PARTICLE EXHAUST EXPERIMENTS WITH PUMP LIMITER, ERGODIC DIVERTOR AND VENTED LIMITER IN TORE-SUPRA

In Tore Supra, plasma particle exhaust has been studied by means of mo dular pump limiters, with either throats (ion collection) or vented st ructures (neutral collection), and with an ergodic divertor. Detailed study of active plasma density control has been performed in these thr ee configurations for ohmic conditions. In Tore Supra, emphasis has be en put on achieving highly radiating edge conditions, essentially in t he ergodic divertor configuration. Indeed, this device has already dem onstrated its capability of creating favourable plasma edge conditions without modification of the central plasma parameters. It is shown ex perimentally that for ohmic shot, when the plasma detaches the paralle l particle flux in the scrape off layer is strongly reduced. Consequen tly, the resulting neutral flux from the neutralizer plates of the thr oat limiter drops as well as the particle exhaust. Preliminary experim ents have been achieved with a modular vented limiter and exhibit sign ificant hydrogen exhaust even for ohmic detached plasmas and such a ve nted structure is presently planned to be installed on the ergodic div ertor. Finally, particle balance with active pumping has to include wa ll particle inventory. This term is shown to be dominant for hydrogen experiments, in contrast to helium shots where the wall contribution i s negligible.