Electron Temperature Fluctuations in the Core of High-Performance DIII-D Plasmas

Electron temperature fluctuations have been measured for the first time in the core of high-performance, neutral-beam-heated DIII-D plasmas. Simultaneous local characterization of temperature and density fluctuations presents an opportunity to challenge theoretical/simulation predictions. Data from long-duration quiescent H-mode plasmas indicate that, at $r/a$=0.75, \underline {normalized} fluctuation levels are reduced by a factor of 5 below L-mode levels, with a detectability limit of $\le $0.25{\%}. In these QH-mode plasmas, the \underline {absolute} temperature fluctuation amplitude is observed to decrease by a factor of 2, correlating with increasing electron temperatures and improved electron thermal confinement. Temperature fluctuation levels and frequency spectra, $k_{\theta}\rho_{s}\le $0.5, are determined via correlation electron cyclotron emission radiometry [1]. In L-mode, temperature fluctuations (20$