Effects of central electron cyclotron power on plasma rotation and on triggerless onset of NTMs in the TCV tokamak

Experiments on the TCV tokamak show that high power central electron cyclotron heating (ECH) and current drive (ECCD) produce significant direct modification of the plasma rotation profile, as well as the effect on the equilibrium current density. These effects contribute to the onset of neoclassical tearing instabilities, in absence of triggers such as sawteeth, ELMS or relevant error field, but in a regime of unsteady rotation. In turn the growing tearing modes breaking axisymmetry provide a nonlinear magnetic torque which converts the power absorption in co-directed rotation with flattening of the profile at the rational surfaces. The experimental results are presented and discussed in the frame of the theoretical models of neoclassical toroidal viscosity and ion inertial effects.