Fig. 1. Transversal electric field distribution ofTE06mode in the confocal waveguide overlaid with the distinct beamlets of annular electron beam

Fig. 2. Distribution of F0612along a line y=Rc/4 in the x-direction and y-axis

Fig. 3. Distribution of F0612 around the circle of Rb=1.12mm

Fig. 4. Cross section of cofocal waveguide with the misaligned electron beam

Fig. 5. The coupling factor with the increase of electron beam misalignment distance

Fig. 6. Gain with different electron beam misalignment versus frequency

Fig. 7. Critical current of absolute instability versus voltage

Fig. 8. Starting current of BWO versus length

Fig. 9. Coordinate system for gyrating electrons with misalignment in a confocal waveguide

Fig. 10. Axial distributions of output power with electron beam misalignment

Fig. 11. The beam-wave efficiency and the saturation length versus misalignment distance d

Fig. 12. Power versus frequency with electron beam misalignment

Fig. 13. Axial distributions of output power with velocity spread

Fig. 14. Power versus frequency with velocity spread and guiding center spread

Fig. 15. The power versus the electron beam misalignment distance