Expansion of a mildly relativistic hot pair cloud into an electron-proton plasma

Dieckmann, Mark E; Alejo, A.; Sarri, Gianluca

doi:10.1063/1.5036954

Cited by 8 publications

(8 citation statements)

References 25 publications

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“…The distributions along v y and along |V| hardly differ apart from the wrap-around at v y = 0 and they have thus also been accelerated mainly along y. Their peak speed 10 7 m/s is comparable to that of the protons in the simulation by Dieckmann et al (2018b) and they have thus been accelerated by the filamentation instability that formed initially between the pair cloud and the ambient plasma.…”

Section: The Electromagnetic Piston and The Pair Flow At The Headmentioning

confidence: 76%

“…These waves eventually break and form electrostatic shocks (Malkov et al 2016), which can accelerate protons to high energies. Dieckmann et al (2018b) studied this expansion in two dimensions. A filamentation instability between the cloud particles and the ambient plasma resulted in the growth of magnetic fields that separated in space the protons and positrons.…”

Section: Collisionless Plasma and Previous Workmentioning

confidence: 99%

“…They will eventually drive a collisionless shock in the ambient plasma that will form the boundary of the jet's outer cocoon. The head of the jet is mediated by a filamentation instability between the ambient electrons and the pairs of the pair cloud [16]. Its magnetic field moves relative to the protons, which accelerates them by their convective electric field [16,17].…”

Section: Introductionmentioning

confidence: 99%

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Structure of a collisionless pair jet in a magnetized electron–proton plasma: flow-aligned magnetic field

Dieckmann

Folini

Hotz

et al. 2019

A&A

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Aims. We study the effect a guiding magnetic field has on the formation and structure of a pair jet that propagates through a collisionless electron–proton plasma at rest. Methods. We model with a particle-in-cell (PIC) simulation a pair cloud with a temperature of 400 keV and a mean speed of 0.9c (c - light speed). Pair particles are continuously injected at the boundary. The cloud propagates through a spatially uniform, magnetized, and cool ambient electron–proton plasma at rest. The mean velocity vector of the pair cloud is aligned with the uniform background magnetic field. The pair cloud has a lateral extent of a few ion skin depths. Results. A jet forms in time. Its outer cocoon consists of jet-accelerated ambient plasma and is separated from the inner cocoon by an electromagnetic piston with a thickness that is comparable to the local thermal gyroradius of jet particles. The inner cocoon consists of pair plasma, which lost its directed flow energy while it swept out the background magnetic field and compressed it into the electromagnetic piston. A beam of electrons and positrons moves along the jet spine at its initial speed. Its electrons are slowed down and some positrons are accelerated as they cross the head of the jet. The latter escape upstream along the magnetic field, which yields an excess of megaelectronvolt positrons ahead of the jet. A filamentation instability between positrons and protons accelerates some of the protons, which were located behind the electromagnetic piston at the time it formed, to megaelectronvolt energies. Conclusions. A microscopic pair jet in collisionless plasma has a structure that is similar to that predicted by a hydrodynamic model of relativistic astrophysical pair jets. It is a source of megaelectronvolt positrons. An electromagnetic piston acts as the contact discontinuity between the inner and outer cocoons. It would form on subsecond timescales in a plasma with a density that is comparable to that of the interstellar medium in the rest frame of the latter. A supercritical fast magnetosonic shock will form between the pristine ambient plasma and the jet-accelerated plasma on a timescale that exceeds our simulation time by an order of magnitude.

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Section: The Electromagnetic Piston and The Pair Flow At The Headmentioning

confidence: 76%

Section: Collisionless Plasma and Previous Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structure of a collisionless pair jet in a magnetized electron–proton plasma: flow-aligned magnetic field

Dieckmann

Folini

Hotz

et al. 2019

A&A

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“…We examine here how a cloud of electrons and positrons interacts with an ambient plasma, which consists of electrons and protons. We select values for the cloud's density, temperature and mean speed for which the ensuing instabilities accelerate protons [30] and generate strong magnetic fields [31]. In these works, the ambient plasma and the pair cloud were uniform in the direction orthogonal to the expansion direction.…”

Section: Introductionmentioning

confidence: 99%

Cocoon formation by a mildly relativistic pair jet in unmagnetized collisionless electron-proton plasma

Dieckmann¹,

Sarri

Folini

et al. 2018

Physics of Plasmas

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By modelling the expansion of a cloud of electrons and positrons with the temperature 400 keV that propagates at the mean speed 0.9c (c : speed of light) through an initially unmagnetized electron-proton plasma with a particle-in-cell (PIC) simulation, we find a mechanism that collimates the pair cloud into a jet. A filamentation (beam-Weibel) instability develops. Its magnetic field collimates the positrons and drives an electrostatic shock into the electron-proton plasma. The magnetic field acts as a discontinuity that separates the protons of the shocked ambient plasma, known as the outer cocoon, from the jet's interior region. The outer cocoon expands at the speed 0.15c along the jet axis and at 0.03c perpendicularly to it. The filamentation instability converts the jet's directed flow energy into magnetic energy in the inner cocoon. The magnetic discontinuity cannot separate the ambient electrons from the jet electrons. Both species rapidly mix and become indistinguishable. The spatial distribution of the positive charge carriers is in agreement with the distributions of the ambient material and the jet material predicted by a hydrodynamic model apart from a dilute positronic outflow that is accelerated by the electromagnetic field at the jet's head.

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“…Of particular interest is the study of pair-shocks along the propagation of the jet, after saturation of the filamentation instability, which has been speculated as a possible origin for the production of gamma-ray bursts and may be studied in upcoming laser facilities [99]. Such facilities may also enable the study of the propagation of lower temperature electron-positron plasmas into a background plasma, predicted to generated bipolar electric fields capable of accelerating ions in unmagnetised ambient plasmas, such as the inter-galactic medium [113,114].…”

Section: Prospectsmentioning

confidence: 99%

Laser-Wakefield Electron Beams as Drivers of High-Quality Positron Beams and Inverse-Compton-Scattered Photon Beams

et al. 2019

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The fast-paced development of laser-wakefield electron acceleration has recently culminated in the generation of electron beams with extreme characteristics, including femtosecond-scale duration, mrad divergence, and high-energy. It is now customary to attain tens to hundreds of pC of charge with an energy of hundreds of MeV per particle with small-scale commercial laser systems, with multi-GeV electron beams being demonstrated from cm-scale accelerators. The interaction of such electron beams with either a solid target or the focus of a second high-power laser can result in the generation of high-quality positron beams and MeV-photon beams. The unrivaled properties of these secondary sources make them ideal for both fundamental and practical applications. In the present article, some of their main characteristics will be discussed, with particular emphasis on their potential applications in fundamental and applied physics. A discussion of potential future developments enabled by near-term laser facilities will also be presented.

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Expansion of a mildly relativistic hot pair cloud into an electron-proton plasma

Cited by 8 publications

References 25 publications

Structure of a collisionless pair jet in a magnetized electron–proton plasma: flow-aligned magnetic field

Structure of a collisionless pair jet in a magnetized electron–proton plasma: flow-aligned magnetic field

Cocoon formation by a mildly relativistic pair jet in unmagnetized collisionless electron-proton plasma

Laser-Wakefield Electron Beams as Drivers of High-Quality Positron Beams and Inverse-Compton-Scattered Photon Beams

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