An extreme ultraviolet spectrometer working at 10–130 Å for tungsten spectra observation with high spectral resolution and fast-time response in Experimental Advanced Superconducting Tokamak

Abstract

A newly developed flat-field extreme ultraviolet (EUV) spectrometer working at 10–130 Å wavelength range with high spectral resolution and fast-time response has been developed to observe line emissions from highly ionized tungsten ions in the Experimental Advanced Superconducting Tokamak (EAST). This flat-field EUV spectrometer is equipped with a laminar-type varied-line-spacing (VLS) concave holographic grating (2400 grooves/mm at grating center) fixed at an angle of incidence of 88.6°, and a back-illuminated charge-coupled device (CCD) with pixel numbers of 1024 × 255 (26 × 26 μm2/pixel). The CCD is routinely operated at 5 ms per frame with full vertical binning (FVB) mode. An excellently high spectral resolution of Δλ0=4–6 pixels (full width at foot position of spectral line profile), which corresponds to full width of half maximum (FWHM) of 0.1 Å at 20 Å, has been obtained by carefully adjusting angles and positions of the grating and CCD. Thus, the line identification of complicated tungsten spectra became possible, when a precise wavelength calibration was done. Typical tungsten spectra are recorded at low (Te=1.0 keV) and high (Te=2.6 keV) electron temperatures. Tungsten unresolved transition arrays (W-UTA) existing at wavelength ranges of 15–35 and 45–65 Å were preliminarily identified as line emissions from W24+–W33+ and W27+–W45+ ions, respectively, by referring to previous experimental results and National Institute of Standards and Technology (NIST) database. Developing a set of analytical computer programs, line spectra observed with the EUV spectrometer have been automatically identified after data acquisition basically for all discharges during daily EAST experiment.