The m=2, n=1 mode suppression by ECRH on the T-10 tokamak

Abstract

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

Numerical studies on the stabilization of neoclassical tearing modes by radio frequency current drive

“…The experimental results suggest that the fast electron transport coefficient is much larger than the neoclassical one. 35,37,38 Assuming for a reactor plasma with plasma density nϭ5 ϫ10 19 m Ϫ3 , the fast electron temperature 50 keV, a ϭ2.0 m, and Ќf ϭ1.0 m 2 /s, it is found that f ϭ0.30 ϫ10 3 s and w pt /aϭ2.9ϫ10 Ϫ2 . Such a w pt value is comparable with the rf wave deposition width, and therefore f is an important parameter in determining the stabilizing effect.…”

“…The perpendicular transport of the fast electrons broadens the driven current profile and leads to a smaller local current density. 37,38 This effect is measured by the parameter w pt ϭ( Ќf / f ) 1/2 . 39 The total width of j d is approximately given by w d Ϸw ds ϩw pt .…”

Consequences of plasma rotation for neoclassical tearing mode suppression by electron cyclotron current drive

“…3 NTM suppression experiments have been performed successfully using both ECRH and ECCD. [4][5][6][7][8][9][10][11][12][13][14] The generalized Rutherford equation (GRE) 15,16 provides a theoretical model for the growth and stabilization of tearing modes. It describes the nonlinear temporal evolution of the full width w of the associated magnetic island as a function of different stabilizing and destabilizing mechanisms.…”

Using High-Power Gyrotrons in the T-10 Tokamak

“…In the T-10 tokamak, the microwave radiation at the first and second ECR harmonics was used for this purpose [8,9]. changes in the character of the sawtooth oscillations related to the development of the internal disruptive instability during variation in the location of the ECR region with respect to the resonance surface q = 1, where q is the stability margin, due to the plasma-column displacement along the large radius.…”