Measurements of symmetric vortex merger

Magnetically confined columns of electrons are excellent experimental realizations of extended two-dimensional vortices in an inviscid fluid. Here, we consider two nearly identical vortices orbiting around one another inside a cylindrical wall. The vortices merge symmetrically, in a time which varies from less than 1 to about 10⁴ orbit periods as the vortex separation is increased by 30%. We have obtained images of the vorticity distribution during this merger process, and observe filamentary tails and mixing. These experimental results are consistent with analytic models and numerical simulations.