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In this paper, the design of an interaction structure for a 10-kW, W-band gyrotron is presented. The beam voltage and beam current are chosen as 30 kV and 1 A, respectively. The mode of interaction...

The spectral properties of terahertz (THz) continuous-wave (CW) clinotrons have been studied both theoretically and experimentally. The resonant properties of clinotrons having strong influence on the spectral linewidth have been analyzed both for the frequencies below 150 GHz where resonances are determined by reflections of surface wave, and for THz tubes where resonances are caused mainly by the effect of mode transformations in oversized cavities. The influence of beam voltage ripples in THz clinotron on spectral line broadening has been studied and discussed. The clinotron spectral linewidth of 1.18 MHz has been demonstrated at 346.4 GHz with the output power of 100 mW when the output voltage stability of high-voltage power supply (HVPS) was 5 ppm.

A highly efficient and compact metamaterial extended interaction oscillator (MEIO) is characterized and designed. The power exchange function of the multiple-gap extended interaction resonant cavity loading the proposed metamaterial is investigated for the π mode. Furthermore, the cavity diameter of 5-gap MEIO is only 37 mm at S-band. The CST PIC simulations show the peak output power of about 10 MW and the electronic efficiency up to 48% at 2.866 GHz when the beam voltage and current are 130 kV and 80 A, respectively, and the focusing magnetic field is 2000 G. The simulation results suggest that the proposed MEIO has the potential application in the future accelerators as an MW-level high-efficiency, miniaturized microwave source.

in this paper, we present a design on a 30 GHz 100 kW-level gyrotron. The cold-cavity of the gyrotron has been studied by using an in-house gyrotron simulation code and CST microwave studio, respectively. Meanwhile, in the hot-cavity analyses, the behavior of multi-mode beam-wave interaction has been studied in detail by using PIC simulation with the help of CST particle studio. The results present that the gyrotron can operate at TE 0.3 mode stably with the output power of 150 kW under the operating conditions: beam voltage of 50 kV, beam current of 10 A, magnetic field of 1.14 T, and pitch factor of 1.3.

Sheet beam electron gun and focusing system are key parts of sheet beam traveling wave tube. In this paper, a 220 GHz sheet beam electron gun is designed and a novel tunable periodic cusped magnet (NTPCM) focusing system for this sheet beam electron gun is proposed. The beam current of the designed sheet beam electron gun is 0.13 A at 22 kV beam voltage, and the sheet beam size at beam waist is around 0.5 mm × 0.1 mm. Furthermore, the simulation results show that the sheet beam with current density greater than 260 A/cm2 can transport more than 90 mm under the focusing of this NTPCM.

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.

To increase output power of W-band pulsed millimeter-wave traveling-wave tubes, a prototype tube with phase velocity step-tapering circuits was designed and fabricated. The simulation methodology involved the optimization of the phase velocity step-tapering, cold characteristics, and particle-in-cell (PIC) simulation. The testing data show that it was capable of delivering an output power of over 250 W in a frequency range of 89.6–97.6 GHz (8 GHz), with a maximum power of ~424 W and electronic efficiency of ~10% at 92.9 GHz, with 189-mA beam current and 22.5-kV beam voltage. Besides, more than 4-GHz bandwidth with output power of over 300 W and electronic efficiency of over 7% was obtained with saturated gain over 36 dB. It was also found that the tested output power from the prototype tube was in an excellent agreement with the PIC simulated result.

Conventional klystrons using single beam of electrons have several limitations for increasing of beam voltage or current which can be overcome using multiple electron beams. The paper presents the design of a single beam electron gun for a practical 100 kW CW conventional klystron and then translation of the design into a five-beam gun for reducing operating voltage and overall improvement in tube performance. The design parameters of multi beam electron gun have been derived from existing single beam parameters using some scaling laws, and are further optimized through CST Particle Studio. The simulation results of CST have been cross-validated using Opera-3D code. The electron gun is currently under development.

In this paper, a 28GHz second harmonic gyrotron with gradually tapered complex cavity is simulated and designed. In order to achieve high efficiency at second harmonic, we analyse the influences of the structural parameters on interaction efficiency, the effects of the electron beam parameters are also analyzed. The simulation results shows that the designed gyrotron can obtain output power of 28.47kW when the beam current is 2A, beam voltage is 49kV. The corresponding efficiency can reach to 29.06%.

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.

A novel two-beam oscillator-amplifier based on planar helix slow-wave structure with straight-edge connections is presented. The device combines the operation of both oscillator and amplifier in a single slow-wave structure. the simulation results show that the operating frequency of the oscillator-amplifier tunes from 14.1 GHz to 19.1 GHz when the beam voltage for backward-wave synchronization varies from 3 KV to 8 KV. The output performance of the oscillator-amplifier is compared with that of the conventional backward wave oscillator (BWO) using the same slow-wave structure. The comparison shows that the oscillator-amplifier gives an efficiency improvement of at least two times compared to that of the conventional BWO. Significantly, the oscillator-amplifier preserves the size as well as the tuneable bandwidth of the conventional BWO.

650 GHz FWTWT designs have been presented using 3-D simulations. The preliminary simulation results show that the amplifier can produce an output power of over 1 W, 23dB gain, and a 10GHz bandwidth where beam voltage and current are l6kV and 10rnA, respectively.

This paper presents the design and simulation of CEPC 650MHz/800kW CW multibeam klystron. To get high efficiency, single beam perveance is chosen to be as low as $\pmb{0.2\mu} \mathbf{P}$ . On the other hand, beam voltage is 54kV which could be considered as a safe vale in CW operation. Three dimensional PIC simulations of CEPC MBK predict an efficiency of 80%.

A kind of gradually tapered cavity for a high-order mode 140 GHz, 1 MW gyrotron has been Studied to effectively suppress the parasitic modes at the University of Electronic Science and Technology of China recently. The $\mathbf{TE}_{\pmb{29,8}}$ mode is selected as an operating mode of the desired gyrotron. A gyrotron with optimized parameters have been designed and constructed. An output power of 1.2 MW is obtained by calculation at an accelerating beam voltage of 75 kV by simulation, a beam current of 45 A, corresponding to an overall efficiency of 35.5%.

A Ka-band high gain extended interaction klystron (EIK) with five Hughes-type three-gap coupled cavities is designed and 3D particle-in-cell (PIC) simulation by CST code is performed to calculate the performances of the EIK in this abstract. Under the beam voltage of 14 kV and the current of 1 A, the RF output power is 2.15 kW at the operating frequency of 35 GHz. The corresponding gain and efficiency are 43.78 dB and 15.36%, respectively, and the 3 dB bandwidth reaches 248 MHz.

The preparation of high-quality, economic and scalable thin films are crucial for future applications in efficient thermoelectric devices. Ion Beam sputtering deposition appears as an elegant solution to tackle this challenge and in this context it will be used in this work. Thus herein, we assess the influence of the beam voltage in the thermoelectric properties through a thorough study of the morphological, chemical and transport properties in the produced thin films. It outcome that beam voltage drastically influences the stoichiometry leading to different crystalline structures that directly affect the thermoelectric properties of the Bi-Te deposited thin films.

For future broadband wireless links, we have designed a 300 GHz band traveling wave tube (TWT) with a folded waveguide fabricated by microelectromechanical systems (MEMS). The TWT operates at a beam voltage of 12 kV and a beam current of 8.3 mA. The classical large signal simulation code predicts the output power greater than 1 W and gain larger than 20 dB over the bandwidth from 280 to 300 GHz.

For most conductive materials, resistance remains constant over time in the absence of external physical stimulation. Here, we report the time-dependent resistance of a quasi-two-dimensional electron gas (Q2DEG) on a KTaO3 substrate. Ar+-ion bombardment is used to achieve a Q2DEG of high density. Such a Q2DEG shows a linear increase in resistance with time without further physical stimulus. Both the resistance and its increase rate can be determined by the beam voltage of Ar+ bombardment. Furthermore, we find that light illumination strongly influences the increase rate of resistance, with the effect depending primarily on the wavelength of incident light. The Hall effect reveals that this phenomenon can be attributed to the spontaneous decrease in carrier density over time due to the migration of oxygen vacancies. Our work offers a pathway toward a self-excited resistance timer in a Q2DEG system.

A 140 GHz high power gyrotron has been developed at the University of Electronic Science and Technology of China recently. The TE29, 8 mode is selected as an operating mode of the desired gyrotron. A gyrotron with optimized parameters has been designed and constructed. An output power of more than 1 MW is obtained by calculation at an accelerating beam voltage of 75 kV by simulation, a beam current of 45 $A$ , corresponding to an overall efficiency of 35.5%.

To gain higher power, a novel rectangular beam folded waveguide traveling wave tube (RBFWG-TWT) was proposed in this paper. A 3-D CHIPIC code was introduced to analyze the amplification performance of RBFWG-TWT. The output power varying with voltage andfrequency was observed. The nonlinear phenomenon was simulated and analyzed in detail. It reveals that when the beam voltage and current are set to be 14.6 kV and 120 mA, respectively, the output power gain of RBFWG-TWT can reach 30.58dB, with a 3dB bandwidth of 30 GHz.

The bandwidth of the high power klystron strongly depends on its output power level. Usually, the relative bandwidth is about 1~2% for X-band CW klystron with output power of several kilowatts. The relative bandwidth of 3~4% is required for some application for 5kW X-band CW klystron. In this paper, the design and calculation of the X-band klystron are presented. By optimizing the parameters of electron beam and RF interaction section, the relative bandwidth of 4%, efficiency of 25%, gain of 25dB have been obtained for 5kW X band CW klystron at beam voltage of 14kV and beam current of 1.66A. The influence of beam filling factor and radius of beam channel on the efficiency-frequency characteristics are described and discussed.

The technology of photonic crystals (PhCs) is investigated here to improve the performance of THz vacuum electron devices. Compared with conventional metallic waveguides, the PhC arrangement alleviates typical issues in THz vacuum electron tubes, i.e. difficult vacuum pumping process and assembling, and improves the input/output coupling. A slow-wave structure (SWS) based on a corrugated waveguide assisted by PhC lateral walls and the efficient design of a PhC coupler for sheet-beam interaction devices are demonstrated. Based on the proposed technology, a backward-wave oscillator (BWO) is designed in this paper. Cold parameters of the novel PhC SWS as well as 3-D particle-in-cell simulations of the overall BWO are investigated, obtaining more than 70-mW-peak output power at 0.650 THz for beam voltage of 11 kV and beam current of 6 mA.

A G-band rectangular beam multi-gap Extended Interaction Klystron (EIK) with unequal-length gaps is proposed. The high-frequency features indicates that the designed model has wide frequency intervals with π mode, which has a good uniformity in field distribution with the maximum (R/Q)•M2. The PIC simulation shows a stable output power of 1378 W without oscillation in 218.9 GHz, with the efficiency of 16.7% and 3dB bandwidth over 1 GHz under the 16.5 kV beam voltage, 0.50 A beam current.

Communications & Power Industries LLC has designed and manufactured the VKP-8292A, a high peak power, high efficiency, UHF band klystron. The klystron operates at 704.42 MHz, with 1.59 MW peak output power, 78 kW average output power, and a gain of 45 dB. The klystron is designed to operate between 0.3 MW and 1.2 MW in the linear range of the transfer curve. The klystron is over 67% efficient at nominal beam voltage and includes optimization for efficiency at lower beam voltages. Experimental and predicted performance data are compared.

The extended interaction klystron (EIK) operating at high order mode has many advantages compared with conventional EIK in high frequency band for its oversized structure. A five-gap cavity operating at the TM31-2π mode with resonant frequency of 0.34 THz is investigated in this paper. Resonant modes in the overmoded cavity are analyzed for mode selection and stable operation. Finally, the cavity is theoretically approved stable operation at the TM31-2π mode without self-oscillation and mode competition under 15 kV beam voltage and 300 mA beam current.

In this paper, a 220GHz folded waveguide traveling wave tube (FW-TWT) was designed based on theory and simulation. Firstly, the FW-TWT was analyzed by small signal theory. The small signal gain varying with the beam voltage and current was solved by the small signal theory. Then the FW-TWT was simulated by the Particle-in-cell (PIC) simulation. The output power varying with voltage and frequency was simulated. According to the theory calculation and simulation, the performance of the 220GHz FW-TWT can be predicted.

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.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 pr...

A 140 GHz high power gyrotron with a gradually tapered cavity has been investigated and formed at the University of Electronic Science and Technology of China recently. After the study of cold cavities, a set of operating parameters of the optimized cavity is obtained as the TE29,8 mode is selected as the operating mode. The startup-scenarios of the potential competition modes have been investigated by simulation, which is based on a kind of quasi-self-consistent nonlinear theory for gyrotrons. After a lot of calculations, a better startup scenario is confirmed. Under the conditions that the beam voltage varies in 5 kV steps and the beam current and DC magnetic field are of 45 A and 5.64 T, respectively, the gyrotron with the operating mode TE29,8 brings out a theoretical power level of 1.2 MW at 140 GHz, corresponding to an overall efficiency of 35.5%. Meanwhile, the powers of parasitic modes are very low when the gyrotron operates at the proper parameters. At the same time, to study the limit state and its parameters of the designed gyrotron, further research has been carried out.

In this paper, a novel extended interaction klystron output cavity is presented. With the help of a three-dimensional (3D) particle-in-cell (PIC) simulation, design and optimization geometry of the cavity is performed, which is composed of ladder loaded rectangular waveguide. In present work, the output continue wave (CW) power 724W is achieved, the efficiency and bandwidth reaches 7.5% and 1300MHz, which is operating at beam voltage and beam current is 16 kV and 0.6A , respectively.

The beam-wave interaction calculation of a Ka-band Extended Interaction Klystron with five double-gap coupled cavities is presented in this abstract. 1D large signal results are in good agreement with 3D Particle-in-Cell (PIC) results simulated by CST code. Under the beam voltage of 14 kV and the current of 1 A, the RF output power is 3.86 kW, and the corresponding gain reach 46.84 dB with a 3 dB bandwidth of 175 MHz at the operating frequency of 35 GHz.

A multiple gap ladder structure resonant cavity is designed for a G-band extended interaction klystron (EIK) with an unequal-length periodic structure. With a beam voltage of 16.5 kV, the resonant frequency of 220.20GHz which is working on p mode is obtained by theoretical calculation and cold simulation. The results show that the unequal-length periodic structure can have higher characteristic impedance comparing with the same gaps equal-length structures, which is more important for the broad-band EIK later.