Studies of Electron Temperature Fluctuations in the Core of Alcator C-Mod Plasmas via Correlation ECE

A correlation electron cyclotron emission (CECE) diagnostic has been designed and installed at the Alcator C-Mod tokamak to measure long wavelength fluctuations in electron temperature [C. Sung, this conference, C-Mod oral session]. It is important to characterize turbulent fluctuations in the plasma in order to better understand and predict transport, since the cross-magnetic field transport of particles and energy in fusion plasmas exceeds the values predicted by neoclassical theory. The first electron temperature fluctuation data collected from Alcator C-Mod ohmic plasmas has shown that as the ohmic confinement regime transitions from Linear Ohmic Confinement (LOC) to Saturated Ohmic Confinement (SOC) there is a decrease in the core electron temperature fluctuation level. The edge electron temperature fluctuations are similar between the two modes, suggesting that mainly the core turbulence characteristics change when there is a shift between LOC and SOC regimes. In both ohmic and ICRH plasmas, the measured spectrum is seen to broaden in response to increases in plasma rotation; and fluctuation level increases with radius. A description of the C-Mod CECE diagnostic will be presented, along with the initial measurements of turbulent electron temperature fluctuations.