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

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 le...

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Bibliographic Details
Published in:arXiv.org 2024-07
Main Authors: Nelson, A O, Vincent, C, Anand, H, Lovell, J, Parisi, J F, Wilson, H S, Imada, K, Wehner, W P, Kochan, M, Blackmore, S, McArdle, G, Guizzo, S, Rondini, L, Freiberger, S, Paz-Soldan, C
Format: Article
Language:English
Subjects:
Ballooning modes
Electron energy
Low aspect ratio
Online Access:Get full text
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Summary: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.
ISSN:2331-8422