  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.
