Fast ion Doppler spectroscopy (FIDA) in C-2W

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 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. We present new results from the Fast Ion D-Alpha (FIDA) on C-2W using modulation of the heating neutral beams, as an alternative to the diagnostic neutral beam. The heating neutral beams provide larger signals, but the close proximity of multiple neutral beams introduces beam emission background. Three viewports were selected to provide a variety of perspectives on the fast ion velocity space. An image intensifier is also employed to increase the signal levels when viewing the diagnostic beam. We have characterized the intensifier to understand its performance. We make use of synthetic diagnostic modeling (using FIDASIM [2,3]) based on Monte Carlo fast ion simulations. The simulations results show highly non-gyrotropic fast ion velocity distributions and large fast ion orbits. These features break the assumptions of standard fast ion orbit tomography techniques & will necessitate use of the more advanced orbit-space reconstruction method (inferring fast ion distribution as parameterized by constants-of-motion.)

[1] H. Gota et al., Nucl. Fusion 59, 112009 (2019).

[2] B. Geiger et al, PPCF 2020

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