Studies of electron temperature fluctuations in the core of Alcator C-Mod plasmas via correlation electron cyclotron emission

Abstract

Transport in tokamak plasmas is higher than predicted by neoclassical theory; this anomalous transport is believed to be attributed to turbulent fluctuations. New Correlation Electron Cyclotron Emission (CECE) experiments on Alcator C-Mod show lower levels of electron temperature fluctuations in the saturated ohmic confinement (SOC) regime than in the linear ohmic confinement (LOC) regime, however the lineaveraged density fluctuation data collected from ohmic plasmas previously showed the opposite trends. The apparent contradiction is explained by a change in the dominant turbulence modes in each confinement regime. Linear stability analysis shows that the LOC regime is dominated by trapped electron mode (TEM) turbulence and the SOC regime is on the border between the ion temperature gradient (ITG) and TEM turbulence modes being dominant. It is reasonable to believe that the TEM turbulence mode drives electron temperature fluctuations, which explains the higher electron temperature fluctuation levels seen in the LOC regime compared to the SOC regime.