MAGNETOPLASMADYNAMIC THRUSTOR RESEARCH

This program is a follow-on study to a three-year feasibility investigation of using lithium propellant in a steady state electric plasma thrustor for eventual use in space propulsion. During that program, accelerator development was largely empirical. The present research is aimed at obtaining a detailed knowledge of the mechanisms in the accelerator and using this information to design and then test engines operating near their optimum capability. A theory of the engine mechanisms is presented, and predictions based upon this theory are compared with experimental results. In particular, it is postulated that the fundamental thrust mechanism in the ALPHA (ALkali Plasma Hall Accelerator) consists of the electrostatic acceleration of ions in the electric field through the electrons which are trapped in an applied magnetic field. The theory divides the engine into two parts: an interaction zone and an electromagnetic nozzle, and the physical processes occurring in each are treated separately. The predicted correlation between the accelerating potential and the effective exhaust velocity (or Isp) is shown experimentally to exist. Other conclusions drawn from the analysis are likewise corroborated. Finally, a detailed study was made of various unsteady arc phenomena which had been observed in the past. Results of this investigation are presented in parametric form.