Absolute intensity calibration of the Wendelstein 7-X high efficiency extreme ultraviolet overview spectrometer system

Abstract

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 %.

Plans for the first plasma operation of Wendelstein 7-X

“…• Two X-ray imaging spectrometers [21,22,23], a pulse height analysis system [24] and an extreme ultraviolet (XUV) overview spectrometer [25,26] will allow to observe the emission of electrons and impurity ions in different locations with different spectral, temporal and spatial resolution and to obtain information on electron and impurity density, temperature and velocities.…”

Test of prototype ITER vacuum ultraviolet spectrometer and its application to impurity study in KSTAR plasmas

“…(2) with reference emission power I of He 1 A, Ne 1 A discharge, 11 the incident photon number, P was derived for emission lines of Ch. 4 range (29-60 nm).…”

Absolute radiometric calibration of a VUV spectrometer in the wavelength range 46–300 nm

“…As a results one obtains ±63 % for the absolute radiometric calibration of the PMT. Regarding the HCHC for the range 104.8-106.7 nm and its relative uncertainty, several error sources may play a role like an uncertainty of the calibrated line intensities (±13 %), the long term stability of the source (±10 % [13]), the accuracy of the voltage drop over the discharge (±5 %) as well as the integration of the measured lines (±10 %) [2]. As already mentioned above the applied copy of the hollow cathode was not directly calibrated against an electron storage ring.…”

“…However, the recent years show a growing interest in VUV spectroscopy especially for plasma diagnostic purposes in diverse contexts. VUV spectrometers allow monitoring of relevant impurities present in magnetically confined plasmas [2,3] and VUV photon fluxes were identified to be able to play a significant role in plasma surface treatment processes [4,5,6]. Quantification of VUV radiation is necessary for the control of arising VUV photon fluxes and hereinafter for an optimization of the specific application.…”