Multi-beam Klystron Research Articles

A Novel Efficient Computational Method for the Electron Optics System in Multibeam Klystrons With Applications to Manufacturing Sensitivities

A Novel Efficient Computational Method for the Electron Optics System in Multibeam Klystrons With Applications to Manufacturing Sensitivities

Design and simulation of an S-band compact multi-beam klystron

The miniaturization and high power of klystron are the main concerns of accelerators. Multi-beam klystron (MBK) can accommodate higher power and a lower operating voltage than single-beam klystrons, significantly reducing volume and weight. This paper introduces the design and simulation of the beam-wave interaction system and multi-beam electron gun for S-band compact MBK. The 3-D particle simulation results show that the output power of the MBK is 12.6 MW, driven by an input signal with a frequency of 2856 MHz and a power of 13 W. The corresponding efficiency is 70%. In addition, the gain of the MBK is 59.9 dB. The design goal of S-band miniaturized high-power MBK is realized.

Simulation study for efficiency optimization of multi-beam klystron output cavity

Increasing klystron tubes’ efficiency is essential in developing new-generation colliders and free-electron lasers. Different factors can affect the efficiency of a multi-beam klystron. One of the significant factors is the electric field symmetry inside cavities, especially in the output section. In this research, two different types of couplers are investigated in the extraction cavity of a 40-beam klystron. The first approach is a single slot coupler, which is frequently utilized and easier to fabricate but disturbs the electric field symmetry inside the extraction cavity. The second method has a more complex structure with symmetric electric fields. In this design, the coupler consists of 28 mini slots on the inner wall of the coaxial extraction cavity. Both designs are evaluated via particle in cell simulations, and the results exhibit around 30% more power extracted from the structure with a symmetric field distribution. The symmetric structures can also decrease the number of back-streamed particles by up to 70%.

An Overview of Multibeam Klystron Technology

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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 15%, peak power <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 1 MW, average power up to 40 kW, and efficiencies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 40%. In recent years, driven by the needs of high-energy particle accelerators, ultra high frequency (UHF) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{L}$</tex-math> </inline-formula> -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.

Ka-band linearizer structure studies for a compact light source

The CompactLight design for a next-generation x-ray free-electron laser utilizes a C-band injector. This requires that the harmonic system used to linearize the beam's phase space must operate at X-band rf or higher. We investigate the optimum frequency for the harmonic system in the range of frequencies from 12 to 48 GHz. We describe the reasoning behind selecting 36 GHz (Ka-band) as our working harmonic frequency. The full linearizer system design including the power source, pulse compressor, and linearizing structure, along with options, is considered and presented. These designs are compared in terms of rf and beam dynamics performance. Two potential MW-level rf sources are discussed; a multibeam klystron and a gyro-klystron, while a klystron-based upconverter with an X-band driver is briefly discussed as an alternative path if even higher peak powers are needed. To further increase peak power, novel options for pulse compressors at Ka-band are discussed. Traveling and standing wave solutions for the structure are presented.

Beam Optics Study on a Two-Stage Multibeam Klystron for the Future Circular Collider

The two-stage (TS) multibeam klystron (MBK) technology has recently attracted significant research attention due to its compactness and high-efficiency (HE) performance. However, there is still a lack of scientific research on the beam optics for such microwave power sources integrated with a postacceleration (PA) gap. In this article, a comprehensive optics study based on the newly developed 2-D optics code CGUN is conducted for the first time to demonstrate the most critical steps in the optics design process, by adopting the 400-MHz TS MBK for the future circular collider (FCC) as an example. Two specific challenges arise in this TS MBK, which are studied in this article, and solutions are given. First, due to the combination of slow electrons, impedance change from individual beamtubes into common volume, and the mild decay of the magnetic field, there are possible reflected electrons at the collector entrance. This requires an increase in the beam voltage to 80 kV, beyond the requirements from considering the output gap alone, as well as tighter control on bouncing electrons. The beam scalloping is also found to be highly sensitive to the position of the PA gap and magnetic field, which later demonstrates that large gap length and magnetic field are required. Final all-in-one particle-in-cell (PIC) simulations of this klystron equipped with this special optics design demonstrate that the specification of 1.2-MW continuous wave (CW) power is practically attainable with an efficiency of 77.5% and without the presence of reflected electrons at any point in the whole circuit.

Multi-beam gun design for an S-band klystron

This paper introduces the detailed design scheme of a multi-beam electron gun applied to an S-band high power multi-beam klystron. The multi-beam gun adopts a coaxial cavity arrangement, and the total number of electron beams are 40 (19 in the inner layer and 21 in the outer layer). The working voltage of the electron gun is 60 kV, the total current is 300 A (evenly distributed on 40 electron beams), and the single beam perveance is 0.51 μP. The total perveance is 20.4 μP. The cathode loading of the gun is 12 A/cm2, which can meet the requirements of cathode operational lifetime. The beam focusing system uses a periodic reversal permanent magnet to realize miniaturization of the klystron.

Modeling and Design of a High-Efficiency Multibeam Klystron

The efficiency of the RF power sources is one of the major concerns in the large-scale high-energy accelerator projects such as the future circular collider (FCC) and the compact linear collider (CLIC). The new bunching method, the core stabilization method (CSM), can achieve high efficiency in the case of shorter interactive length. The multibeam klystron (MBK) could accommodate high RF power with a low operating voltage, compared with a single-beam klystron. This article presents the design and simulation of a 650-MHz, 0.9-MW continuous wave (CW) CSM MBK. The detailed design of a six-beam optics system is also elaborated in this article. The performance of such a device was validated by the 3-D particle-in-cell (PIC)-code computer simulation. With an operating voltage of 50 kV, PIC simulation predicts an efficiency of 81.8&#x0025;.

On Prospects of Output Power Increasing in Low-Voltage Multibeam Klystrons for Electron Accelerators

Physical principles of output power limitation in low-voltage multibeam klystrons are considered. It is demonstrated that metamaterial consisting of array of metal inductive inserts and located in the cavity’s interaction region makes possible significant increasing of phase velocity of transversal wave in the gap. This reveals the opportunity to enhance uniformity of the RF field interacting with the beams in the gap, interaction region diameter, beams current and power of the klystron without cathode voltage increase. Resonators in S and Ka bands are analyzed.

Design study and modeling of multi-beam Klystron for Circular Electron Positron Collider

Aimed at energy-saving for the Circular Electron Positron Collider of China, a multi-beam klystron is designed for a higher efficiency than existing commercial klystrons in a continuous-wave UHF band range. The design considerations for every constituent part of the multi-beam klystron are discussed in detail, including modeling of the realistic structures and results of simulations. The electron gun and beam focusing solenoids, which are the fundamental basis for a high average power klystron, are brought out by establishing a good beam transportation rate. The interaction region is designed with the new bunching method using three-dimensional PIC simulation software. The resulted efficiency from the PIC simulation is higher than 80%, considering realistic RF coupling structures in the input and output cavities. The collector is capable of the full beam power dissipation. In the meanwhile, efforts have been taken to avoid reflecting electrons from the collector due to the space-charge depression. The scheme and considerations of the output windows are also introduced.

Investigation of the Two-Mode Regime of Two-Gap Photonic-Crystal Resonance Systems Produced on a Printed Circuit Board with Fractal Elements "Minkowski Island

Introduction. The development of new amplifiers and generators of the Ku- and K-bands (12…27 GHz) for use in onboard equipment is increasingly attracting research interest. Low-voltage multi-beam klystrons (LMBK) can be a promising element base for such devices. Serious problems are associated with the need to suppress parasitic modes of oscillations in NMLK operating in the centimeter and millimeter range. A possible solution is to use double-gap photonic-crystal resonators (DPCR) in LMBK. Another promising direction for improving the characteristics of such resonators is to use resonant segments of strip lines with fractal elements. In this case, the strip lines are placed on a dielectric substrate in the interaction space. Such resonators exhibit new properties that are useful for klystrons (an increase in characteristic impedance, suppression of the spectrum of unwanted frequencies, a reduction in mass and dimensions).Aim. Determination of an optimal set of electrodynamic and electronic parameters of double-gap photonic-crystal resonance systems with fractal elements "Minkowski Island" when operated as part of the LMBK resonator system, excited on π- and 2π-modes of oscillation.Materials and methods. To calculate the electrodynamic parameters of resonators, the method of finite differences in the time domain was used. The well-known Wessel-Berg method was used to calculate electronic parameters, such as the Ge / G0 electronic conductivity and the coupling coefficient M.Results. The main electrodynamic parameters of the resonator – Q-factor, resonant frequency and characteristic impedance – were investigated. The electronic parameters of the resonator, the coefficient of coupling with the electron beam, and the relative electronic conductivity for π- and 2π-modes of oscillations were calculated. In this case, three variants of the resonator with zero, first and second iterations of the fractal element were investigated. The amplitude-frequency characteristics of the resonator were investigated with a change in the pitch of the photonic crystal lattice. An estimation of the inhomogeneity of the high-frequency field in the interaction spaces of the resonator was carried out. Operational conditions were determined simultaneously for two types of oscillations without self-excitation.Conclusion. The results can find application in the development of resonator systems for klystron-type devices in the centimeter and millimeter ranges.

Трехзазорный резонатор для миниатюрного многолучевого клистрона

The paper presents the results of a study of a three-gap resonator for a miniature multi-beam klystron. A feature of the resonator is the use in the construction of a suspended dielectric substrate with strip resonant conductors located on it. The main electrodynamic parameters of the resonator were calculated. The analysis of the high-frequency electric field along the interaction space is carried out for each of the modes. For the antiphase and in-phase modes, the possibility of tuning the resonator to multiple resonant frequencies is shown. Electronic parameters were calculated for the frequency multiplicity mode. The investigated resonator can find application in miniature multi-beam klystrons of the centimeter and millimeter range.

Design and Simulation of Extended Interaction Cavities for a Ka band Multi beam Klystron

This article reports about the design approach, electromagnetic simulation and analysis results of high-frequency ladder-type input, output, and intermediate RF cavaties for Ka-band multi-beam extended interaction klystron. Several parameters of the cavity, such as quality factor, shunt impedance, etc., have been investigated by the assistance of electromagnetic software CST microwave studio.

Concept and Simulations of 800 MHz Two-Stage MBK for FCC

Energy consumption is one of the major concerns when planning large-scale high energy accelerator projects such as the future circular collider (FCC) and similar accelerators. To address this problem, we will describe the concept and simulations of a 1.4 MW, 800 MHz two-stage multibeam klystron (TS MBK) having a high efficiency (~80%) and compact design.

Исследование параметров процесса электронно-волнового взаимодействия в двухзазорном фотонно-кристаллическом резонаторе низковольтного двуствольного многолучевого клистрона Х-диапазона.

This paper presents the results of comparing data from three-dimensional electromagnetic modeling of two designs of double-gap photonic crystal resonators of a two-barrel multi-beam klystron operating in the X-band at an accelerating voltage of 3.6 kV. These resonators are designed to operate on the main π-type oscillation with an output power level of about 2 kW. They are characterized by different profiles of the beam-let tubes. Each of the beam-let tubes in these structures contains 19 beam channels arranged in linear rows. The results of optimization of the complex of electronic and electro-dynamic parameters are presented. The optimal parameters and designs of resonant systems are found, which make it possible to significantly reduce the degree of inhomogeneity of the effective characteristic resistance in the interaction space.

90% Efficient Two-Stage Multibeam Klystron: Modeling and Design Study

The efficient generation of microwave power has recently gained broad attention in the accelerator community because energy consumption is one of the major concerns for future large-scale high-energy accelerator projects. For the first time, we present a concept of the two-stage multibeam klystron with annular beams (TS MABK). It allows for a remarkably high RF power production efficiency (90%), using a compact design and delivering a cost-effective electro-mechanical solution. The design is for a 1-GHz, 20-MW klystron. The performance of the tube is validated using particle-in-cell computer simulations. In this article, we focus on technological novelties and on mitigation of specific issues.

Design Study of a High-Power Ka-Band High-Order-Mode Multibeam Klystron

Compactness and cost-effectiveness are two major concerns in the development of a Ka-band linearizer, which is a crucial accelerator component of the European CompactLight project. A higher order mode (HOM) multibeam Klystron (MBK) could accommodate a higher distributed electron current with a low operating voltage of 60 kV, thus making it competitive to deliver high RF power at high frequency compared with a single beam Klystron or a fundamental mode MBK. In this article, the modeling and design study of the 36-GHz HOM MBK is presented. The development of a double compression multibeam (MB) optics system is also elaborated in this article. The performance validation of such a device was done using sophisticated 3-D particle-in-cell (PIC) computer simulations of the entire device. PIC simulations confirmed that a power level of 2.5 MW is attainable with an efficiency of 35%.

Optimization of multibeam klystron double gap cavities loaded by metal rods

AbstractIn this paper, the results of numerical investigation of a metal photonic band gap cavity are presented. The investigated resonator is dual‐gap and is considered as an intermediate for the K‐band multibeam klystron. A working mode is a 2n mode with a frequency of 24.15 GHz. Electrodynamic characteristics of the cavity (characteristic impendance, beam coupling factor, relative electronic conductivity, Q‐factor) were calculated and the conditions for achieving the maximum effciency are found. Based on the obtained data, the required number of gaps in the output cavity was estimated, as well as the power and efficiency of the multibeam klystron with this type of cavities, depending on the microperveance of the electron beam.

Fractal double‐gap resonators with electromagnetic band gap for miniature X‐band multi‐beam klystrons

This article is devoted to the study of beam-wave interaction behavior of a double gap electromagnetic band-gap resonator for a cluster miniature multi-beam klystron (MMBK) with 114 beams operating at 12 GHz of a higher order 2π mode. We propose to use a fractality as a basic concept for modeling, analysis, and design for a new spatially developed quasi-fractal resonators with six sub-group of beam-clusters. The tree-like fractal double-gap resonator contains electromagnetic band gap “traps” for parasitic types of oscillations in the form of clusters of metal and ceramic rods, which allow us to suppress higher parasitic types of oscillations. The results of calculations show the possibility of development a super-multi-beam miniature klystron with an output power of 7 kW when the overall efficiency is 30%.

The Physical Limitations of the Efficiency of High Power Multibeam Klystrons

The Physical Limitations of the Efficiency of High Power Multibeam Klystrons