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The improvement of the beam–wave interaction efficiency of the sheet beam extended interaction oscillator (SBEIO) is studied and presented in this article. A novel multi-parameter optimization scheme is developed, which is based on the simulated annealing global optimization algorithm, the nonlinear theory, and 3-D simulations, including the axial electric field distribution and the distances between each gap. The 3-D particle-in-cell (PIC) simulations are performed to verify the scheme. A $\textit {Ka}$ -band SBEIO with nine gaps is optimized with a 36.25-kV and 3.5-A electron beam. The final optimized efficiency obtained from the developed code is 31%, which shows a good agreement with the 32.6% results of the PIC simulation. Compared with the uniform axial electric field distribution, the optimized design increased the efficiency from 15.8% to 32.6%. [ABSTRACT FROM AUTHOR]

RF circuit design, thermal analysis, fabrication, and measurement of a continuous wave (CW) high-power sheet beam traveling wave tube (SB-TWT) operating in the Ku-band were demonstrated in this paper. The slow wave structure circuit was constructed by double staggered grating waveguides (DSGWs), and the lossy dielectrics attached in the H-plane were applied to suppress parasitic oscillations. The Particle-in-cell simulation predicted that the CW SB-TWT can provide >20-kW output power in the band range of 16.2–18.5 GHz, with a maximum small signal gain of 38 dB. Microchannel cooling, which has been proved to be an efficient cooling method for microelectronic chip, very large scale integration, and power electronic modules with very high heat flux were introduced to improve the thermal capacity and heat dissipation ability. A thermal analysis of the RF circuit considering attenuated losses and electrons interception was studied in detail. Investigation shows that the RF circuit can operate with maximum $\sim 1$ -kW dielectric loss power (1.5 times of the loss power generated from the saturated output power at center frequency) and a maximum of 7% interception of electrons. Furthermore, an interaction circuit, including 23 DSGWs implanted with BeO–SiC to provide necessary attenuation, was fabricated and cold tested. Vector network analyzer RF measurement shows excellent performance and agrees very well with our prediction. [ABSTRACT FROM AUTHOR]