Long-Pulse Improved Central Electron Confinement in the TCV Tokamak with Electron Cyclotron Heating and Current Drive

Current profile tailoring by electron cyclotron heating (ECH) and current drive (ECCD) is used to improve central electron energy confinement in the TCV tokamak. Counter-ECCD on axis alone achieves this goal in a transient manner only. A stable scenario is obtained by a two-step sequence of off-axis ECH, which stabilizes magnetohydrodynamics modes, and on-axis counter-ECCD, which generates a flat or inverted current profile. This high-confinement regime, with central temperatures up to 9 keV (at a normalized ${\beta }_N\sim 0.6$), has been sustained for the entire duration of the heating pulse, or over 200 electron energy confinement times and 5 current redistribution times.