Fig. 1. Cavity structure and its internal field distribution

Fig. 2. Resonant frequency and Q factor versus length of uniform section

Fig. 3. Coupling coefficient of working mode and its neighboring modes

Fig. 4. Starting current of working mode and its neighboring modes

Fig. 5. Results of multimode time domain calculation (a) Output power versus magnetic field and beam current, (b) Output frequency versus magnetic field and beam current

Fig. 6. Output power of each mode versus time at B=5.3 T

Fig. 7. Magnetic field distribution of the superconducting magnet

Fig. 8. Trajectory of electron beam in the gun

Fig. 9. Emitted beam current versus time

Fig. 10. Velocity ratio and longitude velocity spread versus voltage between A-K gap

Fig. 11. Electrical field distribution of TE73 mode at the input port of prebunching launcher

Fig. 12. Simulation results of beam propagation (a) left view of electric field amplitude distribution in the tube, (b) electric field amplitude distribution in output window plane

Fig. 13. Reflection coefficient and transmission coefficient of output window

Fig. 14. Overall diagram of experimental system (left) and picture of gyrotron (right)

Fig. 15. Output microwave beam spot obtained by thermal paper

Fig. 16. Comparison of starting current curves between experimental test and theoretical calculation

Fig. 17. Signal waveform monitored by oscilloscope, in which the yellow line is voltage on cathode with detection ratio of 2 000: 1, the green line is emission current with detection ratio of 1: 1, the blue line is microwave signal on the detector, the red line is IF signal of harmonic mixer

Fig. 18. Variation of microwave frequency (a) frequency versus magnetic field, (b) frequency versus beam current

Fig. 19. Output power versus magnetic field

Fig. 20. Oscillograph monitoring waveform and power measurement results of continuous operation for 1 minute, in which the blue line is the cathode high voltage, with the proportion of 2 000: 1, the red line is the detector signal output by the geophone, the green line is the emission beam current, with the proportion of 0.6: 1

Fig. 21. power measurement results of continuous operation for 1 minute

Fig. 22. The current waveform of electron beam intercepted by the modulation anode

Fig. 23. The current waveform of electron beam intercepted by the second anode