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 , 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.
This paper reports the first achievement of a plasma scenario with negative triangularity (NT) shaping on the MAST-U device. While edge localized modes (ELMs) are eventually suppressed as the triangularity is decreased, an extended period of H-mode operation with Type-III ELMs is sustained at less negative triangularity. The electron temperature at the pedestal top drops across the transition to ELM-free operation, but a steady rise in core temperature as triangularity is decreased allows for similar normalized beta in the ELM-free NT and H-mode positive triangularity shapes.