In the presence of a vertical magnetic field, the rotating disk generates an electromotive force which drives a current. The current generates a field which amplifies the existing field. The seed field can then be turned off and the system will be self-sustaining. This process is called a (disk) dynamo. Let be the seed voltage, then
(in MKS) where v is the speed of the disk, B is the magnetic field, and r is the radius of the disk. The current is then
where R is the resistance of the disk. This current creates a magnetic field
where is the permeability of free space, which will be self sustaining if
Alpha Effect, Dynamo Equation, Frozen Flux Approximation, Omega Effect
