Chaotic Neo-Classical Transport and Damping

A novel {\it chaotic} form of Neo-Classical Transport has now been characterized experimentally and theoretically, as distinct from the traditional {\it collisional} NCT. Experimentally, an electrostatic or magnetic trapping separatrix is applied to pure electron plasma columns, and this separatrix is given controlled $\cos (m \theta )$ variations (ruffles). Equilibrium plasma drift rotation across the ruffles then causes dissipative separatrix crossings, giving enhanced particle transport and wave damping. Similar chaotic separatrix effects occur from wave-induced separatrix $\theta$-ruffles and temporal variations. For spatially separated trapping regions (``superbanana'' regime), traditional NCT scales with collisionality $\nu$ as $\nu^{1/2} B^{- 1/2}$, whereas the chaotic NCT scales as $\nu^0 B^{-1}$. Fortunately, the chaotic particle transport has a distinctive $\sin^2 ( \alpha )$ signature, where $\alpha$ is the angle between the $\theta$-ruffle and the global $\theta$-asymmetry (error field) which drives the transport. Quantitative correspondence with theory has now been obtained for particle transport, diocotron (drift) wave damping, and dissipative wave-wave couplings; also observed is chaotic damping of higher frequency Langmuir waves. This chaotic separatrix dissipation may occur in low-collisionality stellarator and tokamak plasmas also.