One can then imagine an initial situation with no velocity field and a magnetic field only present at two wavevectors p and q . We assume a fully helical magnetic field, which means that it saturates the realizability condition: | H ^ ^ p M | = 2 E p M | p | and | H ^ ^ q M | = 2 E q M | q | . Assuming that all the energy and magnetic helicity transfers are done to another wavevector k , the conservation of magnetic helicity on the one hand and of the total energy E T = E M + E K (the sum of magnetic and kinetic energy) on the other hand gives: