Control of the eITB formation and performance in fully non-inductively sustained ECCD discharges in TCV

The X2 ECH antennas on TCV are used to sustain and tailor the plasma current profile, forming either a centrally peaked or hollow profile. During the transition from peaked to hollow profile, an eITB is observed to form rapidly and in a localized region, which correlates with the appearance of a zero shear flux surface off‐axis according to the ASTRA transport code. The barrier position can be controlled via the co‐ECCD off‐axis deposition location, and the barrier strength with central heating or counter‐ECCD (increasing the depth of the hollow current profile), achieving H‐factors of up to ⩽6. In these discharges, the current in the ohmic transformer coil is held constant to avoid an inductively driven current contribution. After the eITB is created, a small amount of ohmically driven counter (co‐) current has been added as a perturbative current source, transfering only a few kW of ohmic power compared to 1.4MW of ECCD. The ohmic current increases (decreases) the eITB performance demonstrating the clea...