Feedback control on edge plasma parameters with ergodic divertor in Tore Supra

In order to control highly radiative plasmas with the ergodic divertor, fee dback procedures based on real time Langmuir probes measurements have been implemented in Tore Supra. The prediction of the detachment density thresho ld, which leads to disruption, is a major experimental difficulty. On the o ther hand, it has been observed that the edge electron temperature limit, m easured by probes, is quite reproducible in many different operating scenar ios. Therefore, feedback procedures on the edge electron temperature have b een developed to control the gas injection. When the plasma reaches detachm ent, the fuelling efficiency abruptly increases and the feedback loop can b ecome unstable. A detachment criterion, defined as the ratio of the saturat ion current of the probes scaled from the high recycling regime phase to it s current value? has been used to manage detached plasmas. These techniques have been successfully applied in Tore Supra discharges with ergodic diver tor for the study of edge density regimes and plasma detachment in ohmic, I CRH heating, and impurity seeded experiments. (C) 2001 Published by Elsevie r Science B.V.