  Salient features of the remarkable band structure seen in the high-frequency
interpulse of the Crab pulsar are summarized. It is argued that its source must
lie in a current sheet, probably coincident with the open-closed magnetosphere
separatrix, and that the mechanism is a form of one-pass free-electron laser.
An outward moving electron component in the current sheet interacts with the
longitudinal electric field of an inward directed ion-proton Lamgmuir mode. The
band structure is then a natural consequence of the differing charge-to-mass
ratios of the ions, which are a return current component of those accelerated,
as in almost all pulsars, from the polar cap to the light cylinder.
