Modeling of an advanced concept of a double stage Hall effect thruster

Abstract

We present a study of the principle and operation of a two-stage Hall effect thruster, the SPT-MAG, using a two-dimensional quasineutral hybrid model coupled with a Monte Carlo simulation of electron transport. The purpose of the two-stage design is the separation of ion production and acceleration in two separate chambers, the ionization stage and the acceleration stage, with separate control of acceleration voltage and total ionization. The originality of the SPT-MAG lies in the magnetic field configuration in the ionization chamber. Electrons are confined by this magnetic field while ions are supposed to be trapped in the electric potential well supposedly resulting from the magnetic configuration, and guided toward the acceleration stage. The acceleration stage is similar to the channel of a conventional Hall effect thruster. The purpose of this paper is to clarify the physics of the SPT-MAG and to understand the formation of the positive ion trap in the ionization chamber. Using a hybrid model and a Monte Carlo simulation we show that under typical operating conditions most of the ionization in the chamber is due to high energy electrons accelerated in the channel and entering the chamber rather than to electrons accelerated by the voltage applied in the ionization chamber. We also raise the question of the possible role of an additional emissive cathode inside the ionization chamber. The model predicts that an electric potential well guiding the ions to the channel entrance forms in the chamber only if the intermediate electrode inside the chamber is an emissive cathode (which is not the case in recent configurations used for this thruster).