Development of Fast-Ion D alpha in C-2W

In TAE Technologies, C-2W (also called “Norman”) [1], advanced beam-driven field reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (NBs), advanced divertors, end bias electrodes, and an active plasma control system. Understanding the physics of NB injected fast ions is critical since they carry the current to maintain the FRC and are the primary source of heating. To investigate the behavior of the fast-ions, a Fast-ion D-Alpha (FIDA) diagnostic was installed on C-2W[2] which measures the Doppler-shifted H-alpha or D-alpha light produced by charge-exchange reactions between neutrals and fast ions[3,4]. In this experimental campaign, FIDA sightlines originate from multiple ports to provide a variety of perspectives on the fast-ion velocity distribution, and we have characterized these sightlines to understand their performance. The many neutral beams on C-2W complicate the spectrum with multiple beam emission components but we found regions of the spectra which can be used for analysis. Finally, synthetic diagnostic modeling (FIDASIM [5,6]) is being used to compare measured spectra with expectations based on Monte Carlo fast ion simulations.

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

[2] L. Morton et al., Bulletin of the American Physical Society 66, 2021

[3] W. W. Heidbrink, Rev. Sci. Instrum. 81, 10D727 (2010).

[4] Y. Fujiwara et al., Nucl. Fusion 60, 112014 (2020).

[5] B. Geiger et al, PPCF 62, 105008 (2020).

[6] L. Stagner et al., doi:10.5281/zenodo.1341369.