Scaling and Systems Considerations in Pulsed Inductive Plasma Thrusters

Performance scaling in pulsed inductive thrusters is discussed in the context of previous experimental studies and modeling results. Two processes, propellant ionization and acceleration, are interconnected, where overall thruster performance and operation are concerned, but they are separated here to gain physical insight into each process and arrive at quantitative criteria that should be met to address or mitigate inherent inductive thruster difficulties. The use of preionization to lower the discharge energy relative to the case where no preionization is employed, and to influence the location of the initial current sheet, is described. The relevant performance scaling parameters for the acceleration stage are reviewed, emphasizing their physical importance and the numerical values required for efficient acceleration. The scaling parameters are then related to the design of the acceleration coil and the pulsed power train that provides current to the acceleration stage. An accurate numerical technique that allows computation of the inductance of a planar acceleration coil using an axisymmetric magnetostatic solver is described and validated against measured coil inductance values. Requirements for the pulsed power train are reviewed. Several power train and circuit topologies are described, highlighting the impact that each can have on inductive thruster performance and on systems issues associated with high-current switching, lifetime, and power consumption.