Sustained fully non-inductive scenarios using pressure and current profile control with ECCD

The ECW system on Tokamak à configuration variable (TCV) allows the study of a wide range of poloidal and toroidal launch angles. Both electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) experiments have been performed to demonstrate the modification of the electron temperature and current profiles. In particular a multi-channel hard X-ray camera (on loan from Cadarache) clearly shows the generation of a high energy electron tail, which increases with increasing toroidal launch angle. Using a scenario with three 0.5 MW gyrotrons providing on-axis co-current drive (CO-CD), we have obtained full current replacement of 150 kA. However, this leads to very peaked profiles which are MHD unstable and the discharge disrupts. By careful distribution of the power deposition and current source profiles over the minor radius, we have obtained steady-state scenarios up to 124 kA with Te0 ≈3.5 keV and n̄e=1019 m−3. These scenarios are sustained for 1.9 s, that is, more than 900 confinement times and more than ten current redistribution times. Therefore, both the pressure and current profiles are sustained by the 1.5 MW of ECCD power. By lowering the feedback plasma current demand, the ohmic transformer is recharged; this provides a very good diagnostic of the total non-inductive current driven in these scenarios.