Fridays at 12:30pm, Dome Room, Peyton Hall
Next seminar: October 23rd 2020
Turbulence, Dynamo, and Dissipation in Magnetized, Weakly Collisional Astrophysical Plasmas
Prof. Matthew Kunz (Princeton)
Abstract: The transport of energy and momentum, the amplification and sustenance of magnetic fields, and the heating of plasma particles by waves and turbulence are key ingredients in many problems at the frontiers of heliospheric and astrophysics research. This includes the heating and acceleration of the solar wind; the observational appearance of black-hole accretion flows on event-horizon scales; and the properties of the hot, dilute plasma that fills dark-matter halos. All of these plasmas are magnetized and weakly collisional, with plasma beta parameters of order unity or even much larger (“high-beta”). In this regime, deviations from local thermodynamic equilibrium ("pressure anisotropies") and the kinetic instabilities they excite can dramatically change the material properties of such plasmas and thereby influence the macroscopic evolution of their host systems. I will highlight selected results from an ongoing program of calculations aimed at elucidating from first principles the physics of waves, turbulence, heating, and transport under these conditions. Three key results will be featured. (1) Turbulent amplification of magnetic fields is possible, efficient, and likely self-accelerating in weakly collisional plasmas such as the intracluster medium (ICM). (2) Pressure anisotropies generated either by fluctuations (as in the ICM) or by global expansion (as in the solar wind) qualitatively change the properties of magnetized turbulence by triggering kinetic instabilities, reducing the plasma viscosity, and altering the so-called “critical balance”. (3) Thermal disequilibration of ions and electrons is a generic outcome of magnetized, collisionless turbulence, with ions receiving a majority of the cascaded energy for beta >~ 1. In the waning minutes of the talk, I will advertise (briefly!) our group's ongoing efforts to understand the role of magnetic reconnection in the turbulent dynamo, the nature of collisionless heat conduction and convection, and the formation and evolution of protostellar accretion disks..