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Description
The suppression of ion temperature gradient (ITG) turbulence by the nonlinear evolution of toroidicity-induced Alfvén eigenmodes (TAEs) is demonstrated in the DIII-D tokamak [1]. Systematic measurements of plasma parameters reveal that this phenomenon is characterized by: (1) a reduction in the poloidal correlation length of ITG from 5 cm to 2 cm and a 30% decrease in the radial correlation length, coinciding with the formation of a local transport barrier; (2) the emergence of a narrow shear flow layer with a shearing rate exceeding the ITG decorrelation rate; (3) increased Reynolds stress in electron diamagnetic drift direction, with a radial broadening of ~2 cm, which is correlated to the significantly contracted TAE radial mode structure; (4) a deviation of TAE polarization from the conventional shear Alfvén wave towards a more electrostatic polarization by 15%. (5) a localized change in the safety factor during the ITG suppression phase, measured by Motional Stark Effect diagnostics and (6) imaging neutral particle analyzer tomography indicating an increased fast-ion content during ITG suppression, despite the increased total amplitudes of TAEs. Furthermore, a series of the experiments reveals that TAEs routinely suppress ITG turbulence in plasma with higher local safety factor, elevated fast ion beta and larger population of fast ions on passing orbits, i.e., conditions consistent with high linear growth rate of TAEs. Database analysis further identifies the existence of a threshold in TAE drive required for ITG suppression.
Work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences,
using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Award(s) DE-FC02-04ER54698,DE-SC0020337, DE-FG02-08ER54999, DE-SC0020287, DESC0015878, DE-FG02-97ER54415, DE-SC0014664.
[1] X.D. Du et al., Phys. Rev. Lett. 135, 265101 (2025).