Abstract Details
Abstracts
Author: Elena V Belova
Requested Type: Poster
Submitted: 2026-03-15 16:53:44
Co-authors: C. Liu, E. D. Fredrickson, N. A. Crocker, N. N. Gorelenkov
Contact Info:
PPPL
MS 18, 100 Stellarator Road,
Princeton, NJ 08540
United States
Abstract Text:
Self-consistent hybrid MHD-kinetic simulations of Alfvén eigenmodes (AEs) in NSTX-U have been performed with the HYM code using full-orbit beam ions. Calculations for n=3-4 show unstable modes in the TAE frequency range, with mode localization and structure in good agreement with experiment, as well as nonlinear saturation and frequency chirping. The simulations show that the compressional magnetic perturbation can be comparable to the shear component, indicating strong finite-β effects. HYM results are being compared with simulations of the same NSTX-U discharge using the M3D-C1-K code with gyrokinetic energetic particles. The comparison shows qualitative agreement in mode structure, frequency range, and the presence of large compressional perturbation. Recent beam-density scans for the n=3 mode at fixed total pressure reveal two competing branches: a lower-frequency interchange-like mode that is stabilized by energetic particles, and a higher-frequency beam-driven TAE whose drive increases with beam density. At intermediate beam fraction, both branches are present with comparable growth rates, indicating a transition from thermal-plasma-driven interchange instability to energetic-particle-driven TAE activity; a similar qualitative transition is found in M3D-C1-K simulations. Phase-space diagnostics indicate different resonant-particle populations for the two branches, with the lower-frequency mode coupling mainly to trapped particles and the TAE interacting with passing particles. Ongoing work includes extending both codes to include energetic-particle source/sink terms for more realistic modeling of TAE excitation and nonlinear evolution. In parallel, machine-learning methods are being developed to classify NOVA-calculated Alfvén eigenmodes as part of a surrogate-based linear-stability capability within the broader NSTX-U digital-twin project, and in support of future reduced models of energetic-particle effects in STs.
Characterization: 1.0
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