Inviscid damping of the m=2 mode on a two-dimensional vortex subject to a strain flow

Inviscid damping is an important process in the dynamics of rotating vortices that leads to axisymmetry in isolation, or to an elliptical steady state in the presence of an external strain field. Here, relaxation of the m=2 mode of a two-dimensional vortex under external strain is studied using an electron plasma in Penning-Malmberg trap. The ExB motion of the plasma is analogous to the dynamics of a rotating vortex in a 2D inviscid, incompressible fluid. Eight-sector electrodes are used to apply an external ExB strain flow. Without strain, a perturbed vortex with a smoothly decreasing profile exterior to the core can undergo inviscid spatial Landau damping. A novel technique to control the smoothness of the vorticity profile is described, and the effect of angularly asymmetric initial condition on mode damping is studied. Trapping oscillations and the formation of cat's eye patterns in phase space are observed. These dynamics are studied in the presence of strain. The effect of external strain on the mode decay rate, rotation frequency of the mode about equilibrium, and trapping oscillations will be discussed. These results are compared to particle-in-cell simulations and available theoretical results.