Asymmetric vortex merger:: Experiments and simulations

The two-dimensional (2-D) merging of an intense, pointlike vortex with a diffuse, extended vortex is investigated with experiments using strongly magnetized electron columns in a Malmberg-Penning trap, and with numerical simulations using a 2-D particle-in-cell code. The study is restricted to highly nonlinear conditions, where the perturbative approach does not apply. A very good agreement between experiment and simulation is obtained. The pointlike vortex wraps the extended vortex about itself, moving toward the center of the system during the process. The interaction generates filaments of zero vorticity within the extended vortex that subsequently evolve into vorticity holes. During the evolution, energy is fed to the extended vortex from the background curl-free flow via the stirring action of the pointlike vortex, whose energy remains approximately constant. (C) 2001 American Institute of Physics.