A new asymmetry-induced transport mechanism in pure electron plasmas is shown to be proportional to the damping rate of the corresponding trapped-particle mode, with simple scalings for all other parameters. This transport occurs when axial particle trapping exists due to variations in the electric or magnetic confinement fields. This new transport is strong for even weak unintentional trapping (deltaB/B approximately 10(-3)), and may be prevalent in transport experiments with magnetic or electrostatic theta asymmetries.

Trapped particle modes and the associated asymmetry-induced transport are characterized experimentally in cylindrical electron plasmas. Axial variations in the electric or magnetic confinement fields cause the particle trapping, and enable the E×B drift trapped-particle modes. Collisional diffusion across the trapping separatrix causes the modes to damp, and causes bulk radial transport when the confinement fields also have θ asymmetries. The measured asymmetry-induced transport rates are directly proportional to the measured mode damping rates, with simple scalings for all other plasma parameters. Significant transport is observed for even weak trapping fields (δB/B∼10−3), possibly explaining the “anomalous” background transport observed so ubiquitously in single species plasmas.

The fluid motion of Eq. (3) is written in a form that inadvertently omits a contribution from the rise in the trapped (and the fall in the untrapped) particle density at the interface between trapped and untrapped particles (i.e., at r r s ). The equation should readwhere the trapped and untrapped densities are written in terms of Heaviside step functions Q as follows:and n u ͑r͒ n 0 ͑r͒Q͑r s 2 r͒ .The dispersion relation of Eq. (4) for top hat density profiles [n 0 ͑r͒ n 0 Q͑R p 2 r͒] then becomes µ R p r swhere I m ϵ I m ͑r s ͞l D ͒ are modified Bessel functions of the first kind and f 0 ϵ m 2 f͞f E . This new dispersion relation has two solutions, with only the lower frequency solution being relevant here. The remaining discussion and results in the paper are not affected by this correction, since the two dispersion relations are equivalent in the limit of l D ! 0, and the correct equation was used in the kinetic treatment for comparison to experiments.

Experiments and theory characterize a novel type of spatial Landau damping, caused by a flux of particles through the wave or rotation resonance (critical) layer. Pure electron plasma experiments demonstrate that a steady flux of particles causes algebraic damping of diocotron mode amplitudes for azimuthal modes m = 1 and m = 2, and a simple model of dynamics in the nonlinear cat's eye clarifies the observations. This flux-driven algebraic damping is related to, but distinct from, the exponential decay characteristic of Landau damping. This flux-driven damping applies also to Kelvin waves on 2D vortices, and so may be broadly relevant to plasmas and geophysical flows.

The damping mechanism of a recently discovered trapped-particle mode is identified as collisional velocity scattering of marginally trapped particles. The mode exists on non-neutral plasma columns that are partially divided by an electrostatic potential. This damping mechanism is similar to that responsible for damping of the dissipative trapped-ion mode. The damping rate is calculated using a Fokker-Planck analysis and agrees with measurement to within 50%. Also, an experimental signature confirms a causal relation between scattering of marginally trapped particles and damping.