Existence of quasihelically symmetric stellarators

Quasihelically symmetric stellarators are nonaxisymmetric, toroidal configurations in which the strength of the magnetic field depends on only one angular coordinate, instead of two, within the constant pressure surfaces. The confinement properties of these configurations are similar to those of axisymmetric tokamaks. Although stellarators with exact quasihelical symmetry are proven not to exist, good approximations can be found.