"Cosmic Magnetism and Plasma Microphysics (or, I get by with help from my little friends)"

The Universe is magnetized. While magnetic-field strengths of just ~10^{-18} G are required to achieve this both in our Galaxy and in clusters of galaxies, observations of Faraday rotation, Zeeman splitting, and synchrotron emission all make the case of ubiquitous ~μG fields. That these systems are not content with hosting weaker fields is surprising, at least until one realizes that the energy density of a ~μG field is comparable to that of the observed turbulent motions. It is then natural to attribute the amplification and sustenance of (at least the random component of) the interstellar and intracluster magnetic fields to the fluctuation (or “turbulent”) dynamo. In this talk, we will explore the various ways in which plasma microphysics makes magnetic-field amplification in weakly collisional plasmas by macroscale turbulent motions possible, with application to the intracluster medium of galaxy clusters. Connections with the plasma physics of the collisionless solar wind and of radiatively inefficient black-hole accretion flows will also be made.