Improved core electron confinement on JET

Formation of core regions with reduced electron transport is reported in regimes with current profile shaping at JET. The electron heat diffusivity (χe) is reduced down to 0.5 m 2 /s in the region of low magnetic shear with an ICRH power of 1MW with no indication of a threshold. In the high performance optimised shear regime, obtained in scenarios dominated by ion heating, internal transport barriers on the ion temperature profiles are simultaneously accompanied by a significant reduction of the electron heat diffusivity at two-third of the plasma radius. In this regime, recent results and measurements obtained with the new gas-box divertor configuration are reported together with their transport analyses. The results indicate that χe is reduced by one order of magnitude in a spatially localised region. Formation of internal transport barriers (ITB) with dominant ion heating schemes has produced high performance plasmas in JET (1-2). In order to extrapolate this regime to fusion tokamak reactors one must establish whether an ITB can be formed and sustained with mostly electron heating and low particle fuelling rates as expected in burning plasmas. To address these long term problems, current profile control experiments performed at JET using dominant electron heating schemes alone together with their analyses are reported in the first section. Then, in the second section thermal electron transport in the optimised shear regime with clear ITB on the ion temperature profiles is described (3) in the light of the recent experiments performed with the recently installed gas-box divertor. 1. Improved core electron confinement with RF heating scheme