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

概要

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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 ne(0) ≥ 1014 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.