On seed island generation and the non-linear self-consistent interaction of the tearing mode with electromagnetic gyro-kinetic turbulence

TL;DR

This study investigates how electromagnetic turbulence influences the formation and growth of magnetic islands in plasma, revealing that turbulence seeds islands that grow rapidly and maintain their structure despite stochastic effects.

Contribution

It demonstrates that electromagnetic turbulence can seed and accelerate magnetic island growth, maintaining linear mode structures even at large widths within a gyro-kinetic framework.

Findings

Turbulence seeds islands through nonlinear interactions.

Islands grow faster than linear rates initially.

Turbulence causes stochasticity and X-point breakdown.

Abstract

The multi-scale interaction of self-consistently driven magnetic islands with electromagnetic turbulence is studied within the three dimensional, toroidal gyro-kinetic framework. It can be seen that, even in the presence of electromagnetic turbulence the linear structure of the mode is retained. Turbulent fluctuations do not destroy the growing island early in its development, which then maintains a coherent form as it grows. The island is seeded by the electromagnetic turbulence fluctuations, which provide an initial island structure through nonlinear interactions and which grows at a rate significantly faster than the linear tearing growth rate. These island structures saturate at a width that is approximately $\rho_{i}$ in size. In the presence of turbulence the island then grows at the linear rate even though the island is significantly wider than the resonant layer width, a regime where the island is expected to grow at a significantly reduced non-linear rate. A large degree of stochastisation around the separatrix, and an almost complete break down of the X-point is seen. This significantly reduces the effective island width.