Evolution of radiation profiles during detached plasmas and radiative collapse in LHD

Abstract

The divertor heat loads can be efficiently controlled by plasma detachment, hence it is foreseen as a suitable operational regime for divertor operation of future machines. Detachment regime is normally approached by raising the plasma density to a point where plasma detaches from the divertor. If such an approach is adapted to detach the Large Helical Device (LHD) plasma, the plasma goes to radiative collapse due to thermal instabilities. Another approach to detach LHD plasma is by intrinsic impurity seeding using Ne. The discharges detach but ultimately collapse at comparatively lower densities. The detachment is achieved and sustained at high densities by the induction of an m/n=1/1 resonant magnetic perturbation (RMP) in the stochastic edge of the LHD plasma. First quantitative measurements of the two-dimensional (2D) impurity radiation profiles from the three-dimensional (3D) plasma edge of LHD showing the time evolution of radiative collapse and RMP assisted detachment measured by recently upgraded and calibrated Infrared imaging Video Bolometer (IRVB) are presented in this article.