Particle Acceleration by Collisionless Shocks Containing Large-scale Magnetic-field Variations

• Published in: The Astrophysical journal Vol. 725; no. 1; pp. 128 - 133
• Main Authors: Guo, F, Jokipii, J. R, Kota, J
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 10.12.2010; IOP
• Subjects: ACCELERATION; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CHARGED PARTICLES; COSMIC RADIATION; Earth, ocean, space; Exact sciences and technology; EXPLOSIONS; IONIZING RADIATIONS; MAGNETIC FIELDS; PLASMA; RADIATIONS; SHOCK WAVES; SOLAR ACTIVITY; SOLAR WIND; STELLAR ACTIVITY; STELLAR WINDS; TRANSPORT THEORY; Field line; Supernovae; acceleration of particles; Magnetic forces; Particle acceleration; Large-scale structure; Spatial variation; Cosmic radiation; Heliosphere; Turbulent plasma; Particle distribution; Magnetic line; Diffusion coefficient; Solar wind; Transport equation; Hot spots; Galactic cosmic rays; Milky Way; Shock front; Shock waves; cosmic rays; Models; Relativistic particle; Magnetic fields; Charged particles; Trapped particle
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/725/1/128

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. Here we 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 Delta *k is generally much smaller than the parallel diffusion coefficient Delta *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 observed in propagating heliospheric shocks, galactic cosmic rays accelerated by supernova blast waves, etc.