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  • 101.
    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.

  • 102.
    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.

  • 103.
    McClements, K. G.
    et al.
    UKAEA Culham Division Culham Science Centre.
    Dendy, R. O.
    UKAEA Culham Division Culham Science Centre.
    Dieckmann, Mark E
    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.
    Department of Physics University of Warwick.
    Surfatron and stochastic acceleration of electrons in astrophysical plasmas2005Inngår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 71, nr 2, s. 127-141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electron acceleration by large amplitude electrostatic waves in astro-physical plasmas is studied using particle-in-cell (PIC) simulations. The waves are excited initially at the electron plasma frequency ωpe by a Buneman instability driven by ion beams: the parameters of the ion beams are appropriate for high Mach number astrophysical shocks, such as those associated with supernova remnants (SNRs). If ωpe is much higher than the electron cyclotron frequency Ωe, the linear phase of the instability does not depend on the magnitude of the magnetic field. However, the subsequent time evolution of particles and waves depends on both ωpe/Ωeand the size of the simulation box L. If L is equal to one wavelength, λ0, of the Buneman-unstable mode, electrons trapped by the waves undergo acceleration via the surfatron mechanism across the wave front. This occurs most efficiently when ωpe/Ω ≃ 100: in this case electrons are accelerated to speeds of up c/2 where c is the speed of light. In a simulation with L = 4λ0 and ωpe/ Ωe = 100, it is found that sideband instabilities give rise to a broad spectrum of wavenumbers, with a power law tail. Some stochastic electron acceleration is observed in this case, but not the surfatron process. Direct integration of the electron equations of motion, using parameters approximating to those of the wave modes observed in the simulations, suggests that the surfatron is compatible with the presence of a broad wave spectrum if Ωpe/Ωe > 100. It is concluded that a combination of stochastic and surfatron acceleration could provide an efficient generator of mildly relativistic electrons at SNR shocks.

  • 104. McClements, KG
    et al.
    Dieckmann, Mark E
    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, SC
    Dendy, RO
    Surfatron and stochastic acceleration of electrons at supernova remnant shocks2001Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 87, nr 25Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surfatron offers the possibility of particle acceleration to arbitrarily high energies, given a sufficiently large system. Surfatron acceleration of electrons by waves excited by ions reflected from supernova. remnant (SNR) shocks is investigated using particle simulations. It is shown that surfatron and stochastic acceleration could provide a seed population for the acceleration of cosmic ray electrons at SNR shocks.

  • 105.
    Moreno, Quentin
    et al.
    ELI-Beamlines, Institute of Physics, Czech Academy of Sciences, 5 Kvetna 835, 25241 Dolní Brěžany, Czech Republic.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Folini, Doris
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69007, Lyon, France.
    Walder, Rolf
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69007, Lyon, France.
    Ribeyre, Xavier
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, F-33405 Talence, France.
    Tikhonchuk, Vladimir
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, F-33405 Talence, France.
    d'Humieres, Emanuel
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, F-33405 Talence, France.
    Shocks and phase space vortices driven by a density jump between two clouds of electrons and protons2020Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 62, nr 2, s. 1-13, artikkel-id 025022Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study with 1D PIC simulations the expansion of a dense plasma into a dilute one for density ratios 2.5 ≤ α ≤ 20. Both are unmagnetized and consist of electrons and protons. Shocks form in all cases. We determine how α affects the speed of the shock, that of the trailing velocity plateau and the proton beam instabilities in its upstream region. The speed of the velocity plateau relative to the upstream plasma increases significantly with α. Faster shocks reflect more upstream protons and fewer protons make it downstream, which slows down the shock in the downstream frame. This slow-down reduces noticably the increase with α of the shock speed in the upstream frame. All simulations demonstrate that an ion acoustic instability develops between the shock-reflected proton beam and the ambient protons. We solve the linear dispersion relation for ion acoustic waves that have wave vectors which are parallel to the beam velocity vector. Upstream conditions, for which their growth rate is largest, lead to the most unstable upstream plasmas also in the simulation. Even though linear theory predicts the growth of sine waves, which reach a small amplitude in the simulations, solitary waves become the dominant ones upstream of the shock. They enforce the formation of new shocks and ion phase space vortices. We discuss the relevance of our findings to laser-plasma experiments.

  • 106.
    Moreno, Quentin
    et al.
    Centre Lasers Intenses et Applications, University of Bordeaux, CNRS, CEA, UMR 5107, Talence, France.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Ribeyre, Xavier
    Centre Lasers Intenses et Applications, University of Bordeaux, CNRS, CEA, UMR 5107, Talence, France.
    d'Humieres, Emanuel
    Centre Lasers Intenses et Applications, University of Bordeaux, CNRS, CEA, UMR 5107, Talence, France.
    Quasi-perpendicular fast magnetosonic shock with wave precursor in collisionless plasma2018Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, nr 7, artikkel-id 074502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A one-dimensional particle-in-cell simulation tracks a fast magnetosonic shock over time scales comparable with an inverse ion gyrofrequency. The magnetic pressure is comparable to the thermal pressure upstream. The shock propagates across a uniform background magnetic field with a pressure that equals the thermal pressure upstream at the angle 85° at a speed that is 1.5 times the fast magnetosonic speed in the electromagnetic limit. Electrostatic contributions to the wave dispersion increase its phase speed at large wave numbers, which leads to a convex dispersion curve. A fast magnetosonic precursor forms ahead of the shock with a phase speed that exceeds the fast magnetosonic speed by about ∼30%. The wave is slower than the shock, and hence, it is damped.

  • 107.
    Moreno, Quentin
    et al.
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, Talence, France.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Ribeyre, Xavier
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, Talence, France.
    Jequier, Sophie
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, Talence, France.
    Tikhonchuk, Vladimir
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, Talence, France.
    d'Humieres, Emanuel
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, Talence, France.
    Impact of the electron to ion mass ratio on unstable systems in particle-in-cell simulations2018Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, nr 6, artikkel-id 062125Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The evolution of the Buneman and two-stream instabilities driven by a cold dilute mildly relativistic electron beam is studied as a function of the ion-to-electron mass ratio. The growth rates of both instabilities are comparable for the selected parameters if the realistic ion-to-electron mass ratio is used and the Buneman instability outgrows the two-stream instability for an artificially reduced mass ratio. Particle-in-cell simulations show that both instabilities grow independently during their linear growth phase. The much lower saturation amplitude of the Buneman instability implies that it saturates first even if the linear growth rates of both instabilities are equal. The electron phase space holes it drives coalesce. Their spatial size increases in time and they start interacting with the two-stream mode, which results in the growth of electrostatic waves over a broad range of wave numbers. A reduced ion-to-electron mass ratio results in increased ion heating and in an increased energy loss of the relativistic electron beam compared to that in a simulation with the correct mass ratio.

  • 108.
    Moreno, Quentin
    et al.
    ELI-Beamlines, Institute of Physics, Czech Academy of Sciences, 5 Kvetna 835, 25241 Dolní Břežany, Czech Republic.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Ribeyre, Xavier
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, F-33405 Talence, France.
    Tikhonchuck, Vladimir
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, F-33405 Talence, France.
    Folini, Doris
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69007, Lyon, France.
    Walder, Rolf
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69007, Lyon, France.
    D'Humieres, Emmanuel
    University of Bordeaux, Centre Lasers Intenses et Applications, CNRS, CEA, UMR 5107, F-33405 Talence, France.
    Failed self-reformation of a sub-critical fast magnetosonic shock in collisionless plasma2019Inngår i: Plasma Research Express, ISSN 2516-1067, Vol. 1, nr 3, artikkel-id 035001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study with a 1D particle-in-cell (PIC) simulation the evolution of a subcritical perpendicular fast magnetosonic shock. The shock propagates at 1.5 times the fast magnetosonic speed. Some upstream protons are reflected by the shock's electric potential. They form a beam which carries less energy than those that are reflected magnetically by super-critical shocks. The beam triggers the growth of a fast magnetosonic solitary wave upstream of the shock, which reflects the beam protons back to the shock. Extracting the momentum and energy of this beam allows the solitary wave to grow into a proto-shock that is trailed by a short downstream region. Protons from the shock-reflected proton beam increase the density of the plasma between the shock and the proto-shock reducing its potential difference relative to both surrounding structures. Bulk protons, which cross the proto-shock, react to the decreased potential jump. The plasma behind the proto-shock accelerates and so does the shock. The trailing end of the proto-shock speeds up in order to continue reflecting the beam protons and eventually it catches up with its front; the proto-shock collapses and the self-reformation fails. A more energetic proton beam could decrease the potential jump across the shock, let it collapse and replace it with the proto-shock.

  • 109.
    Murphy, G. C.
    et al.
    Dublin Institute for Advanced Studies, Dublin 2, Ireland.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Drury, LOC
    Dublin Institute for Advanced Studies, Dublin 2, Ireland.
    Kinetic particle-in-cell simulations of asymmetric quasi-parallel mildly relativistic plasma collisions: Field and electron dynamics2010Inngår i: International Journal of Modern Physics D, ISSN 0218-2718, Vol. 19, nr 6, s. 707-713Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A gamma-ray burst (GRB) is triggered by a stellar implosion and the subsequent ejection of an ultrarelativistic jet. The prompt emissions are attributed to mildly relativistic collisions of plasma clouds within this jet. The resulting internal shocks are instrumental in the generation of the magnetic fields and the energetic electrons, which excite the observed electromagnetic emissions. We use particle-in-cell (PIC) simulations to examine such a shock. The colliding hot magnetized plasma clouds have densities that differ by a factor of 10. Current channels form rapidly in the 3D simulation, which resemble those in a Hammer–Rostoker equilibrium, are observed also in the 2D simulation. The 2D simulation also shows the formation of a shock, which is mediated by a strong electromagnetic wave, and the energy equipartition between electrons and ions.

  • 110.
    Murphy, GC
    et al.
    Dublin Institute for Advanced Studies (DIAS), Dublin 2, Ireland.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Bret, Antoine
    ETSI Industriales Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
    Drury, LOC
    Dublin Institute for Advanced Studies (DIAS), Dublin 2, Ireland.
    Magnetic field amplification and electron acceleration to near-energy equipartition with ions by a mildly relativistic quasi-parallel plasma protoshock2010Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 524, s. A84-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. The prompt emissions of gamma-ray bursts (GRBs) are seeded by radiating ultrarelativistic electrons. Kinetic energy dominated internal shocks propagating through a jet launched by a stellar implosion, are expected to dually amplify the magnetic field and accelerate electrons.

    Aims. We explore the effects of density asymmetry and of a quasi-parallel magnetic field on the collision of two plasma clouds.

    Methods. A two-dimensional relativistic particle-in-cell (PIC) simulation models the collision with 0.9c of two plasma clouds, in the presence of a quasi-parallel magnetic field. The cloud density ratio is 10. The densities of ions and electrons and the temperature of 131 keV are equal in each cloud, and the mass ratio is 250. The peak Lorentz factor of the electrons is determined, along with the orientation and the strength of the magnetic field at the cloud collision boundary.

    Results. The magnetic field component orthogonal to the initial plasma flow direction is amplified to values that exceed those expected from the shock compression by over an order of magnitude. The forming shock is quasi-perpendicular due to this amplification, caused by a current sheet which develops in response to the differing deflection of the upstream electrons and ions incident on the magnetised shock transition layer. The electron deflection implies a charge separation of the upstream electrons and ions; the resulting electric field drags the electrons through the magnetic field, whereupon they acquire a relativistic mass comparable to that of the ions. We demonstrate how a magnetic field structure resembling the cross section of a flux tube grows self-consistently in the current sheet of the shock transition layer. Plasma filamentation develops behind the shock front, as well as signatures of orthogonal magnetic field striping, indicative of the filamentation instability. These magnetic fields convect away from the shock boundary and their energy density exceeds by far the thermal pressure of the plasma. Localized magnetic bubbles form.

    Conclusions. Energy equipartition between the ion, electron and magnetic energy is obtained at the shock transition layer. The electronic radiation can provide a seed photon population that can be energized by secondary processes (e.g. inverse Compton).

  • 111.
    Murphy, GC
    et al.
    Dublin Institute for Advanced Studies (DIAS), Dublin 2, Ireland.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Drury, LOC
    Dublin Institute for Advanced Studies (DIAS), Dublin 2, Ireland.
    Magnetic field amplification and electron acceleration to near-energyequipartition by a mildly relativistic quasi-parallel plasma protoshock.2010Konferansepaper (Fagfellevurdert)
  • 112.
    Murphy, GC
    et al.
    Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland.
    Dieckmann, Mark Eric
    Dublin Institute for Advanced Studies.
    Drury, LOC
    Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland.
    Magnetic vortex growth in the transition layer of a mildly relativisticplasma shock2010Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 11, s. 110701-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A two-dimensional particle simulation models the collision of two electron-ion plasma clouds along a quasiparallel magnetic field. The collision speed is 0.9c and the density ratio, 10. A current sheet forms at the front of the dense cloud, in which the electrons and the magnetic field reach energy equipartition with the ions. A structure composed of a solenoidal and a toroidal magnetic field grows in this sheet. It resembles the cross-section of the torus of a spheromak, which may provide the coherent magnetic fields in gamma-ray burst jets needed for their prompt emissions.

  • 113.
    Murphy, GC
    et al.
    Dublin Institute for Advanced Studies (DIAS), Dublin, Ireland.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Drury, LOC
    Dublin Institute for Advanced Studies (DIAS), Dublin, Ireland.
    Multidimensional Simulations of Magnetic Field Amplification and Electron Acceleration to Near-Energy Equipartition With Ions by a Mildly Relativistic Quasi-Parallel Plasma Collision2010Inngår i: IEEE Transactions on Plasma Science, ISSN 0093-3813, E-ISSN 1939-9375, Vol. 38, nr 10, s. 2985-2992Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The energetic electromagnetic eruptions observed during the prompt phase of gamma-ray bursts are attributed to synchrotron emissions. The internal shocks moving through the ultrarelativistic jet, which is ejected by an imploding supermassive star, are the likely source of this radiation. Synchrotron emissions at the observed strength require the simultaneous presence of powerful magnetic fields and highly relativistic electrons. We explore with 1-D and 3-D relativistic particle-in-cell simulations the transition layer of a shock, which evolves out of the collision of two plasma clouds at a speed 0.9$c$ and in the presence of a quasi-parallel magnetic field. The cloud densities vary by a factor of 10. The number densities of ions and electrons in each cloud, which have the mass ratio 250, are equal. The peak Lorentz factor of the electrons is determined in the 1-D simulation, as well as the orientation and the strength of the magnetic field at the boundary of the two colliding clouds. The relativistic masses of the electrons and ions close to the shock transition layer are comparable as in previous work. The 3-D simulation shows rapid and strong plasma filamentation behind the transient precursor. The magnetic field component orthogonal to the initial field direction is amplified in both simulations to values that exceed those expected from the shock compression by over an order of magnitude. The forming shock is quasi-perpendicular due to this amplification. The simultaneous presence of highly relativistic electrons and strong magnetic fields will give rise to significant synchrotron emissions.

  • 114.
    Palodhi, Lopamudra
    et al.
    Department of Mathematics, Iowa State University, Ames, USA.
    Califano, Francesco
    Department of Physics, University of Pisa, Pisa, Italy.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Pegoraro, Francesco
    Department of Physics, University of Pisa, Pisa, Italy.
    Counterstreaming beams in magnetized Vlasov plasma2019Inngår i: Pramana (Bangalore), ISSN 0304-4289, E-ISSN 0973-7111, Vol. 93, s. 1-10, artikkel-id 87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we investigate nonrelativistic, kinetic, linear phase of the filamentation instability when an external magnetic field is present in the direction of the counterstreaming electron beams using Vlasov simulations in 1D-3V space. We first investigate the growth rate of instability. In the linear growth regime, our results correspond to the previous conclusions that with the increase in strength of the ambient magnetic field, there is a suppression of instability. Interestingly, we established that at a critical / threshold magnetic field, Vlasov simulations and particle-in-cell (PIC) simulations differ in their instability behaviour. At this particular magnetic field, there is a complete suppression of the growth of instability in Vlasov results compared to PIC simulations, where a strong growth of instability is shown. It is believed that thermal noise in the PIC leads to the growth. However, Vlasov simulations show wave–wave coupling which stabilises the modes. In this work, our focus is to demonstrate the difference in this behaviour and to thoroughly analyse the spectra and wave generation for the same.

  • 115.
    Parviainen, Madelene Jeanette
    et al.
    Theoretische Physik IV, Ruhr-Universität Bochum, Bochum, Germany.
    Dieckmann, Mark E
    Theoretische Physik IV, Ruhr-Universität Bochum, Bochum, Germany.
    Shukla, Padma Kant
    Theoretische Physik IV, Ruhr-Universität Bochum, Bochum, Germany.
    Phase Space Modulations in Magnetised Plasmas by a Mildly Relativistic Two-Stream Instability2007Inngår i: Applied Parallel Computing. State of the Art in Scientific Computing: 8th International Workshop, PARA 2006, Umeå, Sweden, June 18-21, 2006, Revised Selected Papers / [ed] Bo Kågström, Erik Elmroth, Jack Dongarra, Jerzy Waśniewski, Springer Berlin/Heidelberg, 2007, s. 361-370Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A kinetic particle-in-cell simulation and 3D point-rendering visualisation are used to investigate a two-stream plasma instability, possibly found in the accretion disc of black holes. A plasma in an oblique external magnetic field is considered. The instability gives rise to a quasi-electrostatic wave able to trap electrons and accelerate them by cross-field transport. The results of the simulation show an acceleration of the electrons to speeds similar to the bulk speed of microquasar jets.

  • 116.
    Quinn, K.
    et al.
    The Queen’s University of Belfast, United Kingdom.
    Romagnani, Lorenzo
    LULI, École Polytechnique, Palaiseau, France.
    Ramakrishna, B.
    The Queen’s University of Belfast, United Kingdom.
    Sarri, Gianluca
    The Queen’s University of Belfast, United Kingdom.
    Dieckmann, Mark Eric
    The Queen’s University of Belfast, United Kingdom.
    Wilson, P. A.
    The Queen’s University of Belfast, United Kingdom.
    Fuchs, J.
    LULI, École Polytechnique, Palaiseau, France.
    Lancia, L.
    LULI, École Polytechnique, Palaiseau, France.
    Pipahl, A.
    Heinrich-Heine-Universitaet, Duesseldorf, Germany.
    Toncian, T.
    Heinrich-Heine-Universitaet, Duesseldorf, Germany.
    Willi, Oswald
    Institut für Laser- und Plasmaphysik, Heinrich-Heine-Universitaet, Duesseldorf, Germany.
    Clarke, R. J.
    Rutherford Appleton Laboratory, Chilton, United Kingdom.
    Notley, M.
    Rutherford Appleton Laboratory, Chilton, United Kingdom.
    Macchi, Andrea
    Instituto Nazionale di Ottica, CNR, Pisa, Italy.
    Borghesi, Marco
    The Queen’s University of Belfast, United Kingdom.
    Weibel-Induced Filamentation during an Ultrafast Laser-Driven Plasma Expansion2012Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 108, nr 13, s. 135001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The development of current instabilities behind the front of a cylindrically expanding plasma has been investigated experimentally via proton probing techniques. A multitude of tubelike filamentary structures is observed to form behind the front of a plasma created by irradiating solid-density wire targets with a high-intensity (I∼1019  W/cm2), picosecond-duration laser pulse. These filaments exhibit a remarkable degree of stability, persisting for several tens of picoseconds, and appear to be magnetized over a filament length corresponding to several filament radii. Particle-in-cell simulations indicate that their formation can be attributed to a Weibel instability driven by a thermal anisotropy of the electron population. We suggest that these results may have implications in astrophysical scenarios, particularly concerning the problem of the generation of strong, spatially extended and sustained magnetic fields in astrophysical jets.

  • 117.
    Rowlands, George
    et al.
    Physics Department Warwick University.
    Dieckmann, Mark E
    Ruhr-University Bochum.
    Shukla, Padma K
    Institute of Theoretical Physics IV Ruhr-University Bochum.
    The plasma filamentation instability in one dimension: nonlinear evolution2007Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 9, nr August, s. 247-1-247-15Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The plasma filamentation instability or beam-Weibel instability generates magnetic fields and accelerates particles in collisionless astrophysical plasma. This instability has been examined with multi-dimensional particle-in-cell (PIC) simulations, demonstrating the formation of current flux tubes. Such simulations could not model a statistically significant number of filaments. Here, we model with a PIC simulation the filamentation instability that is driven by nonrelativistic, cool electron beams in one spatial dimension at an unprecedented resolution. We show unambiguously that the gradient of the magnetic pressure which develops during the quasi-linear evolution of the filamentation instability, gives rise to an electrostatic field component. The interplay of the magnetic and electrostatic fields results in a wavenumber spectrum of the magnetic field that is a power-law, which has been reported previously for multi-dimensional PIC simulations. The magnetic field power spectrum decreases with the exponent -5.7 and that of the electrostatic field with -3.8, yielding a ratio of 3:2. The electromagnetic fields thermalize the electrons. The electrons develop a velocity distribution in the simulation direction that decreases exponentially at low speeds and faster at high speeds. The filamentation instability can thus not efficiently accelerate electrons to high energies. The filaments develop into a stationary final state. The probability distribution of the filament sizes is a Gumbel distribution. In astrophysical settings, this implies that the long exponential tail of this distribution may lead with a reasonable probability to large current filaments, if the filamentation instability develops in a large enough volume. The coherent magnetic fields of large filaments are required to explain the synchrotron emissions of gamma ray bursts.

  • 118.
    Sarri, G
    et al.
    Queen's University of Belfast.
    Cecchetti, C A
    Queen's University of Belfast.
    Romagnani, L
    Queen's University of Belfast.
    Brown, C M
    Atomic Weapon Establishment, Aldermaston, Reading, Berkshire .
    Hoarty, D J
    Atomic Weapon Establishment, Aldermaston, Reading, Berkshire.
    James, S
    Atomic Weapon Establishment, Aldermaston, Reading, Berkshire.
    Morton, J
    Atomic Weapon Establishment, Aldermaston, Reading, Berkshire.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Jung, R
    Heinrich-Heine-Universitaat, Dusseldorf.
    Willi, O
    Heinrich-Heine-Universitaat, Dusseldorf.
    Bulanov, S V
    APRC, JAEA, Kizugawa, Kyoto.
    Pegoraro, F
    Universit di Pisa.
    Borghesi, Marco
    Queen's University of Belfast.
    The application of laser-driven proton beams to the radiography of intense laser–hohlraum interactions2010Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 12, nr 4, s. 045006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plasma expansion following the interaction of an intense laser beam with the inner surface of gold hohlraums, emulating conditions relevant to indirect drive inertial confinement fusion (ICF), has been investigated by a radiographic technique which employs a beam of laser-accelerated protons. This probing technique has made it possible to measure the electric field distribution associated with the plasma front and its propagation throughout the interior of the hohlraum with a temporal and spatial resolution of the order of a few ps and μm, respectively. The data indicate that the expanding plasma slows down approaching the opposite walls, possibly due to the interaction with x-ray heated plasma from the non-irradiated walls. The electric field at the plasma front shows a bipolar structure, suggesting the presence of ion-acoustic soliton-like structures cotraveling with the front. Data obtained using enclosed hohlraums suggest the feasibility of this type of diagnosis in gas-filled hohlraums, as currently employed in ICF experiments.

  • 119.
    Sarri, Gianluca
    et al.
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Brown, CRD
    AWE, Aldermaston, Reading, UK.
    Cecchetti, CA
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Hoarty, DJ
    AWE, Aldermaston, Reading, UK.
    James, SF
    AWE, Aldermaston, Reading, UK.
    Jung, R
    Institute for Laser and Plasma Physics, Heinrich-Heine-University Duesseldorf, Germany.
    Kourakis, Ioannis
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Schamel, Hans
    Physikalisches Institut, Universität Bayreuth, Germany.
    Willi, Oswald
    Institute for Laser and Plasma Physics, Heinrich-Heine-University Duesseldorf, Germany.
    Borghesi, Marco
    Centre for Plasma Physics, Queen's University Belfast, UK.
    Observation and characterization of laser-driven phasespace electron holes2010Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 1, s. 010701-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The direct observation and full characterization of a phase space electron hole (EH) generated during laser-matter interaction is presented. This structure, propagating in a tenuous, nonmagnetized plasma, has been detected via proton radiography during the irradiation with a ns laser pulse (I21014  W/cm2) of a gold hohlraum. This technique has allowed the simultaneous detection of propagation velocity, potential, and electron density spatial profile across the EH with fine spatial and temporal resolution allowing a detailed comparison with theoretical and numerical models.

  • 120.
    Sarri, Gianluca
    et al.
    Queen's University Belfast; UK.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Kourakis, Ioannis
    Queen's University Belfast; UK.
    Borghesi, Marci
    Queen's University Belfast; UK.
    Magnetic field suppression in collision-less shocks generated during the expansion of a dense plasma into a rarefied mediu2013Inngår i: EAS Publications Series, ISSN 1633-4760, E-ISSN 1638-1963, Vol. 58, s. 33-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A two-dimensional numerical study of the expansion of a dense plasma through a more rarefied one is reported. The electrostatic ion-acoustic shock, which is generated during the expansion, accelerates the electrons of the rarefied plasma inducing a superthermal population which reduces electron thermal anisotropy. The Weibel instability is therefore not triggered and no self-generated magnetic fields are observed, in contrast with published theoretical results dealing with plasma expansion into vacuum.

  • 121.
    Sarri, Gianluca
    et al.
    Queen's University Belfast.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Kourakis, Ioannis
    Queen's University Belfast.
    Borghesi, Marco
    Queen's University Belfast.
    Generation of a purely electrostatic collisionless shock during the expansion of a dense plasma through a rarefied medium2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 2, s. 025003-1-025003-4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A two-dimensional numerical study of the expansion of a dense plasma through a more rarefied one is reported. The electrostatic ion-acoustic shock, which is generated during the expansion, accelerates the electrons of the rarefied plasma inducing a superthermal population which reduces electron thermal anisotropy. The Weibel instability is therefore not triggered and no self-generated magnetic fields are observed, in contrast with published theoretical results dealing with plasma expansion into vacuum. The shock front develops a filamentary structure which is interpreted as the consequence of the electrostatic ion-ion instability, consistently with published analytical models and results.

  • 122.
    Sarri, Gianluca
    et al.
    Centre for Plasma Physics, The Queen’s University of Belfast, Belfast BT7 1NN, United Kingdom .
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Kourakis, Ioannis
    Centre for Plasma Physics, The Queen’s University of Belfast, Belfast BT7 1NN, United Kingdom .
    Borghesi, Marco
    Centre for Plasma Physics, The Queen’s University of Belfast, Belfast BT7 1NN, United Kingdom .
    Shock creation and particle acceleration driven by plasma expansion into a rarefied medium2010Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, nr 8, s. 082305-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The expansion of a dense plasma through a more rarefied ionized medium is a phenomenon of interest in various physics environments ranging from astrophysics to high energy density laser-matter laboratory experiments. Here this situation is modeled via a one-dimensional particle-in-cell simulation; a jump in the plasma density of a factor of 100 is introduced in the middle of an otherwise equally dense electron-proton plasma with an uniform proton and electron temperature of 10 eV and 1 keV, respectively. The diffusion of the dense plasma, through the rarefied one, triggers the onset of different nonlinear phenomena such as a strong ion-acoustic shock wave and a rarefaction wave. Secondary structures are detected, some of which are driven by a drift instability of the rarefaction wave. Efficient proton acceleration occurs ahead of the shock, bringing the maximum proton velocity up to 60 times the initial ion thermal speed.

  • 123.
    Sarri, Gianluca
    et al.
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Kourakis, Ioannis
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    Di Piazza, Antonio
    Max Planck Institute for Nuclear Physics, Heidelberg, Germany.
    Reville, Brian
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    Keitel, Christian
    Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany .
    Zepf, Matt
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    Overview of laser-driven generation of electron–positron beams2015Inngår i: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 81, nr 04, s. 1-14, artikkel-id 455810401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 124.
    Sarri, Gianluca
    et al.
    School of Mathematics and Physics, The Queen’s University of Belfast, Belfast, BT7 1NN, United Kingdom.
    Macchi, Andrea
    Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche, research unit “Adriano Gozzini”, Pisa, Italy.
    Ceccheti, C. A.
    Light4Tech s.r.l, Scandicci, Italy.
    Kar, S.
    School of Mathematics and Physics, The Queen’s University of Belfast, Belfast, BT7 1NN, United Kingdom.
    Liseykina, T.V.
    Institut für Physik, Universität Rostock, Rostock, Germany.
    Yang, X. H.
    School of Mathematics and Physics, The Queen’s University of Belfast, Belfast, BT7 1NN, United Kingdom.
    Dieckmann, Mark Eric
    School of Mathematics and Physics, The Queen’s University of Belfast, Belfast, BT7 1NN, United Kingdom .
    Fuchs, J.
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Galimberti, M.
    Rutherford Appleton Laboratory, Central Laser Facility, Chilton, OX11 0QX, United Kingdom.
    Gizzi, L. A.
    Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche, research unit “Adriano Gozzini”, Pisa, Italy.
    Jung, R.
    Institute for Laser and Plasma Physics, Heinrich Heine University, Dusseldorf, Germany.
    Kourakis, Ioannis
    School of Mathematics and Physics, The Queen’s University of Belfast, Belfast, BT7 1NN, United Kingdom.
    Osterholz, J.
    Institute for Laser and Plasma Physics, Heinrich Heine University, Dusseldorf, Germany.
    Pegoraro, Francesco
    Istituto Nazionale di Ottica, Consiglio Nazionale delle Ricerche, research unit “Adriano Gozzini”, Pisa, Italy.
    Robinson, APL
    Rutherford Appleton Laboratory, Central Laser Facility, Chilton, OX11 0QX, United Kingdom.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Willi, Oswald
    Institute for Laser and Plasma Physics, Heinrich Heine University, Dusseldorf, Germany.
    Borghesi, Marco
    School of Mathematics and Physics, The Queen’s University of Belfast, Belfast, BT7 1NN, United Kingdom.
    Dynamics of Self-Generated, Large Amplitude Magnetic Fields Following High-Intensity Laser Matter Interaction2012Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, nr 20, s. 205002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamics of magnetic fields with an amplitude of several tens of megagauss, generated at both sides of a solid target irradiated with a high-intensity (∼1019  W/cm2) picosecond laser pulse, has been spatially and temporally resolved using a proton imaging technique. The amplitude of the magnetic fields is sufficiently large to have a constraining effect on the radial expansion of the plasma sheath at the target surfaces. These results, supported by numerical simulations and simple analytical modeling, may have implications for ion acceleration driven by the plasma sheath at the rear side of the target as well as for the laboratory study of self-collimated high-energy plasma jets.

  • 125.
    Sarri, Gianluca
    et al.
    Queen's University of Belfast, UK.
    Murphy, Gareth Charles
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Bret, Antoine
    ETSI Ind, University of Castilla-LaMancha, Spain.
    Quinn, Kevin
    Queen's University of Belfast, UK.
    Kourakis, Ioannis
    Queen's University of Belfast, UK.
    Borghesi, Marco
    Queen's University of Belfast, UK.
    Drury, Luke o'C
    Dublin Institute for Advanced Studies, Dublin, Ireland.
    Ynnerman, Anders
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Two-dimensional particle-in-cell simulation of the expansion of a plasma into a rarefied medium2011Inngår i: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 13, nr 7, s. 073023-1-073023-23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The expansion of a dense plasma through a more rarefied ionized medium has been studied by means of two-dimensional particle-in-cell simulations. The initial conditions involve a density jump by a factor of 100, located in the middle of an otherwise equally dense electron-proton plasma with uniform proton and electron temperatures of 10 eV and 1keV, respectively. Simulations show the creation of a purely electrostatic collisionless shock together with an ion-acoustic soliton tied to its downstream region. The shock front is seen to evolve in filamentary structures consistently with the onset of the ion-ion instability. Meanwhile, an un-magnetized drift instability is triggered in the core part of the dense plasma. Such results explain recent laser-plasma experiments, carried out in similar conditions, and are of intrinsic relevance to non-relativistic shock scenarios in the solar and astrophysical systems.

  • 126.
    Sarri, Gianluca
    et al.
    Queen's University Belfast, UK.
    Schumaker, W
    University of Michigan, Ann Arbor, USA.
    Di Piazza, A
    Max-Planck-Institut für Kernphysik, Germany.
    Poder, K
    Imperial College, London, UK.
    Cole, JM
    Imperial College, London, UK.
    Vargas, M
    University of Michigan, Ann Arbor, USA.
    Doria, Domenico
    The Queen's University of Belfast, UK.
    Kushel, S
    Helmholtz Institute Jena, Germany.
    Dromey, Brendan
    The Queen's University of Belfast, UK.
    Grittani, G
    Consiglio Nazionale delle Ricerche, Italy.
    Gizzi, L
    Consiglio Nazionale delle Ricerche, Italy.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Green, A
    The Queen's University of Belfast, UK.
    Chvykov, V
    University of Michigan, Ann Arbor, USA.
    Maksimchuk, A
    University of Michigan, Ann Arbor, USA.
    Yanovsky, V
    University of Michigan, Ann Arbor, USA.
    He, ZH
    University of Michigan, Ann Arbor, USA.
    Hou, BX
    University of Michigan, Ann Arbor, USA.
    Nees, JA
    University of Michigan, Ann Arbor, USA.
    Kar, S
    The Queen's University of Belfast, UK.
    Najmudin, Z
    Helmholtz Institute Jena, Germany.
    Thomas, AGR
    University of Michigan, Ann Arbor, USA.
    Keitel, CH
    Max-Planck-Institut für Kernphysik, Germany.
    Krushelnick, K
    University of Michigan, Ann Arbor, USA.
    Zepf, Matt
    The Queen's University of Belfast, UK.
    Laser-driven generation of collimated ultra-relativistic positron beams2013Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 55, nr 12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on recent experimental results concerning the generation of collimated (divergence of the order of a few mrad) ultra-relativistic positron beams using a fully optical system. The positron beams are generated exploiting a quantum-electrodynamic cascade initiated by the propagation of a laser-accelerated, ultra-relativistic electron beam through high-Z solid targets. As long as the target thickness is comparable to or smaller than the radiation length of the material, the divergence of the escaping positron beam is of the order of the inverse of its Lorentz factor. For thicker solid targets the divergence is seen to gradually increase, due to the increased number of fundamental steps in the cascade, but it is still kept of the order of few tens of mrad, depending on the spectral components in the beam. This high degree of collimation will be fundamental for further injection into plasma-wakefield afterburners.

  • 127.
    Sarri, Gianluca
    et al.
    Queen’s University of Belfast, UK.
    Schumaker, W.
    University of Michigan, Ann Arbor, USA.
    Di Piazza, A.
    Max-Planck-Institut für Kernphysik, Heidelberg, Germany.
    Vargas, M.
    University of Michigan, Ann Arbor, USA.
    Dromey, Brendan
    Queen’s University of Belfast, UK.
    Dieckmann, Mark Eric
    Queen’s University of Belfast, UK.
    Chvykov, V.
    University of Michigan, Ann Arbor, USA.
    Maksimchuk, A.
    University of Michigan, Ann Arbor, USA.
    Yanovsky, V.
    University of Michigan, Ann Arbor, USA.
    He, Z. H.
    University of Michigan, Ann Arbor, USA.
    Hou, B. X.
    University of Michigan, Ann Arbor, USA.
    Nees, J. A.
    University of Michigan, Ann Arbor, USA.
    Thomas, A. G. R.
    University of Michigan, Ann Arbor, USA.
    Keitel, C. H.
    Max-Planck-Institut für Kernphysik, Heidelberg, Germany.
    Zepf, Matt
    Queen’s University of Belfast, UK.
    Krushelnick, K.
    University of Michigan, Ann Arbor, USA.
    Table-Top Laser-Based Source of Femtosecond, Collimated, Ultrarelativistic Positron Beams2013Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, nr 25, s. 255002-1-255002-5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The generation of ultrarelativistic positron beams with short duration (τe+≃30  fs), small divergence (θe+≃3  mrad), and high density (ne+≃1014–1015  cm-3) from a fully optical setup is reported. The detected positron beam propagates with a high-density electron beam and γ rays of similar spectral shape and peak energy, thus closely resembling the structure of an astrophysical leptonic jet. It is envisaged that this experimental evidence, besides the intrinsic relevance to laser-driven particle acceleration, may open the pathway for the small-scale study of astrophysical leptonic jets in the laboratory.

  • 128.
    Sarri, Gianluca
    et al.
    Queen's University Belfast, Northern Ireland, UK.
    Schumaker, W.
    University of Michigan, USA.
    Di Piazza, A.
    Max-Planck-Institut für Kernphysik, Heidelberg, Germany.
    Vargas, M.
    University of Michigan, USA.
    Dromey, Brendan
    University of Michigan, USA.
    Dieckmann, Mark Eric
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan. Queen's University Belfast, Northern Ireland, UK.
    Chvykov, V.
    University of Michigan, USA.
    Maksimchuk, A.
    University of Michigan, USA.
    Yanovsky, V.
    University of Michigan, USA.
    He, ZH
    University of Michigan, USA.
    Hou, BX
    University of Michigan, USA.
    Nees, J.A.
    University of Michigan, USA.
    Thomas, A.G.R.
    University of Michigan, USA.
    Keitel, C.H.
    University of Michigan, USA.
    Zepf, Matt
    Queen's University Belfast, Northern Ireland, UK.
    Krushelnick, K.
    University of Michigan, USA.
    A table-top laser-based source of short, collimated, ultra-relativistic positron beams2013Inngår i: Laser Acceleration of Electrons, Protons, and Ions II; and Medical Applications of Laser-Generated Beams of Particles II; and Harnessing Relativistic Plasma Waves III / [ed] Eric Esarey, SPIE - International Society for Optical Engineering, 2013, s. 87790Z-1-87790Z-7Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An ultra-relativistic electron beam passing through a thick, high-Z solid target triggers an electromagnetic cascade, whereby a large number of high energy photons and electron-positron pairs are produced. By exploiting this physical process, we present here the first experimental evidence of the generation of ultra-short, highly collimated and ultra-relativistic positron beams following the interaction of a laser-wakefield accelerated electron beam with high-Z solid targets. Clear evidence has also been obtained of the generation of GeV electron-positron jets with variable composition depending on the solid target material and thickness. The percentage of positrons in the overall leptonic beam has been observed to vary from a few per cent up to almost fifty per cent, implying a quasi-neutral electron-positron beam. We anticipate that these beams will be of direct relevance to the laboratory study of astrophysical leptonic jets and their interaction with the interstellar medium

  • 129.
    Shukla, Padma K
    et al.
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Bingham, Robert
    CCLRC Rutherford-Appleton Labs, UK.
    Eliasson, Bengt
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Stenflo, Lennart
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Nonlinear aspects of the solar coronal heating2006Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 48, nr 12 B, s. B249-B255Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    The heating of the solar coronal plasma has remained one of the most important problems in solar physics. An explanation of the electron and ion heating rests on the identification of the energy source and appropriate physical mechanisms via which the energy can be channelled to the plasma particles. In this paper, we discuss two important nonlinear aspects of the electron and ion heating caused by finite amplitude obliquely propagating dispersive Alfvén (DA) waves and magnetic field-aligned circularly polarized electromagnetic ion-cyclotron Alfvén (EMICA) waves that may exist in the solar terrestrial environment. Specifically, DA waves may contribute to the solar coronal electron heating via Joule heating involving electron-wave interactions, and resonant ion EMICA wave interactions may contribute to differential ion heating in the solar corona.

  • 130.
    Shukla, Padma K
    et al.
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Eliasson, Bengt
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Marklund, Mattias
    Physics Department Umea University.
    Stenflo, Lennart
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Kourakis, Ioannis
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Parviainen, Madelene
    Institute of Theoretical Physics IV Ruhr-University Bochum, Germany.
    Dieckmann, Mark E
    Ruhr-Universität Bochum.
    Instability and dynamics of two nonlinearly coupled laser beams in a plasma2006Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 5, s. 053104-1-053104-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The nonlinear interaction between two laser beams in a plasma is investigated in the weakly nonlinear and relativistic regime. The evolution of the laser beams is governed by two nonlinear Schrödinger equations that are coupled with the slow plasma density response. A nonlinear dispersion relation is derived and used to study the growth rates of the Raman forward and backward scattering instabilities as well of the Brillouin and self-focusing/modulational instabilities. The nonlinear evolution of the instabilities is investigated by means of direct simulations of the time-dependent system of nonlinear equations.

  • 131.
    Sircombe, Nathan J
    et al.
    Space and Astrophysics Group University of Warwick, UK.
    Dieckmann, Mark E
    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.
    Arber, Tony D
    Space and Astrophysics Group University of Warwick, UK.
    Stabilisation of BGK modes by relativistic effects2006Inngår i: Astronomy & astrophysics, ISSN 1432-0746, Vol. 452, nr 2, s. 371-381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Context. We examine plasma thermalisation processes in the foreshock region of astrophysical shocks within a fully kinetic and self-consistent treatment. We concentrate on proton beam driven electrostatic processes, which are thought to play a key role in the beam relaxation and the particle acceleration. Our results have implications for the effectiveness of electron surfing acceleration and the creation of the required energetic seed population for first order Fermi acceleration at the shock front. Aims. We investigate the acceleration of electrons via their interaction with electrostatic waves, driven by the relativistic Buneman instability, in a system dominated by counter-propagating proton beams. Methods. We adopt a kinetic Vlasov-Poisson description of the plasma on a fixed Eulerian grid and observe the growth and saturation of electrostatic waves for a range of proton beam velocities, from 0.15c to 0.9c. Results. We can report a reduced stability of the electrostatic wave (ESW) with increasing non-relativistic beam velocities and an improved wave stability for increasing relativistic beam velocities, both in accordance with previous findings. At the highest beam speeds, we find the system to be stable again for a period of $\approx $160 plasma periods. Furthermore, the high phase space resolution of the Eulerian Vlasov approach reveals processes that could not be seen previously with PIC simulations. We observe a, to our knowledge, previously unreported secondary electron acceleration mechanism at low beam speeds. We believe that it is the result of parametric couplings to produce high phase velocity ESW's which then trap electrons, accelerating them to higher energies. This allows electrons in our simulation study to achieve the injection energy required for Fermi acceleration, for beam speeds as low as 0.15c in unmagnetised plasma.

  • 132.
    Stockem, Anne
    et al.
    Institut fuer Theoretische Physik IV Ruhr-University Bochum.
    Dieckmann, Mark E
    Ruhr-University Bochum.
    Schlickeiser, Reinhard
    Institut fuer Theoretische Physik IV Ruhr-University Bochum.
    Suppression of the filamentation instability by a flow-aligned magnetic field: testing the analytic threshold with PIC simulations2008Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, nr 2, s. 025002-1-25002-18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The impact of a flow-aligned and spatially homogeneous magnetic field on the filamentation instability (FI) is examined in a system of two equal counterstreaming non-relativistic cool electron beams. Particle-in-cell simulations that represent the plane perpendicular to the flow velocity vector confirm the reduction of the linear growth rate by the initial magnetic field. The FI is, however, not inhibited by a magnetic field with the critical strength, for which the solution of the linear dispersion relation predicts a full suppression. The saturation of the electromagnetic fields in the plasma involves a balance between the magnetic pressure gradient and the electric field resulting from the charge displacement. The simulations demonstrate that the magnetic energy gain and the field structure upon saturation do not depend on the initial magnetic field strength. This can be explained by the qualitative similarity of the spectrum of unstable wavenumbers, at least for subcritical strengths of the background magnetic field, and by the vanishing of the pressure gradient of a spatially homogeneous magnetic field. Magnetic trapping is apparently not the saturation mechanism for the considered plasma parameters. The spatial power spectrum of the saturated magnetic fields in the simulation plane can be approximated by a power-law function and the magnetic and electric spectra are similar at high wavenumbers. The final electron velocity distributions are comparable for all magnetic field strengths.

  • 133.
    Stockem, Anne
    et al.
    Theoretical Physics IV, Ruhr-University Bochum, Germany.
    Dieckmann, Mark Eric
    Ruhr-University Bochum.
    Schlickeiser, R
    Theoretical Physics IV, Ruhr-University Bochum, Germany.
    PIC simulations of the temperature anisotropy-driven Weibel instability: analysing the perpendicular mode2010Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 52, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An instability driven by the thermal anisotropy of a single electron species is investigated in a 2D particle-in-cell (PIC) simulation. This instability is the one considered by Weibel and it differs from the beam driven filamentation instability. A comparison of the simulation results with analytic theory provides similar exponential growth rates of the magnetic field during the linear growth phase of the instability. We observe, in accordance with previous works, the growth of electric fields during the saturation phase of the instability. Some components of this electric field are not accounted for by the linearized theory. A single-fluid-based theory is used to determine the source of this non-linear electric field. It is demonstrated that the magnetic stress tensor, which vanishes in a 1D geometry, is more important in this two-dimensional model used here. The electric field grows to an amplitude, which yields a force on the electrons that is comparable to the magnetic one. The peak energy density of each magnetic field component in the simulation plane agrees with previous estimates. Eddy currents develop, which let the amplitude of the third magnetic field component grow, which is not observed in a 1D simulation.

  • 134.
    Stockem, Anne
    et al.
    Theoretical Physics IV, Ruhr-University Bochum, Germany.
    Dieckmann, Mark Eric
    Ruhr-University Bochum.
    Schlickeiser, Reinhard
    Theoretical Physics IV, Ruhr-University Bochum, Germany.
    PIC simulations of the thermal anisotropy-driven Weibel instability: field growth and phase space evolution upon saturation2009Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 51, nr 7, s. 075014-1-075014-13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Weibel instability is investigated with PIC simulations of an initially unmagnetized and spatially uniform electron plasma. This instability, which is driven by the thermally anisotropic electron distribution, generates electromagnetic waves with wave vectors perpendicular to the direction of the higher temperature. Two simulations are performed: a 2D simulation, with a simulation plane that includes the direction of higher temperature, demonstrates that the wave spectrum is initially confined to one dimension. The electric field components in the simulation plane generated by the instability equalize at the end of the simulation through a secondary instability. A 1D PIC simulation with a high resolution, where the simulation box is aligned with the wave vectors of the growing waves, reveals details of the electron phase space distribution and permits a comparison of the magnetic and electric fields when the instability saturates. It is shown that the electrostatic field is driven by the magnetic pressure gradient and that it and the magnetic field redistribute the electrons in space.

  • 135.
    Trier Frederiksen, Jacob
    et al.
    Niels Bohr Institute Copenhagen University.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Visuell informationsteknologi och applikationer. Linköpings universitet, Tekniska högskolan.
    Electromagnetic turbulence driven by the mixed mode instability2008Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 15, nr 9, s. 094503-1-094503-4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In continuation of a previous work, numerical results are presented, concerning relativistically counterstreaming plasmas. Here, the relativistic mixed mode instability evolves through and beyond the linear saturation, well into the nonlinear regime. Besides confirming earlier findings that wave power initially peaks on the mixed mode branch, it is observed that during late time evolution, wave power is transferred to other wave numbers. It is argued that the isotropization of power in wavenumber space may be a consequence of weak turbulence. Further, some modifications to the ideal weak turbulence limit is observed. Development of almost isotropic predominantly electrostatic-partially electromagnetic-turbulent spectra holds relevance when considering the spectral emission signatures of the plasma, namely, bremsstrahlung-partially magnetobremsstrahlung (synchrotron radiation and jitter radiation)-from relativistic shocks in astrophysical jets and from shocks in gamma-ray bursts and active galactic nuclei.

  • 136.
    Warwick, J.
    et al.
    Queens University of Belfast, North Ireland.
    Dzelzainis, T.
    Queens University of Belfast, North Ireland.
    Dieckmann, Mark E
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Schumaker, W.
    SLAC National Accelerator Lab, CA 94025 USA.
    Doria, D.
    Queens University of Belfast, North Ireland.
    Romagnani, L.
    UPMC, France.
    Poder, K.
    Imperial Coll London, England.
    Cole, J. M.
    Imperial Coll London, England.
    Alejo, A.
    Queens University of Belfast, North Ireland.
    Yeung, M.
    Queens University of Belfast, North Ireland.
    Krushelnick, K.
    University of Michigan, MI 48109 USA.
    Mangles, S. P. D.
    Imperial Coll London, England.
    Najmudin, Z.
    Imperial Coll London, England.
    Reville, B.
    Queens University of Belfast, North Ireland.
    Samarin, G. M.
    Queens University of Belfast, North Ireland.
    Symes, D. D.
    Rutherford Appleton Lab, England.
    Thomas, A. G. R.
    University of Michigan, MI 48109 USA; University of Lancaster, England.
    Borghesi, M.
    Queens University of Belfast, North Ireland.
    Sarri, G.
    Queens University of Belfast, North Ireland.
    Experimental Observation of a Current-Driven Instability in a Neutral Electron-Positron Beam2017Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, nr 18, artikkel-id 185002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the first experimental observation of a current-driven instability developing in a quasineutral matter-antimatter beam. Strong magnetic fields (amp;gt;= 1 T) are measured, via means of a proton radiography technique, after the propagation of a neutral electron-positron beam through a background electron-ion plasma. The experimentally determined equipartition parameter of epsilon(B) approximate to 10(-3) is typical of values inferred from models of astrophysical gamma-ray bursts, in which the relativistic flows are also expected to be pair dominated. The data, supported by particle-in-cell simulations and simple analytical estimates, indicate that these magnetic fields persist in the background plasma for thousands of inverse plasma frequencies. The existence of such long-lived magnetic fields can be related to analog astrophysical systems, such as those prevalent in lepton-dominated jets.

  • 137.
    Yang, X. H.
    et al.
    Queen's University of Belfast, United Kingdom and National University of Defense Technology, Changsha, China .
    Dieckmann, Mark Eric
    Queen's University of Belfast, United Kingdom .
    Sarri, Gianluca
    Queen's University of Belfast, United Kingdom and Queen's University of Belfast, United Kingdom .
    Borghesi, Marco
    Queen's University of Belfast, United Kingdom and Institute of Physics of the ASCR, Prague, Czech Republic .
    Simulation of relativistically colliding laser-generated electron flows2012Inngår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, nr 11, s. 113110-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The plasma dynamics resulting from the simultaneous impact, of two equal, ultra-intense laser pulses, in two spatially separated spots, onto a dense target is studied via particle-in-cell simulations. The simulations show that electrons accelerated to relativistic speeds cross the target and exit at its rear surface. Most energetic electrons are bound to the rear surface by the ambipolar electric field and expand along it. Their current is closed by a return current in the target, and this current configuration generates strong surface magnetic fields. The two electron sheaths collide at the midplane between the laser impact points. The magnetic repulsion between the counter-streaming electron beams separates them along the surface normal direction, before they can thermalize through other beam instabilities. This magnetic repulsion is also the driving mechanism for the beam-Weibel (filamentation) instability, which is thought to be responsible for magnetic field growth close to the internal shocks of gamma-ray burst jets. The relative strength of this repulsion compared to the competing electrostatic interactions, which is evidenced by the simulations, suggests that the filamentation instability can be examined in an experimental setting.

123 101 - 137 of 137
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