Negative Triangularity (NT) plasmas have demonstrated robustly ELM-free high-performance operation and provide a unique testbed to study how plasma shaping affects turbulent transport. The Beam Emission Spectroscopy diagnostic provides localized 2D measurements of low-k () density fluctuations. In a sweep of upper triangularity at fixed power, H-mode access is suppressed and an NT-edge is observed. The turbulence amplitude () is shown to decrease by for ρ < 0.9 in the NT-edge phase as compared to the H-mode phase. Additionally, low-velocity edge modes below 70 kHz are suppressed by triangularity and the dominant mode propagating in the electron diamagnetic direction is seen to broaden in wavenumber space in the NT-edge phase. In a strong NT plasma (), low amplitude modes () propagating in the ion-diamagnetic direction with radially-poloidally symmetric eddy structure are identified for consistent with Ion Temperature Gradient turbulence. Modes consistent with Trapped Electron Mode turbulence are observed propagating in the electron-diamagnetic direction for with poloidally extended eddy structure and reduced amplitudes observed at the separatrix. The turbulence properties presented in this paper help validate our understanding of NT turbulence and help explain the improved confinement and unique edge features of NT plasmas.
This paper investigates how the shape of the plasma, specifically negative triangularity, affects turbulence and transport in fusion devices. The researchers used advanced diagnostics to measure fluctuations and found that negative triangularity can suppress certain turbulent modes, leading to improved confinement. These findings help us understand the complex relationship between plasma shaping and turbulence, which is crucial for designing high-performance fusion reactors.