Abstract Details
Abstracts
Author: Eamon J Hartigan-O'Connor
Requested Type: Poster
Submitted: 2026-03-18 12:10:29
Co-authors: T. Barberis, E. G. Devin, V. N. Duarte
Contact Info:
Princeton University
307 Court St
Princeton, NJ 08540
United States
Abstract Text:
Instabilities driven by energetic particles are central to describing the physics of a burning plasma. Analytical saturation levels and reduced models have been derived for near-marginal and far-from-
marginal kinetic instabilities assuming that the unstable distribution is fully established. While typically the mode growth occurs much faster than the slowing down timescale for the unstable
distribution to form, the effective timescale on which injected energetic particles accumulate around narrow resonances can compete with the mode growth. We study the behavior of these instabilities
in the presence of such a dynamically forming distribution, evaluating two distinct metrics which measure how close a mode remains near its linear marginal stability and how close a mode is to
saturation. Saturation at large ωb/νeff (where ωb is the bounce frequency of deeply trapped particles and νeff is the effective scattering rate at a resonance), normally associated with strongly driven excitation, can be achieved even if dynamically the mode remains at all times near its instantaneous nonlinear excitation threshold. We extend existing analytic models for near-marginal and far from marginal modes allowing for a time-dependent linear growth rate, deriving explicit forms for the mode amplitude evolution which agree with nonlinear kinetic simulations. This development shows
that, while distinct time histories are allowed, the parameter ωb/νeff determines the evolution regime and the mode saturation level, as it does in the time-independent case.
Characterization: 4.0
Comments: