Phase-space diffusion of charged particles induced by random fluctuations of relative gyrophases in the presence of finite amplitude circularly polarized electromagnetic waves

摘要

A stochastic model to describe the phase-space diffusion of charged particles induced by random fluctuations of relative gyrophases in the presence of parallel propagating, circularly polarized electromagnetic waves is discussed. The perturbation analysis around the equilibrium points of the noiseless system shows the coexistence of classical diffusion and trapping oscillation. Even if the equation of motions for pitch angle does not include noise terms, the pitch angle diffusion occurs due to the noise term in the equation of the relative gyrophase and the existence of the finite amplitude wave. The resultant theory is validated by using numerical results of test particle simulations; when distributions of the relative gyrophases and pitch angle cosines are close to Gaussian, the classical diffusion and trapping oscillation are observed. With increasing wave amplitude and/or the strength of noise, the pitch angle diffusion becomes subdiffusive. (C) 2019 Author(s).