Jason Parisi (Princeton Plasma Physics Lab, Princeton, NJ)

"Pedestal Width-Height Scalings and Geometric Burn Control in Spherical Tokamaks"

Abstract: In the first part of this talk, I discuss the pedestal width-height scaling [0] for multiple tokamaks using a new kinetic ballooning mode (KBM) gyrokinetic threshold model [1]. At low aspect-ratio, we reproduce NSTX’s experimental linear pedestal width-height scaling for ELMy H-modes [2], overcoming previous issues with low aspect-ratio pedestal prediction [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. I discuss the effect of aspect-ratio and plasma shaping on width-height scalings, showing the dependence on various shaping parameters [5]. We also incorporate heat and particle transport physics into our stability model, showing how transport can change significantly near the KBM stability boundary [6].

In this second part of this talk, I discuss a new burn control scheme for tokamaks where the total fusion power is controlled by adjusting the plasma volume fraction that is packed into power dense regions. In an example spherical tokamak burning plasma, by modifying the plasma edge squareness the total fusion power is doubled at almost constant total plasma volume and fusion power density. Therefore, increased plasma squareness could be extremely beneficial to a fusion reactor and squareness control could be desirable for power load balancing. Experiments on NSTX have observed the impact of increased edge squareness on modified core plasma volume, highlighting the practical relevance of this approach.

[0] P.B. Snyder et al 2009 Phys. Plasmas 16, 056118
[1] J.F. Parisi et al 2023 arXiv:2308.05238
[2] A. Diallo et al 2011 Nucl. Fusion 51 103031
[3] R.J. Groebner et al 2013 Nucl. Fusion 53 093024
[4] S. Kruger et al 2022, PP11.00057, APS DPP Meeting
[5] J.F. Parisi et al 2024 Phys. Plasmas 31, 030702
[6] J.F. Parisi et al 2024 arXiv:2401.14260