Gyrokinetic Simulations of Global Tearing Modes and Multi-Scale Interaction with Micro-Turbulence

The existence of macro-scale tearing modes during plasma operations on the Madison Symmetric Torus, a reversed-field pinch (RFP), even in improved-confinement regimes has significant impacts on micro-scale instabilities and turbulent transport. This observation has motivated the modeling of the interplay of fluctuations at different scales using the gyrokinetic code GENE. Previous work modeled tearing-mode activity by implementing current-gradient drive as part of the fluctuating distribution function, coupled nonlinearly with turbulence fluctuations and zonal flows. To be able to more realistically model tearing modes, a shifted-Maxwellian distribution has been implemented in GENE for global simulations, consistent with the q-profile. The implementation has been benchmarked against linear flux-tube simulations through scans over plasma parameters. Additionally, comparisons are shown with global tearing results from other gyrokinetic and gyrofluid codes. Tearing modes in the RFP are then simulated, analyzed, and used to study multi-scale interactions with gyroradius-scale instabilities.