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  • 51.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Lerche, Ian
    Institute of Theoretical Physics IV Ruhr-University Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum.
    Drury, Luke O C
    School of Cosmic Physics Dublin Institute for Advanced Studies.
    Aspects of self-similarity of the filamentation instability2007Inngår i: 34th European Physical Society Conference on Plasma Physics,2007, Warsaw: European Physical Society , 2007, s. P2.080-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The filamentation instability (FI) is an aperiodically growing instability driven by counterpropagating electron beams. Its ability to generate magnetic fields is important for the energetic plasmas in gamma ray burst jets and inertial confinement fusion plasmas. The FI has been examined both analytically and with particle-in-cell (PIC) simulations. We perform PIC simulations and follow the FI through its nonlinear saturation. The power spectrum of the flow-aligned current component is self-similar during the linear phase. We show that the perpendicular current distribution is self-similar during the nonlinear evolution and that the filament size increases linearly with time. We demonstrate that, at least for warm plasmas, the current filaments can't be described by simple flux tubes. Instead, the filaments merge by magnetic reconnection to form larger, partially overlapping current sheets. In the filament overlap region the electrons are accelerated.

  • 52.
    Dieckmann, Mark E
    et al.
    Ruhr-University Bochum.
    Lerche, Ian
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Drury, Luke OC
    School of Cosmic Physics Dublin Institute for Advanced Studies, Ireland.
    Aspects of self-similar current distributions resulting from the plasma filamentation instability2007Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 9, s. 10-1-10-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Colliding plasmas can form current filaments that are magnetically confined and interact through electromagnetic fields during the nonlinear evolution of this filamentation instability. A nonrelativistic and a relativistic electron flow are examined. Two-dimensional (2D) particle-in-cell (PIC) simulations evolve the instability in a plane orthogonal to the flow vector and confirm that the current filaments move, merge through magnetic reconnection and evolve into current sheets and large flux tubes. The current filaments overlap over limited spatial intervals. Electrons accelerate in the overlap region and their final energy distribution decreases faster than exponential. The spatial power spectrum of the filaments in the flow-aligned current component can be approximated by a power-law during the linear growth phase. This may reflect a phase transition. The power spectrum of the current component perpendicular to the flow direction shows a power-law also during the nonlinear phase, possibly due to preferential attachment. The power-law distributed power spectra evidence self-similarity over a limited scale size and the wavenumber of the maximum of the spatial power spectrum of the filament distribution decreases linearly in time. Power-law correlations of velocity fields, which could be connected to the current filaments, may imply super-diffusion.

  • 53.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Ljung, Patric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    McClements, KG
    Linkoping Univ, Inst Technol & Nat Sci, S-60174 Norrkoping, Sweden UKAEA Euratom Fus Assoc, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.
    Large-scale numerical simulations of ion beam instabilities in unmagnetized astrophysical plasmas2000Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 7, nr 12, s. 5171-5181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Collisionless quasiperpendicular shocks with magnetoacoustic Mach numbers exceeding a certain threshold are known to reflect a fraction of the upstream ion population. These reflected ions drive instabilities which, in a magnetized plasma, can give rise to electron acceleration. In the case of shocks associated with supernova remnants (SNRs), electrons energized in this way may provide a seed population for subsequent acceleration to highly relativistic energies. If the plasma is weakly magnetized, in the sense that the electron cyclotron frequency is much smaller than the electron plasma frequency omega (p), a Buneman instability occurs at omega (p). The nonlinear evolution of this instability is examined using particle-in-cell simulations, with initial parameters which are representative of SNR shocks. For simplicity, the magnetic field is taken to be strictly zero. It is shown that the instability saturates as a result of electrons being trapped by the wave potential. Subsequent evolution of the waves depends on the temperature of the background protons T-i and the size of the simulation box L. If T-i is comparable to the initial electron temperature T-e, and L is equal to one Buneman wavelength lambda (0), the wave partially collapses into low frequency waves and backscattered waves at around omega (p). If, on the other hand, T-i much greater thanT(e) and L = lambda (0), two high frequency waves remain in the plasma. One of these waves, excited at a frequency slightly lower than omega (p), may be a Bernstein-Greene-Kruskal mode. The other wave, excited at a frequency well above omega (p), is driven by the relative streaming of trapped and untrapped electrons. In a simulation with L = 4 lambda (0), the Buneman wave collapses on a time scale consistent with the excitation of sideband instabilities. Highly energetic electrons were not observed in any of these simulations, suggesting that the Buneman instability can only produce strong electron acceleration in a magnetized plasma. [S1070-664X(00)02712-9].

  • 54.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Ljung, Patric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    McClements, K.G.
    EURATOM/UKAEA Fusion Association, Culham Science Center, Abingdom, Oxfordshire OX 14 3DB, United Kingdom.
    Three-dimensional visualization of electron acceleration in a magnetized plasma2002Inngår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 30, nr 1 I, s. 20-21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine wave-particle interactions in a magnetized plasma. We present snapshots of an animation of the three-dimensional electron phase space distribution produced by an electrostatic wave propagating across a magnetic field. The distribution function has been evolved by a particle in cell simulation. The electron phase space has been visualized by distributing the simulation electrons over an array representing phase space density and by volume rendering this array. The results are, due to the choice of initial plasma and wave parameters, of relevance for electron acceleration at astrophysical shocks.

  • 55.
    Dieckmann, Mark E
    et al.
    Ruhr-Universität Bochum.
    Meli, Athina
    Department of Physics National University of Athens, Greece.
    Shukla, Padma Kant
    Institut für Theoretische Physik IV Ruhr-Universität Bochum, D-44780 Bochum, Germany.
    Drury, Luke OC
    Cosmic Rays Section Dublin Institute for Advanced Studies, Dublin, Ireland.
    Mastichiadis, Apostolos
    Department of Physics, National University of Athens National University of Athens.
    Two-dimensional PIC simulations of ion beam instabilities in Supernova-driven plasma flows2008Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, s. 065020-1-14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Supernova remnant blast shells can reach the flow speed vs = 0.1c and shocks form at its front. Instabilities driven by shock-reflected ion beams heat the plasma in the foreshock, which may inject particles into diffusive acceleration. The ion beams can have the speed vb vs. For vb vs the Buneman or upper-hybrid instabilities dominate, while for vb vs the filamentation and mixed modes grow faster. Here the relevant waves for vb vs are examined and how they interact nonlinearly with the particles. The collision of two plasma clouds at the speed vs is modelled with particle-in-cell simulations, which convect with them magnetic fields oriented perpendicular to their flow velocity vector. One simulation models equally dense clouds and the other one uses a density ratio of 2. Both simulations show upper-hybrid waves that are planar over large spatial intervals and that accelerate electrons to ~10 keV. The symmetric collision yields only short oscillatory wave pulses, while the asymmetric collision also produces large-scale electric fields, probably through a magnetic pressure gradient. The large-scale fields destroy the electron phase space holes and they accelerate the ions, which facilitates the formation of a precursor shock. 

  • 56.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Moreno, Quentin
    Universite de Bordeaux, CNRS, CEA, CELIA, Talence, France.
    Doria, Domenico
    Centre for Plasma Physics (CPP), Queen's University Belfast, UK.
    Romagnani, Lorenzo
    Ecole Polytechnique, CNRS, LULI, Palaiseau, France.
    Sarri, Gianluca
    Centre for Plasma Physics (CPP), Queen's University Belfast, UK.
    Folini, Doris
    Ecole Nationale Superieure, Lyon, CRAL, Universite de Lyon, France.
    Walder, Rolf
    Ecole Nationale Superieure, Lyon, CRAL, Universite de Lyon, France.
    Bret, Antoiine
    ETSI Industriales, Universidad de Castilla-La Mancha, Spain.
    d'Humieres, Emmanuel
    Universite de Bordeaux, CNRS, CEA, CELIA, Talence, France.
    Borghesi, Marco
    Centre for Plasma Physics (CPP), Queen's University Belfast, UK.
    Expansion of a radially symmetric blast shell into a uniformly magnetized plasma2018Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, nr 5, artikkel-id 052108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The expansion of a thermal pressure-driven radial blast shell into a dilute ambient plasma is examined with two-dimensional PIC simulations. The purpose is to determine if laminar shocks form in a collisionless plasma which resemble their magnetohydrodynamic counterparts. The ambient plasma is composed of electrons with the temperature of 2 keV and cool fully ionized nitrogen ions. It is permeated by a spatially uniform magnetic field. A forward shock forms between the shocked ambient medium and the pristine ambient medium, which changes from an ion acoustic one through a slow magnetosonic one to a fast magnetosonic shock with increasing shock propagation angles relative to the magnetic field. The slow magnetosonic shock that propagates obliquely to the magnetic field changes into a tangential discontinuity for a perpendicular propagation direction, which is in line with the magnetohydrodynamic model. The expulsion of the magnetic field by the expanding blast shell triggers an electron-cyclotron drift instability.

  • 57.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    OC Drury, Luke
    School of Cosmic Physics Dublin Institute for Advanced Studies, Ireland.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    On the ultrarelativistic two-stream instability, electrostatic turbulence and Brownian motion2006Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experimental evidence indicates that bulk plasma flow at ultrarelativistic speeds is common in astrophysical settings, e.g. the collimated jets of active galactic nuclei and gamma ray bursts. The low-plasma density of such flows implies their collisionless relaxation by means of wave-particle interactions. Such processes are not well understood in the ultrarelativistic regime. The thermalization of two interpenetrating equally dense electron-proton (e -p) beams in the absence of a magnetic field is examined here by means of 1.5D particle-in-cell simulations. The relative beam speeds correspond to Lorentz factors in the range 200-1000. The constraint to one spatial simulation dimension, which is aligned with the beam velocity vectors, implies that only the two-stream (TS) instability and the Weibel-type instability can grow, while filamentation instabilities are excluded. With this constraint and for our plasma parameters, the TS instability dominates. The electrostatic waves grow, saturate by the trapping of electrons, and collapse. The interaction of the electrons with the electric fields after the wave collapse represents a relativistic Wiener process. In response, the electrons are rapidly thermalized. The final electron distribution can be interpreted as a relativistic Maxwellian distribution with a high-energy tail arising from ultrarelativistic phase space holes. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

  • 58.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Parviainen, M.
    ITN/Media Technology Linköping University.
    Visualization of 4-D particle data sets2005Inngår i: Plasma Science, IEEE Transactions on, ISSN 0093-3813, Vol. 33, nr 2, s. 536-537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine the phase space evolution of electrons under the influence of two counter-propagating electrostatic waves that move obliquely to an ambient magnetic field. The waves are driven by proton beams and their interaction with the electrons yields phase space structures that involve one spatial and three velocity components. We show how using color allows us to integrate the full four-dimensional electron data provided by a particle-in-cell (PIC) simulation into a single image. We find an initially developing antisymmetric electron phase space distribution and what appears to be a locking of the phase of the trapped electrons relative to the magnetic field. The phase space distribution at later times shows that there is no separatrix between the trapped electron islands of both waves.

  • 59.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Rowlands, G
    Eliasson, B
    Shukla, PK
    Particle-in-cell simulations of electron acceleration by a simple capacitative antenna in collisionless plasma2004Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, nr A12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine the electron acceleration by a localized electrostatic potential oscillating at high frequencies by means of particle-in-cell (PIC) simulations, in which we apply oscillating electric fields to two neighboring simulation cells. We derive an analytic model for the direct electron heating by the externally driven antenna electric field, and we confirm that it approximates well the electron heating obtained in the simulations. In the simulations, transient waves accelerate electrons in a sheath surrounding the antenna. This increases the Larmor radii of the electrons close to the antenna, and more electrons can reach the antenna location to interact with the externally driven fields. The resulting hot electron sheath is dense enough to support strong waves that produce high-energy sounder-accelerated electrons (SAEs) by their nonlinear interaction with the ambient electrons. By increasing the emission amplitudes in our simulations to values that are representative for the ones of the sounder on board the OEDIPUS C (OC) satellites, we obtain electron acceleration into the energy range which is comparable to the 20 keV energies of the SAE observed by the OC mission. The emission also triggers stable electrostatic waves oscillating at frequencies close to the first harmonic of the electron cyclotron frequency. We find this to be an encouraging first step of examining SAE generation with kinetic numerical simulation codes.

  • 60.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Rowlands, George
    Physics Department Warwick University, U.K..
    Shukla, Padma Kant
    Institute for Theoretical Physics IV Ruhr-University Bochum, Germany.
    The plasma filamentation instability in one dimension2008Inngår i: 35th EPS Conference on Plasma Physics,2008, Switzerland: Europhysics Conference Abstracts , 2008, Vol. 32F, s. P4.182-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The filamentation instability between counter-propagating beams of electrons is important for the magnetic field generation in astrophysical jets. Here this instability is considered for equally dense counterpropagating electron beams. It is demonstrated that the plasma evolves into a state, in which the electric fields driven by the magnetic pressure gradient balance the magnetic forces. This system is stationary in the 1D PIC simulation. The size distribution of the current filaments closely follows a Gumbel distribution within the statistical limitations.

  • 61.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Rugovaj, S.
    ITN/Media Technology Linköping University.
    Electron acceleration by fast electrostatic waves moving orthogonally across a magnetic field2005Inngår i: Plasma Science, IEEE Transactions on, ISSN 0093-3813, Vol. 33, nr 2, s. 530-531Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine electron acceleration in magnetized plasma by electrostatic waves that move orthogonally across a magnetic field with a phase speed that is comparable to the light speed. We evolve the plasma phase space distribution with a particle-in-cell code. We distribute the computational electrons over an array and we volume-render this phase space density. We show key images of an animation by which we follow the electron phase space distribution throughout the simulation and which shows that the electron transport across the magnetic field, the collapse of the electrostatic wave and the resulting turbulent wave fields can accelerate electrons to gigaelectronvolt energies for wave speeds that we may find in some astrophysical environments. © 2005 IEEE.

  • 62.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Sarri, G.
    Queens University of Belfast, North Ireland.
    Doria, D.
    Queens University of Belfast, North Ireland.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Borghesi, M.
    Queens University of Belfast, North Ireland.
    Particle-in-cell simulation study of a lower-hybrid shock2016Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 23, nr 6, s. 062111-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 63.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Sarri, Gianluca
    Centre for Plasma Physics (CPP), Queen's University Belfast, Belfast, United Kingdom.
    Folini, Doris
    École Normale Supérieure, Université de Lyon, Lyon, France.
    Walder, Rolf
    École Normale Supérieure, Université de Lyon, Lyon, France.
    Borghesi, Marco
    Centre for Plasma Physics (CPP), Queen's University Belfast, Belfast, United Kingdom.
    Cocoon formation by a mildly relativistic pair jet in unmagnetized collisionless electron-proton plasma2018Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, nr 11, artikkel-id 112903Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By modelling the expansion of a cloud of electrons and positrons with the temperature of 400 keV which propagates at the mean speed of 0.9c (c: speed of light) through an initially unmagnetized electron-proton plasma with a particle-in-cell 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 of 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.

  • 64.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Shukla, P. K.
    Theoretische Physik IV, Ruhr-University Bochum.
    Parviainen, M.
    Theoretische Physik IV Ruhr-University Bochum.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Numerical simulation and visualization of stochastic and ordered electron motion forced by electrostatic waves in a magnetized plasma2005Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, nr 9, s. 92902-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interaction of electrons with strong electrostatic waves and an external magnetic field, which is oriented obliquely to the wave vector, leads to stochastic acceleration and acceleration by the cross-field transport of trapped electrons. This wave-particle interaction involves three velocity components of the electrons and, for a plane wave, one spatial position. The phase-space evolution is also affected by nonlinear oscillations in the amplitude of the saturated wave, and the system becomes explicitly time dependent. Here, the wave-particle interactions are investigated with a particle-in-cell simulation, and the results are visualized by examining orbits of individual electrons and also time-evolving phase-space structures. Two clearly distinct electron populations are identified, one due to cross-field transport and the other due to stochastic interactions, which are robust against growing secondary modes. © 2005 American Institute of Physics.

  • 65.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Shukla, P K
    Ruhr University Bochum.
    Stenflo, Lennart
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Simulation study of the filamentation of counter-streaming beams of the electrons and positrons in plasmas2009Inngår i: PLASMA PHYSICS AND CONTROLLED FUSION, ISSN 0741-3335, Vol. 51, nr 6, s. 065015-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The filamentation instability (FI) driven by two spatially uniform and counter-streaming beams of charged particles in plasmas is modelled by a particle-in-cell simulation. Each beam consists of electrons and positrons. The four species are equally dense and have the same temperature. The one-dimensional simulation direction is orthogonal to the beam velocity vector. The magnetic field grows spontaneously and rearranges the particles in space, such that the distributions of the electrons of one beam and the positrons of the second beam match. The simulation demonstrates that as a result no electrostatic field is generated by the magnetic field through its magnetic pressure gradient prior to its saturation. This electrostatic field would be repulsive at the centres of the filaments and limit the maximum charge and current density. The filaments of electrons and positrons in this simulation reach higher charge and current densities than in one with no positrons. The oscillations of the magnetic field strength induced by the magnetically trapped particles result in an oscillatory magnetic pressure gradient force. The latter interplays with the statistical fluctuations in the particle density and it probably enforces a charge separation, by which electrostatic waves grow after the FI has saturated.

  • 66.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan. Institute of Theoretical Physics IV, Ruhr‐University Bochum, Bochum, Germany.
    Shukla, Padma
    Institute of Theoretical Physics IV, Ruhr‐University Bochum, Bochum, Germany.
    Wakefield acceleration in relativistic plasma flows: Electron acceleration to cosmic ray energies2007Inngår i: GAMMA-RAY BURSTS: PROSPECTS FOR GLAST: Stockholm Symposium on GRB's / [ed] Magnus Axelsson and Felix Ryde, Melville, N.Y. USA: American Institute of Physics (AIP), 2007, s. 59-68Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Energetic particles observed in astrophysical environments imply the existence of efficient particle accelerators. These accelerators could be driven by relativistically colliding plasma. Collision-less plasmas thermalize through the growth of electromagnetic and electrostatic waves and the subsequent wave-particle interactions. Kinetic interactions are potentially important in this context, since they can transfer significant energy to limited plasma phase space intervals and they thus constitute energy-efficient accelerators. Kinetic processes relevant to astroplasma physics can be modelled by relativistic particle-in-cell simulations. Here we revise this simulation method and apply it to ion-beam driven plasma wave accelerators that may be involved in the thermalization of supernova remnant shocks and the internal shocks of relativistic astrophysical jets.

  • 67.
    Dieckmann, Mark E
    et al.
    Ruhr-Universität Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Electron surfing acceleration by the electron two-stream instability in a weak magnetic field2006Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, nr October, s. 1515-1530Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermalization of relativistically flowing colliding plasmas is not well understood. The transition layer, in which both plasmas interact and thermalize, is wide and highly structured and the instabilities in this layer may yield non-thermal particle distributions and shock-less energy dissipation. The objective in this work is to explore the ability of an electron two-stream instability for thermalizing a plasma beam that moves at the mildly relativistic speed 0.3c through weakly magnetized plasma and to identify the resulting particle distributions. It is demonstrated here with particle-in-cell simulations that the electron two-stream instability leads to waves that propagate within a wide angular range relative to the flow velocity. The waves are thus not planar, as required for efficient electron surfing acceleration (ESA). The short lifetime of the waves implies, however, only weak modifications of the ESA by the oblique modes, since the waves are sufficiently homogeneous. The ion (proton) beams are not modulated, which would be required to extract some of their energy. The instability can thus heat the electrons significantly, but it fails to accelerate them to relativistic energies and it cannot form a shock layer by thermalizing the protons, at least not for the system and the resolved timescales considered here.

  • 68.
    Dieckmann, Mark E
    et al.
    Ruhr-Universität Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Drury, Luke OC
    School of Cosmic Physics Dublin Institute for Advanced Studies, Ireland.
    The formation of a relativistic partially electromagnetic planar plasma shock2008Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 675, nr 1, s. 586-595Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Relativistically colliding plasma is modeled by particle-in-cell simulations in one and two spatial dimensions, with an ion-to-electron mass ratio of 400 and a temperature of 100 keV. The energy of an initial quasi-parallel magnetic field is 1% of the plasma kinetic energy. Energy dissipation by a growing wave pulse of mixed polarity, probably an oblique whistler wave, and different densities of the colliding plasma slabs result in the formation of an energetic electromagnetic structure within milliseconds. The structure, which develops for an initial collision speed of 0.9c, accelerates electrons to Lorentz factors of several hundred. A downstream region forms, separating the forward and reverse shocks. In this region, the plasma approaches an energy equipartition between electrons, ions, and the magnetic field. The electron energy spectrum resembles a power law at high energies, with an exponent close to −2.7, or . The magnetic field reflects upstream ions, which form a beam and drag the electrons along to preserve the plasma quasineutrality. The forward and reverse shocks are asymmetric due to the unequal slab densities. The forward shock may be representative for the internal shocks of gamma-ray bursts.  

  • 69.
    Dieckmann, Mark E
    et al.
    Ruhr-University Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Eliasson, Bengt
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Formation of electrostatic structures by wakefield acceleration in ultrarelativistic plasma flows: Electron acceleration to cosmic ray energies2006Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 6, s. 062905-1-062905-8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ever increasing performance of supercomputers is now enabling kinetic simulations of extreme astrophysical and laser produced plasmas. Three-dimensional particle-in-cell (PIC) simulations of relativistic shocks have revealed highly filamented spatial structures and their ability to accelerate particles to ultrarelativistic speeds. However, these PIC simulations have not yet revealed mechanisms that could produce particles with tera-electron volt energies and beyond. In this work, PIC simulations in one dimension (1D) of the foreshock region of an internal shock in a gamma ray burst are performed to address this issue. The large spatiotemporal range accessible to a 1D simulation enables the self-consistent evolution of proton phase space structures that can accelerate particles to giga-electron volt energies in the jet frame of reference, and to tens of tera-electron volt in the Earth's frame of reference. One potential source of ultrahigh energy cosmic rays may thus be the thermalization of relativistically moving plasma.

  • 70.
    Dieckmann, Mark E
    et al.
    Ruhr-University Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Eliasson, Bengt
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Particle-in-cell simulations of plasma slabs colliding at a mildly relativistic speed2006Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 8, nr October, s. 225-1-225-21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plasmas collide at relativistic speeds in many astrophysical and high-energy density laboratory environments. The boundaries that develop between such plasmas and expand at much larger speeds than the ion sound speed cs are not well understood. Here, we address two identical electron-proton plasma slabs that collide with a relativistic speed and a Mach number v/cs of over 400. The collision speed, the plasma temperature and magnetic field are such that the growth rate of the two-stream instability exceeds that of all other instabilities. We model a planar turbulent boundary (TB) with one-dimensional (1D) and 2D particle-in-cell (PIC) simulations. We show that the boundary dissipates its energy via electron phase space holes (EPSHs) that accelerate electrons at the boundary to relativistic speeds and increase significantly the speed of some protons. Our results are put into the context of a dynamic accretion disc and the jet of a microquasar. It is shown that the accelerated electrons could contribute to the disc wind and to relativistic leptonic jets, and possibly to the hard radiation component of the accretion disc.

  • 71.
    Dieckmann, Mark E
    et al.
    Ruhr-University Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    OC Drury, Luke
    School of Cosmic Physics Dublin Institute for Advanced Studies, Ireland.
    Particle-in-cell simulation studies of the non-linear evolution of ultrarelativistic two-stream instabilities2006Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 367, nr 3, s. 1072-1082Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Gamma-ray bursts are associated with relativistic plasma flow and intense X-ray and soft gamma-ray emissions. We perform particle-in-cell simulations to explore the growth and saturation of waves driven by the electrostatic two-stream instability that may contribute to the thermalization of the relativistic plasma flows and to the electromagnetic emissions. We evolve self-consistently the instability driven by two charge-neutral and cool interpenetrating beams of electrons and protons that move at a relative Lorentz factor of 100. We perform three simulations with the beam density ratios of 1, 2 and 10. The simulations show that the electrostatic waves saturate by trapping the electrons of only one beam and that the saturated electrostatic wave fields spatially modulate the mean momentum of the second beam, while retaining its temperature. Cavities form in the charge density of the latter beam which, in turn, compress the electrostatic waves to higher intensities. A runaway process develops that terminates with the collapse of the waves and the development of an exponential electron high-energy tail. We bring forward evidence that this energetic tail interacts stochastically with the charge density fluctuations of the relativistic proton beam. In response, an electron momentum distribution develops that follows an inverse power law up to a spectral break at four times the beam Lorentz factor.

  • 72.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    OC Drury, Luke
    School of Cosmic Physics Dublin Institute for Advanced Studies, Ireland.
    Simulation study of a two stream instability with a beam gamma = 1002004Inngår i: 33rd European Physical Society Conference of Plasma Physics,2006, Rome: European Physical Society , 2004, s. P2.049-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A better understanding of the relaxation of relativistic plasma flow is required to identify particle acceleration and radiation generation mechanisms at gamma ray bursts (GRBs). We perform particle-in-cell (PIC) simulations of the electrostatic two-stream instability for a beam speed VB with Gamma (v_b) = 100. The two p+e- beams are charge neutral and have comparable densities. The instability saturates by trapping the electrons of one beam and it modulates the electron density of the second beam. The electrostatic fields are compressed in the forming cavities to high intensities. The waves collapse, after which the electrons show an exponential tail that is eventually transformed into a power law tail.

  • 73.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Shukla, Padma Kant
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Drury, Luke O.C.
    Cosmic Physics Dublin Institute for Advanced Studies, Ireland.
    The formation of a relativistic planar plasma shock2008Inngår i: 35th EPS Conference on Plasma Physics,2008, Switzerland: Europhysics Conference Abstracts , 2008, Vol. 32F, s. O5.067-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The shock is considered that develops, when two plasma clouds collide at the speed 0.9 c. Initially, an almost flow-aligned magnetic field is introduced, which decreases the growth rates of the oblique mixed mode instability and of the filamentation instability. A 2D PIC simulation demonstrates that a planar, electromagnetic wave structure is growing that amplifies the magnetic field component orthogonal to the flow velocity vector. The formation of the forward and reverse shocks is followed with a 1D PIC simulation and it is shown that an energy equi-partition is established downstream between the ions, the electrons and the magnetic field. 

  • 74.
    Dieckmann, Mark E
    et al.
    Ruhr-Universität Bochum.
    Sircombe, Nathan J
    Space and Astrophysics Group University of Warwick, UK.
    Parviainen, Madelene
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Dendy, Richard O
    Space and Astrophysics Group University of Warwick.
    Phase speed of electrostatic waves: the critical parameter for efficient electron surfing acceleration2006Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, nr 4, s. 489-508Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Particle acceleration by means of nonlinear plasma wave interactions is of great topical interest. Accordingly, in this paper we focus on the electron surfing process. Self-consistent kinetic simulations, using both relativistic Vlasov and particle-in-cell (PIC) approaches, show here that electrons can be accelerated to highly relativistic energies (up to 100mec2) if the phase speed of the electrostatic wave is mildly relativistic (0.6c to 0.9c for the magnetic field strengths considered). The acceleration is strong because of relativistic stabilization of the nonlinearly saturated electrostatic wave, seen in both relativistic Vlasov and PIC simulations. An inverse power law momentum distribution can arise for the most strongly accelerated electrons. These results are of relevance to observed rapid changes in the radio synchrotron emission intensities from microquasars, gamma ray bursts and other astrophysical objects that require rapid acceleration mechanisms for electrons.

  • 75.
    Dieckmann, Mark E
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Chapman, S.C.
    Rowlands, G.
    Andersson, N.
    National Supercomputer Centre (NSC), University of Linköping, Valla Campus, SE-58183 Linköping, Sweden.
    Simulating thermal noise2004Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 69, nr 6, s. 456-460Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermal noise measurements by space-borne antennas are commonly used to determine plasma parameters like the electron density and the plasma temperature from the noise spectra. It would be desirable to have a controlled experiment in which noise from a plasma with known properties is sampled in space and in time and which results can then be used to reproduce the satellite measurements. Here we examine the possibility to use particle-in-cell (PIC) simulations as such an experiment. In this work we present a statistically averaged noise spectrum computed with a PIC code for a simple single-Maxwellian and unmagnetized electron plasma and we compare it to both, the thermal noise spectrum for the corresponding real plasma and the noise spectrum we would anticipate from our numerical scheme. We find that we can produce noise fields with sufficiently low amplitudes to keep the plasma in a linear regime. We show that the simulation noise at low and at large wave numbers differs not only from thermal noise of a physical plasma but also from the numerical noise we would expect from our numerical scheme. We explain the drop of the noise power at low wave numbers by our initial conditions. We find experimentally the relation that connects the theoretical noise spectrum for our simulation code with that we actually measure, provided that the phase velocity of the noise is less than the maximum velocity of the computational particles.

  • 76.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    The filamentation instability driven by warm electron beams: statistics and electric field generation2009Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 51, nr 12, s. 124042-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The filamentation instability of counterpropagating symmetric beams of electrons is examined with 1D and 2D particle-in-cell simulations, which are oriented orthogonally to the beam velocity vector. The beams are uniform, warm and their relative speed is mildly relativistic. The dynamics of the filaments is examined in 2D and it is confirmed that their characteristic size increases linearly in time. Currents orthogonal to the beam velocity vector are driven through the magnetic and electric fields in the simulation plane. The fields are tied to the filament boundaries and the scale size of the flow aligned and the perpendicular currents are thus equal. It is confirmed that the electrostatic and the magnetic forces are equally important, when the filamentation instability saturates in 1D. Their balance is apparently the saturation mechanism of the filamentation instability for our initial conditions. The electric force is relatively weaker but not negligible in the 2D simulation, where the electron temperature is set higher to reduce the computational cost. The magnetic pressure gradient is the principal source of the electrostatic field, when and after the instability saturates in the 1D simulation and in the 2D simulation.

  • 77.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Ahmed, Hamad
    Center for Plasma Physics, Queen's University Belfast, UK.
    Sarri, Gianluca
    Center for Plasma Physics, Queen's University Belfast, UK.
    Doria, Domenico
    Center for Plasma Physics, Queen's University Belfast.
    Kourakis, Ioannis
    Center for Plasma Physics, Queen's University Belfast, UK.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, Université Pierre et Marie Curie, Palaiseau, France.
    Pohl, Martin
    Institute of Physics & Astronomy, University of Potsdam, Germany .
    Borghesi, Marco
    Center for Plasma Physics, Queen's University Belfast, UK.
    Parametric study of non-relativistic electrostatic shocks and the structure of their transition layer2013Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, nr 4, s. 042111-1-042111-10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nonrelativistic electrostatic unmagnetized shocks are frequently observed in laboratory plasmas and they are likely to exist in astrophysical plasmas. Their maximum speed, expressed in units of the ion acoustic speed far upstream of the shock, depends only on the electron-to-ion temperature ratio if binary collisions are absent. The formation and evolution of such shocks is examined here for a wide range of shock speeds with particle-in-cell simulations. The initial temperatures of the electrons and the 400 times heavier ions are equal. Shocks form on electron time scales at Mach numbers between 1.7 and 2.2. Shocks with Mach numbers up to 2.5 form after tens of inverse ion plasma frequencies. The density of the shock-reflected ion beam increases and the number of ions crossing the shock thus decreases with an increasing Mach number, causing a slower expansion of the downstream region in its rest frame. The interval occupied by this ion beam is on a positive potential relative to the far upstream. This potential pre-heats the electrons ahead of the shock even in the absence of beam instabilities and decouples the electron temperature in the foreshock ahead of the shock from the one in the far upstream plasma. The effective Mach number of the shock is reduced by this electron heating. This effect can potentially stabilize nonrelativistic electrostatic shocks moving as fast as supernova remnant shocks.

  • 78.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Alejo, Aaron
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, UK.
    Sarri, Gianluca
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, UK.
    Expansion of a mildly relativistic hot pair cloud into an electron-proton plasma2018Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, nr 6, artikkel-id 062122Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The expansion of a charge-neutral cloud of electrons and positrons with the temperature 1 MeV into an unmagnetized ambient plasma is examined with a 2D particle-in-cell simulation. The pair outflow drives solitary waves in the ambient protons. Their bipolar electric fields attract electrons of the outflowing pair cloud and repel positrons. These fields can reflect some of the protons, thereby accelerating them to almost an MeV. Ion acoustic solitary waves are thus an efficient means to couple energy from the pair cloud to protons. The scattering of the electrons and positrons by the electric field slows down their expansion to a nonrelativistic speed. Only a dilute pair outflow reaches the expansion speed expected from the cloud's thermal speed. Its positrons are more energetic than its electrons. In time, an instability grows at the front of the dense slow-moving part of the pair cloud, which magnetizes the plasma. The instability is driven by the interaction of the outflowing positrons with the protons. These results shed light on how magnetic fields are created and ions are accelerated in pair-loaded astrophysical jets and winds.

  • 79.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Bock, Alexander
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Ahmed, Hamad
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, Belfast, UK.
    Doria, Domenico
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, Belfast, UK.
    Sarri, Gianluca
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, Belfast, UK.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Borghesi, Marco
    Centre for Plasma Physics (CPP), Queen's University Belfast, BT7 1NN, Belfast, UK.
    Shocks in unmagnetized plasma with a shear flow: Stability and magnetic field generation2015Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, nr 7, s. 1-9, artikkel-id 072104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A pair of curved shocks in a collisionless plasma is examined with a two-dimensional particle-in-cell simulation. The shocks are created by the collision of two electron-ion clouds at a speed that exceeds everywhere the threshold speed for shock formation. A variation of the collision speed along the initially planar collision boundary, which is comparable to the ion acoustic speed, yields a curvature of the shock that increases with time. The spatially varying Mach number of the shocks results in a variation of the downstream density in the direction along the shock boundary. This variation is eventually equilibrated by the thermal diffusion of ions. The pair of shocks is stable for tens of inverse ion plasma frequencies. The angle between the mean flow velocity vector of the inflowing upstream plasma and the shock's electrostatic field increases steadily during this time. The disalignment of both vectors gives rise to a rotational electron flow, which yields the growth of magnetic field patches that are coherent over tens of electron skin depths.

  • 80.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Bret, Antoine
    ETSI Ind Univ Castilla-La Mancha.
    Electric field generation by the electron beam filamentation instability: filament size effects2010Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 81, nr 1, s. 015502-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The filamentation instability (FI) of counter-propagating beams of electrons is modelled with a particle-in-cell simulation in one spatial dimension and with a high statistical plasma representation. The simulation direction is orthogonal to the beam velocity vector. Both electron beams have initially equal densities, temperatures and moduli of their non-relativistic mean velocities. The FI is electromagnetic in this case. A previous study of a small filament demonstrated that the magnetic pressure gradient force (MPGF) results in a nonlinearly driven electrostatic field. The probably small contribution of the thermal pressure gradient to the force balance implied that the electrostatic field performed undamped oscillations around a background electric field. Here, we consider larger filaments, which reach a stronger electrostatic potential when they saturate. The electron heating is enhanced and electrostatic electron phase space holes form. The competition of several smaller filaments, which grow simultaneously with the large filament, also perturbs the balance between the electrostatic and magnetic fields. The oscillations are damped but the final electric field amplitude is still determined by the MPGF.

  • 81.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Bret, Antoine
    University of Castilla La Mancha, ETSI Ind, Ciudad Real, Spain.
    Simulation study of the formation of a non-relativistic pair shock2017Inngår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 83, s. 1-19, artikkel-id 905830104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We examine with a particle-in-cell (PIC) simulation the collision of two equally dense clouds of cold pair plasma. The clouds interpenetrate until instabilities set in, which heat up the plasma and trigger the formation of a pair of shocks. The fastest-growing waves at the collision speed $c/5$, where $c$ is the speed of light in vacuum, and low temperature are the electrostatic two-stream mode and the quasi-electrostatic oblique mode. Both waves grow and saturate via the formation of phase space vortices. The strong electric fields of these nonlinear plasma structures provide an efficient means of heating up and compressing the inflowing upstream leptons. The interaction of the hot leptons, which leak back into the upstream region, with the inflowing cool upstream leptons continuously drives electrostatic waves that mediate the shock. These waves heat up the inflowing upstream leptons primarily along the shock normal, which results in an anisotropic velocity distribution in the post-shock region. This distribution gives rise to the Weibel instability. Our simulation shows that even if the shock is mediated by quasi-electrostatic waves, strong magnetowaves will still develop in its downstream region.

  • 82.
    Dieckmann, Mark Eric
    et al.
    Centre for Plasma Physics, Queen's University Belfast, UK .
    Bret, Antoine
    Harvard-Smithsonian Center for Astrophysics, Cambridge, MA , USA .
    Sarri, Gianluca
    Centre for Plasma Physics, Queen's University Belfast, UK .
    Perez Alvaro, Erica
    ETSI Industriales, Universidad de Castilla-La Mancha, Ciudad Real, Spain .
    Kourakis, Ioannis
    Centre for Plasma Physics, Queen's University Belfast, UK .
    Borghesi, Marco
    Centre for Plasma Physics, Queen's University Belfast, UK .
    Particle simulation study of electron heating by counter-streaming ion beams ahead of supernova remnant shocks2012Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, nr 8, s. 085015-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The growth and saturation of Buneman-type instabilities is examined with a particle-in-cell (PIC) simulation for parameters that are representative for the foreshock region of fast supernova remnant shocks. A dense ion beam and the electrons correspond to the upstream plasma and a fast ion beam to the shock-reflected ions. The purpose of the 2D simulation is to identify the nonlinear saturation mechanisms, the electron heating and potential secondary instabilities that arise from anisotropic electron heating and result in the growth of magnetic fields. We confirm that the instabilities between both ion beams and the electrons saturate by the formation of phase space holes by the beam-aligned modes. The slower oblique modes accelerate some electrons, but they cannot heat up the electrons significantly before they are trapped by the faster beam-aligned modes. Two circular electron velocity distributions develop, which are centred around the velocity of each ion beam. They develop due to the scattering of the electrons by the electrostatic wave potentials. The growth of magnetic fields is observed, but their amplitude remains low.

  • 83.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Folini, Doris
    Centre de Recherche Astrophysique de Lyon UMR5574, Université de Lyon 1, ENS de Lyon, CNRS, F-69007 Lyon, France.
    Walder, Rolf
    Centre de Recherche Astrophysique de Lyon UMR5574, Université de Lyon 1, ENS de Lyon, CNRS, F-69007 Lyon, France.
    The interplay of the collisionless non-linear thin-shell instability with the ion acoustic instability2017Inngår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 465, nr 4, s. 4240-4248Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The non-linear thin-shell instability (NTSI) may explain some of the turbulent hydrodynamic structures that are observed close to the collision boundary of energetic astrophysical outflows. It develops in non-planar shells that are bounded on either side by a hydrodynamic shock, provided that the amplitude of the seed oscillations is sufficiently large. The hydrodynamic NTSI has a microscopic counterpart in collisionless plasma. A sinusoidal displacement of a thin shell, which is formed by the collision of two clouds of unmagnetized electrons and protons, grows and saturates on time-scales of the order of the inverse proton plasma frequency. Here we increase the wavelength of the seed perturbation by a factor of 4 compared to that in a previous study. Like in the case of the hydrodynamic NTSI, the increase in the wavelength reduces the growth rate of the microscopic NTSI. The prolonged growth time of the microscopic NTSI allows the waves, which are driven by the competing ion acoustic instability, to grow to a large amplitude before the NTSI saturates and they disrupt the latter. The ion acoustic instability thus imposes a limit on the largest wavelength that can be destabilized by the NTSI in collisionless plasma. The limit can be overcome by binary collisions. We bring forward evidence for an overstability of the collisionless NTSI.

  • 84.
    Dieckmann, Mark Eric
    et al.
    Queen’s University Belfast.
    Kourakis, Ioannis
    CPP, Queen's University Belfast, UK.
    Borghesi, Marco
    CPP, Queen's University Belfast, UK.
    Rowlands, George
    Physics Department, Warwick University, UK.
    One-dimensional particle simulation of the filamentation instability: Electrostatic field driven by the magnetic pressure gradient force2009Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, nr 7, s. 074502-1-074502-4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two counterpropagating cool and equally dense electron beams are modeled with particle-in-cell simulations. The electron beam filamentation instability is examined in one spatial dimension, which is an approximation for a quasiplanar filament boundary. It is confirmed that the force on the electrons imposed by the electrostatic field, which develops during the nonlinear stage of the instability, oscillates around a mean value that equals the magnetic pressure gradient force. The forces acting on the electrons due to the electrostatic and the magnetic field have a similar strength. The electrostatic field reduces the confining force close to the stable equilibrium of each filament and increases it farther away, limiting the peak density. The confining time-averaged total potential permits an overlap of current filaments with an opposite flow direction.

  • 85.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Murphy, Gareth
    Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland .
    Meli, Athina
    Center for Astroparticle Physics, Friedrich-Alexander-University Erlangen-Nuremberg, 91058 Erlangen, Germany .
    Drury, Luke O'C
    Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland .
    Particle-in-cell simulation of a mildly relativistic collision of an electron-ion plasma carrying a quasi-parallel magnetic field: Electron acceleration and magnetic field amplification at supernova shocks2010Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 509, nr 1, s. A89-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. Plasma processes close to supernova remnant shocks result in the amplification of magnetic fields and in the acceleration of electrons, injecting them into the diffusive acceleration mechanism.

    Aims. The acceleration of electrons and the magnetic field amplification by the collision of two plasma clouds, each consisting of electrons and ions, at a speed of 0.5c is investigated. A quasi-parallel guiding magnetic field, a cloud density ratio of 10 and a plasma temperature of 25 keV are considered.

    Methods. A relativistic and electromagnetic particle-in-cell simulation models the plasma in two spatial dimensions employing an ion-to-electron mass ratio of 400.

    Results. A quasi-planar shock forms at the front of the dense plasma cloud. It is mediated by a circularly left-hand polarized electromagnetic wave with an electric field component along the guiding magnetic field. Its propagation direction is close to that of the guiding field and orthogonal to the collision boundary. It has a frequency too low to be determined during the simulation time and a wavelength that equals several times the ion inertial length. These properties would be indicative of a dispersive Alfvén wave close to the ion cyclotron resonance frequency of the left-handed mode, known as the ion whistler, provided that the frequency is appropriate. However, it moves with the super-alfvénic plasma collision speed, suggesting that it is an Alfvén precursor or a nonlinear MHD wave such as a Short Large-Amplitude Magnetic Structure (SLAMS). The growth of the magnetic amplitude of this wave to values well in excess of those of the quasi-parallel guiding field and of the filamentation modes results in a quasi-perpendicular shock. We present evidence for the instability of this mode to a four wave interaction. The waves developing upstream of the dense cloud give rise to electron acceleration ahead of the collision boundary. Energy equipartition between the ions and the electrons is established at the shock and the electrons are accelerated to relativistic speeds.

    Conclusions. The magnetic fields in the foreshock of supernova remnant shocks can be amplified substantially and electrons can be injected into the diffusive acceleration, if strongly magnetised plasma subshells are present in the foreshock, with velocities an order of magnitude faster than the main shell.

  • 86.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Murphy, GC
    Dublin Institute for Advanced Studies (DIAS), Dublin 2, Ireland .
    Drury, LOC
    Dublin Institute for Advanced Studies (DIAS), Dublin 2, Ireland .
    Particle-in-cell simulation of a fast nonrelativistic oblique shock: Extreme electron acceleration and magnetic field amplification2010Inngår i: EUROPEAN CONFERENCE ABSTRACTS ECA, European Physical Society , 2010, s. P2.402-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Plasma processes close to astrophysical shocks result in the amplification of magnetic fields and in the acceleration of electrons.We examine with PIC simulations the magnetic field amplification by the collision of two plasma clouds at a speed 0.5c, each consisting of electrons and ions. A quasi-parallel guiding magnetic field, a cloud density ratio of 10 and a plasma temperature of 25 keV are considered.We demonstrate that the magnetic energy density reaches that of the ions and that electrons are accelerated to highly relativistic speeds.

  • 87.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Quinn, Kevin
    Queen's University Belfast, UK.
    Sarri, Gianluca
    Queen's University Belfast, UK.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Murphy, Gareth Charles
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Kourakis, Ioannis
    Queen's University Belfast, UK.
    Macchi, Andrea
    CNR, Istituto Nazionale di Ottica, Pisa, Italy.
    Fuchs, Julien
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Willi, Oswald
    Univ. Düsseldorf, Inst. Laser & Plasmaphys., Düsseldorf, Germany.
    Borghesi, Marco
    Queen's University Belfast.
    The Weibel instability in a circular rarefaction wave2012Inngår i: Proceedings of the 39th European Physical Society Conference & 16th Int. Congress on Plasma Physics, 2012, s. P1.176-1-P1.176-4Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Instabilities behind the front of a cylindrically expanding plasma have been investigated experimentally and with a particle-in-cell simulation. Tubelike filamentary structures form behind the front of a plasma created by irradiating wire targets with a ps-duration and intense ( 1019 W cm-2) laser pulse. These filaments exhibit coherent magnetic fields with a remarkable stability ( 103 / wp: plasma frequency). PIC simulations indicate that an instability driven by a thermal anisotropy of the electron population is the cause. This instability requires a plasma density gradient and hot electrons. It can thus contribute to the generation of strongsustained magnetic fields in astrophysical jets.

  • 88.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Sarri, Gianluca
    Queen's University of Belfast, UK.
    Borghesi, Marco
    Queen's University of Belfast, UK.
    Magnetic instability in a dilute circular rarefaction wave2012Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, nr 12, s. 122102-1-122102-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The growth of magnetic fields in the density gradient of a rarefaction wave has been observed in simulations and in laboratory experiments. The thermal anisotropy of the electrons, which gives rise to the magnetic instability, is maintained by the ambipolar electric field. This simple mechanism could be important for the magnetic field amplification in astrophysical jets or in the interstellar medium ahead of supernova remnant shocks. The acceleration of protons and the generation of a magnetic field by the rarefaction wave, which is fed by an expanding circular plasma cloud, is examined here in form of a 2D particle-in-cell simulation. The core of the plasma cloud is modeled by immobile charges, and the mobile protons form a small ring close to the cloud's surface. The number density of mobile protons is thus less than that of the electrons. The protons of the rarefaction wave are accelerated to 1/10 of the electron thermal speed, and the acceleration results in a thermal anisotropy of the electron distribution in the entire plasma cloud. The instability in the rarefaction wave is outrun by a TM wave, which grows in the dense core distribution, and its magnetic field expands into the rarefaction wave. This expansion drives a secondary TE wave.

  • 89.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Sarri, Gianluca
    Queen's University Belfast, UK.
    Doria, Domenico
    Queen's University Belfast, UK.
    Ahmed, Hamad
    Queen's University Belfast, UK.
    Borghesi, Marco
    Queen's University Belfast, UK.
    Evolution of slow electrostatic shock into a plasma shock mediated by electrostatic turbulence2014Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 16, s. 073001-1-073001-25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The collision of two plasma clouds at a speed that exceeds the ion acoustic speed can result in the formation of shocks. This phenomenon is observed not only in astrophysical scenarios, such as the propagation of supernova remnant (SNR) blast shells into the interstellar medium, but also in laboratory-based laser-plasma experiments. These experiments and supporting simulations are thus seen as an attractive platform for small-scale reproduction and study of astrophysical shocks in the laboratory. We model two plasma clouds, which consist of electrons and ions, with a 2D particle-in-cell simulation. The ion temperatures of both clouds differ by a factor of ten. Both clouds collide at a speed that is realistic for laboratory studies and for SNR shocks in their late evolution phase, like that of RCW86. A magnetic field, which is orthogonal to the simulation plane, has a strength that is comparable to that of SNR shocks. A forward shock forms between the overlap layer of both plasma clouds and the cloud with cooler ions. A large-amplitude ion acoustic wave is observed between the overlap layer and the cloud with hotter ions. It does not steepen into a reverse shock because its speed is below the ion acoustic speed. A gradient of the magnetic field amplitude builds up close to the forward shock as it compresses the magnetic field. This gradient gives rise to an electron drift that is fast enough to trigger an instability. Electrostatic ion acoustic wave turbulence develops ahead of the shock, widens its transition layer, and thermalizes the ions, but the forward shock remains intact.

  • 90.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Sarri, Gianluca
    Queen's University Belfast, UK.
    Doria, Domenico
    Queen's University Belfast, UK.
    Pohl, Martin
    University of Potsdam, Germany .
    Borghesi, Marco
    Queen's University Belfast, UK.
    Modification of the formation of high-Mach number electrostatic shock-like structures by the ion acoustic instability2013Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, nr 10, s. 102112-1-102112-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The formation of unmagnetized electrostatic shock-like structures with a high Mach number is examined with one-and two-dimensional particle-in-cell (PIC) simulations. The structures are generated through the collision of two identical plasma clouds, which consist of equally hot electrons and ions with a mass ratio of 250. The Mach number of the collision speed with respect to the initial ion acoustic speed of the plasma is set to 4.6. This high Mach number delays the formation of such structures by tens of inverse ion plasma frequencies. A pair of stable shock-like structures is observed after this time in the 1D simulation, which gradually evolves into electrostatic shocks. The ion acoustic instability, which can develop in the 2D simulation but not in the 1D one, competes with the nonlinear process that gives rise to these structures. The oblique ion acoustic waves fragment their electric field. The transition layer, across which the bulk of the ions change their speed, widens and their speed change is reduced. Double layer-shock hybrid structures develop.

  • 91.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Sarri, Gianluca
    Queen's University Belfast. BT7 1NN, Belfast, United Kingdom.
    Markoff, Sera
    University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
    Borghesi, Marco
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    Zepf, Matt
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    PIC simulation study of the interaction between a relativisticallymoving leptonic micro-cloud and ambient electrons.2015Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 577, nr A137, s. 1-10Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 92.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Sarri, Gianluca
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Murphy, Gareth
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Bret, Antoine
    Harvard-Smithsonian Center for Astrophysics.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France .
    Kourakis, Ioannis
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Borghesi, Marco
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Drury, Luke o'c
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    PIC simulation of a thermal anisotropy-driven Weibel instability in a circular rarefaction wave2012Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 14, nr 023007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The expansion of an initially unmagnetized planar rarefaction wave has recently been shown to trigger a thermal anisotropy-driven Weibel instability (TAWI), which can generate magnetic fields from noise levels. It is examined here whether the TAWI can also grow in a curved rarefaction wave. The expansion of an initially unmagnetized circular plasma cloud, which consists of protons and hot electrons, into a vacuum is modelled for this purpose with a two-dimensional particle-in-cell (PIC) simulation. It is shown that the momentum transfer from the electrons to the radially accelerating protons can indeed trigger a TAWI. Radial current channels form and the aperiodic growth of a magnetowave is observed, which has a magnetic field that is oriented orthogonal to the simulation plane. The induced electric field implies that the electron density gradient is no longer parallel to the electric field. Evidence is presented here that this electric field modification triggers a second magnetic instability, which results in a rotational low-frequency magnetowave. The relevance of the TAWI is discussed for the growth of small-scale magnetic fields in astrophysical environments, which are needed to explain the electromagnetic emissions by astrophysical jets. It is outlined how this instability could be examined experimentally.

  • 93.
    Dieckmann, Mark Eric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Sarri, Gianluca
    Centre for Plasma Physics, Queen's University Belfast, Belfast BT7 1NN, UK.
    Romagnani, Lorenzo
    Centre for Plasma Physics, Queen's University Belfast, Belfast BT7 1NN, UK.
    Kourakis, Ioannis
    Centre for Plasma Physics, Queen's University Belfast, Belfast BT7 1NN, UK.
    Borghesi, Marco
    Centre for Plasma Physics, Queen's University Belfast, Belfast BT7 1NN, UK.
    Simulation of a collisionless planar electrostatic shock in a proton–electron plasma with a strong initial thermal pressure change2010Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 52, nr 2, s. 025001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The localized deposition of the energy of a laser pulse, as it ablates a solid target, introduces high thermal pressure gradients in the plasma. The thermal expansion of this laser-heated plasma into the ambient medium (ionized residual gas) triggers the formation of non-linear structures in the collisionless plasma. Here an electron–proton plasma is modelled with a particle-in-cell simulation to reproduce aspects of this plasma expansion. A jump is introduced in the thermal pressure of the plasma, across which the otherwise spatially uniform temperature and density change by a factor of 100. The electrons from the hot plasma expand into the cold one and the charge imbalance drags a beam of cold electrons into the hot plasma. This double layer reduces the electron temperature gradient. The presence of the low-pressure plasma modifies the proton dynamics compared with the plasma expansion into a vacuum. The jump in the thermal pressure develops into a primary shock. The fast protons, which move from the hot into the cold plasma in the form of a beam, give rise to the formation of phase space holes in the electron and proton distributions. The proton phase space holes develop into a secondary shock that thermalizes the beam.

  • 94.
    Eliasson, B.
    et al.
    Fakultät f Physik und Astronomie, Institut f Theoretische Physik IV Ruhr-Universität Bochum.
    Dieckmann, Mark E
    Ruhr-Universität Bochum.
    Shukla, P. K.
    Fakultät f Physik und Astronomie, Institut f Theoretische Physik IV Ruhr-Universität Bochum.
    Simulation study of surfing acceleration in magnetized space plasmas2005Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a numerical study of the surfing mechanism in which electrons are trapped in Bernstein-Greene-Kruskal (BGK) modes, and are accelerated across the magnetic field direction by the Lorentz force in magnetized space plasmas. The BGK modes are the product of an ion-beam Buneman instability that excites large-amplitude electrostatic upper-hybrid waves in the plasma. Our study, which is performed with particle-in-cell (PIC) and Vlasov codes, reveals the stability of the BGK mode as a function of the magnetic field strength and the ion beam speed. It is found that the surfing acceleration is more effective for a weaker magnetic field owing to the longer lifetime of the BGK modes. The importance of our investigation to electron acceleration in astrophysical environments has been emphasized. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

  • 95.
    Eliasson, Bengt
    et al.
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Dieckmann, Mark E
    Ruhr-Universität Bochum.
    Theoretical and simulation studies of relativistic ion holes in astrophysical plasmas2006Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 8, nr April, s. 55-1-55-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theoretical and numerical studies of relativistic ion holes in a relativistically hot electron-ion plasma are presented. Previous particle-in-cell (PIC) simulations have shown that the ion holes are formed as a result of relativistic beam-plasma instabilities in the foreshock region of internal shocks of gamma-ray bursts and the relativistic jets of active galactic nuclei. In this process, the electrons are heated to ultra-relativistic temperatures so that their relativistic mass becomes comparable to the proton mass, and relativistic ion holes are formed by a secondary ion beam instability. The electrostatic potentials associated with the ion holes are large enough to accelerate particles to GeV energies. We use a semi-analytical model to construct relativistic ion holes and investigate their stability by means of fully relativistic Vlasov simulations. This investigation is relevant for astrophysical settings where the ion holes may work as efficient particle accelerators.

  • 96.
    Eliasson, Bengt
    et al.
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Shukla, Padma K
    Institute of Theoretical Physics IV Institute of Theoretical Physics IV.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Theory and simulations of nonlinear kinetic structures in plasmas2006Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, nr 12 B, s. B257-B265Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    We present analytical and numerical studies of the dynamics of relativistic electron and ion holes in a collisionless plasma. Electromagnetic radiation can be trapped in relativistic electron phase-space holes mainly due to the relativistic mass increase of the electrons that are accelerated by the potential of the phase-space hole and by the quivering component of the electromagnetic field. Relativistic ion holes may exist in plasmas where the electrons are thermalized to extremely ultra-relativistic energies. They may be responsible for the acceleration of particles to GeV energies in active galactic nuclei and supernova remnant shocks. The analytic solutions are employed as initial conditions for numerical simulations in which the dynamics and stability of the phase-space holes are investigated. The results have relevance for intense laser-plasma experiments and for astrophysical plasmas.

  • 97.
    Lazar, Marian
    et al.
    Leuven University, Belgium.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Resonant Weibel instability in counterstreaming plasmas with temperature anisotropies2010Inngår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 76, nr 1, s. 49-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Weibel instability, driven by a plasma temperature anisotropy, is non-resonant with plasma particles: it is purely growing in time, and does not oscillate. The effect of a counterstreaming plasma is examined. In a counterstreaming plasma with an excess of transverse temperature, the Weibel instability arises along the streaming direction. Here it is proved that for large wave-numbers the instability becomes resonant with a finite real (oscillation) frequency, ωr ≠ 0. When the plasma flows faster, with a bulk velocity larger than the parallel thermal velocity, the instability becomes dominantly resonant. This new feature of the Weibel instability can be relevant for astrophysical sources of non-thermal emissions and the stability of counterflowing plasma experiments.

  • 98.
    Ljung, Patric
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Andersson, Niclas
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Interactive Visualization of Particle-In-Cell Simulations2000Inngår i: Proceedings of IEEE Visualization 2000, Salt Lake City, USA, 2000, s. 469-472Konferansepaper (Annet vitenskapelig)
  • 99.
    Marcowith, Alexandre
    et al.
    Laboratoire Univers et Particules de Montpellier CNRS/Université de Montpellier, Place E. Bataillon, 34095 Montpellier, France.
    Bret, Antoine
    ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
    Bykov, Andrei
    A.F. Ioffe Institute for Physics and Technology, 194021, St. Petersburg, Russia.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Drury, Luke
    School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland.
    Lembege, Bertrand
    LATMOS—CNRS—UVSQ—IPSL, 11 Bd. d’Alembert , 78280, Guyancourt, France.
    Lemoine, Martin
    Institut d’Astrophysique de Paris, CNRS—UPMC, 98 bis boulevard Arago, F-75014 Paris, France.
    Morlino, Guiseppe
    INFN, Gran Sasso Science Institute, viale F. Crispi 7, 67100 LAquila, Italy.
    Murphy, Gareth Charles
    Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17 Copenhagen 2100 Denmark.
    Pelletier, Guy
    Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR 5274 F-38041 Grenoble, France.
    Plotnikov, Ilya
    Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR 5274 F-38041 Grenoble, France.
    Reville, Brian
    Department of Physics and Astronomy, Queen’s University Belfast, University Road, Belfast, BT7 1NN, UK.
    Riquelme, Mario
    Department of Physics, (FCFM)—University of Chile, Santiago, Chile.
    Sironi, Lorenzo
    Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
    Stockem Novo, Anne
    Institut fur Theoretische Physik, Lehrstuhl IV: Weltraum- Astrophysik, Ruhr-Universität, 44801 Bochum, Germany.
    The microphysics of collisionless shock waves2016Inngår i: Reports on progress in physics (Print), ISSN 0034-4885, E-ISSN 1361-6633, Vol. 79, nr 4, artikkel-id 046901Artikkel, forskningsoversikt (Fagfellevurdert)
    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.

  • 100.
    Marklund, Mattias
    et al.
    Physics Department Umea University.
    Eliasson, Bengt
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Stenflo, Lennart
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Dieckmann, Mark E
    Ruhr-Universität Bochum.
    Parviainen, Madelene
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Electrostatic pair creation and recombination in quantum plasmas2006Inngår i: JETP Letters: Journal of Experimental And Theoretical Physics Letters, ISSN 0021-3640, E-ISSN 1090-6487, Vol. 83, nr 8, s. 313-317Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The production of electron-positron pairs by electrostatic waves in quantum plasmas is investigated. In particular, a semiclassical governing set of equations for a self-consistent treatment of pair creation by the Schwinger mechanism in a quantum plasma is derived.

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