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Space Physics, Plasma Astrophysics
Hot and tenuous gasses in space are in an ionized state often termed as a collisionless plasma, in which binary collisions between particles are negligible in the sense that the collisional mean free path is larger than the typical size of the system. Instead, the energy and momentum exchanges between particles are mediated by the electromagnetic field fluctuations in a collective manner. A lot of interesting phenomena unique to such a collisionless system occur as a result. Research has been conducted on those intriguing plasma phenomena in space and astrophysical plasmas, with particular emphasis on the understanding of universal and elementary physical processes.
Current research subjects include collisionless shocks and associated high-energy particle acceleration, kinetic plasma instabilities in the earth's magnetosphere, relativistic plasma physics and its application to high-energy astrophysics. Development of new numerical techniques is also a subject of research related to the above-mentioned physics applications. Theoretical analysis and numerical simulations are two major approaches, but data analysis of direct plasma measurements by spacecraft is also employed.