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 a nd cross-field ion thermal transport reduced. Fully saturated turbulence in the range 0.1 less than or equal to k(perpendicular to)rho(s) less than or equal to 0.6 is measured at rho = 0.7 and exhibits a factor of 5 reduction in total power after neon injection, with almost complete suppression for k(perpendicular to)rho(s) > 0.35. These observations are consistent with a reduction in the calculated linear growth rate fur k(perpendicular to)rho(s ) > 0.5 and an increase in the measured E x B flow shearing rate.