Enhanced phase space diffusion due to chaos in relativistic electron–whistler mode wave particle interactions with applications to Jupiter

Using numerical solutions of single-particle dynamics, we consider a chaotic electron–whistler interaction mechanism for enhanced diffusion in phase space. This process, when applied to parameters consistent with the Jovian magnetosphere, is a candidate mechanism for pitch angle scattering in the Io torus, thus providing a source of auroral precipitating electrons. We initially consider the interaction between two oppositely directed monochromatic whistler mode waves. We generalize previous work to include relativistic effects. The full relativistic Lorentz equations are solved numerically to permit application to a more extensive parameter space. We use this simplified case to study the underlying behaviour of the system. For large-amplitude monochromatic waves the system is stochastic, with strong diffusion in phase space. We extend this treatment to consider two oppositely directed, broad band whistler wave packets. Using Voyager 1 data to give an estimate of the whistler wave amplitude at the Io torus at Jupiter, we calculate the degree of pitch angle scattering as a function of electron energy and initial pitch angle. We show that for relatively wide wave packets, significant pitch angle diffusion occurs (up to ±25°), on millisecond timescales, for electrons with energies from a few keV up to a few hundred keV.