Space-resolved extreme ultraviolet spectroscopy free of high-energy neutral particle noise in wavelength range of 10-130 angstrom on the large helical device

作者：Huang Xianli^*; Morita Shigeru; Oishi Tetsutarou; Goto Motoshi; Dong Chunfeng

来源：Review of Scientific Instruments, 2014, 85(4): 043511.

DOI：10.1063/1.4872384

A flat-field space-resolved extreme ultraviolet (EUV) spectrometer system working in wavelength range of 10-130 angstrom has been constructed in the Large Helical Device (LHD) for profile measurements of bremsstrahlung continuum and line emissions of heavy impurities in the central column of plasmas, which are aimed at studies on Z(eff) and impurity transport, respectively. Until now, a large amount of spike noise caused by neutral particles with high energies (%26lt;= 180 keV) originating in neutral beam injection has been observed in EUV spectroscopy on LHD. The new system has been developed with an aim to delete such a spike noise from the signal by installing a thin filter which can block the high-energy neutral particles entering the EUV spectrometer. Three filters of 11 mu m thick beryllium (Be), 3.3 mu m thick polypropylene (PP), and 0.5 mu m thick polyethylene terephthalate (PET: polyester) have been examined to eliminate the spike noise. Although the 11 mu m Be and 3.3 mu m PP filters can fully delete the spike noise in wavelength range of lambda %26lt;= 20 angstrom, the signal intensity is also reduced. The 0.5 mu m PET filter, on the other hand, can maintain sufficient signal intensity for the measurement and the spike noise remained in the signal is acceptable. As a result, the bremsstrahlung profile is successfully measured without noise at 20 angstrom even in low-density discharges, e. g., 2.9 x 10(13) cm(-3), when the 0.5 mu m PET filter is used. The iron n = 3-2 L alpha transition array consisting of FeXVII to FeXXIV is also excellently observed with their radial profiles in wavelength range of 10-18 angstrom. Each transition in the L alpha array can be accurately identified with its radial profile. As a typical example of the method a spectral line at 17.62 angstrom is identified as FeXVIII transition. Results on absolute intensity calibration of the spectrometer system, pulse height and noise count analyses of the spike noise between holographic and ruled gratings and wavelength response of the used filters are also presented with performance of the present spectrometer system.

• 出版日期2014-4
• 单位核工业西南物理研究院