Kinetic simulation of a magnetized plasma in an electron cyclotron resonance plasma thruster with magnetic nozzle

Overview & Synopsis

The framework for this work is the development of a new space propulsion technology. The device is based on the cyclotron resonance phenomenon to heat a plasma using microwaves. This work aims at simulating for the first time the magnetized plasma inside an Electron Cyclotron Resonance (ECR) thruster with self-consistent calculations of the electromagnetic fields to gain insight into the thruster's working principles. An electromagnetic solver for Maxwell's equations was developed based on the Constrained Interpolation Profile (CIP) method to simulate the electron-microwave interaction in a quasi-1D (1D3V) model of the thruster. This semi-Lagrangian method enables the use of large time steps in planar 1D to 3D cases while using an explicit formulation. However, the thruster modeling in a 2D cylindrical coordinate system (2D3V) faced the problem that the scheme was still limited by the Courant-Friedrichs-Lewy (CFL) condition. Therefore, we developed a procedure to overcome this constraint and extend the ability of this method to handle CFL greater than one in 2D axisymmetric domains. A ghost node method was also proposed to deal with boundary conditions such as the singularity on the axis or the perfectly conducting walls. The solvers were integrated into the electrostatic Particle-In-Cell/Monte-Carlo Module (PIC-MCC) code developed at Onera. They allowed the self-consistent electromagnetic full-PIC simulations of the ECR thruster in 1D and 2D axisymmetric. The results provided insight into the mechanisms affecting the plasma, like its heating and confinement, the energy lost by collisions and at the thruster's walls by cross-field diffusion, and the possibility of mode conversion for the microwaves due to its interaction with the plasma. In the 1D3V model, we show that the electron's energy perpendicular to the magnetic field lines increased near the heating zone and has a second unexpected peak in the nozzle due to the confinement of highly energetic electrons and loss at the close end of the thruster of low energy electrons. We carried out a parametric analysis with this model that allowed us to understand better the influence of some of the thruster's parameters on its performance and assess the sensibility of our model to have a more detailed view of the validity of the results. The cross-field diffusion towards the thruster's walls appeared as a dominant mechanism for energy lost over the collisions between the charged particles and the neutral background. The results of this research work will contribute to the efforts of the propulsion community to improve this technology.