Selectivity Properties of Cylindrical Waveguides with Longitudinal Wall Corrugations for Second-Harmonic Gyrotrons

Tkachova, Tetiana I.; Shcherbinin, Vitalii I.; Ткаченко, В. І.

doi:10.1007/s10762-019-00623-y

Cited by 14 publications

(23 citation statements)

References 28 publications

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“…The phenomenon of superscattering from a corrugated cylinder has been validated against full-wave simulations by RF module of COMSOL Multiphysics R solver. In simulations, the corrugation period p is taken to satisfy the condition p/λ < 0.03 and thus is small enough to avoid coupling of spatial harmonics due to corrugations [45]. The results of full-wave simulations are shown in Fig.…”

Section: Superscattering Of the Tez Wavesmentioning

confidence: 99%

Superscattering from Subwavelength Corrugated Cylinders

et al. 2020

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Wave scattering from a cylinder with a tensor impedance surface is investigated based on the Lorentz-Mie theory. A practical example of such a cylinder is a subwavelength metallic rod with helical dielectric-filled corrugations. The investigation is performed with the aim to maximize scattering cross-section by tailoring the surface impedance of cylindrical scatterers. For the normally incident TEz and TMz waves the required surface impedance of a subwavelength cylinder can be produced by longitudinal (axial) and transverse (circumferential) corrugations, respectively. It is shown that such corrugations induce superscattering at multiple frequencies, which can be widely tuned with either or both the size and permittivity of dielectric-filled corrugations. In the microwave band, this effect is demonstrated to be robust to material losses and is validated against the fullwave simulations and experiment. For the TEz waves the enhanced scattering from the cylinder is found to have a broad frequency bandwidth, provided that the relative permittivity of corrugations is low or equal unity. In the latter case, the corrugated cylinder acts as an all-metal superscatterer. For such cylinders the near-field measurements are implemented and provide the first experimental evidence of the superscattering phenomenon for all-metal objects. In addition to multifrequency superscattering, the dielectric-filled corrugations are shown to provide multifrequency cloaking of the cylinder under the incidence of the TMz waves. Simultaneous superscattering and cloaking at multiple frequencies distinguishes corrugated cylinders from other known practicable scatterers for potential applications in antenna designing, sensing, and energy harvesting.Enhancement of wave scattering from small objects is a vital issue in present-day technologies [1-7], including miniaturized antennas, sensors and energy harvesting devices. This issue is directly related to the natural constraint inherent in most subwavelength scatterers [8]. This constraint is known as a single-channel limit [9], which represents an upper limit to scattering crosssection for such scatterers and is attained under resonance condition for one of the scattering modes (channels). The only way to overcome this constraint is to ensure resonant scattering of several modes at a single frequency. Such a resonance overlapping magnifies scattering from a given object and is known as superscattering [9,10]. The larger the number of resonant modes, the larger the superscattering cross-section. Therefore, theoretically, superscattering opens a way to arbitrary enhancement of wave scattering from subwavelength objects. In practice, however, this effect is often hindered by the lack of low-loss materials and appropriate design solutions.In the infrared and visible parts of spectrum, the superscattering can be realized in cylindrical structures formed by several plasmonic and dielectric layers. In the pioneering work [9], for such a structure the total scattering cross-section was optimized to excee...

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Section: Superscattering Of the Tez Wavesmentioning

confidence: 99%

Superscattering from Subwavelength Corrugated Cylinders

et al. 2020

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“…for the operating TE 13,2 mode. Under this condition, the effect of wall corrugations on the operating mode is generally weak [13,14].…”

Section: Eigenvalues and Ohmic Losses Of The Cavity With Longitudinal Wallmentioning

confidence: 99%

“…CORRUGATIONS In a gyrotron cavity, the effect of longitudinal wall corrugations is mainly determined by the ratio of corrugation depth d to mode cutoff wavelength 2 R     and therefore is different for the first-harmonic ( 1 s  ) and secondharmonic ( 2 s  ) modes [13,21]. It alters the mode eigenvalue  , ohmic quality factor ohm Q and beam-wave coupling coefficient s C .…”

Section: Eigenvalues and Ohmic Losses Of The Cavity With Longitudinal Wallmentioning

confidence: 99%

“…Mode-converting wall corrugations can be applied to further improve the selectivity properties of advanced cavities for second-harmonic gyrotrons [13,14]. Contrary to impedance corrugations [15][16][17][18][19], such corrugations induce coupling between normal modes (azimuthal Bloch harmonics) of the cavity and thereby affect frequencies of cavity modes, their ohmic losses and coupling with an electron beam [20][21][22].…”

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“…Contrary to impedance corrugations [15][16][17][18][19], such corrugations induce coupling between normal modes (azimuthal Bloch harmonics) of the cavity and thereby affect frequencies of cavity modes, their ohmic losses and coupling with an electron beam [20][21][22]. According to [13,14], in a cavity of a secondharmonic gyrotron, the depth of mode-converting corrugations should be selected close to half wavelength of the operating mode. In this case, the operating mode is generally weakly affected by corrugations of the cavity wall, while characteristics of the first-harmonic competing modes undergo a material change.…”

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Mode-Converting Corrugations for Cavities of Second-Harmonic Gyrotrons with Improved Performance

Tkachova

Shcherbinin

Ткаченко

2021

EEJP

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Mode-converting longitudinal corrugations are used as a means of improving the selectivity properties of cavities for second-harmonic gyrotrons. As an example, 100-kW 0.3-THz second-harmonic gyrotron is considered. For the operating second-harmonic mode and most dangerous first-harmonic competing modes, the eigenvalues, ohmic losses and beam-wave coupling coefficients are investigated with respect to dimensions of a corrugated cavity. The most optimal parameters are found for a gyrotron cavity with mode-converting corrugations, which ensure the widest range of a single mode operation for the 0.3-THz second-harmonic gyrotron. It is shown that, in this range, the gyrotron output power can be increased up to 180 kW. It is found that output mode purity of the 0.3-THz second-harmonic gyrotron falls off due to mode-converting corrugations, which induce undesirable coupling of the operating mode with neighboring Bloch harmonics in the output section of the gyrotron cavity.

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Mode Discrimination by Lossy Dielectric Rods in Cavities of Second-Harmonic Gyrotrons

Shcherbinin

Avramidis

Thumm

et al. 2021

J Infrared Milli Terahz Waves

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The influence of a coaxial dielectric rod on eigenvalues, ohmic losses, transverse field structure and beam-wave coupling coefficients is investigated for TE modes of a gyrotron cavity. It is shown that such dielectric insert, when made from a moderate-loss material, results in strong attenuation of all cavity modes, with the exception of those having caustic radii much larger than the insert radius. It is proposed to employ such dielectric loading for selective suppression of competing modes in cavities of second-harmonic gyrotrons. The high performance and flexibility of the proposed method of mode discrimination is demonstrated for the example of the cavity of the high-power 0.39-GHz second-harmonic gyrotron developed at the University of Fukui. In addition, some fascinating capabilities enabled by coaxial inserts made of ultralow-loss dielectrics are discussed.

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Selectivity Properties of Cylindrical Waveguides with Longitudinal Wall Corrugations for Second-Harmonic Gyrotrons

Cited by 14 publications

References 28 publications

Superscattering from Subwavelength Corrugated Cylinders

Superscattering from Subwavelength Corrugated Cylinders

Mode-Converting Corrugations for Cavities of Second-Harmonic Gyrotrons with Improved Performance

Mode Discrimination by Lossy Dielectric Rods in Cavities of Second-Harmonic Gyrotrons

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