Steady-state operation of tokamaks: Key physics and technology developments on Tore Supra

Full text: The Tore Supra tokamak routinely addresses the physics and technology of very long duration discharges. Progresses in RT controls have allowed establishing new world records in fully non-inductive 6 min. discharges (ITER discharge length in standard scenarios) with a coupled energy of 1 GJ. Such capabilities allow a thorough investigation of new and exciting physics at vanishing loop voltage in a situation where the resistive current diffusion has fully taken place, and where the plasma facing components (PFC) work at steady-state temperature. Synergy effects between electron cyclotron and lower hybrid current drive have been unambiguously demonstrated with prospects toward an improved current profile control. Turbulent particle transport has been clearly observed and is shown to be consistent with micro stability analyses. Gas balance on consecutive long discharges exhibits steady-state hydrogen retention. All of them display the same fuelling dynamic with three different time constants, suggesting various mechanisms of retention. Such observations are of direct relevance to ITER and benefit from a strong effort in modelling (predator/prey modelling of transport/current profile coupling observed at 0 loop voltage. . .) and progress in long pulse technology for ITER (plasma test of a load resilient ICRH antenna, PFC development and assessment in plasma device and high heat flux test bed. . . ). (author)