Frequency-Poloidal Wave Number Spectral Analysis of Turbulence in QH-mode plasmas Measured with BES on DIII-D

Quiescent H-mode (QH) is an ELM-free scenario with good energy confinement, constant density, and radiated power, with a pedestal localized electromagnetic mode (edge harmonic oscillation, EHO) providing continuous particle transport. The features and characteristics of QH-mode plasma turbulence in the wavenumber-frequency domain are crucial to understanding the mechanisms and dynamics of the enhanced particle transport. Frequency-wavenumber spectral analysis was applied to localized density fluctuation data measured with BES on DIII-D in the region of 0.8$\textless$\rho$\textless1.0. In the analysis, a Maximum Entropy Method is applied in the space domain, instead of an FFT, to estimate a well resolved \textit{k}-spectrum spectrum from truncated data. The fundamental frequency of the EHO was typically $\sim$10 kHz with long poloidal wavelength ($\textit{k}_\theta\sim0.02$ $cm^{-1}$), while broadband turbulence was observed in the range of 50–200 kHz with correlation lengths of a few cm. The broadband turbulence measured at ${\rho\sim0.9}$ was found to have poloidal phase velocity of $\sim10\hspace{1.1 mm}km/s$, which corresponds to the E$\times$B velocity.