Broadband terahertz-power extracting by using electron cyclotron maser

Shi Pan,Xiang-Bo Qi,Chao-Hai Du,Pu-Kun Liu

doi:10.1038/s41598-017-07545-6

Abstract

Terahertz applications urgently require high performance and room temperature terahertz sources. The gyrotron based on the principle of electron cyclotron maser is able to generate watt-to-megawatt level terahertz radiation, and becomes an exceptional role in the frontiers of energy, security and biomedicine. However, in normal conditions, a terahertz gyrotron could generate terahertz radiation with high efficiency on a single frequency or with low efficiency in a relatively narrow tuning band. Here a frequency tuning scheme for the terahertz gyrotron utilizing sequentially switching among several whispering-gallery modes is proposed to reach high performance with broadband, coherence and high power simultaneously. Such mode-switching gyrotron has the potential of generating broadband radiation with 100-GHz-level bandwidth. Even wider bandwidth is limited by the frequency-dependent effective electrical length of the cavity. Preliminary investigation applies a pre-bunched circuit to the single-mode wide-band tuning. Then, more broadband sweeping is produced by mode switching in great-range magnetic tuning. The effect of mode competition, as well as critical engineering techniques on frequency tuning is discussed to confirm the feasibility for the case close to reality. This multi-mode-switching scheme could make gyrotron a promising device towards bridging the so-called terahertz gap.

Highlights

Terahertz (THz) sources mainly include two families, namely optical sources[1] and electronic sources[2]
In order to achieve continuous broadband THz radiation in a step-tunable gyrotron, this paper proposes a scheme based on magnetic-field-controlled multi-mode switching in backward-wave interaction
The basic principle is that the Electron Cyclotron Maser (ECM) system (Fig. 1c) is treated as an extractor of the electron cyclotron frequency

Summary

Introduction

Terahertz (THz) sources mainly include two families, namely optical sources[1] and electronic sources[2]. A gyrotron oscillator mostly operates in a single rotating waveguide mode It produces coherent high-power output on a fixed frequency or in a limited tunable bandwidth. The experiment generates a 6-GHz tuning range on the TE1,2 mode, which preliminarily demonstrates the competence of continuous broadband tuning They further investigated an open-cavity scheme tapered at the upstream end to improve the interaction efficiency[23]. Du et al proposed a pre-bunched circuit to realize a 10-GHz continuous tuning range[24] Such pre-bunched interaction compresses the energy-modulation length and extends the energy-releasing length of the beam-wave interaction process, and demonstrates simultaneous advantages of broadband tuning and high efficiency. In order to achieve continuous broadband THz radiation in a step-tunable gyrotron, this paper proposes a scheme based on magnetic-field-controlled multi-mode switching in backward-wave interaction. Detailed discussions about mode competition and critical engineering techniques ensure the feasibility of broadband frequency sweeping and provide guidance for future proof of principle experiment

Methods

Results

Conclusion