Spatially Localized Fields in Density Cavities and Associated Ion Acceleration

Details Spatially Localized Fields in Density Cavities and Associated Ion Acceleration Spatially Localized Fields in Density Cavities and Associated Ion Acceleration

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm51b1299r&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM51B-1299

Physics

2407 Auroral Ionosphere (2704), 2451 Particle Acceleration, 2471 Plasma Waves And Instabilities (2772), 2483 Wave/Particle Interactions (7867), 7839 Nonlinear Phenomena (4400, 6944)

Scientific paper

In the auroral ionosphere density depleted regions with enhanced electromagnetic fields are routinely observed by rockets and satellites [1]. The enhanced fields are spatially localized with transverse (to the geomagnetic field) dimensions that are smaller than the ion Larmor radius. We have been studying the eigenmode structure of electrostatic fields in density cavities. The description of the fields is obtained from Maxwell's equations with a cold plasma model including spatially varying density profiles. In the vicinity of the lower hybrid resonance enhanced field amplitudes in spatially localized regions are obtained. The characteristic features of the fields and the associated eigenvalues will be discussed. Along with the enhanced fields transverse acceleration of ions is also observed in the ionosphere [1]. From the observed characteristics of the fields and the ambient plasma distribution, it is difficult to explain the ion acceleration using a linear model of wave-particle interactions as is conventionally done in quasilinear theories [2]. Furthermore, since the transverse spatial extent of the fields is smaller than the ion Larmor radius, the fields cannot be modeled as plane waves. We have been studying the nonlinear interaction of localized fields with ions and find that the ions can be accelerated only for certain characteristic features of the fields. The phase space of the accelerated ions is chaotic. However, under some circumstances, the ions can undergo large energy gains akin to Lévy flights. Detailed analytical and numerical results on the acceleration of ions by localized fields and comparisons with ion acceleration by plane waves will be presented. Work supported by NSF Grant No. ATM-98-06328.
[1] K.A. Lynch et al., J. Geophys. Res. 104, 28,515 (1999).
[2] A.K. Ram, A. Bers, and D. Benisti, J. Geophys. Res. 103, 9431 (1998).

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