Analysis of turbulence diffusion and H-mode transition in conjunction with gyrocentre shift at the boundary of fusion devices

A new concept of turbulence transport and diffusion coefficient are derived from the microscopic ( is the localized electric field and B is the magnetic field) drifts at the boundary of fusion devices by characterization of the gyrocentre shift induced by the collisions among electrons, ions and neutrals. It is found that when the viscosity force of the ion–neutral collision is counted, Reynolds numbers of the poloidal ion flow in the vicinity of the tokamak separatrix vary over the critical value between turbulent and laminar flows depending on the plasma parameters such as temperature, neutral density and density fluctuation level, which explains the mechanism of the fast transition from the low confinement mode to the high confinement mode (L/H transition) for the examplar cases.