Energy Repartition and Entropy Generation across the Earth’s Bow Shock: MMS Observations

Agapitov, Oleksiy; Krasnoselskikh, V.; Balikhin, M. A.; Bonnell, J. W.; Mozer, F. S.; Avanov, L. A.

doi:10.3847/1538-4357/acdb7b

Cited by 6 publications

(1 citation statement)

References 42 publications

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“…At present, heliospheric shocks are the only natural CSWs accessible for direct in situ study, making them essential for comprehending shock structure, evolution, and particle energization mechanisms. In particular, the shock transition, which marks the finite region between the upstream and downstream flows, plays a crucial role in understanding the redistribution of kinetic energy (Balikhin et al 1993;Krasnosselskikh et al 1995;Agapitov et al 2023). Consequently, heliospheric shocks, which may in many aspects be similar to young SNR shocks, have become a key focus of research (Terasawa 2003).…”

Section: Introductionmentioning

confidence: 99%

Acceleration of Electrons and Ions by an “Almost” Astrophysical Shock in the Heliosphere

Jebaraj,

Agapitov,

Krasnoselskikh

et al. 2024

ApJL

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Collisionless shock waves, ubiquitous in the Universe, are crucial for particle acceleration in various astrophysical systems. Currently, the heliosphere is the only natural environment available for their in situ study. In this work, we showcase the collective acceleration of electrons and ions by one of the fastest in situ shocks ever recorded, observed by the pioneering Parker Solar Probe at only 34.5 million km from the Sun. Our analysis of this unprecedented, near-parallel shock shows electron acceleration up to 6 MeV amidst intense multiscale electromagnetic wave emissions. We also present evidence of a variable shock structure capable of injecting and accelerating ions from the solar wind to high energies through a self-consistent process. The exceptional capability of the probe’s instruments to measure electromagnetic fields in a shock traveling at 1% the speed of light has enabled us, for the first time, to confirm that the structure of a strong heliospheric shock aligns with theoretical models of strong shocks observed in astrophysical environments. This alignment offers viable avenues for understanding astrophysical shock processes and the self-consistent acceleration of charged particles.

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Section: Introductionmentioning

confidence: 99%

Acceleration of Electrons and Ions by an “Almost” Astrophysical Shock in the Heliosphere

Jebaraj,

Agapitov,

Krasnoselskikh

et al. 2024

ApJL

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Relativistic electron beams accelerated by an interplanetary shock

Jebaraj,

Dresing,

Krasnoselskikh

et al. 2023

A&A

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Context. Collisionless shock waves have long been considered to be among the most prolific particle accelerators in the universe. Shocks alter the plasma they propagate through, and often exhibit complex evolution across multiple scales. Interplanetary (IP) traveling shocks have been recorded in situ for over half a century and act as a natural laboratory for experimentally verifying various aspects of large-scale collisionless shocks. A fundamentally interesting problem in both heliophysics and astrophysics is the acceleration of electrons to relativistic energies (> 300 keV) by traveling shocks. Aims. The reason for an incomplete understanding of electron acceleration at IP shocks is due to scale-related challenges and a lack of instrumental capabilities. This Letter presents the first observations of field-aligned beams of relativistic electrons upstream of an IP shock, observed thanks to the instrumental capabilities of Solar Orbiter. This study presents the characteristics of the electron beams close to the source and contributes to the understanding of their acceleration mechanism. Methods. On 25 July 2022, Solar Orbiter encountered an IP shock at 0.98 AU. The shock was associated with an energetic storm particle event, which also featured upstream field-aligned relativistic electron beams observed 14 min prior to the actual shock crossing. The distance of the beam’s origin was investigated using a velocity dispersion analysis (VDA). Peak-intensity energy spectra were anaylzed and compared with those obtained from a semi-analytical fast-Fermi acceleration model. Results. By leveraging Solar Orbiter’s high temporal resolution Energetic Particle Detector (EPD), we successfully showcase an IP shock’s ability to accelerate relativistic electron beams. Our proposed acceleration mechanism offers an explanation for the observed electron beam and its characteristics, while we also explore the potential contributions of more complex mechanisms.

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Numerical simulations of laser-driven experiments of ion acceleration in stochastic magnetic fields

Moczulski,

Wen,

Campbell

et al. 2024

Physics of Plasmas

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We present numerical simulations used to interpret laser-driven plasma experiments at the GSI Helmholtz Centre for Heavy Ion Research. The mechanisms by which non-thermal particles are accelerated in astrophysical environments, e.g., the solar wind, supernova remnants, and gamma ray bursts, is a topic of intense study. When shocks are present, the primary acceleration mechanism is believed to be first-order Fermi, which accelerates particles as they cross a shock. Second-order Fermi acceleration can also contribute, utilizing magnetic mirrors for particle energization. Despite this mechanism being less efficient, the ubiquity of magnetized turbulence in the universe necessitates its consideration. Another acceleration mechanism is the lower-hybrid drift instability, arising from gradients of both density and magnetic field, which produce lower-hybrid waves with an electric field that energizes particles as they cross these waves. With the combination of high-powered laser systems and particle accelerators, it is possible to study the mechanisms behind cosmic-ray acceleration in the laboratory. In this work, we combine experimental results and high-fidelity three-dimensional simulations to estimate the efficiency of ion acceleration in a weakly magnetized interaction region. We validate the FLASH magneto-hydrodynamic code with experimental results and use OSIRIS particle-in-cell code to verify the initial formation of the interaction region, showing good agreement between codes and experimental results. We find that the plasma conditions in the experiment are conducive to the lower-hybrid drift instability, yielding an increase in energy ΔE of ∼ 264 keV for 242 MeV calcium ions.

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Energy Repartition and Entropy Generation across the Earth’s Bow Shock: MMS Observations

Cited by 6 publications

References 42 publications

Acceleration of Electrons and Ions by an “Almost” Astrophysical Shock in the Heliosphere

Acceleration of Electrons and Ions by an “Almost” Astrophysical Shock in the Heliosphere

Relativistic electron beams accelerated by an interplanetary shock

Numerical simulations of laser-driven experiments of ion acceleration in stochastic magnetic fields

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