Gyrokinetic simulations of turbulence-driven magnetic islands in toroidal geometry

We report a universal mechanism for turbulence-driven magnetic islands in fusion plasmas that operates independently of the parity of the destabilizing micro-instability. Using gyrokinetic simulations of a linearly stable tearing mode in a large-aspect-ratio toroidal geometry under collisionless conditions, we demonstrate that micro-instabilities generate an E×B flow that is consistent with magnetic field line reconnection. This process forms multiple small-scale islands along the resonant surface, which interact non-linearly and eventually coalesce into large-scale magnetic islands. These islands are capable of significantly flattening the equilibrium profile across the island O-points and can potentially act as a seed for further neoclassical growth. Notably, the mechanism operates independently of the parity of the destabilizing micro-instability.