Search

This article presents a demonstration of the improved performance of an X‐ray free‐electron laser (FEL) using the optical klystron mechanism and helical undulator configuration, in comparison with the common planar undulator configuration without optical klystron. The demonstration was carried out at Athos, the soft X‐ray beamline of SwissFEL. Athos has variable‐polarization undulators, and small magnetic chicanes placed between every two undulators to fully exploit the optical klystron. It was found that, for wavelengths of 1.24 nm and 3.10 nm, the required length to achieve FEL saturation is reduced by about 35% when using both the optical klystron and helical undulators, with each effect accounting for about half of the improvement. Moreover, it is shown that a helical undulator configuration provides a 20% to 50% higher pulse energy than planar undulators. This work represents an important step towards more compact and high‐power FELs, rendering this key technology more efficient, affordable and accessible to the scientific community. [ABSTRACT FROM AUTHOR]

In this paper the design of the free‐electron laser (FEL) in the SXL (Soft X‐ray Laser) project at the MAX IV Laboratory is presented. The target performance parameters originate in a science case put forward by Swedish users and the SXL FEL is foreseen to be driven by the existing MAX IV 3 GeV linac. The SXL project is planned to be realized in different stages and in this paper the focus is on Phase 1, where the basic operation mode for the FEL will be SASE (self‐amplified spontaneous emission), with an emphasis on short pulses. Simulation results for two linac bunches (high and low charge) with different pulse duration are illustrated, as well as the performance for two‐color/two‐pulses mode and power enhancement through tapering. Besides standard SASE and optical klystron configurations, the FEL setup is also tailored to allow for advanced seeding schemes operations. Finally possible upgrades that will be implemented in a second phase of the project are discussed. [ABSTRACT FROM AUTHOR]

In 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. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

Neutron sources like European Spallation Source consist of linear proton accelerator and beam target. The linear accelerator is supplied by inductive output tubes (IOTs) or klystrons that require high‐voltage DC supply (40 kV). This study describes the design and experimental evaluation of high‐voltage dry‐isolation pulse transformer design evaluation prototype for interleaved IOT supply modules. In order to withstand high‐voltage stress, a modular secondary winding module with multistage voltage field equalisation are designed. Inter‐winding connections are realised in the air as the separate winding outputs are routed together through common high‐voltage isolators. The novelties of the current manuscript are new pulse transformer design and the experimental work. Experiments with full‐scale prototype verified the advantages and revealed, also, some drawbacks of this construction. Proposed transformer design could be used not only in IOT or klystron power supplies but also in high‐voltage DC/DC or AC/AC converters and power electronic transformers, used in the medium‐voltage distribution grids. [ABSTRACT FROM AUTHOR]

The extended interaction klystron, which has high power, high efficiency, and high gain characteristics in the millimeter wave and terahertz frequency bands, is a compact electric vacuum device. In this paper, a multisection coupling cavity, each of which consists of multiple gaps, is proposed as the high‐frequency circuit of the extended interaction klystron and the beam‐wave interaction is studied. According to the space charge wave theory, the electronic conductance in the multigap cavity is studied. With the operating frequency of 225 GHz and the electron beam voltage of 12 to 13.65 kV, the system can achieve a stable operation. In the multigap cavity, the amplitude of electronic conductance increases with gap number. It means that the large gap number can enhance the beam‐wave interaction. The beam‐wave interaction is studied by establishing the impedance matrix of the multigap coupling cavity and using the electronic disk model. Under the condition of the electron beam voltage of 13.03 kV, the current density of 65A/cm2, and the signal frequency range of 225.63 to 225.67 GHz, the electron conversion efficiency is about 6.5%. Compared with the particle‐in‐cell simulation, the theoretical research results agree well with the simulation results. It verifies that the method in this paper is accuracy and reliability. [ABSTRACT FROM AUTHOR]

A simple and compact scheme that enhances the brightness of self‐amplified spontaneous‐emission (SASE) free‐electron lasers is presented. The method combines the high‐brightness SASE scheme and the optical klystron concept to increase the temporal coherence of the produced radiation and to reduce the required length of the undulator beamline at the same time. The scheme is very simple and only requires compact chicanes between the modules of the undulator beamline. Simulations show that, in comparison with SASE, the brightness can be improved by up to a factor of ten and the required length to achieve saturation can be reduced by 20% or more. [ABSTRACT FROM AUTHOR]

Abstract: Electrodynamic characteristics and parameters of the double‐gap klystron resonator with the inductive microstrip elements on the suspended ceramic substrate has been investigated. The inductive part of a resonator made on the basis of a quasi‐fractal Sierpinski's triangle, and a capacitor part, made between end faces of the multi‐channel drift tubes and forming a double gridless gap. The developed resonator can find application in micro vacuum klystron devices working in the systems of telecommunication and navigation in 1‐ and multi‐frequency mode of operation. [ABSTRACT FROM AUTHOR]

Klystrons are vacuum electronic devices widely used for microwave amplification up to the millimetre-wave region. The opportunity to push the operating frequency of conventional klystrons above 30-40 GHz is limited by the fabrication difficulties of the cavities that have very small dimensions. A high order mode micro re-entrant square cavity was purposely devised to be compatible with the available micro fabrication processes and represents a viable solution for the design of millimetre-wave klystrons. In this study, a coupler to correctly excite the higher order mode of the square re-entrant cavities for W-band operation is proposed. The design of the proposed novel coupler structure has been validated by realisation and measurement of a scaled X-band prototype. The post-realisation tuning methods adopted to improve the matching of the high order mode are also presented. [ABSTRACT FROM AUTHOR]

In this paper spontaneous emission of radiation by relativistic electrons in a gyro-klystron is studied. The scheme consists of two solenoid sections separated by a dispersive section. In the dispersive section the electrons are made non-resonant with the radiation. The dispersive section transforms a small change of the velocity into changes of the phases of the electrons. This leads to enhanced radiation due to klystron-type modulation as compared with a conventional gyrotron-type device driven by cyclotron maser interaction. It is shown that the klystron-modulated spectrum depends on the dispersive field strength, finite perpendicular velocity component and length of the solenoids but is independent of the axial magnetic field strength. A simple scheme to design a gyro-klystron is discussed. [ABSTRACT FROM AUTHOR]

The suitability of the transmission line modelling method for studying field–particle interaction devices is assessed through an example of a simple two-cavity klystron amplifier. Two separate numerical studies are presented, covering both beam bunching in the buncher cavity and field generation in the catcher cavity. Also addressed are the possibility of modelling the effect of the finite thickness of the cavity wall and beam coupling. The modelling of these practical aspects has not only resulted in some important insights into the field–particle interaction problem, but also demonstrated that the computer code developed is a powerful and versatile design tool. © 1997 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A novel pulsed depressed collector biasing scheme is proposed. This topology feeds forward energy recovered during one RF pulse for use on the following RF pulse. The presented 'inverse' Marx charges biasing capacitors in series, and discharges them in parallel. Simulations are shown along with experimental demonstration on a 62 kW klystron. [ABSTRACT FROM AUTHOR]

Klystron microwave amplifiers play a vital role in addressing the increasing demands of high‐average microwave power for strategic applications such as linear accelerators, active denial technologies, radar, and so forth. Typically, klystrons have an efficiency of 50%‐60% that demands an efficient thermal design for dissipating the unused DC power in the form of spent electron beam in collector. Hence, thermal modeling of the collector for efficient heat dissipation is highly critical in design of high average power klystrons. Of several types of design, grooved collector design is widely employed so as to increase the surface area between the collector and coolant and thereby enhance heat transfer. In this article, a mathematical model and design strategy have been demonstrated to obtain the optimum dimensions, that is, height, depth, and width of fins based on film coefficient and Reynolds number. For validation, the dimensions are then simulated in a computational fluid dynamics software (ANSYS‐Fluent) demonstrating excellent agreement with the mathematical modeling. In addition, the optimum choice of grooving method (longitudinal or crossed) for the given power level has also been provided. The demonstrated strategy can also potentially be employed to other devices, which uses groove based design with water as coolant medium such as gyrotrons, plasma devices, and so forth. [ABSTRACT FROM AUTHOR]

Purpose: To use a finite-element method (FEM) model to study the feasibility of producing a short s-band (2.9985 GHz) waveguide capable of producing x-rays energies up to 10 MV, for applications in a linac-MR, as well as conventional radiotherapy. Methods: An existing waveguide FEM model developed by the authors' group is used to simulate replacing the magnetron power source with a klystron. Peak fields within the waveguide are compared with a published experimental threshold for electric breakdown. The RF fields in the first accelerating cavity are scaled, approximating the effect of modifications to the first coupling cavity. Electron trajectories are calculated within the RF fields, and the energy spectrum, beam current, and focal spot of the electron beam are analyzed. One electron spectrum is selected for Monte Carlo simulations and the resulting PDD compared to measurement. Results: When the first cavity fields are scaled by a factor of 0.475, the peak magnitude of the electric fields within the waveguide are calculated to be 223.1 MV/m, 29% lower than the published threshold for breakdown at this operating frequency. Maximum electron energy increased from 6.2 to 10.4 MeV, and beam current increased from 134 to 170 mA. The focal spot FWHM is decreased slightly from 0.07 to 0.05 mm, and the width of the energy spectrum increased slightly from 0.44 to 0.70 MeV. Monte Carlo results show dmax is at 2.15 cm for a 10 × 10 cm2 field, compared with 2.3 cm for a Varian 10 MV linac, while the penumbral widths are 4.8 and 5.6 mm, respectively. Conclusions: The authors' simulation results show that a short, high-energy, s-band accelerator is feasible and electric breakdown is not expected to interfere with operation at these field strengths. With minor modifications to the first coupling cavity, all electron beam parameters are improved. [ABSTRACT FROM AUTHOR]