Design and engineering challenges of a multi-energy hard x-ray camera for long-pulse profile measurements at WEST tokamak

•A multi-energy hard x-ray camera has been designed and built by PPPL for installation on the WEST tokamak. The flexible energy configuration of its detector allows different setups to measure several physical quantities of interest, such as the electron temperature, fast electron profile, beam-target emission. The design of the diagnostic was driven by the need to satisfy the measurement requirement of a large field of view covering most of the cross section, and at the same time to solve the engineering challenges posed by the close vicinity to the plasma and by the long pulse operations expected at WEST. The final design resulted in a compact structure that is easy to build, install and maintain, and robust and reliable.•Vacuum stress calculations show that the diagnostic aluminum window, designed with the twofold function of cutting the unwanted x-ray radiation and as vacuum interface, is properly designed to withstand the prescribed pressure difference. Heat transfer calculation shows that the vacuum window and the detector remains within safety limits in the long pulse scenario without additional cooling. The WEST tokamak has recently been prepared for long pulse operation with a water-cooled full first wall. Heating is provided by radiofrequency systems, including Lower Hybrid Current Drive (LHCD). The Princeton Plasma Physics Laboratory has developed a multi-energy hard x-ray camera for profile measurements at WEST. The camera is based on a new generation of 2D pixel array detectors that allow the energy threshold to be independently set for each pixel. The diagnostic will provide spatial, temporal and energy resolved measurements of the hard x-ray emission from the full plasma cross-section, investigating several physical quantities such as the electron temperature from continuum emission, the fast electron tail density produced by radiofrequency current drive and runaway electrons, as well as characteristic tungsten x-rays due to beam-target emission at the edge. This work describes the engineering challenges that the WEST long pulse scenario poses for this diagnostic and how the design addresses and solves them. Vacuum, thermal stress and heat transfer calculations are presented and discussed.