Limited stochastic electron acceleration induced by an intense cyclotron wave in a plasma

An investigation of the stochastic electron acceleration in a magnetized plasma due to an intense electron cyclotron wave is performed for the case of a stochastic regime where only a few resonances overlap and the stochastic region in phase space is bounded. The electron dynamics is described by a Hamiltonian function H(theta,I,t), and the stochastic properties of the system are investigated by means of the Poincare-section method and the analytical estimates of the phase-correlation function. The behavior of the system is then analyzed through the Fokker-Planck-Kolmogorov (FPK) diffusion equation in action space. The theoretical FPK predictions are compared with the results of a numerical simulation of the particle motion. It is found that the system satisfies the diffusion equation at times that are short compared to the saturation time of the quasilinear diffusion. Appreciable deviations from the diffusive results are found at longer times, since the particle motion is influenced by the region of local stochasticity in phase space.