Interaction between a magnetic island and turbulence

Interaction between a magnetic island and turbulence has been intensively studied in recent years with advance of plasma diagnostics in various plasma experiment devices such as LHD, J-TEXT, TJ-II, DIII-D, KSTAR, and HL-2A. Simultaneous measurements of plasma turbulence and pressure and flow profiles have provided a comprehensive understanding of their interaction. Experiments found that plasma turbulence becomes strongly inhomogeneous around a magnetic island due to the combined effect of the pressure gradient (driver) and flow shear (regulator) modifications by the island. Those experimental observations are consistent with gyrokinetic simulations results obtained using GKW, GTC, GENE, and gKPSP, and imply the limitation of conventional understanding of the island evolution. The effect of inhomogeneous and nonlinear characteristic of plasma turbulence would complicate the island evolution which depends on ambient transport physics. In addition, more complex turbulence phenomena which can affect the island stability in fusion plasmas as well as the underlying magnetic reconnection process have been suggested from theoretical and numerical studies. Some of them whose experimental evidences are being accumulated from both fusion and laboratory plasmas are introduced; turbulence spreading, nonlinear mode coupling, turbulence driven flow, and turbulent magnetic reconnection. They can either suppress or facilitate the island growth. Since turbulence spreading and turbulent magnetic reconnection can be a universal feature of magnetized plasmas, their observations would provide general physical insights into the island turbulence dynamics.