Linear analysis of corrugated-wall waveguides driven by annular beam with finite-strength guiding magnetic field

Corrugated-wall waveguides have been widely used in Backward-Wave Oscillators (BWOs) which are commonly drove by annular beam with certain thickness. With finite-strength guiding magnetic field the beam region tends to be dispersive medium and the dielectric tensor makes the axial RF electric field correlative with RF magnetic field even under axisymmetric mode. The linear dispersion relation is obtained according to the described condition by expressing the fields in the beam region as coupled ordinary and extra-ordinary modes. Numerical analysis is carried out using the parameters of a BWO which has been studied in UESTC [1], from which series of the complex angular frequencies assuming real wave number are obtained by varying the magnetic field. Comparison is made with the reported result [2]. The results also show the cyclotron absorption during certain range of the magnetic field.