A fast-response extreme ultraviolet spectrometer for measurement of impurity line emissions in EAST

In the next EAST campaign, the auxiliary heating power increases up to 24MW in total, including lower hybrid heating of 10MW, electron cyclotron resonance heating of 2MW, ion cyclotron range of frequency heating of 8MW and neutral beam heating of 4MW. Various materials are planned to use for plasma facing components in EAST, e.g., molybdenum for main vacuum chamber, W/Cu monoblocks for upper divertor and SiC-coated graphite tiles for lower divertor. The high heat load on divertor plates enhances the impurity production through physical and chemical sputterings during the steady state operation. The lithium coating is also scheduled for wall conditioning to suppress the hydrogen and deuterium recycling. Therefore, the impurity diagnostics are very important to improve the plasma performance of EAST discharges in the next experimental campaign. In particular, the measurement of intrinsically existing high-Z impurities of Mo and W is crucially important in addition to light impurities of Li, C and O because radiation loss from such high-Z impurities is really big. For the purpose an extreme ultraviolet (EUV) spectrometer working in 50-500Å wavelength range has been newly developed in EAST to measure line emissions from such impurities. A flat-field focal plane for spectral image detection is made by a laminar-type varied line spacing concave holographic grating with an angle of incidence of 87deg. A back-illuminated charge-coupled device (CCD: Andor DO920P-BN) with 1024 x 255 pixels is used for measuring the focal image of spectral lines. The high readout rate and the pixel binning of the CCD can improve the temporal resolution of time-resolved spectrum, at least a few milliseconds per frame. It makes possible a variety of studies, e.g., impurity behavior during edge-localized mode (ELM) activity and ELM mitigation in long pulse discharges. In the seminar the progress on the EUV spectrometer newly developed for the impurity diagnostics in EAST is presented. (author)