Wave-Growth-Limited Particle Confinement in a Near-Parallel Interplanetary Shock Observed by Parker Solar Probe
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 Efold∝Δt α with α≃0.34, where Δt is the time remaining before shock arrival. One precursor convective time before arrival this boundary is at Ec≃ 2.46~MeV, a characteristic confinement energy of a precursor of scale LEP. Read through the quasi-linear marginal-stability condition, the same evolution implies a resonant wave-growth timescale τgrowth(E)∝ E1/α≃ E2.92 that exceeds the precursor convective time above Ec. The post-shock pitch-angle anisotropy reverses 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
@misc{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},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.10067},
eprint = {2610.10067},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.10067},
note = {CC BY 4.0},
}
RIS
TY - UNPB
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 - 2026/10/07
PB - arXiv
DO - 10.48550/arxiv.2610.10067
UR - https://arxiv.org/abs/2610.10067
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∝Δt^ α with α≃0.34, where Δt is the time remaining before shock arrival. One precursor convective time before arrival this boundary is at E_c≃ 2.46~MeV, a characteristic confinement energy of a 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 post-shock pitch-angle anisotropy reverses 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.
ER -