Gyrokinetic Analysis of KBM and MTM Behavior Across Stability Boundaries in the H-Mode Pedestal

The evolution of electromagnetic pedestal micro-instabilities during the inter-ELM cycle is examined using the gyrokinetic code GENE, with a focus on kinetic ballooning modes (KBMs) and microtearing modes (MTMs). For KBMs, major questions include the nature of the transition from KBM instability towards the ideal ballooning limit, and the role of first and second stability boundaries. New insights into the properties and the role of MTMs are also discussed. Notably, MTMs acquire some characteristics that are typically associated with KBMs during the inter-ELM cycle, including: (1) smaller parallel electric field fluctuations (i.e., cancelation between the electrostatic potential and the magnetic vector potential terms); and (2) gradient drive from both the temperature and density gradients (i.e., pressure gradient drive). Moreover, the ratio of particle to thermal diffusivity increases. Nevertheless, MTMs retain key features of conventional behavior: (1) thermal transport primarily driven by magnetic fluctuations, and (2) mode frequencies near the electron diamagnetic direction. Together, these features suggest that MTMs can impose a pressure gradient limit during the inter-ELM phase, while also accounting for observed high-frequency magnetic fluctuations in the pedestal. These findings are explored in the context of several experimental scenarios.