Investigating the Role of Turbulence-driven Reynolds Stress in the Generation of Intrinsic Rotation in DIII-D

The turbulence-driven poloidal and toroidal Reynolds stress is directly determined from measurements of correlated density, poloidal and toroidal velocity fluctuations in DIII-D. A toroidal rotation drive is observed at the plasma edge, and changes in this drive are consistent with changes in the rotation profile. The radial gradient of turbulence-driven Reynolds stress is predicted to generate intrinsic torque through symmetry breaking mechanisms. The Reynolds Stress was measured in low density L-mode plasmas using BES and UF-CHERS with torque-controlled neutral beam injection to achieve a near-zero toroidal rotation profile, which minimizes the diffusive and convective contributions to momentum flux and extracts the residual stress. Velocimetry is applied to 2D BES data to derive radial and poloidal velocity fluctuations. Toroidal velocity fluctuations are measured by UF-CHERS and cross-correlated with BES. ECH changes the edge toroidal rotation from the counter-Ip to co-Ip direction and shifts poloidal rotation toward electron diamagnetic direction. Multi-field cross-spectra analysis shows turbulence changes from electron-dominated to ion-dominated. The q₉₅ and T_e/T_i dependence of intrinsic rotation are measured and compared with theoretical predictions.