Harmonic mode competition in a terahertz gyrotron backward-wave oscillator

Open cavities are often employed as interaction structures in a new generation of coherent millimeter, sub-millimeter, and terahertz (THz) radiation sources called the gyrotron. One of the open ends of the cavity is intended for rapid extraction of the radiation generated by a powerful electron beam. Up to the sub-THz regime, the diffraction loss from this open end dominates over the Ohmic losses on the walls, which results in a much lower diffraction quality factor (Qd) than the Ohmic quality factor (Qohm). Early analytical studies have led to various expressions for Qd and shed much light on its properties. In this study, we begin with a review of these studies, and then proceed with the derivation of an analytical expression for Qd accurate to high order. Its validity is verified with numerical solutions for a step-tunable cavity commonly employed for the development of sub-THz and THz gyrotrons. On the basis of the results, a simplified equation is obtained which explicitly expresses the scaling laws of Qd with respect to mode indices and cavity dimensions.

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“…Properties of hot cavities have been studied in recent papers. 21,26 For example, it is shown in Figs. 11 and 12 of Ref.…”

Section: E Effect Of Beam Loadingmentioning

confidence: 98%

An analytical study on the diffraction quality factor of open cavities

2014

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“…Loading wall loss is most effective for stabilizing those low-(close-to-cutoff) oscillations, and imposes minor influence to the high-(far-from-cutoff) interaction [37]- [39]. In Fig.…”

Section: Mode Competition In Pre-bunched Ecmmentioning

confidence: 97%

“…The converged field profiles under start-oscillation condition, matured interaction, or any steady state under given system parameters can be self-consistently determined. Details were previously revealed in [16], [27], [37]- [39], [41]- [44].…”

Section: B Traveling-wave Resonancementioning

confidence: 99%

See 1 more Smart Citation

Broadband Tunable Pre-Bunched Electron Cyclotron Maser for Terahertz Application

Du¹,

Qi²,

Liu³

et al. 2015

IEEE Trans. THz Sci. Technol.

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The relativistic electron cyclotron maser (ECM) has been successfully applied to generating high-power THz wave. In order to realize the additional advantages of broadband tuning and high efficiency interaction, this paper is devoted to exploring the THz pre-bunched ECM. Other than a conventional open-cavity tunable gyrotron consecutively switching between axial modes to realize frequency tuning, a pre-bunched ECM system operates on the backward traveling-wave resonance to achieve broadband smooth tuning. Especially, an interaction circuit of specified axial profile of beam-wave detuning frequency is built to achieve high efficiency. An optimized 0.1 THz pre-bunched ECM system using an electron beam of 30 kV voltage and 3 A current is predicted to generate broad bandwidth of 10 GHz and efficiency between 10% 25%. The broadband tuning pre-bunched ECM is promising for a new generation of broadband and high-power THz source.Index Terms-Broadband tuning, coherent radiation, electron cyclotron maser (ECM), terahertz (THz).

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“…On one hand, the high-harmonic mode requires a relatively long cavity with high-Q value to compensate for the weak beam-wave coupling, as a way to achieve high interaction efficiency. On the other hand, when considering multimode interaction, the long cavity structure typically leads to much more severe mode competition [11]- [21]. In order to achieve a balance between the interaction efficiency and the mode competition, a high-harmonic gyrotron, especially with the harmonic number s ≥ 3, typically employs a low-Q cavity, which imposes limitation on generating high interaction efficiency [4]- [7].…”

Section: Introductionmentioning

confidence: 99%

High-Efficiency Excitation of a Third-Harmonic Gyrotron

Liu

2015

IEEE Trans. Electron Devices

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High-harmonic gyrotrons are challenging to generate high interaction efficiency and simultaneously suppress the mode competition. Investigation in this paper reveals that a high-Q cavity is potential to realize high efficiency in a 94-GHz third-harmonic TE02 mode gyrotron. Unfortunately, the high-Q cavity exhibits severe mode competition from the lower harmonic modes. A start-up scenario of active parameter control is employed to suppress the mode competition. The third-harmonic TE02 mode gyrotron finally achieves the steady single-mode operation with efficiency up to 20%. The physical mechanism during the mode formation process is theoretically investigated according to frequency-domain and time-domain nonlinear theories. The theoretical investigation in this paper is of guidance for future developing high-harmonic gyrotrons, especially toward terahertz applications.

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Harmonic mode competition in a terahertz gyrotron backward-wave oscillator

Cited by 19 publications

References 55 publications

An analytical study on the diffraction quality factor of open cavities

An analytical study on the diffraction quality factor of open cavities

Broadband Tunable Pre-Bunched Electron Cyclotron Maser for Terahertz Application

High-Efficiency Excitation of a Third-Harmonic Gyrotron

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