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Title: Diffusive shock re-acceleration

Abstract

Here, we have performed two-dimensional hybrid simulations of non-relativistic collisionless shocks in the presence of pre-existing energetic particles (‘seeds’); such a study applies, for instance, to the re-acceleration of galactic cosmic rays (CRs) in supernova remnant (SNR) shocks and solar wind energetic particles in heliospheric shocks. Energetic particles can be effectively reflected and accelerated regardless of shock inclination via a process that we call diffusive shock re-acceleration. We determine that re-accelerated seeds can drive the streaming instability in the shock upstream and produce effective magnetic field amplification. This can later trigger the injection of thermal protons even at oblique shocks that ordinarily cannot inject thermal particles. We characterize the current in reflected seeds, finding that it tends to a universal value$$J\simeq en_{\text{CR}}v_{\text{sh}}$$, where $$en_{\text{CR}}$$ is the seed charge density and $$v_{\text{sh}}$$ is the shock velocity. When applying our results to SNRs, we find that the re-acceleration of galactic CRs can excite the Bell instability to nonlinear levels in less than$${\sim}10~\text{yr}$$, thereby providing a minimum level of magnetic field amplification for any SNR shock. Finally, we discuss the relevance of diffusive shock re-acceleration also for other environments, such as heliospheric shocks, galactic superbubbles and clusters of galaxies.

Authors:
ORCiD logo [1];  [2];  [2]
  1. Univ. of Chicago, IL (United States); Princeton Univ., NJ (United States)
  2. Princeton Univ., NJ (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Sponsoring Org.:
USDOE Office of Science (SC); NASA, National Science Foundation (NSF)
OSTI Identifier:
1544276
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Plasma Physics
Additional Journal Information:
Journal Volume: 84; Journal Issue: 3; Journal ID: ISSN 0022-3778
Publisher:
Cambridge University Press
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; astrophysical plasmas; plasma nonlinear phenomena; plasma simulation

Citation Formats

Caprioli, Damiano, Zhang, Horace, and Spitkovsky, Anatoly. Diffusive shock re-acceleration. United States: N. p., 2018. Web. doi:10.1017/S0022377818000478.
Caprioli, Damiano, Zhang, Horace, & Spitkovsky, Anatoly. Diffusive shock re-acceleration. United States. doi:10.1017/S0022377818000478.
Caprioli, Damiano, Zhang, Horace, and Spitkovsky, Anatoly. Tue . "Diffusive shock re-acceleration". United States. doi:10.1017/S0022377818000478. https://www.osti.gov/servlets/purl/1544276.
@article{osti_1544276,
title = {Diffusive shock re-acceleration},
author = {Caprioli, Damiano and Zhang, Horace and Spitkovsky, Anatoly},
abstractNote = {Here, we have performed two-dimensional hybrid simulations of non-relativistic collisionless shocks in the presence of pre-existing energetic particles (‘seeds’); such a study applies, for instance, to the re-acceleration of galactic cosmic rays (CRs) in supernova remnant (SNR) shocks and solar wind energetic particles in heliospheric shocks. Energetic particles can be effectively reflected and accelerated regardless of shock inclination via a process that we call diffusive shock re-acceleration. We determine that re-accelerated seeds can drive the streaming instability in the shock upstream and produce effective magnetic field amplification. This can later trigger the injection of thermal protons even at oblique shocks that ordinarily cannot inject thermal particles. We characterize the current in reflected seeds, finding that it tends to a universal value$J\simeq en_{\text{CR}}v_{\text{sh}}$, where $en_{\text{CR}}$ is the seed charge density and $v_{\text{sh}}$ is the shock velocity. When applying our results to SNRs, we find that the re-acceleration of galactic CRs can excite the Bell instability to nonlinear levels in less than${\sim}10~\text{yr}$, thereby providing a minimum level of magnetic field amplification for any SNR shock. Finally, we discuss the relevance of diffusive shock re-acceleration also for other environments, such as heliospheric shocks, galactic superbubbles and clusters of galaxies.},
doi = {10.1017/S0022377818000478},
journal = {Journal of Plasma Physics},
number = 3,
volume = 84,
place = {United States},
year = {2018},
month = {5}
}

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