Analysis of reasonable diffraction loss rate in 220 GHz confocal waveguide gyro-TWT amplifier

An Chenxiang; Zhou Ning; Chen Kun; Wang Dengpan; Li Chong; Gui Youyou; Yang Yihang; Wang Junqing; Shi Yanchao

doi:10.11884/HPLPB202537.250041

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An Chenxiang, Zhou Ning, Chen Kun, et al. Analysis of reasonable diffraction loss rate in 220 GHz confocal waveguide gyro-TWT amplifier[J]. High Power Laser and Particle Beams. doi: 10.11884/HPLPB202537.250041

Citation:

An Chenxiang, Zhou Ning, Chen Kun, et al. Analysis of reasonable diffraction loss rate in 220 GHz confocal waveguide gyro-TWT amplifier[J]. High Power Laser and Particle Beams. doi: 10.11884/HPLPB202537.250041

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Analysis of reasonable diffraction loss rate in 220 GHz confocal waveguide gyro-TWT amplifier

doi: 10.11884/HPLPB202537.250041

Key Laboratory of Advanced Science and Technology on High Power Microwave, Northwest Institute of Nuclear Technology, Xi’an 710024, China

Received Date: 2025-03-08
Accepted Date: 2025-07-18
Rev Recd Date: 2025-07-10

Available Online: 2025-07-19

Abstract

Abstract

Background
The confocal waveguide structure can effectively suppress mode competition due to its characteristic of reducing mode density through diffraction loss, thereby facilitating stable operation of gyro-traveling-wave-tube (gyro-TWT) amplifiers in the terahertz (>100 GHz) frequency range.
Purpose
This study aims to conduct a comprehensive analysis of the diffraction loss rate (DLR) in a 220 GHz confocal waveguide gyro-TWT, employing a combination of theoretical analysis and three-dimensional particle-in-cell (3D-PIC) simulations.
Methods
The research integrates field distribution theory with 3D-PIC simulations to investigate the DLR of the confocal waveguide. A non-ideal waveguide model incorporating the mirror width angle was utilized, and simulations were performed to evaluate beam-wave interaction dynamics under varying DLR conditions.
Results
The study reveals that a low DLR induces gyro-backward-wave oscillation (GBWO) in low-order competing modes, while a high DLR significantly reduces beam-wave interaction efficiency, gain, and bandwidth, and lowers tolerance to electron beam velocity spread.
Conclusions
For stable single-mode operation of the HE₀₇ mode in the designed gyro-TWT, the DLR should not be less than 0.38 dB/cm, with the corresponding mirror-surface width angle not exceeding 47°. These findings provide crucial design guidelines for terahertz gyro-TWTs.
- confocal waveguide,
- diffraction loss rate,
- terahertz generation,
- gyro-TWT

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References(23)

References

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