Current sheet evolution in a planar inductive pulsed plasma thruster

The evolution of the current sheet is fundamental to the understanding and operation of planar inductive pulsed plasma thrusters. Methods for experimentally determining the time-varying mutual inductance and plasma resistance associated with the current sheet are presented. From these, time-histories of the resistive heating in and electromagnetic acceleration of the sheet are found. Analysis of experimental data obtained from a compact, low discharge energy inductive pulsed plasma thruster shows that current sheet evolution is well described by three phases: ionization, formation, and acceleration. Evidence is provided for the plasma current and resistive heating becoming localized near the upstream edge of the current sheet as the sheet forms. The influence of initial propellant density and pre-ionization on the characteristics of the sheet are examined. Both higher propellant densities and increased pre-ionization are found to produce current sheets which exhibit greater magnetic impermeability. Higher densities cause the sheet to form closer to the coil face, improving coupling, while stronger pre-ionization leads to more rapid resistive heating, causing the sheet to form earlier in time.