This article introduces the design and experimental study of a Ku-band continuous wave tunable klystron. The device mentioned above adopts a single electron beam and six tunable resonant cavities, it operates at a cathode voltage of 9.5 kV, and the cathode emission current is 1.05 A with an axial guiding magnetic field of 0.34 T. To reduce the heat dissipation of the collector and improve the efficiency, the device adopts a four-stage depressed collector design, and the collector adopts forced air cooling for heat dissipation. Finally, the assembled sample tube is tested in detail. The dc beam transmission is over 99% and the high-frequency beam transmission rate is above 97%. The device can output continuous wave power of over 2.6 kW in 1.2-GHz tuning frequency range, with 1-dB instantaneous bandwidth (BW) exceeding 60 MHz at each working frequency channel. Tube gain exceeds 51 dB, and efficiency exceeds 40%. The experimental results are in good agreement with those obtained by the 1-D and 3-D simulation. The development of this device provides important technical reference for wideband mechanically tuned klystron products and has significant importance.

This article presents some important improvements of the S -band broadband klystron development. In the course of hot test of an S -band 800-kW peak power klystron with 250-MHz instantaneous bandwidth (the equal-driving input power), the power dip and RF breakdown phenomenon has described. Through simulation analysis and experimental investigation, the technological problems have been solved. The retrofitted klystron has been conducted and tested, the fluctuation of output power is less than 0.5 dB within 250-MHz bandwidth at constant drive power, and the RF breakdown problem of the output system is overcome. The improvement of the waveform of the klystron has also been made.

The multibeam klystron (MBK) is a compact high-power microwave vacuum electronic device that features low beam voltage, high efficiency, wide bandwidth, and low volume and weight. Since the 1960s, high-performance broadband MBKs have been developed that cover the entire microwave frequency band with relative instantaneous bandwidths $>$ 15%, peak power $>$ 1 MW, average power up to 40 kW, and efficiencies $>$ 40%. In recent years, driven by the needs of high-energy particle accelerators, ultra high frequency (UHF) and ${L}$ -band MBKs with peak powers of more than 20 MW and efficiencies of nearly 80% are being developed. This article presents an overview of the development of broadband MBKs used in microwave electronic systems, such as radar and communication, and high-power MBKs used in the RF systems of particle accelerators. It also introduces the latest progress and development trends in MBKs leading to higher frequency, output power, bandwidth, efficiency, and lifetime.

High peak power multi-beam klystrons (MBKs) often use coaxial cavity as RF interaction circuits. Due to the influence of the coupling port between the cavity and the waveguide, the electric field distribution in the electron beam channels is uneven, so that the efficiency of the MBKs cannot reach the maximum. Based on the design of X band 3MW MBK, the electric field distribution of several types of coaxial cavity output circuits is calculated by using CST microwave studio. It is found that adding a fan-shaped metal ring to the inner conductor of the coaxial cavity can make the electric field distribution distortion, thus compensating for the electric field non-uniformity caused by the coupling port. This structure combined with filter loaded circuit can further improve the electric field uniformity. Comparing with the traditional output structure, the ratio of the maximum value to the minimum value of the characteristic impedance R/Q of the electron beam channels of this structure decreases from 9.83 to 1.45, and the efficiency of the MBK increases from 43.7% to 52.15%.

In addition to the working mode $TM_{010}$ mode, there are also many high-order modes in the cavity of the klystron. These modes have an important influence on the stability, output spectrum and other performances of the klystrons, especially broadband klystrons. This paper introduces the problem of high second harmonic level (-10dBc) and the breakdown of RF output system at certain frequency of the low frequency end of the S-band broadband klystron. Through analysis and simulation, it is determined that the problem is caused by the $TM_{011}$ mode of the front cavity of the double gap coupling cavity (DGCC) broadband output circuit. By placing a metal ring at the middle of the front cavity, the resonant frequency of the $TM_{011}$ mode decreases from 4.634GHz to 4.552GHz, which is lower than 2 FL (Lowest operating frequency of the klystron). The test of this klystron shows that the second harmonic level of the operating frequency is lower than - 30dBc. At the same time, the breakdown problem of the output system is overcome. The performance of the klystron fully meets the user's requirements.

In order to meet the high-power source requirement of compact submillimeter-wave systems, a high-power G-band extended interaction klystron (EIK) has been developed at the Aerospace Information Research Institute, Chinese Academy of Sciences (AIRCAS), and reported for the first time. The extended interaction circuit design based on over-synchronous voltage and high quality factor is proposed to enhance the output power and gain. In this manner, the designed EIK has achieved excellent test results compared with the same type of compact devices. Driven by a 20.3 kV, 198 mA pencil electron beam, the EIK can deliver a pulsed output power greater than 120 watts at around 0.22 THz, corresponding to a gain of 32 dB with a 5% duty cycle, and the average power and −1 dB bandwidth are 6 watts and 180 MHz respectively. Constrained by an axial magnetic field of about 1.03 T, the beam transmission is around 92% in RF operation.

This paper presents the design and measurement results of an X-band broadband klystron with a peak power of 1MW developed at Aerospace Information Research Institute, Chinese Academy of Science (AIRCAS). In the development of this klystron, the single electron beam with an electromagnetic focusing system was adopted to achieve a high beam transmission rate. Meanwhile, a filter-loaded over-lapping mode double gap coupling cavities output circuit (OMDGOC) and a pill-box output window were used to ensure the klystron has an operating bandwidth of 650MHz. The 1# klystron was tested under a 1 % duty ratio at 27 operating frequency points. The technical specifications of this klystron are as follows: peak power: over 1MW, efficiency: over 24.3 %, gain: over 37.1dB, beam transmission rate: over 96%, which meet the design requirements.

To predict the stability of a multi-gap extended interaction cavity used in the klystrons, a general electron conductance expression has been rigorously derived from the small-signal space charge wave theory, where the field shape at the gap edge is described by a uniform distribution or a hyperbolic cosine function. Moreover, it is also pointed out that a simplified expression is acceptable in applications. This formula can be readily applied to the solid and annular beams, and its validity has been demonstrated through the stability analysis of a triple-gap extended interaction cavity, where the effect of adopting different gap field shapes is presented. This general expression is very useful for the parameter choice during the cavity design of extended interaction klystrons.

The triple-gap cavity technology is an important means to expand the bandwidth of the klystron output circuit. In order to realize 1 GHz output bandwidth for $X$ band klystron, the equivalent circuit simulation of the triple-gap cavity is carried out. The actual cavity size is determined by the designed electrical parameters and the cold test model is processed. Based on the microwave network analysis theory and perturbation theory, a test method for the gap impedance of the triple-gap cavity was designed, and the output circuit of the klystron with a bandwidth of 1 GHz (9150 MHz-10150 MHz) was tested, which laid an important technical foundation for the development of broadband klystrons.

This study reviews the research progress of high-power electromagnetic pulse generation. It introduces the physical model, different technologies, and the experimental generation of ultrafast, ultrashort, and ultra-high-power electromagnetic pulses. Progress on the radiation effects of electromagnetic pulses and the measured damage thresholds of microcontroller and photo-electronic devices are also discussed. Finally, future research prospects in this field are suggested.

In this paper, a new physical model of the resonant microwave pulse compression is proposed. In the new model, opposite to the traditional theory and technology, the branch-output waveguide are set at the peak of the standing wave of the microwave resonant cavity, rather than at the node as in traditional model. The simulation results shown that, for the rectangular TE10 mode in the over-sizeded microwave resonant cavity, the following requirements of the energy-coupling coefficient ßs=0.5, the TW-power gain G=120, and the combined peak power Po=480MW/3.5ns can be realized at 2.92GHz, when the cavity is driven by an advanced high-power klystron with input of IMW/2.92GHz/50µs.

为了计算高品质因数谐振腔的储能过程和泄能过程,将高品质因数谐振腔的输入膜片和输出结构分别建模为一个二端口网络和一个三端口网络,根据高品质因数谐振腔的信号流图,提出了一种基于递推的数值计算方法.用该方法设计了一个工作在2.92 GHz附近的基于BJ32波导的高品质因数谐振腔,给出了谐振腔的储能过程和泄能过程.当输入膜片开口宽度取20 mm、输出膜片开口宽度取60 mm时,计算得出的谐振频率为2.9198 GHz,饱和储能时间为2.6μs,输出脉冲宽度6.82 ns,输出峰值增益为129.6,能量效率为0.169.

大功率速调管是一种基于速度调制原理将电子注能量转换成微波能量的微波真空电子器件,它具有高功率、高效率、高增益和高稳定性等优点,是微波真空电子器件中脉冲功率和平均功率最高的器件.速调管自20世纪30年代发明以来,在粒子加速器、雷达和通信等微波电子系统,以及真空电子技术进步的推动下,已发展成功多种类型大功率速调管,其频率覆盖整个微波,并扩展到毫米波和太赫兹波段,最大脉冲功率达200 MW,最大平均(连续波)功率达MW级.近年来,在高能粒子加速器、宽带雷达系统、毫米波和太赫兹波电子系统的推动下,大功率速调管取得了令人瞩目的进步,本文比较系统地介绍了大功率速调管的技术现状和在提高功率、提高效率、提高工作频率、展宽带宽等方面取得的最新进展.

A continuous wave X-band klystron producing output power of 4 kW and bandwidth of over150MHz has been designed in Institute of Electronics, Chinese Academy of Sciences (IECAS). The design, manufacture, and test results have been reported in this paper. The results indicate that the performance of the tube satisfies the design requirement. The improved tube has a beam transmission rate over 97%, and operates very stably.

This paper introduces a method of response analysis of RF circuit system for the design of a W-band Extended Interacting Oscillator (EIO). The RF system design adopts $\pmb{2\pi}$ operating mode, trapezoidal slow wave structure with dual coupling slots. With regard to the frequency response of the output circuit, it can be analyzed and compared by CST software and the vector net test. The electric field distribution of three frequency responses is observed by simulation. Among them, the groove can be confirmed by short circuit, and the other clutter needs to be confirmed by PIC simulation to verify the reliability of the design scheme.

The Institute of Electronics, Chinese Academy of Sciences (IECAS) is developing a new Ka-band 1kW CW extended interaction klystron (EIK) for using in microwave power transmission system. The designs of the EIK are presented in the paper. And the results of design and calculation can reach the required specification.

This paper introduces the research progress of a W-band Extended Interaction Oscillator (EIO). The EIO is designed to produce a continuous wave power of over 100 Watts at nearby 95GHz operating frequency, and adopts 2π operating mode, trapezoidal slow wave structure with 24 periods and a beam-to-tunnel radial fill factor of less than 0.625, whose operating voltage is 11 kV with a beam current of 0.15 A. Then, the first sample tube is manufactured under the condition of low assembly precision recently. The preliminary hot test results show that, the output peak power is more than 30W when the operating frequency is 95.16GHz and the operating voltage is 11.4kV with a beam current of 0.14A, while the beam transmission is ~50%. Next, it is necessary to use a more effective method to improve the assembly precision in the process of manufacture.

This paper introduces the design results of RF circuit system for use in a G-band Extended Interaction Klystron (EIK). And the EIK can produce an output power of over 100 W, whose operating voltage is 16 kV with a beam current of 0.35 A. The RF system design adopts 2π operating mode and trapezoidal slow wave structure, meanwhile the tuning structure for cavity is considered by choke piston. Considering the power loss caused by the roughness and itself of copper material in the practical engineering, the conductivity of copper material is respectively set to 1.5e+7S/m. Structure parameters of the RF system are simulated and optimized by PIC (Particle in Cell) code. Then, simulation results of final RF system show that: When the material loss is considered, in the case of bandwidth great than 1.4 GHz, the output power is greater than 100 W, the gain is over 33.4 dB, the efficiency is over 3.4%, the spectral characteristics is good, to meet the requirements.

A modeling approach is proposed based on transmission line theory for the characterization of the periodic rectangular waveguide grating (RWG) structure. Using an equivalent circuit (EC) model the dispersion equation of the structure is derived with largely reduced workloads as compared to the conventional field-theory method. An EC based analysis of the RWG structure is performed. Numerical results show a good consistency between the two methods as varying structural parameters of significance. The proposed approach is also used for the taper design with the objective of minimizing wave reflection of the structure. A resulting multistage taper can deliver a low cumulative reflection coefficient on the order of 10^{-3}. Furthermore, the coherence performance of an RWG based planar Cerenkov maser (PCM) is studied on the driving electron beam interacting with the traveling harmonic wave. This includes the impacts of the grating height uniformity, due to practical machining uncertainty, on the net wave reflection as well as on the growth rate of the wave in the maser. The obtained results show, that a non-uniformity on the order of 50 micrometers in the grating height can increase the reflection level by at least one order of magnitude. The PCM coherence can be considerably degraded, in terms of a significant reduction in the wave growth rate of more than 30% with respect to its theoretical value.

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.