Particle acceleration in the dynamic magnetotail
- Los Alamos National Laboratory, MS D466, Los Alamos, New Mexico 87545 (United States)
- Code 696, NASA Goddard Space Flight Center, Greenbelt, Maryland 20770 (United States)
The acceleration of charged particles to suprathermal energies is investigated in the context of magnetospheric substorms. Ion and electron test particle orbits are studied in dynamically evolving fields obtained from a three-dimensional resistive magnetohydrodynamic (MHD) simulation of reconnection in the near magnetotail. The simulation leads to plasmoid formation and ejection into the distant tail and an earthward collapse of the field in the inner tail. Energization of particles takes place predominantly in the inner tail region earthward of the neutral line, rather than in the vicinity of the neutral line. The test particle studies reproduce major observed characteristics of energetic particle flux increases (''injections'') in the inner magnetotail; a fast rise, a limited energy range of the flux increases, and spatially varying delays between the onsets of ion and electron injections. Acceleration mechanisms include a ''quasipotential'' acceleration, resulting from nonadiabatic particle motion in the direction of the cross-tail electric field, as well as betatron and Fermi-type acceleration. The major source region for accelerated ions (electrons) in the hundreds of keV range is the central plasma sheet at the dawn (dusk) flank, outside the reconnection site. Since this source plasma is already hot and dense, a moderate energization by a factor of approximately 2 is sufficient to explain the observed increases in the energetic particle fluxes. Differences between ions and electrons at energies of a few tens of keV are found to be associated with differences in the bounce periods, which enables ions to circumvent the acceleration region, so that only electron fluxes in that energy range become enhanced. (c) 2000 American Institute of Physics.
- OSTI ID:
- 20216078
- Journal Information:
- Physics of Plasmas, Vol. 7, Issue 5; Other Information: PBD: May 2000; ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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