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Academic Lecture: Kinetic simulations of plasma waves in the radiation belts

Author:Administrator Source:website Time:2018-01-03 09:17:55


Topic : Kinetic simulations of plasma waves in the radiation belts
Speaker : LIU, Kaijun   Associate professor of physics at Auburn University
Time : 10:00am    Thursday, January 4,2018
Place : 320 Conference Room in Electronic and Information School


Abstract:
       Kinetic simulations aided by linear instability analyses are performed to study the excitation of various plasma waves and their interactions with charged particles in the radiation belts. In particular, fast magnetosonic waves at frequencies close to the proton cyclotron frequency and its harmonics (up to the lower hybrid frequency) are observed near the geomagnetic equator in the terrestrial magnetosphere. They can pitch-angle scatter as well as energize radiation belt electrons. The waves arise from the ion Bernstein instability driven by ring-like proton velocity distributions with a positive slope with respect to the perpendicular velocity (∂f(v┴)/∂v┴>0). The unstable waves are essentially ion Bernstein waves but occur near the intersections of the cold-plasma dispersion relation for fast magnetosonic waves and the multiple dispersion branches of the ion Bernstein modes when the plasma is dominated by a cool background. The growth rate patterns are very different when the proton distribution varies from a ring to an isotropic shell. In addition, a ring distribution can simultaneously drive the Aflvén cyclotron instability and excite electromagnetic ion cyclotron (EMIC) waves.  The kinetic simulations revealed that, despite their generally smaller linear growth rates, EMIC waves saturate at higher levels than fast magnetosonic waves unless the proton distribution is sufficiently wide in pitch angle space and close to an isotropic shell. Moreover, EMIC waves mainly lead to pitch angle scattering of the protons while fast magnetosonic waves can cause significant energy scattering. The study is also relevant to the pickup ion dynamics in the heliosphere.