Confinement in TCV electron cyclotron heated discharges was studied as a function of plasma shape, i.e. as a function of elongation, 1.1 < κ < 2.15, and triangularity, −0.65 ≤ δ ≤ 0.55. The electron energy confinement time was found to increase with elongation, owing in part to the increase of plasma current with elongation. The beneficial effect of negative triangularities was most effective at low power and tended to decrease at the higher powers used. The large variety of sawtooth types observed in TCV for different power deposition locations, from on-axis to the q = 1 region, was simulated with a model that included local power deposition, a growing m/n = 1 island (convection and reconnection), plasma rotation and finite heat diffusivity across flux surfaces. Furthermore, a model with local magnetic shear reproduced the experimental observation that the sawtooth period is at a maximum when the heating is close to the q = 1 surface.
The velocity of plasma rotation and the potential distributions are measured in the TM-4 device in the Ohmic-heating regime. The potential is negative at the centre of the column, and its magnitude is significantly larger than the ion temperature. At the edge, the potential is positive while the rotation velocities are considerably lower than their neoclassical values.
Experiments on m=2, n=1 tearing mode suppression and on avoidance of density limit disruptions by electron cyclotron resonance heating (ECRH) were performed on the T-10 tokamak. Partial suppression of the m=2, n=1 mode by the high frequency (HF) power deposition in the vicinity of the q=2 surface was observed. Development of external kink modes with HF power injection can result in m=2, n=1 mode destabilization under specific operating conditions. ECRH suppresses m=2, n=1 mode activity at extremely high values of electron densities and prevents the density limit disruptions practically independently of EC resonance position. Complete compensation of the additional peripheral heat losses near the density limit by ECRH should be responsible for this result. No effect of electron cyclotron current drive (ECCD) on m=2, n=1 mode stability has been observed because of insufficient values of HF driven current in the vicinity of the q=2 surface under the operating conditions of the experiment
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