this page is about helicity in magnetic fields. For fluid mechanical helicity, see helicity
In electromagnetism, magnetic helicity is the extent to which a magnetic field "wraps around itself". If magnetic field lines follow the strands of a twisted rope, this configuration would have nonzero magnetic helicity; left handed ropes would have negative values and right handed ropes would have positive values.
Formally,
where
is the magnetic field strength
Where 
is the vector potential of
Magnetic helicity is a conserved quantity. It is conserved in electromagnetic fields, even when magnetic reconnection dissipates energy. The concept is useful when considering solar dynamics.
