Diocotron and Kelvin mode damping from a flux through the critical layer.

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.

Chaotic neoclassical separatrix dissipation in parametric drift-wave decay.

Experiments and theory characterize a parametric decay instability between plasma drift waves when the nonlinear coupling is modified by an electrostatic barrier. Novel mode coupling terms representing enhanced dissipation and mode phase shifts are caused by chaotic separatrix crossings on the wave-ruffled separatrix. Experimental determination of these coupling terms is in broad agreement with new chaotic neoclassical transport analyses.

Chaotic transport and damping from θ-ruffled separatrices.

Variations in magnetic or electrostatic confinement fields give rise to trapping separatrices, and neoclassical transport theory analyzes effects from collision-induced separatrix crossings. Experiments on pure electron plasmas now quantitatively characterize a broad range of transport and wave damping effects due to "chaotic" separatrix crossings, which occur due to equilibrium plasma rotation across θ-ruffled separatrices, and due to wave-induced separatrix fluctuations.

Resonant drift-wave coupling modified by nonlinear separatrix dissipation.

Resonant drift-wave coupling experiments characterize a new dissipative coupling term caused by a trapping separatrix. The system is a cylindrical pure-electron plasma with an axial trapping separatrix generated by an applied theta-symmetric wall voltage. The resonant decay of m_{theta}=2 diocotron modes into m_{theta}=1 trapped-particle diocotron modes is measured and compared to parametric mode coupling theory. Experiments quantify the traditional nonlinear mode coupling term, plus a new separatrix-generated dissipative coupling term which is not yet characterized theoretically.

Trapped-particle-mediated collisional damping of nonaxisymmetric plasma waves.

Weak axial variations in magnetic or electric confinement fields in pure electron plasmas cause slow electrons to be trapped locally, and collisional diffusion across the trapping separatrix then causes surprisingly large trapped-particle-mediated (TPM) damping and transport effects. Here we characterize TPM damping of m theta not equal to 0, m(z) = +/-1 Trivelpiece-Gould plasma modes in large-amplitude long-lived Bernstein-Greene-Kruskal states. The TPM damping gives gammaBGK/omega approximately 10(-4) and seems to dominate in regimes of weak interparticle collisions.

Damping of the trapped-particle diocotron mode.

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.

Trapped-particle modes and asymmetry-induced transport in single-species plasmas.

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 asymmetry modes in single-species plasmas.

Novel trapped-particle asymmetry modes propagate on cylindrical electron columns when axial variations in the wall voltage cause particle trapping. These modes consist of E x B drifts of edge-trapped particles, partially shielded by axial flows of interior untrapped particles. A simple model agrees well with the observed frequencies and eigenfunctions, but the strong mode damping is as yet unexplained. These modes may be important in coupling trap asymmetries to particle motions and low frequency E x B drift modes.