2D Measurements of TEM Structure at Varying Driven Toroidal Rotation on DIII-D

The first experimental 2D mapping of drift modes, trapped electron mode (TEM) spatial evolution, $T_e$ fluctuation levels, and dispersion relations are achieved using electron cyclotron emission imaging (ECEI) in a regime far from ITG parameter space in DIII-D. Linear gyrokinetic simulations with the GEM code find that the TEM is most unstable in the parameter regimes studied ($a/L_n=1.27$, $a/L_{Ti}=1.9$, $a/L_{Te}=3.3$), and exhibit a similar real frequency and eigenmode structure to that observed with ECEI. Measurements are made in L-mode discharges with neutral beam and electron cyclotron waves at fixed heating power over a range of driven toroidal rotation rates. 2D maps of the mode structure are determined using correlation techniques, and dispersion plots are constructed from the cross-phase and cross-spectral power. For different levels of NBI momentum input, $T_e$ fluctuation levels measured over a range of poloidal wavenumbers ($\sim$0.5\%, up to 200 kHz) decrease with increasing imposed toroidal rotation, which may be related to local shearing rates.