Kinetic simulations of plasma waves in the radiation belts
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.
刘凯军, 2007年美国康奈尔大学（Cornell University）博士，2002年北京大学硕士， 1999年本科毕业于北京大学空间物理专业。博士毕业后曾在Finnish Meteorological Institute 和美国Los Alamos National Laboratory 从事博士后研究，目前在美国阿拉巴马州奥本大学（Auburn University）物理系任副教授。学术专长是空间等离子体动力学理论和相应的计算机数值模拟，近期主要从事地球辐射带中等离子体波的激发及与带电粒子相互作用方面的研究。在国际学术刊物共发表论文40余篇，累积引用600余次。