Steady-state fully non-inductive reverse shear scenarios with electron ITB and dominant bootstrap current

The relation between the safety factor profile, q, the electron transport and the bootstrap current is of crucial importance for predicting advanced scenarios in burning plasmas which will have dominant electron heating and small momentum input. In recent experiments in the Tokamak TCV, the full plasma current has been sustained with only off-axis co-current drive and bootstrap current. As soon as the EC power is turned on, the inductive current is set to zero. Therefore the current profile evolves from the original ohmic profile to the one driven by the off-axis beams without any externally applied loop voltage. Due to the resulting reverse shear profile an electron internal transport barrier (eITB) is formed and the bootstrap current increases up to 50% of the total plasma current. Adding heating or counter CD in the center exhibits clear difference in the time evolution of the electron temperature profile. With less current driven in the center, and therefore a more reversed q profile, the eITB is more pronounced and better global electron energy confinement time is obtained. Increasing plasma density and EC power, electron internal transport barrier discharges with up to 80% bootstrap current have been sustained in steady-state with no ohmic current.