DYNAMOS DRIVEN BY POLOIDAL FLOW EXIST

We have discovered a class of dynamos driven by purely poloidal fluid motion, thereby demonstrating that toroidal motion is not essential fo r dynamo action and that there is no counterpart to the anti-dynamo th eorem that purely toroidal motions cannot generate magnetic fields. Th e fully three-dimensional (3D) dynamo action of these models results f rom the pushing and twisting of magnetic field lines by helical motion ill a manner akin to the alpha(2) mechanism of mean-field electrodyna mics. No dynamo with dipole symmetry was found for an axisymmetric dis tribution of helicity; indeed, some azimuthal variation in helicity is required. Among the suite of dynamos that we have investigated, the p oloidal flow dynamo with the smallest critical magnetic Reynolds numbe r is very nearly the dynamo with the most nonaxisymmetric distribution of helicity.