Chaos generated pinch effect in toroidal confinement devices

Particle transport in a toroidal plasma confinement device is shown to be nondiffusive when magnetic chaos is present. A phenomenological fit to density profiles gives a diffusion constant and also a pinch velocity directed up the density gradient. We show that the combination of diffusion and pinch is actually an expression of the nonlocal, subdiffusive nature of the transport. The effect is illustrated by numerical modelling of the magnetic structure and associated particle transport in conditions relevant for the reversed-field pinch experiment at the Consorzio RFX, Padova, Italy [G. Rostagni, Fusion Eng. Des. 25, 301 (1995)]. The relevance of this result is quite general, and could be applied also to other systems with chaos induced particle transport, such as electron transport in the tokamak.