Kinetic-Ballooning-Limited Pedestals in Spherical Tokamak Plasmas

• Published in: arXiv.org
• Main Authors: Parisi, J F, Guttenfelder, W, Nelson, A O, Gaur, R, Kleiner, A, Lampert, M, Avdeeva, G, Berkery, J W, Clauser, C, Curie, M, Diallo, A, Dorland, W, Kaye, S M, McClenaghan, J, Parra, F I
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 07.04.2024
• Subjects: Height; Low aspect ratio; Magnetohydrodynamic stability; Physics - Plasma Physics; Spherical plasmas; Temperature profiles; Tokamak devices
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2308.05238

A theoretical model is presented that for the first time matches experimental measurements of the pedestal width-height Diallo scaling in the low-aspect-ratio high-\(\beta\) tokamak NSTX. Combining linear gyrokinetics with self-consistent pedestal equilibrium variation, kinetic-ballooning, rather than ideal-ballooning plasma instability, is shown to limit achievable confinement in spherical tokamak pedestals. Simulations are used to find the novel Gyrokinetic Critical Pedestal constraint, which determines the steepest pressure profile a pedestal can sustain subject to gyrokinetic instability. Gyrokinetic width-height scaling expressions for NSTX pedestals with varying density and temperature profiles are obtained. These scalings for spherical tokamaks depart significantly from that of conventional aspect ratio tokamaks.