  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 is released and most of this energy goes into
energetic ions with significant but smaller amounts of energy going into
electrons. The energy gain of the most energetic ions results from their
reflection from the ends of contracting magnetic islands, a first order Fermi
process. The energy gain of the ions in contracting islands increases their
parallel (to the magnetic field ${\bf B}$) pressure $p_\parallel$ until the
marginal firehose condition is reached, causing magnetic reconnection and
associated particle acceleration to shut down. The model calls into question
the strong scattering assumption used to derive the Parker transport equation
and therefore the absence of first order Fermi acceleration in incompressible
flows. A simple 1-D model for particle energy gain and loss is presented in
which the feedback of the energetic particles on the reconnection drive is
included. 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 Voyager observations, including the similarities in the
spectra of different ion species.
