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System study using injection phase locked magnetron as an alternative source for superconducting radio frequency accelerator
Abstract
As a drop-in replacement of Continuous Electron Beam Accelerator Facility (CEBAF) 5kW CW klystron system, a 1497MHz, high efficiency magnetron using injection phase lock [1] and slow amplitude variation using magnetic field trimming and anode voltage modulation has been studied systematically using MatLab/Simulink simulations. The magnetron model is based the characteristics of experiment and manufacture chart on a 2.45GHz cooker type CW magnetron. To achieve high performance of a superconducting radio frequency (SRF) acceleration cavity with an electron beam loading, the magnetron's low level radio frequency (LLRF) control has been studied in two lock loops. In the frequency lock loop, the characterized anode V-I curve, output power (the tube electronic efficiency) and frequency dependence to the anode current (pushing by Vaughan model) and the Rieke diagram (frequency pulling by the reactive load) are simulated. The magnetic field B and anode voltage V in Hartree condition are satisfied and the effect of filament heater power to the frequency lock is also included. In the phase lock loop, the Adler equation governing injection phase stability is included in this study. The control of the magnet trim-coil power-supply and of the anode voltage modulation-switching power-supply has been also simulated to achieve the amplitude modulation. The result of linear responses to the amplitude and phase of SRF cavity will be presented in this paper. The requirement of LLRF control will be given by this result.
... Achieving precise phase control of magnetrons opens the possibility of their application to drive accelerators where multiple microwave sources are required [23]. Linear RF amplifiers as klystrons and Inductive Output Tubes (IOTs) are used in high-power transmitter's providing power up to hundreds kW in CW mode at the carrier frequency in GHz range and the bandwidth of modulation in MHz range, that is acceptable for superconducting LINAC and telecommunication. ...
... For example cost per unit power of industrial L-band CW high-power magnetron RF source is ≈ $1/1 W [25]. Many research groups around the world are working on the phase stability and phase locked magnetron have published their work in different litratures [23]- [25]. Phase stability and phase locked magnetron is the need of the hour for a high power magnetron array system. ...
Magnetrons have been the most efficient high power microwave sources for decades. In the twenty-first century, many of the development works are headed towards the performance improvement of CW industrial magnetrons. In this review article, the development works and techniques, used on different types of magnetrons, for the performance enhancement in the past two decades have been discussed. The article focuses on the state of the art of CW magnetron and the direction it will take in foreseeable future. In addition it also glimpses some of the major variants of magnetron which have further opened up scope in mm-THz spectrum of electromagnetism.
... For more information, see https://creativecommons.org/licenses/by/4.0/ controlling and fixing the phase and frequency of a magnetron to the extent of the precision required for a phased array antenna or a linear accelerator overcoming the critical and inherent shortcomings of magnetrons [16]- [22]. Previous studies on the noise in high-power microwave tubes [23]- [25] concluded that the noises on the electron beam play an important role, which is mainly attributed to the technical parameters such as beam current and voltage near their nominal values. ...
Compact but powerful and efficient magnetrons are in service for various high-power microwave applications owing to their additional superiority of low-cost mass production. However, the magnetron’s inherent instability in frequency and phase over a relatively wide spectrum limits the versatile availability of the magnetron for possible advanced applications, including a long-distance wireless power transfer system (WPTS) that employs the magnetron as a unit source of a phased array system. The authors present a methodology suppressing a long-term instability of the S-band commercial magnetron harnessed by the phase-locking-loop (PLL) injection controlling and fixing the phase and frequency of the magnetron to the extent of the precision for a WPTS. The long-term drift of the phase exactly replicating the anode voltage fluctuations is successfully suppressed by the implementation of a DC power supply to compensate the cooling effects of the heater, which contributes to extreme stabilization of the phase (peak to peak 0.2°) for high-power (1kW). And eligibility for the unit source of a phase-arrayed WPTS is proven by varying the output power while maintaining the phase at a constant.
... Because of such competitiveness, magnetrons have been widely adapted in various fields such as microwave ovens of home appliances, radars, communication, medical accelerators, generation of processing plasmas, industrial heating and chemical process intensification [15]- [19]. In addition, capital cost of a magnetron is superior compared to other high-power microwave modules [20]. ...
We demonstrate noise suppression and precise phase control of a commercial 2.45GHz magnetron aiming for wireless power transfer application. The impurity of the microwave spectrum was confirmed to be due to the switching frequency of 76kHz in the power supply. With the decoupling capacitor installed to the output of the high-voltage power-supply driving the magnetron, the spectral purity of the magnetron was significantly enhanced. And we achieved extreme precision in phase-control (peakto-peak 0.3°) for the high-power (1 kW) microwave magnetron by applying the phase locking loop to the noise-suppressed magnetron system.
... With the increasing demands for clean energy, substantive microwave industrial applications require high power capacity, such as microwave plasma diamond film deposition [1,2]. Therefore, microwave coherent power combining technology has become an effective solution [3,4]. In order to realize multiple magnetrons coherent power combining, it is necessary to solve the problem of frequency and phase instability of magnetron output [5]. ...
In order to meet the requirements of large-power capacity in microwave-energy industry, the microwave coherent power combining by multiple magnetrons is a valid method to gain a large-power and high efficiency microwave source. In microwave energy applications, microwave absorption of industrial materials is varying in the heating duration and dependent on the dynamic change of materials. It is the first time that a 20-kW continuously power-adjustable injection-locked magnetron source has been achieved, and according to the experiment results, the maximum microwave coherent power combining output reaches 33.1 kW, and the coherent power combining efficiency is higher than 93%. The experiments show that the unbalanced output power between the two magnetrons does not affect greatly on the microwave coherent power combining efficiency. It is a great progress to develop the microwave power source which satisfies the power capacity requirement of microwave energy industry with the real-time power adjustment for the microwave industrial applications.
There are many modern day niche applications that may benefit if the output power of several magnetrons is combined together to produce a high power output at microwave frequencies. However, this requires all the magnetrons to be phase-locked to a reference. Phase locking of multiple magnetrons to a reference phase needs careful design, implementation, and considerable hardware. This article presents the design and computational studies on cascaded magnetron topologies, which may reduce the number of phase-locking circuits and power supply units by a factor of two and deliver a high output power. Furthermore, the evolution of output power and efficiency with changes in critical dimensions of the cascaded magnetrons is reported and an attempt is made to provide a qualitative understanding of its working. This article also proposes a new cascaded magnetron structure, which enhances the power output. All simulation studies are carried out for 2.45-GHz magnetron to validate the design. The novel design presented in this article gives a maximum continuous wave (CW) power of around 45 kW with an efficiency of around 49%.
As a low operating cost microwave source, magnetron has been fully considered for superconducting radio frequency (SRF) accelerator. A 1497-MHz, 13.5-kW continuous-wave (CW) magnetron for SRF accelerator is designed and manufactured, and the test results meet the design requirements. Two simulation steps of designing magnetron with Computer Simulation technology (CST) Studio Suite are presented. First, the Microwave Studio helped to simulate the microwave coupled output structure and the resonant cavity. Then, the output performance of magnetron was simulated with particle-in-cell (PIC) solver. The cold test results show that the circuit efficiency is 93.14 %. A magnetron hot test platform was used to measure an output power of 14.23 kW and an electronic efficiency of 84.23 %. The injection locking experiment is completed at 4.5 kW. The frequency of the magnetron is adjustable, with a tunable bandwidth of 7 MHz through a mechanical tuning rod. The problems and solutions in the process of design and manufacture are summarized, which can provide a reference for the development of high-power magnetron with different frequency. The development of 1497-MHz magnetron broadens the selectable frequency of high-power magnetron, which is beneficial to its industrial applications.
The operation of a high-power nonrelativistic strapped ultra-high-frequency (UHF) multicavity magnetron with transparent cathode is simulated using the Improved Concurrent Electromagnetic Particle-in-Cell (ICEPIC) code. Results of the simulations are compared with simulations of the same magnetron with a solid cylindrical cathode. Both cathodes are explosive-emission electron sources that operate in the space-charge-limited mode of the electron extraction from the cathode. Simulations are part of an effort searching for methods and technologies that enable an increase of output microwave power of strapped nonrelativistic high-power UHF magnetrons by replacing thermionic direct-heated cathodes with a non-thermionic-emission cathode. Results of the simulations show that the anode current Ia and the output power Pout of the magnetron with the transparent cathode are higher than Ia and Pout of the same magnetron with a solid cathode. At the same time, the electronic efficiency ηe of the magnetron with the transparent cathode is less, and the startup time ts is shorter than ηe and ts of the magnetron with the solid cathode.
This paper presents the results of particle-in- cell (PIC) simulations of a strapped nonrelativistic ultrahigh- frequency (890-915 MHz) magnetron whose geometrical and operational parameters are close to the parameters of the high- power industrial heating magnetron producing 75-100 kW of continuous-wave microwave power. Simulations of the magnetron operation are performed without artificial RF priming, but rather in natural conditions, when magnetron oscillations start to grow from electromagnetic “noise.” This approach reveals many important details of the “preoscillating” phase of the magnetron operation. It is found, for example, that the start-up time of the magnetron with a solid cathode, operating in the explosive electron emission mode, is determined by the time needed for the electron cloud formed near the cathode to reach the anode, where the fringing dc electric fields of the periodic anode structure begin to perturb the electron cloud and to facilitate the magnetron oscillations to start to grow. The PIC simulations are performed at one magnetic held (0.238 T) and a range of applied voltages, allowing the magnetron to operate in the π mode characterized by five magnetron spokes and T E51-like mode of the induced electromagnetic held distribution within the resonant system of the ten-cavity magnetron.
The applications of magnetrons to high power proton and cw electron linacs are discussed. An experiment is described where a 2.45 GHz magnetron has been used to drive a single cell superconducting cavity. With the magnetron injection locked, a modest phase control accuracy of 0.95° rms has been demonstrated. Factors limiting performance have been identified.
An Efficient RF Source for JLab
- M Neubauer
- A Dudas
- R Rimmer
- H Wang