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arXiv · 2606.26362

Integrating Gyrokinetic Flux Predictions with Ideal MHD Stability Boundaries

J. McClenaghan·K. E. Thome·T. F. Neiser·J. Candy·F. D. Halpern·T. H. Osborne·S. Saarelma·the MAST-U team
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Abstract

Accurate prediction of pedestal height and width in tokamaks remains a critical issue as it strongly influences the predicted plasma performance of all future reactors. We present an integrated pedestal-stability workflow that combines equilibrium scans with magnetohydrodynamic (MHD) stability analysis using ELITE and GATO and gyrokinetic transport predictions using CGYRO/QLGYRO. The workflow reproduces the characteristic KBM first- and second-stability structure previously identified in gyrokinetic pedestal studies. Applied to spherical tokamaks (STs), the workflow shows good agreement with past studies when low-n peeling stability is included, emphasizing the importance of resolving low-n physics in ST pedestals. Extending the analysis to SPARC-like, high toroidal field plasmas, kinetic ballooning mode (KBM) and microtearing mode (MTM) heat fluxes are found to increase strongly with toroidal field, suggesting that access to the KBM second-stability region may become significantly more difficult in high toroidal field devices. Comparison with global ELITE finite-n analysis at SPARC parameters suggests that the H-mode pedestal lies in an intermediate regime bounded by local KBM second stability on one side and global finite-n ballooning instability on the other, consistent with the EPED picture once global effects are included

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J. McClenaghan, K. E. Thome, T. F. Neiser, J. Candy, F. D. Halpern, T. H. Osborne, S. Saarelma, the MAST-U team. 2026-06-24. Integrating Gyrokinetic Flux Predictions with Ideal MHD Stability Boundaries. https://arxiv.org/abs/2606.26362

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