Estimation of partial carbon radiation at each ionization stage of C2+ to C5+ ions in large helical device

Abstract

Detached plasma has been successfully achieved with use of m/n = 1/1 resonant magnetic perturbation (RMP) coils in a large helical device (LHD) without any additional impurity gas puffing. Study of the impurity radiation is then important to clarify the physical mechanism triggering the RMP-assisted detachment. Resonance lines of CIII (977.02 Å, 2s2p-2s2), CIV (1548.2 Å, 2p-2s), CV (40.27 Å, 1s2p-1s2), and CVI (33.73 Å, 2p-1s) measured by vacuum ultraviolet (VUV) and extreme ultraviolet (EUV) spectrometers are used to estimate the radiation power from C2+-C5+ ions because carbon is the most abundant impurity element in LHD. For the purpose the spectral intensity from the VUV spectrometer is absolutely calibrated using the EUV spectrometer, with which the spectral intensity has already been calibrated. The partial carbon radiation at each ionization stage of C2+ to C5+ ions, Prad(Cq+), can be estimated for attached and detached plasmas by calculating the ratio of the partial carbon radiation to the resonance line based on ADAS atomic code. It is found that the radiation from C3+ ions existing near a radial location of ℓ/2π = 1 in the ergodic layer increases up to 40% of the total radiation loss and becomes a dominant origin to trigger the detached plasma, whereas carbon radiation is negligible in the attached plasma.