The ripple-averaged kinetic theory of neoclassical transport inmultiple-helicity stellarators is presented anew, using a formulation whichameliorates several shortcomings of the conventional approach. Inparticular, during the averaging procedure the usual simplifyingassumptions of symmetric local ripples and `small' rotational transform perfield period are avoided through an appropriate choice of coordinate systemand local model for the magnetic field strength; averages are trulyperformed along a field line and not along the toroidal-angle coordinate,as is common. Phase space divides naturally into three portions inwhich particles are (1) locally trapped, (2) locally reflected but nottrapped, and (3) locally passing; the second of these is lacking in the conventionaldescription. As an example of the theory's many possible applications, themonoenergetic radial transport coefficient in the asymptotic 1/ν regimeis derived and radial profiles of this quantity are determined for theLarge Helical Device and Wendelstein 7-X. The results are compared withthose obtained using the conventional approach; significant differences arefound in the case of Wendelstein 7-X and verified numerically usingthe Drift Kinetic Equation Solver (DKES).
A model magnetic field for the calculation of particle-drift motions in a toroidal stellarator