Topology of plasma equilibria and the current closure condition.

A virtually complete description of the topology of stationary incompressible Euler flows and the magnetic field satisfying the magnetostatic equation is given by a theorem due to Arnol'd. We apply this theorem to describe the topology of stationary states of plasmas with significant fluid flow, obeying the Hall magnetohydrodynamics model equations. In the context of the integrability (nonchaotic topology) of the magnetic and velocity fields, we discuss the validity of conditions analogous to that of Greene and Johnson, which, in the case of magnetostatic equations, states that the line integral dl/B is the same for each closed magnetic field line on a given magnetic surface. We also show how this property follows from the existence of a continuous volume-preserving symmetry of the magnetic field.