Effects of different slow wave structures and finite magnetic field on microwave emission in a BWO

Summary form only given. In a backward wave oscillator (BWO) an electron beam, guided by a strong applied magnetic field flows into a waveguide with periodic ripple imposed on its wall. The periodic ripple in the waveguide causes oscillations in the electron beam to grow and allows high power microwave radiation to be extracted. Although a variety of slow wave structures have been used to produce high power microwaves in BWOs. No systematic study has been done to determine the effects of the shape of slow wave structure. We have carried out computer simulations, using the PIC code MAGIC, to study these effects by using sinusoidal, square well. And saw tooth ripple structures along the waveguide. Electrons an emitted as a beam at the entrance of the waveguide at a fraction of the space charge limiting current with energy on the order of 1 MeV. Ripple amplitudes are set less than 5 mm with a period of between 5 mm to 15 mm. The waveguide has typical radius between 10 mm to 25 mm. Preliminary results suggest that in smoothly varying ripples, such as sinusoidal ripples, less output microwave power is produced than in angular structures, such as square well ripples. Since the UNM long-pulse BWO experiment has produced higher output microwave power by using nonuniform slow wave structures, particle simulations have also been carried out to examine effects of shape of nonuniform structure as well.