Gyrokinetic Investigations of Microinstabilities, Turbulence, and Transport in MST during QSH Operation

Recent experiments on the Madison Symmetric Torus (MST), operating in Quasi-Single-Helicity, observed high frequency fluctuations in the magnetic field that may be attributable to microturbulence activity. This project primarily concerns itself with local gyrokinetic analysis of linear instabilities and nonlinear transport associated with those experiments. Linear simulations are conducted at a variety of radial locations which are broadly categorized as either "inner" or "outer" regions, which differ in dominating gradients and magnetic geometry. Linear analysis identifies ion temperature gradient as the dominant instability in the inner region and gradient-driven-TEM in the outer region. Nonlinear analysis of the outer region reveals transport levels that are very sensitive to radial magnetic fluctuations (used to model residual tearing effects in MST) that modify and degrade zonal flows. Features of turbulence and transport and their variation with these magnetic perturbations and driving gradients are discussed. Comparisons between simulation results and experimental measurements are also discussed.