Plasma edge characterisation and control in ergodic divertor experiments on Tore Supra

The upgrading of the power handling capability of the Ergodic Divertor of Tore Supra has been accompanied by the installation of a new set of edge plasma diagnostics. The characterisation of the edge plasma (electron density and temperature measured with Langmuir probes) is presented for ohmic shots in deuterium. The edge plasma density exhibits a linear and then a cubic dependence with the plasma density while for larger plasma density, detachment occurs. Two methods of defining detachment are presented: one based on local measurements obtained with the Langmuir probes and one using integrated measurements from edge bolometry. These two different definitions produce very similar values. Active pumping, using a pump limiter inserted in the ergodic layer, is shown to be efficient for both low plasma density and ohmic power. The edge plasma density is shown to be strongly linked to active pumping while the edge electronic temperature is shown to be less sensitive. Experimental evidence of active edge density control is shown when active pumping is applied. Finally, particle exhaust with the vented structure of the ergodic divertor is shown to become efficient for high recycling regime obtained at large plasma density and/or large input power. (C) 1999 Elsevier Science B.V. All rights reserved.