Vortex dynamics of 2D electron plasmas

Electron columns confined magnetically in vacuum evolve in ðr; hÞ as N 10 field-aligned rods of charge, or point vortices. Neglecting discreteness, the column evolves as would vorticity in an inviscid, incompressible fluid, governed by the Euler equations. The macroscopic flow dynamics is readily imaged, including effects such as surface waves and inviscid damping, two vortex merger, and gradient-driven vortex motion. Turbulent initial states are observed to relax to ‘‘vortex crystal’’ meta-equlibria, due to vortex ‘‘cooling’’ from entropic mixing of background vorticity; and characteristics of this process are predicted by theory. The microscopic discreteness gives rise to point-vortex diffusion, which is strongly affected by the overall flow shear. Macroscopically and microscopically, the vortex dynamics depends critically on whether the vortex is prograde or retrograde with respect to the flow shear. 2001 Elsevier Science B.V. All rights reserved.