Effects of Ignition on Discharge Symmetry in Gas-Fed Pulsed Plasma Thrusters

We present the results from a new diagnostic tool for investigating the effects of ignition on the discharge symmetry in gas-fed pulsed plasma thrusters (GFPPTs). Using a fast-framing camera, up to 16 individual pictures of a single GFPPT discharge can be captured at frequencies as high as 20 MHz. This high framing rate capability allows the discharge initiation and current sheet formation to be visualized with a large degree of temporal resolution. Varying the frame rate, number and size of pictures per discharge, as well as the trigger delay sent to the camera allowed multiple discharges at different stages to be visualized. Various configurations of GFPPT electrode geometry and discharge ignition systems were photographed in operation. It is shown that the large surface flash-over ignitors used in early GFPPT designs are unreliable in providing a constant, symmetric discharge initiation. Smaller semi-conductor spark gap ignitors used in later GFPPT designs have demon∗Research supported by the Air Force Office of Scientific Research, grant number: F49620-95-1-0291 †Graduate Student, Research Assistant supported by Princeton University’s Program in Plasma Science and Technology. Member AIAA. ‡Graduate Student. Air Force Palace Knight. Member AIAA. §Chief Scientist at EPPDyL. Assistant Professor, Applied Physics Group. Associated Faculty at the Department of Astrophysical Sciences. Senior Member AIAA. ¶Presented at the 34 AIAA Joint Propulsion Conference, Cleveland, OH, July 14-17, 1998. strated more reliable ignition individually, however, asymmetries in the entire discharge still exist. The effect of a modification to the propellant feed system on the asymmetry of the discharge is also presented.