Fast-ion charge-exchange losses in C-2W

In TAE Technologies' current experimental device, C-2W (also called ``Norman'')\footnote{H. Gota, et al. Nuclear Fusion 59, 112009 (2019)}, record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (15--40 keV, total power up to 20 MW), advanced divertors, end bias electrodes, and an active plasma control system. Beam injection produces large-orbit fast ions that sample both the core FRC and the surrounding axisymmetric mirror plasma, where they can be lost via charge-exchange with neutrals. Since collisional energy transfer from fast ions is a primary heating source for the bulk plasma, their spatial and velocity distribution affects the overall power balance and understanding fast ion loss is critical. Balmer-$\alpha$ emission measured with filtered high-speed cameras is used with DEGAS2 neutral particle modeling to reconstruct the neutral distribution consisting of a cold population from wall recycling and a non-axisymmetric warm population generated from beam capture (via charge-exchange with the bulk plasma). Monte Carlo modeling is then used to estimate the rate and distribution of fast ions lost by charge-exchange, which is compared to bolometer measurements.