Simulating NASA’s Next Generation Xenon Ion Thruster (NEXT) Discharge Chamber Plasma Processes

Problem Description

Ion thrusters are used for in-space electric propulsion and satellite station-keeping needs. In this device, the plasma ions are produced inside the cylindrical discharge chamber cavity. These ions are accelerated out of the chamber through the electrostatic grid optics system at high delta-V to produce the thrust required to propel spacecraft in space. The device has following components: anode biased discharge chamber, cathode biased discharge hollow cathode assembly, permanent magnetic rings, neutral propellant feed system, grid optics (screen and accelerator plates), and neutralizer hollow cathode. Primary electrons emitted from the discharge cathode undergo ionizing collisions with neutral gas filled inside the chamber to to produce plasma ions. The electrons resulting from the ionization collisions are called the secondary electrons. Also, the energetic electrons inside the discharge chamber can impact ionize the singly charged xenon ions and produce doubly charged xenon ions. The permanent magnetic rings placed inside the discharge chamber effectively confine the electrons so that they stay longer in the chamber and ionize the neutrals before being collected on the anode biased discharge chamber walls.

ion thruster
Figure 1: NEXT ion thruster discharge chamber plasma potential results obtained using VSim simulations. These results are in good agreement with experimental plasma potential measurements made on the laboratory model NEXT ion thruster.


As part of a NASA funded SBIR project, Tech-X Corporation applied VSim to model and simulate the plasma discharge processes occurring inside the discharge chamber of a NEXT ion thruster. VSim models the hollow cathode primary electron emission, neutral sources, static magnetic fields by the permanent magnets, and solves the electrostatic fields every time step. The discharge chamber plasma was modeled using a fully kinetic approach, which treats electrons, xenon ions, and xenon neutrals as particles. VSim simulations calculated a number of results for the NEXT ion thruster: plasma potential, plasma particle number density distributions, discharge currents, beam ion current, single-to-double ion ratio, ion wall flux, beam efficiency, and performance results. The calculated VSim performance results are in good agreement with experimental data.

Why VSim?

VSim is a fully kinetic particle-in-cell code capable of self-consistently simulating the discharge chamber plasma processes occurring inside of an ion thruster discharge chamber. VSim also utilizes the multi-physics data library available from TxPhysics, which allows users to consider different neutral gas kinds in the simulations. Also, VSim provides a design and test tool for studying an ion thruster under various design and operating conditions.


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