The flow of e+e− plasma ejected by an axisymmetrically rotating magnetized neutron star is considered in a hydrodynamical approximation. It is shown that in the vicinity of the light cylinder a helical discontinuity is formed. The transformation of toroidal magnetic field energy into plasma energy takes place at this discontinuity. Particles are accelerated to an energy of 10TeV for a neutron star with the characteristics of the Crab pulsar.