The interplay of the collisionless non-linear thin-shell instability with the ion acoustic instability

Dieckmann, Mark E; Folini, Doris; Walder, Rolf

doi:10.1093/mnras/stw3014

Cited by 5 publications

(11 citation statements)

References 43 publications

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“…The interpenetration of the jet plasma with the ISM or with plasma clouds within the jet that move at a different speed gives rise to anisotropic particle velocity distributions and to charged particle beams. They relax via the Weibel [18,19] or the filamentation instability also known as the beam-Weibel instability [20][21][22][23][24][25][26][27][28][29] that drive strong magnetic fields that are coherent on small scales. Particle-in-cell simulations of cylindrical plasma clouds, which consist of cool electrons and positrons, that propagate through an ambient medium show that beam-Weibel instabilities, mushroom instabilities and kinetic Kelvin-Helmholtz instabilities (See Ref.…”

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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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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“…4. The breather mode was found also for a different set of initial conditions for the PIC simulations [21].…”

Section: Varying the Perturbation Amplitude A Imentioning

confidence: 72%

“…The boundaries of the thin shell are no longer sine curves at t = 1600. An ion acoustic instability develops upstream of the electrostatic shocks, which starts to disrupt the thin shell's boundaries [21]. Figure 4 shows the proton density distribution computed by simulation 3 for the same times that were shown in Fig.…”

Section: Varying the Perturbation Amplitude A Imentioning

confidence: 89%

“…The PIC simulations in Refs. [19,20,21] have shown that a collisionless analogue of the NTSI exists. A thin-shell, which is bounded by two solitary waves that are growing into electrostatic shocks [24], is destabilized by a spatial displacement of its central curve along the plasma flow direction that varies as a function of the orthogonal direction.…”

Section: Discussionmentioning

confidence: 99%

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Electrostatic shock waves in the laboratory and astrophysics: similarities and differences

Dieckmann¹,

Doria²,

Sarri³

et al. 2017

Plasma Phys. Control. Fusion

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Contemporary lasers allow us to create shocks in the laboratory that propagate at a speed that matches that of energetic astrophysical shocks like those that ensheath supernova blast shells. The rapid growth time of the shocks and the spatio-temporal resolution, with which they can be sampled, allow us to identify the processes that are involved in their formation and evolution. Some laser-generated unmagnetized shocks are mediated by collective electrostatic forces and effects caused by binary collisions between particles can be neglected. Hydrodynamic models, which are valid for many large-scale astrophysical shocks, assume that collisions enforce a local thermodynamic equilibrium in the medium; laser-generated shocks are thus not always representative for astrophysical shocks. Laboratory studies of shocks can improve the understanding of their astrophysical counterparts if we can identify processes that affect electrostatic shocks and hydrodynamic shocks alike. An example is the nonlinear thin-shell instability (NTSI). We show that the NTSI destabilizes collisionless and collisional shocks by the same physical mechanism.

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“…Filamentation instabilities between colliding unmagnetized or magnetized pair clouds [1][2][3][4][5][6] and between initially unmagnetized counterstreaming clouds of electrons and ions 7,8 have been studied widely with particle-in-cell (PIC) simulations. These simulations showed that a filamentation instability rapidly thermalizes the interpenetrating plasma clouds.…”

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confidence: 99%

Collisionless tangential discontinuity between pair plasma and electron–proton plasma

Dieckmann

2020

Physics of Plasmas

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We study with a one-dimensional particle-in-cell (PIC) simulation the expansion of a pair cloud into a magnetized electron-proton plasma as well as the formation and subsequent propagation of a tangential discontinuity that separates both plasmas. Its propagation speed takes the value that balances the magnetic pressure of the discontinuity against the thermal pressure of the pair cloud and the ram pressure of the protons. Protons are accelerated by the discontinuity to a speed that exceeds the fast magnetosonic speed by the factor 10. A supercritical fast magnetosonic shock forms at the front of this beam. An increasing proton temperature downstream of the shock and ahead of the discontinuity leaves the latter intact. We create the discontinuity by injecting a pair cloud at a simulation boundary into a uniform electron-proton plasma, which is permeated by a perpendicular magnetic field. Collisionless tangential discontinuities in the relativistic pair jets of X-ray binaries (microquasars) are in permanent contact with the relativistic leptons of its inner cocoon and they become sources of radio synchrotron emissions.Filamentation instabilities between colliding unmagnetized or magnetized pair clouds 1-6 and between initially unmagnetized counterstreaming clouds of electrons and ions 7,8 have been studied widely with particle-in-cell (PIC) simulations. These simulations showed that a filamentation instability rapidly thermalizes the interpenetrating plasma clouds. Strong electromagnetic fields exist only in a layer that is close to the boundary that separates the inflowing upstream plasma from the thermalized one; this layer corresponds to a shock if the collision speed is high enough. See 9 for a review of such shocks.Mechanisms, that can enforce the separation of a fast plasma flow from an ambient plasma at rest rather than their thermalization, are interesting in the context of relativistic astrophysical jets 10,11 . Their plasma is dilute, which implies that binary (Coulomb) collisions between particles are rare on the time scales of interest. We call a plasma collisionless if its dynamics is determined by the electromagnetic fields generated by the collective of the particles rather than by binary collisions.Black hole X-ray binaries can emit such jets, in which case they are called microquasars 12 . Material from the companion star is attracted by the black hole and forced onto an accretion disk. Instabilities transform some of the inner disk's kinetic and magnetic energies into thermal energy heating up the disk's corona to MeV temperatures. Large clouds of electrons and positrons form (See 13 for a review and 14 for an observation of pair annihilation lines). If we assume that the temperature of this pair cloud is relativistic at its source then its initial expansion speed should be at least mildly relativistic. Open magnetic field lines that start at the inner disk allow the pair cloud to escape from the black hole's vicinity. It flows through an ambient plasma, which is initially that of the corona foll...

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The interplay of the collisionless non-linear thin-shell instability with the ion acoustic instability

Cited by 5 publications

References 43 publications

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

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

Electrostatic shock waves in the laboratory and astrophysics: similarities and differences

Collisionless tangential discontinuity between pair plasma and electron–proton plasma

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