Effect of the Gas Pressure and the Charging Voltage on the Plasma Current Density Distribution in Conical Z Pinch Plasma Thruster

Abstract

Plasma current density is measured inside the chamber of a conical z-pinch device using helium as the working gas. The gas pressure and the charging voltage are the major factors affecting the magnitude of the plasma current, pinching time, and the pinch duration. Calculations are carried out at different radial positions between the pin electrode and the chamber wall. The experimental results show that the current density reaches a maximum value of about 8.7 kA/cm² above the pin electrode for 7 kV charging voltage and 1 Torr pressure, and this value decreases toward the chamber wall. The gas pressure has a significant effect on the current density at radial position of 0.5 cm from the pin indicating that the plasma could not be confined to a radius less than that. This result is confirmed by the recorded plasma current signal in which one peak only is recorded at the pin and two or three are recorded near the wall as a result of sequent compression and expansion. The experimental results show that a time of 2–2.5 μs is needed for the pinch to occur. Increasing the discharge voltage decreases both pinch time and the pinch duration due to the faster confinement process.