The ambipolarity paradox in toroidal diffusion, revisited

The radial current in an axisymmetric toroidal plasma is shown to damp away because of parallel ion viscosity on the ion-ion collision time scale. After this transient phase, the electrostatic potential is quasi-statically related to the toroidal angular momentum of each flux surface, and the cross-field particle fluxes are ambipolar and independent of the radial electric field.