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 power is radiated in steady state attached plasma conditions. The observed radiated 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 divertors, or with the enhanced impurity screening observed in Tore Supra. Indeed, a new scaling is derived for impurity radiation in a region of parallel ion transport. It shows that impurity screening is the dominant mechanism controlling divertor radiation, impurity transport along the open field lines having only little influence on P rad .