Effect of collisionless detrapping on nonaxisymmetric transport in a stellarator with radial electric field

A derivation is given for expressions describing transport rates in a stellarator operating at low collisionality ν, in the presence of a radial electric field. It is shown that collisionless detrapping (and retrapping) of particles in superbanana orbits can substantially modify this transport. The detrapping provides a collisionless lower bound on the width of the collisional boundary layer which, in previous work, gave rise to transport coefficients scaling as ν1/2. With this lower bound, these coefficients will instead scale as ν, implying more favorable confinement than indicated by the ν1/2 result commonly employed.