Asymmetric vortex merger: Experiments and simulations

The two-dimensional (2-D) merging of an intense, pointlike vortex with a di ffuse, extended vortex is investigated with experiments using strongly magn etized electron columns in a Malmberg-Penning trap, and with numerical simu lations using a 2-D particle-in-cell code. The study is restricted to highl y nonlinear conditions, where the perturbative approach does not apply. A v ery good agreement between experiment and simulation is obtained. The point like vortex wraps the extended vortex about itself, moving toward the cente r of the system during the process. The interaction generates filaments of zero vorticity within the extended vortex that subsequently evolve into vor ticity holes. During the evolution, energy is fed to the extended vortex fr om the background curl-free flow via the stirring action of the pointlike v ortex, whose energy remains approximately constant. (C) 2001 American Insti tute of Physics.