Papers

Title:
Kinetic Simulations of Electron Acceleration at Mercury
Authors:
Büchner, Jörg; Kilian, Patrick; Muñoz, Patricio A.; Spanier, Felix; Widmer, Fabien; Zhou, Xiaowei; Jain, Neeraj
Publication:
Magnetic Fields in the Solar System. Series: Astrophysics and Space Science Library, ISBN: 978-3-319-64291-8. Springer International Publishing (Cham), Edited by Hermann Lühr, Johannes Wicht, Stuart A. Gilder and Matthias Holschneider, vol. 448, pp. 201-240
Publication Date:
00/2018
Origin:
CROSSREF
DOI:
10.1007/978-3-319-64292-5_8
Bibliographic Code:
2018ASSL..448..201B

Abstract

In preparation of the ESA-JAXA mission Bepi Colombo we reconsidered the electron acceleration near Mercury. We first reviewed the existing observations starting from NASA’s Mariner-10 (1974–1975). Some of them later were shown to be inaccurate. Recently NASA’s Messenger mission newly observed energetic electrons including bursts of energies up to 100–200 keV. This by far exceeds the electron energies in the upstream solar wind. The acceleration mechanisms are, however, still not well understood. We derive models of electron acceleration near Mercury by passing strong interplanetary shocks, by reconnection at the magnetopause and in the Hermean magnetotail. We obtained the resulting electron energies and spectra in the near-Mercury MHD- and kinetic plasma turbulence as well as due to electric field structures by means of test particle calculations and also by fully self-consistent kinetic two- and three-dimensional PIC-code simulations whose results and, therefore, the acceleration mechanisms should be verified by the coming ESA-JAXA Bepi-Colombo mission to Mercury.


Title:
Two-stage electron acceleration by 3D collisionless guide field magnetic reconnection
Authors:
Muñoz, P. A.; Büchner, J.
Publication:
eprint arXiv:1705.01066
Publication Date:
05/2017
Origin:
ARXIV
Keywords:
Physics - Plasma Physics, Astrophysics - Solar and Stellar Astrophysics, Physics - Space Physics
Comment:
15 pages. 11 figures. Revised version. Published in The Astrophysical Journal; The Astrophysical Journal 864, 92 (2018); doi:10.3847/1538-4357/aad5e9
Bibliographic Code:
2017arXiv170501066M

Abstract

We report a newly found two-stage mechanism of electron acceleration near X-lines of 3D collisionless guide-field magnetic reconnection in the non-relativistic regime typical, e.g., for stellar coronae. We found that after electrons are first pre-accelerated during the linear growth of reconnection, they become additionally accelerated in the course of the nonlinear stage of 3D guide-field magnetic reconnection. This additional acceleration is due to the filamentation of electric and magnetic fields caused by streaming instabilities. In addition to enhanced parallel electric fields, the filamentation leads to additional curvature-driven electron acceleration in the guide-field direction. As a result, part of the the accelerated electron spectra becomes a power law with a spectral index of $\sim-1.6$ near the X-line. This second stage of acceleration due to nonlinear reconnection is relevant for the production of energetic electrons in, e.g., thin current sheets of stellar coronae.


Title:
Recovering the Damping Rates of Cyclotron Damped Plasma Waves from Simulation Data
Authors:
Schreiner, Cedric; Kilian, Patrick; Spanier, Felix
Publication:
Communications in Computational Physics, vol. 21, issue 04, pp. 947-980
Publication Date:
04/2017
Origin:
CROSSREF
DOI:
10.4208/cicp.OA-2016-0091
Bibliographic Code:
2017CCoPh..21..947S

Abstract

Plasma waves with frequencies close to the particular gyrofrequencies of the charged particles in the plasma lose energy due to cyclotron damping. We briefly discuss the gyro-resonance of low frequency plasma waves and ions particularly with regard to particle-in-cell (PiC) simulations. A setup is outlined which uses artificially excited waves in the damped regime of the wave mode's dispersion relation to track the damping of the wave's electromagnetic fields. Extracting the damping rate directly from the field data in real or Fourier space is an intricate and non-trivial task. We therefore present a simple method of obtaining the damping rate {\Gamma} from the simulation data. This method is described in detail, focusing on a step-by-step explanation of the course of actions. In a first application to a test simulation we find that the damping rates obtained from this simulation generally are in good agreement with theoretical predictions. We then compare the results of one-, two- and three-dimensional simulation setups and simulations with different physical parameter sets.


Title:
Turbulent transport in 2D collisionless guide field reconnection
Authors:
Muñoz, P. A.; Büchner, J.; Kilian, P.
Affiliation:
AA(Max-Planck-Institut für Sonnensystemforschung, D-37077 Göttingen, Germany; Max-Planck/Princeton Center for Plasma Physics, D-37077 Göttingen, Germany 0000-0002-3678-8173), AB(Max-Planck-Institut für Sonnensystemforschung, D-37077 Göttingen, Germany; Max-Planck/Princeton Center for Plasma Physics, D-37077 Göttingen, Germany), AC(Centre for Space Research, North-West University, 2520 Potchefstroom, South Africa 0000-0002-8906-7783)
Publication:
Physics of Plasmas, Volume 24, Issue 2, id.022104 (PhPl Homepage)
Publication Date:
02/2017
Origin:
AIP
Abstract Copyright:
2017: Author(s)
DOI:
10.1063/1.4975086
Bibliographic Code:
2017PhPl...24b2104M

Abstract

Transport in hot and dilute, i.e., collisionless, astrophysical and space, plasmas is called "anomalous." This transport is due to the interaction between the particles and the self-generated turbulence by their collective interactions. The anomalous transport has very different and not well known properties compared to the transport due to binary collisions, dominant in colder and denser plasmas. Because of its relevance for astrophysical and space plasmas, we explore the excitation of turbulence in current sheets prone to component- or guide-field reconnection, a process not well understood yet. This configuration is typical for stellar coronae, and it is created in the laboratory for which a 2.5D geometry applies. In our analysis, in addition to the immediate vicinity of the X-line, we also include regions outside and near the separatrices. We analyze the anomalous transport properties by using 2.5D Particle-in-Cell code simulations. We split off the mean slow variation (in contrast to the fast turbulent fluctuations) of the macroscopic observables and determine the main transport terms of the generalized Ohm's law. We verify our findings by comparing with the independently determined slowing-down rate of the macroscopic currents (due to a net momentum transfer from particles to waves) and with the transport terms obtained by the first order correlations of the turbulent fluctuations. We find that the turbulence is most intense in the "low density" separatrix region of guide-field reconnection. It is excited by streaming instabilities, is mainly electrostatic and "patchy" in space, and so is the associated anomalous transport. Parts of the energy exchange between turbulence and particles are reversible and quasi-periodic. The remaining irreversible anomalous resistivity can be parametrized by an effective collision rate ranging from the local ion-cyclotron to the lower-hybrid frequency. The contributions to the parallel and the perpendicular (to the magnetic field) components of the slowly varying DC-electric fields, balanced by the turbulence, are similar. This anomalous electric field is, however, smaller than the contributions of the off-diagonal pressure and electron inertia terms of Ohm's law. This result can now be verified by in-situ measurements of the turbulence, in and around the magnetic reconnection regions of the Earth's magnetosphere by the multi-spacecraft mission MMS and in laboratory experiments like MRX and VINETA-II.


Title:
Particle Scattering off of Right-handed Dispersive Waves
Authors:
Schreiner, C.; Kilian, P.; Spanier, F.
Affiliation:
AA(Centre for Space Research, North-West University, 2520 Potchefstroom, South Africa ; Lehrstuhl für Astronomie, Universität Würzburg, D-97074 Würzburg, Germany; ), AB(Centre for Space Research, North-West University, 2520 Potchefstroom, South Africa), AC(Centre for Space Research, North-West University, 2520 Potchefstroom, South Africa)
Publication:
The Astrophysical Journal, Volume 834, Issue 2, article id. 161, 18 pp. (2017). (ApJ Homepage)
Publication Date:
01/2017
Origin:
IOP
Astronomy Keywords:
plasmas, scattering, Sun: heliosphere, waves
DOI:
10.3847/1538-4357/834/2/161
Bibliographic Code:
2017ApJ...834..161S

Abstract

Resonant scattering of fast particles off low frequency plasma waves is a major process determining transport characteristics of energetic particles in the heliosphere and contributing to their acceleration. Usually, only Alfvén waves are considered for this process, although dispersive waves are also present throughout the heliosphere. We investigate resonant interaction of energetic electrons with dispersive, right-handed waves. For the interaction of particles and a single wave a variable transformation into the rest frame of the wave can be performed. Here, well-established analytic models derived in the framework of magnetostatic quasi-linear theory can be used as a reference to validate simulation results. However, this approach fails as soon as several dispersive waves are involved. Based on analytic solutions modeling the scattering amplitude in the magnetostatic limit, we present an approach to modify these equations for use in the plasma frame. Thereby we aim at a description of particle scattering in the presence of several waves. A particle-in-cell code is employed to study wave-particle scattering on a micro-physically correct level and to test the modified model equations. We investigate the interactions of electrons at different energies (from 1 keV to 1 MeV) and right-handed waves with various amplitudes. Differences between model and simulation arise in the case of high amplitudes or several waves. Analyzing the trajectories of single particles we find no microscopic diffusion in the case of a single plasma wave, although a broadening of the particle distribution can be observed.


Title:
A new hybrid code (CHIEF) implementing the inertial electron fluid equation without approximation
Authors:
Muñoz, P. A.; Jain, N.; Kilian, P.; Büchner, J.
Publication:
eprint arXiv:1612.03818
Publication Date:
12/2016
Origin:
ARXIV
Keywords:
Physics - Plasma Physics, Physics - Computational Physics
Comment:
42 pages, 16 figures
Bibliographic Code:
2016arXiv161203818M

Abstract

We present a new hybrid code (CHIEF) with kinetic ions modelled using the Particle-in-Cell (PiC) method, and a massive electron fluid adapting the full electron-MHD (EMHD) model. This kind of code is appropriate to model a large variety of quasineutral phenomena where kinetic electron effects can be neglected, but full ion kinetic effects are considered. Different from most other hybrid codes with massless electrons, our model considers properly, without approximations, the full electron inertial effects, relevant in, e.g., scenarios like magnetic reconnection, where it can break the frozen-in condition of ideal MHD. We present here the governing equations of the model, how these are discretized and implemented numerically, as well as six test problems to validate our numerical approach. They are mostly 1D problems where the ion kinetic effects play the essential role. Our chosen test problems are: 1) parallel (to a background magnetic field) propagating electromagnetic waves, 2) perpendicular propagating electrostatic waves (ion Bernstein modes), 3) ion beam right-hand instability (resonant and non-resonant), 4) ion Landau damping, 5) ion firehose instability, and 6) 2D oblique ion firehose instability. Our results reproduce successfully the predictions of linear and non-linear theory for all these problems, validating our code. All properties of this hybrid code make it ideal to study multi scale phenomena between electron and ion scales involving dissipation and turbulence in a more efficient way than traditional, fully kinetic approaches.


Title:
Plasma Waves as a Benchmark Problem
Authors:
Kilian, Patrick; Muñoz, Patricio A.; Schreiner, Cedric; Spanier, Felix
Publication:
eprint arXiv:1611.01127
Publication Date:
11/2016
Origin:
ARXIV
Keywords:
Physics - Plasma Physics, Physics - Computational Physics
Bibliographic Code:
2016arXiv161101127K

Abstract

A large number of wave modes exist in a magnetized plasma. Their properties are determined by the interaction of particles and waves. In a simulation code, the correct treatment of field quantities and particle behavior is essential to correctly reproduce the wave properties. Consequently, plasma waves provide test problems that cover a large fraction of the simulation code. The large number of possible wave modes and the freedom to choose parameters make the selection of test problems time consuming and comparison between different codes difficult. This paper therefore aims to provide a selection of test problems, based on different wave modes and with well defined parameter values, that is accessible to a large number of simulation codes to allow for easy benchmarking and cross validation. Example results are provided for a number of plasma models. For all plasma models and wave modes that are used in the test problems, a mathematical description is provided to clarify notation and avoid possible misunderstanding in naming.


Title:
Non-Maxwellian electron distribution functions due to self-generated turbulence in collisionless guide-field reconnection
Authors:
Muñoz, P. A.; Büchner, J.
Affiliation:
AA(Max-Planck-Institut für Sonnensystemforschung, D-37077 Göttingen, Germany; Max-Planck/Princeton Center for Plasma Physics, D-37077 Göttingen, Germany 0000-0002-3678-8173), AB(Max-Planck-Institut für Sonnensystemforschung, D-37077 Göttingen, Germany; Max-Planck/Princeton Center for Plasma Physics, D-37077 Göttingen, Germany)
Publication:
Physics of Plasmas, Volume 23, Issue 10, id.102103 (PhPl Homepage)
Publication Date:
10/2016
Origin:
AIP
Abstract Copyright:
2016: Author(s)
DOI:
10.1063/1.4963773
Bibliographic Code:
2016PhPl...23j2103M

Abstract

Non-Maxwellian electron velocity space distribution functions (EVDFs) are useful signatures of plasma conditions and non-local consequences of collisionless magnetic reconnection. In the past, EVDFs were obtained mainly for antiparallel reconnection and under the influence of weak guide-fields in the direction perpendicular to the reconnection plane. EVDFs are, however, not well known, yet, for oblique (or component-) reconnection in case and in dependence on stronger guide-magnetic fields and for the exhaust (outflow) region of reconnection away from the diffusion region. In view of the multi-spacecraft Magnetospheric Multiscale Mission (MMS), we derived the non-Maxwellian EVDFs of collisionless magnetic reconnection in dependence on the guide-field strength bg from small ( b g ≈ 0 ) to very strong (bg = 8) guide-fields, taking into account the feedback of the self-generated turbulence. For this sake, we carried out 2.5D fully kinetic Particle-in-Cell simulations using the ACRONYM code. We obtained anisotropic EVDFs and electron beams propagating along the separatrices as well as in the exhaust region of reconnection. The beams are anisotropic with a higher temperature in the direction perpendicular rather than parallel to the local magnetic field. The beams propagate in the direction opposite to the background electrons and cause instabilities. We also obtained the guide-field dependence of the relative electron-beam drift speed, threshold, and properties of the resulting streaming instabilities including the strongly non-linear saturation of the self-generated plasma turbulence. This turbulence and its non-linear feedback cause non-adiabatic parallel electron acceleration. We further obtained the resulting EVDFs due to the non-linear feedback of the saturated self-generated turbulence near the separatrices and in the exhaust region of reconnection in dependence on the guide field strength. We found that the influence of the self-generated plasma turbulence leads well beyond the limits of the quasi-linear approximation to the creation of phase space holes and an isotropizing pitch-angle scattering. EVDFs obtained by this way can be used for diagnosing collisionless reconnection by using the multi-spacecraft observations carried out by the MMS mission.


Title:
Energy loss in intergalactic pair beams: Particle-in-cell simulation
Authors:
Kempf, A.; Kilian, P.; Spanier, F.
Affiliation:
AA(Lehrstuhl für Theoretische Physik IV, Ruhr-Universitàt Bochum, 44780, Bochum, Germany ), AB(Centre for Space Research, North-West University, 2520, Potchefstroom, South Africa), AC(Centre for Space Research, North-West University, 2520, Potchefstroom, South Africa)
Publication:
Astronomy & Astrophysics, Volume 585, id.A132, 7 pp. (A&A Homepage)
Publication Date:
01/2016
Origin:
EDP Sciences
Astronomy Keywords:
plasmas, galaxies: active, galaxies: jets, quasars: general, gamma rays: general
DOI:
10.1051/0004-6361/201527521
Bibliographic Code:
2016A&A...585A.132K

Abstract


Aims: The change in the distribution function of electron-positron pair beams determines whether GeV photons can be produced as secondary radiation from TeV photons. We will discuss the instabilities driven by pair beams.
Methods: The system of a thermal proton-electron plasma and the electron-positron beam is collision free. We have, therefore, used the particle-in-cell simulation approach. It was necessary to alter the physical parameters, but the ordering of growth rates has been retained.
Results: We were able to show that plasma instabilities can be recovered in particle-in-cell simulations, but their effect on the pair distribution function is negligible for the beam-background energy density ratios typically found in blazars.


Title:
Gyrokinetic and kinetic particle-in-cell simulations of guide-field reconnection. I. Macroscopic effects of the electron flows
Authors:
Muñoz, P. A.; Told, D.; Kilian, P.; Büchner, J.; Jenko, F.
Affiliation:
AA(Max-Planck-Institut für Sonnensystemforschung, D-37077 Göttingen, Germany 0000-0002-3678-8173), AB(Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany; Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA 0000-0001-9810-6724), AC(Max-Planck-Institut für Sonnensystemforschung, D-37077 Göttingen, Germany), AD(Max-Planck-Institut für Sonnensystemforschung, D-37077 Göttingen, Germany), AE(Max-Planck-Institut für Plasmaphysik, D-85748 Garching, Germany; Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA)
Publication:
Physics of Plasmas, Volume 22, Issue 8, id.082110 (PhPl Homepage)
Publication Date:
08/2015
Origin:
AIP
Abstract Copyright:
2015: AIP Publishing LLC
DOI:
10.1063/1.4928381
Bibliographic Code:
2015PhPl...22h2110M

Abstract

In this work, we compare gyrokinetic (GK) with fully kinetic Particle-in-Cell (PIC) simulations of magnetic reconnection in the limit of strong guide field. In particular, we analyze the limits of applicability of the GK plasma model compared to a fully kinetic description of force free current sheets for finite guide fields (bg). Here, we report the first part of an extended comparison, focusing on the macroscopic effects of the electron flows. For a low beta plasma (βi = 0.01), it is shown that both plasma models develop magnetic reconnection with similar features in the secondary magnetic islands if a sufficiently high guide field (bg ≳ 30) is imposed in the kinetic PIC simulations. Outside of these regions, in the separatrices close to the X points, the convergence between both plasma descriptions is less restrictive (bg ≳ 5). Kinetic PIC simulations using guide fields bg ≲ 30 reveal secondary magnetic islands with a core magnetic field and less energetic flows inside of them in comparison to the GK or kinetic PIC runs with stronger guide fields. We find that these processes are mostly due to an initial shear flow absent in the GK initialization and negligible in the kinetic PIC high guide field regime, in addition to fast outflows on the order of the ion thermal speed that violate the GK ordering. Since secondary magnetic islands appear after the reconnection peak time, a kinetic PIC/GK comparison is more accurate in the linear phase of magnetic reconnection. For a high beta plasma (βi = 1.0) where reconnection rates and fluctuations levels are reduced, similar processes happen in the secondary magnetic islands in the fully kinetic description, but requiring much lower guide fields (bg ≲ 3).


Title:
Effects of dispersive wave modes on charged particles transport
Authors:
Schreiner, C.; Spanier, F.
Publication:
Proceedings of the 34th International Cosmic Ray Conference (ICRC2015). 30 July - 6 August, 2015. The Hague, The Netherlands. Online at http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=236, id.177
Publication Date:
07/2015
Origin:
POS
Bibliographic Code:
2015ICRC...34..177S

Abstract

The transport of charged particles in the heliosphere and the interstellar medium is governed by the interaction of particles and magnetic irregularities. For the transport of protons a rather simple model using a linear Alfv\'en wave spectrum which follows the Kolmogorov distribution usually yields good results. Even magnetostatic spectra may be used. For the case of electron transport, particles will resonate with the high-k end of the spectrum. Here the magnetic fluctuations do not follow the linear dispersion relation, but the kinetic regime kicks in. We will discuss the interaction of fluctuations of dispersive waves in the kinetic regime using a particle-in-cell code. Especially the scattering of particles following the idea of Lange et al. (2013) and its application to PiC codes will be discussed. The effect of the dispersive regime on the electron transport will be discussed in detail.


Title:
Instabilities of collisionless current sheets revisited: The role of anisotropic heating
Authors:
Muñoz, P. A.; Kilian, P.; Büchner, J.
Affiliation:
AA(Max-Planck-Institut für Sonnensystemforschung, 37077 Göttingen, Germany), AB(Max-Planck-Institut für Sonnensystemforschung, 37077 Göttingen, Germany), AC(Max-Planck-Institut für Sonnensystemforschung, 37077 Göttingen, Germany)
Publication:
Physics of Plasmas, Volume 21, Issue 11, id.112106 (PhPl Homepage)
Publication Date:
11/2014
Origin:
AIP
Abstract Copyright:
2014: AIP Publishing LLC
DOI:
10.1063/1.4901033
Bibliographic Code:
2014PhPl...21k2106M

Abstract

In this work, we investigate the influence of the anisotropic heating on the spontaneous instability and evolution of thin Harris-type collisionless current sheets, embedded in antiparallel magnetic fields. In particular, we explore the influence of the macroparticle shape-function using a 2D version of the PIC code ACRONYM. We also investigate the role of the numerical collisionality due to the finite number of macroparticles in PIC codes. It is shown that it is appropriate to choose higher order shape functions of the macroparticles compared to a larger number of macroparticles per cell. This allows to estimate better the anisotropic electron heating due to the collisions of macroparticles in a PIC code. Temperature anisotropies can stabilize the tearing mode instability and trigger additional current sheet instabilities. We found a good agreement between the analytically derived threshold for the stabilization of the anisotropic tearing mode and other instabilities, either spontaneously developing or initially triggered ones. Numerical effects causing anisotropic heating at electron time scales become especially important for higher mass ratios (above m i / m e = 180 ). If numerical effects are carefully taken into account, one can recover the theoretical estimated linear growth rates of the tearing instability of thin isotropic collisionless current sheets, also for higher mass ratios.


Title:
Wave-particle-interaction in kinetic plasmas
Authors:
Schreiner, C.; Spanier, F.
Affiliation:
AA(Center for Space Research, North-West University, 2520 Potchefstroom, South Africa), AB(Center for Space Research, North-West University, 2520 Potchefstroom, South Africa)
Publication:
Computer Physics Communications, Volume 185, Issue 7, pp.1981-1986 ScienceDirect Homepage
Publication Date:
07/2014
Origin:
ELSEVIER
Abstract Copyright:
2014 Elsevier B.V.
DOI:
10.1016/j.cpc.2014.03.028
Bibliographic Code:
2014CoPhC.185.1981S

Abstract

Resonant scattering of energetic protons off magnetic irregularities is the main process in cosmic ray diffusion. The typical theoretical description uses Alfvén waves in the low frequency limit. We demonstrate that the usage of Particle-in-Cell (PiC) simulations for particle scattering is feasible. The simulation of plasma waves is performed with the relativistic electromagnetic PiC code ACRONYM and the tracks of test particles are evaluated in order to study particle diffusion. Results for the low frequency limit are equivalent to those obtained with an MHD description, but only for high frequencies results can be obtained with reasonable effort. PiC codes have the potential to be a useful tool to study particle diffusion in kinetic turbulence.


Title:
Fundamental and harmonic plasma emission in different plasma environments
Authors:
Ganse, U.; Kilian, P.; Spanier, F.; Vainio, R.
Affiliation:
AA(Department of PhysicsUniversity of Helsinki, 00014, Helsinki, Finland ), AB(Max-Planck Institut für Sonnensystemforschung, 37077, Göttingen, Germany), AC(Center for Space Research, North-West University, 2520, Potchefstrom, South Africa), AD(Department of PhysicsUniversity of Helsinki, 00014, Helsinki, Finland; Department of Physics and Astronomy, University of Turku, 20014, Turku, Finland)
Publication:
Astronomy & Astrophysics, Volume 564, id.A15, 5 pp. (A&A Homepage)
Publication Date:
04/2014
Origin:
EDP Sciences
Astronomy Keywords:
Sun: radio radiation, waves, plasmas
DOI:
10.1051/0004-6361/201322834
Bibliographic Code:
2014A&A...564A..15G

Abstract


Aims: Emission of radio waves from plasmas through plasma emission with fundamental and harmonic frequencies is a familiar process known from solar type II radio bursts. Current models assume the existence of counterstreaming electron beam populations excited at shocks as sources for these emission features, which limits the plasma parameters to reasonable heliospheric shock conditions. However, situations in which counterstreaming electron beams are present can also occur with different plasma parameters, such as higher magnetisation, including but not limited to our Sun. Similar radio emissions might also occur from these situations.
Methods: We used particle-in-cell simulations to compare plasma microphysics of radio emission processes from counterstreaming beams in different plasma environments that differed in density and magnetization.
Results: Although large differences in wave populations are evident, the emission process of type II bursts appears to be qualitatively unaffected and shows the same behaviour in all environments.


Title:
Different Choices of the Form Factor in Particle-in-Cell Simulations
Authors:
Kilian, P.; Ganse, U.; Spanier, F.
Publication:
Numerical Modeling of Space Plasma Flows (ASTRONUM2012). Proceedings of a 7th International Conference held at Big Island, Hawaii, USA June 25-29, 2012. Edited by N.V. Pogorelov, E. Audit and G.P. Zank. San Francisco: Astronomical Society of the Pacific, 2013., p.208
Publication Date:
04/2013
Origin:
ASP
Bibliographic Code:
2013ASPC..474..208K

Abstract

Numerical simulations have proven a valuable tool to study plasma behavior, especially for conditions in astrophysical scenarios and which are not readily accessible under laboratory conditions. Whenever single particle behavior becomes important or the development of non-thermal components is of interest fluid descriptions have to be replaced by more accurate but also more expensive kinetic descriptions. A very popular such method is the Particle-in-Cell method. Conceptually this method combines the integration of motion if individual elementary particles with field quantities that are restricted to a spatial grid. Both the analytic derivation of the method as well as the computational feasibility require the use of phase space samples instead of the more readily envisioned individual elementary particles. Each macroparticle represents an ensemble of particles of one species that are close to each other in phase space and carries the total charge and mass of the ensemble. Unlike the elementary particles the macroparticle does not necessarily have a vanishing spatial extent. Different choices of the form factor, that is spatial distribution of the particle quantities within the macroparticle, are investigated. Included are the standard choices NGP, CIC and TSC as well as new schemes of higher order.


Title:
Emission of Type II Radio Bursts - Single-Beam Versus Two-Beam Scenario
Authors:
Ganse, U.; Kilian, P.; Vainio, R.; Spanier, F.
Affiliation:
AA(Lehrstuhl für Astronomie, Universität Würzburg), AB(Lehrstuhl für Astronomie, Universität Würzburg), AC(Department of Physics, University of Helsinki), AD(Lehrstuhl für Astronomie, Universität Würzburg)
Publication:
Solar Physics, Volume 280, Issue 2, pp.551-560 (SoPh Homepage)
Publication Date:
10/2012
Origin:
SPRINGER
Keywords:
Radio bursts, Type II, Radio bursts, theory, Plasma physics
Abstract Copyright:
(c) 2012: Springer Science+Business Media B.V.
DOI:
10.1007/s11207-012-0077-7
Bibliographic Code:
2012SoPh..280..551G

Abstract

The foreshock region of a CME shock front, where shock accelerated electrons form a beam population in the otherwise quiescent plasma is generally assumed to be the source region of type II radio bursts. Nonlinear wave interaction of electrostatic waves excited by the beamed electrons are the prime candidates for the radio waves' emission. To address the question whether a single, or two counterpropagating beam populations are a requirement for this process, we have conducted 2.5D particle-in-cell simulations using the fully relativistic ACRONYM code. Results show indications of three-wave interaction leading to electromagnetic emission at the fundamental and harmonic frequency for the two-beam case. For the single-beam case, no such signatures were detectable.


Title:
Numerical Challenges in Kinetic Simulations of Three-wave Interactions
Authors:
Ganse, U.; Kilian, P.; Siegel, S.; Spanier, F.
Publication:
Numerical modeling of space plasma flows (astronum 2011). Proceedings of a 6th internation conference held at Velancia, Spain June 13-17, 2011. ASP Conference Series, Vol. 459. Edited by N.V. Pogorelov, J.A. Font, E. Audit, and G.P. Zank. San Francisco: Astronomical Society of the Pacific, 2012., p.265
Publication Date:
07/2012
Origin:
ASP
Bibliographic Code:
2012ASPC..459..265G

Abstract

Generation of radio bursts in CME foreshock regions and turbulent cascades in the solar wind are assumed to be results of three-wave interaction processes of dispersive plasma modes. Using our Particle in Cell code ACRONYM, we have studied the behaviour of kinetic wavemodes in the presence of beamed electron populations, with a focus on type II radio burst emission processes. We discuss the numerical challenges in generating and analyzing self-consistently evolving wave coupling processes with a PiC-Code and present preliminary results of said project.


Title:
Nonlinear Wave Interactions as Emission Process of Type II Radio Bursts
Authors:
Ganse, Urs; Kilian, Patrick; Spanier, Felix; Vainio, Rami
Affiliation:
AA(Lehrstuhl für Astronomie, Universität Würzburg, Würzburg, Germany ), AB(Lehrstuhl für Astronomie, Universität Würzburg, Würzburg, Germany ), AC(Lehrstuhl für Astronomie, Universität Würzburg, Würzburg, Germany ), AD(Department of Physics, University of Helsinki, Helsinki, Finland)
Publication:
The Astrophysical Journal, Volume 751, Issue 2, article id. 145, 6 pp. (2012). (ApJ Homepage)
Publication Date:
06/2012
Origin:
IOP
Astronomy Keywords:
plasmas, Sun: heliosphere, Sun: radio radiation
DOI:
10.1088/0004-637X/751/2/145
Bibliographic Code:
2012ApJ...751..145G

Abstract

The emission of fundamental and harmonic frequency radio waves of type II radio bursts are assumed to be products of three-wave interaction processes of beam-excited Langmuir waves. Using a particle-in-cell code, we have performed simulations of the assumed emission region, a coronal mass ejection foreshock with two counterstreaming electron beams. Analysis of wavemodes within the simulation shows self-consistent excitation of beam-driven modes, which yield interaction products at both fundamental and harmonic emission frequencies. Through variation of the beam strength, we have investigated the dependence of energy transfer into electrostatic and electromagnetic modes, confirming the quadratic dependence of electromagnetic emission on electron beam strength.


Title:
Kinetic Simulations of Solar Type II Radio Burst Emission
Authors:
Ganse, U.; Kilian, P.; Spanier, F.; Vainio, R.
Affiliation:
AA(Lehrstuhl für Astronomie, Universität Würzburg, Germany ), AB(Lehrstuhl für Astronomie, Universität Würzburg, Germany ), AC(Lehrstuhl für Astronomie, Universität Würzburg, Germany ), AD(Department of Physics, University of Helsinki, Finland)
Publication:
EGU General Assembly 2012, held 22-27 April, 2012 in Vienna, Austria., p.2081
Publication Date:
04/2012
Origin:
COPERNICUS
Bibliographic Code:
2012EGUGA..14.2081G

Abstract

Propagation of coronal mass ejection (CME) shock fronts in the heliosphere is often accompanied by the emission of so-called type II radio bursts, which are multi banded emission features. Their complex emission spectra indicate that interaction processes of multiple plasma waves are responsible for their creation, but the requirement for kinetic treatmet of the problem, together with the large separation of involved lengthscales have made simulations of this phenomenon challenging. Using the ACRONYM particle-in-cell code, we have investigated the plasma microphysics in the CME foreshock region. We were able to consistently reproduce the electron beam-driven excitation of electrostatic waves and their subsequent nonlinear coupling to form fundamental and harmonic radio emissions.


Title:
The Influence of the Mass Ratio on the Acceleration of Particles by Filamentation Instabilities
Authors:
Burkart, Thomas; Elbracht, Oliver; Ganse, Urs; Spanier, Felix
Affiliation:
AA(Lehrstuhl für Astronomie, Universität Würzburg, Germany ), AB(Lehrstuhl für Astronomie, Universität Würzburg, Germany), AC(Lehrstuhl für Astronomie, Universität Würzburg, Germany), AD(Lehrstuhl für Astronomie, Universität Würzburg, Germany)
Publication:
The Astrophysical Journal, Volume 720, Issue 2, pp. 1318-1324 (2010). (ApJ Homepage)
Publication Date:
09/2010
Origin:
IOP
Astronomy Keywords:
acceleration of particles, galaxies: jets, instabilities, methods: numerical, plasmas
DOI:
10.1088/0004-637X/720/2/1318
Bibliographic Code:
2010ApJ...720.1318B

Abstract

Almost all sources of high-energy particles and photons are associated with jet phenomena. Prominent sources of such highly relativistic outflows are pulsar winds, active galactic nuclei (AGNs), and gamma-ray bursts. The current understanding of these jets assumes diluted plasmas which are best described as kinetic phenomena. In this kinetic description, particle acceleration to ultrarelativistic speeds can occur in completely unmagnetized and neutral plasmas through insetting effects of instabilities. Even though the morphology and nature of particle spectra are understood to a certain extent, the composition of the jets is not known yet. While Poynting-flux-dominated jets (e.g., occurring in pulsar winds) are certainly composed of electron-positron plasmas, the understanding of the governing physics in AGN jets is mostly unclear. In this paper, we investigate how the constituting elements of an electron-positron-proton plasma behave differently under the variation of the fundamental mass ratio mp /me . We initially studied unmagnetized counterstreaming plasmas using fully relativistic three-dimensional particle-in-cell simulations to investigate the influence of the mass ratio on particle acceleration and magnetic field generation in electron-positron-proton plasmas. We covered a range of mass ratios mp /me between 1 and 100 with a particle number composition of n_{p^+} / n_{e^+} of 1 in one stream, therefore called the pair-proton stream. Protons are injected in the other one, therefore from now on called the proton stream, whereas electrons are present in both to guarantee charge neutrality in the simulation box. We find that with increasing proton mass the instability takes longer to develop and for mass ratios >20 the particles seem to be accelerated in two phases which can be accounted for by the individual instabilities of the different species. This means that for high mass ratios the coupling between electrons/positrons and the heavier protons, which occurs in low mass ratios, disappears.