Wave-growth-limited Particle Confinement in a Near-parallel Interplanetary Shock Observed by Parker Solar Probe
8 affiliations
- 1The Johns Hopkins University Applied Physics Laboratory
- 2University of Turku
- 3University of California
- 4Eureka Scientific
- 5Ben Gurion University of the Negev
- 6Centre for mathematical Plasma Astrophysics
- 7California Institute of Technology
- 8Princeton University
Abstract
Collisionless shocks confine the particles they accelerate with the upstream wave field they themselves drive. Streaming particles resonantly amplify Alfvén waves, and the waves then confine the same particles by pitch-angle scattering. The rigidity a shock precursor can hold is therefore capped by how fast those waves grow, and that coupling has not previously been constrained in situ at any interplanetary shock. Here, we report Parker Solar Probe measurements of a fast, near-parallel coronal mass ejection-driven shock at 0.24 au on 2023 March 13 that constrain this wave–particle coupling through the energetic-particle population it accelerates. We measure the spectral folding energy, the boundary between the confined and the upstream-escaping protons, and find that it falls from ∼6 to ∼1.5 MeV as E fold ∝ Δ t α with α ≃ 0.34, where Δ t is the time remaining before the shock arrival. One precursor convective time before the shock arrival, this boundary is at E c ≃ 2.46 MeV, defining a characteristic confinement energy for the precursor of scale L EP . Read through the quasi-linear marginal-stability condition; the same evolution implies a resonant wave-growth timescale τ growth ( E ) ∝ E 1/ α ≃ E 2.92 that exceeds the precursor convective time above E c . The postshock pitch-angle anisotropy reverses its sign across the same confinement–escape transition at 2–5 MeV. The rigidity to which a shock precursor can confine particles is therefore set, in situ, by how quickly the streaming population builds its own confining waves.
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BibTeX
@article{kouloumvakos2026wavegrowthlimited,
title = {{Wave-growth-limited Particle Confinement in a Near-parallel Interplanetary Shock Observed by Parker Solar Probe}},
author = {A. Kouloumvakos and I. C. Jebaraj and M. A. Malkov and G. D. Berland and M. Gedalin and N. Wijsen and C. M. S. Cohen and O. V. Agapitov and D. J. McComas and D. G. Mitchell and E. Husidic and S. Yadav and M. E. Hill and R. McNutt},
journal = {The Astrophysical Journal Letters},
year = {2026},
month = oct,
doi = {10.3847/2041-8213/aeaf56},
url = {https://iopscience.iop.org/article/10.3847/2041-8213/aeaf56},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Wave-growth-limited Particle Confinement in a Near-parallel Interplanetary Shock Observed by Parker Solar Probe
AU - A. Kouloumvakos
AU - I. C. Jebaraj
AU - M. A. Malkov
AU - G. D. Berland
AU - M. Gedalin
AU - N. Wijsen
AU - C. M. S. Cohen
AU - O. V. Agapitov
AU - D. J. McComas
AU - D. G. Mitchell
AU - E. Husidic
AU - S. Yadav
AU - M. E. Hill
AU - R. McNutt
PY - 2026
DA - 2026/10/21
JO - The Astrophysical Journal Letters
DO - 10.3847/2041-8213/aeaf56
UR - https://iopscience.iop.org/article/10.3847/2041-8213/aeaf56
AB - Collisionless shocks confine the particles they accelerate with the upstream wave field they themselves drive. Streaming particles resonantly amplify Alfvén waves, and the waves then confine the same particles by pitch-angle scattering. The rigidity a shock precursor can hold is therefore capped by how fast those waves grow, and that coupling has not previously been constrained in situ at any interplanetary shock. Here, we report Parker Solar Probe measurements of a fast, near-parallel coronal mass ejection-driven shock at 0.24 au on 2023 March 13 that constrain this wave–particle coupling through the energetic-particle population it accelerates. We measure the spectral folding energy, the boundary between the confined and the upstream-escaping protons, and find that it falls from ∼6 to ∼1.5 MeV as E fold ∝ Δ t α with α ≃ 0.34, where Δ t is the time remaining before the shock arrival. One precursor convective time before the shock arrival, this boundary is at E c ≃ 2.46 MeV, defining a characteristic confinement energy for the precursor of scale L EP . Read through the quasi-linear marginal-stability condition; the same evolution implies a resonant wave-growth timescale τ growth ( E ) ∝ E 1/ α ≃ E 2.92 that exceeds the precursor convective time above E c . The postshock pitch-angle anisotropy reverses its sign across the same confinement–escape transition at 2–5 MeV. The rigidity to which a shock precursor can confine particles is therefore set, in situ, by how quickly the streaming population builds its own confining waves.
SN - 2041-8205
SN - 2041-8213
ER -