A 1-D Model of the Hall-Effect Thruster with an Exhaust Region

A one-dimensional model of the HallEffect thruster is presented with results for the SPT-100 engine. This numerical model allows much faster convergence in comparison to other particle methods. The physical models include collisions of electrons with neutrals, ions, and walls. The electron fluid energy is due to ohmic heating, thermal diffusion and convection, and includes losses due to ionization, collisions with walls and atomic excitation. The 4cm-long computational region simulating the acceleration channel of the SPT-100 has been extended by 1cm for the purpose of studying plasma conditions in the region near the exit plane. The radial magnetic field is assumed to peak within the channel (-0.02T), and decreases linearly in the external region. The SPT-100 model yields good agreement between measured and computed performance parameters (within 10-20%). The characteristic oscillatory behavior of the discharge current is also captured. Modeling of the exhaust region reveals that electric potentials remain at relatively high values at the channel exit, 150-200V, and gradually decrease to the imposed zero value at the end of the extended region. By comparison with previous versions of the model, the addition of heat diffusion yields three times higher temperatures in the anode region, and reduced values in the area of peak magnetic field. INTRODUCTION Since the introduction of the Hall-Effect Thruster concept' numerical modeling of these devices has mainly concentrated either on the physical processes within the acceleration channel''' or on the expansion of the plasma in the plume region.' The plume models commonly employ conditions at the thruster exit as input. However, a substantial amount of plasma is generated in the region immediately external to the thruster channel. This offers the opportunity for sustained electric potentials in the region outside the channel. The latter is a concern for a variety plasma-surface interactions (e.g. sputtering). A one-dimensional numerical model has been developed in the interest of investigating plasma behavior within the accelerating channel and in a region outside the thruster exit. The numerical approach assumes that macroscopic variations in the thruster, such as changes in the potential, occur at a much longer time scale than the ion transit time. A Lagrangian approach is employed for modeling neutrals. The motivation is to minimize numerical diffusion and to elude the high computational times commonly associated with other particle methods (e.g. PIC/DSMC). Measurements from experiments on the Stationary Plasma Thruster (SPT) are used for comparisons. The SPT-100 computer model simulates a 4cmlong acceleration channel with a 1 cm-long exhaust region and 45deg divergence angle. * Senior Staff Scientist, SAIC, Member AIAA f Chief Scientist, SAIC, Senior Member AIAA 1 Senior Staff Scientist, SAIC, Senior Member AIAA Engineering Specialist, Space Systems/Loral, Member AIAA Copyright © 2001 The American Institute of Aeronautics and Astronautics Inc. All rights reserved. 1 American Institute of Aeronautics and Astronautics (c)2001 American Institute of Aeronautics & Astronautics or Published with Permission of Author(s) and/or Author(s)' Sponsoring Organization.