Modeling a Hall Thruster from Anode to Plume Far Field

MODELING A HALL THRUSTER FROM ANODE TO PLUME FAR FIELD AFOSR GRANT FA9550-05-l-0042 lain D. Boyd Department of Aerospace Engineering University of Michigan Ann Arbor, MI 48109-2140 Hall thrusters represent an efficient form of electric propulsion that is being implemented on USAF satellites for station-keeping tasks. Numerical simulation of the plasma flow inside Hall thrusters is playing an increasingly significant role in the development of the thrusters to better understand propulsion and lifetime performance. Numerical simulation of the plumes of Hall thrusters is required to accurately assess spacecraft integration issues. The work being pursued here seeks to develop for the first time an end-to-end Hall thruster simulation capability that begins with propellant injection at the thruster anode, and ends in the plume far field. The development of a comprehensive simulation capability is critical for a number of reasons. The main motivation stems from the need to directly couple simulation of the plasma discharge processes inside the thruster and the transport of the plasma to the plume far field. The simulation strategy will employ two existing codes, one for the Hall thruster device and one for the plume. The coupling will take place in the plume near field region that has not previously been modeled in detail. The simulation process will be assessed through application to Hall thrusters for which measured data exist. Recent accomplishments Significant progress has been made in improving and extending the modeling capabilities for both Hall thruster devices and Hall thruster plumes. In particular, we have focused on thruster and plume modeling of the D55 anode layer Hall thruster due to the wide availability of detailed flow field and performance measurements. In the following sections, we summarize this progress. Hall Thruster Channel Modeling Hall thruster device modeling efforts were focused on calculating the thruster exit condition. A model for the thruster channel is developed [ 1]. This model is used to simulate the flow within the channel of the D55 TAL thruster. We consider three conditions corresponding to three different experiments. These experiments conducted at the University of Michigan [2] [3], TsNIIMASH [4], and the University of Tennessee Space Institute (UTSI) and Lockheed Martin Astronautics (LMA) [5]. It is reported [6] that some portion of the plasma plume of a D55 thruster consists of doubly charged ions. In this research, the number fraction of double xenon ions is assumed to be 0.2. Contour plots of the plasma density and potential fields are shown in Figs. 1 and 2, respectively. The anode is on the left side of the figure, while the exit plane is at the right border. The white spaces above and below the channel in the figures represent the outer and inner wall thicknesses, respectively, in relation to the channel domain. The velocity distributions are based on the ion temperature, which can be assumed to be the same as the initial neutral temperature, which in turn is based on a wall temperature of 1000 K. The velocity distributions are used to create a distribution of ion flow angles. The radial distribution of the ion number density and velocity at the thruster channel exit are used for the plasma plume simulation.