Space-resolved extreme ultraviolet spectrometer system for impurity behavior research on experimental advanced superconducting Tokamak

A flat-field extreme ultraviolet (EUV) spectrometer, which covers a wavelength range of 5-50 nm, has been developed for the experimental advanced superconducting tokamak (EAST). The spectrometer mainly consists of an entrance slit, a varied line spacing groove grating (1200 grooves/mm at the grating center), and a charge coupled device (CCD). The spectral resolution of the spectrometer is Delta lambda=0.015 nm at 20 nm when the width of entrance slit is set at 0.03 mm. The spectrometer is capable of surveying impurity line emissions, for both intrinsic low-Z impurities and highly ionized medium- and high-Z impurities. The obtained best time resolution is 25 ms and with entrance slit height at 1 mm the spatial resolution has reached 45 mm. Preliminary experimental results from the recent EAST campaign were presented. The system was shown to be able to measure the spectral lines of C, O, He, Li and metal impurities under various auxiliary heating conditions. By translating the CCD with a step motor, spectral lines from a full wavelength of 5-50 nm can be covered. In particular the wavelength interval of 15-20.5 nm showed strong line emissions of metal impurities. Time evolutions of second order spectral line of C VI (6.674 nm) and Ni XVI (19.219 nm) lines are presented and detailed analysis is done while taking into account electron density, electron temperature, auxiliary heating power, C III (464.7 nm) and XUV intensities. The profile of Ni XVI is presented to show its good spatial resolution. The EUV spectrometer will be an important addition to the current EAST diagnostic systems in the area of impurity survey and transport research. (C) 2012 Elsevier B.V. All rights reserved.