IET Conference on High Power RF Technologies
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- Location: London, UK
- Conference date: 26 Feb. 2009
- ISBN: 978 1 84919 060 2
- Conference number: CP548
- The following topics are dealt with: photonic crystals and metamaterials for high-power microwave applications; high-power maser; microwave terahertz source; electron beam source; electron gun development; power device reliability; microwave plasma applications; RF generation in photonic crystals; photonic band gap resonant structures; nonlinear dynamics and chaos; co-harmonic gyro-montron; superconducting RF photoinjector; microwave plasma drill; power combined tube transmitters; solid state modulator system; and RF system design.
1 - 20 of 21 items found
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High voltage, high frequency transformer switching converter integration
- Author(s): T. Filchev ; D. Cook ; J. Clare ; P. Wheeler
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This paper presents a high voltage (HV), high frequency (HF) transformer with high voltage rectifier. The described systems employ a low profile HV, HF transformers and voltage bridge technology multiplier. A model of the converter of 150 kW is presented and verified by Saber simulator. Design methodology and models of the HV, HF transformers are presented. (4 pages)
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The design of RF crab cavities for particle accelerators
- Author(s): G. Burt ; P. Ambattu ; P. Goudket ; B. Hall ; P. Mcintosh ; A. Dexter ; C. Beard ; I. Tahir ; R. Carter ; R. Jones ; M. Dykes ; A. Kalinin ; L. Ma
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A number of particle accelerators worldwide require RF crab cavities for a number of applications, including maximizing collision luminosity, production of short X- ray pulses, and diagnostics. The Cockcroft Institute has led the development crab cavities for the LHC, ELC and CLIC colliders. The design for each of these cavities is very different due to the different bunch structures in each accelerator. For the CLIC accelerator we have chosen an X-band traveling wave normal conducting cavity, the ILC uses an S-band superconducting cavity and the LHC is proposed to use a novel compact shape superconducting cavity with an operating frequency between 200-800 MHz. The general design considerations for crab cavities will be discussed as well as special constraints for each of the three systems and their current designs. (3 pages)
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X-band RF generation and coupling in photonic crystals
- Author(s): Y. Xu and R. Seviour
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2D Photonic crystals (PC) with single site defects behave as standing-wave resonators and offer exceptional mode selectivity. This high mode selectivity offers many advantages for higher-order mode suppression and applications at frequencies higher than X-band. In this paper we focus on the RF excitation by electron bunches and RF coupling in a PC cavity resonator. We first compare the RF excitation with that seen in a traditional pill-box cavity operating at the same frequency. We find that in a single defect PC cavity only the TM 010 mode can be excited and confined in the central defect region. We then expand this analysis to include application towards pre-buncher and power extraction cavities for particle acceleration. Power extraction cavity is designed in the form of a two-coupled-cavity structure, in which the excited field is mutually coupled between two defects sites. The pre-buncher cavity is constructed by introducing a stub coupler to one of the cavities in a two-coupled-cavity structure, which detunes the cavity to exclude the fundamental mode from the cavity. In this case the excited field propagates into the adjacent cavity which confines the mode. We cold test and analyse the transmission curve of a stub-coupled structure against the full-band-gap plot. We also discuss the sensitivity of the observed field due to the perturbation of the detecting probe. (5 pages)
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The dependence of frequency and field on stochastic ordering in photonic band gap resonant structures
- Author(s): C.J. Matthews and R. Seviour
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In recent years the application of 2-Dimensional (2D) metallic Photonic Crystal (PC) structures to high power microwave devices, such as particle accelerators and gyrotrons, has gained increased interest. The work presented here focuses on the effect disorder has on the resonant frequency and peak electric field in the defect site of a 2D PC structure. For disorders up to a maximum of 15% variation in position and radius, we found that disorder applied to the inner-most scatterers surrounding the defect site dominates in determining the peak field and resonant frequency of the structure. We also show that small disorder (~1%) can lead to an increase in peak field in certain cases. We find increasing levels of disorder lead to a decreasing average peak field for all structures. Whereas the mean resonant frequency remains constant for increasing disorder while the standard deviation increases. We then develop an understanding for this behaviour in terms of frequency detuning and mode confinement. (3 pages)
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Nonlinear dynamics and chaos in a circuitry model of magnetron
- Author(s): D. Li ; Y. Alfadhl ; X. Chen
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The basic operation principle of microwave oscillators, such as magnetrons, is based on the motion of electrons under a combined influence of electric and magnetic fields. In such process, the DC energy is converted into the RF energy via the interaction process between the electrons and the surrounding electromagnetic field. This nonlinear process provides sufficient conditions in generating rather complicated dynamics, even chaos. In this paper, a circuitry model is utilized to simulate the fundamental operation dynamics of a magnetron by considering its electrical and geometrical characteristics. (4 pages)
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A co-harmonic gyro-monotron with a novel corrugated interaction cavity
- Author(s): D.A. Constable ; K. Ronald ; A.D.R. Phelps ; W. He ; A.W. Cross ; A.V. Savilov ; V.L. Bratman ; I.V. Bandurkin ; S.L. McConville ; I.V. Konoplev
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A novel interaction cavity has been designed for a gyro-monotron, allowing co-harmonic generation at the 2nd and 4th harmonic resonances of the cyclotron frequency. The output aperture of the cavity has been designed to trap the lower harmonic, whilst allowing output of the upper harmonic. Results from recent numerical simulations, performed using MAGIC 3-D, are presented. The intended co-harmonic behaviour is observed, with simultaneous excitation of the 2nd and 4th harmonics. Refinement of the output structure is now being undertaken to ensure only the 4th harmonic signal is emitted. (2 pages)
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Superconducting RF photoinjector for light source and FEL accelerators
- Author(s): C.D. Beard ; J.W. McKenzie ; B.L. Militsyn ; B.D. Muratori
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A high average current photoinjector is required to delivery high brightness electron bunches for many proposed light sources and free electron laser (FEL) based facilities. A possible solution to provide such high brilliance sources might be a Superconducting RF (SRF) gun. In order to match into the accelerator, the gun has to be operational at L-band frequencies (1.3 GHz or 1.5 GHz) or a harmonic of this frequency. The development of a high current RF gun based on the TESLA type technology (1.3 GHz) has been carried out. For the Next Light Source Project, a suitable design Free Electron Laserhas been developed to provide the full specification for the machine. Further studies of the acceleration technique is being carried out to fully understand the optimum beam parameters. An overview of the requirements, system design and injector performances is offered. Optimisation of the launch cavity was carried out to achieve CW beam properties; Average beam current 100 mA, nominal beam energy of 10 MeV, with bunch parameters of 1 1 π.mm.mrad, 20 ps bunch length, and RMS energy spread of 0.1%. As was required by the 4 GLS light source design, whilst similar properties have been proposed for the NLS, a pulsed FEL light source. These studies have provided an indication as to the fully optimum shape of the launch cavity as a function of the machine requirements. These concepts will also be presented. (3 pages)
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A microwave plasma drill
- Author(s): S.R. Wylie ; A.I. Al-Shamma'a ; A. Shaw
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A technique has been developed for melting holes in masonry as an alternative to conventional drilling. Microwaves are applied to a tungsten rod inside a section of waveguide, which is terminated by a short circuit. The rod protrudes from the waveguide, via a small hole, and is placed against the masonry to be drilled. The rod is rapidly heated by the currents that flow across the surface of the tungsten, and in addition, plasma is generated by the electric field which develops between the tip of the rod and the brick face. The temperatures achieved allow the rod to be pushed into the brick, displacing molten vitreous material. The main advantage of this technique over conventional drilling is that it is very quiet and produces no dust. (3 pages)
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Power combined tube transmitters with graceful degradation
- Author(s): R. Patrick
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This paper describes power combined microwave tube transmitters for very high peak and average power, with the attribute of graceful degradation. This technology replaces single high power microwave tubes (which have low Mean Time Between Critical Failures, and consequently poor Availability), and provides a lower cost and higher efficiency solution compared to solid state. (4 pages)
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High power RF capabilities at Loughborough University
- Author(s): B.M. Novac ; I.R. Smith ; W. Whittow
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Members of the plasma and pulsed power group at Loughborough University are engaged in several experimental activities related to the generation of high power radio frequency radiation. The paper reviews some of the more important projects that have recently been successfully completed. (5 pages)
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Compact solid state modulator system development
- Author(s): M. Iskander
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The paper describes the MPT5838/9, a successful development and commercial application of pulsed RF power manifested in a solid state modulator and magnetron as an RF source at a sub system level. The design is rated at 55 kV peak pulse amplitude at 250 A peak current with 10 kW mean power continuous operation driving high power magnetrons with output RF power of up to 5MW peak and 4 kW mean. It is based substantially on the FET- based solid-state direct-switched repetitive pulse modulator developed in the early part of the 21st century (Ref ). We highlight the key technical challenges addressed during the development, including performance issues, fault handling, and control of a compact solid state modulator. (4 pages)
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The transparent cathode: rejuvenator of magnetrons and inspiration for new RF sources
- Author(s): E. Schamiloglu and M.I. Fuks
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The relativistic magnetron has been studied as a high power microwave source since the 1970's. It is a simple, passive device requiring only a uniform magnetic field. It is possible to design a relativistic magnetron with center frequency from L-band to X-band, and it is possible to provide some modest frequency agility about the center frequency as well. Recently, researchers at the University of New Mexico proposed that a transparent cathode can significantly improve the output characteristics of magnetrons. Since then, a comprehensive study using particle-in-cell simulations has identified the many benefits of using this cathode. This paper will review the salient features of operating relativistic and non-relativistic magnetrons using a transparent cathode. In addition, progress from ongoing experiments at the University of New Mexico on an A6 magnetron driven by a short-pulse Sinus-6 accelerator will be presented. The presentation will conclude with a discussion of novel variants of the rippled-field magnetron (what we call the "Simplest Ubitron") that can produce coherent radiation as well as noise. Other devices benefiting from the transparent cathode will be discussed as well. (5 pages)
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RF system design for the EMMA FFAG
- Author(s): C.D. Beard ; N. Bliss ; S.A. Griffiths ; C. Hill ; P.A. McIntosh ; A. Moss ; A. Wheelhouse ; C. White ; D. Teytelman
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In this report the RF system design for EMMA (Electron Machine with Many Applications) is described. EMMA is a proof of principle Non-scaling FFAG that adopts an acceleration scheme will prove useful for fast acceleration of particles. For instance in medical applications, such as Hadron Therapy and future neutrino factory designs for Muon acceleration. The worlds first accelerator of this kind is currently under construction at Daresbury Laboratories. The EMMA RF power source options, power supplies, waveguide distribution scheme and control system is discussed. The nature of the machine requires a large degree of adjustment and flexibility than compared with conventional accelerators. So, to enhance the versatility of this machine, a complex RF system has been designed. This report details the RF schematic included to meet this requirement. This accelerator requires a bespoke RF Cavity, a complex distribution scheme from a single RF source to 19 cavities and a low level RF control system to provide sufficient operating conditions for the accelerator. In order to meet the budget, a number of developments were required to minimize RF power requirements. A design is now under construction that will provide the full flexibility of the machine parameters This includes an efficient cavity and coupler design, low loss distribution and pulsed RF source. A digital low level RF system has been developed to provide within 0.3 degrees and 0.3% phase and amplitude control. This has been modelled and demonstrated, and is currently under construction. An overview of the design requirements for each part of the system will be provided including any improvements on the specification. (3 pages)
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HPM systems based on NLTL technologies
- Author(s): C.R. Spikings ; N. Seddon ; R.A. Ibbotson ; J.E. Dolan
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Non linear transmission line (NLTL) technologies have been proposed over a number of years as a means of achieving various high power pulse shaping functions. BAE SYSTEMS has been involved in the development of a particular form of NLTL technology capable of producing high power pulsed RE waveforms with frequencies between 100's of MHz and l-2 GHz and with powers of the order of 25 MW and above. Benefits due to the use of NLTLs are the all-solid-state nature of the RE modulator system and the accurate pulse to pulse frequency and timing control which may be achieved. In this paper the fundamentals of the technology are explored and the potential for a system to array a number of NLTL elements and produce extremely high peak powers and radiated fields is discussed. Novel antenna systems are also described, exploiting high impedance surface technologies and suitable for the peak RE powers as well as being extremely compact. (3 pages)
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Towards photonic crystal and metamaterial high-power microwave applications
- Author(s): R. Seviour
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In recent years increasing interest has focused on the use of photonic and metamaterial structures for microwave applications. Predominately this work has focused on the development of novel antenna based technologies. Recently interest has grown into the possible use of photonic and metamaterials for high-powered microwave applications. In this paper we consider the use of photonic and metamaterial structures for applications such as; travelling wave-structures, RF generation, standing wave resonators and applications diverse as inverse Cherenkov accelerators. We review the physical processes and length scales that define photonic crystals and metamaterials, and introduce a theoretical approach to describe the interaction between charged particles and these structures. We also discuss the advantages photonic and metamaterials offer such as; high mode selectivity, zero-reflection, selective phase shifting, novel dispersion relationships, and effective negative permittivity / permeability. Discussing the advantages photonic crystal and metamaterial based technologies offer compared to their conventional counterparts. (5 pages)
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High power maser based on 2D periodic structure and operating in the w-band frequency range
- Author(s): I.V. Konoplev ; L. Fisher ; A.W. Cross ; A.D.R. Phelps ; K. Ronald
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Periodic structures are studied in many branches of physics including photonics, optics, electronics and physics of condensed matter, resulting in the appearance of photonic band gap materials, lasers, passive and active devices based on such lattices. Here the concept and the results of studies of a Cherenkov maser based on a surface two-dimensional periodic lattice are presented. The basic model of the maser, its parameters and the principles of operation are presented. The cavity of the maser was designed and the eigenmodes having the highest Q-factor derived. It is shown that the coupling between surface waves also known as Localised Plasmon Polaritons and volume waves (propagating waveguide modes) takes place in the vicinity of the Bragg resonance. The single mode operation of the maser is demonstrated and discussed. (5 pages)
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Compact tuneable microwave Terahertz source
- Author(s): R.A. Stuart ; A.I. Al-Shamma'a ; C.C. Wright
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Recently, it has been suggested that the next generation of millimetre/terahertz wave devices should be the result of the combination of the virtues of vacuum tubes with solid-state microfabrication methods. Vacuum devices can be very efficient if what is called a depressed collector system is used, so much so that efficiencies as high as 40% are commonplace at microwave frequencies. In addition, the electron mobility is essentially infinite, whereas in a solid-state component, carrier mobility is a serious limitation and leads to device heating problems and reduced efficiency. On the other hand, solid-state fabrication methods lead to micron size accuracy, with good yields and the economy of mass production, so that it is now possible to construct the miniature vacuum electronic device components required for operation at very short wavelengths. In addition, electron guns manufactured in silicon are now available, and these operate at much lower temperatures and produce higher beam current densities than are achievable with conventional thermionic emitters. It has recently been proposed that a folded waveguide travelling wave tube could be constructed using silicon microfabrication technology. When configured as an oscillator this device could provide a high power (>100 mW), highly efficient (>15%), reliable, compact and cheap source for the Terahertz Gap. This paper will present a comprehensive up to date on the current status of Liverpool John Moores University electromagnetic wave. (4 pages)
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Magnetic cusp-based electron beam source for a helically corrugated gyro-twa
- Author(s): A.R. Young ; C.G. Whyte ; C.W. Robertson ; D.H. Rowlands ; A.D.R. Phelps ; W. He ; K. Ronald ; A.W. Cross
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The latest results of experiments of an X-band gyro-TWA with a helically corrugated interaction region and a cusp electron beam source are presented. The cusp electron beam source uses a cold field emission emitter to produce a 37A beam accelerated with a potential of 130kV. Numerical investigations of the gyro-TWA have been completed and used to predict the saturated and small signal gain of the gyro- TWA devices. These predictions are compared with the experimental results obtained. (4 pages)
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150 kV electron gun development
- Author(s): G. Phillips
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A gridded electron gun was designed to produce a 150 keV electron beam for a Gyro TWA amplifier. The gun was required to operate into the magnetic focusing field of the TWA and produce a well collimated beam. This paper describes the design, and construction of the gun and also the design, construction and testing of a test device designed to test the beam collimation under operating conditions. (5 pages)
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Development and power device reliability assessment of resonant pulsed power converters for RF applications
- Author(s): F. Carastro ; J.C. Clare ; M.J. Bland ; C.M. Johnson ; P.W. Wheeler
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This paper considers the calorimetric measurements of losses and the semiconductor thermal cycling monitoring of high power resonant converters. For the tests a single phase resonant converter rated at 1 kV, 250 A (250 kW peak power, duty ratio 10%, 25 kW average power, pulse length 1 ms) has been developed. This represents one phase of a multi-phase resonant power supply designed for long-pulse modulation (typically 1 ms-2 ms) of RF tubes when equipped with a suitable output transformer. Pulsed operation is obtained by direct modulation of the high frequency power supply. The main aim of the work reported here is to monitor semiconductor losses of the IGBT modules through calorimetry and the device temperature using high speed thermal imaging, during the pulse, to identify the limitations and reliability of the modulator technology proposed. The paper provides an overview of the technology and design of the prototype test rig studied. Experimental results, showing semiconductor losses obtained through calorimetry and high quality chip thermal images are provided to validate the effectiveness of the proposed approaches. (5 pages)
