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Dieckmann, M. E. & Bret, A. (2018). Electrostatic and magnetic instabilities in the transition layer of a collisionless weakly relativistic pair shock. Monthly notices of the Royal Astronomical Society, 473(1), 198-209.
Open this publication in new window or tab >>Electrostatic and magnetic instabilities in the transition layer of a collisionless weakly relativistic pair shock
2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 473, no 1, 198-209 p.Article in journal (Refereed) Published
Abstract [en]

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 two-stream 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.

Place, publisher, year, edition, pages
Oxford University Press, 2018
Keyword
relativistic pair jet, collisionless instability, PIC simulations
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:liu:diva-141947 (URN)10.1093/mnras/stx2387 (DOI)000415653600017 ()
Note

Funding agencies: Ministerio de Educacion y Ciencia, Spain [ENE2013-45661-C2-1-P, ENE2016-75703-R]; Junta de Comunidades de Castilla-La Mancha [PEII-2014-008-P]; Grand Equipement National de Calcul Intensif (GENCI) [x2016046960]

Available from: 2017-10-13 Created: 2017-10-13 Last updated: 2017-12-12Bibliographically approved
Bret, A., Pe'er, A., Sironi, L., Dieckmann, M. E. & Narayan, R. (2017). Departure from MHD prescriptions in shock formation over a guiding magnetic field. Laser and particle beams (Print), 35, 513-519.
Open this publication in new window or tab >>Departure from MHD prescriptions in shock formation over a guiding magnetic field
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2017 (English)In: Laser and particle beams (Print), ISSN 0263-0346, E-ISSN 1469-803X, Vol. 35, 513-519 p.Article in journal (Refereed) Published
Abstract [en]

In plasmas where the mean-free-path is much larger than the size of the system, shock waves can arise with a front much shorter than the mean-free path. These so-called "collisionless shocks" are mediated y collective plasma interactions. Studies conducted so far on these shocks found that although binary collisions are absent, the distribution functions are thermalized downstream by scattering on the fields, so that magnetohydrodynamic prescriptions may apply. Here we show a clear departure from this pattern in the case of Weibel shocks forming over a flow-aligned magnetic field. A micro-physical analysis of the particle motion in the Weibel filaments shows how they become unable to trap the flow in the presence of too strong a field, inhibiting the mechanism of shock formation. Particle-in-cell simulations confirm these results.

Place, publisher, year, edition, pages
Cambridge University Press, 2017
Keyword
plasma shock, kinetic theory, PIC simulation
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:liu:diva-140164 (URN)10.1017/S0263034617000519 (DOI)000409042200017 ()
Note

Funding agencies: European Union Seventh Framework Program [618499]; NASA [NNX12AO83G, TCAN NNX14AB47G, NAS8-03060]; NASA - Chandra X-ray Center [PF4-150126];  [ENE2013-45661-C2-1-P];  [PEII-2014-008-P];  [ANR-14-CE33-0019 MACH];  [SNIC2015-1-305]

Available from: 2017-09-02 Created: 2017-09-02 Last updated: 2017-11-03Bibliographically approved
Dieckmann, M. E., Folini, D., Walder, R., Romagnani, L., d'Humieres, E., Bret, A., . . . Ynnerman, A. (2017). Emergence of MHD structures in a collisionless PIC simulation plasma. Physics of Plasmas, 24(9), Article ID 094502.
Open this publication in new window or tab >>Emergence of MHD structures in a collisionless PIC simulation plasma
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2017 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 9, 094502Article in journal (Refereed) Published
Abstract [en]

The expansion of a dense plasma into a dilute plasma across an initially uniform perpendicular magnetic field is followed with a one-dimensional particle-in-cell simulation over magnetohydrodynamics time scales. The dense plasma expands in the form of a fast rarefaction wave. The accelerated dilute plasma becomes separated from the dense plasma by a tangential discontinuity at its back. A fast magnetosonic shock with the Mach number 1.5 forms at its front. Our simulation demonstrates how wave dispersion widens the shock transition layer into a train of nonlinear fast magnetosonic waves.

Place, publisher, year, edition, pages
Melville, NY, United States: A I P Publishing LLC, 2017
Keyword
PIC simulation, fast magnetosonic shock
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:liu:diva-140648 (URN)10.1063/1.4991702 (DOI)000412107400120 ()
Note

Funding agencies: CRAL; Grand Equipement National de Calcul Intensif (GENCI) [x2016046960]

Available from: 2017-09-06 Created: 2017-09-06 Last updated: 2017-11-03Bibliographically approved
Dieckmann, M. E., Doria, D., Ahmed, H., Romagnani, L., Sarri, G., Folini, D., . . . Borghesi, M. (2017). Expansion of a radial plasma blast shell into an ambient plasma. Physics of Plasmas, 24(9), Article ID 094501.
Open this publication in new window or tab >>Expansion of a radial plasma blast shell into an ambient plasma
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2017 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 9, 094501Article in journal (Refereed) Published
Abstract [en]

The expansion of a radial blast shell into an ambient plasma is modeled with a particle-in-cell simulation. The unmagnetized plasma consists of electrons and protons. The formation and evolution of an electrostatic shock is observed, which is trailed by ion-acoustic solitary waves that grow on the beam of the blast shell ions in the post-shock plasma. In spite of the initially radial symmetric outflow, the solitary waves become twisted and entangled and, hence, they break the radial symmetry of the flow. The waves and their interaction with the shocked ambient ions slow down the blast shell protons and bring the post-shock plasma closer to equilibrium.

Place, publisher, year, edition, pages
Melville, NY, United States: A I P Publishing LLC, 2017
Keyword
Laser plasma, PIC simulation, collisionless shock, solitary waves
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:liu:diva-140165 (URN)10.1063/1.4991694 (DOI)000412107400119 ()
Available from: 2017-09-02 Created: 2017-09-02 Last updated: 2017-11-03Bibliographically approved
Bret, A. & Dieckmann, M. E. (2017). Hierarchy of instabilities for two counter-streaming magnetized pair beams: Influence of field obliquity. Physics of Plasmas, 24(6), Article ID 062105.
Open this publication in new window or tab >>Hierarchy of instabilities for two counter-streaming magnetized pair beams: Influence of field obliquity
2017 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 6, 062105Article in journal (Refereed) Published
Abstract [en]

The hierarchy of unstable modes when two counter-streaming pair plasmas interact over a flow-aligned magnetic field has been recently investigated [Phys. Plasmas 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 γ0, 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.

Place, publisher, year, edition, pages
A I P Publishing LLC, 2017
Keyword
instabilities, plasma waves, magnetic field
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:liu:diva-138195 (URN)10.1063/1.4985321 (DOI)000404639000010 ()
Note

Funding agencies: Ministerio de Educacion y Ciencia, Spain [ENE2013-45661-C2-1-P, ENE2016-75703-R]; Junta de Comunidades de Castilla-La Mancha [PEII-2014-008-P]

Available from: 2017-06-12 Created: 2017-06-12 Last updated: 2017-11-03Bibliographically approved
Dieckmann, M. E., Sarri, G., Doria, D., Ynnerman, A. & Borghesi, M. (2016). Particle-in-cell simulation study of a lower-hybrid shock. Physics of Plasmas, 23(6), 062111.
Open this publication in new window or tab >>Particle-in-cell simulation study of a lower-hybrid shock
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2016 (English)In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 23, no 6, 062111- p.Article in journal (Refereed) Published
Abstract [en]

The expansion of a magnetized high-pressure plasma into a low-pressure ambient medium is examined with particle-in-cell simulations. The magnetic field points perpendicular to the plasmas expansion direction and binary collisions between particles are absent. The expanding plasma steepens into a quasi-electrostatic shock that is sustained by the lower-hybrid (LH) wave. The ambipolar electric field points in the expansion direction and it induces together with the background magnetic field a fast E cross B drift of electrons. The drifting electrons modify the background magnetic field, resulting in its pile-up by the LH shock. The magnetic pressure gradient force accelerates the ambient ions ahead of the LH shock, reducing the relative velocity between the ambient plasma and the LH shock to about the phase speed of the shocked LH wave, transforming the LH shock into a nonlinear LH wave. The oscillations of the electrostatic potential have a larger amplitude and wavelength in the magnetized plasma than in an unmagnetized one with otherwise identical conditions. The energy loss to the drifting electrons leads to a noticeable slowdown of the LH shock compared to that in an unmagnetized plasma. Published by AIP Publishing.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2016
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:liu:diva-130440 (URN)10.1063/1.4953568 (DOI)000379172200017 ()
Note

Funding Agencies|EPSRC [EP/N022696/1]

Available from: 2016-08-15 Created: 2016-08-05 Last updated: 2017-11-28
Marcowith, A., Bret, A., Bykov, A., Dieckmann, M. E., Drury, L., Lembege, B., . . . Stockem Novo, A. (2016). The microphysics of collisionless shock waves. Reports on progress in physics (Print), 79(4), Article ID 046901.
Open this publication in new window or tab >>The microphysics of collisionless shock waves
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2016 (English)In: Reports on progress in physics (Print), ISSN 0034-4885, E-ISSN 1361-6633, Vol. 79, no 4, 046901Article, review/survey (Refereed) Published
Abstract [en]

Collisionless shocks, that is shocks mediated by electromagnetic processes, are customary in space physics and in astrophysics. They are to be found in a great variety of objects and environments: magnetospheric and heliospheric shocks, supernova remnants, pulsar winds and their nebulæ, active galactic nuclei, gamma-ray bursts and clusters of galaxies shock waves. Collisionless shock microphysics enters at different stages of shock formation, shock dynamics and particle energization and/or acceleration. It turns out that the shock phenomenon is a multi-scale non-linear problem in time and space. It is complexified by the impact due to high-energy cosmic rays in astrophysical environments. This review adresses the physics of shock formation, shock dynamics and particle acceleration based on a close examination of available multi-wavelength or in situ observations, analytical and numerical developments. A particular emphasis is made on the different instabilities triggered during the shock formation and in association with particle acceleration processes with regards to the properties of the background upstream medium. It appears that among the most important parameters the background magnetic field through the magnetization and its obliquity is the dominant one. The shock velocity that can reach relativistic speeds has also a strong impact over the development of the micro-instabilities and the fate of particle acceleration. Recent developments of laboratory shock experiments has started to bring some new insights in the physics of space plasma and astrophysical shock waves. A special section is dedicated to new laser plasma experiments probing shock physics.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:liu:diva-126458 (URN)10.1088/0034-4885/79/4/046901 (DOI)000373216700006 ()27007555 (PubMedID)
Note

Funding agencies: ISSI; french ANR MACH project; Ministerio de Educacion y Ciencia, Spain [ENE2013-45661-C2-1-P]; Junta de Comunidades de Castilla-La Mancha, Spain [PEII-2014-008-P]

Available from: 2016-03-26 Created: 2016-03-26 Last updated: 2017-11-30
Bret, A., Stockem Novo, A., Narayan, R., Ruyer, C., Dieckmann, M. E. & Silva, L. O. (2016). Theory of the formation of a collisionless Weibel shock: pair vs. electron/proton plasmas. Laser and particle beams (Print), 34(2), 362-367.
Open this publication in new window or tab >>Theory of the formation of a collisionless Weibel shock: pair vs. electron/proton plasmas
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2016 (English)In: Laser and particle beams (Print), ISSN 0263-0346, E-ISSN 1469-803X, Vol. 34, no 2, 362-367 p.Article in journal (Refereed) Published
Abstract [en]

Collisionless shocks are shocks in which the mean-free path is much larger than the shock front. They are ubiquitous in astrophysics and the object of much current attention as they are known to be excellent particle accelerators that could be the key to the cosmic rays enigma. While the scenario leading to the formation of a fluid shock is well known, less is known about the formation of a collisionless shock. We present theoretical and numerical results on the formation of such shocks when two relativistic and symmetric plasma shells (pair or electron/proton) collide. As the two shells start to interpenetrate, the overlapping region turns Weibel unstable. A key concept is the one of trapping time τp, which is the time when the turbulence in the central region has grown enough to trap the incoming flow. For the pair case, this time is simply the saturation time of the Weibel instability. For the electron/proton case, the filaments resulting from the growth of the electronic and protonic Weibel instabilities, need to grow further for the trapping time to be reached. In either case, the shock formation time is 2τp in two-dimensional (2D), and 3τp in 3D. Our results are successfully checked by particle-in-cell simulations and may help designing experiments aiming at producing such shocks in the laboratory.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:liu:diva-127503 (URN)10.1017/S0263034616000197 (DOI)000378358100019 ()
Available from: 2016-05-27 Created: 2016-04-28 Last updated: 2017-11-30
Sarri, G., Dieckmann, M. E., Kourakis, I., Di Piazza, A., Reville, B., Keitel, C. & Zepf, M. (2015). Overview of laser-driven generation of electron–positron beams. Journal of Plasma Physics, 81(04), 1-14, Article ID 455810401.
Open this publication in new window or tab >>Overview of laser-driven generation of electron–positron beams
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2015 (English)In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, no 04, 1-14 p., 455810401Article in journal (Refereed) Published
Abstract [en]

Electron–positron (e–p) plasmas are widely thought to be emitted, in the form of ultra-relativistic winds or collimated jets, by some of the most energetic or powerful objects in the Universe, such as black-holes, pulsars, and quasars. These phenomena represent an unmatched astrophysical laboratory to test physics at its limit and, given their immense distance from Earth (some even farther than several billion light years), they also provide a unique window on the very early stages of our Universe. However, due to such gigantic distances, their properties are only inferred from the indirect interpretation of their radiative signatures and from matching numerical models: their generation mechanism and dynamics still pose complicated enigmas to the scientific community. Small-scale reproductions in the laboratory would represent a fundamental step towards a deeper understanding of this exotic state of matter. Here we present recent experimental results concerning the laser-driven production of ultra-relativistic e–p beams. In particular, we focus on the possibility of generating beams that present charge neutrality and that allow for collective effects in their dynamics, necessary ingredients for the testing pair-plasma physics in the laboratory. A brief discussion of the analytical and numerical modelling of the dynamics of these plasmas is also presented in order to provide a summary of the novel plasma physics that can be accessed with these objects. Finally, general considerations on the scalability of laboratory plasmas up to astrophysical scenarios are given.

Place, publisher, year, edition, pages
Cambridge University Press, 2015
Keyword
lepton beams, laser experiment
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:liu:diva-119503 (URN)10.1017/S002237781500046X (DOI)000356436400015 ()
Available from: 2015-06-18 Created: 2015-06-18 Last updated: 2017-12-04
Dieckmann, M. E., Sarri, G., Markoff, S., Borghesi, M. & Zepf, M. (2015). PIC simulation study of the interaction between a relativisticallymoving leptonic micro-cloud and ambient electrons.. Astronomy and Astrophysics, 577(A137), 1-10.
Open this publication in new window or tab >>PIC simulation study of the interaction between a relativisticallymoving leptonic micro-cloud and ambient electrons.
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2015 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 577, no A137, 1-10 p.Article in journal (Refereed) Published
Abstract [en]

Context. The jets of compact accreting objects are composed of electrons and a mixture of positrons and ions. These outflows impinge on the interstellar or intergalactic medium and both plasmas interact via collisionless processes. Filamentation (beam-Weibel) instabilities give rise to the growth of strong electromagnetic fields. These fields thermalize the interpenetrating plasmas.

Aims. Hitherto, the effects imposed by a spatial non-uniformity on filamentation instabilities have remained unexplored. We examine the interaction between spatially uniform background electrons and a minuscule cloud of electrons and positrons. The cloud size is comparable to that created in recent laboratory experiments and such clouds may exist close to internal and external shocks of leptonic jets. The purpose of our study is to determine the prevalent instabilities, their ability to generate electromagnetic fields and the mechanism, by which the lepton micro-cloud transfers energy to the background plasma.

Methods. A square micro-cloud of equally dense electrons and positrons impinges in our particle-in-cell (PIC) simulation on a spatially uniform plasma at rest. The latter consists of electrons with a temperature of 1 keV and immobile ions. The initially charge- and current neutral micro-cloud has a temperature of 100 keV and a side length of 2.5 plasma skin depths of the micro-cloud. The side length is given in the reference frame of the background plasma. The mean speed of the micro-cloud corresponds to a relativistic factor of 15, which is relevant for laboratory experiments and for relativistic astrophysical outflows. The spatial distributions of the leptons and of the electromagnetic fields are examined at several times.

Results. A filamentation instability develops between the magnetic field carried by the micro-cloud and the background electrons. The electromagnetic fields, which grow from noise levels, redistribute the electrons and positrons within the cloud, which boosts the peak magnetic field amplitude. The current density and the moduli of the electromagnetic fields grow aperiodically in time and steadily along the direction that is anti-parallel to the cloud’s velocity vector. The micro-cloud remains conjoined during the simulation. The instability induces an electrostatic wakefield in the background plasma.

Conclusions. Relativistic clouds of leptons can generate and amplify magnetic fields even if they have a microscopic size, which implies that the underlying processes can be studied in the laboratory. The interaction of the localized magnetic field and high-energy leptons will give rise to synchrotron jitter radiation. The wakefield in the background plasma dissipates the kinetic energy of the lepton cloud. Even the fastest lepton micro-clouds can be slowed down by this collisionless mechanism. Moderately fast charge- and current neutralized lepton micro–clouds will deposit their energy close to relativistic shocks and hence they do not constitute an energy loss mechanism for the shock.

Place, publisher, year, edition, pages
EDP Sciences, 2015
Keyword
PIC simulations, lepton clouds
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:liu:diva-117985 (URN)10.1051/0004-6361/201424797 (DOI)000357345900089 ()
Available from: 2015-05-19 Created: 2015-05-19 Last updated: 2017-12-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-4055-0552

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