Analysis and Simulation of a Gigawatt-Class Ka -Band Radial Transit Time Oscillator

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An overmoded coaxial Ku-band relativistic backward wave oscillator (RBWO) with high efficiency is proposed. The distance between the inner and outer conductors of the slow wave structure (SWS) in the RBWO is smaller than the space wavelength of output microwave. The overmoded structure can increase the power capacity of the oscillator by increasing the transversal size of the device. The higher-order modes are introduced into the beam-wave interaction region intentionally, so that the intense relativistic electron beams (IREB) interacts with the fundamental and higher-order modes. Dual-mode operation leads impure mode component to output microwave, so the simple trapezoid inner conductor is designed to achieve mode purification and output pure TEM mode. The extractor is added at the end of the SWS, which enhances the axial electric field near the location and increases the modulation depth of the electron beam current passing through the region. The particle-in-cell (PIC) simulation results show that under the input power of 3.5 GW, the output microwave power is 1.8 GW, and the corresponding working efficiency is 51.4%, which is much higher than that of similar periodic devices. The mode of output microwave is pure TEM mode, and the maximum surface electric field intensity is 0.96 MV/cm, which means that the probability of radio-frequency breakdown is low.

Section: Dual-mode Operating Mechanism and The Drift Cavitymentioning

confidence: 99%

Analysis and design of overmoded coaxial Ku-band Cerenkov high power microwave oscillator with high efficiency

Yang¹,

Meng²,

Deng³

et al. 2022

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“…In the four-gap buncher, there are four longitudinal modes in TM 01 mode, namely 0 mode, π/3 mode, 2π/3 mode and π mode [8]. The small-signal theory can be used to analyze the energy conversion process of electron beam and electric field in different modes, which is the principle for mode selection.…”

Section: Beam-microwave Energy Exchangementioning

confidence: 99%

Design and simulation of a compact Ku-band RTTO with power divider extraction structure

Yang¹,

Meng²,

Wang³

et al. 2021

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The radial transit time oscillator (RTTO) has attracted much attention because of its high power capacity and pure mode of output microwave. To make the high power microwave (HPM) source devices more compact and to enable it to measure the output microwave mode quantitatively, this paper proposed a compact Ku-band RTTO with the power divider extraction structure (PDES). The radial decreasing magnetic field is applied to decreasing the mass of excitation system. Compared the conventional uniform solenoids, it can reduce the mass by about 30%. In the coaxial output waveguide, the PDES is used instead of the traditional support rods connecting the inner and outer conductors so as to convert TEM mode into TE10 mode efficiently. This structure can not only help shorten the axial dimension of the device, but also make it possible to measure the output microwave mode more accurately online. In particle-in-cell (PIC) simulation, the proposed Ku-band RTTO can output HPMs with the power of 3.05 GW and the frequency of 14.36 GHz, and the working efficiency is 40.3%. The maximum radial electric field intensity in the extraction cavity is 0.92 MV/cm, and the maximum electric field intensity in the PDES is 0.52 MV/cm, both of which are lower than the radio frequency (RF) breakdown threshold of metal materials.

“…Finally, the high power millimeterwaves are extracted through the coaxial waveguide. In the fourgap buncher, the detailed analysis of the mode selection as well as energy transfer are illustrated in [12,13].…”

Section: Model and Physical Analysismentioning

confidence: 99%

A high power radial Ka-band transit time oscillator with nonuniform extractor

Wang¹,

Zhang²,

Dang³

et al. 2020

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The radial transit time oscillator is promising to realize high power output of millimeter-waves. However, the enhancement of the electric field in extractor and the microwave extraction are two main problems to be overcome. A high power radial Ka-band transit time oscillator is proposed in the paper. Increasing the third gap by integer multiples of half the wavelength, the nonuniform extractor will be introduced. In the extractor, the radial mode of the electric field in the modified extractor is the same as that in the uniform extractor. Due to volume increase of the beam-wave interaction region, this structure can improve power capacity to a certain degree. In particle-incell simulation, the proposed radial Ka-band oscillator can output high power microwave with the power of 1.0 GW, the frequency of 31.3 GHz and the efficiency of 33%. Besides, the modified structure can decrease the maximum radial electric field in extractor to 0.9 MV cm −1 . As the diode voltage ranges from 350 to 450 kV, efficiency of the oscillator is larger than 20% and the center frequency will not change, which proves the steady operation of this device. To realize high output power, the materials with high conductivity need to be employed, such as copper and aluminum. Besides, the microwave channel goes through the inner space of the high current coils, this design can decrease the number of the support posts to 50 and increase the bandwidth where the transmission efficiency is larger than 99% to be over 1.8 GHz.