A refined spectroscopic assessment of in situ net erosion at WEST

As part of the ongoing validation of tungsten (W) as a high-Z plasma facing component (PFC), in situ observation of net W erosion into the scrape-off layer is critical to ensuring the longevity of tokamak fusion reactors. Net erosion may be simply defined as the difference between gross erosion and prompt re-deposition. Under this reduced paradigm, W-I (400.87 nm) and W-II (434.81 nm) spectroscopic emission lines can be converted to particle fluxes of gross erosion and prompt re-deposition with the aid of ionization per photon (or S/XB) ratios. Here, we present preliminary in situ calculations of net erosion at the limiter and divertor of the W Environment in Steady-state Tokamak (WEST), an all-W-PFC device that allows for poloidally resolved study of net W erosion in the absence of all but intrinsic impurities. Central to this study is a spectroscopic fitting routine that is shown to reduce uncertainty in the fitting function parameters (necessary to extract W radiances) by time-averaging the spectral data before fitting compared to previously reported approaches at WEST, which time-average the fitted data. The uncertainty refinement is particularly important for off-divertor PFCs where small line emission over continuum is typical.