Appearance of a low-frequency turbulence feature during saturated ohmic confinement plasma discharges

A low-frequency turbulence feature appears in high-density ohmically heated plasma discharges in the DIII-D tokamak in which the ion temperature gradient (ITG) mode is predicted to be unstable. The feature is observed only when the density is greater than the linear ohmic confinement saturation density. Gyrokinetic stability calculations indicate that the ITG mode frequency is comparable to the measured frequency, the wavenumber measured is comparable to that predicted for the ITG mode, and the linear growth rate is significantly greater in the high-density regime.