Spatially resolved measurements of two-dimensional turbulent structures in DIII-D plasmas

Two-dimensional observations of spatially coherent electron temperature fluctuations at drift-wave scales (k ∼ 1 cm−1) have been made using the electron cyclotron emission imaging diagnostic on the DIII-D tokamak. These measurements enable the extraction of spectral properties, including poloidal dispersion relations. Temperature fluctuation levels are found to be Te/⟨Te⟩=1.2%, and the phase velocity of the fluctuations is found to be constant across frequencies, consistent with modes having real frequencies low compared to the rotation-induced Doppler shifts. Comparisons with radially global linear gyrokinetic simulations suggest that the observed modes may be trapped electron modes.