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| Titel |
Cosmic ray momentum diffusion in the presence of nonlinear Alfvén waves |
| VerfasserIn |
G. Michałek, M. Ostrowsky |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 3, no. 1 ; Nr. 3, no. 1, S.66-76 |
| Datensatznummer |
250000705
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| Publikation (Nr.) |
 copernicus.org/npg-3-66-1996.pdf |
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| Zusammenfassung |
| The relation between the
spatial diffusion
coefficient along the magnetic field, kII, and the momentum
diffusion coefficient, Dp, for
relativistic cosmic ray
particles is modelled using Monte Carlo
simulations. Wave
fields with vanishing wave helicity and cross-helicity,
constructed by superposing 'Alfvén-like' waves
are considered.
As the result, particle trajectories in high
amplitude wave
fields and then - by averaging over these
trajectories - the
values of transport coefficients are derived. The modelling is
performed at various wave amplitudes, from δ B/B0 = 0.15 to
2.0, and for a number of wave field types. At
our small
amplitudes approximately the quasi-linear theory (QLT)
estimates for kII and Dp are reproduced. However, with growing
wave amplitude the simulated results show a small
divergence
from the QLT ones, with kII decreasing slower than theoretical
prediction and the opposite being true for Dp. The wave field
form gives only a slight influence on the
wave-particle
interactions at large wave amplitudes δ B/B0
~ 1. The parameter
characterizing the relative efficiency of the
second-order to the first-order acceleration at shock waves, Dp
κII is given
in the QLT approximation by the Skilling formula V2A
p2 / 9. In
simulations together with increasing δ B it
increases above
this scale in all the cases under our study.
Consequences of
the present results for the second-order Fermi
acceleration at
shock waves are briefly addressed. |
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