Development of Microwave Imaging Diagnostics for WEST Tokamak

Abstract

WEST is an upgrade of the Tore Supra tokamak to test ITER like divertor elements over very long pulses. For the studies of MHD instabilities affected by tungsten impurities, two microwave imaging diagnostics have been developed to obtain density and temperature fluctuation maps. The core reflectometer was refurbished and now measures the core density profiles in few microseconds. Measurements of several thousand profiles in sequence with microsecond dead time (burst mode) will be available in 2019 enabling the reconstruction of density maps with unprecedented time resolution. The major issue for the implementation of an electron cyclotron emission imaging diagnostic was the heat radiation during long pulses on the large vacuum window and the first optics. Two metallic in-vessel mirrors inside the personnel access tube solved this issue. The first mirror can withstand the heat radiation without water cooling, the second mirror redirects the beam toward the personnel access port. The oblique and small view angle of this access eases also the thermomechanical constraints on the vacuum window. As the space between the port flange and the tokamak access lobby was tight, a compact optical enclosure with vertical aligned optics was designed. To ensure a good reproducibility of the mirrors and the optical enclosure positions after a maintenance period and thus avoid re-alignment, different mechanical systems are used to manipulate the mirrors and the optical enclosure and to fine tune their position and their orientation. The first channel covers the low field side and will provide 192 pixel images of temperature fluctuations with 1-2 microsecond time resolution. The installation of the in-vessel mirrors is scheduled during March 2019. Diagnostic qualification tests will be done before the restart of the experiments late May 2019.