Suppression of vortex splitting due to spatial Landau damping in elliptical pure electron plasmas

Experiments and numerical simulations are conducted to study how initially elliptical, two-dimensional E×B vortices in magnetized, non-neutral electron plasmas can split into multiple pieces. We show that for vortices with realistic, smooth edges, the lowest aspect ratio at which splitting occurs is up to twice as large as that predicted by the commonly used vortex-patch model with infinite edge vorticity gradient. The experiments are conducted in a regime where the drift dynamics are isomorphic to the 2D Euler equations describing ideal fluids. High-aspect-ratio elliptical vortices are prepared using strong external E×B strain flows, then the strain is removed and the vortices allowed to relax freely. Splitting occurs at sufficiently large aspect ratio due to growth of the Love instability, the elliptical counterpart of the Kelvin-Helmholtz instability. The aspect ratio splitting threshold for smooth vortices is increased due to spatial Landau damping, a wave-particle resonance associated with the finite vorticity gradient which causes the vortex aspect ratio to decrease over time, and thus stabilizes the Love modes before splitting can occur. These results lend deeper insight into vortex splitting phenomena observed in planetary atmospheres, and possibly in drift-wave eddies in tokamaks.