Advance in the JT-60SA VUV divertor spectrometer design

Abstract

The Vacuum Ultraviolet (VUV) Spectrometer designed to monitor the divertor region of JT-60SA is presented. JT-60SA is starting its activity in support of the exploitation of ITER and complementing it in resolving key physics and engineering issues for DEMO. The aim of the spectrometer is to characterize the contribution of impurities to the radiation emitted in the divertor region in different scenarios and to study the divertor physics including plasma detachment.

Positioned on an upper port with a vertical line of sight aiming at the divertor, the spectrometer is based on the double SPRED spectrometer originally employed on TEXTOR that has been refurbished with two new toroidal gratings specially designed to allow the 1D imaging detection and to cover the desired spectral range. The two channels of the instrument together cover a wavelength range from 10 nm to 125 nm in two ranges of 10–48 nm and 44–125 nm, with an overlapping region to perform the cross calibration. The wavelength resolution in the two ranges is 0.08 nm and 0.14 nm respectively, with a 50 μm wide entrance slit. Given the extended length of the JT-60SA port ducts, the system is equipped with a custom-designed optical relays based on gold-coated toroidal mirrors with possibility of remote control of the alignment. These mirrors focus the plasma emission at the divertor onto the two slits. The dispersed radiation is then recorded by two high sensitivity CCD detectors.