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arXiv · 2408.00180

First Access to ELM-free Negative Triangularity at Low Aspect Ratio

A. O. Nelson·C. Vincent·H. Anand·J. Lovell·J. F. Parisi·H. S. Wilson·K. Imada·W. P. Wehner·M. Kochan·S. Blackmore·G. McArdle·S. Guizzo·L. Rondini·S. Freiberger·C. Paz-Soldan
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Abstract

A plasma scenario with negative triangularity (NT) shaping is achieved on MAST-U for the first time. While edge localized modes (ELMs) are eventually suppressed as the triangularity is decreased below $\delta$ < -0.06, an extended period of H-mode operation with Type-III ELMs is sustained at less negative $\delta$ even through access to the second stability region for ideal ballooning modes is closed. This documents a qualitative difference from the ELM-free access conditions documented in NT scenarios on conventional aspect ratio machines. The electron temperature at the pedestal top drops across the transition to ELM-free operation, but a steady rise in core temperature as $\delta$ is decreased allows for similar normalized beta in the ELM-free NT and H-mode positive triangularity shapes.

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A. O. Nelson, C. Vincent, H. Anand, J. Lovell, J. F. Parisi, H. S. Wilson, K. Imada, W. P. Wehner, M. Kochan, S. Blackmore, G. McArdle, S. Guizzo, L. Rondini, S. Freiberger, C. Paz-Soldan. 2024-07-31. First Access to ELM-free Negative Triangularity at Low Aspect Ratio. https://arxiv.org/abs/2408.00180

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