Influence of large-scale variations in the magnetic field direction on the acceleration of interstellar pickup protons at the heliospheric termination shock

The spectra of energetic protons measured on the Voyager-1 and Voyager-2 spacecraft in the inner heliospheric shock layer can be explained in terms of the classical theory of the shock drift acceleration of interstellar pickup protons with allowancemade for theirmultiple reflection from the front. The spacecraft entered this region after the heliospheric termination shock crossing in 2004 and 2007, respectively. The large-scale variations of the magnetic field direction near the shock front associated with the passage of sector structures through it are the decisive factor in explaining the measurements.