Ion Thermal Turbulence Measurements with UF-CHERS in Plasmas with Electron Cyclotron Heating and Impurity Injection

In plasmas with electron cyclotron heating (ECH) confinement degradation is observed as T_e/T_i increases. Simultaneous measurements of electron density (via BES, k_perp<3 cm^-1; reflectometer, k_perp<6 cm^-1; DBS, k_perp~3-6 cm^-1; & mm-wave backscattering, k_r~35 cm^-1) indicate excitation of high-k fluctuations (k_perp≥10 cm^-1) & low-k electron temperature fluctuations (CECE, k_perp<1 cm^-1) that propagate in the electron diamagnetic direction. However, these measurements do not explain increased ion energy transport (ion modes wavenumber: k_perp≤3 cm^-1). In a recent L-mode experiment, ion fluctuations between 0.55≤ρ≤0.85 at near-unity T_e/T_i was obtained with the Ultra Fast Charge Exchange Recombination Spectroscopy (UF-CHERS) diagnostic on DIII-D. Initial analysis showed increased T_i & v_φ fluctuations when ECH was added to neutral beam injection (NBI) plasmas, compared to NBI-only plasmas. Impurities were injected during ECH to mitigate confinement deterioration & to study the mechanisms behind the reduced turbulence in radiative improved (RI-mode) plasmas. Impurity injection led to partial confinement recovery & reproduced RI-mode results (i.e. increased τ_E). Further analysis will be presented.