Stationary regimes of improved confinement in Tore Supra

Abstract

Recent stationary improved confinement experiments with current density profile modifications in non-inductive Tore Supra operation are reported. Significant progress has been obtained by achieving long duration discharges using lower hybrid (LH) waves: (i) 2 min in the 4 T improved confinement LHEP (LH enhanced performance) regime, at a current MA, loop voltage V, LH power MW (, are the electron energy content and Rebut - Lallia - Watkins L-mode prediction), (ii) 75 s long in a fully non-inductive LHEP regime (, V, MA, MW) using a new plasma control scheme, (iii) 30 s at 1.7 MA ( V, MW) in the L-mode regime. MHD stability in full current drive operation and the role of weak - or reversed - central magnetic shear in the central LHEP electron temperature transition (reproduced in full current drive in a systematic manner and measured by independent electron temperature diagnostics) are discussed. Stationary high- experiments were performed with fast-wave direct electron heating (FWEH) in a large range of operation: 42 - 76 MHz and - 3.9 T. Maximum coupled power of 9.5 MW is obtained in the 48 MHz/2T configuration with good electron heating performance and improved confinement at high density (central density ). By increasing the magnetic shear in the gradient region, stationary improved confinement states (6 MW during 5 s, ) are reached in a reproducible manner with poloidal beta, , approaching 1 and 40% of bootstrap current. The high-bootstrap FWEH experiments have been recently combined with LHCD at reduced loop-voltage ( V and up to 70% of non-inductive current). A total injected power up to 7.2 MW (LH: 3.6 MW, FW: 3.6 MW) has produced stationary improved confinement with a peaked electron temperature profile (central value up to 8.0 keV) at a central density of .