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arXiv · 2505.09101

Turbulent Transport-Limited Pedestals in Tokamaks

J. F. Parisi·D. R. Hatch·P. Y. Li·J. W. Berkery·A. O. Nelson·S. M. Kaye·K. Imada·M. Lampert
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Abstract

H-mode operation of tokamak fusion plasmas free of dangerous Type 1 edge-localized-modes (ELMs) requires a non-ELM mechanism for saturating the edge pedestal growth. One possible mechanism is turbulent transport. We introduce a transport threshold model to find pedestal width-height scalings for turbulent transport-limited pedestals. The model is applied to electron heat transport resulting from electron-temperature-gradient (ETG) turbulence. The width-height scalings are highly sensitive to the relative contribution of density and temperature to the pedestal pressure. Pressure that builds up mainly through temperature is more likely to be transport-limited, and hence ELM-free. A relative radial inward shift of the temperature to density pedestal location is also more likely to transport-limit the pedestal. A second constraint such as flow shear is required to saturate pedestal growth. We also calculate width-height transport scalings resulting from particle and heat transport arising from ETG and kinetic-ballooning-mode turbulence. Comparisons are performed for ELMy and ELM-free experiments in MAST-U, NSTX, and DIII-D. This is a first step towards a pedestal width-height scaling for transport-limited ELM-free pedestals.

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J. F. Parisi, D. R. Hatch, P. Y. Li, J. W. Berkery, A. O. Nelson, S. M. Kaye, K. Imada, M. Lampert. 2025-05-14. Turbulent Transport-Limited Pedestals in Tokamaks. https://arxiv.org/abs/2505.09101

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