2D Core Turbulence Properties on DIII-D

Quantitative measurements of the inherently 2D turbulence characteristics in magnetized plasmas are compared with nonlinear simulation. This comparison substantiates key aspects of the $E\times B$ shear model of turbulence suppression that explains enhanced confinement. The critical dynamics underlying turbulent transport occur in the plane perpendicular to the magnetic field $(k_\| \ll k_\perp)$. These localized long-wavelength $(k_\perp \rho_i < 1)$ density turbulence measurements are obtained in the core $(0.3 < r/a < 0.9)$ of DIII-D L-mode plasmas with a 2D rectangular array of Beam Emission Spectroscopy channels. Radial and poloidal correlation lengths are found to scale with the ion gyroradius and demonstrate a poloidally elongated eddy structure. $S(k_r,k_\theta )$ spectra are compared with GYRO simulations: key features (wavenumber peak, correlation lengths) compare well, however the simulations indicate a sheared eddy structure at outer radii that is not observed. Measured local decorrelation and shearing rates are also compared.