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Problems and Issues for Tokamak Long-Pulse Operation: Major Progress on Tore Supra

Jérôme Bucalossi, Tore Supra Team

Fusion Science and Technology

Volume 46 / Number 1 / July 2004 / Pages 184-191


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During winter 2001-2002, the Tore Supra tokamak went through a major upgrade to provide a heat extraction capability of 25 MW in steady state (composants internes et limiteur project). In the new configuration, the operational domain has experienced a rapid extension. Indeed, discharges of more than 4 min have been performed with a world-record-breaking discharge accounting for 0.75 GJ of injected/extracted energy. Stationary discharges with fully noninductively driven current are performed routinely (typical parameters: plasma current, 0.52 MA; toroidal magnetic field, 4 T; lower hybrid power, ~3 MW, electron line density, 2.5 × 1019 m-2), limited in duration by the original lower hybrid current drive (LHCD) system. Ion cyclotron waves [ion cyclotron resonance heating (ICRH)] have been coupled to plasma for 1 min in combination with LHCD in a higher-density scenario (Greenwald fraction of 0.8, 0.11 GJ of injected ICRH power for 0.42 GJ total injected power) and with a substantial fraction of bootstrap current (15 to 20%). Electron cyclotron current drive experiments are also carried out: A new world record of electron cyclotron injected energy has been established in a single electron cyclotron resonance heating 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 electric field, suggesting the existence of a turbulent inward pinch. Finally, particle balance analyses indicate that the in-vessel deuterium inventory never reaches saturation. Many carbon deposits and flakes have been found in the inner vessel, possibly playing a role in the fuel retention.

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