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14THz-O-4
NONLINEAR AND TERAHERTS PHOTONICS
Five-Fold Frequency Multiplication in MW-Level Gyrotrons as a Way to
High-Power THz Radiation Sources
I. Zotova, G. Denisov, A. Malkin, A. Sergeev, I. Zheleznov, M. Glyavin
Institute of Applied Physics RAS (IAP RAS), 46 Ul'yanov str., Nizhny Novgorod, Russia
zotova@ipfran.ru
Multiple applications, including spectroscopy with high resolution, remote sensing, high-speed wireless communications, biomedicine, security and many others [1-3], require CW, compact and powerful radiation sources operating in the terahertz gap, i.e., at frequencies from 0.3 to 10 THz, to be developed. This problem still remains pretty much unresolved, as THz frequencies are "too low" for quantum devices and "too high" for classical electronics associated with radiation of rectilinear electron beams in slow-wave structures. Lack of powerful radiation sources is especially critical in the 1 to 2 THz band.
We propose the concept of high-power THz radiation sources based of fivefold frequency multiplication in high-power gyrotrons intended for plasma applications. The efficient excitation at the 5th cyclotron harmonic is due to the specific property of the eigenmodes of cylindrical waveguides, as a result of which the conditions of simultaneous electrody-namic resonance can be asymptotically satisfied at two selected TE modes suitable for multiplication effect. At the previous stage of research, the proposed approach was verified in the proof-of-principle experiment based on the setup of the fundamental harmonic 45 GHz/20 kW gyrotron [4]. In the experiment, the 5th harmonic excitation of TE3012 at the frequency of 225 GHz was obtained with power-level of 100 mW.
The possibility of reaching the THz range based on a fivefold frequency multiplication with a higher power level is associated with the use of higher frequency MW-level gyrotrons. However, this scheme may be limited by mode competition at the fundamental harmonic. Within the frame of time-domain averaged model, we demonstrate possibility of Watt-level 1.25 THz 5th harmonic excitation in a recently developed sub-MW 0.25 THz gyrotron with TE198 operating mode [5]. The operating zone with efficient excitation of the 5th cyclotron harmonic can be significantly expanded when the gyrotron is locked by an external signal which suppresses parasitic oscillations [6].
The work is supported by the government contract of IAP RAS #0030-2019-0027 (Program "Development of equipment, technologies and research in the field of atomic energy use in the Russian Federation for the period up to 2024").
[1] E. Brundermann, H.-W Hubers and M.F. Kimmitt. Terahertz techniques. Springer Series in Optical Sciences, Springer, Berlin/ Heidelberg, 2012
[2] M. Tonouchi. "Cutting-edge terahertz technology", Nature Photon. 1, 97 (2007) doi: 10.1038/nphoton.2007.3
[3] S. Sabchevski, M. Glyavin, S. Mitsudo et al. "Novel and Emerging Applications of the Gyrotrons Worldwide: Current Status and Prospects", J Infrared Milli Terahz Waves, 42, 715-741 (2021) doi: 10.1007/s10762-021-00804-8
[4] G. Denisov, M. Glyavin, A. Tsvetkov et al. "A 45-GHz/20-kW gyrotron-based microwave setup for the fourth-generation ECR ion sources", IEEE Trans. Electron Dev. 65, 3963 (2018) doi: 10.1109/TED.2018.2859274
[5] G. Denisov, M. Glyavin, A. Fokin et al. "First experimental tests of powerful 250 GHz gyrotron for future fusion research and collective Thomson scattering diagnostics", Rev. Sci. Instr. 89, 084702 (2018) doi: 10.1063/1.5040242
[6] V. Bakunin, G. Denisov and Yu. Novozhilova. "Principal enhancement of THz-range gyrotron parameters using injection locking", IEEE Electron Dev. Lett. 41, 777 (2020) doi: 10.1109/LED.2020.2980218
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