Stochastic pitch angle diffusion due to electron-whistler wave-particle interactions

In the Earth's magnetosphere, electron-whistler mode wave-particle interactions are a candidate mechanism for auroral precipitation via electron phase space diffusion. Of particular interest are stochastic interactions between relativistic electrons and (as often observed) waves of more than one wave number. It can be shown that the interaction between electrons and two oppositely directed monochromatic whistlers is stochastic. Once a threshold is exceeded, stochastic trajectories exist in addition to regular orbits (Kolmogorov-Arnold-Moser, or KAM, surfaces) near resonance, and here their corresponding pitch angle diffusion is estimated. The treatment is extended to consider broad band whistler wave packets and it is shown that the stochastic diffusion mechanism is again present for interactions with one or two wave packets. The pitch angle diffusion coefficient is estimated from the dynamics of stochastic electrons. For wave amplitudes consistent with planetary magnetospheres, such as at the Earth and Jupiter, pitch angle diffusion due to stochastic interactions occurs on fast (millisecond) time scales resulting in significant increases in the pitch angle diffusion coefficient. (C) 2001 American Institute of Physics