Statistical analysis of refraction-induced power loss for the C-2W Far-Infrared Interferometer

In TAE Technologies’ current experimental device, C-2W (also called “Norman”) [1], record breaking, advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state. Line-integrated electron density measurements from the multi-chord far-infrared (FIR) interferometer system provide critical information about plasma profiles and performance, and many derived quantities depend on reliable density measurements. Transient reductions in signal power due to refraction through strong plasma density gradients can cause phase counting errors, and system susceptibility to refraction is notably challenging at longer FIR wavelengths. We apply a feature based analysis to events with refraction-induced power loss, examining the spatial and temporal behavior of the density measurements for clearly identifiable behavior. A large set of human-identified phase counting errors is used to evaluate the features for fitness in automatic corrections. We also compare events with other plasma measurements, including MHD activity, to determine the most commonly correlated plasma behavior. This work will assist in planning for Copernicus diagnostics by identifying the requirements for robustness to refraction.

[1] H. Gota et al., Nucl. Fusion 61, 106039 (2021)