Fluid helicity and dynamo effect

Using the incompressible magnetohydrodynamic equations, we have numerically studied the dynamo effect in electrically conducting fluids. The necessary energy input into the system was modeled either by an explicit forcing ter m in the Navier-Stokes equation or fully selfconsistently by thermal convec tion in a fluid layer heated from below. If the fluid motion is capable of dynamo action, the dynamo effect appears in the form of a phase transition or bifurcation at some critical strength of the forcing. Both the dynamo bi furcation and subsequent bifurcations that occur when the strength of the f orcing is further raised were studied, including the transition to chaotic states. Special attention was paid to the helicity of the flow as well as t o the symmetries of the system and symmetry breaking in the bifurcations. T he magnetic field tends to be accumulated in special regions of the flow, n otably in the vicinity of stagnation points or near the boundaries of conve ction cells.