Neoclassical transport in the helical Reversed-field pinch

In this work we study particle transport in the Reversed-Field Pinch magnetic field topology. The guiding centre test particle code \textsc{Orbit} is used. We find that passing particles, which in the chaotic multiple helicity (MH) state experience long-correlation L\'{e}vy flights, in the low-chaos, Single Helical Axis (SHAx) regime~\footnote{R.Lorenzini, E.Martines, P.Piovesan \emph{et al}, Nature Physics in press} remain well confined within magnetic surfaces. Residual diffusion is given by trapped particles and the associated neoclassical diffusion coefficient $D$ is explored as a function of collisionality. Helically trapped (superbanana) particles appear to provide negligible contribution~\footnote{M. E. Puiatti, In {\em Proc. of the 36$^{\mathrm th}$ EPS Conference on Controlled Fusion and Plasma Physics, Sofia (Bulgaria), 29 June- 3 July, 2009}}. As a result, we recover the classical Tokamak and Stellarator transition from the banana to the plateau and Pfirsch-Schl\"uter regimes, but without the $1/\nu$ dependence at low collisionality which is typical of the un-optimized stellarator.