The Coupling Structure Features Between (2,1) NTM and (1,1) Internal Mode in EAST Tokamak

In the discharge of EAST tokamak, it is observed that (2,1) neoclassical tearing mode (NTM) is triggered by mode coupling with a (1,1) internal mode. Using singular value decomposition (SVD) method for soft X-ray emission and for electron cyclotron emission (ECE), the coupling spatial structures and coupling process between these two modes are analyzed in detail. The results of SVD for ECE reveal that the phase difference between these two modes equals to zero. This is consistent with the perfect coupling condition. Finally, performing statistical analysis of r _1/1, ξ _1/1 and w 2/1, we find that r _1/1 more accurately represents the coupling strength than ξ _1/1, and r _1/1 is also strongly related to the (2,1) NTM triggering, where r 1/1 is the width of (1,1) internal mode, ξ _1/1 is the perturbed amplitude of (1,1) internal mode, and w 2/1 denotes the magnetic island width of (2,1) NTM.