The second adiabatic invariant and neoclassical transport in stellarators

The second adiabatic invariant J∥ for locally trapped particles is used for calculating neoclassical transport in stellarators. A numerical method for calculating the variation of J∥ on a magnetic surface is developed, which allows one to make the calculations in an arbitrary stellarator magnetic field given in real-space coordinates without transforming the field to magnetic coordinates. Equations for neoclassical particle and energy fluxes for the 1/ν transport regime are derived, which are expressed through the variation of J∥. By making use of these method and equations, an evaluation of neoclassical transport properties is made for a real-space realization of quasihelical symmetry, which has been examined recently in magnetic coordinates.