Abstract
The longitudinal wiggler, beam interaction is a novel source of submillimeter wave radiation. It comprises a relativistic electron beam gyrating in a longitudinally rippled, periodic magnetic field of the form B = ẑ[B0+B1 sin(k0 z)], where k0 = 2π/l and l is the period. Axial and transverse electron density bunching gives rise to a convectively unstable wave that propagates along the guiding magnetic field ẑB0. Its growth rate has been computed for the case of a cold beam.