Wave-Particle Interaction in Electrostatic Plasma Turbulences
The stochastic nature of non-resonant acceleration of electrons in one-dimensional electrostatic turbulence is observed in velocity spaces. This stochasticity is found to violate the traditional criterion of resonance overlapping. According to the observation, there are two aspects in the violations: One is that when islands of two adjacent resonances are not mixed, which is there being no overlapping islands, there is still a well-defined diffusion for certain duration of plasma periods; the other is that when field amplitude is far below what overlapping criterion requires, there is stochastic acceleration of particle. A non-Gaussian spectrum of turbulence is studied to foster the understanding of wave-particle interaction. First, in a Gaussian spectrum, electrons escape from the turbulent region in a few plasma periods when this turbulence is strong. This non-Gaussian spectrum can extend the interaction between waves and particles, providing better measurement for resonant transport coefficient. Second, it is attributed to the self-consistency between wave and particle density, particle diffusion modifies field distribution. A Gaussian spectrum then changes into a non-Gaussian one. Statistics of particle diffusion in such a non-Gaussian power spectrum is calculated. The classical Hamilton-Jacobi theory together with the Vlasov theory is applied to present a diffusion coefficient in weak plasma turbulence, while resonance broadening theory is reviewed for strong turbulence. A new diffusion coefficient of wave-particle interaction in the non-Gaussian spectrum is given. These two analytical diffusion coefficients are in good agreement with data obtained in numerical experiments so long as electrons are resonantly interacting with waves within the domain of turbulence.
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