Physics studies with Electron Cyclotron Resonance Heating and Current Drive on TEXTOR

The new 800 kW, 3 s, 140 GHz gyrotron has been applied on TEXTOR for physics studies with ECRH and ECCD. Slow magnetic field ramps demonstrate control of the sawtooth period: both co-ECCD and ECRH leading to long periods when positioned just outside the inversion radius, while counter-ECCD results in long sawtooth periods when positioned inside the inversion radius. Co-ECCD results in much shorter sawtooth periods when positioned inside the inversion radius. Switch-off of off-axis ECRH is seen to result in a transient improvement of confinement near the q=1 radius. This effect is observed to depend sensitively on both the position, power, and pulse length of ECRH. When properly localized at the q=2 surface, ECRH and ECCD are found to be capable to fully suppress the m=2, n=1 tearing modes induced by the Dynamic Ergodic Divertor. (author)