Stability of the detachment front in a tokamak divertor

Experimental observations show that when a divertor plasma detaches, radiation regions (fronts) move towards the X-point. This indicates that the localization of the fronts in the divertor is unstable. We study theoretically the stability of detached divertor operation and compare our results with experimental data. We show that the impurity radiation and plasma recombination effects play a crucial role in the evolution of detached plasma parameters. In the tokamak SOL these effects result in the saturation of upstream plasma density and temperature as the total number of particles (ions and neutrals) in the SOL is increased, and cause both impurity radiation and ionization-recombination fronts propagation towards the X-point. These conclusions are supported by experimental data from Alcator C-Mod. (C) 1999 Elsevier Science B.V. All rights reserved.