On higher asymptotic analogs of the helicity invariant in MHD.
Peter M. Akhmetiev.

A new asymptotic invariant of magnetic field is constructed: a quadratic
(and polynomial) helicity. A high-order asymptotic invariant
of magnetic field is proposed. Various problems related with helicity are
discussed.

Codes MSC: 35Qxx, 57Mxx, 76Fxx.