Helical Plasma Confinement Devices with Good Confinement Properties

The criterion of approximate omnigeneity (i.e., having bounce-averaged drift lying within the magnetic surfaces) is much easier to satisfy than quasihelicity, the condition that B, the magnitude of the magnetic field, is a function of only a single linear combination of the toroidal angles. Simple criteria for omnigeneity are presented and used to construct exactly omnigenous forms for B that are far from quasihelical. Though this construction gives a nonanalytic function B, close to the constructed systems there exist other systems with analytic B. These results indicate that finding helical plasma confinement systems with minimal neoclassical transport is much easier than previously believed.