题目： Cosmic Ray Transport and acceleration in Magnetohydrodynamic Turbulence

主讲： 北京大学Kavli天文与天体物理所闫慧荣教授

时间： 2012年8月24日（周五）下午3:00-4:50

地点： 科学实验楼报告厅

内容简介: Recent advances in MHD turbulence call for revisions in the paradigm of cosmic ray transport. We use the models of magnetohydrodynamic turbulence that were tested in numerical simulation, in which turbulence is injected at large scale and cascades to small scales. I shall discuss both the transport and acceleration of CRs, and demonstrate that compressible fast modes dominate the interactions. Implications for solar flares will be provided. I shall address the issue of perpendicular to the magnetic field and show that the concept of cosmic ray subdiffusion is only important for restricted cases when the ambient turbulence is far from that suggested by numerical simulations and on small scales, it is actually superdiffusive. Then I'll discuss the feedback of cosmic rays on turbulence through gyroresonance instability. If time is allowed, I shall also present our recent results on the acceleration and propagation of cosmic rays in the vicinity of supernova remnants.

报告人简介：

Professor Huirong Yan is a theoretical astrophysicist with interest both in fundamental astrophysical processes and in relating her work to observations. She graduated on Astrophysics in 1998 from Peking University, obtained her Master degree on Astronomy from the University of Wisconsin-Madison (USA) in 2002. There, Professor Yan also got her PhD on Astronomy in 2005.

Her research experience began during her doctoral in the year of 2000 in the University of Wisconsin-Madison. Then she was working as independent postdoctoral fellow at Canadian Institute of Theoretical Astrophysics, University of Arizona, respectively, after a one year pre-doctoral stay at Stanford University. Starting from 2009, she is a faculty member at Kavli Institute of Astronomy and Astrophysics in Peking U.

Her research encompasses a wide variety of topics related to the particle acceleration and interaction with magnetohydrodynamic (MHD) turbulence, as well as plasma instabilities, high energy astrophysics. Huirong Yan's interests also include technique of studying astrophysical magnetic field. Her major contribution can be briefly summarized as below:

•advancing the theory of cosmic ray transport and acceleration in tested model of turbulence. Predicting the super-diffusive transport on small scales, quantifying the feedback of cosmic rays on turbulence through kinetic instability, application of the results to supernova remnants and solar flares;

•identifying new diagnostics for astrophysical magnetic field based on alignment of atoms and ions on their ground states, opening a new window for direct detection of 3D magnetic field in all diffuse medium from the interplanetary medium to early universe, making predictions for polarization of multiple atomic species and lines ranging from far infrared (FIR) to ultraviolet (UV) arising from the ground state alignment.

•proposing new acceleration mechanism for dust grains, demonstrating that turbulence dominates the dynamics of dust grains, applying the model to the grain size distribution and extinctions in both galactic and extragalactic environments.