Development of an Array System of Soft X-ray Detectors with Large Sensitive Area on the Large Helical Device

概要

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A new 17-channel soft X-ray diagnostic system was developed for a study of magnetohydrodynamics (MHD) fluctuations and installed on the Large Helical Device (LHD). The Absolute X-ray Ultraviolet Photodiodes (AXUV diode) with a large sensitivity area 10 mm × 10 mm were adopted as the detectors. The sightlines were designed to cover the whole plasma with 3.8 cm space separation and the expected radial resolution was 7 cm at the equatorial plane of LHD. The toroidally elongated pin hole (25 mm × 7 mm) was used to increase the signal to noise ratio and a Be foil of 15 µm in thickness was used to shut the visible light. The detector array was placed inside the vertically elongated section of the LHD vacuum vessel, being shielded by an aluminum box. In the experimental campaign of LHD, this fiscal year 2011, various kinds of MHD fluctuations excited in core and edge plasma regions have clearly been detected by this newly installed diagnostic system. The characteristic behaviors of the ELM activity in H-mode plasmas and the "Fishbone"-like instabilities induced by the perpendicular neutral beam injection (NBI) were derived from the soft X-ray data.