Extreme UV spectrometers for the tungsten 40-70 Å emission in the WEST tokamak

Since the decision to implement a tungsten (W) divertor in ITER, several tokamaks have introduced W in their plasma facing components. For these devices, W monitoring in the core plasma has thus become an important topic of research as its high radiation capability can lead to excessive radiative losses. We have used our extreme UV (EUV) grazing incidence spectrometer (GIS) to investigate the 40-70 angstrom range where W ions of intermediate charge emit in WEST tokamak discharges. The spectrometer is mounted on a mobile frame controlled with a jack so that it can measure the dependence of the brightness of any spectral feature lying in the observed wavelength interval as a function of the line of sight angle. The quasi-continuum and W line brightnesses in the 40-70 angstrom range are shown to be much larger when the observed region has a temperature above 3 keV. The brightness profiles as a function of the line of sight position also provides qualitative information on the emitting ions. The delivery and the current installation of a new imaging EUV spectrometer dedicated to the 40-70 angstrom range are reported. This spectrometer will allow to image the lower inner half of the plasma with an expected time resolution down to 10 ms. The absolute brightness calibration will be performed before the spectrometer is installed on the tokamak at the beginning of the coming experimental campaign.