Backward test particle simulations of nonlinear wave-particle interactions in the radiation belts
Abstract
The Earth's magnetosphere can support various electromagnetic wave modes that play a vital role in near-Earth space dynamics. The propagation of these waves is governed by the 'cold' (~ 1 eV) and dense (~ 100-1000 el/cc) particle population. These plasma waves concurrently interact with higher energy (~ 0.1 - 10 MeV) radiation belt particles and results in complex nonlinear phenomena. The two primary aspects of these wave-particle interactions are the amplification of the wave by an unstable particle distribution, and the precipitation and/or acceleration of these particles by the waves.
In general, modeling wave amplification along with particle scattering and acceleration is a difficult problem that requires a self-consistent solution to the Vlasov-Maxwell system of equations. Several researchers have approached the self-consistent problem using particle-in-cell or hybrid simulations; however, such simulations are computational intensive in scenarios where modifications to the wave are small and particle scattering is of greater interest. A common method is to specify the wave-fields and neglect feedback which results in an approximate but simpler system of equations. For small amplitude and incoherent signals, quasi-linear diffusion theory is a common method to track the time-evolution of a particle distribution. For arbitrary wave-fields, however, the dynamics of the particle distribution is more accurately investigated using test particle simulations with a large number of particles. In order to alleviate the computational cost of traditional test-particle methods, a backward test particle simulation is employed to evaluate the nonlinear effects of coherent waves on the energetic particle distribution function. The approach allows regions of interest in phase-space to be defined a-priori which greatly reduces the number of particles that need to be tracked in the simulations. The method is utilized to efficiently model particle precipitation and energization since the loss-cone as well as the MeV band of phase-space are well defined. The temporal dynamics of the wave-induced phase-space trap is shown at a high resolution that has not be seen in previous works. The method is used to estimate resonant currents and scattered fields and demonstrate salient features of amplified and triggered waves.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSM31B..06H
- Keywords:
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- 2774 Radiation belts;
- MAGNETOSPHERIC PHYSICS;
- 7803 Active perturbation experiments;
- SPACE PLASMA PHYSICS;
- 7867 Wave/particle interactions;
- SPACE PLASMA PHYSICS;
- 7868 Wave/wave interactions;
- SPACE PLASMA PHYSICS