A magnetic reconnection mechanism for the generation of anomalous cosmic rays
Abstract
The recent observations of the anomalous cosmic ray (ACR) energy spectrum as Voyagers 1 and 2 crossed the heliospheric termination shock have called into question the conventional shock source of these energetic particles. We suggest that the sectored heliospheric magnetic field, which results from the flapping of the heliospheric current sheet, piles up as it approaches the heliopause, narrowing the current sheets that separate the sectors and triggering the onset of collisionless magnetic reconnection. Particle-in-cell simulations reveal that the current layers break up into a turbulent bath of magnetic islands that merge to release a large fraction of the energy in the sectored magnetic field. Most of the magnetic energy goes into energetic ions with significant but smaller amounts of energy going into electrons. The dominant acceleration mechanism is through reflection in contracting islands, a first-order Fermi mechanism. Particle energy gain is regulated by the approach to the marginal firehose condition. The ACR differ-ential energy spectrum for all of the ion species takes the form of a power law with a spectral index slightly above 1.5, which is consistent with observations.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38.1608D