Effect of the toroidal flow and flow shear on the m/n = 2/1 tearing mode in J-TEXT tokamak

It has been found that a higher-frequency rotating resonant magnetic perturbation (RRMP) can suppress a large tearing mode (TM) and avoid subsequent disruption [Da Li, et al, 2020 Nucl. Fusion 60 056022]. To clarify the mechanism of the stabilizing effect of the higher-frequency RRMP, experiments on the effects of RRMPs with different frequencies on the TM amplitude are presented in this paper. After eliminating the destabilizing effect of RRMP, the statistical analysis reveals a notable negative correlation between changes in the amplitude of the TM and changes in the mode frequency. Further investigation indicates an absence of a suppressive effect of the toroidal flow on the TM. Instead, the data shows a clear linear relationship between changes in the TM amplitude and the flow shear in proximity to the resonant surface, with a high coefficient of determination (r2). Those experimental results suggest that the flow shear plays a significant role in the suppression of TMs and offer a plausible method to prevent disruptions in future devices.

Section: Introductionmentioning

confidence: 99%

Effect of the toroidal flow shear on the m/n = 2/1 tearing mode by using the rotating resonant magnetic perturbations in the J-TEXT Tokamak

Jia

Ding

et al. 2023

“…As for the control of MHD instabilities, an active-control system is implemented in HBT-EP to control mode rotation with a biased electrode inserted into the plasma [21]. Previous experiments in J-TEXT have also demonstrated that bias can control the 2/1 tearing mode [22] and even unlock the locked mode [23]. In recent years, long-range correlation (LRC) structures have been observed in several devices during positive bias voltage.…”

Section: Introductionmentioning

confidence: 99%

Effects of negative and positive bias voltages on turbulence characteristics in J-TEXT tokamak

Zhang¹,

Liu²,

Xu³

et al. 2022

Self Cite

The effects of positive and negative bias voltages on the turbulence characteristics in edge plasmas of J-TEXT are studied using Langmuir probe arrays. The experimental results illustrate that the turbulent particle transport fluxes are suppressed in both positive and negative bias cases, while the suppression mechanisms are quite different. For the positive bias (+300 V), the long-range correlation (LRC) structures with frequencies of about 10 ~ 30 kHz are generated, which are beneficial for the turbulent transport suppression. In the -300 V bias case, no LRCs appear, while a strong mean flow shear exists which can reduce the amplitudes of potential and density fluctuations and thus decreases the turbulent transport.

“…Toroidal rotation is thought to have a significant influence on MHD instabilities, including tearing modes and neoclassical tearing modes. It was observed that the tearing modes and neoclassical tearing modes were significantly affected by toroidal rotation in some experiments [2][3][4][5][6][7][8][9]. The mode amplitude of observed m/n = 2/1 tearing mode tended to be reduced by rotation and rotation shear in the Korea Superconducting Tokamak Advanced Research [10] (KSTAR) [2].…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, in ASDEX Upgrade, the onset threshold of neoclassical tearing modes was found to increase with co-and counter-current directed rotation, and also with positive and negative rotation gradient [7]. The effect of the toroidal flow and flow shear on the m/n = 2/1 tearing mode has been investigated in J-TEXT tokamak, which showed that the saturated island width of the tearing mode is more correlated to the toroidal flow amplitude than the flow shear [8].…”

Section: Introductionmentioning

confidence: 99%

Influence of toroidal rotation on nonlinear evolution of tearing mode in tokamak plasmas

Ren¹,

Wang²,

Cai³

et al. 2022

The nonlinear evolution of the tearing mode instability with toroidal rotation is investigated using a three-dimensional toroidal geometry magnetohydrodynamic code (M3D). It is found that toroidal rotation plays a significantly stable role in reducing the width of magnetic island, which is independent of the direction of toroidal rotation. Comparing with the stabilizing effect in the linear phase, the stabilizing effect of toroidal rotation is much stronger in the nonlinear phase. The magnetic island is almost suppressed by large enough rotation, even though the linear growth rate is weakly reduced in the linear phase. It is observed that the flow shear has a stabilizing effect, which is significant when the rotation frequency is large. However, it is shown that the magnitude of rotation plays a dominant role in stabilizing the magnetic island when the rotation frequency is small. The Coriolis force, rather than the centrifugal force, is found to play a dominant role in stabilizing the tearing mode in the nonlinear phase. When m/n=3/2 and m/n=2/1 tearing modes exist simultaneously, the sheared toroidal rotation is shown to effectively suppress the overlap of magnetic islands and field stochasticity caused by the coupling of neighboring islands.