ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-25-575-2007 Unexpected sites of efficient stochastic acceleration in the inner heliosheath Chalov S. V. 1 Fahr H. J. 2 Malama Y. G. 1 3 Institute for Problems in Mechanics, Russian Academy of Sciences, Moscow, Russia Argelander Institut für Astronomie, Abt.: Astrophysik, Universität Bonn, Bonn, Germany Space Research Institute (IKI), Russian Academy of Sciences, Moscow, Russia 29 03 2007 25 3 575 580 Copyright: © 2007 S. V. Chalov et al. 2007 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/25/575/2007/angeo-25-575-2007.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/25/575/2007/angeo-25-575-2007.pdf

Up until the recent past, it was generally believed that the solar wind termination shock (TS) is the favourite site to accelerate ions from the keV- to the MeV- energy levels by means of Fermi-1 processes. When Voyager 1 was crossing the TS at the end of 2004, the registrations of this spacecraft showed, however, that beyond the shock passage fluxes of anomalous cosmic rays kept increasing with time. This obviously called for an acceleration site further downstream of the shock in the heliosheath which had not been identified before. In this paper we thus investigate the process of energy diffusion due to wave-particle interactions (Fermi-2) operating on pick-up ions which are convected downstream of the TS with the subsonic solar wind. We investigate the continuous effect of stochastic acceleration processes suffered by pick-up ions at their interaction with heliosheath turbulences, while they are slowly convected with the subsonic solar wind towards the heliotail. As we can show, the inner heliosheath region, with an extent of about 100 AU around the solar wind stagnation point, is specifically favourable for the energy processing of pick-up ions by Fermi-2 processes up to MeV energies. In addition, we claim that this region is the origin of multiply-charged anomalous cosmic ray particles that have been registered in recent times.

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