Design and synthetic diagnostic of a vertical multi-energy soft x-ray camera for the WEST tokamak

A vertical multi-energy soft x-ray (SXR) camera is presently under design for installation on the Tungsten (W) Environment in Steady-state Tokamak (WEST). This camera will complement an already installed equivalent horizontal system to enable 2D tomographic reconstruction of the plasma soft x-ray emissivity at different energies. The two cameras employ two identical PILATUS3 pixelated x-ray detectors, in which the lower energy threshold for photon detection can be adjusted independently on each pixel in the range of 2–21 keV. Energy-resolved measurements are used to infer impurity concentrations, effective charge (Zeff), electron temperature, plasma centroid position, and radiated power density. With the installation of the vertical camera, all these quantities will be determined in 2D and possibly in real time. This contribution presents the design of the vertical camera. The detector is mounted inside a retractable stainless steel vacuum chamber, which is inserted into a re-entrant sleeve installed on a vertical port. A pinhole located after a beryllium vacuum window determines the geometry of the sightlines, which cover a large portion of the plasma cross section. A synthetic diagnostic is created using the FAST tool, which simulates the SXR emissivity for typical WEST plasma parameters and impurity mixtures, coupled with the ToFu tool, which computes the camera synthetic signal. The expected photon count rate on the detector is determined for a typical WEST plasma scenario. The tomographic inversion capability using measurements from the two cameras is investigated with ToFu using phantom emissivities of different shapes.