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Astron. Astrophys. 331, 1066-1069 (1998)

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Cosmic ray acceleration by fast magnetosonic waves

Brigitte R. Ragot and Reinhard Schlickeiser *

Max-Planck-Institut für Radioastronomie, Postfach 2024, D-53010 Bonn, Germany

Received 19 September 1997 / Accepted 25 November 1997

Abstract

Recently, Schlickeiser and Miller have calculated anew the acceleration rate of cosmic rays by fast magnetosonic plasma waves in a small-beta plasma, using a linear dispersion relation. They found that the transit-time damping of fast mode waves provides the dominant contribution to the stochastic acceleration rate of cosmic ray particles, both, in pure fast mode wave turbulence as well as in a mixture of isotropic fast mode turbulence and slab Alfven turbulence. Here it is shown that the use of the linear dispersion relation is fully justified for protons down to kinetic energies of a few tens of keV, whereas for electrons, the dispersive part of the dispersion relation should be included for energies below [FORMULA] MeV. By retaining the largest scales of the turbulence only (for which the linear dispersion relation holds), an upper limit is computed, which shows that possible strong damping of the turbulence spectrum at high wavenumber would not reduce the efficiency of the acceleration process in a dramatic way, and that a strong modification induced by the waves dispersivity at high wavenumber could only be in the sense of an enhanced efficiency.

Key words: acceleration of particles – plasmas – turbulence – cosmic rays – Sun: flares

* After March 1st, 1998 at: Institut für Theoretische Physik, Lehrstuhl 4: Weltraum & Astrophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany

Send offprint requests to: B.R. Ragot

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© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998
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