Self-consistent interaction of the tearing mode with electromagnetic gyro-kinetic turbulence

Magnetic islands in a tokamak can lead to loss of confinement through a change of magnetic topology via magnetic reconnection. Their growth can lead to major disruptions of confined plasmas. As a matter of fact the tearing mode and specifically the neoclassical tearing mode (NTM) is expected to set the beta limit in a reactor. Early in their evolution, islands can be very narrow and thus comparable to turbulent length scale and consequently, their evolution should not be considered independent of each other. The evolution of the tearing mode and its multi-scale interaction with turbulence is studied for the first time in the three dimensional, toroidal framework utilising the state-of-the-art global, gyro-kinetic, turbulence code, GKW [1] utilising realistic fusion plasma parameters. The linear tearing mode is benchmarked with MHD theory and new findings presented [2]. Turbulence is shown to be critical to the onset and development of the tearing mode, affecting its growth and rotation [3]. Turbulent fluctuations do not destroy the growing island early in its development, in fact, nonlinear interactions provide an initial island structure which then maintains a coherent form as it grows. The islands rotation frequency is determined by nonlinear interactions between it and the turbulence. When present, turbulence has the effect of rotating the island in the ion-diamagnetic direction while an island dissociated from turbulence naturally rotates in the electron direction. In the presence of turbulence the seeded island grows at the linear rate even though the it 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 turbulent modification of the electrostatic field in and around the island greatly affects the size of the singular layer width, and the island is seen to grow at the linear rate even though the island is significantly wider than the singular layer width. The layer width is the maximum island size at which linear theory is usually considered valid. [1] Peeters AG, Camenen Y, Casson FJ, Hornsby WA, Snodin AP and Strintzi D, and Szepesi G, 2009 Comp. Phys. Comm. 18