July 25, 2023
Neutral beam injection, electrode biasing, and expander tank are TAE critical systems designed to generate hotter, denser, and more stable plasma with greater reproducibility. Specifically, the expander tank and the electrode biasing perform several key roles, among them: (1) decouple hot electrons from the wall to reduce electron heat losses; (2) applied voltage (bias) at end electrodes propagates to the middle of the machine to setup a radial electric field and stabilize the Field-Reversed Configuration (FRC) plasma against rotational modes. These enhancements depend on the electrostatic potential generated in the expander divertor as well as the propagation of the electrode applied bias along the magnetic flux lines. Both can be dramatically modified and diminished by the presence of neutrals, plasma-material interactions such as secondary electron emission, or the presence of molecular gas. In this RFA we propose to collaborate with Sandia National Lab to leverage the DOE developed code Aleph to conduct an integrated modeling of the expander tank and the biased electrodes in the presence of plasma, neutrals, plasma material interaction and secondary electron emission processes. In particularly we will concentrate on modeling (1) the relationship between the plasma jet into the expander and resultant current on the electrodes, and (2) the relationship of the return bias current on neutral and plasma condition in front of the electrodes. Furthermore, we will use the results to design a diagnostic electron beam for probing the pre-sheath and sheath structure.