On the Role of Charge Exchange in Generating Unstable Waves in the Ring Current.
AEROSPACE CORP EL SEGUNDO CALIF SPACE SCIENCES LAB
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The role of charge exchange in generating anisotropy in the ring current during recovery phase inside the plasmapause is explored. A simplified scenario is studied, in which the anisotropy evolves from an initially isotropic distribution. Other cases may be easily studied by shifting the time axis. When the anisotropy becomes large enough, the proton ring current just inside the plasmapause will emit ion electromagnetic cyclotron waves which can cause SAR arcs by electron heating, with subsequent destruction of anisotropy in the wave-emission process. As long as finite-amplitude waves are present, gain and loss of anisotropy will be in rough equilibrium, and the pitch-angle distribution will no longer evolve as it would if only charge exchange were operating. The amount of energy lost to the waves is related to the charge-exchange loss rate with the aid of quasi-linear moment equations it seems to be adequate to power SAR arcs. The role of heavy ions is considered generally, these ions tend to damp the proton-generated waves. This damping is quite sensitive to the very-low-energy portion of the heavy-ion distribution function, but not to the thermal component. If the heavy-ion fraction at beginning of recovery phase is less than or equal to 0.2 proton EMC waves will most likely not be generated by charge exchange beginning from initial isotropy. Author
- Atmospheric Physics
- Plasma Physics and Magnetohydrodynamics