Canted Current Sheet Mass Leakage and its Impact on Pulsed Plasma Thruster Performance

Abstract

An analytical model of the leakage of the current sheet in a parallel plate pulsed electromagnetic accelerator is proposed and measurements of the velocity, electron number density, and impulse of the current sheet are presented. The theoretical and experimental results are compared to gain insight on the impact of plasma leakage on the impulse of the device. Plasma leakage is due to a fraction of propellant being forced under and past the current sheet due to the canting of the current sheet, which is a ubiquitous feature of such devices. The model uses a force balance to predict the current sheet velocity, and a mass balance to predict the mass of the current sheet and that of it plasma wake. The impulse resulting from the sheet and its wake is calculated and compared to momentum plate measurements. It is found that, with increasing propellant fill pressure, the wake impulse makes up an increasing percentage of the total impulse, indicating increasing plasma leakage. The impulse of the wake increases from about 10% to nearly 67% of the total impulse in argon discharges over the range of 75 − 400 mTorr, and from 20% to 50% for neon. Although the impulse added by the plasma wake causes the total impulse to increase, the specific impulse and efficiency decrease. Overall, the plasma leakage phenomenon is detrimental to pulsed plasma thruster performance.