Physics – Plasma Physics
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11605215s&link_type=abstract
Journal of Geophysical Research, Volume 116, Issue A5, CiteID A05215
Physics
Plasma Physics
2
Space Plasma Physics: Wave/Particle Interactions (2483, 6984), Space Plasma Physics: Kinetic Waves And Instabilities, Space Plasma Physics: Particle Acceleration
Scientific paper
The full kinetic linear dispersion relation in a warm plasma with He+ and O+ ions is used to estimate the minimum resonant electron energies required for resonant scattering of relativistic electrons by electromagnetic ion cyclotron waves. We find two significant differences from the cold-plasma approximation: (1) waves can be excited inside the stop bands and at ion gyrofrequencies for relatively small wave numbers k < Ωp/vA and (2) short wavelengths with k > Ωp/vA experience strong cyclotron damping. We show that, in general, minimum resonant energy of electrons Emin depends only on the wave number k, magnetic field strength B, and plasma mass density ρ and depends on the wave frequency ω only implicitly, via the dispersion relation. Formulae for Emin as function of ω based on cold-plasma approximation predict the lowest energy loss where ω → ΩHe+, since in this approximation k → ∞ at these frequencies. We show this inference is incorrect and that kinetic effects mean that the ion gyrofrequencies are no longer necessarily preferential for low energy loss. The lowest values of Emin are obtained where the dispersion supports the largest wave numbers k and in the regions of the largest mass densities ρ and the lowest magnetic fields B. For realistic magnetospheric conditions Emin ˜ 2 MeV and can only drop to ˜500 keV inside dense plasmaspheric plumes, with plasma density of the order of 500 cm-3, or during plasmaspheric expansions to high L shells (L ˜ 7).
Mace Richard L.
Mann Ian R.
Silin I.
Summers Donald
Sydora Richard D.
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