Speaker
Description
We report the first experimental detection of a zero-frequency fluctuation that is pumped by an Alfvén mode in a magnetically confined plasma. Core-localized toroidal Alfvén eigenmodes (TAEs) of frequency inside the toroidicity-induced gap (and higher frequency gaps) exhibit three-wave coupling interactions with a zero-frequency fluctuation. The observation of the zero-frequency fluctuation is consistent with theoretical and numerical predictions of zonal modes pumped by Alfvén modes, and is correlated with an increase in the deep-core ion temperature, temperature gradient, confinement factor H89P, and a reduction in the main ion heat flux. The TAEs also nonlinearly couple to higher frequency sidebands, and exhibit predator-prey-like behavior with the measured turbulence fluctuations. Nonlinear gyrokinetic simulations with the CGYRO code reproduce the nonlinear coupling with the sidebands and with the zero-frequency fluctuation. Despite the energetic particle transport induced by the Alfvén eigenmodes, the generation of a zero-frequency fluctuation that can suppress the turbulence leads to an overall improvement of confinement.
| Presentation type | Oral |
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