Author:
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ISBN:
Category :
Languages : en
Pages :

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Author: Chao-Hai Du
Publisher: Springer
ISBN: 3642547281
Category : Technology & Engineering
Languages : en
Pages : 200

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Book Description
A gyrotron traveling-wave amplifier (gyro-TWT) with the high-power and broad-band capabilities is considered as a turn-on key for next generation high-resolution radar. The book presents the most advanced theory, methods and physics in a gyro-TWT. The most challenging problem of instability competition has been for the first time addressed in a focused and systematic way and reported via concise states and vivid pictures. The book is likely to meet the interest of researchers and engineers in radar and microwave technology, who would like to study the gyro-TWTs and to promote its application in millimeter-wave radars. Chao-Hai Du and Pu-Kun Liu are both professors at Peking University.

Author: Craig Ross Donaldson
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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This thesis presents the results of a successful W-band gyrotron backward wave oscillator experiment. Three major achievements presented in this thesis are: 1) The design, simulation, construction and operation of a cusp electron gun; 2) The design, simulation, optimisation, construction and experimental measurement of a W-band helically corrugated waveguide and 3) the operation of the world's first W-band gyro-BWO using both a helically corrugated waveguide and a cusp electron gun. Gyro-BWO interaction with a 2nd cyclotron harmonic axis-encircling annular electron beam was observed. The interaction region was constructed through an accurate electroplating method while the designed dispersion characteristics agreed well to the experimental measurements. The loss through the optimised construction method was low, recorded around 1dB through the frequency range of interest. The following work presents the analytical, numerical and experimental investigation of a proof of principle gyro-BWO experiment. The design, simulation and optimisation of a thermionic cusp electron gun that can generate a 1.5A, 40kV axisencircling electron beam are discussed. Simulations showed a high quality electron beam with ~8% velocity spread and ~10% alpha spread. Experiments were conducted using this electron gun and the accelerating voltage pulse, diode current, transported beam current are presented. The electron beam profile was recorded showing a clear axis-encircling beam image from which the electron beam diameter and alpha values can be measured. Microwave radiation was measured over a frequency range of ~91-100GHz with a approximate maximum power of ~0.37kW. Operating over the magnetic field range 1.79T to 1.9T and measured over a range of alpha values this result was very impressive and proved the successful operation of the gyro-BWO.

Author: David Samuel Tax
Publisher:
ISBN:
Category :
Languages : en
Pages : 205

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Book Description
The gyrotron is a source capable of producing megawatt power levels at millimeter-wave frequencies for many important applications, including electron cyclotron heating and current drive in magnetic fusion devices. It is important that the gyrotron operates with high efficiency and provides a high quality output beam to minimize system size, maximize reliability and avoid additional losses in external systems. This thesis presents the experimental study of such a gyrotron designed to operate at MW power levels and whose initial 110 GHz operation was expanded to include operation at 124.5 GHz. To this end, a new set of components, including a cavity, mode converter, and output window were designed for operation at both frequencies. The cavity was designed using the code MAGY and the Q factors of 830 for the TE22,6,1mode at 110 GHz and 1060 for the TE24,7,1 mode at 124.5 GHz would be suitable for CW operation in an industrial gyrotron. The mode converter consisting of a dimpled-wall launcher and 4 phasecorrecting mirrors could theoretically produce an output beam with 99 % Gaussian beam content at each frequency while a single-disc window was implemented with over 99.5 % power transmission at both frequencies. The achieved output power in experiment was 1.1 MW at 110 GHz and 850 kW at 124.5 GHz for the design parameters of 96 kV and 40 A. At 98 kV and 42 A, the gyrotron achieved 1.25 MW and 1 MW at 110 and 124.5 GHz, respectively. Mode competition is typically a major limitation in such gyrotrons, and stable single-mode operation was demonstrated at both frequencies. At 110 GHz, the output beam had 98.8 % Gaussian beam content, while at 124.5 GHz, the output beam quality was 94.4 %. Another experiment within this thesis demonstrated the implementation of a mode converter with smooth mirrors that would be less susceptible to machining and misalignment errors. A Gaussian beam content of 96 % was measured in that experiment. In addition, a thorough study of the gyrotron start-up scenario was performed, for which experimental work had been lacking in the literature. The start-up scenario is the sequence of modes that are excited during the rise of the voltage pulse and is essential for the gyrotron to operate in its most efficient regime known as the hard self-excitation regime. This gyrotron operates nominally in the TE22,6,1 mode near the 110 GHz cutoff frequency with an axial field profile that is approximately Gaussian at the steady-state peak voltage. In experiments performed in the smooth mirror mode converter configuration, lower frequency modes were observed at lower voltages as opposed to higher frequency modes as predicted by theory. Analysis of these modes showed that they are backward-wave modes far from their cutoff frequency which have higher order axial field profiles, i.e. TE21,6,3 and TE21,6,4 modes at frequencies of 108-109 GHz. The excitation of these modes was investigated and shown to be possible by using theory and single-mode simulations with the code MAGY. This discovery was important as these modes were not included in past code runs, and thus future improvements can be made to incorporate this effect.

Author: Liang Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages :

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This thesis is based on the research project of a W-band gyrotron backward wave oscillator (gyro-BWO) using a helically corrugated waveguide which is currently being built and upgraded in the University of Strathclyde. The gyro-BWO was optimally designed through numerical simulations to achieve an output maximum power of ~ 10 kW with a -3 dB frequency tuning range of 84 - 104 GHz. To increase the overall efficiency of the W-band gyro-BWO, an energy recovery system of four-stage depressed collector was designed, numerically optimized and fabricated on the gyro-BWO. Microwave components including the Bragg reflectors, the side-wall coupler, the three-layer microwave window and the pillbox window were designed, simulated and measured to facilitate the practical use of the energy recovery system. This thesis includes the analytically calculated results, the numerical simulations as well as the experimental results of the said components and system. A 14-section Bragg reflector together with the side-wall coupler located at the upstream of the helically corrugated interaction cavity was used to couple the microwave radiation out. This allowed the installation of the depressed collector at the downstream side of the gyro-BWO. The transmission coefficient of the coupler was numerically optimized to achieve -1.0 dB over the frequency tuning range, from 84 - 104 GHz. The Bragg reflector measurement agrees well with the simulation. The input coupler achieves an average -13 dB reflection over the frequency in the measurement. Theoretical analysis of the pillbox type window and multi-layer window based on mode-matching method was carried out. The simulation and optimization of the pillbox window achieved a reflection of less than -15 dB in the whole operating frequency range of 84 - 104 GHz. The three-layer window can achieve less than 30 dB reflection in the frequency range of 84 - 104 GHz in the simulation. A three-layer window and a pillbox window which particularly optimized in frequency range of 90 - 100 GHz (the operating frequency range of the gyro- TW A that shares the same experimental setup as the gyro-BWO) were fabricated. With manufacturing constraints the design of the three-layer window achieved an average -10 dB measured reflection in 84 - 104 GHz and better than -15 dB in 90 - 100 GHz. In the downstream side of the gyro-BWO, another 18-section Bragg reflector was used to reflect the radiation back into the upstream interaction cavity. And the transmission coefficient of -30 dB was obtained in the microwave measurements using a VNA, which means the microwave power leakage was less than 1%. The measurement results agreed well with the simulations. A four-stage depressed collector was designed to recover the energy from the spent electrons. The 3D PlC code MAGIC and a genetic algorithm were used to simulate and optimize the geometry of the electrodes. Secondary electron emissions were simulated and a few emission models were compared to investigate their effects on the overall recovery efficiency and the backstreaming rate for the multistage collector. The optimization of the shape and dimensions of each stage of the collector using a genetic algorithm achieved an overall recovery efficiency of about 70%, with a minimized backstreaming rate of 4.9%. The heat distribution on the collector was calculated and the maximum heat density on the electrodes was 240W/cm2 and the generation of "hot spots" could be avoided. The electric field distribution inside the depressed collector was calculated and the geometries of these electrodes were properly shaped to avoid the voltage breakdown in vacuum.

Author: David Reed Gunderson
Publisher:
ISBN:
Category : Oscillators, Electric
Languages : en
Pages : 240

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The objective of the study was to investigate the use of magnetoelectrically focused electron beams in two-millimeter backward-wave oscillators at or near kilowatt power levels. An oscillator was constructed as a part of the investigation, designed from data obtained from previous work, resulting in a device that barely oscillated. This device demonstrated the practical solution to several significant problems: (1) the construction of ladder-line slow-wave structure; (2) a method of matching a ladder-type structure to a wave-guide transmission line; (3) demonstration in a microwave tube of a magnetoelectrically focused electron beam with an average radius of 6.8 mils and a current of 1.2 amps. Detailed field analyses of both a thick-ladder and a vane-type structure were carried out. Theoretical results obtained for dispersion, interaction impedance, and circuit loss are presented. Since known starting conditions for backward-wave oscillators as a function of loss and loss of space charge were too limited, start oscillation conditions were computed for values of QC from 0-25 and for values of loss from 0-225 db. Theoretical results computed for the dispersion and the loss of a thick-ladder circuit agreed with experimental data within 1-2 percent. The observed starting current in the oscillator was consistent with starting conditions calculated from the theoretical characteristics of the thick-ladder structure. (Author).

Author: Jennifer Margaret Butler
Publisher:
ISBN:
Category :
Languages : en
Pages : 566

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 47

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Book Description
Experimental and theoretical analyses, including particle-in-cell computer code simulations, are presented for the Gyrotron Backward Wave oscillator (Gyro-BWO) highpower microwave device. The Gyro-BWO has been designed, constructed, and initially tested as a frequency tunable device. The design has concentrated on a TE01, 4- to 6- GHz annular beam device. The annular beam is produced by the RAMBO pulser, which has a diode voltage of -300 to -800 kV and diode current of 1 to 20 kA. Initial results have shown that the device is operating in the backward wave mode. Initial results have also demonstrated that the device is magnetically tunable; that is, the frequency is tunable by adjusting the magnetic field. A Vlasov-type antenna is used for the extraction of the microwave signal on the diode end of the experiment, with initial power extraction of up to 2 MW ... High power microwave, HPM, Gyro-BWO, Gyrotron, Gyrotron backward wave oscillator.

Author: THOMAS ALLEN SPENCER
Publisher:
ISBN:
Category :
Languages : en
Pages : 340

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the existence of the gyro-backward-wave, as well as show the magnetic tunability of the gyrotron-backward-wave. In the solid beam case (1-2 kA), about 300-800 kW of extracted microwave power was detected in the waveguide detection system, implying that approximately 3-8 MW (efficiency $\sim$1-2%) of power is generated from the gyro-BWO device. The pulselengths for the solid beam case were from 300-600 ns (essentially the total flat-top voltage pulselength) over a frequency range of 4.5-6 GHz. The

Author: Malygin, Anton
Publisher: KIT Scientific Publishing
ISBN: 3731505843
Category : Technology (General)
Languages : en
Pages : 162

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Book Description
Gyrotrons are high-power mm-wave tubes. Here, the design, construction and experimental investigation of a 20 kW, 28 GHz gyrotron (2nd harmonic) are reported. This tube was designed to evaluate new emitters for future highly efficient and reliable fusion gyrotrons and for material processing applications. Following experimental results have been achieved in CW operation: 22.5 kW output power at 23.4 kV electron beam voltage and 2.23 A beam current with the world record efficiency of 43 %.