Particle Acceleration to Ultrarelativistic Energies by Magnetic Reconnection in Electron- Positron Plasmas

Details Particle Acceleration to Ultrarelativistic Energies by Magnetic Reconnection in Electron- Positron Plasmas Particle Acceleration to Ultrarelativistic Energies by Magnetic Reconnection in Electron- Positron Plasmas

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm53b1277b&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SM53B-1277

Astronomy and Astrophysics

Astrophysics

2723 Magnetic Reconnection (7526, 7835), 7514 Energetic Particles (2114), 7835 Magnetic Reconnection (2723, 7526), 7845 Particle Acceleration

Scientific paper

Particle acceleration by magnetic reconnection in electron-positron (or pair) plasmas is of great interest not only because of its relevance to astrophysical objects such as pulsar winds and extragalactic jets, but also because in contrast with hydrogen plasmas, the generalized Ohm's law for pair plasmas contains no Hall currents. Hence, studies of particle acceleration in pair plasmas by collisionless magnetic reconnection enable one to focus on the essential role of particle pressure tensors and kinetic effects. We have carried out studies of particle acceleration by reconnection in pair plasmas by using 2D particle-in-cell simulations, and shown that fast reconnection is realized in non-relativistic [Phys. Rev. Lett., 95, 245001 (2005)] as well as relativistic regimes [Phys. Plasmas, 14, 056503 (2007)]. We have studied a long current sheet which breaks up into multiple magnetic islands and X-lines due to the tearing instability, and located sites where particles are accelerated. We have observed that ultrarelativistic particles (with Lorentz factors > 100), which produce non-thermal tails in distribution functions, are generated primarily by the reconnection electric field in the vicinity of an X-line. This acceleration mechanism appears to be independent of the presence of the guide field. We have shown that the parallel electric field is localized at the X-line when there is a guide field instead of localized at separatrices as shown in hydrogen plasmas, and this electric field accelerates particles to ultrarelativistic energies. However, the energy spectrum depends on the magnitude of the guide field and the background density, and we have observed a harder energy spectrum in the presence of a finite guide field than when the guide field is absent. Lessons learned from these studies for hydrogen plasmas in the corona and the magnetosphere will be discussed.

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