On the Source of the Anomalous Cosmic Rays

In the years 2004 and 2007, the instruments onboard the Voyager 1&2 spacecraft delivered unprecedented data on the structure of the solar wind termination shock. This shock has been assumed to be responsible for the acceleration of the anomalous component of cosmic rays (ACRs) from a pick-up ion seed population derived from the interstellar neutral gas penetrating the heliosphere. In this article, we present model results on the evolution of solar wind turbulence and suprathermal tails with heliocentric distance to support the hypothesis that stochastic acceleration all over the heliosphere but in particular in the heliosheath is an important process to energize the ACRs if not the most important one.