Axisymmetric magnetic flux surface ($\psi =\mathrm{constant}$)

A regular level surface of the axisymmetric poloidal magnetic flux function contains both the poloidal and toroidal magnetic field directions. Conservation along field lines can be expressed locally as a function of the flux label on connected regular surfaces. Degenerate points with no poloidal magnetic field and disconnected branches with the same label require separate treatment.