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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 6
Ann. Geophys., 15, 603–613, 1997
https://doi.org/10.1007/s00585-997-0603-3
© European Geosciences Union 1997
Ann. Geophys., 15, 603–613, 1997
https://doi.org/10.1007/s00585-997-0603-3
© European Geosciences Union 1997

  30 Jun 1997

30 Jun 1997

Nongyrotropy in magnetoplasmas: simulation of wave excitation and phase-space diffusion

U. Motschmann1,2, H. Kafemann2, and M. Scholer3 U. Motschmann et al.
  • 1Deutsche Forschungsanstalt für Luft- und Raumfahrt e. V., Rudower Chaussee 5, D-12484 Berlin, Germany
  • 2Institut für Geophysik und Meteorologie, Technische Universität Braunschweig, Mendelssohnstrasse 3, D-38106 Braunschweig, Germany
  • 3Max-Planck-Institut für Extraterrestrische Physik, D-85740 Garching, Germany

Abstract. Nongyrotropic (gyrophase bunched) ion distributions in a magnetoplasma are studied by analytical methods and by two-dimensional hybrid code simulations. Nongyrotropy may not occur in a plasma being simultaneously homogeneous, stationary, and solenoidal in phase space. A detailed study is performed for a homogeneous and stationary plasma with sources and sinks in phase space. The analytical investigation cast in the framework of linearized Maxwell-Vlasov theory yields a coupling of low-frequency left-handed, right-handed, and longitudinal modes. Nongyrotropic ion distributions are unstable; they excite left-handed waves. The growth rate is comparable to that of the ion ring instability. The hybrid code simulation study confirms the expected propagation direction parallel to the background magnetic field. Three diffusion processes are studied: arc lengthening, arc broadening, and arc radius decreasing corresponding to particle energy diffusion. The characteristic diffusion time-scales are found to be of the order of 101 wave cycles.

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