Descriptions of Nonlinear Wave-Particle Interactions

Abstract:

It is well known that cyclotron-resonant interactions with
small amplitude, broadband VLF waves lead to quasi-linear diffusion,
while large amplitude, narrowband waves give nonlinear behavior
characterized by phase bunching or phase trapping.
The coherent, nonlinear interactions can be treated analytically,
but their long-term, statistical combination is
sensitive to details of how the situation is modeled.
One version reverts to a (modified) diffusive description.
Departures from the idealized description, such as
frequency sweeping, the coexistence of coherent and incoherent waves,
and phenomena associated with chorus wave subpackets,
all further complicate the picture.
Test particle simulation remains essential, but must be
guided by the available theoretical results if progress is to be made.