Kinetic ballooning mode constraints for tokamak pedestals with varying aspect ratio and plasma shaping

We find the pedestal width-height scaling [0] for multiple tokamaks using a new kinetic ballooning mode (KBM) gyrokinetic threshold model. At tight aspect ratio, we reproduce NSTX’s experimental linear pedestal width-height scaling for ELMy H-modes [1], overcoming previous issues with tight aspect ratio pedestal prediction [2]. We reproduce the square root pedestal width-height scaling [0] at regular aspect ratio for previously published DIII-D discharges [3]. Our model uses EFIT-AI [4] to calculate global equilibria with self-consistent bootstrap current and can be applied to any H-mode equilibria. For ELMy NSTX discharges, KBM physics is needed to match the experimental data: we find that infinite-n MHD stability overpredicts pedestal pressure and underpredicts pedestal width. In addition to device-specific results, we report the effect of aspect ratio and plasma shaping on width-height scalings, showing the dependence on various shaping parameters. Combined with peeling ballooning mode (PBM) stability [5,6], our model will calculate a maximum inter-ELM pedestal width and height based on KBM and non-ideal PBM stability. This work is an important step towards a unified predictive capability of pedestal stability and transport for tokamak equilibria across a range of operating space.

This work was supported by US Department of Energy Contract No. DE-AC02- 09CH11466.

 

[0] P.B. Snyder et al 2009 Phys. Plasmas 16, 056118

[1] A. Diallo et al 2011 Nucl. Fusion 51 103031 

[2] R.J. Groebner et al 2013 Nucl. Fusion 53 093024 

[3] W. Guttenfelder et al 2021 Nucl. Fusion 61 056005

[4] S. Kruger et al 2022, PP11.00057, APS DPP Meeting

[5] A. Kleiner et al 2021 Nucl. Fusion 61 064002 

[6] A. Kleiner et al 2022 Nucl. Fusion 62 076018