Performance study of the ablative Z-pinch pulsed plasma thruster

Abstract

The ablative Z-pinch PPT utilizes the Z-pinch effect to produce an axially streaming plasma. When the current is fully pinched in this device, a large axial pressure gradient exists and thus plasma accelerates in the axial direction due to the gasdynamic force. In the present paper, a model of the electrical discharge in the Ablative Z-pinch Pulsed Plasma Thruster is developed. The model includes Joule heating of the plasma, heat transfer to the Teflon, and Teflon ablation. Mechanisms of energy transfer from the plasma column to the propellant include heat transfer by particle convection and by radiation. The computation of Teflon ablation is based on a recently developed kinetic ablation model. The average current density in the pinched region is used as a parameter of the model. The model predicts that the electron temperature peaks at about 4 eV and the plasma density peaks at about 8⋅10 23 m -3 . Thruster performance characteristics such as impulse bit, specific impulse and the mass bit are calculated. In the case of low pulse energy, all measured thruster performance characteristics agree with our model predictions when the average current density to the anode current density ratio α is about 0.55. In the case of high pulse energy, such an agreement with the experiment occurs when α≈ 0.7-0.8, that suggests that in the case of higher pulse energy the current is more constricted near the anode tip. The model also predicts that the impulse bit decreases with increasing propellant inner diameter in agreement with experiment. The comparison of the model prediction with experimental data suggests that the pinch effect and the thrust-to-power ratio increase with the pulse energy.