Spectroscopic In Situ Measurements of Neutral Beam Divergence in C-2W

In TAE Technologies’ current experimental device C-2W (also known as “Norman”), steady-state field reversed configuration (FRC) plasmas are sustained by neutral beam injection (NBI), edge biasing, and a robust real-time plasma control system [1]. C-2W's eight heating beams are the primary source of current drive, fueling, and plasma stability; therefore, regular characterization of beam energy and divergence is critical to optimizing beam energy capture and plasma performance. Doppler-shift spectroscopy is a time-resolved method of measuring the angular divergence and energy component fractions of the injected beam in situ by extracting information from the intensity and shape of the Doppler-shifted neutral beam spectrum [2]. Unlike traditional, more intrusive beam detection methods, Doppler-shift spectroscopy is completely non-perturbative, allowing for regular characterization and optimization of beam parameters during machine operation. Here, we report on preliminary beam divergence measurements obtained with a multi-chord Doppler-shift spectroscopy system on C-2W, and discuss future applications of this diagnostic.

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

2. Deka, A. J. et al. E. J. Appl. Phys. 123 (2018)