Development and testing of a high-power S-band klystron at BINP SB RAS

This paper details the development and testing of the first working prototype of the S-band high-power klystron,accomplished at the Budker Institute of Nuclear Physics,Siberian Branch,Russian Academy of Sciences(BINP SB RAS).Upon testing,the klystron demonstrated the following parameters:an operating frequency of 2856 MHz and a peak power output of 50 MW.The paper presents the klystron's design,its constituent units,and pertinent processing procedures,along with discussions on the measurement of its parameters.

Design and development of radio frequency output window for circular electron–positron collider klystron

This paper presents the first phase of design, analysis, and simulation for the klystron coaxial radio frequency（RF）output window. This study is motivated by 800 kW continuous wave（CW）, 650 MHz klystrons for the future plan of circular electron–positron collider（CEPC） project. The RF window which is used in the klystron output section has a function to separate the klystron from the inner vacuum side to the outside, and high RF power propagates through the window with small power dissipation. Therefore, the window is a key component for the high power klystron. However, it is vulnerable to the high thermal stress and multipacting, so this paper presents the window design and analysis for these problems. The microwave design has been performed by using the computer simulation technology（CST） microwave studio and the return loss of the window has been established to be less than-90 d B. The multipacting simulation of the window has been carried out using MultiPac and CST particles studio. Through the multipacting analysis, it is shown that with thin coating of TiN, the multipacting effect has been suppressed effectively on the ceramic surface. The thermal analysis is carried out using ANSYS code and the temperature of alumina ceramic is lower than 310 K with water cooling.The design result successfully meets the requirement of the CEPC 650 MHz klystron. The manufacturing and high power test plan are also described in this paper.

Design and high-power test of 800-kW UHF klystron for CEPC

To reduce the energy demand and operation cost for circular electron positron collider(CEPC), the high efficiency klystrons are being developed at Institute of High Energy Physics, Chinese Academy of Sciences. A 800-k W continuous wave(CW) klystron operating at frequency of 650-MHz has been designed. The results of beam–wave interaction simulation with several different codes are presented. The efficiency is optimized to be 65% with a second harmonic cavity in three-dimensional(3D) particle-in-cell code CST. The effect of cavity frequency error and mismatch load on efficiency of klystron have been investigated. The design and cold test of reentrant cavities are described, which meet the requirements of RF section design. So far, the manufacturing and high-power test of the first klystron prototype have been completed.When the gun operated at DC voltage of 80 k V and current of 15.4 A, the klystron peak power reached 804 k W with output efficiency of about 65.3% at 40% duty cycle. The 1-d B bandwidth is ±0.8 MHZ. Due to the crack of ceramic window, the CW power achieved about 700 kW. The high-power test results are in good agreement with 3D simulation.

DEVELOPMENT OF 50MW S-BAND KLYSTRON

This letter reports the development of a 50MW S-band klystron in the Institute of Electronics, Chinese Academy of Sciences （IECAS）. It adopted a structure of six-cavity and single output window. Under conditions of an RF （Radio Frequency） pulse width of 4t, ts, a beam voltage of 305,9kV and a beam current of 368A, the peak output power has achieved 51.4MW with an efficiency of 45.6% and a gain of 54dB.

METHODS FOR IMPROVING EQUIDRIVING POWER-FREQUENCY CHARACTERISTICS OF BROADBAND HIGH POWER KLYSTRON

Two methods for improving the equidriving power-frequency characteristics of broad-band high power klystrons are presented. One is that a comb-line bandpass filter with someattenuation properties is inserted between the TWT driver and the klystron for compensatingthe gain-frequency characteristics of the klystron to get the required equidriving power-frequencycharacteristics. The other is that a reactive element is connected with the input cavity to changeits resonance frequencies f0 and QL, and thus to improve the power-frequency characteristics ofthe klystron.

Reconstruction of -35 kV/200 kW HVPS for Test of Klystron Units in LHCD System

The paper introduces the -35 kV/200 kW high voltage power supply (HVPS) which is specially used to test klystron units in LHCD system. The new klystrons must be tested under high voltage level before operation and the old klystrons which have worked for a longtime must be exercised by HVPS in lower hybrid current drive (LHCD) system. As the former HVPS has some shortages in engineering design and operation design, the HVPS has to be modified and rebuilt by adopting new method and technology to solve existing bottle-neck problems.

DESIGN OF BEAM-WAVE INTERACTION BASED ON HIGH EFFICIENCY OF A HIGH-POWER BROADBAND KLYSTRON

The paper mainly presents the design of beam-wave interaction of a C-band high-peakpower high-efficiency broadband klystron.The beam-wave interaction section is designed based on considerations of efficiency and bandwidth synthetically.As a part of beam-wave interaction section,buncher section is simulated by Particle-In-Cell(PIC) code to observe the bunching process of electron beam to achieve high conversion efficiency of electron beam and RF field.When it comes to the other part,output circuit is designed as a three-section filter by an output cavity loaded with Chebyshev filter,and the cold test results are given.The beam-wave interaction is simulated by EGUN code and Arsenal-MSU code respectively.The simulated results indicated that,the existence of power dips in the operating bandwidth is verified by Arsenal-MSU code,comparing proper results by EGUN code.Then,the method that design parameters are not adjusted except parameters of buncher cavities to remove potential power dips is described.What is more,the simulated results of electron optics system are given by EGUN code and Arsenal-MSU code respectively.The further hot test results of klystron prove that the whole design of beam-wave interaction is effective.

AES Encrypted FSK Generation at X-Band Frequency using a Single Reflex Klystron

This paper describes a high security data transmission system over X-band microwave frequency. The paper has two parts. The first part deals with encryption of binary data by Advanced Encryption Standard (AES) using VHDL modeling of Field Programmable Gate Array (FPGA). The second part deals with a novel idea of transmitting the encrypted data by using a single klystron. This requires the simultaneous generation of a pair of two independent RF frequencies from a reflex klystron working for X-band frequency range. In this scheme, the klystron is suitably biased on the repeller terminal and superimposed on a train of AES encrypted binary data so as to create two RF frequencies one corresponding to negative peaks and the other one to the positive peaks of the data resulting in an Frequency Shift Keying (FSK) signal. The results have been verified experimentally.

DEVELOPMENT OF AN S-BAND KLYSTRON WITH BANDWIDTH OF 11%

This letter introduces the design ideas, simulation and test results of an S-band klystron with bandwidth of 11%, which was developed by the Institute of Electronics, Chinese Academy of Sciences (IECAS). On the peak power level of 800 kW, the efficiency of klystron is more than 30%; the gain is more than 41 dB; the equal-driving relative instantaneous bandwidth is over 11%; the average power is larger than 8 kW, and the power fluctuation within bandwidth is less than 1.5 dB.

RECENT PROGRESS IN MULTI-BEAM KLYSTRON IN IECAS

Recent research progresses in Multi-Beam Klystron (MBK) in IECAS are briefly introduced in the letter. The S-band MBKs of IECAS have peak power of 120-250 kW, average power of 4-9 kW, efficiency of 35-45%, gain of 41-46 dB, beam voltage of 15-19 kV, and weight of 40-45 kg. Some key technical problems of MBK are also described and discussed. Among them,improving the design of MBK to obtain the required bandwidth, raising beam transmission to increase average power, eliminating oscillation and spray spectrum, overcoming window breakdown caused by magic mode, reducing breakdown times of electrongun, are most important things for the practical MBK. Besides, further research work in MBK in IECAS is commented.

The Design of the Microwave Exciter for Klystron

To carry out lower hybrid wave heating and current drive plasma experiment on tokamak, we need mega-watt order of microwave power generated by the parallel-running klystrons. Those klystrons must be driven by the microwave exciter. Now our microwave exciter is used for many years and its performance is decreased very much. It can not satisfy any more the hybrid wave heating and current drive plasma experiment. So we set out to design a new microwave exciter that is consist of the microwave solid components, amplitudestabilization control, modularization design with multitude-outputs, microwave phase control in order to satisfy the demand of the different work in the hybrid wave heating and current drive plasma experiment.

Analysis of the measurement field of the optical klystron

The measured fields of the optical klystron in NSRL (National Sy-chrotron Radiation Laboratory) are given, including the distribution on the axis, and the integrated field distribution. The harmonic magnet field and the spectra of the spontaneous emission are analyzed, and the multiple field is presented by fitting the diagram. The infiuence of the integrated field on the close orbit of the beam and on the operation parameters of the storage ring, and the compensation in the experiment are also discussed.

Periodic atomization characteristics of simplex swirl injector induced by klystron effect

The atomization dynamic characteristics of a simplex swirl injector was investigated experimentally by using a hydrodynamic mechanical pulsator and the shadow photography technique. The frequency response characteristics of the fluid film and atomization fluctuations and their correlations with pressure fluctuations were obtained by using an in-house code of image processing. It is demonstrated that the klystron effect induced by periodic pressure fluctuations results in periodic liquid film fluctuation with large amplitudes, periodic superposition of droplets and reduction of the breakup length. It was found that the atomization of the simplex swirl injector only responds to the pressure fluctuation in frequency range approximately from 0 to 300 Hz, and it is particularly sensitive to pressure fluctuations at frequencies from 100 to 200 Hz. According to this experiment, the responsive frequency limitation is merely affected by injector configuration, rather than the supply line.

Periodic atomization characteristics of an impinging jet injector element modulated by Klystron effect

An experimental study on the Klystron effect of periodic injection modulated by pressure drop fluctuations on subsequent atomization is conducted. Time-resolved atomization backlit images and atomization Mie scatter images are captured by using the high speed camera. It is found that periodicity of forced atomization relies on pressure drop fluctuation amplitude and phase differences between atomization and pressure drop fluctuations relate to fluctuation frequencies. This feature of periodic atomization induced by Klystron effect corresponds to periodicities and high amplitudes of pressure fluctuations in unstable combustion chambers and chaos and low amplitudes of pressure fluctuations in stable combustions chambers. Drastically periodic varying of gross surface area of droplets with time was shown in Mie scatter images. The importance of periodic impinging jet atomization modulated by pressure drop fluctuations for acoustic liquid propellant combustion instabilities is illustrated.

Mode control in a high gain relativistic klystron amplifier with3 GW output power

Higher mode excitation is very serious in the relativistic klystron amplifier, especially for the high gain relativistic amplifier working at tens of kilo-amperes. The mechanism of higher mode excitation is explored in the FIC simulation and it is shown that insufficient separation of adjacent cavities is the main cause of higher mode excitation. So RF lossy material mounted on the drift tube wall is adopted to suppress higher mode excitation. A high gain S-band relativistic klystron amplifier is designed for the beam current of 13 kA and the voltage of 1 MV. PIC simulation shows that the output power is 3.2 GW when the input power is only 2.8 kW.

Design of a C-band relativistic extended interaction klystron with coaxial output cavity

In order to overcome the disadvantages of conventional high frequency relativistic klystron amplifiers in power capability and RF conversion efficiency, a C-band relativistic extended interaction klystron amplifier with coaxial output cavity is designed with the aid of PIC code MAGIC. In the device, disk-loaded cavities are introduced in the input and intermediate cavity to increase the beam modulation depth, and a coaxial disk-loaded cavity is employed in the output cavity to enhance the RF conversion efficiency. In PIC simulation, when the beam voltage is680 k V and current is 4 k A, the device can generate 1.11 GW output power at 5.64 GHz with an efficiency of 40.8%.

RF phase jitter in a klystron amplifier

RF phase jitter is a very important parameter for a relativistic klystron amplifier. This parameter is closely linked with the physics processes in the klystron. RF phase jitter is theoretically studied together with Particle in Cell （PIC） simulations in the paper. The main factor is deduced and verified in the PIC simulation. RF phase jitter is significantly affected by the fluctuation of the beam voltage. The relation between the phase jitter and the voltage fluctuation is linear in certain ranges.

Arcing-based protection system for the klystron output window of the BEPCII Linac

Purpose The Beijing Electron–Positron Collider II(BEPCII)Linac is powered by 20 klystrons,and the output windows of each klystron need to be protected from being broken,which are currently protected by a system based on reflected radiofrequency(RF)power and vacuum levels.The primary weak point of reflection-based protection is the difficulty of accurately measuring the value caused by an uneven waveform.Moreover,vacuum protection is restricted by the long response time,which results in delayed protection.Both of the weak points may damage the output window of the klystron.An arcing-based protection system is then introduced into the BEPCII Linac,considering the constant presence of light during arcing and the experiences of other laboratories and colleagues in the RF group.Methods The system development mainly consists of the design and test of the E-bend waveguide observation window,selection of the arcing detection module,offline joint test,system assembling and online operation.Results The system was assembled with a new klystron at the K6 position on the summer of 2018.During the following annual operation year,the light signal was captured,and the interlock was successfully realized.Conclusion The arcing-based protection system assembled online was found to work well.Moreover,the light signal was successfully captured,and the interlock function worked fine.The system is planned to be applied in other klystron locations in the future.

应用型电子直线加速器用C波段大功率速调管研究与开发

为满足C波段应用型直线加速器功率源要求,研制了一支C波段大功率速调管。通过对电子枪结构模拟计算并利用正反向组合式聚焦线圈调整过渡区磁场,完成了电子光学系统设计,电子注通过率达到100%,电子注波动率为4.8%。综合应用一维至三维计算程序对注-波互作用段开展参数优化及PIC仿真,最终确定了6个谐振腔的速调管方案。腔体加工冷测调配后焊接形成整管,并开展了高功率测试,在电子注电压为115 kV、电流为79.6 A条件下,馈入频率为5712 MHz、功率为100 W的信号时,该速调管可输出的峰值功率为3.52 MW,增益为45.5 dB,效率为38.5%,达到了预期研制目标。

TH2103A型速调管阳极电流测量和保护系统

[目的]工作频率3.7 GHz的TH2103A型高功率速调管广泛应用在托卡马克实验装置中。为了简化高压供电系统(去掉阳极调制中的电真空四极管),在HL-2A装置的TH2103A型速调管中引入了一种基于分压模式的供电方式。为了保证速调管在该供电模式下安全运行,研制了阳极电流的测量和保护系统。[方法]对该供电模式下的阳极电流特点进行了分析:阳极电流会出现正常、正向过流或反向过流的情况。当阳极电流出现正向过流或反向过流时,代表有大量的电子轰击阳极或大量电子从阳极流出,这些现象对速调管来说都是非常危险的,通常会引起速调管钛泵过流,甚至损坏速调管。因此对阳极电流进行准确的测量以及当阳极电流出现过流时切断高压对速调管进行保护非常重要。文章介绍了阳极电流测量系统的原理和供电模式,阳极保护系统的原理和实施方案,在实验过程中对阳极电流的测量和保护系统的可靠性进行了验证。[结果]证明了该供电模式下阳极电流测量和保护系统的有效性和可靠性。[结论]文章所述供电模式和阳极测量保护系统对基于TH2103A型速调管的运行和维护具有重要参考意义。