Dynamics of electron plasma vortices subject to time-dependent external strain flows*

The behavior of two-dimensional (2D) vortices in response to time-dependent strain flows is studied experimentally using pure electron plasmas. These plasmas obey guiding-center drift dynamics in the plane perpendicular to the magnetic field which are isomorphic to the dynamics of a 2D inviscid, incompressible fluid, where electron density plays the role of fluid vorticity [1]. External strain flows are applied by imposing a time-dependent, quadrupolar boundary condition on the circular container [2]. The experiments focus on dynamical orbits of the vortices [3] and shear instabilities which occur when the vortices are highly distorted [4]. Vortex-in-cell simulations are carried out to complement the experimental data. These studies are potentially relevant to a variety of quasi-2D fluid systems, including geophysical fluids, astrophysical disks, and magnetically confined plasmas.
[1] C. F. Driscoll and K. S. Fine, Phys. Fluids B 2, 1359 (1990)
[2] N. C. Hurst, et. al., Phys. Rev. Lett. 117, 235001 (2016) and J. Fluid Mech. 848, 256-287 (2018)
[3] S. Kida, J. Phys. Soc. Japan 50, 3517 (1981)
[4] D. G. Dritschel, et. al., J. Fluid Mech. 230, 647-665 (1991)