Space-resolved 3 m normal incidence spectrometer for edge impurity diagnostics in the large helical device.

A space-resolved vacuum ultraviolet (VUV) spectroscopy using a 3 m normal incidence spectrometer has been developed to measure the impurity profile in the edge ergodic layer composed of stochastic magnetic field by which the edge plasma in the large helical device (LHD) is uniquely characterized. It vertically measures the spatial profile of VUV lines emitted from impurities in the wavelength range of 300-3200 Å. The wavelength interval, Δλ, which can be measured in a single discharge, is about 37 Å.

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

A flat-field space-resolved extreme ultraviolet (EUV) spectrometer system working in wavelength range of 10-130 Å 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 Zeff and impurity transport, respectively. Until now, a large amount of spike noise caused by neutral particles with high energies (≤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.