April 15-17

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Author: Chang Liu
Requested Type: Pre-Selected Invited
Submitted: 2019-02-22 15:10:58

Co-authors: Dylan P. Brennan, Amitava Bhattacharjee

Contact Info:
Princeton Plasma Physics Laboratory
100 Stellarator Road
Princeton, NJ   08540
United States

Abstract Text:
A quasilinear analysis of a sub-cyclotron resonance mechanism between plasma waves and magnetized particles is presented. This mechanism has previously been studied by test-particle simulation and Hamiltonian analysis using the Lie-perturbation method. It was demonstrated that a large amplitude plasma wave, even with frequency below cyclotron frequency, can have resonance with charged particles, and lead to chaotic trajectories in phase space. This mechanism has been used to explain the particle heating by low-frequency Alfven waves in lab and in solar wind, and frequency gaps observed in magnetospheric chorus. In the work presented here, it is found that the nonlinear term caused by a finite wave length and Lorentz force can drive effective forces on particles with frequencies being harmonics of the original wave. This effective force can thus lead to resonant energy exchange between waves and particles. Based on this method, we calculate the nonlinear mode growth or damping rate, and the diffusion term on the particle distribution function, similar to the quasilinear theory for cyclotron resonance. Application of the results are also discussed, including Alfven wave heating, and diffusion of runaway electrons in tokamaks by injecting waves.

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