EX/P5-35 Observation of Reduced Core Electron Temperature Fluctuations and Intermediate Wavenumber Density Fluctuations in H- and QH-mode Plasmas

In this paper, we report observations of reduced low-k core electron temperature and intermediate-k density fluctuations in H-mode and quiescent (QH)-mode. L-mode electron temperature fluctuation levels (0.5% ̃ T e /Te 2% for k s 0.5 as measured by correlation ECE (CECE) radiometry) are observed to decrease by at least a factor of four in H and QH-mode regimes in the DIII-D tokamak (r/a = 0.7). Recent results from DIII-D provide the first experimental evidence that, in addition, intermediate-scale turbulence (0.5 < k s 3) is also reduced promptly at the L-H transition. A 20%–30% prompt reduction (r/a > 0.7) has been found at the L-H transition in co-injected plasmas, with a larger decrease (~75%) observed near the pedestal top. Very substantial reductions have been observed in the core of counter-injected, low-density QHmode plasmas (r/a < 0.8) at the L-H transition, and suppression has been observed for r/a 0.5. Experimental results and linear stability calculations (using the TGLF trapped gyro-Landau fluid code) indicate that intermediate/small scale turbulence persists in H-mode at a reduced amplitude for r/a > 0.5 and may dominate residual anomalous electron heat transport in the QH-mode plasmas examined here.