Multi-Scale Interactions between Global Tearing Modes and Trapped Electron Modes

Interactions between tearing modes (TMs) and small-scale instabilities and turbulence, particularly in reversed-field pinches (RFPs) where these instabilities coexist, can alter the saturation mechanism and increase transport. Understanding their interactions has been hindered by limitations in previous modeling of global TMs in the gyrokinetic code GENE. Correct modeling is accomplished by implementing a shifted Maxwellian distribution into the global version of GENE. The modified code is benchmarked against ORB5, GKW, a fluid model, and theory through parameter scans, demonstrating good agreement. Linear simulations of an MST RFP non-reversed discharge provide insights into TM structure, growth rate, and frequency. Collisionality scans confirm destabilization consistent with theoretical predictions. Linear analysis reveals that TMs predominantly occur in the plasma core, with toroidal mode number n<35, while TEMs reside near the plasma edge, with 35<n<250. TM saturation is achieved by modes in the core coupling to smaller-scale stable TMs close to the edge, allowing interactions with microinstabilities. The multi-scale interactions of TMs with TEMs are explored, including the degradation of zonal flows by TMs and the resulting increase in TEM transport. This study informs the understanding of the influence of large-scale magnetic perturbations on small-scale instabilities, and vice versa, in tokamak plasmas.