(N)TM Onset by Central EC Power Deposition in FTU and TCV Tokamaks

The presence in plasmas of conventional and neoclassical tearing modes is a key problem for the confinement. The investigation of their onset is still an open issue to avoid plasma degradation and possible disruptions. The destabilization of the modes by on-axis or nearly central EC power deposition is a field still not well understood and responses from devices with different shape and comparable size and operation parameters can give more information. D-shaped TCV and circular FTU plasmas show that the NTM onset/amplification are associated with direct effects of ECCD on the stability parameter Δ'0 with concomitant effects on rotation. An EC torque can affect the destabilization role of the ion polarization current. Calculations using transport codes yield small modifications of the plasma current density profile, however the effect on Δ'0 is hard to quantify given the dependence on d2q/dρ2. This is why experimental comparison is important.