Abstract
Abstract
An experimental study of azimuthally rotating spokes in the plasma sheet of an inductive pulsed plasma thruster is presented. High-speed imaging reveals the formation of spokes with mode number ≈ 18 for a range of background pressure and coil discharge conditions. The spoke widths increase and the corresponding spoke orders decrease through an inverse cascade of energy flowing from higher-order to lower-order spokes, resulting in a more uniform plasma sheet. Secondary plasma sheets form in the half-cycle of the current discharge following primary sheet formation. It is observed that the plasma sheet forms earlier in the discharge as the pre-ionizer discharge energy increases, and increasing the background pressure results in higher uniformity when the other conditions are held constant. Spokes rotate predominantly in the
E
⃗
×
B
⃗
drift direction at speeds on the order of critical ionization velocity, and orders of magnitude smaller than the
E
⃗
×
B
⃗
drift speed. Simultaneously counter-rotating spokes are observed under various operating conditions.
Funder
Air Force Office of Scientific Research