Observation of Reduced Electron-Temperature Fluctuations in the Core of H-Mode Plasmas

摘要

Core electron-temperature fluctuations [0.5% ≤ T_e/T_e ≤ 2%, k_θ ρ_s ≤ 0.3 in neutral-beam-heated low confinement-mode (L-mode) plasmas] are observed to decrease by at least a factor of 4 in standard and quiescent high-confinement-mode (H-mode and QH-mode) regimes in the DⅢ-D tokamak (r/a = 0.7). These fluctuations are attributed to ion temperature gradient (ITG) modes stabilized by rotational shear at the H-mode transition. The simultaneous reduction in electron heat diffusivity (X_e~(QH)/X_e~L < 0.25) suggests that T_e fluctuations can contribute significantly to L-mode electron heat transport.