Seminar Series

Magnetised turbulence and the nonlinear dynamics of Alfvén waves in weakly collisional plasmas

Speaker

Jonathan Squire

Institute

PhD (Princeton), Sherman Fairchild Postdoctoral Scholar in Theoretical Physics with Caltech

Time & Place

Fri, 03 Feb 2017 11:00:00 NZDT in Rutherford 531, Level 5

All are welcome

Abstract

Magnetised turbulence is fundamental to a wide variety of geophysical and astrophysical processes, from the Earth's magnetic field to the magnetisation of the universe on the largest scales. Further, it differs enormously from neutral fluid turbulence in some situations. In this talk, I explore some of the intriguing behaviour that occurs as the scale of plasma motions decreases below the particle mean free path. Under such conditions, the temperature can have different values in the directions perpendicular and parallel to the magnetic field. This temperature anisotropy is coupled to the magnetic field, and if it grows too large the plasma erupts in a sea of micro-instabilities. Such behaviour has dramatic consequences for the most fundamental low-frequency plasma wave -- the shear-Alfvén wave. When the wave's amplitude is large, the changing magnetic field generates a temperature anisotropy that removes the wave's restoring force. The result is the sudden damping of plasma motions and bizarre zig-zag structures in the magnetic field. I will conclude with recent evidence for this effect in spacecraft data and a discussion of the implications for turbulence in collisionless plasmas.