地球物理和天体物理流体力学系列讲座

报告题目：New perspectives on helical and nonhelical large-scale dynamos

报告人：周竑喆 博士(李政道研究所)

报告地点: 三楼中会议室

报告时间：2024年 12 月 13 日（周五） 上午10:00

腾讯会议: 656-580-793

报告摘要：

Magnetic fields are ubiquitous in astrophysical systems, with notable examples including planets, the Sun, galaxies, and accretion disks in AGNs and X-ray binaries. The amplification of magnetic fields on scales larger than the turbulence scale is driven by a process known as the large-scale dynamo (LSD). Traditionally, LSDs rely on the presence of a net kinetic helicity, i.e., the alignment between the velocity and the vorticity fields. However, whether this mechanism remains efficient at the very high magnetic Reynolds numbers (Rm) relevant to astrophysical conditions has been a long-standing question. More recently, a novel type of LSD has been identified that operates without requiring kinetic helicity, though its underlying mechanism remains unclear. In this talk, I will present our recent findings on (i) the behavior of helical LSDs at high Rm, and (ii) the mechanisms driving nonhelical LSDs. I will also briefly discuss their implications for accretion disk magnetization and variability in AGNs.