Breaking of rotational symmetry in cylindrically bounded 2D electron plasmas and 2D fluids.

Off-axis final states of cylindrically bounded 2D fluids can develop from initially unstable, but cylindrically symmetric, 2D vorticity distributions. Experiments with electrons in a Malmberg-Penning trap, as well as 2D fluid simulations, demonstrated that such states result when the initial vorticity distribution is close to the boundary, while less extended distributions lead to on-axis states. A simple thermodynamic model, maximizing the entropy of a state consisting of a diffuse background surrounding a strong coherent vortex, is shown to quantitatively predict this bifurcation, while conserving circulation, angular momentum, and energy.

Decay of the diocotron rotation and transport in a new low-density asymmetry-dominated regime.

The decay of the diocotron rotation was studied in a new regime in which trap asymmetries dominate. Decay within a few diocotron periods was observed, sometimes orders of magnitude faster than predicted by the traditional "rotational pumping" theory. The decay does not conserve angular momentum, and is strongest for small, low-density columns.