On a force balance and role of cathode plasma in Hall effect thrusters

The cathode plasma is a specific transition region in the Hall effect thruster (HET) discharge that localizes between the strongly magnetized acceleration layer (magnetic layer or B-layer) and non-magnetized exhaust plume. Cathode plasma provides a flow of electron current that supplies losses in the magnetic layer (due to ionization, excitation, electron-wall interactions, etc). The electrons' transport in this region occurs in collisionless mode through the excitation of plasma instabilities. This effect is also known as 'anomalous transport/conductivity'. In this work, we present the results of a 2D (drift-plane) kinetic simulation of the HET discharge, including the outside region that contains cathode plasma. We discuss the process of cathode plasma formation and the mechanisms of 'anomalous transport' inside it. We also analyze how fluid force balance emerges from collisionless kinetic approach. The acceleration mechanism in HETs is commonly described in terms of force balance. Namely, the reactive force produced by accelerated ions has the same value as Ampere's force acting on a drift current loop. This balance written in integral form provides the basis for quantitative estimations of HETs' parameters and scaling models.