Study on Efficiency-Enhancing Mechanism for SB TWT by Evenly Distributing SWS Impedance

In this article, we propose a novel approach to enhance beam-wave interaction intensity in sheet beam (SB) traveling-wave tubes (TWTs). By reshaping previously reported nonquasi-2-D slow wave structure (NQSWS) from a cosine tunnel to an undulate-roofed tunnel, the interaction impedance distribution of the improved NQSWS is more uniform than that of the original NQSWS under the same tunnel area and average interaction impedance. Surprisingly, this evolution indeed leads to a significant boost in the TWT's output power and efficiency. Through PIC simulations under a voltage of 23.7 kV and current of 250 mA, the improved NQSWS TWT achieves a maximum average output power of 328 W and a 3-dB power bandwidth of 42 GHz. These results represent improvements of 35.5% in conversion efficiency and 16.7% in bandwidth compared to the original NQSWS. Furthermore, the improved NQSWS TWT has a lower beam expansion rate (BER) (about 50% reduction) and better beam transmission performance under equivalent magnetic field amplitude compared to the original NQSWS TWT, benefiting from more evenly distributed beam edge potentials. This efficiency-enhancing mechanism via pursuing better field uniformity could also be applied to other SB vacuum electronic devices (VEDs) to boost their performance, especially in millimeter-wave and terahertz region.