Title: Simulating Cosmic-ray Kinetic Physics from First Principles 

Speaker: Xuening Bai

Abstract：

Cosmic-rays are energetic charged particles. Their origin, transport and feedback of are of fundamental importance over a wide range of astrophysical systems. Typically, the kinetic physics of the CRs lies in their gyro-scale and above, while conventional kinetic simulation methods require resolving much smaller microscopic scales of the background plasmas. This issue can be substantially alleviated thanks to the development of the magnetohydrodynamic-particle-in-cell (MHD-PIC) method. As one major application, I will describe our simulations of the CR gyro-resonant instabilities, being the key microphysical mechanism behind CR feedback that involves substantial scale separation. Our simulations enable first-principle characterization of the CR transport coefficients, which can be eventually incorporated into subgrid prescriptions of CR feedback. Finally, I will describe the extension of the method to MHD-gPIC, where particles are integrated under the guiding center approximation with drift motion, with the potential to study particle acceleration in magnetic reconnection.

Bio:

Xuening Bai is a professor at the Institute for Advanced Study and Department of Astronomy, Tsinghua University. He graduated from Tsinghua University with a B.S. in mathematics and physics in 2007, and obtained his PhD in astrophysics from Princeton University in 2012. He was a Hubble Fellow and Institute for Theory and Computation (ITC) fellow at the Harvard-Smithsonian Center for Astrophysics from 2012-2017. He joined Tsinghua University as a research professor in 2017, and became a full professor in 2023. Prof. Bai is a theoretical and computational astrophysicist. His research group studies protoplanetary disks and planet formation, as well as several aspects of plasma astrophysics especially on cosmic-ray acceleration and transport, and develops computational tools for related applications.

 

Time: 14:00-15:00, 20/May, Tuesday

Venue: Room 506 (Large seminar room), Department of Astronomy