Suppression of first-wall interaction in negative triangularity plasmas on TCV
W. Han, N. Offeddu, T. Golfinopoulos, C. Theiler, C.K. Tsui, J.A. Boedo, E. S. Marmar, the TCV Team
Abstract
Abstract Magnetically confined fusion plasmas with negative triangularity ( δ ) exhibit greater L-mode confinement than with positive δ . 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 < δ < +0.64 in limited and diverted ohmic L-mode plasmas; these reveal a strong reduction in SOL fluctuation amplitudes at δ ≲ −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 δ plasmas as a reactor solution. An exploration of several physical mechanisms suggests that a reduced connection length—intrinsic to negative δ plasmas—plays a critical role in the origin of this phenomenon.