A multi-energy soft x-ray diagnostic for T_e measurements and W transport studies on the WEST tokamak

A Multi-Energy Soft X-Ray (ME-SXR) pinhole camera has been implemented at the WEST tokamak for electron temperature profile measurements and high-Z impurity transport studies. This novel imaging diagnostic technique employs a PILATUS3 x-ray detector in which the lower energy threshold for photon detection can be adjusted independently on each pixel in the range 3-22 keV. As the local x-ray emissivity is measured for multiple energy thresholds (E_th) simultaneously, it is possible to infer the electron temperature profile through the exp(-E_th/T_e) dependence of the SXR emissivity profiles, in a region of the spectrum free from W line-emission (typically E>11 keV). Emissivity profiles are reconstructed from line-integrated measurements using an inversion algorithm based on B-splines [1]. Data from the last campaign at WEST will be presented, showing reliable T_e measurements during the record >6 min steady-state discharge with lower hybrid heating and current drive. SXR emissivity profiles at lower energy (3-6 keV) will be also presented, which help assess W concentration and transport in the core plasma. W concentration is deduced by comparing measured emissivity with modelled one with the FAST code [2] assuming D and W sole radiating species. Initial collisional W transport studies in which the tungsten ions are modeled with a few tungsten bundles [3] will be also presented.

[1] D. Vezinet et al 2016 Nucl. Fusion 56 086001

[2] O. Chellai et al 2021 47^th EPS Conference on Plasma Physics P4.1013

[3] J. Dominski et al 2024 Phys. Plasmas 31 032303