The new High Efficiency XUV Overview Spectrometer system HEXOS has been developed to study impurity concentrations and impurity transport properties in the plasma of the stellarator W7-X. The HEXOS system consists of four different grating based spectrometers, which provide large etendue and good spectral resolution over a broad wavelength range (2.5 nm -160 nm, divided into four subsections with some overlapping). The mechanical arrangement as two double spectrometers allows for a compact installation geometry on W7-X. Laboratory testing, wavelength and intensity calibration have been performed using a DC hollow cathode discharge (24 nm -150 nm) and a pinch discharge (2.5 nm -30 nm).-2 -

The new High Effiency eXtreme ultraviolet Overview Spectrometer system (HEXOS) for the stellarator Wendelstein 7-X (W7-X) is now mounted for testing and adjustment at the Tokamak EXperiment for Technology Oriented Research (TEXTOR). One part of the testing phase was the intensity calibration of the two double spectrometers which in total cover a spectral range from 2.5 nm to 160.0 nm with overlap. This work presents the current intensity calibration curves for HEXOS and describes the method of calibration. The calibration was implemented with calibrated lines of a hollow cathode light source and the branching ratio technique. The hollow cathode light source provides calibrated lines from 16 nm up to 147 nm. We could extend the calibrated region in the spectrometers down to 2.8 nm by using the branching line pairs emitted by an uncalibrated pinch XUV light source as well as emission lines from boron and carbon in TEXTOR plasmas.In total HEXOS is calibrated from 2.8 nm up to 147 nm, which covers most of the observable wavelength region. The approximate density of carbon in the range of the minor radius from 18 cm to 35 cm in a TEXTOR plasma determined by simulating calibrated VUV emission lines with a transport code was 5.5 · 10 17 m −3 which corresponds to a local carbon concentration of 2 %.

Since ergodic divertors are proposed to control the impurity concentration in tokamak plasmas the influence of a resonant magnetic perturbation (RMP) from the dynamic ergodic divertor (DED) in the m/n = 3/1 mode on argon impurity transport is studied at the tokamak TEXTOR. Although the application of a DED current below the threshold for m/n = 3/1 tearing mode excitation in an NBI-heated L-mode plasma does not change the argon transport coefficients in r/a < 0.8, an additional transport mechanism within an error of 34% cannot be excluded. Observed changes of the iron ion density distribution for r/a < 0.6 can only be explained by a change of the transport. In addition the argon injection experiments show that an RMP reduces the inflow of particles into r/a < 0.8 and that a tearing mode seems to increase the local transport although at first view the experimental data indicate a reduction of the transport.

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