The evolution of a strongly magnetized electron system is identical to that of an ideal two-dimensional ͑2-D͒ fluid; an electron column is equivalent to a fluid vortex. We have studied the stability of 2-D vortex patterns with electron columns confined in a Malmberg-Penning trap. The following cases are presented: the stability of N vortices arranged in a ring; the stability of N vortices arranged in a ring with a central vortex; the stability of more complicated vortex patterns.
We report the experimental dynamics of a new two-dimensional (2D) fluid phenomenon that occurs when an intense, pointlike vortex is placed within a diffuse, circular vortex. Our observations, made using strongly magnetized electron columns to model the 2D fluid, support the analysis performed by Jin and Dubin.
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.
Magnetized electron columns are a valuable experimental tool used to study two-dimensional ͑2D͒ fluid phenomena. Traditionally, the electrons have been generated with thermionic sources, typically limiting the initial electron distribution to one filled circle and thereby restricting the range of accessible fluid phenomena. Here, we describe a new electron source based on a cesium antimonide photocathode that can generate more complicated initial electron distributions. Experiments so far have focused on the stability of 2D vortex patterns.
Abstract. The merging of an intense localized vortex with an extended vortex is investigated by means of an experimental analysis performed on a Malmberg-Penning trap with photocathode, and numerical simulations with a two-dimensional (2D) particle in cell (PIC) code. The study is restricted to highly nonlinear conditions, where the perturbative approach does not hold. A very good agreement between experimental results and simulations is obtained. It is found that the localized vortex is firstly wrapped around by the extended vortex, then moves towards the center of the system, eventually approaching an almost stationary state of rotation characterized by the formation of vorticity holes. During the whole evolution the extended vortex gains energy from the field surrounding the vortices, while the energy of the localized vortex remains constant.
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