Understanding the effect of resonant magnetic perturbations on tearing mode dynamics

Abstract

Abstract. Numerical understandings of the effect of resonant magnetic perturbations (RMPs) on 2/1 tearing mode (TM) dynamics observed on J-TEXT tokamak (Hu Q. et al 2012 Nucl. Fusion 52 083011) are presented in this paper. The non-uniform mode rotation frequency, modulated by electromagnetic force (F em ) and viscous force (F vs ), results in the applied RMPs contributing both net stabilizing and braking effect on TM. Numerical evaluation based on analytical theory shows the applied RMP contributes a dominant stabilizing effect, which are responsible for the suppression of TM. The dynamics of the first discovered small locked island (SLI) are investigated. It is found that the island is locked at the stabilizing phase and the saturated island width is less than the linear layer width. The simulated Mirnov signal indicates the small locked island is likely to be the complete suppression case observed in experiments. Associated with the application of RMP, the shape of Mirnov signal deviates from sinusoidal before mode locking, which is explained by numerical modeling. The comparisons between the numerical and experimental results are in good agreement phenomenally.

Linear and nonlinear effect of sheared plasma flow on resistive tearing modes

“…However, the mode becomes more unstable for a sufficiently strong shear flow in low S regime because of approaching AR (i.e. S~110 7 for J-TEXT ohmic plasma [21][22] and S~110 8 for DIII-D H-mode plasma [5][6][7]. Similarly, in the nonlinear phase sheared plasma flow leads to a smaller (larger) saturated island width for a moderate (strong) shear plasma flow.…”

Mode locking and island suppression by resonant magnetic perturbations in Rutherford regime

“…After combining the above with the no-slip condition (22) in steady state, the following relation for locked mode is found:…”

“…The toroidal magnetic field B t ¼ 1:8T and the major radius R 0 ¼ 1:05m. For the plasma mass density q ¼ 1:34 Â 10 À8 kg=m 3 and the electron temperature T e ¼ 0:3 KeV, the Spitzer resistivity is estimated as g ¼ 1:1 Â10 À7 X m. The corresponding Lundquist number S ' 4 Â10 7 and the linear resistive tearing layer width 22,24 is about 0.0077a. For the choice of other parameters shown in the caption of Fig.…”

“…Our theory findings can qualitatively explain the mode locking and island suppression phenomena observed in J-TEXT experiments and simulations. [21][22][23] It should be noted that the complete scenarios for mode locking and RMP suppression of ELMs are different. In the mode locking case, the tearing mode is linearly unstable, whereas in the RMP suppression experiments, the plasma is believed to be stable to linear tearing modes.…”

“…The RMP induced mode locking and island suppression was later reproduced in simulations based on a 2-field reduced resistive MHD model. 22,23 The physics mechanism for the RMP induced island suppression and the relation between island suppression and mode locking are not entirely clear from those studies.…”