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Title: TWO-FLUID MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION

Abstract

We investigate the large-scale evolution of a relativistic magnetic reconnection in an electron-positron pair plasma by a relativistic two-fluid magnetohydrodynamic (MHD) code. We introduce an interspecies friction force as an effective resistivity to dissipate magnetic fields. We demonstrate that magnetic reconnection successfully occurs in our two-fluid system, and that it involves Petschek-type bifurcated current layers in a later stage. We further observe a quasi-steady evolution thanks to an open boundary condition, and find that the Petschek-type structure is stable over the long time period. Simulation results and theoretical analyses exhibit that the Petschek outflow channel becomes narrower when the reconnection inflow contains more magnetic energy, as previously claimed. Meanwhile, we find that the reconnection rate goes up to {approx}1 in extreme cases, which is faster than previously thought. The role of the resistivity, implications for reconnection models in the magnetically dominated limit, and relevance to kinetic reconnection works are discussed.

Authors:
; ;  [1]
  1. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States), E-mail: Seiji.Zenitani-1@nasa.gov
Publication Date:
OSTI Identifier:
21300674
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 696; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/696/2/1385; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; 99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; ASTROPHYSICS; BOUNDARY CONDITIONS; EVOLUTION; MAGNETIC FIELDS; MAGNETIC RECONNECTION; MAGNETOHYDRODYNAMICS; PLASMA; POSITRONS; RELATIVISTIC RANGE; SIMULATION

Citation Formats

Zenitani, Seiji, Hesse, Michael, and Klimas, Alex. TWO-FLUID MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION. United States: N. p., 2009. Web. doi:10.1088/0004-637X/696/2/1385; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Zenitani, Seiji, Hesse, Michael, & Klimas, Alex. TWO-FLUID MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION. United States. doi:10.1088/0004-637X/696/2/1385; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Zenitani, Seiji, Hesse, Michael, and Klimas, Alex. Sun . "TWO-FLUID MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION". United States. doi:10.1088/0004-637X/696/2/1385; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21300674,
title = {TWO-FLUID MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION},
author = {Zenitani, Seiji and Hesse, Michael and Klimas, Alex},
abstractNote = {We investigate the large-scale evolution of a relativistic magnetic reconnection in an electron-positron pair plasma by a relativistic two-fluid magnetohydrodynamic (MHD) code. We introduce an interspecies friction force as an effective resistivity to dissipate magnetic fields. We demonstrate that magnetic reconnection successfully occurs in our two-fluid system, and that it involves Petschek-type bifurcated current layers in a later stage. We further observe a quasi-steady evolution thanks to an open boundary condition, and find that the Petschek-type structure is stable over the long time period. Simulation results and theoretical analyses exhibit that the Petschek outflow channel becomes narrower when the reconnection inflow contains more magnetic energy, as previously claimed. Meanwhile, we find that the reconnection rate goes up to {approx}1 in extreme cases, which is faster than previously thought. The role of the resistivity, implications for reconnection models in the magnetically dominated limit, and relevance to kinetic reconnection works are discussed.},
doi = {10.1088/0004-637X/696/2/1385; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal},
number = 2,
volume = 696,
place = {United States},
year = {Sun May 10 00:00:00 EDT 2009},
month = {Sun May 10 00:00:00 EDT 2009}
}
  • The nonlinear evolution of relativistic magnetic reconnection in sheared magnetic configuration (with a guide field) is investigated by using two-dimensional relativistic two-fluid simulations. Relativistic guide field reconnection features the charge separation and the guide field compression in and around the outflow channel. As the guide field increases, the composition of the outgoing energy changes from enthalpy-dominated to Poynting-dominated. The inertial effects of the two-fluid model play an important role to sustain magnetic reconnection. Implications for the single-fluid magnetohydrodynamic approach and the physics models of relativistic reconnection are briefly addressed.
  • Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfvenic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the 'diamond-chain' structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of criticalmore » importance for RRMHD modeling of relativistic magnetic reconnection.« less
  • Through a direct comparison between numerical simulations in two and three dimensions, we investigate topological effects in reconnection. A simple estimate on increase in reconnection rate in three dimensions by a factor of √(2), when compared with a two-dimensional case, is confirmed in our simulations. We also show that both the reconnection rate and the fraction of magnetic energy in the simulations depend linearly on the height of the reconnection region. The degree of structural complexity of a magnetic field and the underlying flow is measured by current helicity and cross-helicity. We compare results in simulations with different computational boxmore » heights.« less
  • Two-dimensional fully kinetic simulations are performed using global boundary conditions relevant to model the Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Phys Plasmas 4, 1936 (1997)]. The geometry is scaled in terms of the ion kinetic scales in the experiment, and a reconnection layer is created by reducing the toroidal current in the flux cores in a manner similar to the actual experiment. The ion-scale features in these kinetic simulations are in remarkable agreement with those observed in MRX, including the reconnection inflow rate and quadrupole field structure. In contrast, there are significant discrepancies in the simulated structure ofmore » the electron layer that remain unexplained. In particular, the measured thickness of the electron layers is 3-5 times thicker in MRX than in the kinetic simulations. The layer length is highly sensitive to downstream boundary conditions as well as the time over which the simulation is driven. However, for a fixed set of chosen boundary conditions, an extrapolation of the scaling with the ion to electron mass ratio implies that at realistic mass ratio both the length and width will be too small compared to the experiment. This discrepancy implies that the basic electron layer physics may differ significantly between MRX and the two-dimensional, collisionless simulations. The two leading possibilities to explain the discrepancy are weak Coulomb collisions and three-dimensional effects that are present in the experiment but not included in the simulation model.« less
  • Turbulent reconnection process in a one-dimensional current sheet is investigated by means of a two-dimensional compressible one-fluid magnetohydrodynamic simulation with spatially uniform, fixed resistivity. Turbulence is set up by adding to the sheet pinch small but finite level of broadband random-phased magnetic field components. To clarify the nonlinear spatial-temporal nature of the turbulent reconnection process the reconnection system is treated as an unforced initial value problem without any anomalous resistivity model adopted. Numerical results demonstrate the duality of turbulent reconnection, i.e., a transition from Sweet-Parker-like slow reconnection to Petschek-like fast reconnection in its nonlinear evolutionary process. The initial slow reconnectionmore » phase is characterized by many independent microreconnection events confined within the sheet region and a global reconnection rate mainly dependent on the initially added turbulence and insensitive to variations of the plasma {beta} and resistivity. The formation and amplification of the major plasmoid leads the following reconnection process to a rapid reconnection stage with a fast reconnection rate of the order of 0.1 or even larger, drastically changing the topology of the global magnetic field. That is, the presence of magnetohydrodynamic turbulence in large-scale current sheets can raise the reconnection rate from small values on the order of the Sweet-Parker rate to high values on the order of the Petscheck rate through triggering an evolution toward fast magnetic reconnection. Meanwhile, the backward coupling between the small- and large-scale magnetic field dynamics has been properly represented through the present high resolution simulation. The undriven turbulent reconnection model established here expresses a solid numerical basis for the previous schematic two-step magnetic reconnection models and a possible explanation of two-stage energy release process of solar explosives.« less