Edge particle transport reduction via MHD coupling in highdensity discharges on J-TEXT

Mode coupling is commonly observed in density-limit experiments and is generally associated with magnetic stochasticity and confinement degradation. In contrast to this conventional picture, experiments on the J-TEXT tokamak reveal that toroidal coupling between the core m/n=1/1 mode and the edge 2/1 tearing mode can lead to a transient edge particle transport reduction. During the coupling phase, phase locking between the two modes modifies the edge density profile and steepens the local density gradient. The enhanced gradient strengthens the drive for edge turbulence. Fluctuation analysis indicates that the dominant edge microturbulence exhibits characteristics consistent with trapped electron modes (TEM). The strengthened TEM turbulence nonlinearly enhances the geodesic acoustic mode (GAM) through three-wave interactions. The enhanced GAM shear subsequently suppresses the turbulence intensity and reduces radial particle transport, leading to a temporary edge particle transport reduction. Despite this transient stabilization mechanism induced by mode coupling, the density-limit disruption is ultimately triggered by the collapse of zonal flows. These results highlight the complex multi-scale interactions between macroscopic MHD activity and microscopic turbulence in high-density plasmas.