Analytic Ion Conics in the Magnetosphere

Abstract

Consider the formation of ion conics through the agency of lower-hybrid-wave turbulence in the Earth's magnetosphere. This process begins within a layer where significant wave-particle interactions result in a velocity space diffusion of the initially cold ion population. The conic results from subsequent adiabatic motion along geomagnetic field lines. A model for this process is discussed that permits an asymptotic determination of the ion distribution function. A suitable model for the energy spectral density of the turbulence is available. Identification of the ratio of ion thermal speed to mean wave speed as a small parameter leads to a uniformly valid asymptotic solution of the resulting quasi-linear diffusion equation. These results are compared to a different approach in which a Monte Carlo procedure is used to obtain the ion distribution function. In this method, while approximations are not required in order to solve the equation, the solution is restricted by the need to include a sufficient number of particles in order to have reliable statistics. The two approaches are thus complementary, and used together can provide a wealth of information about the conic-formation process. In particular, we have found that conic formation is significantly affected by the presence of field-aligned potentials,more » as well as, the spatial extent and spectrum of the turbulence.« less