Kinetic-ballooning-bifurcation in tokamak pedestals across shaping and aspect-ratio
J. F. Parisi, A. Nelson, Rahul Gaur, S. Kaye, F. I. Parra, J.W. Berkery, K. Barada, C. Clauser, A. J. Creely, A. Diallo, W. Guttenfelder, J. W. Hughes, L. A. Kogan, A. Kleiner, A.Q. Kuang, M. Lampert, Tanmay Macwan, J. Ménard, M.A. Miller
Abstract
We use a new gyrokinetic threshold model to predict a bifurcation in tokamak pedestal width-height scalings that depends strongly on plasma shaping and aspect-ratio. The bifurcation arises from the first and second stability properties of kinetic-ballooning-modes that yields wide and narrow pedestal branches, expanding the space of accessible pedestal widths and heights. The wide branch offers potential for edge-localized-mode-free pedestals with high core pressure. For negative triangularity, low-aspect-ratio configurations are predicted to give steeper pedestals than conventional-aspect-ratio. Both wide and narrow branches have been attained in tokamak experiments.