Effects of Nonlinear Resonance Broadening on Bounce-averaged Diffusion Coefficients Between Electrons and Whistler Mode Waves

Abstract:

Effects of nonlinear resonance broadening on bounce-averaged diffusion coefficients for interactions between parallel propagating whistler mode waves and relativistic electrons in a dipole magnetic field are investigated in this work using test particle simulations. In quasi-linear theory, variations of pitch angle and energy are calculated along the unperturbed trajectory, resulting in difficulties when the pitch angle is near 90 ◦ or when wave amplitudes are large. As shown by our previous work, the nonlinear resonance broadening theory with finite trapping width has the potential to give more accurate diffusion coefficients than standard quasi-linear theory. Here we further investigate the use of nonlinear resonance broadening theory for bounce-averaged diffusion coefficients in a dipole field using a test particle simulation code and compare the results with the nonlinear theory by Karimabadi et al. We demonstrate that nonlinear resonance broadening theory gives better agreement with test particle simulations compared with standard quasi-linear theory in a dipole field configuration. Our result suggests further development of the nonlinear theory and should be useful to improve radiation belt modeling.