Abstract
We report the detection of nonstationary quadratic coupling between toroidicity-induced Alfvén eigenmodes (TAEs) on sub-millisecond time scales. Identification of phase coherency between multiple TAEs and nonlinearly generated modes is facilitated by wavelet-based bicoherence analysis of time-series from inductive coils, taken from a DIII-D discharge heated by neutral beam injection (NBI). Characterization of nonlinear three-wave interaction is inferred by stationary local bispectrum phase (biphase) and confirmed via bandpass filtering. Biphase dynamics associated with prominent bispectral features are well-resolved in time and consistent with transient quadratic coupling. Onset and duration of nonlinearity are correlated with enhanced amplitude of participating TAEs; coincident changes in amplitude are observed for modes at difference frequency | f TAE , 1 − f TAE , 2 | .
| Original language | English |
|---|---|
| Article number | 042305 |
| Journal | Physics of Plasmas |
| Volume | 31 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 1 2024 |
Funding
This material is based upon 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-NA0003874, DE-SC0021404, and DE-FC02-04ER54698. G.R. and M.K. express deep gratitude to the DIII-D team for necessary support and impactful collaboration during this project.