Two dimensional, stationary, magnetic structures are described by the balance of pressure forces and magnetic forces, i.e.: ∇ ∇ p = j × × B , where p is the plasma pressure and j is the electric current. It is known that p is a constant along any field line, (again since ∇ ∇ p is everywhere perpendicular to B). Additionally, the two-dimensional assumption ( ∂ ∂ ∂ ∂ z = 0 ) means that the z- component of the left hand side must be zero, so the z-component of the magnetic force on the right hand side must also be zero. This means that j ⊥ ⊥ × × B ⊥ ⊥ = 0 , i.e. j ⊥ ⊥ is parallel to B ⊥ ⊥ .