of electrons via this electrostatic instability can only happen if ions are initially accelerated to velocities larger than the Alfven critical ionization velocity. When this occurs the mechanism will be initiated and the ions decelerated to velocities near the critical velocity. This mechanism ceases to be limiting when all neutrals are ionized. A model of MPD thruster terminal behavior, incorporating Alfven's hypothesis, is presented. Experiments with three different propellants reveal that operation at values of the current squared to total mass flow ratio corresponding to the Alfven critical velocity is marked by a transition wherein low frequency voltage oscillations and a notable change in the voltage-current dependence occurs. One major result of this study is the demonstration that the critical velocity uAC is not a fundamental limitation on MPD exhaust velocity.
|Original language||English (US)|
|State||Published - Jan 1 1985|
|Event||AlAA/DGLR/JSASS International Electric Propulsion Conference, 1985 - Alexandria, United States|
Duration: Sep 30 1985 → Oct 2 1985
|Other||AlAA/DGLR/JSASS International Electric Propulsion Conference, 1985|
|Period||9/30/85 → 10/2/85|
All Science Journal Classification (ASJC) codes