Influence of Reflections on Frequency Tunability and Mode Competition in the Second-Harmonic THz Gyrotron

Khutoryan, Eduard; Idehara, T.; Melnikova, Maria M.; Ryskin, Nikita M.; Dumbrājs, O.

doi:10.1007/s10762-017-0378-x

Cited by 28 publications

(4 citation statements)

References 25 publications

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“…For high-power gyrotrons used for plasma heating for fusion applications, the reflections could stem from the output window, the transmission line between the gyrotron and the plasma, or by the first layer of the plasma itself [3]. Reflections can be favorable for gyrotron operation when they are controlled and limited, and have been shown to increase the rf output power [4,5], lock the gyrotron oscillation frequency [6], decrease the sensitivity of the radiation frequency to variation of the magnetic field [2], extend the frequency range by exciting different axial modes [7,8], and suppress parasitic modes [9]. However, when not controlled, even a limited amount of reflection can lead to a complete loss of oscillation by driving the gyrotron to a non-stationary or chaotic phase or into unstable operation in an undesired mode.…”

Section: Introductionmentioning

confidence: 99%

Study of the Effect of Reflections on High-Power, 110-GHz Pulsed Gyrotron Operation

Genoud

Picard

Schaub

et al. 2021

J Infrared Milli Terahz Waves

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The effect of reflection is studied experimentally and theoretically on a high-power 110 GHz gyrotron operating in the TE 22,6 mode in 3 µs pulses at 96 kV, 40 A. The experimental setup allows variation of the reflected power from 0 to 33 % over a range of gyrotron operating conditions. The phase of the reflection is varied by translating the reflector along the axis. Operating at a higher efficiency point, at 4.40 T with 940 kW of output power, reflected power exceeding 11% causes a switch from operation in the TE 22,6 to simultaneous operation in the TE 22,6 and TE 21,6 modes with a large decrease of the total gyrotron output power. This switching effect is in good agreement with simulations using the MAGY code. Operating at a more stable point, 4.44 T with 580 kW of output power, when the reflection is increased, the output power remains in the TE 22,6 mode but it decreases monotonically with increasing reflection, dropping to 200 kW at 33% reflection. Furthermore, at a reflection above 22%, a power modulation at 25 to 30 MHz is observed, independent of the phase of the reflected wave. Such a modulated signal may be useful in spectroscopic and other applications.

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Section: Introductionmentioning

confidence: 99%

Study of the Effect of Reflections on High-Power, 110-GHz Pulsed Gyrotron Operation

Genoud

Picard

Schaub

et al. 2021

J Infrared Milli Terahz Waves

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“…Here, E c is the electric field on the cathode, which is varied by the anode voltage, U 0 is the accelerating voltage and α is the magnetic compression ratio 22 . Variation of the electron pitch factor perturbs the electron motion, changing the active and reactive components of susceptibility and, therefore, changes the power 23 and operating frequency of the gyrotron 24 ; Passive methods based on lock by an external signal 25 or the impact of the reflected signal on the gyrotron operation 26 . …”

Section: Resultsmentioning

confidence: 99%

“…Passive methods based on lock by an external signal 25 or the impact of the reflected signal on the gyrotron operation 26 .…”

Section: Resultsmentioning

confidence: 99%

High-power sub-terahertz source with a record frequency stability at up to 1 Hz

Fokin

Glyavin

Golubiatnikov

et al. 2018

Sci Rep

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Many state-of-the-art fundamental and industrial projects need the use of terahertz radiation with high power and small linewidth. Gyrotrons as radiation sources provide the desired level of power in the sub-THz and THz frequency range, but have substantial free-running frequency fluctuations of the order of 10−4. Here, we demonstrate that the precise frequency stability of a high-power sub-THz gyrotron can be achieved by a phase-lock loop in the anode voltage control. The relative width of the frequency spectrum and the frequency stability obtained for a 0.263 THz/100 W gyrotron are 4 × 10−12 and 10−10, respectively, and these parameters are better than those demonstrated so far with high-power sources by almost three orders of magnitude. This approach confirms its potential for ultra-high precision spectroscopy, the development of sources with large-scale radiating apertures, and other new projects.

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“…Therefore, their spectral characteristics are of great interest to the community, and the gyrotron frequency tuning and stabilization are actively investigated. A number of studies considered active frequency manipulation by variation of the electron beam parameters [1]- [5], as well as phase locking by the external signal [6]- [8] and changing the spectral characteristics of the radiation (spectrum control), in particular, frequency stabilization by the wave reflected from the nonresonant load (theoretically [9]- [13] and experimentally [14]- [19]). Each of the methods has its advantages and limitations.…”

Section: Introductionmentioning

confidence: 99%

Experimental Demonstration of Gyrotron Frequency Stabilization by Resonant Reflection

Fokin

Богдашов

Novozhilova

et al. 2021

IEEE Electron Device Lett.

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This letter presents the results of an experimental and theoretical study of the gyrotron frequency stabilization by a partial reflection of its radiation from an external high-Q resonator. The experiment was carried out with a gyrotron operating in a continuous wave regime at a frequency of 28 GHz at the second cyclotron harmonic. The use of an external quasi-optical two-mirror resonator as a reflector made it possible to reduce the variation of the radiation frequency upon modulation of the guiding magnetic field by order of magnitude to 0.8 GHz/T. The experimental results are in good agreement with the calculations.

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Influence of Reflections on Frequency Tunability and Mode Competition in the Second-Harmonic THz Gyrotron

Cited by 28 publications

References 25 publications

Study of the Effect of Reflections on High-Power, 110-GHz Pulsed Gyrotron Operation

Study of the Effect of Reflections on High-Power, 110-GHz Pulsed Gyrotron Operation

High-power sub-terahertz source with a record frequency stability at up to 1 Hz

Experimental Demonstration of Gyrotron Frequency Stabilization by Resonant Reflection

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