  At the end of their birth process, neutron stars can be subject to a
magnetorotational instability in which a conversion of kinetic energy of
differential rotation into radiation and kinetic energies is expected to occur
at the Alfv\'en timescale of few ms. This birth energy conversion predicts the
observed large velocity of neutron stars if during the evolving of this
instability the periods are of few ms and the magnetic fields reach values of
$10^{16}$G.
