University of Maryland
Atlantic Building, Room 2400 4:30 PM Monday, September 14, 2009
Coffee, Tea & Snacks 4:15-4:30 PM

James F. Drake
University of Maryland

A New Mechanism for the Generation of Anomalous Cosmic Rays

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 most of the magnetic energy goes into energetic ions with significant but smaller amounts of energy going into electrons. The most energetic ions gain energy as they reflect from contracting magnetic islands, a first order Fermi process. An analytic model is constructed in which the Fermi drive is balanced by convective loss. The ACR differential energy spectrum takes the form of a power law with a spectral index slightly above 1.5. The model has the potential to explain several key ACR observations, including the similarities in the spectra of different ion species. Implications for flare ion acceleration will also be discussed.