On the efficiency of several thruster configurations

Summary form only given, as follows. Limits on the efficiency of several thruster configurations are discussed. The efficiency of the Pulsed Plasma Thruster (PPT) is reduced when part of the magnetic field energy that is converted into particle energy does not become directed kinetic energy but rather a thermal energy. This thermal energy can still be used for propellant ionization. The partitioning of the power when the propellant exhibits slug, snowplow or specular-reflection accelerations is analyzed. Steady acceleration is examined in two configurations: the magneto-plasma dynamics (MPD) and the Hall thrusters. The smooth acceleration to supersonic velocities in the two configurations is compared. A limit on the efficiency of the MPD thruster in a non-diverging geometry is derived. The efficiency of the Hall thruster in the limit of intense full ionization is discussed. Two steady-state flows in the Hall thruster are compared for two different boundary conditions at the anode. The first flow is of a zero ion current and velocity at the anode. The second is the recently-analyzed case of an ion backflow at the anode, in which the profile of the electric potential along the thruster is expected to be nonmonotonic. By employing certain asymptotic relations together with considerations of momentum and energy balance, analytic expressions for the efficiency of the Hall thruster for the two flows are derived. The possible existence of these two types of flow for different values of the applied voltage due to the characteristics of secondary electron emission, is discussed.