Experimental Investigation of Current Sheet Instabilities

Configuration space instabilities of propagating current sheets were studied in order to better understand acceleration mechanisms in pulsed plasma thrusters. Experiments were carried out in a parallel plate accelerator with argon as propellant. Propagating current sheets were visualized using fast framing cameras with inter-frame delays ranging between 0.05 - 2 microsecond. Schlieren photography using a pulse-burst Nd:YAG laser was used to image electron density gradients in the discharge. Magnetic field probes were used to map the magnetic field topology during the evolution of the discharge. Pressure probes were used to monitor axial pressure gradients. Emission spectroscopy was used to estimate the electron temperature in the arc. The motivation for applying all of these diagnostics was to gain an understanding of what parameters influence the macroscopic stability of a propagating current sheet. Since a stable current sheet is required for any effective snowplow-type of accelerator, an understanding of the processes which can cause current sheets to break apart into filaments is essential for the design of future pulsed plasma thrusters.