Charged-particle acceleration at the heliospheric termination shock

The paradigm of the diffusive acceleration of pickup ions by the heliospheric termination shock to form the anomalous cosmic rays (ACR) has successfully accounted for many observed features of the ACR, including electrical charge, composition, energy spectrum, time variations and spatial gradients. Recent observations from the Voyager 1 spacecraft as it approaches the heliospheric termination shock, and other data, have forced a more detailed confrontation between this theoretical paradigm and observations. This has provided new insights and constraints concerning the structure of the heliospheric termination shock. In particular, the observed three-dimansional vector anisotropy provides valuable constraints. Here it is shown that all three components of the anisotropy may be understood if the global shape of the termination shock is as expected from simulation and analogy.