Hierarchy of instabilities for two counter-streaming magnetized pair beams

Bret, Antoine

doi:10.1063/1.4954307

Cited by 14 publications

(18 citation statements)

References 26 publications

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“…We examine here the shock that emerges out of the collision of two equal pair clouds at the speed 0.5c. The exponential growth rate of electrostatic instabilities exceeds that of the filamentation instability for a collision speed ≤ 0.57c (Bret 2016) and the shock forms on the electrostatic time scale. The interaction of the twostream modes with the pair plasma mixes the particles of the counterstreaming beams, which inhibits the growth of the filamentation instability and compresses the plasma density to a value above that expected from a beam superposition.…”

Section: Introductionmentioning

confidence: 97%

Electrostatic and magnetic instabilities in the transition layer of a collisionless weakly relativistic pair shock

Dieckmann

Bret

2017

Monthly Notices of the Royal Astronomical Society

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Energetic electromagnetic emissions by astrophysical jets like those that are launched during the collapse of a massive star and trigger gamma-ray bursts are partially attributed to relativistic internal shocks. The shocks are mediated in the collisionless plasma of such jets by the filamentation instability of counterstreaming particle beams. The filamentation instability grows fastest only if the beams move at a relativistic relative speed. We model here with a particle-in-cell simulation, the collision of two cold pair clouds at the speed c/2 (c: speed of light). We demonstrate that the two-stream instability outgrows the filamentation instability for this speed and is thus responsible for the shock formation. The incomplete thermalization of the upstream plasma by its quasi-electrostatic waves allows other instabilities to grow. A shock transition layer forms, in which a filamentation instability modulates the plasma far upstream of the shock. The inflowing upstream plasma is progressively heated by a twostream instability closer to the shock and compressed to the expected downstream density by the Weibel instability. The strong magnetic field due to the latter is confined to a layer 10 electron skin depths wide.Key words: instabilities -plasmas -shock waves -methods: numerical. I N T RO D U C T I O NBinaries with an accreting compact object, which are known as microquasars, can emit relativistic jets (Falcke & Biermann 1996;Mirabel & Rodriguez 1999;Madejski & Sikora 2016). The jets are composed of electrons, positrons (Siegert et al. 2016) and an unknown fraction of ions and they are sources of intense electromagnetic radiation, which can be observed over astronomical distances. Some of this radiation is attributed to synchrotron emissions by relativistic electrons and positrons that gyrate in a strong magnetic field. The source of the jet's magnetic field is under debate. A plasma is a good conductor and, hence, the jet will carry with it the strong magnetic field that is present at its base. Instabilities, which develop in a non-equilibrium collisionless plasma, can also magnetize the jet.Instabilities can be driven by a large variation of the jet's mean velocity, which is caused by a non-uniform plasma acceleration efficiency of its engine. A velocity variation steepens if a faster plasma cloud catches up with a slower one, which ultimately results in the formation of an internal shock in the jet. Shocks in the jet heat up its plasma and compress the magnetic field. We expect that these E-mail: mark.e.dieckmann@liu.se internal shocks are powerful sources of electromagnetic emissions. The internal shock model has initially been invoked by Rees (1978) to explain the emissions by the knots in the jets of active galactic nuclei and the model also explains the prompt emissions of gammaray bursts (Piran 1999(Piran , 2004. Malzac (2014) and Drappeau et al. (2015) have examined to what extent the emissions of the relativistic jets of microquasars can be explained by internal shocks.The large mean-free pa...

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Section: Introductionmentioning

confidence: 97%

Electrostatic and magnetic instabilities in the transition layer of a collisionless weakly relativistic pair shock

Dieckmann

Bret

2017

Monthly Notices of the Royal Astronomical Society

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“…The case θ = 0 has already been treated in Ref. [8] and shows 4 different kinds of modes are likely to govern the linear phase. For finite obliquities, the hierarchy maps tends to simplify for 2 reasons:…”

Section: Discussionmentioning

confidence: 91%

“…Another feature of Fig. 5 is that for large γ 0 's, condition (8) translates to a condition of the type σ < σ T (θ), where σ T is a magnetization threshold beyond which the present calculations are no longer relevant.…”

Section: A Relativistic Regimementioning

confidence: 85%

“…For these calculations to be relevant, the growth-rate must be larger than the cyclotron frequency of the charges in the field component normal to the initial flow. This sets condition (8), which restricts the relevant (σ, γ 0 ) domain.…”

Section: Discussionmentioning

confidence: 99%

“…In the relativistic regime, upper-hybrid-like (UHL) and Weibel modes mostly share the map until θ ∼ 0.78 (44 • ). Beyond this critical obliquity, the UHL domain is ruled out by the validity condition (8), and the Weibel instability always governs.…”

Section: Discussionmentioning

confidence: 99%

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Hierarchy of instabilities for two counter-streaming magnetized pair beams: Influence of field obliquity

Bret

Dieckmann²

2017

Physics of Plasmas

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The hierarchy of unstable modes when two counter-streaming pair plasmas interact over a flowaligned magnetic field has been recently investigated [PoP 23, 062122 (2016)]. The analysis is here extended to the case of an arbitrarily tilted magnetic field. The two plasma shells are initially cold and identical. For any angle θ ∈ [0, π/2] between the field and the initial flow, the hierarchy of unstable modes is numerically determined in terms of the initial Lorentz factor of the shells γ 0 , and the field strength as measured by a parameter denoted σ. For θ = 0, four different kinds of mode are likely to lead the linear phase. The hierarchy simplifies for larger θ's, partly because the Weibel instability can no longer be cancelled in this regime. For θ > 0.78 (44 • ) and in the relativistic regime, the Weibel instability always govern the interaction. In the non-relativistic regime, the hierarchy becomes θ-independent because the interaction turns to be field-independent. As a result, the two-stream instability becomes the dominant one, regardless of the field obliquity.

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Neutron Production from Structured Targets Irradiated By an Ultrashort Laser Pulse

et al. 2021

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We study the laser-driven generation of thermonuclear neutrons from targets with a microstructured surface in the form of deuterated microwires, using three-dimensional numerical simulation with previously obtained results of large-scale structural optimization of the target, which provides its best heating by femtosecond laser pulses of moderate intensity. We show that, for modern laser technologies, femtosecond lasers of low (several mJ) energy are even better for creating a neutron source than more powerful (∼1 J) lasers because the mode of high (∼1 kHz) pulse repetition rate is practically available. Microlayers (relief) and cylindrical microholes on the irradiated side are considered as alternative microstructured targets. For the latter, we demonstrate accumulation of ions on the axis of the holes, which leads to increase in the ion density above the initial value and consequently to a possible increase in the yield of thermonuclear neutrons.

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Hierarchy of instabilities for two counter-streaming magnetized pair beams

Cited by 14 publications

References 26 publications

Electrostatic and magnetic instabilities in the transition layer of a collisionless weakly relativistic pair shock

Electrostatic and magnetic instabilities in the transition layer of a collisionless weakly relativistic pair shock

Hierarchy of instabilities for two counter-streaming magnetized pair beams: Influence of field obliquity

Neutron Production from Structured Targets Irradiated By an Ultrashort Laser Pulse

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