Gyrokinetic Study of the Interchange Instability and Associated Turbulence in Differentially Rotating Plasmas*

It is known that differential rotation is able to suppress certain linear instabilities in plasmas. However, numerical studies have demonstrated that even in the absence of unstable eigenmodes, time varying sub-critical fluctuations can still drive turbulence. This hinders the ability of the rotation in suppressing the instabilities as well as being a cause of turbulent heat transport which prevents the plasma from reaching the necessary high temperatures required to sustain the fusion reaction.

A previous study examined time-dependent electrostatic fluctuations which resulted from the ion temperature gradient (ITG) and parallel velocity gradient (PVG) instabilities, in the scenario of a shearing box with a uniform magnetic field, using the framework of gyrokinetics [1]. Despite having no initial unstable modes, it was demonstrated that some stable modes could still be amplified transiently, resulting in unwanted turbulence.

We propose to extend the study to investigate fluctuations that arise from the interchange instability. Previous work done on this instability in the presence of flow shear was investigate in the framework of MHD [2–4], for which we would like to apply the framework of gyrokinetics to explore further. We also intend to test any obtained results for the amplification exponent numerically with known gyrokinetic codes.