Extension of Wavelength Range in Absolute Intensity Calibration of Space-Resolved EUV Spectrometer for LHD Diagnostics

Abstract

A space-resolved extreme ultraviolet (EUV) spectrometer has been upgraded by extending the wavelength range to 30-650 Å to explore impurity line emissions existing at shorter and longer wavelength sides. The absolute intensity calibration is implemented for measurement in the extended wavelength based on bremsstrahlung profiles simultaneously measured in EUV and visible ranges. For the purpose a wider entrance slit of 200 µm and a wider space-resolved slit of 1.0 mm are adopted to increase the number of photons to the spectrometer. As a result, the bremsstrahlung intensity can be enhanced by order of magnitude. A centrally peaked high-density discharge at n e (0) ≥ 10 14 cm −3 is also used for the accurate calibration. Thus, the calibration becomes possible, even in longer wavelength side at λ ≥ 400 Å. The result at shorter wavelength range of 30-90 Å shows a flat calibration factor, suggesting sudden changes of holographic grating efficiency and CCD detection efficiency, while the result at longer wavelength side of λ ≥ 400 Å shows a simple extension of the previous calibration factor. InroductionExtreme ultraviolet (EUV) spectroscopy plays an essential role in the impurity diagnostics of high-temperature plasmas, since impurities are ionized into highly charge states and wavelengths emitted from such impurity ions become shorter. A space-resolved EUV spectrometer working in wavelength range of 60-400Å has been installed in Large Helical Device (LHD) to measure radial profiles of impurity line emissions and bremsstrahlung continuum for the impurity transport study and effective ion charge (Z eff ) measurement, respectively [1]. For these purposes the absolute intensity calibration of the space-resolved EUV spectrometer is required. Due to a qualitative limitation of conventional methods for the absolute intensity calibration using synchrotron orbital radiation source and branching ratio technique, a new method based on the bremsstrahlung continuum measurement in EUV and visible range has been developed, and could be successfully applied to calibration of the space-resolved EUV spectrometer in wavelength range of 80-400 Å [2].Recently, the wavelength range of the space-resolved EUV spectrometer was extended to 30-650 Å to measure the first resonance lines of BIV (61.1 Å), BV (48.6 Å), CV (40.3 Å) and CVI (33.7 Å) as well as NeVII (465.2 Å: 2s2p-2 s 2 ) and OV (629.7 Å: 2s2p-2 s 2 ). As dominant impurity in LHD is only carbon, measurement of the first resonance lines of CV and CVI are essentially imporauthor 's e-mail: dong.chunfeng@nifs.ac.jp * ) This article is based on the presentation at the 21st International Toki Conference (ITC21).tant for studying the edge impurity transport. The impurity line emissions of BIV and BV appeared after the boronization are also useful for studying the boron behavior. The edge electron temperature measurement using impurity line intensity ratio, e.g., NeVII (97.5 Å: 2s3p-2 s 2 )/NeVII (465.2 Å: 2s2p-2 s 2 ), is also possible. In order to quantitatively analyze the spectral...

Line identification of extreme ultraviolet (EUV) spectra from low-Z impurity ions in EAST tokamak plasmas

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Effective screening of iron impurities in the ergodic layer of the Large Helical Device with a metallic first wall

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