This Physical Review Letters paper reports DIII-D observations in which toroidicity-induced Alfven eigenmodes suppress low-$k$ ion-temperature-gradient turbulence. Beam emission spectroscopy shows that turbulence mitigation starts as the dominant TAE departs from ordinary shear-Alfven polarization, followed by a transition to more discrete, higher-amplitude, radially localized modes. During full suppression, a narrow shear-flow layer forms with a shearing rate exceeding the turbulence decorrelation rate. The authors connect this sequence to an imbalance between Reynolds and Maxwell stress forces during nonlinear TAE evolution. The turbulence suppression is radially localized but correlates with improved thermal confinement, including electron-temperature and stored-energy changes. Alternative explanations such as fast-ion dilution and profile changes are examined and disfavored. The result provides direct experimental evidence for energetic-particle-mode control of microturbulence and suggests that externally driven edge Alfven spectra might be used to form transport barriers in future devices.
- Observed localized low-$k$ turbulence mitigation and suppression during nonlinear TAE evolution in DIII-D.
- Measured a shear-flow layer whose shearing rate exceeds the turbulence decorrelation rate.
- Linked turbulence reduction to Reynolds-Maxwell stress imbalance and altered TAE polarization.
- Connected the localized suppression to improved thermal-plasma confinement indicators.
- Excluded fast-ion dilution and profile-change explanations for the observed suppression phase.