Particle acceleration by collisionless shocks containing large-scale magnetic-field variations

F. Guo, J. R. Jokipii, J. Kota

Research output: Contribution to journalArticle

32 Scopus citations

Abstract

Diffusive shock acceleration at collisionless shocks is thought to be the source of many of the energetic particles observed in space. Large-scale spatial variations of the magnetic field have been shown to be important in understanding observations. The effects are complex, so here we consider a simple, illustrative model. Herewe solve numerically the Parker transport equation for a shock in the presence of large-scale sinusoidal magnetic-field variations. We demonstrate that the familiar planar-shock results can be significantly altered as a consequence of large-scale, meandering magnetic lines of force. Because the perpendicular diffusion coefficient K⊥ is generally much smaller than the parallel diffusion coefficient K∥ the energetic charged particles are trapped and preferentially accelerated along the shock front in the regions where the connection points of magnetic field lines intersecting the shock surface converge, and thus create the "hot spots" of the accelerated particles. For the regions where the connection points separate from each other, the acceleration to high energies will be suppressed. Further, the particles diffuse away from the "hot spot" regions and modify the spectra of downstream particle distribution. These features are qualitatively similar to the recent Voyager observations in the Heliosheath. These results are potentially important for particle acceleration at shocks propagating in turbulent magnetized plasmas as well as those which contain large-scale nonplanar structures. Examples include anomalous cosmic rays accelerated by the solar wind termination shock, energetic particles observedin propagating heliospheric shocks, galactic cosmic rays accelerated by supernova blast waves, etc.

Original languageEnglish (US)
Pages (from-to)128-133
Number of pages6
JournalAstrophysical Journal
Volume725
Issue number1
DOIs
StatePublished - Dec 10 2010

Keywords

  • Acceleration of particles
  • Cosmic rays
  • Magnetic fields
  • Shock waves

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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