Radiation efficiency of high power ergodic divertor plasmas in Tore Supra

Highly radiative edge layer experiments in Tore Supra ergodic divertor (ED) plasmas are reported. In these experiments, up to 88% of the injected powe r is radiated in steady state attached plasma conditions. The observed radi ated power is higher than the prediction of Matthews' multi-machine scaling . Such behaviour is consistent with the fact that the ratio of the ergodic divertor volume to the main plasma volume is higher for an ergodic divertor than for axisymmetric diverters, or with the enhanced impurity screening o bserved in Tore Supra. Indeed, a new scaling is derived for impurity radiat ion in a region of parallel ion transport. It shows that impurity screening is the dominant mechanism controlling divertor radiation, impurity transpo rt along the open field lines having only little influence on P-rad. (C) 19 99 Elsevier Science B.V. All rights reserved.