Acceleration of anomalous cosmic rays at the heliospheric termination shock

The acceleration of anomalous cosmic rays (ACRs) at the heliospheric termination shock and their influence on the shock structure and location are analyzed in terms of a self-consistent nonlinear kinetic model. The ACR spectrum, the structure of the heliospheric termination shock, and its location are shown to be very sensitive to the ACR acceleration efficiency, i.e., to the injection rate of the pick-up ions produced by the ionization of interstellar neutral atoms penetrating into the heliosphere. A relatively high injection rate of pick-up protons, when ∼1% of the pick-up ions are drawn into the acceleration process, is required to reproduce the observed ACR proton spectrum.