MHD activity in Tore Supra gigajoule scenario

The Tore Supra gigajoule (GJ) scenario was developed during the 2002 experimental campaign, with the goal of realizing long pulses in a stationary state, at a loop voltage therefore close to zero. This challenge has led to very successful results, with a record injected energy of 0.75 GJ and perfect control of the plasma density over 4 min 25 s. The performance is however limited by the lower hybrid system reliability and MHD limits. This paper focuses on the three kinds of MHD activity that were observed in the development of this scenario. The first one, probably a manifestation of the feedback control on the plasma position, is benign and, once triggered, stays at a low level. The second one is the triggering of a fast growing instability, which leads to a strong degradation of the confinement in the core region and to a redistribution of the plasma current. After such events, a regime with a persistent MHD activity sets in and represents the third kind of MHD activity in the GJ experiments. This paper reports on the analysis of this MHD activity. Perspectives for the future development of the GJ scenario in Tore Supra are drawn.