Simplified plasma experiment for investigation of plasma diffusion and transport mechanisms

Marlene Patino Taylor Matlock Richard Wirz

The interaction of charge-exchange collisions ions created in the plume of ion and Hall-effect thrusters interacting with background electric fields contribute to unwanted spacecraft surface sputtering and grid erosion, thereby limiting the thruster and spacecraft operation and lifetime. Improving our understanding of heavy species collisions (e.g. momentum-exchange and charge exchange collisions between ions and neutrals) in intermediately-ionized plasma is necessary for furthering the development and use of electric propulsion devices for deep space missions.

This effort acquires detailed measurements from a simple, well-characterized plasma experiment that can precisely capture the behavior of heavy species collisions. This is accomplished by accelerating and steering an ion beam into an axisymmeteric test cell populated with neutrals, and taking precise low-current measurements of the test cell walls (from scattered ions that experience collisions) and downstream of the test cell (from unscattered beam ions). The simplified setup reveals ion transport mechanisms in a collisional environment that are otherwise hidden by complicated conditions of most electric propulsion devices. By providing full disclosure, these canonical experiments supply benchmark data for the development and validation of analytical techniques and computational codes that model plasma behavior, including the 3-D Improved Concurrent Electromagnetic Particle –In-Cell (ICEPIC) code developed by AFRL. Additionally, semi-analytical and computational models aid in the interpretation of laboratory measurements and to provide insight into future experimental modifications and design.

Current work is focused on characterization of the ion beam (with various facility diagnostics and electrostatic modeling) throughout the facility and at the entrance of the Test Cell. Electron emission from plasma-confining materials due to ion impact are investigated by modifying the test cell to hold the target material in the beam’s line of sight.