Intrinsically Multi-Scale Microturbulence in a Stochastic Magnetic Field

Nowadays, due to the fact that resonant magnetic perturbation can raise the L-H power threshold, we need to reconcile good confinement with good power handling. To determine how stochastic magnetic fields affect L-H transition, it is essential to study their influence on the instability process such as the resistive interchange in this work. The highlight of this work is the appearance of microscopic convective cells when div J=0 is maintained at all scales. These small-scale convective cells can generate a turbulent viscosity and a turbulent diffusivity, which may explain RMP pump-out. By using method of averaging and quasi-linear theory, an integro-differential equation describing the evolution of the potential profile is obtained. From this equation, we can see small-scale convective cells can electrostatically scatter the large-scale resistive interchange mode in addition to the stochastic scattering of stochastic magnetic fields. As the large-scale mode is the drive of small-scale cells, micro and macro scales are thus connected. The modified growth rate of the large-scale convective cell and the turbulent viscosity are calculated by exploiting perturbation theory.