Power enhancement of a Doppler-frequency-up-shift scattered wave by a relativistic electron beam drifting in a reversed, tapered axial guide magnetic field

A transverse-electric (TE) wave with a Doppler-upshift frequency may be excited when a backward wave is scattered by a relativistic electron beam. Credible three-dimensional nonlinear simulations are presented to demonstrate the power enhancement of the scattered wave by making use of a properly reversed, tapered axial guide magnetic field. The influences of the taper slope and the taper starting point of the reversed axial guide magnetic field on the power of radiation fields are discussed. Simulations show that the peak power of 93 kW at a wavelength of 3 mm observed in a recent experiment could be increased up to 500 kW through the proposed method. Compared to the case of a tapered positive guide magnetic field, the method studied in the present paper is more effective to enhance the power of the scattered wave.