MAGNETIC-FIELD EFFECTS IN A FREE-ELECTRON LASER WITH LONGITUDINAL ELECTRIC WIGGLER

An analysis of the parametric instability which forms the basis for op eration of a ubitron-type free electron laser with a longitudinal elec tric wiggler is presented. Excitation of a space charge wave and a pre dominantly transverse magnetic waveguide mode results from passage of a relativistic electron beam through a static spatially periodic longi tudinal electric field. The beam is contained in a cylindrical metal w aveguide and an axial magnetic field of arbitrary magnitude. Effects o f the magnetic field on the growth rate, efficiency, radiation wavelen gth and the required pump wavelength are studied. Suitable values of t he magnitude of the magnetic field and other parameters for generating millimetre wavelength radiation are indicated.