Generation of Intrinsic Rotation due to Turbulence by Investigating Rotation Reversal Layers in the HL-2A Tokamak*

The mechanisms that drive toroidal rotation in torque-free tokamak plasmas have not been clearly identified, but the generation of intrinsic torque by turbulence via Reynolds Stress is a leading theoretical mechanism. Beam Emission Spectroscopy (BES) results from previous experiments on HL-2A L-mode plasmas exhibit a poloidal velocity reversal at $\rho \approx 0.7$. The poloidal velocity switches direction across the profile despite the only external momentum being input from a co-current neutral beam, suggesting that either the momentum is redistributed through transport, or a significant amount of intrinsic rotation is generated. To investigate this velocity reversal, experiments with varying temperature and q profiles will be performed and 2D density fluctuation data will be measured with BES. Spectral and correlation analysis are applied to derive spatiotemporal characteristics of turbulence. Velocimetry analysis is applied to obtain a 2D fluctuating velocity field and the derived Reynolds Stress. These BES results combined with other diagnostics will be used to predict the dominant instabilities, estimate the turbulent transport, and derive the intrinsic torque.