Suppression of first-wall interaction in negative triangularity plasmas on TCV

Magnetically confined fusion plasmas with negative triangularity (delta) exhibit greater L-mode confinement than with positive delta. Recent experiments in the TCV and DIII-D tokamaks have correlated the confinement improvement to a reduction of fluctuations within the plasma core. We report on fluctuation measurements in the scrape-off layer (SOL) for -0.61 < delta < +0.64 in limited and diverted ohmic L-mode plasmas; these reveal a strong reduction in SOL fluctuation amplitudes at delta less than or similar to -0.25, and, surprisingly, an almost full suppression of plasma interaction with the main-chamber first-wall, which could have important implications for the prospects of using negative delta plasmas as a reactor solution. An exploration of several physical mechanisms suggests that a reduced connection length-intrinsic to negative delta plasmas-plays a critical role in the origin of this phenomenon.

Automated summary

Recent experiments in tokamaks have shown that magnetically confined fusion plasmas with negative triangularity exhibit better confinement compared to those with positive triangularity. This improvement in confinement may be attributed to a reduction in fluctuations within the plasma core. Furthermore, measurements in the scrape-off layer (SOL) have revealed a strong reduction in fluctuation amplitudes in plasmas with negative triangularity, indicating almost complete suppression of plasma interaction with the main-chamber first-wall.