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  • 1.
    Ahmed, Hamad
    et al.
    Queen's University Belfast, UK.
    Dieckmann, Mark Eric
    Queen's University Belfast, UK.
    Romagnani, Lorenzo
    Ecole Polytechnique, Palaiseau, France.
    Doria, Domenico
    Queen's University Belfast, UK.
    Sarri, Gianluca
    Queen's University Belfast.
    Cherchez, Mirelie
    University of Düsseldorf, Germany.
    Ianni, E.
    Universita di Pisa, Italy.
    Kourakis, Ioannis
    Queen's University Belfast, UK.
    Giesecke, Anna Lena
    University of Düsseldorf, Germany.
    Notley, Margaret
    Rutherford Appleton Laboratory, Chilton, Oxfordshire, UK.
    Prasad, R.
    Queen's University Belfast, UK.
    Quinn, Kevin
    Queen's University Belfast, UK.
    Willi, Oswald
    University of Düsseldorf, Germany.
    Borghesi, Marco
    Queen's University Belfast, UK.
    Time-Resolved Characterization of the Formation of a Collisionless Shock2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 20Article in journal (Refereed)
    Abstract [en]

    We report on the temporally and spatially resolved detection of the precursory stages that lead to the formation of an unmagnetized, supercritical collisionless shock in a laser-driven laboratory experiment. The measured evolution of the electrostatic potential associated with the shock unveils the transition from a current free double layer into a symmetric shock structure, stabilized by ion reflection at the shock front. Supported by a matching particle-in-cell simulation and theoretical considerations, we suggest that this process is analogous to ion reflection at supercritical collisionless shocks in supernova remnants.

  • 2.
    Ahmed, Hamad
    et al.
    Centre for Plasma Physics, Queen’s University of Belfast, Belfast BT7 1NN, UK.
    Doria, Domenico
    Centre for Plasma Physics, Queen’s University of Belfast, Belfast BT7 1NN, UK.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Sarri, Gianluca
    Centre for Plasma Physics, Queen’s University of Belfast, Belfast BT7 1NN, UK.
    Romagnani, Lorenzo
    LULI, École Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Bret, Antoine
    ETSI Industriales, Universidad Castilla La Mancha, E-13 071 Ciudad Real, Spain.
    Cerchez, M
    Institute for Laser and Plasma Physics, University of Düsseldorf, Germany.
    Giesecke, AL
    Institute for Laser and Plasma Physics, University of Düsseldorf, Germany.
    Ianni, E
    Centre for Plasma Physics, Queen’s University of Belfast, Belfast BT7 1NN, UK.
    Kar, Satya
    Centre for Plasma Physics, Queen’s University of Belfast, Belfast BT7 1NN, UK.
    Notley, Margaret
    Central Laser Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX, UK.
    Prasad, R
    Centre for Plasma Physics, Queen’s University of Belfast, Belfast BT7 1NN, UK.
    Quinn, Kevin
    Centre for Plasma Physics, Queen’s University of Belfast, Belfast BT7 1NN, UK.
    Willi, Oswald
    Institute for Laser and Plasma Physics, University of Düsseldorf, Germany.
    Borghesi, Marco
    Centre for Plasma Physics, Queen’s University of Belfast, Belfast BT7 1NN, UK.
    Experimental Observation of Thin-shell Instability in a Collisionless Plasma2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 834, no 2, article id L21Article in journal (Refereed)
    Abstract [en]

    We report on the experimental observation of the instability of a plasma shell, which formed during the expansion of a laser-ablated plasma into a rarefied ambient medium. By means of a proton radiography technique, the evolution of the instability is temporally and spatially resolved on a timescale much shorter than the hydrodynamic one. The density of the thin shell exceeds that of the surrounding plasma, which lets electrons diffuse outward. An ambipolar electric field grows on both sides of the thin shell that is antiparallel to the density gradient. Ripples in the thin shell result in a spatially varying balance between the thermal pressure force mediated by this field and the ram pressure force that is exerted on it by the inflowing plasma. This mismatch amplifies the ripples by the same mechanism that drives the hydrodynamic nonlinear thin-shell instability (NTSI). Our results thus constitute the first experimental verification that the NTSI can develop in colliding flows.

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  • 3.
    Babu, Swetha Suresh
    et al.
    Univ Iceland, Iceland.
    Rudolph, Martin
    Leibniz Inst Surface Engn IOM, Germany.
    Lundin, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Shimizu, Tetsuhide
    Tokyo Metropolitan Univ, Japan.
    Fischer, Joel
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Raadu, Michael A.
    KTH Royal Inst Technol, Sweden.
    Brenning, Nils
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering. KTH Royal Inst Technol, Sweden.
    Gudmundsson, Jon Tomas
    Univ Iceland, Iceland; KTH Royal Inst Technol, Sweden.
    Modeling of high power impulse magnetron sputtering discharges with tungsten target2022In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 31, no 6, article id 065009Article in journal (Refereed)
    Abstract [en]

    The ionization region model (IRM) is applied to model a high power impulse magnetron sputtering discharge with a tungsten target. The IRM gives the temporal variation of the various species and the average electron energy, as well as internal discharge parameters such as the ionization probability and the back-attraction probability of the sputtered species. It is shown that an initial peak in the discharge current is due to argon ions bombarding the cathode target. After the initial peak, the W+ ions become the dominating ions and remain as such to the end of the pulse. We demonstrate how the contribution of the W+ ions to the total discharge current at the target surface increases with increased discharge voltage for peak discharge current densities J (D,peak) in the range 0.33-0.73 A cm(-2). For the sputtered tungsten the ionization probability increases, while the back-attraction probability decreases with increasing discharge voltage. Furthermore, we discuss the findings in terms of the generalized recycling model and compare to experimentally determined deposition rates and find good agreement.

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  • 4.
    Babu, Swetha Suresh
    et al.
    Univ Iceland, Iceland.
    Rudolph, Martin
    Leibniz Inst Surface Engn IOM, Germany.
    Ryan, Peter John
    Univ Liverpool, England.
    Fischer, Joel
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Lundin, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Bradley, James W.
    Univ Liverpool, England.
    Gudmundsson, Jon Tomas
    Univ Iceland, Iceland; KTH Royal Inst Technol, Sweden.
    High power impulse magnetron sputtering of tungsten: a comparison of experimental and modelling results2023In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 32, no 3, article id 034003Article in journal (Refereed)
    Abstract [en]

    Here, we compare the ionization region model (IRM) against experimental measurements of particle densities and electron temperature in a high power impulse magnetron sputtering discharge with a tungsten target. The semi-empirical model provides volume-averaged temporal variations of the various species densities as well as the electron energy for a particular cathode target material, when given the measured discharge current and voltage waveforms. The model results are compared to the temporal evolution of the electron density and the electron temperature determined by Thomson scattering measurements and the temporal evolution of the relative neutral and ion densities determined by optical emission spectrometry. While the model underestimates the electron density and overestimates the electron temperature, the temporal trends of the species densities and the electron temperature are well captured by the IRM.

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  • 5.
    Brenning, Nils
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering. KTH Royal Institute Technology, Sweden; University of Paris Saclay, France.
    Gudmundsson, J. T.
    KTH Royal Institute Technology, Sweden; University of Paris Saclay, France; University of Iceland, Iceland.
    Lundin, D.
    University of Paris Saclay, France.
    Minea, T.
    University of Paris Saclay, France.
    Raadu, M. A.
    KTH Royal Institute Technology, Sweden.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    The role of Ohmic heating in dc magnetron sputtering2016In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 25, no 6, article id 065024Article in journal (Refereed)
    Abstract [en]

    Sustaining a plasma in a magnetron discharge requires energization of the plasma electrons. In this work, Ohmic heating of electrons outside the cathode sheath is demonstrated to be typically of the same order as sheath energization, and a simple physical explanation is given. We propose a generalized Thornton equation that includes both sheath energization and Ohmic heating of electrons. The secondary electron emission yield gamma(SE) is identified as the key parameter determining the relative importance of the two processes. For a conventional 5 cm diameter planar dc magnetron, Ohmic heating is found to be more important than sheath energization for secondary electron emission yields below around 0.1.

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  • 6.
    Brenning, Nils
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering. KTH Royal Institute Technology, Sweden; University of Paris Saclay, France.
    Gudmundsson, J. T.
    KTH Royal Institute Technology, Sweden; University of Paris Saclay, France; University of Iceland, Iceland.
    Raadu, M. A.
    KTH Royal Institute Technology, Sweden.
    Petty, T. J.
    University of Paris Saclay, France.
    Minea, T.
    University of Paris Saclay, France.
    Lundin, D.
    University of Paris Saclay, France.
    A unified treatment of self-sputtering, process gas recycling, and runaway for high power impulse sputtering magnetrons2017In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 26, no 12, article id 125003Article in journal (Refereed)
    Abstract [en]

    The combined processes of self-sputter (SS)-recycling and process gas recycling in high power impulse magnetron sputtering (HiPIMS) discharges are analyzed using the generalized recycling model (GRM). The study uses experimental data from discharges with current densities from the direct current magnetron sputtering range to the HiPIMS range, and using targets with self-sputter yields Y-SS from approximate to 0.1 to 2.6. The GRM analysis reveals that, above a critical current density of the order of J(crit) approximate to 0.2 A cm(-2), a combination of self-sputter recycling and gas-recycling is generally the case. The relative contributions of these recycling mechanisms, in turn, influence both the electron energy distribution and the stability of the discharges. For high self-sputter yields, above Y-SS approximate to 1, the discharges become dominated by SS-recycling, contain few hot secondary electrons from sheath energization, and have a relatively low electron temperature T-e. Here, stable plateau values of the discharge current develop during long pulses, and these values increase monotonically with the applied voltage. For low self-sputter yields, below Y-SS approximate to 0.2, the discharges above J(crit) are dominated by process gas recycling, have a significant sheath energization of secondary electrons and a higher T-e, and the current evolution is generally less stable. For intermediate values of YSS the discharge character gradually shifts between these two types. All of these discharges can, at sufficiently high discharge voltage, give currents that increase rapidly in time. For such cases we propose that a distinction should be made between unlimited runaway and limited runaway: in unlimited runaway the current can, in principle, increase without a limit for a fixed discharge voltage, while in limited runaway it can only grow towards finite, albeit very high, levels. For unlimited runway Y-SS amp;gt; 1 is found to be a necessary criterion, independent of the amount of gas-recycling in the discharge.

  • 7.
    Bret, Antoine
    et al.
    Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
    Dieckmann, Mark E
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Hierarchy of instabilities for two counter-streaming magnetized pair beams: Influence of field obliquity2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 6, article id 062105Article in journal (Refereed)
    Abstract [en]

    The hierarchy of unstable modes when two counter-streaming pair plasmas interact over a flow-aligned magnetic field has been recently investigated [Phys. Plasmas 23, 062122 (2016)]. The analysis is here extended to the case of an arbitrarily tilted magnetic field. The two plasma shells are initially cold and identical. For any angle θ ∈ [0, π/2] between the field and the initial flow, the hierarchy of unstable modes is numerically determined in terms of the initial Lorentz factor of the shells γ0, and the field strength as measured by a parameter denoted σ. For θ = 0, four different kinds of mode are likely to lead the linear phase. The hierarchy simplifies for larger θ's, partly because the Weibel instability can no longer be cancelled in this regime. For θ > 0.78 (44°) and in the relativistic regime, the Weibel instability always govern the interaction. In the non-relativistic regime, the hierarchy becomes θ-independent because the interaction turns to be field-independent. As a result, the two-stream instability becomes the dominant one, regardless of the field obliquity.

  • 8.
    Bret, Antoine
    et al.
    Universidad de Castilla-La Mancha, Ciudad Real, Spain; Campus Universitario de Ciudad Real, Ciudad Real, Spain.
    Dieckmann, Mark E
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Particle trajectories in Weibel filaments: influence of external field obliquity and chaos2020In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 86, no 3, article id 905860305Article in journal (Refereed)
    Abstract [en]

    When two collisionless plasma shells collide, they interpenetrate and the overlapping region may turn Weibel unstable for some values of the collision parameters. This instability grows magnetic filaments which, at saturation, have to block the incoming flow if a Weibel shock is to form. In a recent paper (Bret, J. Plasma Phys., vol. 82, 2016b, 905820403), it was found by implementing a toy model for the incoming particle trajectories in the filaments, that a strong enough external magnetic field 𝘽𝘽0 can prevent the filaments blocking the flow if it is aligned with them. Denoting by Bf the peak value of the field in the magnetic filaments, all test particles stream through them if 𝛼𝛼=B0/Bf>1/2 . Here, this result is extended to the case of an oblique external field B0 making an angle 𝜃𝜃 with the flow. The result, numerically found, is simply 𝛼𝜅𝜃𝜃𝛼>𝜅(𝜃)/cos⁡𝜃 , where 𝜅𝜃𝜅(𝜃) is of order unity. Noteworthily, test particles exhibit chaotic trajectories.

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  • 9.
    Bret, Antoine
    et al.
    Universidad de Castilla-La Mancha, Spain.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    How large can the electron to proton mass ratio be in particle-in-cell simulations of unstable systems?2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 3, p. 032109-Article in journal (Refereed)
    Abstract [en]

    Particle-in-cell simulations are widely used as a tool to investigate instabilities that develop between a collisionless plasma and beams of charged particles. However, even on contemporary supercomputers, it is not always possible to resolve the ion dynamics in more than one spatial dimension with such simulations. The ion mass is thus reduced below 1836 electron masses, which can affect the plasma dynamics during the initial exponential growth phase of the instability and during the subsequent nonlinear saturation. The goal of this article is to assess how far the electron to ion mass ratio can be increased, without changing qualitatively the physics. It is first demonstrated that there can be no exact similarity law, which balances a change in the mass ratio with that of another plasma parameter, leaving the physics unchanged. Restricting then the analysis to the linear phase, a criterion allowing to define a maximum ratio is explicated in terms of the hierarchy of the linear unstable modes. The criterion is applied to the case of a relativistic electron beam crossing an unmagnetized electron-ion plasma.

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  • 10.
    Bret, Antoine
    et al.
    ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology.
    On the proton to electron mass ratio in particle-in-cell simulations2011In: Europhysics conference abstracts, 2011, p. O4.310-1-O4.310-4Conference paper (Refereed)
  • 11.
    Bret, Antoine
    et al.
    ETSI Ind Univ Castilla-La Mancha.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Gremillet, Laurent
    CEA, DAM, DIF, 91297 Arpajon, France.
    Recent progresses in relativistic beam-plasma instability theory2010In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 28, no 11, p. 2127-2132Article in journal (Refereed)
    Abstract [en]

    Beam-plasma instabilities are a key physical process in many astrophysical phenomena. Within the fireball model of Gamma ray bursts, they first mediate a relativistic collisionless shock before they produce upstream the turbulence needed for the Fermi acceleration process. While non-relativistic systems are usually governed by flow-aligned unstable modes, relativistic ones are likely to be dominated by normally or even obliquely propagating waves. After reviewing the basis of the theory, results related to the relativistic kinetic regime of the poorly-known oblique unstable modes will be presented. Relevant systems besides the well-known electron beam-plasma interaction are presented, and it is shown how the concept of modes hierarchy yields a criterion to assess the proton to electron mass ratio in Particle in cell simulations.

  • 12.
    Bret, Antoine
    et al.
    ETSI Ind Univ Castilla-La Mancha.
    Gremillet, Laurent
    CEA, DAM, DIF, 91297 Arpajon, France.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Multidimensional electron beam-plasma instabilities in the relativistic regime2010In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 17, no 12, p. 120501-1-120501-36Article, review/survey (Refereed)
    Abstract [en]

    The interest in relativistic beam-plasma instabilities has been greatly rejuvenated over the past two decades by novel concepts in laboratory and space plasmas. Recent advances in this long-standing field are here reviewed from both theoretical and numerical points of view. The primary focus is on the two-dimensional spectrum of unstable electromagnetic waves growing within relativistic, unmagnetized, and uniform electron beam-plasma systems. Although the goal is to provide a unified picture of all instability classes at play, emphasis is put on the potentially dominant waves propagating obliquely to the beam direction, which have received little attention over the years. First, the basic derivation of the general dielectric function of a kinetic relativistic plasma is recalled. Next, an overview of two-dimensional unstable spectra associated with various beam-plasma distribution functions is given. Both cold-fluid and kinetic linear theory results are reported, the latter being based on waterbag and Maxwell–Jüttner model distributions. The main properties of the competing modes (developing parallel, transverse, and oblique to the beam) are given, and their respective region of dominance in the system parameter space is explained. Later sections address particle-in-cell numerical simulations and the nonlinear evolution of multidimensional beam-plasma systems. The elementary structures generated by the various instability classes are first discussed in the case of reduced-geometry systems. Validation of linear theory is then illustrated in detail for large-scale systems, as is the multistaged character of the nonlinear phase. Finally, a collection of closely related beam-plasma problems involving additional physical effects is presented, and worthwhile directions of future research are outlined.

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  • 13.
    Bret, Antoine
    et al.
    ETSI Industriales, Universidad de Castilla-La Mancha, Ciudad Real, Spain.
    Pe'er, Asaf
    Physics Department, University College Cork, Cork, Ireland.
    Sironi, Lorenzo
    Department of Astronomy, Columbia University, New York, NY, USA.
    Dieckmann, Mark E
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Narayan, Ramesh
    Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Departure from MHD prescriptions in shock formation over a guiding magnetic field2017In: Laser and particle beams (Print), ISSN 0263-0346, E-ISSN 1469-803X, Vol. 35, p. 513-519Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Bret, Antoine
    et al.
    ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
    Stockem Novo, Anne
    Fakultät fuer Physik und Astronomie, Ruhr-Universität Bochum, 44780 Bochum, Germany.
    Narayan, Ramesh
    Harvard-Smithsonian Center for Astrophysics, Harvard University, Cambridge, MA 02138, USA.
    Ruyer, Charles
    High Energy Density Science Division, SLAC National Accelerator Lab., Menlo Park, CA 94025, USA.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Silva, Luis O
    GoLP/Instituto de Plasmas e Fusão Nuclear – Laboratório Associado, Instituto Superior Técnico, Lisboa, Portugal.
    Theory of the formation of a collisionless Weibel shock: pair vs. electron/proton plasmas2016In: Laser and particle beams (Print), ISSN 0263-0346, E-ISSN 1469-803X, Vol. 34, no 2, p. 362-367Article in journal (Refereed)
    Abstract [en]

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

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  • 15.
    Brodin, G.
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    A new decay channel for upper-hybrid waves2016In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 91, no 10, article id 104005Article in journal (Refereed)
    Abstract [en]

    We look here at a three-wave interaction process involving only electrostatic waves in an electron plasma with stationary ions. Special attention is given to the case with an upper-hybrid wave as a pump wave, where a new decay channel is pointed out. The corresponding growth rate is calculated.

  • 16.
    Brodin, G.
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    A simple electron plasma wave2017In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 381, no 11, p. 1033-1035Article in journal (Refereed)
    Abstract [en]

    Considering a class of solutions where the density perturbations are functions of time, but not of space, we derive a new exact large amplitude wave solution for a cold uniform electron plasma. This result illustrates that most simple analytical solutions can appear even if the density perturbations are large. (C) 2016 Elsevier B.V. All rights reserved.

  • 17.
    Brodin, G.
    et al.
    Umeå University, Sweden.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Nonlinear dynamics of a cold collisional electron plasma2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 12, article id 124505Article in journal (Refereed)
    Abstract [en]

    We study the influence of collisions on the dynamics of a cold non-relativistic plasma. It is shown that even a comparatively small collision frequency can significantly change the large amplitude wave solution. Published by AIP Publishing.

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  • 18.
    Brown, M. R.
    et al.
    Swarthmore College, PA, USA.
    Browning, P. K.
    University of Manchester, UK.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Furno, I.
    Ecole Polytechnique Federal de Lausanne, Switzerland .
    Intrator, T. P.
    Los Alamos National Laboratory, NM, USA .
    Microphysics of Cosmic Plasmas: Hierarchies of Plasma Instabilities from MHD to Kinetic2013In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 178, no 2-4, p. 357-383Article, review/survey (Refereed)
    Abstract [en]

    In this article, we discuss the idea of a hierarchy of instabilities that can rapidly couple the disparate scales of a turbulent plasma system. First, at the largest scale of the system, L, current carrying flux ropes can undergo a kink instability. Second, a kink instability in adjacent flux ropes can rapidly bring together bundles of magnetic flux and drive reconnection, introducing a new scale of the current sheet width, , perhaps several ion inertial lengths (δ i ) across. Finally, intense current sheets driven by reconnection electric fields can destabilize kinetic waves such as ion cyclotron waves as long as the drift speed of the electrons is large compared to the ion thermal speed, v D v i . Instabilities such as these can couple MHD scales to kinetic scales, as small as the proton Larmor radius, ρ i .

  • 19.
    Brown, Michael R
    et al.
    Swarthmore College, Swarthmore, PA 19081, USA.
    Browning, Philippa K
    Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, UK.
    Dieckmann, Mark E
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Furno, Ivo
    EPFL Lausanne, CH-1015 Lausanne, Switzerland.
    Intrator, Tom P
    Los Alamos National Lab, USA.
    Microphysics of Cosmic Plasmas: Hierarchies of Plasma Instabilities from MHD to Kinetic2014In: Microphysics of cosmic plasmas / [ed] André Balogh, Andrei Bykov, Peter Cargill, Richard DendyThierry and Dudok de WitJohn Raymond, Boston: Springer, 2014, 1, p. 281-307Chapter in book (Refereed)
    Abstract [en]

    In this article, we discuss the idea of a hierarchy of instabilities that can rapidly couple the disparate scales of a turbulent plasma system. First, at the largest scale of the system, L, current carrying flux ropes can undergo a kink instability. Second, a kink instability in adjacent flux ropes can rapidly bring together bundles of magnetic flux and drive reconnection, introducing a new scale of the current sheet width, , perhaps several ion inertial lengths (δ i ) across. Finally, intense current sheets driven by reconnection electric fields can destabilize kinetic waves such as ion cyclotron waves as long as the drift speed of the electrons is large compared to the ion thermal speed, v D v i . Instabilities such as these can couple MHD scales to kinetic scales, as small as the proton Larmor radius, ρ i .

  • 20.
    Butler, Alexandre
    et al.
    Univ Paris Saclay, France.
    Brenning, Nils
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering. Univ Paris Saclay, France; KTH Royal Inst Technol, Sweden.
    Raadu, Michael A.
    KTH Royal Inst Technol, Sweden.
    Gudmundsson, Jon Tomas
    KTH Royal Inst Technol, Sweden; Univ Iceland, Iceland.
    Minea, Tiberiu
    Univ Paris Saclay, France.
    Lundin, Daniel
    Univ Paris Saclay, France.
    On three different ways to quantify the degree of ionization in sputtering magnetrons2018In: Plasma sources science & technology, ISSN 0963-0252, E-ISSN 1361-6595, Vol. 27, no 10, article id 105005Article in journal (Refereed)
    Abstract [en]

    Quantification and control of the fraction of ionization of the sputtered species are crucial in magnetron sputtering, and in particular in high-power impulse magnetron sputtering (HiPIMS), yet proper definitions of the various concepts of ionization are still lacking. In this contribution, we distinguish between three approaches to describe the degree (or fraction) of ionization: the ionized flux fraction F-flux, the ionized density fraction F-density, and the fraction a of the sputtered metal atoms that become ionized in the plasma (sometimes referred to as probability of ionization). By studying a reference HiPIMS discharge with a Ti target, we show how to extract absolute values of these three parameters and how they vary with peak discharge current. Using a simple model, we also identify the physical mechanisms that determine F-flux, F-density, and a as well as how these three concepts of ionization are related. This analysis finally explains why a high ionization probability does not necessarily lead to an equally high ionized flux fraction or ionized density fraction.

  • 21.
    Dawi, E. A.
    et al.
    Ajman Univ, U Arab Emirates.
    Mustafa, Elfatih Mohammed
    Linköping University, Department of Science and Technology, Physics, Electronics and Mathematics. Linköping University, Faculty of Science & Engineering.
    Siahaan, T.
    Eindhoven Univ Technol, Netherlands.
    Anisotropic deformation of colloidal particles under 4 MeV Cu ions irradiation2022In: Materials Research Express, E-ISSN 2053-1591, Vol. 9, no 8, article id 086506Article in journal (Refereed)
    Abstract [en]

    Anisotropic deformation of colloidal particles was investigated under ion irradiation with 4 MeV Cu ions. In this study, 0.5 mu m-diameter colloidal silica particles, 0.5 mu m-diameter Au-silica core-shell particles, and 15 nm-diameter Au colloids embedding in a planar Si/SiO2 matrix were irradiated with 4 MeV Cu ions at room temperature and normal incidence. In colloidal silica particles, ion beam irradiation causes dramatic anisotropic deformation; silica expands perpendicular to the beam and contracts parallel, whereas Au cores elongate. Au colloids in a planar SiO2 matrix were anisotropically transformed from spherical colloids to elongated nanorods by irradiating them with 4 MeV Cu ions. The degree of anisotropy varied with ion flux. Upon irradiating the embedded Au colloids, dark-field light scattering experiments revealed a distinct color shift to yellow, which indicates a shift in surface plasmon resonance. A surface plasmon resonance measurement reveals the plasmon resonance bands are split along the arrays of Au colloids. Our measurements have revealed resonance shifts that extend into the near-infrared spectrum by as much as 50 nm.

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  • 22.
    Dieckmann, Mark E
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Collisionless tangential discontinuity between pair plasma and electron–proton plasma2020In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 27, no 3, article id 032105Article in journal (Refereed)
    Abstract [en]

    We study with a one-dimensional particle-in-cell simulation the expansion of a pair cloud into a magnetized electron–proton plasma as well as the formation and subsequent propagation of a tangential discontinuity that separates both plasmas. Its propagation speed takes the value that balances the magnetic pressure of the discontinuity against the thermal pressure of the pair cloud and the ram pressure of the protons. Protons are accelerated by the discontinuity to a speed that exceeds the fast magnetosonic speed by the factor of 10. A supercritical fast magnetosonic shock forms at the front of this beam. An increasing proton temperature downstream of the shock and ahead of the discontinuity leaves the latter intact. We create the discontinuity by injecting a pair cloud at a simulation boundary into a uniform electron–proton plasma, which is permeated by a perpendicular magnetic field. Collisionless tangential discontinuities in the relativistic pair jets of x-ray binaries (microquasars) are in permanent contact with the relativistic leptons of their inner cocoon, and they become the sources of radio synchrotron emissions.

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  • 23.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Alejo, Aaron
    Centre for Plasma Physics, Queen's University Belfast, Belfast, UK..
    Sarri, Gianluca
    Centre for Plasma Physics, Queen's University Belfast, Belfast, UK..
    Folini, Doris
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, Lyon, France.
    Walder, Rolf
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, Lyon, France.
    One-dimensional thermal pressure-driven expansion of a pair cloud into an electron-proton plasma2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 5, article id 064502Article in journal (Refereed)
    Abstract [en]

    Recently, a filamentation instability was observed when a laser-generated pair cloud interacted with an ambient plasma. The magnetic field it drove was strong enough to magnetize and accelerate the ambient electrons. It is of interest to determine if and how pair cloud-driven instabilities can accelerate ions in the laboratory or in astrophysical plasma. For this purpose, the expansion of a localized pair cloud with the temperature 400 keV into a cooler ambient electron-proton plasma is studied by means of one-dimensional particle-in-cell simulations. The cloud's expansion triggers the formation of electron phase space holes that accelerate some protons to MeV energies. Forthcoming lasers might provide the energy needed to create a cloud that can accelerate protons.

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  • 24.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Doria, Domenico
    School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, United Kingdom.
    Ahmed, Hamad
    School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, United Kingdom.
    Romagnani, Lorenzo
    LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Palaiseau, France.
    Sarri, Gianluca
    School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, United Kingdom.
    Folini, Doris
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Lyon, France.
    Walder, Rolf
    Université de Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, Lyon, France.
    Bret, Antoine
    ETSI Industriales, Universidad de Castilla-La Mancha, Ciudad Real, Spain.
    Borghesi, Marco
    School of Mathematics and Physics, Queen's University Belfast, University Road, Belfast, United Kingdom.
    Expansion of a radial plasma blast shell into an ambient plasma2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 9, article id 094501Article in journal (Refereed)
    Abstract [en]

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

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  • 25.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Falk, Martin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    Ecole Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, 69622 Lyon, France.
    Walder, Rolf
    Ecole Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, 69622 Lyon, France.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Hotz, Ingrid
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Collisionless Rayleigh–Taylor-like instability of the boundary between a hot pair plasma and an electron–proton plasma: The undular mode2020In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 27, no 11, p. 1-14, article id 112106Article in journal (Refereed)
    Abstract [en]

    We study with a two-dimensional particle-in-cell simulation the stability of a discontinuity or piston, which separates an electron–positron cloud from a cooler electron–proton plasma. Such a piston might be present in the relativistic jets of accreting black holes separating the jet material from the surrounding ambient plasma and when pair clouds form during an x-ray flare and expand into the plasma of the accretion disk corona. We inject a pair plasma at a simulation boundary with a mildly relativistic temperature and mean speed. It flows across a spatially uniform electron–proton plasma, which is permeated by a background magnetic field. The magnetic field is aligned with one simulation direction and oriented orthogonally to the mean velocity vector of the pair cloud. The expanding pair cloud expels the magnetic field and piles it up at its front. It is amplified to a value large enough to trap ambient electrons. The current of the trapped electrons, which is carried with the expanding cloud front, drives an electric field that accelerates protons. A solitary wave grows and changes into a piston after it saturated. Our simulations show that this piston undergoes a collisionless instability similar to a Rayleigh–Taylor instability. The undular mode grows and we observe fingers in the proton density distribution. The effect of the instability is to deform the piston but it cannot destroy it.

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  • 26.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Falk, Martin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    CRAL, École Normale Supérieure, 69622 Lyon, France.
    Hotz, Ingrid
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Nordman, Aida
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Dell'Acqua, Pierangelo
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Walder, Rolf
    CRAL, École Normale Supérieure, 69622 Lyon, France.
    Structure of a collisionless pair jet in a magnetized electron-proton plasma: Flow-aligned magnetic field2019In: High Energy Phenomena in Relativistic Outflows VII (HEPRO VII): Formation and propagation of relativistic outflows, 2019, article id 006Conference paper (Refereed)
    Abstract [en]

    We present the results from a particle-in-cell (PIC) simulation that models the interaction between a spatially localized electron-positron cloud and an electron-ion plasma. The latter is permeated by a magnetic field that is initially spatially uniform and aligned with the mean velocity vector of the pair cloud. The pair cloud expels the magnetic field and piles it up into an electromagnetic piston. Its electromagnetic field is strong enough to separate the pair cloud from the ambient plasma in the direction that is perpendicular to the cloud propagation direction. The piston propagates away from the spine of the injected pair cloud and it accelerates the protons to a high nonrelativistic speed. The accelerated protons form an outer cocoon that will eventually become separated from the unperturbed ambient plasma by a fast magnetosonic shock. No electromagnetic piston forms at the front of the cloud and a shock is mediated here by the filamentation instability. The final plasma distribution resembles that of a hydrodynamic jet. Collisionless plasma jets may form in the coronal plasma of accreting black holes and the interaction between the strong magnetic field of the piston and the hot pair cloud may contribute to radio emissions by such objects.

  • 27.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, D.
    Univ Lyon, France.
    Falk, Martin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Bock, Alexander
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Walder, R.
    Univ Lyon, France.
    Three-dimensional structure and stability of discontinuities between unmagnetized pair plasma and magnetized electron-proton plasma2023In: New Journal of Physics, E-ISSN 1367-2630, Vol. 25, no 6, article id 063017Article in journal (Refereed)
    Abstract [en]

    We study with a 3D particle-in-cell simulation discontinuities between an electron-positron pair plasma and magnetized electrons and protons. A pair plasma is injected at one simulation boundary with a speed 0.6c along its normal. It expands into an electron-proton plasma and a magnetic field that points orthogonally to the injection direction. Diamagnetic currents expel the magnetic field from within the pair plasma and pile it up in front of it. It pushes electrons, which induces an electric field pulse ahead of the magnetic one. This initial electromagnetic pulse (EMP) confines the pair plasma magnetically and accelerates protons electrically. The fast flow of the injected pair plasma across the protons behind the initial EMP triggers the filamentation instability. Some electrons and positrons cross the injection boundary and build up a second EMP. Electron-cyclotron drift instabilities perturb the plasma ahead of both EMPs seeding a Rayleigh-Taylor (RT)-type instability. Despite equally strong perturbations ahead of both EMPs, the second EMP is much more stable than the initial one. We attribute the rapid collapse of the initial EMP to the filamentation instability, which perturbed the plasma behind it. The RT-type instability transforms the planar EMPs into transition layers, in which magnetic flux ropes and electrostatic forces due to uneven numbers of electrons and positrons slow down and compress the pair plasma and accelerate protons. In our simulation, the expansion speed of the pair cloud decreased by about an order of magnitude and its density increased by the same factor. Its small thickness implies that it is capable of separating a relativistic pair outflow from an electron-proton plasma, which is essential for collimating relativistic jets of pair plasma in collisionless astrophysical plasma.

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  • 28.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, F-69622 Lyon, France.
    Bret, Antoine
    Universidad de Castilla La Mancha, ETSI Ind, E-13071 Ciudad Real, Spain.
    Walder, Rolf
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, F-69622 Lyon, France.
    Simulation studies of temperature anisotropy driven pair-Alfvén and aperiodic instabilities in magnetized pair plasma2019In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, no 8, article id 085027Article in journal (Refereed)
    Abstract [en]

    We compare with one-dimensional particle-in-cell simulations the aperiodically growing instabilities driven by a bi-Maxwellian velocity distribution in unmagnetized electron plasma (Weibel instability) and in pair plasma. The simulation box is aligned with the cool direction. The waves in both simulations evolve towards a circularly polarized non-propagating magnetic structure. Its current and magnetic field are aligned and the structure is in a force-free state. We examine how a background magnetic field B 0, which is parallel to the simulation direction, affects the waves in the pair plasma. A weak B 0 cannot inhibit the growth of the aperiodically growing instability but it prevents it from reaching the force-free stable state. The mode collapses and seeds a pair Alfvén waves. An intermediate B 0 couples the thermal anisotropy to the pair Alfvén mode and propagating magnetowaves grow. The phase speed of the pair of Alfvén waves is increased by the thermal anisotropy. Its growth is suppressed when B 0 is set to the value that stabilizes the mirror mode.

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  • 29.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, F-69007 Lyon, France.
    Walder, Rolf
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, F-69007 Lyon, France.
    Romagnani, Lorenzo
    École Polytechnique, CNRS, LULI, F-91128 Palaiseau, France.
    d'Humieres, Emanuel
    Univ Bordeaux, IMB, UMR 5251, F-33405 Talence, France.
    Bret, Antoine
    ETSI Industriales, Universidad de Castilla-La Mancha, 13071 Ciudad Real and Instituto de Investigaciones Energéticas y Aplicaciones Industriales, Campus Universitario de Ciudad Real, 13071 Ciudad Real, Spain.
    Karlsson, Tomas
    KTH Royal Institute of Technology, School of Electrical Engineering, Space and Plasma Physics, Stockholm, Sweden.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Emergence of MHD structures in a collisionless PIC simulation plasma2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 9, article id 094502Article in journal (Refereed)
    Abstract [en]

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

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  • 30.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    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 plasma2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 5, article id 052108Article in journal (Refereed)
    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.

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  • 31.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Palodhi, Lopamudra
    Department of Mathematics, Indian Institute of Technology Ropar, 140001, Punjab, India.
    Fegan, Conor
    Centre for Light-Matter Interactions, School of Mathematics and Physics, The Queen's University of Belfast, University Road, BT7 1NN, Belfast, United Kingdom.
    Borghesi, Marco
    Centre for Light-Matter Interactions, School of Mathematics and Physics, The Queen's University of Belfast, University Road, BT7 1NN, Belfast, United Kingdom.
    Weibel- and non-resonant Whistler wave growth in an expanding plasma in a 1D simulation geometry2024In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 99, no 4, article id 045602Article in journal (Refereed)
    Abstract [en]

    Ablating a target with an ultraintense laser pulse can create a cloud of collisionless plasma. A density ramp forms, in which the plasma density decreases and the ion's mean speed increases with distance from the plasma source. Its width increases with time. Electrons lose energy in the ion's expansion direction, which gives them a temperature anisotropy. We study with one-dimensional particle-in-cell simulations the expansion of a dense plasma into a dilute one, yielding a density ramp similar to that in laser-plasma experiments and a thermal-anisotropy-driven instability. Non-propagating Weibel-type wave modes grow in the simulation with no initial magnetic field. Their magnetic field diffuses across the shock and expands upstream. Circularly polarized propagating Whistler waves grow in a second simulation, in which a magnetic field is aligned with the ion expansion direction. Both wave modes are driven by non-resonant instabilities, they have similar exponential growth rates, and they can leave the density ramp and expand into the dilute plasma. Their large magnetic amplitude should make them detectable in experimental settings.

  • 32.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Sarri, G.
    Queens University of Belfast, North Ireland.
    Doria, D.
    Queens University of Belfast, North Ireland.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Borghesi, M.
    Queens University of Belfast, North Ireland.
    Particle-in-cell simulation study of a lower-hybrid shock2016In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 23, no 6, p. 062111-Article in journal (Refereed)
    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.

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  • 33.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    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 plasma2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 11, article id 112903Article in journal (Refereed)
    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.

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  • 34.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Spencer, Selina-Jane
    Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, CV4 7AL, UK.
    Falk, Martin
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Rowlands, George
    Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry, CV4 7AL, UK.
    Preferential acceleration of positrons by a filamentation instability between an electron–proton beam and a pair plasma beam2020In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 27, no 12, article id 122102Article in journal (Refereed)
    Abstract [en]

    Particle-in-cell simulations of jets of electrons and positrons in an ambient electron–proton plasma have revealed an acceleration of positrons at the expense of electron kinetic energy. We show that a filamentation instability, between an unmagnetized ambient electron–proton plasma at rest and a beam of pair plasma that moves through it at a non-relativistic speed, indeed results in preferential positron acceleration. Filaments form that are filled predominantly with particles with the same direction of their electric current vector. Positron filaments are separated by electromagnetic fields from beam electron filaments. Some particles can cross the field boundary and enter the filament of the other species. Positron filaments can neutralize their net charge by collecting the electrons of the ambient plasma, while protons cannot easily follow the beam electron filaments. Positron filaments can thus be compressed to a higher density and temperature than the beam electron filaments. Filament mergers, which take place after the exponential growth phase of the instability has ended, lead to an expansion of the beam electron filaments, which amplifies the magnetic field they generate and induces an electric field in this filament. Beam electrons lose a substantial fraction of their kinetic energy to the electric field. Some positrons in the beam electron filament are accelerated by the induced electric field to almost twice their initial speed. The simulations show that a weaker electric field is induced in the positron filament and particles in this filament hardly change their speed.

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  • 35.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    The filamentation instability driven by warm electron beams: statistics and electric field generation2009In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 51, no 12, p. 124042-Article in journal (Refereed)
    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.

  • 36.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    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 plasma2018In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 25, no 6, article id 062122Article in journal (Refereed)
    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.

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  • 37.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Bock, Alexander
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    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
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    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 generation2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 7, p. 1-9, article id 072104Article in journal (Refereed)
    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.

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  • 38.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Bret, Antoine
    ETSI Ind Univ Castilla-La Mancha.
    Electric field generation by the electron beam filamentation instability: filament size effects2010In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 81, no 1, p. 015502-Article in journal (Refereed)
    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.

  • 39.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Bret, Antoine
    University of Castilla La Mancha, ETSI Ind, Ciudad Real, Spain.
    Simulation study of the formation of a non-relativistic pair shock2017In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 83, p. 1-19, article id 905830104Article in journal (Refereed)
    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.

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  • 40.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    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 instability2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 465, no 4, p. 4240-4248Article in journal (Refereed)
    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.

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  • 41.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    Univ Lyon, France.
    Walder, Rolf
    Univ Lyon, France.
    Charlet, Arthur
    Univ Lyon, France; Univ Montpellier, France; Open Univ Israel, Israel.
    Marcowith, Alexandre
    Univ Montpellier, France.
    Two-dimensional particle simulation of the boundary between a hot pair plasma and magnetized electrons and protons: Out-of-plane magnetic field2022In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 29, no 9, article id 092103Article in journal (Refereed)
    Abstract [en]

    By means of a particle-in-cell (PIC) simulation, we study the interaction between a uniform magnetized ambient electron-proton plasma at rest and an unmagnetized pair plasma, which we inject at one simulation boundary with a mildly relativistic mean speed and temperature. The magnetic field points out of the simulation plane. The injected pair plasma expels the magnetic field and piles it up at its front. It traps ambient electrons and drags them across the protons. An electric field grows, which accelerates protons into the pair cloud's expansion direction. This electromagnetic pulse separates the pair cloud from the ambient plasma. Electrons and positrons, which drift in the pulse's nonuniform field, trigger an instability that disrupts the current sheet ahead of the pulse. The wave vector of the growing perturbation is orthogonal to the magnetic field direction and magnetic tension cannot stabilize it. The electromagnetic pulse becomes permeable for pair plasma, which forms new electromagnetic pulses ahead of the initial one. A transition layer develops with a thickness of a few proton skin depths, in which protons and positrons are accelerated by strong electromagnetic fields. Protons form dense clumps surrounded by a strong magnetic field. The thickness of the transition layer grows less rapidly than we would expect from the typical speeds of the pair plasma particles and the latter transfer momentum to protons; hence, the transition layer acts as a discontinuity, separating the pair plasma from the ambient plasma. Such a discontinuity is an important building block for astrophysical pair plasma jets.

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  • 42.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Huete, Cesar
    Univ Carlos III Madrid, Grp Mecan Fluidos, Leganes 28911, Spain.
    Cobos Campos, Francisco
    Univ Castilla La Mancha, ETSI Ind, Ciudad Real 13071, Spain.
    Bret, Antoine Claude
    Univ Castilla La Mancha, ETSI Ind, Ciudad Real 13071, Spain.
    Folini, Doris
    Univ Lyon, ENS de Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574 F-69230, Saint-Genis-Laval, France.
    Eliasson, Bengt Erik
    Univ Strathclyde, SUPA, Glasgow G4 0NG, Scotland, United Kingdom.
    Walder, Rolf
    Univ Lyon, ENS de Lyon, Univ Lyon 1, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574 F-69230, Saint-Genis-Laval, France.
    PIC simulations of stable surface waves on a subcritical fast magnetosonic shock front2023In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 98, no 9, article id 095603Article in journal (Refereed)
    Abstract [en]

    We study with particle-in-cell (PIC) simulations the stability of fast magnetosonic shocks. They expand across a collisionless plasma and an orthogonal magnetic field that is aligned with one of the directions resolved by the 2D simulations. The shock speed is 1.6 times the fast magnetosonic speed when it enters a layer with a reduced density of mobile ions, which decreases the shock speed by up to 15% in 1D simulations. In the 2D simulations, the density of mobile ions in the layer varies sinusoidally perpendicularly to the shock normal. We resolve one sine period. This variation only leads to small changes in the shock speed evidencing a restoring force that opposes a shock deformation. As the shock propagates through the layer, the ion density becomes increasingly spatially modulated along the shock front and the magnetic field bulges out where the mobile ion density is lowest. The perturbed shock eventually reaches a steady state. Once it leaves the layer, the perturbations of the ion density and magnetic field oscillate along its front at a frequency close to the lower-hybrid frequency; the shock is mediated by a standing wave composed of obliquely propagating lower-hybrid waves. We perform three 2D simulations with different box lengths along the shock front. The shock front oscillations are aperiodically damped in the smallest box with the fastest variation of the ion density, strongly damped in the intermediate one, and weakly damped in the largest box. The shock front oscillations perturb the magnetic field in a spatial interval that extends by several electron skin depths upstream and downstream of the shock front and could give rise to Whistler waves that propagate along the shock's magnetic field overshoot. Similar waves were observed in hybrid and PIC simulations and by the MMS satellite mission.

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  • 43.
    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 force2009In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 16, no 7, p. 074502-1-074502-4Article in journal (Refereed)
    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.

  • 44.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    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 shocks2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 509, no 1, p. A89-Article in journal (Refereed)
    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.

  • 45.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    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 amplification2010In: EUROPEAN CONFERENCE ABSTRACTS ECA, European Physical Society , 2010, p. P2.402-Conference paper (Refereed)
    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.

  • 46.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Sarri, Gianluca
    Queen's University of Belfast, UK.
    Borghesi, Marco
    Queen's University of Belfast, UK.
    Magnetic instability in a dilute circular rarefaction wave2012In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 19, no 12, p. 122102-1-122102-7Article in journal (Refereed)
    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.

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  • 47.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    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 turbulence2014In: New Journal of Physics, E-ISSN 1367-2630, Vol. 16, p. 073001-1-073001-25Article in journal (Refereed)
    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.

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  • 48.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    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 instability2013In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, no 10, p. 102112-1-102112-12Article in journal (Refereed)
    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.

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  • 49.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    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.2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 577, no A137, p. 1-10Article in journal (Refereed)
    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.

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  • 50.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    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 change2010In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 52, no 2, p. 025001-Article in journal (Refereed)
    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.

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