Double layer formation and thrust generation in an expanding plasma using 1D-3V PIC simulation

Abstract

Due to large particle exhaust velocity and specific impulse, electric propulsion systems have an edge over chemical propulsion for missions targeting regions outside the Earth's atmosphere. Stationary plasma thrusters and helicon plasma thrusters (HPTs) are commonly used electric propulsion devices for a space mission. In HPTs or expanding magnetic field plasma thrusters, plasma expands from the source region to the expansion region in an externally applied expanding magnetic field. Due to plasma expansion in such a magnetic field configuration, a current free double layer is found to form, which accelerates bulk ions, and a directional ion beam is generated, which causes thrust in the opposite direction. A Particle In Cell (PIC) solver with Monte Carlo Collision (MCC) scheme which resolves the axial direction and all three velocity degrees of freedom (1D-3V PIC-MCC) that captures the 2D spatial plasma expansion effect via a 1D flux conserving model is developed to simulate an argon plasma in an expanding magnetic field. Using the 1D-3V PIC-MCC solver, double layer formation due to plasma expansion, thrust generation, and optimization of thrust studies over a large parameter set, such as fill pressure of Ar, is presented. We compare our results with a particle loss model, which is commonly used as the simplest model for HPTs.