Kinetic-Ballooning-Bifurcation in Tokamak Pedestals Across Shaping and Aspect-Ratio

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.

7 pages, 7 figures

References in corpus (4)

• Robust avoidance of edge-localized modes alongside gradient formation in the negative triangularity tokamak edge
• H-mode inhibition in negative triangularity tokamak reactor plasmas
• Simultaneous access to high normalized current, pressure, density, and confinement in strongly-shaped diverted negative triangularity plasmas
• Kinetic-Ballooning-Limited Pedestals in Spherical Tokamak Plasmas