Design of vacuum ultraviolet spectroscopy system on J-TEXT

Abstract

A Vacuum Ultraviolet (VUV) spectroscopy system is designed on J-TEXT tokamak in order to study the transport of the light impurities including carbon and oxygen in edge region with the effect of RMP or ECRH. It covers the wavelength ranging from 30 to 300nm. The normal incidence monochromator with concave grating with the focal length of 1 meter is chosen for light dispersion. A 1024*1024 pixels back illuminated charge-coupled device (CCD) is chosen as the detector for the profile measurement. The observing region is from 1.1a (minor radius) at the lower part of the plasma to 0.6a at the upper part with an adjusting spatial resolution slit. In order to prove the potential for the expected signal intensity, spectra are simulated using the impurity transport code STRAHL. The photons numbers of C II 133.45nm, C III 97.7nm and C IV 154.9nm in J-TEXT plasma are estimated to evaluate the practicability of the system. The wavelength calibration will be achieved using the light from plasma in tokamak at different discharge conditions. The branching ratio technique and bremsstrahlung are combined for the absolute intensity calibration.