Investigation of the Frequency Double-Multiplication Effect in a Sub-THz Gyrotron
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Investigation of the Frequency Double-Multiplication Effect in a Sub-THz Gyrotron M. Glyavin 1 & I. Zotova 1 & R. Rozental 1 & A. Malkin 1 & A. Sergeev 1 & A. Fokin 1 V. Rumyantsev 2 & S. Morozov 2
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Received: 16 April 2020 / Accepted: 22 June 2020/ # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
The effect of frequency multiplication was investigated for a fundamental-harmonic 0.263-THz kW-level gyrotron, in which a certain fraction of its radiation was observed experimentally at the doubled operating frequency. Accurate measurements of the power of such high-frequency generation were carried out based on cyclotron absorption of radiation in a HgTe/CdHgTe quantum-well heterostructure. The maximum power ratio of the second harmonic to the fundamental one is about 10−4 (an absolute power of 10– 15 mW at a frequency of 0.526 THz), which agrees well with the results of simulations within the framework of the self-consistent averaged approach performed to describe the multimode generation in gyrotrons. Keywords Gyrotron . THz radiation . Cyclotron harmonics . Frequency multiplication . Detection . Cyclotron absorption . Quantum heterostructure
1 Introduction Operation of gyrotrons at higher cyclotron harmonics is of interest as a method of increasing the frequency while mitigating the requirements for the guiding magnetic field. One of these possibilities is associated with the well-known effect of frequency multiplication caused by the nonlinear properties of gyrating electron beams. As a result, this leads to the presence of a higher-order cyclotron harmonic content in the radiation of a fundamental-harmonic gyrotron. Such radiation was observed experimentally, for example, in [1, 2] and interpreted theoretically in [3, 4]. It should be noted that in high-power gyrotrons intended for active plasma diagnostics [5–7], additional radiation at higher harmonics of the operating frequency was
* V. Rumyantsev [email protected]
1
Institute of Applied Physics RAS (IAP RAS), Nizhny Novgorod, Russia
2
Institute for Physics of Microstructures RAS (IAP RAS Branch), Nizhny Novgorod, Russia
Journal of Infrared, Millimeter, and Terahertz Waves
considered parasitic because it complicated separation of the scattered signal. On the other hand, the possibility of nonlinear harmonic excitation was discussed repeatedly in the context of the development of gyro-multipliers (see [8–14] and references within). In the latter case, special efforts are being made to increase the efficiency of high-order harmonic generation. In particular, for the single-cavity self-exciting gyro-multiplier, cavities with sophisticated crosssections were used (see, for example, [12–14]) to provide the required frequency divisibility of the low-frequency (LF) and high-frequency (HF) modes. Note that due to the nonequidistant mode spectrum, the optimal interaction conditions for a pair of modes cannot be fulfilled in a conventional gyrotron cavity; thus, the efficiency of frequency multiplication in this case is rather
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