Potential symmetry and invariant solutions of Fokker-Planck equation in   cylindrical coordinates related to magnetic field diffusion in   magnetohydrodynamics including the Hall current
  Lie groups involving potential symmetries are applied in connection with the system of magnetohydrodynamic equations for incompressible matter with Ohm's law for finite resistivity and Hall current in cylindrical geometry. Some simplifications allow to obtain a Fokker-Planck type equation. Invariant solutions are obtained involving the effects of time-dependent flow and the Hall-current. Some interesting side results of this approach are new exact solutions that do not seem to have been reported in the literature. 
A. H. Khater, D. K. Callebaut, S. F. Abdul-Aziz and T. N. Abdelhameed