7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

A gyrokinetic model for pedestal width-height scaling across aspect ratio
14J. F. Parisi, 1W. Guttenfelder, 2A. O. Nelson, 3R. Gaur, 1M. Lampert, 1A. Kleiner,G. Avdeeva, 1J. W. Berkery, 5C. Clauser, 1,3M. Curie, 1A. Diallo, 1S. M. Kaye, 4J. McClenaghan
12Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ, USA

Department of Applied Physics and Applied Mathematics, Columbia University, NY, USA
3Department of Physics, University of Maryland, College Park, MD, USA
45General Atomics, P.O. Box 85608, San Diego, CA, USA

MIT Plasma Science and Fusion Center, Cambridge, MA, USA
Email: jparisi@pppl.gov

We find the pedestal width-height scaling for multiple
tokamaks using a new kinetic ballooning mode (KBM)
gyrokinetic threshold model, GKPED. At tight aspectratio, GKPED reproduces NSTX’s experimental linear
pedestal width-height scaling for ELMy H-modes [1],overcoming previous issues with tight aspect ratiopedestal prediction [2]. We reproduce the square rootpedestal width-height scaling at regular aspect ratio forpreviously published DIII-D discharges [3]. Our model
uses EFIT-AI [4] to calculate global equilibria with selfconsistent bootstrap current and can be applied to any Hmode equilibria. For ELMy NSTX discharges, KBM
physics is needed to match the experimental data: we findthat infinite-n MHD stability overpredicts pedestalpressure. For regular aspect ratio, however, we find closer

Figure 1:NSTX Δped versus βP.ped KBM (GCP) scaling, ideal(BCP) scaling, and ELMy H-mode experimental points.

agreement between ideal and kinetic ballooning mode
width scalings. In addition to device-specific results, wereport 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 amaximum 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 ofpedestal stability and transport across tokamak equilibriaacross a range of operating space.
We combine linear local gyrokinetics with a selfconsistent variation of pedestal width Δped and height βP.pedto predict the critical pedestal scaling Δped=C(βP.ped)γ
across devices [7]. Our prediction imposes theGyrokinetic Critical Pedestal (GCP) pressure gradientconstraint, obtained from KBM stability. The KBM
critical gradient is always lower than the ideal mode,
whose stability we calculate to produce a Ballooning
Critical Pedestal (BCP) width constraint. For NSTX, theGCP gives Δped =0.33(βP.ped)0.99 and the BCP Δped
=0.18(βP.ped)0.99, shown in Fig. 1. The maximum βP.ped at
any given width also depends on how the pedestalpressure is varied, due to the bootstrap current’s
differential dependence on density and temperature
gradients [9]. We discuss transport implications of thedependence of pedestal width on density and temperature,and show pedestal scalings for additional tokamaks.
This work was supported by US Department of Energy
Contract No. DE-AC02- 09CH11466.
References:[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[7] P.B. Snyder et al 2004 Nucl. Fusion 44 320[8] P.B. Snyder et al 2009 Phys. Plasmas 16, 056118[9] O.Sauter and C. Angioni 1999 Phys. Plasmas 6, 2834