Measurements of fluctuation link to low rotation plasmas in the DIII-D tokamak

Fusion reactor plasmas are expected to experience low rotation due to a lack of external momentum sources. Understanding fluctuations under this condition is crucial to predict and optimize fusion performance. A class of ion-scale electron density and magnetic fluctuations is observed in various low-rotation plasmas, including but not limited to the ITER-baseline scenario, wide-pedestal quiescent H-mode, and small edge-localized-modes (ELMs) H-mode, using the line-averaged radial-interferometer-polarimeter (RIP) diagnostic in the DIII-D tokamak. These fluctuations range from 200 to 900 kHz and can be broadband or quasi-coherent in frequency. A defining feature of the fluctuations is that RIP-measured magnetic fluctuation amplitudes are near the measurement noise floor but density fluctuation amplitudes are not. The ratio of magnetic-to-density fluctuation amplitude can be 0.2 or lower, implying a drift-wave origin of the fluctuations [1]. Analysis of the fluctuations and correlations with plasma parameters, such as auxiliary heating power, injected neutral-beam torque, and plasma pressure, will be presented.

[1] Jie Chen et al., submitted to Nuclear Fusion, “Turbulence link to L-mode, I-mode, and H-mode confinement in the DIII-D tokamak”