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To improve the performance of a pencil beam electron gun for terahertz traveling wave tubes (TWT), a support vector regression (SVR) method combined with a goal attainment algorithm, which is used to optimize its structural parameters considering the periodic permanent magnetic (PPM) focusing system, is proposed in this article. Moreover, a parameter correction method to reduce the impact of the thermal expansion on the electron gun is proposed. An electron gun for 0.22-THz TWT gun is developed, in which a 30-mA/23.8-kV electron beam emitted by a curved barium-tungsten cathode with a beam loading of 4 A/cm² is achieved with the optimized parameters. To the high current density for THz beam-wave interaction, the area compression ratio of electron beam is used in beam tunnel and reaches 144. The experimental results are very similar to the simulation results, which indicate that the methods would be beneficial to the development of TWT.

Cherenkov radiation (CR), generated when charged particles move faster than the light velocity in a medium, is an important radiation phenomenon of electron-matter interactions. Here, we demonstrate high-efficiency threshold-less in-plane CR generation in the terahertz (THz) band using a periodic graphene hyperbolic grating (GHG) structure. Our theoretical and numerical analyses proved that the phase velocity in the GHG is always lower than the electron velocity; this is owing to the graphene hyperbolic plasmon polaritons induced biaxially in the GHG. Based on the simulation results, the power of the in-plane CR in the GHG is nearly two orders of magnitude larger than that of the out-of-plane CR in the conventional graphene-dielectric hyperbolic metamaterial bulk. A full electromagnetic dipole source mode is employed to describe the fascinating in-plane hyperbolic-like spatial dispersion in the GHG. Moreover, by adjusting the size of the GHG, graphene chemical potential, and free electron energy, the CR angle and intensity can be completely controlled. This framework provides a new way to develop high-efficiency, threshold-less, and tunable CR sources in the THz range with excellent adjustability and serves as a general approach applicable to other polariton types active in a wide range of materials, such as phonon- and exciton-polaritons.

For the efficient optimization of a multistage depressed collector (MDC), an axis-adjustable MDC optimized using the genetic algorithm (GA) is presented in this article. The optimization processes are realized with a reasonable balance between the collector recovery efficiency and electron reflux rate by modifying the fitness function of GA. Through the proposed method, the best recovery efficiency 88.5% and 0.72% electron reflux rate of MDC are obtained, and a three-stage symmetric collector has been designed with the GA optimization and fabricated, for a 0.22-THz TWT. The experimental results are in well agreement with that of simulations, which indicates that the methods we propose would be beneficial to the design of high efficiency of TWT.

The classical Pierce’s 1-D small-signal theory of backward-wave gain, generalized to allow axially varying the double-graded radius and pitch circuit characteristics, is applied. Numerical calculations demonstrate that the double gradient circuit can effectively suppress the backward-wave oscillation (BWO). Furthermore, the hot test experiment is carried out to predict the performance of the tube. The hot test results show that this helix traveling-wave tube (TWT) based on the double-graded pitch and radius circuit has achieved over 5.06 kW of output power, and the corresponding device gain achieves more than 34.1 dB in the frequency range of 8-18 GHz.

In this article, a 1-THz traveling-wave tube (TWT) based on flat-roofed sine waveguide (SWG) slow wave structure (SWS) has been studied theoretically and experimentally, and parts of the component have been fabricated. First, the flat-roofed SWG SWS has been optimized for working at 1 THz, the normalized phase velocity is around 0.287, and the interaction impedance is over $3.5~\Omega $ in the frequency range of 1.02–1.04 THz. Meanwhile, the performance of the designed TWT has been simulated, whose saturated output power is 720 mW and the corresponding gain is 28.57 dB. What is more, to decrease the transmission loss of the high-frequency structure, the input and output structures have been designed and a transition structure that transforms the waveguide to standard rectangular waveguide has been proposed. The simulation results show that the reflection coefficient of the novel proposed transmission system is less than −20 dB, and the insertion losses of the transition structure with the input and output waveguides are 2.45 and 1.68 dB, respectively. Finally, the designed SWS has been fabricated by deep reactive-ion etching (DRIE) and tested; ${S}_{{11}}$ is generally less than −10 dB in the frequency range of 1020–1040 GHz.

Extramedullary infiltration (EMI), as a concomitant symptom of acute myeloid leukemia (AML), is associated with low complete remission and poor prognosis in AML. However, the mechanism of EMI remains indistinct. Clinical trials showed that increased miR-29s were associated with a poor overall survival in AML [14]. Nevertheless, they were proved to work as tumor suppressor genes by encouraging apoptosis and inhibiting proliferation in vitro. These contradictory results led us to the hypothesis that miR-29s may play a notable role in the prognosis of AML rather than leukemogenesis. Thus, we explored the specimens of AML patients and addressed this issue into miR-29c&b2 knockout mice. As a result, a poor overall survival and invasive blast cells were observed in high miR-29c&b2-expression patients, and the wildtype mice presented a shorter survival with heavier leukemia infiltration in extramedullary organs. Subsequently, we found that the miR-29c&b2 inside leukemia cells promoted EMI, but not the one in the microenvironment. The analysis of signal pathway revealed that miR-29c&b2 could target HMG-box transcription factor 1 (Hbp1) directly, then reduced Hbp1 bound to the promoter of non-muscle myosin IIB (Myh10) as a transcript inhibitor. Thus, increased Myh10 encouraged the migration of leukemia cells. Accordingly, AML patients with EMI were confirmed to have high miR-29c&b2 and MYH10 with low HBP1. Therefore, we identify that miR-29c&b2 contribute to the poor prognosis of AML patients by promoting EMI, and related genes analyses are prospectively feasible in assessment of AML outcome.

The $W$ -band flat-roofed sine waveguide (SWG) slow wave circuit was designed and processed in this article. Considering the limitations on present practical fabrication level, sensitivity analysis was performed on the potential influencing factors for the performance of the flat-roofed SWG slow wave structure (SWS). As indicated by the calculation results, the gap between the SWSs and the side-wall strips could have a significant impact on the dispersion, interaction impedance, and the transmission of the entire slow wave circuit. Based on the theoretical analysis, two types of $W$ -band flat-roofed SWG slow wave circuits were fabricated and tested. The side-wall strips of the two circuits are processed with/without rounded corner. The circuit without rounded corner may cause a large gap and severe reflection. In comparison, the other one with rounded corners can make the parts fit tighter, thus minimizing the potential gap. The test results demonstrate that the $W$ -band flat-roofed SWG traveling-wave tube (TWT) possesses a voltage standing wave ratio less than 1.8, which is basically consistent with the simulation results.

A novel slow wave structure (SWS), named staggered double corrugated waveguide (SDCW), is proposed for the development of wideband high-power terahertz (THz) traveling wave tubes (TWTs). The SDCW-SWS not only has the wideband characteristic of staggered double grating (SDG) but also has the high interaction impedance characteristic of symmetrical double grating. In addition, its tunnel width is independent of the lower cutoff frequency and can be further increased. Numerical Eigen mode calculations show that, under the same dispersion, the passband of SDCW-SWS is increased by more than 10 GHz compared with SDG-SWS, and the average interaction impedance at 195 GHz is increased by about 62%. A particle-in-cell simulation analysis confirms that the average output power, saturated gain, and electron efficiency of SDCW-TWT at 195 GHz are ~110 W, ~20.34 dB, and ~5.46%, respectively, when the operating voltage is 20 kV and the beam current is 100 mA. Therefore, SDCW is a promising slow wave circuit of wideband high-power THz traveling wave amplifier.

In this article, a potentially pseudoperiodic slow wave structure (SWS) for a broadband, high-power, helix traveling-wave tube (TWT) is studied. The structure considered here suppresses the back-wave oscillations caused by a large working current. These oscillations do not have conventional uniform pitch distributions in the radial dimension; rather, the two configurations studied in this article are a uniform pitch gradient and a conical helix. Through a reasonable design and a large number of calculations, the entire tube consists of four tapered, pitch-varying SWSs. In addition, to achieve an 8–18-GHz broadband, high-power output, a double-ridged waveguide window output coupler is designed, fabricated, and tested. The 3-D electromagnetic simulation software CST STUDIO SUITE is used to verify the performance of the tube. The simulation results show that the potentially pseudoperiodic SWS can adequately suppress the backward-wave oscillations, and the tube is capable of achieving an output power of over 6 kW, even with a very wide bandwidth of 8–18 GHz. Additionally, the electronic efficiency varies from 21.5% to 25.8%. The maximum output power is 7.45 kW, corresponding to an electronic efficiency of 25.8% at 14 GHz.

In this article, two types of compact and effective input and output couplers for a 6–18 GHz 5-kW-level helix traveling wave tube (TWT) are designed, fabricated, and cold- tested. The input coupler section includes an impedance transformer, a conical coaxial window, and a transition to a subminiature version A (SMA) connector for a radio frequency (RF) input. For achieving a high-power output, a new type of double-ridged waveguide window is used in the output coupling section. The output coupling structure consists of a standard double-ridged waveguide (WRD650), an impedance transformer, a square sapphire window, and a coaxial to double-ridged waveguide transition. The commercially available 3-D electromagnetic simulation software package CST is used to further optimize these structures, including couplers terminated with an actual complex helix slow-wave structure (SWS). According to the simulation results, the input and output couplers are fabricated and tested. The experimental results of the optimized coupled structures are presented, and both couplers show excellent transmission performance for a 6–18-GHz high-power helix TWT.

A novel power amplifier unit for a phased array radar with 2 × 2 output ports for a vacuum electron device is proposed. Double parallel connecting microstrip meander-lines are employed as the slow-wave circuits of a large power traveling wave tube operate in a Ka-band. The high frequency characteristics, the transmission characteristics, and the beam–wave interaction processes for this amplifier are simulated and optimized. For each output port of one channel, the simulation results reveal that the output power, saturated gain, and 3-dB bandwidth can reach 566 W, 27.5 dB, and 7 GHz, respectively. Additionally, the amplified signals of four output ports have favorable phase congruency. After fabrication and assembly, transmission tests for the 80-period model are performed preliminarily. The tested “cold” S-parameters match well with the simulated values. This type of integratable amplifier combined with a vacuum device has broad application prospects in the field of high power and broad bandwidth on a millimeter wave phased array radar.

This paper explores the thermal characteristics of a helix traveling wave tube (TWT) in the Ka-band (26.5-40 GHz) based on rectangular semi-metallic rods formed by welding boron nitride and copper. The results reveal that the maximum temperature of the helix during TWT operation for this supporting rod structure is 339.2°C. A comparison of the thermal characteristics about this structure with those of a conventional dielectric rod shows that the helix temperature of the former is about 40°C lower than that of the latter during operating conditions.

A high-frequency structure that can be used for the G-band high-power traveling wave tube is proposed to analyz and the slow-wave characteristics of the quasi flat-roofed sine waveguide(QFRSWG). The PIC method is used to obtain the interaction characteristics of the sheet electron beam and the electromagnetic wave in this structure. The calculation results show that the traveling wave tube can produce over 110 W output power in the frequency range of 212 GHz-232 GHz, the gain is greater than 33.94 dB and the maximum electronic efficiency is 5.25 %.

Driven by success in areas such as computer vision and natural language processing, attempts have been made in this work to combine deep learning with the large signal of the Traveling Wave Tube (TWT) to assist in predicting the output performance of the tube and advancing the pre-design of TWT. By feeding the trained artificial neural network with several feature parameters, the output power with the tube length can be predicted.

The development of a 340GHz modified sine waveguide vacuum electron amplifier is presented here. Output power from this structure is predicated to exceed 10W with a pencil beam electron gun at 17 kV and 38mA. Design, fabrication and test of slow wave structure (SWS) and pillbox window are discussed respectively. The cold test results show a good agreement with the simulation, which verified the properties of low loss and wide bandwidth of the high frequency system.

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.

In this article, we propose a classical optimization algorithm named L-BFGS to simulate the thermal behavior of electron gun for terahertz traveling-wave tubes. The L-BFGS algorithm, as a variation of Quasi-Newton optimization method, expert in dealing with the unconstrained optimization problems while keeping the stability of the calculation. Efficiency and accuracy of L-BFGS algorithm are verified by modeling the thermal behavior of an actual electron gun on MATLAB platform successfully with no breakdown. According to the simulation results, this method performs better than some reference methods in terms of computational memory usage and time cost. Our numerical conclusions indicate that it is promising for thermal analysis of electron gun, which would be useful for researchers during the design phase.

In order to make the design results of the traveling wave tube (TWT) coincide with the experiments very well, we need to build a bridge between the actual electron situation and the beam-wave interaction. In this paper, considering the actual magnetic field distribution, the macro particle data at the waist position is processed by MATLAB to meet the needs of the interaction calculation model, so as to realize the integrated design of electron gun, magnetic system and interaction calculation using CST studio suite.

In this paper, the high frequency characteristics of Trapezoidal Staggered Grating Slow-wave Structure for 1THz Traveling Wave Tube has been studied. The transmission structure has been simulated, the reflection coefficient is less than -20dB in the frequency of 1015GHz to 1055GHz and the loss of the structure is over 58dB. The PIC simulation shows that the saturation output power is 405mW at the frequency of 1030GHz, and the corresponding gain is 19.08dB.

In this paper, the method of directly exporting the particle data from the CST interaction results to the collector is used to effectively improve the accuracy of the collector design. A three-stage depressed collector for 220GHz extended interaction klystron was designed with an efficiency of 90% and a reflow rate of zero.

This paper describs a fan-shaped metal loaded helix traveling wave tube working at Ka–band. It has the gain of 37.3-48.7dB, electronic efficiency of 15.18%-19.42% and output power is greater than 286W when it works at a voltage of 9KV and a current of 210mA. The simulation results of VSWR for its coaxial energy coupler are below 1.35, and the test results of it is below 2.1 at the working frequency range.

The high frequency characteristics and beam wave interaction characteristics of a Ka-band (26-40GHz) helix traveling wave tube (TWT) with rectangular semi-metallic rod are presented. The design results show that the TWT has the gain of more than 42dB, the output power of more than 220W and the electronic efficiency of more than 19% in the working bandwidth. Now the high frequency structure of the TWT are manufactured, the preparation for the transmission test is in progress.

This paper introduces a high-stability electron optical system for millimeter wave traveling wave tubes. Firstly, a circular electronic injection Pierce electron gun is designed. The electron channel radius is 0.2mm, the current is 90mA. Then the immersed flow method was used to design a ppm focusing system with a magnetic field period of 7.3 mm and a peak value of 4900 Gauss. The stability of the immersed flow electron gun is compared with the gun under a conventional ppm magnetic field in consideration of thermal deformation and assembly errors.

A W-band multi-beam traveling-wave tube (TWT) based on sine slow-wave structure is designed. The cold bandwidths of the fundamental and higher-order modes in the slow-wave circuit are analyzed using HFSS software. Through reasonable structural design, the fundamental mode and low-order mode are suppressed. The beam-wave interaction capability of the multi-beam TWT is analyzed based on the high-order mode transmission design. At the voltage of 11.7 kV, the current density of the sheet electron beam is 96 A/cm2 which can be produced by the non-convergent electron gun, and the output power is over 150 W in the operating frequency 90 GHz-100 GHz.

A novel planar monopole antenna with dual-band circularly polarisation (CP) is presented here. The antenna consists of a modified L-shaped monopole, an inverted-L strip, and a modified ground. The utilisation of the modified L-shaped monopole not only generates dual-band operation, but also excites CP radiation in the lower band. In order to achieve CP in the upper band, a parasitic inverted-L strip is added on the top plane of the substrate and a modified ground is designed. The proposed antenna has been fabricated and tested, the measured -10 dB reflection coefficient bandwidths are 370 MHz (2.38-2.85 GHz) in the lower band and 2330 MHz (4.05-6.38 GHz) in the upper band. The measured corresponding 3 dB axial ratio (AR) bandwidths are 610 MHz (2.39-3 GHz) and 850 MHz (5.15-6 GHz), respectively. The overlapped -10 dB reflection coefficient and AR bandwidths can totally cover the WLAN bands, Wi-Fi bands, Bluetooth band, and partly cover the WiMAX bands. The proposed antenna owns bidirectional radiation characteristic and reasonable gain at both the lower band and the upper band.

An innovative complementary electric split-ring resonator metamaterial (MTM) structure applied as the slow-wave circuit for a cascade backward-wave oscillator (CBWO) operating in C-band is studied in this paper. The idea of a drift tube in a multiresonant cavity extended interaction klystron is borrowed to design a novel backward-wave oscillator (BWO). The construction of this device features two BWOs separated by a short cutoff waveguide for permitting the flow of the electron beam and stopping the electromagnetic wave. The high-frequency characteristics are analyzed and optimized by using a high-frequency structure simulator and computer simulation technology (CST). Meanwhile, the S-parameter retrieval approach is used to retrieve the effective permittivity and permeability. In addition, the CST code is adopted to investigate the performance of the MTM-based CBWO. The particle-in-cell simulation results show that the novel CBWO is capable of achieving over 51.77% electronic efficiency from 4.8344 to 4.8687 GHz. Meanwhile, the maximum electronic efficiency can reach 82.44%, corresponding to a peak output power of 14.51 MW at 4.8466 GHz. These results indicate that the MTM-based CBWO proposed in this paper has the characteristic of miniaturization, manufacturability, and high electronic efficiency.

A sine waveguide (SWG) traveling-wave tube with sheet electron beam tunnel is proposed to amplify the high-frequency terahertz wave. In this study, the slow wave characteristics including the dispersion properties and interaction impedances have been investigated by using the eigenmode solver in the 3D electromagnetic simulation software Ansoft HFSS. The truncated SWG slow wave structure possesses the relatively large average coupling impedance. The beam–wave interaction characteristics of truncated SWG with sheet electron beam tunnel are calculated by high-frequency simulation software CST. From the particle-in-cell simulation results, this beam–wave interaction circuit can produce >490 mW ranging from 0.845 to 0.855 THz with a corresponding gain over 22 dB.

In this study, a complete and viable plan about a W-band sheet beam travelling wave tube based on a staggered double vane slow wave structure is drawn up. The dispersion characteristics, transposition characteristics of high-frequency system, sheet electron beam gun, vacuum window, periodically cusped magnetic focusing system and beam–wave interaction are analysed by CST Microwave Studio, CST Particle Studio and HFSS. An attenuator is used in this device to suppress oscillation. A phase velocity taper is used to increase output power. The operation voltage is 20.6 kV and the current is 80 mA. With a 10 W input power, the output power is 1100 W versus the gain is 20.41 dB at 95 GHz. The peak amplitude approaches 1200 W versus the gain approaches 20.79 dB at 99 GHz.

Staggered double-vane slow wave structure as the core part of the travelling wave tube (TWT) has been more popular in recent years. However, the electron efficiency of this structure is not enough high for higher frequency, especially THz. In this study, phase-velocity-taper method is utilised for the improvement of TWT's efficiency at 340 GHz. The reflection and transmission coefficients of the whole tube with attenuator show good propagation characteristics over the wide frequency range from 330 to 345 GHz. The particle-in-cell simulation results indicate that the output power can increase about 32% at 340 GHz with respect to that of the without-taper structure. The corresponding electron efficiency is improved from 2.8 to 3.5% by phase-velocity-taper. However, the simulation results also show that the tube can produce over 30 W output power in the frequency range from 330 to 343 GHz with an operating voltage of 21.3 kV, a current of 0.043 A, and an input power of 10 mW. In addition, a sheet beam electron gun with a beam current of 43 mA, a beam voltage of 21.3 kV, and beam waist cross-sectional dimension of 0.3 mm × 0.08 mm is also designed as the particle source of the sheet-beam TWT.

Angle log-periodic meander line microstrip radial sheet beam traveling-wave tube is one kind of novel minimized vacuum device with low beam voltage. To generate and focus the radial sheet electron beam, a novel radial divergent sheet beam electron optical system, including the tractable radial sheet electron beam gun and miniaturized and feasible radial small tunable periodic cusped magnetic focusing system, is proposed in this paper. The fan-shaped radial sheet beam is emitted from the cylindrical surface cathode, compressed in axial direction, and confined in azimuthal direction by the focusing electrode. Simulation results show that the total emission of the angular radial sheet beam gun is 51.2 mA with the dimensions of $0.26~\text {mm} \times 8$ ° under the voltage of 1.7 kV, and the fan-shaped radial sheet beam can totally pass through the fan-shaped drift tunnel under the magnetic field. The experimental results are good in agreement with the simulation results. The tested angular radial sheet beam transmission efficiency is >90% in an 18.8-mm-length beam tunnel with the fill factor of 50%.

A Ka-band sheet electron beam (SEB) traveling-wave tube (TWT) based on three-slot staggered-ladder (TSTL) coupled-cavity slow-wave structure (CC-SWS) is proposed. The high-frequency characteristics of TSTL SWS were analyzed in detail. A well-matched input/output coupling system that solves the problem of energy coupling between the SWS and the external circuit was designed. A new method of loading the distributed attenuator for TSTL SWS was investigated for suppressing backward wave oscillation effectively. In addition, a SEB gun which can produce the SEB conveniently was optimized. A small tunable periodic cusped magnet (STPCM) system was designed to focus the low voltage, high-current SEB, which decreases the whole dimension of the TWT sufficiently. Moreover, the special STPCM system is predicted to exhibit 100% beam transmission efficiency. Finally, the beam-wave interaction was studied. The results obtained by CST simulation show that the SEB TWT can produce output power over 5 kW within the b...

A 140-GHz folded-waveguide traveling wave tube (FWG-TWT) with a relatively larger circular electron beam tunnel was designed and developed. Using simulation software, the high frequency characteristics, the transfer characteristics, and the beam-wave interaction of the TWT were studied in detail. The simulation predicted up to 98 W output power and about 43 dB gain of FWG-TWT at the center frequency. The input and output couplers compatible with the FWG-SWS and the periodic permanent magnet focusing structure were designed. The FWG-TWT thus designed was fabricated and tested. The experimental result shows the output power exceeding 1.6 W and the gain exceeding 25 dB at 140 GHz when the input power is 5 mW. The reasons for the departure of the experimental from the simulated results have been explained.

A new concept of oscillator based on a folded waveguide slow-wave structure (FWG SWS) is studied. The resonant cavity of the oscillator is formed by a section of FWG SWS, a length-adjustable waveguide, and a waveguide loaded by multilayer dielectric. The beam is synchronized with the forward wave on the SWS. If an FWG traveling-wave amplifier (TWA) is driven by this oscillator, there is a possibility that the amplifier and the oscillator share the same design and the same art of manufacturing and power supplier. A forward-wave oscillator based on a design of a TWA in 2-mm band is calculated by both a 1-D nonlinear code and particle-in-cell (PIC) simulation. From both the code and the simulation results, when the oscillator is 30-pitch long, the operation voltage 22000 V and the start current is 3 mA at 138 GHz. When the oscillator is 22-pitch long, operation current 15 mA, and operation voltage 22400 V, simulation result shows that the output power is 58.32 W, and the efficiency is 17.26% at 133.2GHz. When both the voltage and length of the length-adjustable waveguide are tuned, the oscillator can operate within all the first dispersion band of the SWS. If only voltage is tuned, the oscillator can oscillate at several discrete frequencies.

A novel angular log-periodic groove waveguide slow wave structure (SWS) for 340 GHz traveling wave tube (TWT) is proposed in this paper. Due to the unique characteristics of log-periodic form, the novel SWS could achieve a very low operating voltage and small scale at the same time. By using the groove folded waveguide, the high aspect ratio fan-shaped sheet electron beam could interact with electromagnetic wave in the groove tunnel. According to direct mathematical equation, the operating voltage is 6310 V at 340 GHz and the total length of SWS is 8.6 mm, which could get an output power of 36 W with 20.7 dB gain.

In this paper, multiphysics field simulation is applied to analyze the temperature distribution of Ka-band U-shaped microstrip line planar TWT considering the thermal losses induced by ohmic loss and electron collision losses. The beam-wave interaction of the planar TWT is analyzed by using CST particle-in-cell (PIC) solver, at the same time the thermal losses distribution is recorded, which will be the heat source. The simulation results show that the high temperature with a peak value of 263 °C.

A W-band TWT based upon flat-roofed sine waveguide slow-wave structure is designed. The transmission characteristics of high frequency structure with input/output window show that the $\mathbf{S}_{\pmb{2}}$ 1 is more than −4 dB and $\mathbf{S}_{\pmb{11}}$ is less than −16 dB. The beam-wave interaction results show that the output power is more than 40 W range from 90 GHz to 100 GHz with voltage of 19 kV and current density of 50 mA/cm2.

A sheet beam electron gun for 850GHz staggered double vane TWT is designed in this paper. The designed beam achieves a beam current of 20mA, beam voltage of 28.1kV and cross-sectional dimension of $\pmb{0.12}\mathbf{mm}\pmb{\times 0.03}\mathbf{mm}$ . And the beam transmission efficiency with a designed uniform permanent magnetic field is achieved with 95.7%. Finally the beam-wave interaction with above parameters is calculated and the output power is obtained with 33.8mW.

An electron optical system with long-range low emission current density electron gun and H-plane double-slit coupling input-output RF coupler are studied for 340GHz sheet beam staggered double vane traveling wave tube (TWT). The long-range sheet beam electron gun can reduce the difficulties in assembling and adjusting of the whole magnetic system. Low emission current density can reduce the processing difficulty and improve the life of the electron gun. The bandwidth of the microwave circuits with H-plane double-slit input and output couplers is so broad that can approach 45GHz. Taking the high frequency loss of copper into account, the beam-wave interaction simulation shows that the whole design provides 14.6W of output power and 31.6dB gain at 340GHz.

In this paper, a stacked dual beam electron gun and the associated electron optical system are proposed. The stacked dual beam electron gun includes two compact focusing electrodes which help to achieve dual sheet beams. As an application of this dual beam electron gun, a 340 GHz integrated dual beam traveling wave tube (TWT) based on the staggered dual vane slow-wave structure (SWS) is also put forward. In order to reduce the length of the TWT, a novel input/output coupler is introduced. The overall transmission characteristics of the SWS structure together with the input/output couplers show a wide bandwidth covering a frequency range of 306 GHz to 360 GHz. Based on the parameters obtained for the integrated TWT, a stacked dual-beam electron gun with dual focusing electrodes is designed to achieve a beam current of 43 mA, a beam voltage of 21.4 kV, and a cross-sectional size of each beam of 0.3 mm × 0.08 mm. A uniform magnetic field of 0.52 T is utilized to focus the dual electron beams, and a beam transmission efficiency of 97.1% is achieved over a length of 50 mm. Finally, particle in cell simulation results show that the integrated dual-beam TWT can generate an output power of 5 W over the frequency range of 315 GHz to 350 GHz, with the maximum output power of 24.5 W at 330 GHz. Published version

A novel slow-wave structure (SWS), named ridge-loaded sine waveguide (RLSWG), has been proposed to develop the wideband high-power terahertz traveling-wave tube (TWT). The slow-wave characteristics of the RLSWG SWS, including dispersion properties and interaction impedance, are analyzed by using the 3-D electromagnetic simulation software Ansoft high frequency structure simulator (HFSS). From our calculation, the average interaction impedance of the RLSWG SWS at 0.22 THz is 42.2% higher than the conventional SWG SWS. Meanwhile, the simulation results demonstrate that the RLSWG SWS possesses low ohmic losses and reflection. Moreover, the particle-in-cell (PIC) simulation results reveal that, with the cylindrical electron beam of 20.9 kV and 45 mA, the output power and electron efficiency of the RLSWG TWT at the typical frequency of 0.22 THz can reach 52.1 W and 5.54%, respectively. In addition, the 3-dB bandwidth of the RLSWG TWT exceeds 25 GHz. Compared with the SWG TWT, the RLSWG TWT has the shorter tube length and can generate the larger output power.

The symmetrical microstrip angular log-periodic meander-line (ALPML) slow-wave structure (SWS), which is suitable for Ka-band low-voltage traveling-wave tubes, is described in this paper. The dispersion characteristics and coupling impendence of this kind of SWS are achieved by simulation. A radial uniform magnetic field of 0.4 T is developed using radially magnetized permanent magnets to focus the radial sheet electron beam. To exploit the potentialities of the symmetrical ALPML SWS, the beam–wave interaction is carried out with a radial convergent and a divergent sheet electron beam. For the radial divergent electron beam with a voltage of 791 V and a current of 0.3 A, an output power over 60 W with an electron efficiency of 26% at 30 GHz is achieved from particle-in-cell simulation. The effects of misalignments and phase mismatches are carried out at the end.

In order to alleviate the problem of achieving large powers beyond 10 kW at frequencies as high as 220 GHz, a two-stage, two-sheet-beam relativistic TWT (SBRTWT) was proposed. For one-stage SBRTWT, there exists instability phenomenon as the effect of electron noise will become large enough compared with the small input power. To avoid the effect, the gain of the first-stage tube was decreased, and its output power was employed to drive the second-stage tube. A large-width branch-guide energy coupler was proposed, analyzed and designed, which can solve the difficult problem to couple the amplified microwave from a wide waveguide to another wide waveguide. A two-beam SBRTWT of 70 kW output with a gain of 28.5 dB was predicted. The findings establish that the two-stage configuration provides larger output powers than the single-stage configuration of SBRTWT and call for further research in two-stage SBRTWT.

In this paper, a high-power Ka-band traveling-wave tube (TWT) driven by a sheet electron beam is proposed and demonstrated by means of the simulation and experimental methods. The single grating rectangular waveguide with large width-to-height ratio is used as the slow-wave structure (SWS). An $E$ -plane bend energy coupler is put forward to feed this wide SWS. An irregular transition structure between the input waveguide and the SWS is suggested and designed, which is beneficial to suppress the self-excited oscillation. For a practical electron beam (20 mm $\times \,\, 1$ mm, 150.1 kV, 850 A, and 20-ns), the output power of this single rectangular grating sheet beam TWT is larger than 750 kW from 34.5 to 35.4 GHz. The maximum power is 1.21 MW at 35 GHz, corresponding to a gain of 20.4 dB.

This paper presents a novel limited-angle torque motor (LATM) with a moving coil for oscillating mirror system. The proposed LATM has a constant torque coefficient over its operation range, rapid dynamic response, and easy mounting oscillating mirror owing to a special structure of the stator and the rotor. In design process, some design equations are derived to analyze toque coefficient, moment of inertia, and other parameters of the LATM. A novel optimization approach is carried out to obtain the maximum torque/moment of inertia ratio in consideration of the stator outer diameter and volume limitations. Coil parameters have also been optimized by this method so that a less time constant can be obtained. In addition, 3-D finite-element analysis is performed for verifying the proposed optimization method. Finally, a prototype machine is accomplished and its experimental results are presented and discussed. Meanwhile, a conventional position closed loop system of the LATM is established to validate the dynamic performance of the LATM.

The rectangular helix has been proposed to develop a low-voltage, wide-band, and high-power millimeter-wave traveling-wave tube (TWT). This structure, which is evolved from the original circular helix slow-wave structure, is a kind of planar structure, which is suitable for the microfabrication technology. The high-frequency characteristics of the rectangular helix structure, including dispersion properties, interaction impedances, and reflection characteristics are investigated. The interaction between the sheet electron beam and the slow wave in the structure is also obtained by utilizing the particle-in-cell code in CST Particle Studio. A circuit sever is set into the rectangular helix to reduce the backward wave oscillation. Our calculations indicate that, at beam parameters of 9.95 kV and 40 mA, the averaged output power and the electron efficiency can reach 46 W and 11.5% at 140 GHz, respectively, and a transient 3-dB bandwidth of 6 GHz (ranging from 137 to 143 GHz).