Initial active beam diagnosis of beam ions in MAST-U

A solid state neutral particle analyzer (SSNPA) [1] diagnostic oriented to measure trapped ions and a tangentially viewing fast-ion D-alpha (FIDA) [2] diagnostic that measures mainly passing fast ions in MAST-U. For initial validation of the measurements, TRANSP NUBEAM calculates the neoclassical distribution function neglecting fast-ion transport by instabilities and then FIDASIM [3] computes synthetic signals for comparison with the data, including SRIM[4] simulation of the energy cutoffs for the SSNPA diagnostic. Unfortunately, suitable MHD-quiescent discharges for diagnostic validation from the first campaign are unavailable. For a discharge with a locked mode, the radial profile measured by the SSNPA is much narrower than predicted, perhaps due to fast-ion transport by the locked mode. Shots to produce MHD-quiescent validation discharges during the second campaign have been allocated. New comparisons using those discharges, including improved subtraction of soft x-ray backgrounds, are planned.

[1] G. Prechel, et al 2022 24th Topical Conference on HTPD (pp. PC-33)

[2] C. Michael, et al 2021 APS DPP (Vol. 2021, pp. PO07-015)

[3] B. Geiger, et al 2020 Plasma Phys. Contro. Fusion 62 105008

[4] J. F. Ziegler, et al 2010 Nucl. Instruments Methods Phys. Res. B. 268 1818-1823