Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Diffusive Shock Re-Acceleration   We have performed 2D 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
\emph{diffusive shock re-acceleration}. We find that reaccelerated seeds can
drive the streaming instability in the shock upstream and produce effective
magnetic field amplification. This can eventually 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 $J\simeq e n_{cr} v_{sh}$, where $e n_{cr}$ is the
seed charge density and $v_{sh}$ 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 non-linear levels in less than $\sim 10$ 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.

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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: stat
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The categories of this paper are: nucl-th
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The categories of this paper are: eess
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-ex
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The categories of this paper are: adap-org
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci