q-profile evolution and improved core electron confinement in the full current drive operation on Tore Supra

The formation of a core region with improved electron confinement is report ed in the recent full current drive operation of Tore Supra, where the plas ma current is sustained with the lower hybrid (LH) wave. Current profile ev olution and thermal electron transport coefficients are assessed directly b y using the data of the new fast electron bremsstrahlung tomography that pr ovides the most accurate determination of the LH current and power depositi on profiles. The spontaneous rise of the core electron temperature observed a few seconds after the application of the LH power is ascribed to a bifur cation towards a state of reduced electron transport. The role of the magne tic shear is invoked to partly stabilize the anomalous electron turbulence. The electron temperature transition occurs when the q-profile evolves towa rds a non-inductive state with a non-monotonic shape, i.e, when the magneti c shear in the plasma core is reduced to close to zero. The improved core c onfinement phase is often terminated by a sudden MHD activity when the mini mum q approaches 2.