Observation of 1/1 impurity-related ideal internal kink mode locking in the EAST tokamak

Abstract

m/n = 1/1 pressure gradient driven impurity-related ideal internal kink mode locking is observed in EAST limit-cycle state H-mode plasmas. This 1/1 mode has a radial structure with no inversion around the resonance, which implies that the mode has an ideal internal kink structure. The rotation direction of the 1/1 internal kink mode, as obtained by tomography of a high-resolution multi-array soft x-ray system, is the ion diamagnetic drift velocity direction. Impurities accumulated in the central region play a vital role in mode excitation. Remarkable loss of the yield of neutron rate due to 1/1 mode is also observed. A notch at the location in the vicinity of q = 1 is also observed in the local toroidal rotation profile. Furthermore, the frequency chirping behavior of the 1/1 kink mode is related to the toroidal rotation velocity of the plasma.