报告题目：Effects of ion-neutral collisions on Alfven waves: The presence of forbidden zone and heavy damping zone

　　报 告 人：郭政灵 博士（台湾中央大学太空科学研究所）

　　报告人简介：2011年8月任职于台湾中央大学太空科学研究所，主要从事大气电学的研究，现已获得多项重要成果，发表SCI论文26篇，其中在国际学术刊物《Geophys. Res. Lett.》和《J. Geophys. Res.》等上发表第一作者论文10篇。

　　报告摘要：Alfvén waves are low-frequency transverse waves propagating in a magnetized plasma. We define the Alfvén frequency as , where is the wave number, is the Alfvén speed, is the angle between the wave vector and the ambient magnetic field. There are partially ionized plasmas in laboratory, space and astrophysical plasma systems, such as in the solar chromosphere, interstellar clouds,and the Earth ionosphere. The presence of neutral particles may modify the wave frequency and cause damping of Alfvén waves. The effects on Alfvén waves depend on two parameters: (1) , the ratio of neutral density and ion density , and (2) , the ratio of neutral collisional frequency by ions ,, to the Alfvén frequency . Most of previous studies examined only the limiting case with a relatively large neutral collisional frequency or . In the present paper, the dispersion relation for Alfvén waves is solved for all values of and . Approximate solutions in the limit as well as are obtained. It is found for the first time that there is a “forbidden zone (FZ)” in the parameter space, where the real frequency of Alfvén waves becomes zero. We also solve the wavenumber k from the dispersion equation for a given frequency and find the existence of a “heavy damping zone (HDZ)”. We then examine the presence of FZ and HDZ for Alfvén waves in the ionosphere and in the solar chromosphere.

　　C. J. Weng, L. C. Lee*, C. L. Kuo, and C. B. Wang(2013), Effects of ion-neutral collisions on Alfven waves: The presence of forbidden zone and heavy damping zone, Phys. Plasmas 20, 032902, doi: 10.1063/1.4796043

　　时    间：2014年6月24日（星期二）下午14:00

　　地    点：紫金山天文台517会议室

　　联 系 人：杨磊（83332123）

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