SPECTROSCOPIC INVESTIGATIONS OF TUNGSTEN IN THE EUV REGION AND THE DETERMINATION OF ITS CONCENTRATION IN TOKAMAKS

Tungsten was injected by means of laser ablation in both ohmic and add itionally heated plasmas of the ASDEX Upgrade tokamak experiment. Spec troscopic investigations were performed in the extreme ultraviolet (EU V) wavelength region, 4 to 140 nm. Besides the quasi-continuum structu re at approximate to 5 nm emitted by tungsten ions around W27+, isolat ed lines of tungsten were observed in the same spectral region and als o in the range from 12 to 14 nm. By comparison with calculations from the HULLAC and RELAC codes, these lines could be identified as transit ions of bromine to nickel-like tungsten ions. The concentration c(W) o f tungsten after laser ablation was determined from comparisons betwee n the total tungsten radiation P-W and the calculated radiation losses . Calibration of the quasi-continuum intensity with the help of the P- W measurements allows the tungsten concentration to be determined from spectroscopic observations, which are more sensitive. Both concentrat ion measurements (quasi-continuum, P-W) agree well in discharges with laser ablation. From a comparison of the intensity of the isolated lin es with code results, c(W) could be estimated in the central region of hot, additionally heated plasmas. The lower detection limit of the sp ectroscopic method allows the extraction of c(W) during the tungsten d ivertor experiment of ASDEX Upgrade.