Hamiltonian representation for helically symmetric magnetic fields

It is proved that one of the two potentials used in a standard representation of helically symmetric magnetic fields is a Hamiltonian that generates the magnetic lines of force. It is proved also that if the other potential is restricted to be proportional to this Hamiltonian, then the radial components of current density and magnetic field are proportional. This restriction applies, for example, to constant‐λ, helically symmetric, force‐free magnetic fields [j(r)=λB(r)] relevant to both fusion physics and astrophysics.