The acceleration mechanism of anomalous cosmic rays

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

This paper reviews our current understanding of the acceleration mechanism of anomalous cosmic rays (ACRs). ACRs were first discovered in the early 1970s and soon afterwards it was recognized that they were accelerated interstellar pickup ions that obtained most of their energization in the outer heliosphere. Their observed composition and charge state suggest they are accelerated to over 200 MeV total energy in about a year. Diffusive shock acceleration at the solar-wind termination shock, which provided a natural explanation for spacecraft observations prior to the Voyager crossings of the termination shock in 2004 and 2007, was the long-held paradigm for the acceleration mechanism. But when both Voyagers crossed the shock, the ACR energy spectrum remained modulated, suggesting a source more distant than the shock. While shock acceleration remains a popular mechanism, other ideas have emerged recently to explain the observations. This review focuses on three main acceleration mechanisms that have been proposed: (a) acceleration at the termination shock including new effects such as the global blunt-shape of the shock and large-scale turbulence, (b) acceleration by magnetic reconnection in the heliosheath, and (c) acceleration by diffusive compression acceleration in the heliosheath.

Original languageEnglish (US)
Pages (from-to)283-307
Number of pages25
JournalSpace Science Reviews
Volume173
Issue number1-4
DOIs
StatePublished - Nov 2012

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cosmic ray
cosmic rays
shock
heliosphere
solar wind
energy
spacecraft
energy spectra
turbulence
compression
ion
sensors

Keywords

  • Cosmic rays
  • Heliosphere
  • Magnetic reconnection
  • Particle acceleration
  • Shocks

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The acceleration mechanism of anomalous cosmic rays. / Giacalone, Joe; Drake, J. F.; Jokipii, J. Randy.

In: Space Science Reviews, Vol. 173, No. 1-4, 11.2012, p. 283-307.

Research output: Contribution to journalArticle

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