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We show that in perfectly quasi-isodynamic magnetic fields, which aregenerally non-quasisymmetric and which can approximate fields of experimentalinterest, neoclassical calculations can be carried out analytically morecompletely than in a general stellarator. Here, we define a quasi-isodynamicfield to be one in which the longitudinal adiabatic invariant is a fluxfunction and in which the constant-B contours close poloidally. We first deriveseveral geometric relations among the magnetic field components and the fieldstrength. Using these relations, the forms of the flow and current are obtainedfor arbitrary collisionality. The flow, radial electric field, and bootstrapcurrent are also determined explicitly for the long-mean-free-path regime.

Geometry and neoclassical theory in a quasi-isodynamic stellarator