Impurity-Induced Suppression of Core Turbulence and Transport in the DIII-D Tokamak

Turbulence is significantly reduced in a tokamak plasma as a result of neon seeding of an $L$-mode discharge. Correspondingly, confinement is improved and cross-field ion thermal transport reduced. Fully saturated turbulence in the range $0.1\le k_{\perp }{\rho }_s\le 0.6$ is measured at $\rho =0.7\mathrm{}$ and exhibits a factor of 5 reduction in total power after neon injection, with almost complete suppression for $k_{\perp }{\rho }_s>0.35\mathrm{}$. These observations are consistent with a reduction in the calculated linear growth rate for $k_{\perp }{\rho }_s>0.5\mathrm{}$ and an increase in the measured $\mathbf{E}\times \mathbf{B}$ flow shearing rate.