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

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.我们采用一种新型回旋动理学（gyrokinetic）阈值模型，针对托卡马克（tokamak）基座宽度-高度定标关系中的分岔现象开展预测，该分岔强烈依赖于等离子体塑形与纵横比（aspect-ratio）。该分岔源于动力学气球模（kinetic-ballooning-modes）的第一与第二稳定性特性，由此催生宽、窄两类基座分支，拓展了可实现的基座宽度与高度参数空间。宽基座分支有望实现兼具高芯部压强的无边缘局域模（edge-localized-mode）基座。针对负三角性（negative triangularity）等离子体，预测结果表明低纵横比位形可产生较常规纵横比位形更为陡峭的基座。目前托卡马克实验中已成功观测到宽、窄两类基座分支。