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| Titel |
Alfvén wave interaction with inhomogeneous plasmas: acceleration and energy cascade towards small-scales |
| VerfasserIn |
V. Génot, P. Louarn, F. Mottez |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 22, no. 6 ; Nr. 22, no. 6 (2004-06-14), S.2081-2096 |
| Datensatznummer |
250014902
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| Publikation (Nr.) |
 copernicus.org/angeo-22-2081-2004.pdf |
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| Zusammenfassung |
| Investigating the process of electron acceleration in auroral
regions, we present a study of the temporal evolution of the
interaction of Alfvén waves (AW) with a plasma inhomogeneous in
a direction transverse to the static magnetic field. This type of
inhomogeneity is typical of the density cavities extended along
the magnetic field in auroral acceleration regions. We use
self-consistent Particle In Cell (PIC) simulations which are able
to reproduce the full nonlinear evolution of the electromagnetic
waves, as well as the trajectories of ions and electrons in phase
space. Physical processes are studied down to the ion Larmor
radius and electron skin depth scales. We show that the AW
propagation on sharp density gradients leads to the formation of a
significant parallel (to the magnetic field) electric field
(E-field). It results from an electric charge separation generated
on the density gradients by the polarization drift associated with
the time varying AW E-field. Its amplitude may reach a few
percents of the AW E-field. This parallel component accelerates
electrons up to keV energies over a distance of a few hundred Debye
lengths, and induces the formation of electron beams. These beams
trigger electrostatic plasma instabilities which evolve toward the
formation of nonlinear electrostatic structures (identified as
electron holes and double layers). When the electrostatic
turbulence is fully developed we show that it reduces the further
wave/particle exchange. This sequence of mechanisms is analyzed
with the program WHAMP, to identify the instabilities at work and
wavelet analysis techniques are used to characterize the regime of
energy conversions (from electromagnetic to electrostatic
structures, from large to small length scales). This study
elucidates a possible scenario to account for the particle
acceleration and the wave dissipation in inhomogeneous plasmas. It
would consist of successive phases of acceleration along the
magnetic field, the development of an electrostatic turbulence,
the thermalization and the heating of the plasma.
Space plasma physics (charged particle motion and acceleration; numerical studies). |
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