Abstract: The origin, transport and feedback of cosmic-rays (CRs) are of fundamental importance over a wide range of astrophysical systems. Typically, the kinetic physics of the CRs lies in their gyro-scale, with consequences that affect macroscopic scale physics. The issue with scale separation can be substantially alleviated thanks to the development of the magnetohydrodynamic-particle-in-cell (MHD-PIC) method. Using this method, I will describe the first simulations of the CR streaming instability, which is the key underlying mechanism behind CR self-confinement and CR-driven galactic outflows. By introducing a novel simulation setup, we can further characterize the CR transport coefficients in different environments from first principles, offering reliable sub-grid prescriptions for CR feedback. I will also briefly discuss simulations of particle acceleration in non-relativistic shocks and radiatively inefficient accretion flows, as well as new developments towards studying particle acceleration in magnetic reconnection at macroscopic scales.
Bio: Prof. Xuening Bai 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 the faculty at the Institute for Advanced Study, Tsinghua University in 2017, and is jointly affiliated with Department of Astronomy. He 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.