Exploring the Edge/SOL Fluctuations in Negative Triangularity Plasmas on TCV*

Magnetically confined fusion plasmas with a negative triangularity (δ) core shape are known to feature enhanced confinement as compared to standard, D-shaped plasmas. Recently, based on Gas Puff Imaging (GPI) and probe measurements, sufficiently negative δ (δ≲-0.25) plasmas on TCV were also found to feature a complete suppression of first-wall interactions [1]. Reasons for this suppression, which could have important implications for the prospects of negative δ as a reactor solution, were explored, pointing towards the role of reduced connection length intrinsic to negative δ. This work is currently being extended in the upcoming experiment, from the previous range of Greenwald fraction of 0.13-0.42 towards the density limit and edge/SOL fluctuations, and their dependence on δ are explored with GPI. For the analysis of the GPI images, a new machine learning model is used for tracking the position and shape of filaments in GPI images, frame by frame, so that the filament statistics can be used to characterize the edge/SOL turbulence by the intermittency of filaments and other key parameters [2].

[1] W. Han et al 2021 Nucl. Fusion 61 034003

[2] O. E. Garcia et al 2017 Phys. Plasmas 020704