Numerical examination of the operation modes of a weakly relativistic oversized backward wave oscillator

Bansho

et al. 2010

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Studies of coaxial oversized backward wave oscillators (BWOs) are reported. The beam voltage is weakly relativistic (less than 100 kV). The slow-wave structure consists of a periodically corrugated oversized waveguide and periodically corrugated inner conductor, whose target operating frequency due to Cherenkov interaction is in the K-band. A starting energy exists for the coaxial oversized BWO as it does for a hollow oversized BWO. The coaxial slow-wave structure has two surface wave modes caused by the inner and outer corrugations. Operation based on these surface modes can be controlled by the beam diameter. The phase difference between the inner and outer corrugations has little effect on operation of the oversized BWO.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Study of Oversized Backward Wave Oscillator with Coaxial Slow-Wave Structure

Yoshimura

Bansho

et al. 2010

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“…The method of this paper is based on the Rayleigh hypothesis, which assumes that the fields inside and outside the corrugation are expressed by the same Floquet series. To check the applicability of our numerical code, the field properties based on the Rayleigh hypothesis are compared with those obtained by direct numerical integration of Maxwell's equations using the higher-order implicit difference method (HIDM) [12]. The HIDM is free from the Rayleigh hypothesis.…”

Section: Methodsmentioning

confidence: 99%

Numerical Analysis of Slow-Wave Instabilities in an Oversized Sinusoidally Corrugated Waveguide Driven by a Finitely Thick Annular Electron Beam

Otubo

Yamakawa

et al. 2010

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Three kinds of models are used for beam instability analyses: those based on a solid beam, an infinitesimally thin annular beam, and a finitely thick annular beam. In high-power experiments, the electron beam is an annulus of finite thickness. In this paper, a numerical code for a sinusoidally corrugated waveguide with a finitely thick annular beam is presented and compared with other models. Our analysis is based on a new version of the selfconsistent linear theory that takes into account three-dimensional beam perturbations. Slow-wave instabilities in a K-band oversized sinusoidally corrugated waveguide are analyzed. The dependence of the Cherenkov and slow cyclotron instabilities on the annular thickness and guiding magnetic field are examined.

“…The electron beam in an oversized corrugated waveguide interacts with the TM modes, but not with the TE modes. The TM mode becomes dominant in the HE m1 mode in the slow-wave region in which the phase velocity is slower than c and an electron beam interacts with HE m1 modes, whereas the TE mode is dominant in HE mode around k z = 0 [14]. No EH modes become surface waves at frequencies below 150 GHz, so these may not contribute to radiation.…”

Section: Non-axisymmetric Modementioning

confidence: 99%

Non-Axisymmetric Radiation from Surface-Wave Oscillator Driven by Weakly Relativistic Electron Beam

Annaka

Ozawa

et al. 2019

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In this paper, non-axisymmetric radiation from a W-band surface wave oscillator (SWO) is observed. The SWO is based on a cylindrical corrugated waveguide with a periodic structure on its inner wall. This SWO is driven by electron beams with energy of less than 100 keV and a current on the order of 100 A. The waveguide has transverse magnetic (TM) and transverse electric (TE) modes as its axisymmetric normal modes. Nonaxisymmetric modes also appear as a hybrid of TM and TE modes and form surface waves near the periodic structure. The frequencies of the non-axisymmetric modes increase as the azimuthal mode number m increases. By injecting an annular electron beam into the SWO, many non-axisymmetric modes with m up to 30 are excited and intense radiation is generated at frequenies up to 140 GHz.