Nonlocal phase coupling in turbulence spreading across the magnetic island

Abstract

We study the nonlocal phase coupling during turbulence spreading across the magnetic island. It is found that the coherent convective cells (sharing similar features to quasi-coherent mode in experiment) on both sides of the O-point boundary are accumulated during the island formation. The phase entrainment of the convective cells on the turbulence both in the inner and the outer regions of the magnetic island sets up a nonlocal phase coupling channel and leads to a fast spreading of the outer turbulence into the magnetic island by conquering the flow shear at the O-point boundary. This nonlocal coupling mechanism of turbulence spreading is analogous to a turbulence version of the well-known enhanced diffusion of passive scalars in laminar convective flows of neutral fluid system.