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A large signal beam-wave interaction model for the analysis of folded waveguide traveling wave-tube (FWG TWT) is proposed. The slow-wave structure is modeled as a sequence of coupled resonant cavities. The electron beam is treated as a current source that can induce electromagnetic waves in the cavity. The beam-wave interacting process is modeled as an active matrix. Compared with the other models only calculating the in-band characteristic of FWG TWT, our model can provide characteristic analysis in both in-band and near cutoff regions, and thus broaden operating bandwidth and suppress oscillation. As verification, two FWG TWT examples were designed by using our model. Its performances predicted by our code agree well with that obtained by the experiment and particle-in-cell software, respectively. [ABSTRACT FROM AUTHOR]

In order to further improve the output power of W-band traveling wave tube (TWT), a low gain TWT was proposed as a secondary amplifier. It uses a double staggered grating slow wave structure (DSG-SWS) and a sheet beam. Firstly, the design of DSG-TWT was given. Through simulation, the DSG-TWT could provide a saturation output power of more than 1000 W in the frequency range of 93–97 GHz, and the maximum output power could reach 1200 W at 95 GHz. No oscillation and current interception were found. Then DSG-SWS was fabricated by E-plane partition method using high-precision CNC milling. The SWS was fed with a high-power input-output coupler which consists of a mode converter and an impedance transformer. Simulation and cold-test results were presented, showing that the S11 is less than −10 dB and the voltage standing wave ratio (VSWR) is less than 2.0 in the frequency range of 93–100 GHz. [ABSTRACT FROM AUTHOR]

This paper puts forward a novel dual-beam overmoded folded waveguide (FW) slow-wave structure (SWS), which is loaded with photonic crystals. In this novel structure, the two electron beams pass through the small gaps between the photonic crystal structures and the FW; the dimension of the FW is twice larger than that of the fundamental mode structure. The novel dual-beam photonic crystal overmoded FW traveling-wave tube (TWT) is proposed on the basis of the SWS. And, a mode converter is introduced to achieve the connection between the SWS and the input/output structure, and the mode transformation. At the operating voltage of 21.2 kV and the operating current of 320 mA, the proposed TWT can generate 128 W of output power at 220 GHz, and its 3-dB bandwidth is 7 GHz, ranging from 216 to 223 GHz. [ABSTRACT FROM AUTHOR]

We proposed an all-metal metamaterial slow-wave structure (MSWS) that consists of a circular waveguide periodically loaded with complementary electric split-ring resonators (CeSRRs). We set up an equivalent circuit theoretical model of MSWS and analyzed its high-frequency characteristics. Also, based on the surface current distribution on the CeSRR obtained by using the eigenmode solver in the CST Microwave Studio, a method of calculating the resonant frequency of the CeSRR was proposed. Furthermore, an MSWS with RF coupling port was designed, simulated, fabricated, and experimentally characterized. The dispersion characteristics of MSWS obtained by interpreting the experimental transmission characteristics agreed well with those predicted by theory as well as simulation. Based on the results of simulation and experiment, a concept of “resonance-coupling” was proposed for the passband of MSWS for frequencies below the cutoff frequency of an empty circular waveguide. The role of the slot-line in the CeSRR in influencing the performance of MSWS was also analyzed. The proposed MSWS has wide potential applications in vacuum electron devices, such as backward-wave oscillator and extended interaction klystron. [ABSTRACT FROM AUTHOR]

We propose a novel system of input and output couplers, excited in azimuthal symmetric and stable mode of operation, for an oversized coaxial relativistic klystron amplifier (OCRKA) at Ka-band. A mode converter is introduced in the output coaxial waveguide to provide a tunnel for the input waveguide and fix the inner and outer conductors of the OCRKA. After characterizing the proposed input and output couplers, the high-frequency structure of the OCRKA is designed and then optimized by Computer Simulation Technology. The simulated frequency and loaded quality factor of the input, output, and idler cavities are validated against measurement. Also, the beam–wave interaction of the OCRKA using the proposed input and output couplers is simulated by particle-in-cell software, the average saturated output power of 880 MW of the OCRKA at Ka-band, with 29.3% electronic efficiency and 58-dB saturated gain are obtained. Moreover, no pulse shortening of the output power waveform is observed during the simulation time of 100 ns, which indicates that the proposed input and output couplers can suppress the higher order mode self-oscillation in the Ka-band OCRKA studied here. [ABSTRACT FROM AUTHOR]

Variable-width technology applied to the folded waveguide traveling wave tube (FW-TWT) is proposed in this paper to suppress the lower band-edge oscillation and to expand the operating bandwidth when the operating frequency shifts toward the lower band for obtaining larger output power. Changes in the width of the slow wave structure (SWS) determine the variation of the lower-cutoff-frequency (LCF), which makes the LCF's distribution a frequency range rather than a specific frequency-point. The lower band-edge oscillation will not be focused on a special position but distributed in a frequency-band range in which multiple oscillation modes compete with each other near the LCF. The lower band-edge oscillation can be suppressed by mode competition to some extent. In addition, the width variation of SWS also results in the phase-velocity variation, and thus, the operating bandwidth of FW-TWT can be further improved by the optimized design of variable-width-SWS parameters. Beam-wave interaction simulations predicted that power and bandwidth improvements have been achieved without the lower band-edge oscillation. Meanwhile, four solutions are given for further certifying the effectiveness of the variable-width method in lower band-edge oscillation suppression and bandwidth widening. An output power level of over 350 W in a frequency range of 85–90 GHz (5 GHz) is obtained, with a maximum power of ∼648 W and an electron efficiency of ∼12.1% at 88 GHz with a beam current of 260 mA and a beam voltage of 20.5 kV. [ABSTRACT FROM AUTHOR]

In this paper, an oversized coaxial relativistic extended interaction oscillator (OCREIO) with gigawatt-level output at the Ka-band is proposed. We adopt a four-gap buncher cavity and a three-gap output cavity to increase the power capability and improve the electronic efficiency of the OCREIO. The beam-loading conductance for each mode existing in the buncher cavity is derived based on a small-signal theory. The beam-wave interaction and power capability for the 2π/3 and π modes exciting in the buncher cavity are analyzed. The operation mode 2π/3 is chosen by considering the beam-loading conductance and power capability. In addition, an improved method is proposed to mitigate the electric field intensity of the buncher cavity so as to moderate velocity modulation. The weak velocity modulation offers enough distance to make density modulation, thereby obtaining a relatively high fundamental harmonic current amplitude. Our study on the device performance of the proposed OCREIO, using the particle-in-cell simulation code CHIPIC, predicts an output power of 922.7 MW and a high electronic efficiency of 32.9% at 30.5 GHz, as well as the relatively less time of frequency-lock of self-oscillation <20 ns. The simulated results of the proposed OCREIO motivate us to practically develop the device in the near future. [ABSTRACT FROM AUTHOR]

In this paper, a 3-D fast time-domain nonlinear algorithm (FTDNA-3-D) based on particle-in-cell method for the beam–wave interaction of the sheet beam slow wave structure (SWS) is presented. Calculation equations of the circuit electric field and the space charge electric field are given. Calculation approaches of the energy exchange and the particle mover are displayed. A simplified coupling impedance simulation approach for sheet beam SWS is indicated. The FTDNA-3-D takes the transverse electric field and the focusing magnetic field into consideration. The FTDNA-3-D could reach a high simulation speed. This novel algorithm gives a faster accurate choice for the design of sheet beam traveling-wave tube (TWT). It could be used to enhance the design efficiency of sheet beam TWT. A Ka-band staggered double vane TWT is used to verify the FTDNA-3-D. Simulation results of output power and gain versus frequency from FTDNA-3-D are compared with results from CST particle studio. The results of FTDNA-3-D are in accord with CST particle studio well. [ABSTRACT FROM AUTHOR]

In this paper, a mathematical physics model is set up to study dielectric constant profile of aqueous solvent in ionic solution, to revise Brownian dynamics simulation in ionic solution by considering time-variant dielectric constant profile with change in ion positions, and to study the effect of high-intensity electric pulses on the profile. The validation of the model is confirmed with verification calculations. By means of the proposed model, dielectric constant profiles in calcium chloride and sodium chloride solutions and their response to pulses are simulated. Based on numerical results, dielectric constants of aqueous solvent spatially vary instead of being the same value in ionic solutions. And the profiles are variant with time due to ion motion in solutions. From the profiles, overall dielectric constant in calcium chloride solution is lower than that in sodium chloride solution. And overall dielectric constant decreases with increment of solution concentration. In addition, the results show that influence on the profiles depends on solution concentration and field intensity of the pulse. The profile in solutions with low concentration is more vulnerable to the pulse than that with high concentration. And overall dielectric constant decreases dramatically as field intensity increases. Those understandings provide basis for application of pulses in biomedical engineering at the molecular level. Meanwhile, pulse radiation provides a potential way to constrain water molecules at room temperature reflected by significantly reducing dielectric constant, and to lower absorption loss of electromagnetic field in millimeter and far infrared band. [ABSTRACT FROM AUTHOR]

A high-harmonic traveling-wave tube (HHTWT) is designed, developed, and tested in this paper. This device is configured as a multiplier–amplifier with Q-band input signals and its third harmonic, i.e., D-band output power. The tested result demonstrates that 280 mW at 133.5 GHz is obtained as a result of 200 mW at 44.5-GHz input signal. The simulation and experiment validate that the high-harmonic radiation can be generated and amplified in the HHTWT. The approach described in this paper could find application in exploring high power, wideband tunable terahertz source. This paper is expanded from a conference paper on IVEC 2017. The detail design produce and tested result are added in this paper. The explanation of the simulation and tested results is also presented. [ABSTRACT FROM AUTHOR]

In this paper, an extended interaction oversized coaxial relativistic klystron amplifier (EIOC-RKA) with Gigawatt-level output at Ka band is proposed. We introduce the oversized coaxial and multi-gap resonant cavities to increase the power capacity and investigate a non-uniform extended interaction output cavity to improve the electronic efficiency of the EIOC-RKA. We develop a high order mode gap in the input and output cavities to easily design and fabricate the input and output couplers. Meanwhile, we design the EIOC-RKA by using the particle-in-cell simulation. In the simulations, we use an electron beam with a current of 6 kA and a voltage of 525 kV, which is focused by a low focusing magnetic flux intensity of 0.5 T. The simulation results demonstrate that the saturated output power is 1.17 GW, the electronic efficiency is 37.1%, and the saturated gain is 57 dB at 30 GHz. The self-oscillation is suppressed by adopting the absorbing materials. The proposed EIOC-RKA has plenty of advantages such as large power capacity, high electronic efficiency, low focusing magnetic, high gain, and simple structure. [ABSTRACT FROM AUTHOR]

We have theoretically investigated the transport of a sheet electron beam focused by a uniform axial magnetic field in a metamaterial-loaded waveguide. A theoretical model has been proposed to analyze the sheet electron beam transport. In this model, we have used CST simulations to obtain the mean potential on the metamaterial as the boundary condition. According to the boundary condition, the space-charge electric field and the beam curling have been theoretically analyzed. It is found that the beam curling can be greatly reduced by decreasing the spacing between the metamaterial and the sheet electron beam. This model is verified using the CST simulations. This paper can pave the way for developing brand new metamaterial-based vacuum electron devices with a sheet electron beam. [ABSTRACT FROM AUTHOR]

To improve the output power and electron efficiency and broaden the operating bandwidth, the three-gap extended output cavity was used in the relativistic klystron to replace the single-gap output cavity. The high-frequency characteristics of the three-gap extended cavity were studied. The electron load conductance was derived and corrected based on the theory of relativity, by which a more accurate relation of electron load conductance versus transmit angle can be obtained. The characteristic impedance is three times bigger than that of the single-gap cavity under the case of the $2\pi $ mode, which can improve the M^{2}(R/Q) and the beam–wave interaction efficiency. The model of sheet beam klystron (SBK) is comprised of three-gap input cavity, two-gap first idler, three-gap second idler cavity, and three-gap output cavity. The 3-D particle-in-cell simulation results show that for a 500 kV, 1 kA, 40.134 GHz, and 20 W input power, the SBK is capable of generating an output power higher than 142 MW with the gain of 68.5 dB, maximum interaction efficiency of 28.4%, and 3-dB bandwidth of 240 MHz. [ABSTRACT FROM PUBLISHER]

• 1.DA-CTF was synthesized as photocatalysts for RhB and MB degradation. • 2.DA-CTF exhibited excellent RhB and MB degradation efficiency. • 3.DA-CTF showed great response to visible light as metal-free catalyst. • 4. Mechanism of degradation of RhB and MB of DA-CTF was proposed. Covalent triazine frameworks (CTFs) are emerged as heterogeneous photocatalysts for the treatment of polluted water. Herein, DA-CTF (donor-acceptor type covalent triazine-based framework) was synthesized by simple solvothermal process and was applied as metal-free catalyst for the degradation of rhodamine B (RhB) and methylene blue (MB). The structure of DA-CTF was characterized by SEM, FTIR, BET and TGA, and the photodegradation performances of dyes under visible light using the DA-CTF were evaluated. Results indicated that DA-CTF exhibited outstanding photodegradation of RhB and MB with good stability and reusability. 92.3% of RhB and 99.2% of MB (30 mg/L) can be degraded within 60 min and the calculated rate constants (k) were 0.04096 min−1and 0.04843 min−1, respectively. The proposed pathways for the degradation of the organic dyes were further discussed. The results highlight the potential DA-CTF as metal-free photocatalyst for the degradation of organic dyes in wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

A novel slow wave structure (SWS) named angular log-periodic meander-line is proposed for a radial traveling wave tube (TWT). In this paper, a 30 log-periods microstrip angular log-periodic meander-line SWS is studied. The dispersion of this kind of SWS is weak, which shows that it can work in a wide operating bandwidth. The more important advantage is that the operating voltage is much lower than that of the conventional TWT at the same operating frequency and the geometrical dimension is also much smaller than that of the conventional TWT. The beam–wave interaction of the angular log-periodic meander-line TWT is calculated using the particle-in-cell method. When the operating voltage is 1624 V, this kind of TWT can give 156.5-W output power at 35 GHz, the gain is 21.9 dB, and the electron efficiency is \sim17.7\%. With this kind of TWT as mentioned, the concept of radial integrated angular log-periodic meander-line TWT is proposed, which can provide a new way to obtain higher output power. [ABSTRACT FROM PUBLISHER]

YFeO $_{\boldsymbol 3}$ and other rare earth substituted crystals with distorted orthorhombic pervoskite-like structure (space group, Pbnm) have attracted much attention due to their remarkable magnetic properties of primary significance for technological applications. In the present work, the floating zone growth of YFeO $_{\boldsymbol 3}$ crystals has been systematically investigated and high quality YFeO $_{\boldsymbol 3}$ crystal was obtained by optimized process. The magnetic properties of YFeO $_{\boldsymbol 3}$ crystal were investigated, and it indicated the high magneto-optical property in YFeO $_{\boldsymbol 3}$ crystals with specific orientation due to its anisotropy. YFeO $_{\boldsymbol 3}$ crystals display superior performance in the application magneto-optical current sensors and fast latching optical switches. [ABSTRACT FROM AUTHOR]

An experimental study on electromagnetic (EM) radiation in an electron beam‐ion channel system is reported, which indicates the same result predicted by our previous theory. The system is formed in an arc plasma jet with a plasma density of 1017m−3, and the electron beam is driven by a voltage pulse of 20 kV. The result shows that the system can excite EM radiation in the range of the plasma frequency. The scheme is also hopeful to be used for generating high‐frequency and wide‐band EM radiation up to terahertz by enhancing the plasma density. [ABSTRACT FROM AUTHOR]