The non-linear evolution of the tearing mode in electromagnetic turbulence using gyrokinetic simulations

TL;DR

This study uses gyrokinetic simulations to analyze how electromagnetic turbulence influences the non-linear evolution of magnetic islands, revealing turbulence's role in seeding, modifying growth, and affecting rotation, especially at different plasma beta levels.

Contribution

It demonstrates the impact of electromagnetic turbulence on magnetic island evolution, including seeding, growth rates, and rotation, using self-consistent gyrokinetic simulations.

Findings

Turbulence seeds magnetic islands and bypasses linear growth.

Island growth depends on plasma beta and pressure gradients.

Turbulence alters island rotation direction and speed.

Abstract

The non-linear evolution of a magnetic island is studied using the Vlasov gyro-kinetic code GKW. The interaction of electromagnetic turbulence with a self-consistently growing magnetic island, generated by a tearing unstable $\Delta' > 0$ current profile, is considered. The turbulence is able to seed the magnetic island and bypass the linear growth phase by generating structures that are approximately an ion gyro-radius in width. The non-linear evolution of the island width and its rotation frequency, after this seeding phase, is found to be modified and is dependent on the value of the plasma beta and equilibrium pressure gradients. At low values of beta the island evolves largely independent of the turbulence, while at higher values the interaction has a dramatic effect on island growth, causing the island to grow exponentially at the growth rate of its linear phase, even though the island is larger than linear theory validity. The turbulence forces the island to rotate in the ion-diamagnetic direction as opposed to the electron diamagnetic direction in which it rotates when no turbulence is present. In addition, it is found that the mode rotation slows as the island grows in size.