First access to ELM-free negative triangularity at low aspect ratio
/ Authors
A. O. Nelson, C. Vincent, H. Anand, J. Lovell, J. Parisi, H. S. Wilson, K. Imada, W. Wehner, M. Kochan, S. Blackmore
and 5 more authors
G. McArdle, S. Guizzo, L. Rondini, S. Freiberger, C. Paz-Soldan
/ 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 δ≲−0.06, an extended period of H-mode operation with Type-III ELMs is sustained at less negative δ 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 δ is decreased allows for similar normalized β in the ELM-free NT and H-mode positive triangularity shapes.
Journal: Nuclear Fusion