Problems and issues for tokamak long-pulse operation: major progress on Tore Supra

This paper gives an overview of the major progress achieved recently, taking advantage of the new configuration of Tore-Supra. As a background, the main results obtained in the nineties are first recalled, as well as the identified limitations that led to the upgrade project. In the new configuration, the Tore Supra operational domain has experienced a rapid extension. Indeed, discharge of more than 4 minutes have been performed with a record breaking discharge accounting for 0.75 GJ of injected/extracted energy. Primary transformer recharge by Lower Hybrid Current Drive (LHCD) has been observed during 1 minute while fully steady state discharge, with complete diffusion of the resistive current, are performed routinely (typical parameters: plasma current 0.52 MA, toroidal magnetic field 4 T, LH power around 3 MW, electron line density 2.5 1019 m-2), limited in duration by the original LHCD system. Ion cyclotron waves (ICRH) have been coupled to plasma during one minutes in combination with LHCD, in a higher density scenarios (Greenwald fraction of 0.8, 0.11 GJ of injected ICRH power for 0.42 GJ total injected power) and with a significant fraction of bootstrap current (15-20%). Electron cyclotron current drive experiments are also carried out for current profile control and for the study of current drive synergy with LHCD. Opportunely, a new record of EC injected energy has been established in a single ECRH pulse of 32 s (25 MJ). In these discharges, stable central electron temperature oscillations sometimes appear, probably due to the interplay between heat transport and current drive. Density profile peaking is observed despite the absence of toroidal field, suggesting the existence of a turbulent inward pinch. Finally, article balance analysis indicate that the in-vessel deuterium inventory never reach saturation. found any carbon deposits and flakes have in the inner vessel, possibly playing a role in the retention. (author)