Force-Free Foliations
  Electromagnetic field configurations with vanishing Lorentz force density are known as force-free and appear in terrestrial, space, and astrophysical plasmas. We explore a general method for finding such configurations based on formulating equations for the field lines rather than the field itself. The basic object becomes a foliation of spacetime or, in the stationary axisymmetric case, of the half-plane. We use this approach to find some new stationary and axisymmetric solutions, one of which could represent a rotating plasma vortex near a magnetic null point. 
Geoffrey Comp\`ere, Samuel E. Gralla, Alexandru Lupsasca
math-ph astro-ph.HE gr-qc hep-th math.MP