Evolution of an Alfvén wave–driven proton beam in the expanding solar wind
File(s)
Published version
Author(s)
Bianco, JS
Tenerani, A
Gonzalez, C
Matteini, L
Klein, KG
Type
Journal Article
Abstract
We investigate the self-consistent formation and long-term evolution of proton beams in the expanding solar wind using an ensemble of one-dimensional hybrid expanding box simulations. Initial conditions are chosen to represent a range of plasma states observed by the Helios spacecraft at 0.3 au, including an amplitude-modulated Alfvén wave that nonlinearly drives a proton beam aligned with the magnetic field. We compare simulation results with solar wind data out to 1.5 au and show that our model reproduces key observed features of proton beams on average, such as the radial evolution of the drift and the relative core-to-beam density ratio. These findings support the theory that the observed evolution of the proton beam drift in the solar wind is determined by kinetic instabilities. More broadly, our results indicate that the interplay between nonlinear Alfvén wave dynamics, expansion effects, and kinetic instabilities plays a fundamental role in solar wind dynamics, with implications for interpreting solar wind heating rate estimates.
Date Issued
2026-02-20
Date Acceptance
2026-01-16
Citation
The Astrophysical Journal, 2026, 998 (2)
ISSN
0004-637X
Publisher
American Astronomical Society
Journal / Book Title
The Astrophysical Journal
Volume
998
Issue
2
Copyright Statement
© 2026. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
License URL
Publication Status
Published
Article Number
194
Date Publish Online
2026-02-10