PLASMA DETACHMENT FROM DIVERTOR TARGETS AND LIMITERS

Plasma detachment from a divertor target is defined as the state in which large gradients in total plasma pressure (static plus dynamic) are observed parallel to the magnetic field with consequent reductions in the plasma power and ion fluxes to the limiting surfaces. The origins of this concept and the first experiments in a linear divertor simulator are described. Experimental evidence for this phenomenon from the JET, JT60-U, DIII-D, Alcator C-Mod. and ASDEX-U tokamaks is reviewed along with recent advances in the theory and modelling of detached plasmas applicable to current experiments. Plasma detachment from limiters was first reported by TFTR in 1985, shortly followed by DITE and TEXTOR. This phenomenon occurs in low power discharges near the density limit and is characterised by a shrinking of the layer where most of the ionisation occurs away from the limiter. The physics, phenomenology and relevance to fusion of detachment from limiters and diverters are contrasted.