Pickup Ions in the Outer Heliosheath and the IBEX Energetic Neutral Atom Ribbon
by
Tsung-Dao Lee Institute/N6F-N601 - Meeting Room
Tsung-Dao Lee Institute
Host: Gwenael Giacinti/Longqing Yi
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Abstract：
Linear analysis as well as hybrid simulations are performed to examine the stability of pickup ions in the outer heliosheath. This is critical for the validity of the secondary energetic neutral atom (ENA) mechanism, a promising model for the enigmatic ENA ribbon observed by the Interstellar Boundary Explorer (IBEX). According to the secondary ENA mechanism, the ENA ribbon comes from pickup ions in the outer helioshealth after they charge exchange with the local interstellar neutrals. Since the charge-exchange time is about two years, the conventional secondary ENA mechanism needs the pickup ions to keep their velocity distribution at born (generally a ring-beam distribution) for years. The present study examines how the development of various plasma instabilities can quickly scatter the pickup ions. The results suggest a pickup ion scattering time of 10s days, much shorter than that needed by the conventional secondary ENA model. On the other hand, it is found that the IBEX ribbon ENA flux, observed over a full solar cycle, correlates well with the solar wind ion flux measured at 1 au after a time delay of a few years. This supports the secondary ENA mechanism and the time delay (between the two fluxes)
is then used to estimate the heliopause distance and the heliosphere shape.
Biography:
Kaijun Liu is a professor in the Department of Earth and Space Sciences at Southern University of Science and Technology (SUSTech) in Shenzhen, China. He earned his PhD degree in space plasma physics at Cornell University in 2007, after graduating from Peking University with his B.S. and M.S. degrees in 1999 and 2002, respectively. He then worked as Postdoctoral Researcher for one year at Finnish Meteorological Institute, Finland and for three and a half years at Los Alamos National Laboratory, USA. After that, he joined the Department of Physics, Auburn University as Assistant Professor in 2012 and was promoted to Associate Professor with tenure in 2017. In May 2018, he joined SUSTech. Professor Liu specializes in theoretical and computational space plasma physics. His research interest is currently focused on pickup ions at Mars and in the outer heliosphere, while he also
carries out research on kinetic plasma instabilities and wave-particle interactions in the Earth's magnetosphere.
