Abstract
Motivated by some emerging high-frequency applications, a high-power frequency-tunable sub-THz quasi-optical gyrotron cavity based on a confocal waveguide is designed in this paper. The frequency tuning characteristics of different approaches, including magnetic field tuning, mirror separation adjustment, and hybrid tuning, have been investigated by particle-in-cell (PIC) simulation. Results predict that it is possible to realize a smooth continuous frequency tuning band with an extraordinarily broad bandwidth of 41.55 GHz, corresponding to a relative bandwidth of 18.7% to the center frequency of 0.22 THz. The frequency tunability is provided by varying the separation distance between two mirrors and correspondingly adjusting the external magnetic field. During the frequency tuning, the output power remains higher than 20 kW, which corresponds to an interaction efficiency of 10%. Providing great advantages in terms of broad bandwidth, smooth tuning, and high power, this research may be conducive to the development of high-power frequency-tunable THz gyrotron oscillators.
Highlights
A gyrotron is a typical fast-wave vacuum electron device based on the interaction principle between gyrating electrons and the electromagnetic waves propagating in the waveguide [1]
A continuous frequency-tunable gyrotron operating at a single mode has been especially attractive for some modern high-frequency applications [5], such as high-resolution molecular gas spectroscopy [6], nuclear magnetic resonance spectroscopy enhanced by dynamic nuclear polarization (DNP-NMR) [7], and the direct measurement of positronium hyperfine splitting (Ps-HFS) [8], in which radiation sources are required to be high-power and continuously tunable in a wide frequency range
We propose a high-power broadband continuous frequency-tunable gyrotron cavity based on a confocal waveguide
Summary
A gyrotron is a typical fast-wave vacuum electron device based on the interaction principle between gyrating electrons and the electromagnetic waves propagating in the waveguide [1]. High-power continuous frequency-tunable radiation over a 3.1 GHz bandwidth around 0.2 THz has been experimentally observed in a quasi-optical gyrotron with a straight confocal waveguide [20], which does not contain a resonance structure. Lacking a comprehensive theoretical model to explain it, the experimental result still points out the possibility of generating high-power frequency-tunable THz radiation from a quasi-optical gyrotron with a confocal waveguide. Results suggest that the proposed quasi-optical cavity is able to generate high power of no less than 20 kW over a smoothly continuous frequency tuning band with an extraordinarily broad bandwidth of 41.55 GHz around 0.22 THz. Compared with other frequency tuning approaches, this method provides advantages in terms of high power, broad band, and smooth continuity.
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