62 research outputs found
Dissipation in Relativistic Pair-plasma Reconnection: Revisited
Basic properties of relativistic magnetic reconnection in electron-positron
pair plasmas are investigated by using a particle-in-cell (PIC) simulation. We
first revisit a problem by Hesse & Zenitani (2007), who examined the kinetic
Ohm's law across the X line. We formulate a relativistic Ohm's law by
decomposing the stress-energy tensor. Then, the role of the new term, called
the heat-flow inertial term, is examined in the PIC simulation data. We further
evaluate the energy balance in the reconnection system. These analyses
demonstrate physically transparent ways to diagnose relativistic kinetic data.Comment: 14 page
Loading Relativistic Maxwell Distributions in Particle Simulations
Numerical algorithms to load relativistic Maxwell distributions in
particle-in-cell (PIC) and Monte-Carlo simulations are presented. For
stationary relativistic Maxwellian, the inverse transform method and the Sobol
algorithm are reviewed. To boost particles to obtain relativistic
shifted-Maxwellian, two rejection methods are proposed in a physically
transparent manner. Their acceptance efficiencies are for
generic cases and for symmetric distributions. They can be combined
with arbitrary base algorithms.Comment: 16 pages, 3 figure
Magnetohydrodynamic structure of a plasmoid in fast reconnection in low-beta plasmas: Shock-shock interactions
The shock structure of a plasmoid in magnetic reconnection in low-beta
plasmas is investigated by two-dimensional magnetohydrodynamic simulations.
Using a high-accuracy code with unprecedented resolution, shocks,
discontinuities, and their intersections are resolved and clarified. Contact
discontinuities emanate from triple-shock intersection points, separating
fluids of different origins. Shock-diamonds inside the plasmoid appear to
decelerate a supersonic flow. New shock-diamonds and a slow expansion fan are
found inside the Petschek outflow. A sufficient condition for the new
shock-diamonds and the relevance to astrophysical jets are discussed.Comment: 18 pages, 6 figures; fortran 90 code is attached; see ancillary files
in the "Other formats" lin
Some remarks on the diffusion regions in magnetic reconnection
The structure of the diffusion regions in antiparallel magnetic reconnection
is investigated by means of a theory and a Vlasov simulation. The magnetic
diffusion is considered as relaxation to the frozen-in state, which depends on
a reference velocity field. A field-aligned component of the frozen-in
condition is proposed to evaluate a diffusion-like process. Diffusion
signatures with respect to ion and electron bulk flows indicate the ion and
electron diffusion regions near the reconnection site. The electron diffusion
region resembles the energy dissipation region. These results are favorable to
a previous expectation that an electron-scale dissipation region is surrounded
by an ion-scale Hall-physics region
On the Boris solver in particle-in-cell simulation
A simple form of the Boris solver in particle-in-cell (PIC) simulation is
proposed. It employs an exact solution of the Lorentz-force part, and it is
equivalent to the Boris solver with a gyrophase correction. As a favorable
property for stable schemes, this form preserves a volume in the phase space.
Numerical tests of the Boris solvers are conducted by test-particle simulations
and by PIC simulations. The proposed form provides better accuracy than the
popular form, while it only requires few additional computation time.Comment: 7 pages; 3 figure
Multiple Boris integrators for particle-in-cell simulation
We construct Boris-type schemes for integrating the motion of charged
particles in particle-in-cell (PIC) simulation. The new solvers virtually
combine the 2-step Boris procedure arbitrary n times in the Lorentz-force part,
and therefore we call them the multiple Boris solvers. Using Chebyshev
polynomials, a one-step form of the new solvers is provided. The new solvers
give n^2 times smaller errors, allow larger timesteps, and have a long-term
stability. We present numerical tests of the new solvers, in comparison with
other particle integrators.Comment: To appear in Comput. Phys. Commun.; 29 pages, 6 figures. arXiv admin
note: text overlap with arXiv:1809.0437
Two-Fluid Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection
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 inter-species 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 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 ~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.Comment: Astrophysical Journal, 696, 1385; 40 pages, 14 figure
Magnetohydrodynamic structure of a plasmoid in fast reconnection in low-beta plasmas
Plasmoid structures in fast reconnection in low-beta plasmas are investigated
by two-dimensional magnetohydrodynamic simulations. A high-resolution
shock-capturing code enables us to explore a variety of shock structures:
vertical slow shocks behind the plasmoid, another slow shocks in the
outer-region, and the shock-reflection in the front side. The
Kelvin-Helmholtz-like turbulence is also found inside the plasmoid. It is
concluded that these shocks are rigorous features in reconnection in low-beta
plasmas, where the reconnection jet speed or the upstream Alfven speed exceeds
the sound speed.Comment: 25 pages, 7 figures, 1 tables; fortran 90 codes attached as ancillary
files; see "Other formats" link; the publisher's version contains multimedia
file
Plasmoid-dominated Turbulent Reconnection in a Low Plasma
Properties of plasmoid-dominated turbulent reconnection in a low-
background plasma are investigated by resistive magnetohydrodynamic (MHD)
simulations. In the regime, where is
plasma in the inflow region, the reconnection site is dominated by
shocks and shock-related structures and plasma compression is significant. The
effective reconnection rate increases from to as
decreases. We hypothesize that plasma compression allows faster reconnection
rate, and then we estimate a speed-up factor, based on a compressible MHD
theory. We validate our prediction by a series of MHD simulations. These
results suggest that the plasmoid-dominated reconnection can be twice faster
than expected in the environment in a solar corona.Comment: 6 pages, 5 figures; f90 codes are attached; see ancillary files in
the "Other formats" lin
Evidence for the dissipation region in magnetotail reconnection
Signatures of the dissipation region of collisionless magnetic reconnection
are investigated by the Geotail spacecraft for the 15 May 2003 event. The
energy dissipation in the rest frame of the electron's bulk flow is considered
in an approximate form D*_e, which is validated by a particle-in-cell
simulation. The dissipation measure is directly evaluated from the {plasma
moments}, the electric field, and the magnetic field. Using D*_e, a compact
dissipation region is successfully detected in the vicinity of the possible
X-point in Geotail data. The dissipation rate is 45 pWm**{-3}. The length of
the dissipation region is estimated to 1--2 local ion inertial length. The
Lorentz work W, the work rate by Lorentz force to plasmas, is also introduced.
It is positive over the reconnection region and it has a peak around the pileup
region away from the X-point. These new measures D*_e and W provide useful
information to understand the reconnection structure.Comment: to appear in GR
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