The spontaneous destabilization of neoclassical tearing mode with existing energetic ions in low torque tokamak plasmas

Abstract

Periodic destabilization of a neoclassical tearing mode (NTM, m/n = 2/1) in between two edge localized modes (ELMs) is observed with a varying frequency that deviates from the wave-particle resonance determined precession frequency, is instead near the electron diamagnetic drift frequency. This scenario is created by the balanced injection of co- and counter-current neutral beams which give rise to low-torque plasmas with a high confinement on the experimental advanced superconducting tokamak (EAST). The destabilization is obviously dependent on the ratio of the mode frequency to the electron diamagnetic frequency, indicating the effect of relative rotation between the NTM and plasmas on the mode stability. In particular, the role of polarization current in general Rutherford equation is identified by experimental data reported in this letter.

Nonlinear modeling of the effect of n = 2 resonant magnetic field perturbation on peeling-ballooning modes in KSTAR

“…In our case, 80% of total radial particle flux at the center of the pedestal is due to Γ oe . Experimental findings show that the density pump-out under RMP is highly correlated with X-point deformation [22,48]. Since KPM makes large displacement at the X-point, it may play an important role in the density pump-out, which is consistent with the tendency of experimental findings [21,39].…”

“…Previous studies [14][15][16][17][18][19][20] revealed that perpendicular electron flow shields the RMP and suggested the importance of zero electron flow layer at the pedestal to improve the field penetration. Numerical studies found that RMP can drive the kink-peeling response, and it amplifies the field penetration [21][22][23][24]. Moreover, it has been reported that RMP can increase turbulence transport [25,26] in the pedestal.…”

“…The larger perturbations of temperature and density are observed at the Xpoint. In order to identify this response, the linear displacement ξ š H is calculated from Ref [23], and this mode has an edge localized structure as shown in Figure 9 with kink-peeling mode (KPM) [22][23][24]39] characteristics. Notice that, the n=2 mode is linearly stable in our case, and we can say that RMP nonlinearly drives the n=2 KPM.…”