An update on atomic data for the low charge states of W for use in Plasma Facing Component erosion diagnostics

A review is given of recent atomic calculations for tungsten erosion and redeposition diagnostics. This includes electron-impact excitation of W[1] and W⁺, and the results of new R-matrix calculations for W²⁺ for excitation and ionization. Spectral measurements close to plasma facing components are used to diagnose the gross and net erosion, requiring high quality atomic. The major uncertainty in the W charge states is the excited state ionization rate coefficients. This issue is explored via a comparison of existing W I S/XB measurements with a range of ionization datasets, allowing some bounds to be put on the ionization rate coefficients. Comparisons of W-I and W-II synthetic spectra with DIII-D spectral measurements were taken using a new high-resolution high-throughput UV spectrometer. In addition, given recent interest in tantalum as a plasma facing component [2], some initial calculations are shown for the ionization of neutral Ta. The results likely indicate that a large fraction of sputtered Ta is promptly redeposited.



[1] R. Smyth et al., Physical Review A, 97, 052705 (2018)

[2] J.N. Brooks et al, Nucl. Fusion, 55, 043002 (2015)