Low temperature partly ionized plasma in magnetic fusion devices: present status and prospects

Summary form only given. We review a modem physical picture of plasma detachment in fusion devices with magnetic confinement and in linear machines, and discuss new results on the stability of detached plasmas. Experimental observations and 2D modeling show that the impurity radiation, neutral gas ionization and plasma recombination regions (fronts) "jump" from the target towards the bulk plasma when detachment occurs. Simultaneously this affects core plasma confinement. This indicates that the localization of the fronts close to the target is unstable. We show analytically that detached plasma can be unstable with respect to both ionization-recombination instability and thermal bifurcations of impurity radiation front. We show that this instability and bifurcation, driven by violation of the plasma energy balance at low power coming from core to the edge plasma, can restrict the achievable edge plasma density in magnetic fusion devices. We discuss implications of this theoretical insight for the interpretation of experimental data on detached plasmas and density limit.