Absolute sensitivity calibration of an extreme ultraviolet spectrometer for tokamak measurements

An extreme ultraviolet spectrometer installed on the Tore Supra tokamak has been calibrated in absolute units of brightness in the range 10–340 A. This has been performed by means of a combination of techniques. The range 10–113 A was absolutely calibrated by using an ultrasoft-X ray source emitting six spectral lines in this range. The calibration transfer to the range 113–182 A was performed using the spectral line intensity branching ratio method. The range 182–340 A was calibrated thanks to radiative-collisional modelling of spectral line intensity ratios. The maximum sensitivity of the spectrometer was found to lie around 100 A. Around this wavelength, the sensitivity is fairly flat in a 80 A wide interval. The spatial variations of sensitivity along the detector assembly were also measured. The observed trend is related to the quantum efficiency decrease as the angle of the incoming photon trajectories becomes more grazing.