Multiple-beam Klystron Research Articles

Optimal design and experimental research of several-gigawatt multiple electron beam diode

The relativistic klystron amplifier (RKA) is one of the most efficient sources to amplify a high-power microwave signal due to its intrinsic merit of high-power conversion efficiency, high gain and stable operating frequency. However, the transverse dimensions of the RKA dramatically decrease when the operating frequency increases to X band, and the power capacity of the RKA is limited by the transverse dimensions. An X-band multiple-beam relativistic klystron amplifier is proposed to overcome the radiation power limitation. Each electron beam propagates in separate drift tubes and shares the same coaxial interaction cavities in the multiple-beam relativistic klystron amplifier, and the transverse dimensions of the multiple-beam relativistic klystron amplifier are free from the operating frequency restriction and a microwave power of over 1 GW is generated in the experiment. For a high-power electron device, the transmission of electron beam is critical, and the power conversion efficiency of the device is affected. In this paper, we conduct an investigation into the transmission process of the intense relativistic multiple electron beams, and the number of the multiple electron beams is set to be 16. It is found that when the multiple electron beam is transmitted in the device, the electron beam rotates around the center of the whole device, causing the electron beam to deviate from the drift tube channel. At the same time, each electron beam rotates around itself, and the cross section of the electron beam is deformed and expanded. In the improper design of electron beam and drift tube parameters, two kinds of rotating motions cause beam to lose. A multiple-electron-beam diode structure is optimized by the particle-in-cell simulation to reduce beam loss, with the effects of the related factors taken into account. Each pole of the cathodes is made up of graphite and stainless steel. The cathode head is made up of graphite, for the graphite has a lower emission threshold. The cathode base and cathode pole are made up of stainless steel, for the stainless steel has a higher emission threshold. Also the shape and structure of cathode pole, cathode head and anode are optimized to reduce the electric field intensity on the cathode pole and enhance the electric field intensity on the end face of cathode head. At the same time, the electric field distribution of the cathode head is uniform to improve the electron beam emission uniformity. The simulation results demonstrate that the transmission efficiency of multiple electron beams can reach 99%. In the experiment, the transmission efficiency of multiple electron beams is 92% with a beam voltage and beam current of 801 kV and 9.3 kA, respectively.

A Post-Loaded Rectangular Reentrant Cavity for Broadband Multiple-Beam Klystron

In an effort to enhance the bandwidth of a multiple-beam klystron having rectangular double reentrant cavity with circular cylindrical ferrule, reduction of the unloaded quality factor of the cavity was proposed by placing circular cylindrical posts extending from one of the cavity side-walls to the opposite wall in an orientation perpendicular to the electric field. A typical cavity was analyzed using 3D electromagnetic field solver CST Studio and the post-loading was found to reduce the unloaded quality factor by around 90% compared to that for no-post-loading. The proposed method was found to be the only method other than the use of passive loss to achieve this order of reduction in the quality factor with a minor increase in the cavity transverse dimensions. Post made of highly resistive material was found to have pronounced effect in reducing the quality factor. The 3D electromagnetic analysis was validated against measurements on a typical S-band cavity.

BAC-Klystrons: A New Generation of Klystrons in Vacuum Electronics

Two samples of S-band BAC multiple-beam BT258 klystrons were developed, fabricated, and tested at DBT with the support of CERN. A maximum efficiency of 66% was obtained at an output level of 6.6 MW. The 60% efficiency for one of multiple beam klystrons was successively confirmed in dynamic tests at CERN. The BAC method of electron grouping is discussed and the output parameters of multiple-beam BAC-klystron are compared with the existing single-beam klystrons. The possibility of increasing the output power by the BAC method of electron grouping of S-band multiple-beam klystron at an output power level of 10 and 20 MW is discussed.

Development of High-Power Low-Voltage C-Band Klystron for Economic Application

In the paper, we present the development of the powerful multiple-beam klystron amplifier with the peak output power of 3.2 MW and operating frequency of 5712 MHz. We show the capability of suppressing the high-voltage breakdowns in the collector area and increasing the efficiency of the multiple-beam klystron owing to alignment of the electric fields in the output cascade.

Quasi-3-D Modeling of Higher Order Mode Instability in a Two-Gap Input Cavity of Broadband MBK

We present the results of our comprehensive study of the stability of a two-gap input cavity used in an experimental broadband multiple-beam klystron (MBK) with 18 beams and 7 cavities, which was designed for projected >500 kW maximum output power and ~13% bandwidth (so-called NRL MBK-3 design). The device was experimentally observed to be prone to self-excitation at all beam voltages below its designed operational value of ~42 kV. Postexperiment examination of the two-gap input cavity revealed traces of breakdown on its face. Detailed simulations performed using a 3-D computational electromagnetic code HFSS have shown presence of a few high-Q higher order modes (HOMs), which could explain self-excitation of the two-gap input cavity in a wide range of beam voltages. To explore HOM instability of the two-gap input cavity of the MBK in greater details, we applied the code TESLA-MB, which represents a parallel extension of the 2-D large-signal klystron code TESLA and which is suitable for an accurate modeling of multiple-beam devices with unique distributions of R/Qs over gaps in all its beam-tunnels.

Влияние радиальной неоднородности полей резонаторов на группирование электронов в многолучевых клистронах

Влияние радиальной неоднородности полей резонаторов на группирование электронов в многолучевых клистронах

Development of the Radiofrequency Section of a Ku-band Multiple-Beam Klystron

ABSTRACTThe multiple-beam klystrons (MBKs) are well known for some distinct performance advantages over their single-beam versions. The advantages of the MBKs include higher average power, relatively lower operating voltages, higher bandwidth, and low individual beam current. However, the design of the MBKs is more extensive and requires thorough and careful three-dimensional electromagnetic simulations and analysis. In this article, design of a four-beam klystron compatible with a predesigned electron gun is reported. Starting with simple analytical approach, detailed design and electromagnetic simulation results of the radiofrequency (RF) cavities are presented. Uniformity of the RF coupling between the external circuitry and the cavity RF field has been investigated in detail with the help of commercially available three-dimensional electromagnetic design code. A cold-test model of the RF cavity has been fabricated and its resonant frequency has been characterized experimentally. Design of the individual cavities, electromagnetic analysis of the same, simulation results of the beam-wave interaction, as well as the experimental frequency characterization of a fabricated cavity is presented in this paper.

Distortions of the gap impedance of the active cavity of a broadband multiple-beam klystron coupled with the filter system

Distortion of the gap impedance of the active cavity of a broadband multiple-beam klystron is investigated. A technique for averaging of the gap impedance in beam transport channels on the basis of calculation of the coordinates of the center of gravity of the real part of gap impedance function obtained by means of numerical simulation is proposed.

Monotron Oscillation in Double-Gap Coupling Output Cavities of Multiple-Beam Klystrons

This paper presents a method to calculate the admittance of electron beam and of circuits in a multiple-beam klystron output circuit of double-gap coupling cavity. With the conditions of monotron oscillation, the possibility of forming monotron oscillations in a double-gap coupling output cavity is studied based on analytical calculations, and a method for calculating the initial oscillation current of monotron oscillation is derived. To further verify whether monotron oscillations form in the coupling double-gap output cavity and to analyze the characteristics of monotron oscillation, a particle simulation is performed to a particular coupling double-gap output cavity loaded by a cutoff waveguide filter, and the results show that monotron oscillations form in the particular coupling double-gap output cavity with an initial current of about 22 A under the condition of 18 kV accelerating voltage of the beam.

Design of the RF Circuit for a Coaxial Cavity High-Power Multiple-Beam Klystron

This paper presents the design methodology and detailed design of the interaction circuit for use in an L-band 10-MW MBK, which operating in the fundamental mode at a center frequency of 1.3 GHz. Coaxial cavities are adopted to give adequate space for the use of multiple large cathodes, which has a low cathode loading and thereby facilitate a long lifetime. The emphasis for the present design is on efficiency and high-peak output power. The initial design was carried out using the large signal code KLY. To calculate the beam-wave interaction characters conveniently with cavities present, we developed a 2-D single-beam equivalent design methodology, in which the multitunnel coaxial cavities are replaced by the conventional single-tunnel cylindrical cavities with transformed RF parameters. The 3-D PIC simulations with actual coaxial cavity geometries are carried out at last to check on the large signal and the 2-D PIC simulations. The 3-D simulation results indicate that the equivalent design methodology is effective. The final RF circuit consists of six coaxial cavities including a second-harmonic cavity to reduce the device length. The circuit has a predicted gain of 50 dB at a peak pulsed output power of 10.4 MW with a corresponding electronic efficiency of more than 68%. The design and test results of the output system with two windows are also presented.

Six-Beam Gun Design for a High Power Multiple-Beam Klystron

This paper presents the detailed design of a six-beam gun for use in an L-band 10-MW multiple-beam klystron. To facilitate the gun simulation, we developed a joint design methodology with 2-D and 3-D simulation codes. The six-beam gun is designed to produce a total current of 132 A divided equally among the six beams at an accelerating potential of 115 kV. For the design of the gun, special emphasis is placed on the geometric layout of the electrodes to ensure moderate voltage gradient, accurate beam perveance and reasonable cathode loading. The magnetic circuit consists of solenoid magnet structures. Special coils and iron shells are set to ensure a uniform parallel magnetic field in the region between the cathode and the anode. Two set of amendatory coils and shield irons are set in the transition region to optimize the beam radius. Special coils are set in the both ends of the interaction region to trim the radial magnetic fields. The gun design is accomplished with EGUN and CST codes. Simulation results show that the joint design methodology is effective and the magnetic circuit has an excellent flexibility. The final gun has a cathode loading lower than 2.1 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and excellent beam transport characteristics. The dependency relationship between the beam off-centering and the asymmetry radial magnetic fields is analyzed.

Controlling the bandpass characteristics of high-power microwave electronic tubes with the use of filtering systems

A procedure for designing filtering systems of high-power microwave electronic tubes is presented. A quantitative criterion of quality of tuning is given. In simulating a filtering system, it is proposed to use a prototype cavity with specified properties rather than a structurally complex active cavity. An implementation of the proposed procedure is shown using, as an example, a three-section filter of a multiple-beam klystron.

Development of High Power Electron Beam Measuring and Analyzing System for Microwave Vacuum Electron Devices

Abstract The measurement and analysis of high power electron beam during its formation and transmission are the basic scientific problems and key techniques for the development of high performance microwave vacuum electron devices, which are widely used in the fields of military weapon, microwave system and scientific instruments. In this paper, the dynamic parameters measurement and analysis system being built in Institute of Electronics, Chinese Academy of Sciences (IECAS) recently are introduced. The instrument are designed to determine the cross-section, the current density, and the energy resolution of the high power electron beam during its formation and transmission process, which are available both for the electron gun and the electron optics system respectively. Then the three dimension trajectory images of the electron beam can be rebuilt and display with computer controlled data acquisition and processing system easily. Thus, much more complicated structures are considered and solved completely to achieve its detection and analysis, such as big chamber with 10-6 Pa high vacuum system, the controlled detector movement system in axis direction with distance of 600 mm inside the vacuum chamber, the electron beam energy analysis system with high resolution of 0.5%, and the electron beam cross-section and density detector using the YAG: Ce crystal and CCD imaging system et al. At present, the key parts of the instrument have been finished, the cross-section experiment of the electron beam have been performed successfully. Hereafter, the instrument will be used to measure and analyze the electron beam with the electron gun and electron optics system for the single beam and multiple beam klystron, gyrotron, sheet beam device, and traveling wave tube etc. thoroughly.

Study of the Performance Improvement on Coaxial Output Cavity for Higher-order Mode Multiple-beam Klystron

该文针对工作在TM310模的多注速调管同轴输出腔中工作模式的场分布均匀性、外观品质因数及其与邻近模式的频率间隔等问题进行了研究，提出了一种带有短路杆和金属环的多注速调管同轴输出腔结构。分析发现，适当设置短路杆和金属环不仅可以使外观品质因数降低，还可以改善工作模式的场分布；而且设置金属环还可以增大TM310模和邻近模式的频率间隔以实现抑制杂模。利用仿真软件对X波段的同轴输出腔进行了模拟计算，计算结果与理论分析一致。在此基础上加工了冷测模型，测试结果表明TM310模与邻近模式的频率间隔均达到了1.2 GHz以上，外观品质因数从507.4降至193.5，工作模式的场分布也变得均匀。

Research activities on a double-gap output section of a multiple-beam klystron

In this article the double-gap output section of a multiple-beam klystron is studied using modern measurement equipment and computer simulation methods. Well-known techniques of cold two-terminal measurements are adapted to equipment capabilities. A comparison between the measured characteristic and computer simulation results is discussed.

High-Power High-Efficiency L-band Multiple-Beam Klystron Development at CPI

Communications and Power Industries, Inc., has designed and manufactured two versions of a 10-MW-peak high-efficiency multiple-beam klystron (MBK) operating at 1300 MHz. This type of klystron is favored for large particle accelerator projects such as the European X-ray Free-Electron Laser at the Deutsches Elektronen Synchrotron (DESY). Two klystrons have been made for DESY. The first-generation MBK was a vertically oriented prototype using a six-cavity design with higher order mode input and output cavities and conventional intermediate cavities. For cost and performance reasons, the second-generation MBK, designated VKL-8301B, utilized seven coaxial fundamental-mode cavities and is an “industrialized” horizontally oriented klystron. The klystron was designed and optimized using state-of-the-art multidimensional design codes to ensure that all performance requirements are exceeded. Agreement between the simulated and measured performances is good. The VKL-8301B prototype achieved a peak saturated RF output power of 10.4 MW and 67.8% efficiency. The data were measured at the full 1.5% duty and with 1.5-ms pulse width. The klystron satisfied all required operating conditions, including stable operation into an output mismatch of 1.2:1 voltage standing wave ratio at various phases. The prototype has been shipped to DESY and has been successfully tested by a customer.

Broadband High-Power 18-Beam S-Band Klystron Amplifier Design

Fundamental-mode multiple-beam klystrons (MBKs) offer the potential of high power and broad bandwidth with low noise at low beam voltages in a compact amplifier form factor. This paper presents the design approach and methodology for an S-band MBK. This amplifier will be driven by a newly developed 41.6-A 42-kV 18-beam electron gun. The high total beam perveance permits the circuit design to achieve a peak power of 670 kW in S-band and a corresponding 1-dB bandwidth of 13% (16% at 3-dB). The high beam perveance, however, requires special considerations in the common collector design, particularly with respect to the spent modulated electron beams. To fully account for the impact of the time-varying beam current, the time-dependent 3-D gun/collector code MICHELLE was employed for this collector design.

Detailed Analysis of the Interception Current Predicted by the Large-Signal Code TESLA for an Experimental Multiple-Beam Klystron

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We present the results of detailed modeling of an experimental eight-beam four-cavity multiple-beam klystron (MBK) with an emphasis on the effects related to the circuit interception current. The parallel version of the 2.5-D large-signal code TESLA was used as the principal analysis tool. The primary MBK model used eight nonidentical beams/beam tunnels run in eight parallel processes using the measured values of <formula formulatype="inline"><tex Notation="TeX"> $R/Q$</tex></formula> on each gap of each beam tunnel. The simulation results are compared with the available experimental data and show good agreement between the calculations and measurements, including the predicted level of threshold RF drive power at the first appearance of body current. Additional modeling was performed using a less accurate approximation where all eight beams/beam tunnels were assumed to have identical properties. The results of the two different modeling approaches are analyzed in detail and compared with each other to determine the limits on the accuracy of the respective models. </para>

Experimental Study and Analysis of an S-Band Multiple-Beam Klystron With 6% Bandwidth

We present experimental results and analyses of an eight-beam five-cavity multiple-beam klystron (MBK) operating at a center frequency of ~3.2 GHz. The device met its performance goals in its first hardware implementation, generating a peak RF output power of 600 kW and a 3-dB bandwidth of ~6%. The circuit was modeled with TESLA, a 2.5-D large-signal klystron/MBK code that was extended to enable simulations of the low- Q multiple-gap cavities used to increase the bandwidth. Details of the model and underlying theory are described, and the simulation results are compared with experimental measurements. The good agreement between the model and the experiment provides a validation for our tools and techniques that will be used in the design of future devices.

Parallel Simulation of Independent Beam-Tunnels in Multiple-Beam Klystrons Using TESLA

We present an extension of the klystron simulation code TESLA to model multiple-beam klystrons (MBKs) in which interaction parameters may vary significantly from beam-tunnel to beam-tunnel. In earlier work, the single-beam code was applied to model the MBK by assuming that all electron beams and beam-tunnels were identical and all electron beams interacted identically with the fields of the resonant cavities, using averaged values of R/Q to represent interaction with each resonant cavity. To overcome the limitations of this approach and to take into account the effects from nonidentical beams and/or beam-tunnels, we have modified the code to use a parallel algorithm for multiple beams. The implementation of the parallel version of TESLA is based on the latest Fortran-95 version of the serial code and uses the message-passing interface library for communication. For testing and verification purposes, the new version of the code is applied to simulate an experimental four-cavity, eight-beam klystron amplifier, which was designed and successfully tested last year at the Naval Research Laboratory. The results of modeling using the new parallel TESLA and their comparison with experimental data are discussed in detail.