Stability of divertor detachment

Abstract

The 2D simulations of edge plasma transport show that unlike some earlier publications, the impurity radiation loss per se does not cause the bifurcation-like transition to detached divertor regime. However, for the case where anomalous plasma transport is increasing with advancement to detachment, like it was recently observed experimentally, the transition to detachment exhibit the bifurcation-like character. Some other plausible reasons for similar bifurcation-like evolution to detachment are discussed. It is demonstrated that the current convective instability can be triggered in detached inner divertor plasma for the condition when outer divertor is still attached. This can explain the fluctuations of radiation loss observed recently experimentally for similar conditions. The self-sustained oscillations observed recently in numerical simulations and related to the interplay of the thermal force effects in impurity transport and impurity radiation loss are further investigated. It is shown that for some conditions these oscillations are ubiquitous, since no stable solutions possible. Keywords: Divertor detachment, Stability, Bifurcation, Impurity, Anomalous transport, Recycling