SELF-CONSISTENT SIMULATION STUDIES OF NONLINEAR ELECTRON-WHISTLER WAVE-PARTICLE INTERACTIONS

We present results from self-consistent one-dimensional electromagneti c particle-in-cell simulation studies of non-linear electron-whistler wave-particle interactions. In contrast to analytical treatments that assume a constant amplitude, monochromatic wave field, effects on the wave fields due to an evolving electron distribution are self-consiste ntly represented in our simulations (over a wide frequency range from 0.04 omega(ce) to similar to 100 omega(ce)). We analyse the phase spac e trajectories of the entire set of simulation electrons (many thousan ds) through application of the delay-coordinate technique. This enable s us to establish the trapping frequencies of electrons directly from the trajectories. Additional details in the phase space structure and dynamical changes in the properties of the trajectories are also obtai ned. Results from two different simulations, in which the wave spectru m is eventually dominated by a single whistler wave mode of relatively large amplitude (B-w/B-o similar to 0.2 - 0.3), show: (i) the phase s pace trapping of large numbers of simulation electrons (thousands) wit h characteristic frequencies around the expected primary trapping reso nance frequency estimated from the observed wave amplitude; (ii) more than one strong characteristic frequency component in trapped electron phase space motion; (iii) the dynamics of the trapped process is time dependent, there being an evolutionary shift in time of trapped elect ron phase space trajectories towards lower characteristic frequencies. We suspect that (ii) is due to the presence of higher order trapping resonances under the relatively large wave amplitude, whilst (iii) is not explained by time independent analytical treatments that neglect t he effects of particles on the wave field.