High Power Hall Thruster Channel Plasma Simulations and Lifetime Predictions

Problem Description

Electric Hall thrusters are used for in-space propulsion and satellite station-keeping needs. The discharge plasma inside the Hall thruster channel is produced by the ionization of electrons with a neutral propellant gas such as xenon. The electrons are emitted from the neutralizer cathode placed at the exit of the Hall thruster and the xenon neutral gas is fed into the channel from the anode end of the Hall thruster channel. The electrons are confined inside the Hall thruster channel by the radial magnetic field applied through the solenoid magnetic fields. The positively charged xenon ions are accelerated out of the channel at high velocity, which produces the thrust necessary for space propulsion. Recently these thrusters are being designed to support long lifetime, high-power, and high-thrust operations. The channel wall erosion occurring inside of the Hall thruster is one of the main limitations to these design needs. It is important to understand the plasma discharge processes at high power operating conditions and predict the lifetime of the Hall thruster based on the calculations of channel wall erosion of the Hall thruster.

Solution

As part of a NASA funded SBIR project, Tech-X Corporation applied VSim to model and simulate the plasma discharge processes occurring inside of a Stationary Plasma Thruster (SPT-100) channel. The VSim Hall thruster simulation region includes both the coaxial cylindrical Hall thruster channel and the channel exit. The discharge chamber plasma was modeled using a fully kinetic approach, which treats both electrons and xenon ions as particles. The xenon neutral gas is treated as a static background with a linearly varying density distribution. VSim simulations calculated a number of results for the SPT-100 thruster: plasma potential, plasma particle number density distributions, discharge currents, beam ion current, ion wall flux, and ion-induced dielectric wall material sputtering. The calculated VSim performance results are in good agreement with experimental data and other PIC simulation results. Using VSim, Tech-X analyzed different high power operating conditions for NASA, which helps to predict the expected lifetime issues when operating Hall thrusters to meet the high power propulsion needs in space. Figure 1 shows the SPT-100 Hall thruster channel simulation model, VSim plasma potential results, and the VSim calculations of channel erosion profile at high power operating conditions.

hall thruster
Figure 1: VSim simulation results for the SPT-100 Hall thruster
channel plasma processes and prediction of channel erosion
results at high power operating conditions. Click on figure to
view full size image.

Why VSim?

VSim is a fully kinetic particle-in-cell code capable of self-consistently simulating the plasma processes inside of a Hall thruster channel and modeling the channel erosion due to ion impingement. Most of the Hall thruster simulation tools existing in the research sector are based on using either a fluid or hybrid particle-fluid model for simulating the Hall thruster channel erosion problem. VSim also utilizes the multi-physics data library available from TxPhysics, which allows users to consider different neutral gas kinds, dielectric material types, and secondary electron emission models for testing the Hall thruster problem under various design and operating conditions. VSim Hall thruster channel erosion and lifetime predictions can help researchers to minimize the huge costs involved in the experimental based laboratory tests conducted in high power Hall thruster design and development.

 
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