Enhanced Phase Space Diffusion due to Chaos in Relativistic Electron- Whistler Mode Wave Particle Interactions in Planetary Magnetospheres

Abstract

The chaotic interaction between electrons and whistler mode waves has been shown to provide a mechanism for enhanced diffusion in phase space. Pitch angle diffusion is relevant for the scattering of electrons into the loss cones, thus providing a source for auroral precipitating electrons. A single whistler mode wave propagating parallel to the background magnetic field has resonance with the electrons but the process is not stochastic. The presence of a second, oppositely directed whistler wave has been shown previously to introduce stochasticity into the system, thus enhancing phase space diffusion. Here we generalise previous work to include relativistic effects. The full relativistic Lorentz equations are solved numerically to permit application to a more extensive parameter space. We consider parameters scaled to intrinsic planetary magnetospheres, for electron populations with 'pancake' velocity distributions i.e. large anisotropies in velocity space. We show that the diffusion is rapid, occuring on timescales of the order of tens of electron gyroperiods, and is strongly sensitive to the wave amplitude, the wave frequency and the perpendicular velocity. Using Voyager 1 data we give an estimate of the whistler wave amplitude in the Io torus at Jupiter and show that the two whistler mechanism produces pitch angle diffusion of up to 10 degrees from an initial pancake distribution, on millisecond timescales.