Planar anti-dynamo theorem (source code)

= Planar anti-dynamo theorem

In the standard two-dimensional setting, with planar <velocity> and <magnetic field> independent of the third coordinate and homogeneous energy-closed boundary conditions, the in-plane magnetic potential is an advected diffusing scalar. Its quadratic integral decreases, preventing regeneration of a dynamo field. A third field component independent of that coordinate also obeys a passive advection-diffusion equation. A flow depending on two coordinates but possessing a third velocity component is not covered by this strictly planar formulation.