FAST MAGNETIC RECONNECTION AND PARTICLE ACCELERATION IN RELATIVISTIC LOW-DENSITY ELECTRON-POSITRON PLASMAS WITHOUT GUIDE FIELD

Journal Article · Thu May 10 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/750/2/129· OSTI ID:22034504

Bessho, Naoki; Bhattacharjee, A ^[1]

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1. Center for Integrated Computation and Analysis of Reconnection and Turbulence, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824 (United States)

Magnetic reconnection and particle acceleration in relativistic Harris sheets in low-density electron-positron plasmas with no guide field have been studied by means of two-dimensional particle-in-cell simulations. Reconnection rates are of the order of one when the background density in a Harris sheet is of the order of 1% of the density in the current sheet, which is consistent with previous results in the non-relativistic regime. It has been demonstrated that the increase of the Lorentz factors of accelerated particles significantly enhances the collisionless resistivity needed to sustain a large reconnection electric field. It is shown analytically and numerically that the energy spectrum of accelerated particles near the X-line is the product of a power law and an exponential function of energy, {gamma}{sup -1/4}exp (- a{gamma}{sup 1/2}), where {gamma} is the Lorentz factor and a is a constant. However, in the low-density regime, while the most energetic particles are produced near X-lines, many more particles are energized within magnetic islands. Particles are energized in contracting islands by multiple reflection, but the mechanism is different from Fermi acceleration in magnetic islands for magnetized particles in the presence of a guide field. In magnetic islands, strong core fields are generated and plasma beta values are reduced. As a consequence, the fire-hose instability condition is not satisfied in most of the island region, and island contraction and particle acceleration can continue. In island coalescence, reconnection between two islands can accelerate some particles, however, many particles are decelerated and cooled, which is contrary to what has been discussed in the literature on particle acceleration due to reconnection in non-relativistic hydrogen plasmas.

• OSTI ID: 22034504
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 750; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTROPHYSICS
COALESCENCE
COMPUTERIZED SIMULATION
DENSITY
ELECTRIC FIELDS
ELECTRON DENSITY
ENERGY DEPENDENCE
ENERGY SPECTRA
HOSE INSTABILITY
HYDROGEN
INTERSTELLAR MAGNETIC FIELDS
MAGNETIC ISLANDS
MAGNETIC RECONNECTION
PLASMA
PLASMA ACCELERATION
PLASMA SIMULATION
POSITRONS
RELATIVISTIC RANGE
TWO-DIMENSIONAL CALCULATIONS