WEST tokamak hard x-ray tomography inversion

Abstract

Long-pulse steady-state discharges with lower hybrid current drive were successfully obtained in the limiter configuration machine, Tore Supra. The hard x-ray (HXR) diagnostic system in Tore Supra associated with tomographic inversion provided a good approximation of the lower hybrid power deposition profile. The accurate plasma current control through this tomographic reconstruction leads to an improvement of plasma confinement. Tore Supra was upgraded to WEST, Tungsten (W) Environment in Steady-state Tokamak. The plasma geometry was changed to the D-shaped geometry. Therefore, a novel inversion code for WEST has been developed. The method used in the code is based on the Bessel function of the first kind of order zero. The code validation was performed using phantom emissivity profiles and WEST experimental data. It has been found that the line radiation of the tungsten divertor in WEST and noise significantly affect the inversion. The local HXR emissivity profile with acceptable accuracy can be achieved by applying a singular value decomposition filter and suppressing the lines of sight that intersect the divertors.