X-ray tomographic measurement and modeling for inferring tungsten impurity distribution in WEST plasmas: A review

Since the advent of tungsten walls in ITER, the problem of precisely reconstructing the distribution of tungsten (W) concentration in the plasma has become all the more relevant. Among the different possible approaches, those using x-ray measurements seem particularly promising. Indeed, essential plasma parameters can be inferred from x-ray line-integrated measurements such as magnetic equilibrium, electron temperature, concentration of impurities, and their spatial distribution after tomographic inversion. Despite being extremely rich in information, the access to continuous spectral measurements is nevertheless a technical challenge rarely implemented in actual tokamaks. In this work, we review recent work on different techniques dedicated to the inference of the W impurity distribution in WEST plasmas, based on x-ray tomography diagnostics with or without energy discrimination, in particular with semiconductor and gas detectors. For this purpose, synthetic diagnostic tools have been developed for the different used detectors to validate the measurements in the presence of partially ionized W impurities in the core plasma and provide prediction for future applications in ITER.