Design of soft-X-ray tomographic system in WEST using GEM detectors

Mazon, Didier and Chernyshova, Maryna and Jiolat, Guillaume and Czarski, Tomasz and Malard, Philippe and Kowalska-Strzeciwilk, Ewa and Jablonski, Slawomir and Figacz, Waldemar and Zagorski, Roman and Kubkowska, Monika and Kasprowicz, Grzegorz and Pozniak, Krzysztof and Zabolotny, Wojciech and Larroque, Sébastien and Verger, Jean Marc and O'Mullane, Martin and Mlynar, Jan and Byszuk, Adrian and Wojenski, Andrzej (2015) Design of soft-X-ray tomographic system in WEST using GEM detectors. Fusion Engineering and Design, 96-97. pp. 856-860. ISSN 0920-3796 (https://doi.org/10.1016/j.fusengdes.2015.03.052)

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Abstract

In metallic tokamaks, the interplay between particle transport and MagnetoHydroDynamic (MHD) activity might lead to impurities accumulation and finally to disruption. Studying such phenomena is thus essential if stationary discharges are to be achieved. Measuring the soft X-ray (SXR) radiation ([0.1 keV; 20 keV]) of magnetic fusion plasmas is a standard way of accessing valuable information on particle transport and MHD. Generally, like at Tore Supra (TS), the analysis is performed with a 2D tomographic system composed of several cameras equipped with silicon barrier diodes (SBD). On WEST the installation of an upper divertor masks many of the actual TS vertical diodes so that no proper tomography is possible. This paper presents the design of a new SXR diagnostic for the WEST project developed in collaboration with IPPLM (Poland) and the Warsaw University of Technology, based on a triple gas electron multiplier (GEM) detector. Preliminary simulations performed to size and position the detector and its electronics inside the vertical thimble are also presented, in particular estimation of magnetic field and temperature variation affecting GEM spatial resolution and signal quality. As a conclusion, perspectives about tomographic capabilities of the new system for studying impurity transport are given.