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1
Zhang, Liang. "Energy recovery system for a gyrotron backward wave oscillator." Thesis, University of Strathclyde, 2012. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18933.
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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.
2
Donaldson, Craig Ross. "A W-band gyrotron backward wave oscillator with helically corrugated waveguide." Thesis, University of Strathclyde, 2009. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=22627.
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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.
3
Chipengo, Ushemadzoro. "Novel Concepts for Slow Wave Structures used in High Power Backward Wave Oscillators." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1499346841806681.
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Батіщев, А. С. "Дослідження взаємодії гармонік дифракційно-черенковського випромінювання у багатозв’язних квазіоптичних системах з періодичними неоднорідностями." Master's thesis, Сумський державний університет, 2021. https://essuir.sumdu.edu.ua/handle/123456789/87400.
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Об’єктом дослідження дипломної роботи є гармоніки дифракційно-черенковсьго випромінювання у багатозв’язних квазіоптичних системах з періодичними неоднорідностями. Теоретичні методи дослідження, котрі використовуються в роботі, засновані на раніше досліджених класичних прикладах дифракційної електроніки в наближенні до заданого струму, та досліджена взаємодія гармоніки дифракційно-черенковського випромінювання у багатозв’язних квазіоптичних системах з періодичними неоднорідностями. Робота викладена на 84 сторінках, в тому числі включає 28 малюнків, 3 таблиці та список літератури з 45 джерел.
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Yu, Ching-Fang, and 余青芳. "TE01 Gyrotron Backward-Wave Oscillator." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/01593338367789041436.
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博士國立清華大學
物理學系
95
The gyrotron backward-wave oscillator (gyro-BWO) is a continuously tunable source of coherent millimeter-wave radiation based on electron cyclotron maser. The fundamental mode operation is generally adopted to simplify the experiment which can avoid the mode transition problem and the mode competition behavior. As the high frequency requirement increase, high order mode operation is an effective method to solve the structure size limit. A taper structure Ka-band gyro-BWO which operated at TE01 mode in cylindrical waveguide is designed in this thesis. The mode competition behavior is discussed which major unwanted competing mode is TE31 first harmonic oscillation. A single mode stationary code is employed to simulate the start oscillation current and nonlinear behavior of each interaction mode. The relative value of start oscillation current between operating mode and the other waveguide modes are applied to judge the operating stability. The question which we must consider is the short end boundaries to the TE31 mode. As a result, the close cavity structure brings about the gyromonotron dynamic which have lower oscillation threshold. A distributed loss is applied to suppress the unwanted oscillation but operating mode. A novel design and of high spectral purity Ka-band TE01 mode converter are presented to avoid the mode transition when wave coupled out. Back-to-back transmission measurements show excellent agreement with computer simulations. The measured optimum transmissions are 97% with 1-dB bandwidth of 5.8 GHz at center frequency 34 GHz. In addition to high conversion efficiency, high mode purity, and broad bandwidth, this converter also features easy construction and compact size. The preliminary experimental results show the spurious modes can be suppressed by distributed loss. The maximum output power is 46kW with efficiency 8% and the bandwidth is 3.7%.
6
Liao, Cheng-Liang, and 廖宸樑. "Special Smith-Purcell grating backward-wave oscillator." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/a3u668.
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碩士國立清華大學
光電工程研究所
106
THz waves have potential in medicine, biophysics, and imaging. In order to fabricate a simple device with high efficiency, here we propose a special kind of Smith-Purcell grating backward-wave oscillator (BWO) for THz generation. First, the boundary conditions of the Smith-Purcell grating are solved by the Matlab code, and the operating frequency is determined by the dispersion relation and the beam line on the Brillouin diagram. Then we simulate the grating-structure by MAGIC 2D to observe the interaction between the structure and the electrons, and the results of the operating frequency in MAGIC 2D agree with the results in Matlab. Also, we simulate the grating with different current densities and beam-grating distances, and find that the restricted beam condition while operating at THz region. In order to enhance the coupling efficiency, also to make the structure easy to manufacture, “semi-open” grating is proposed. From the result of MAGIC 2D simulation, we find the magnitude of the B_z field is 4 times as large as the conventional Smith-Purcell grating BWO on the surface of the grating. In thick beam simulation, the parameters of the E-gun in NSRRC are applied to the ASTRA simulation to determine the magnetic field for beam focusing. The calculated magnetic field of the solenoids are 130gauss, 120 gauss and 170 gauss at 21.5cm, 33.5cm and 50cm respectively and the rms beam size equals to 0.41mm at 80.5cm. Yet in MAGIC 2D simulation, the upper portion of the electrons is not well modulated due to the asymmetric excited mode profile. We also propose another structure that contains both an optical grating and a dielectric coating metal plate. The dielectric layer provides the condition for stimulated Cherenkov radiation, and the excited magnetic field is 6 times of the field of single-side structure on the surface of the grating. We suppose it is a promising structure for enhancing the energy coupling between the beam and waves.
7
Wu, Ting-Shu, and 吳庭旭. "Second Harmonic TE21 Gyrotron Backward Wave Oscillator." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/42474045171733932471.
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碩士南台科技大學
電機工程系
92
The gyrotron backward wave oscillator (gyro-BWO) is a promising source of coherent millimeter wave radiation based on the electron maser instability on a backward waveguide mode. However, a high magnetic field requirement limit on its applicability as a millimeter-wave source. The required magnetic field is reduced by the harmonic operation in this project. The harmonic gyrotron backward-wave oscillator not only has the feature of the frequency tuning using by the applied magnetic field and beam voltage, but also has the low applied magnetic field and high beam current. A comparative analysis between the fundamental and second cyclotron harmonics of gyrotron backward-wave oscillators (gyro-BWOs) is analyzed presented. The simulation results reveal that the nonlinear field contraction is a common feature for both harmonics interactions. Besides, the electron transit angle, used to characterize the axial modes of the fundamental harmonic TE11 mode at the start-oscillation conditions, is found to be applicable even for the second harmonic TE21 mode. Each axial mode of either the fundamental harmonic TE11 or the second harmonic TE21 modes is maintained at a constant value of the electron transit angle while changing the operating parameters, such as magnetic field and beam voltage. Extensive numerical calculations have been conducted for the starting currents and tuning properties. A single-mode operating regime is suggested where the second harmonic TE21 gyro-BWO is stable with a decent output power, comparing with the fundamental harmonic TE11 gyro-BWO.
8
Chen, Chih-Wei, and 陳致瑋. "Study of X-band Relativistic Backward Wave Oscillator." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/76556307384698868760.
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Cheng, Nai Hao, and 鄭乃豪. "A study of THz gyrotron backward-wave oscillator." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/m6gs8p.
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碩士國立澎湖科技大學
電資研究所
101
High power terahertz (THz) wave can be applied to weather radar, remote detection of explosives, metal and non-metallic weapons, space communications, plasma diagnostics, DNP technique, material processing, electron spin , and resonance spectrum. However, high power and coherent THz sources are difficult to obtain. The gyrotron backward-wave oscillator, studied in this thesis, is capable of generating high-power radiation in the THz band, and its oscillation frequency can be continuously tuned by changing the voltage or magnetic field. A THz gyrotron backward-wave oscillator must operate at a high-order waveguide mode to enlarge the cross-section dimension of the waveguide for high power operation. In order to avoid the mode competition problems resulting from the high-order mode operation, this thesis adopts the coaxial waveguide as the interaction structure and selects a smaller radius ratio to reduce the number of competing modes. In addition, the outer radius of the coaxial waveguide is tapered to shorten the effective interaction length and increase the start-oscillation currents of the competing modes. The simulation results show that tapering the outer radius can not only effectively suppress the competing modes, but also change the operating magnetic field range of the operating mode to avoid the mode competition. Moreover, tapering the outer radius can also enhance the efficiency and increase the tuning bandwidth of the operating mode. Finally, the coaxial-waveguide gyrotron backward-wave oscillator, operating at a voltage of 30 kV and a current of 5 A, can generate an output power of 17 kW (efficiency 11.5%), a stable 3dB tuning bandwidth of 3.2 GHz (305.5 GHz ~ 308.7 GHz, 1.1 % ) .
10
Chen, Nai-Ching, and 陳乃慶. "TE01 Gyrotron Backward-Wave Oscillator with Mode Selective Circuit." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/70691579161214911386.
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Pao, Kuo Feng, and 鮑國峰. "Axial Mode Interaction in the Gyrotron Backward-Wave Oscillator." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/13238400555521453708.
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Fan, Chao-Ta, and 范肇達. "Stability and Tunability of a Gyrotron Backward-Wave Oscillator." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/32062525184521026706.
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博士國立清華大學
物理學系
93
The gyrotron backward-wave oscillator (gyro-BWO) base on electron cyclotron maser is a promising millimeter/submillimeter source for high power capability and broad band tunability. However, the development of the gyro-BWO is hampered by the nonstationary oscillation. We will discuss the stability and tunability form the fundamental physics characters and verify by the Ka band gyro-BWO experiment. The beam-wave interaction forms the axial mode in the gyro-BWO. The number of regions of positive energy deposition rate determines the order of axial mode in the linear operating region. The field contracts to the beam entrance at the nonlinear operating region. The time-dependent particle-in-cell code is used to analyse the nonlinear behavior in the gyro-BWO. The results show the gyro-BWO exhibits the broad and stationary tunability at the shorter interaction length. And the self-modulation could be the reason forming the nonstationary oscillation in the gyro-BWO. We conducted the Ka band gyro-BWO experiment to verify the tunability at the shorter interaction length (3 cm) and analyse the stability at the longer interaction length (9 cm). The experimental results show that the gyro-BWO could broad and stationary operation at the 3 cm interaction length with maximum efficiency 28%, whereas the nonstationary oscillation hampered the tunability at the 9 cm length with 20% efficiency. The signal gating technique was used to analyse the spectra of the nonstationary oscillation. The uneven spatial distribution of the beam deposited energy causes the field energy to bounce back and forth within the feedback loop and modulates the oscillation amplitude and generates the equally spaced sidebands about a main peak in the output spectra.
13
Lin, Guan Nan, and 林冠男. "Study of Efficiency Enhancement of the Gyrotron Backward-wave Oscillator." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/05228747926933330134.
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Yu, Yung-Chi, and 尤永吉. "Stability Analysis of an Injection-Locking Gyrotron Backward-Wave Oscillator." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/09065341984083243837.
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碩士南台科技大學
電機工程系
94
A gyrotron backward wave oscillator is a promising source of coherent millimeter wave radiation based on the electron maser instability on a backward waveguide mode. However, a high magnetic field requirement limit on its applicability as a millimeter-wave source. Controlling the phase and frequency of a gyrotron backward-wave oscillator (gyro-BWO) by means of injection-locking techniques is of practical importance. Using a nonlinear self-consistent time-independent code, this study analyzes the stability of a gyro-BWO with an external injection signal. To examine the stability of steady-state solutions, the perturbation of the phase difference between the oscillator and injected signal must decay in time. A nonlinear time-independent code is employed to study the properties of the injection-locking gyro-BWO, including the locking power, the phase difference between the oscillator and injected signal, and the locking bandwidth curve. The simulation results show that the dependence of the phase difference of stable solutions on the frequency is consistent with the theoretical prediction at the injection-locking regime. Furthermore, the simulated phase differences of all stable solutions correspond with restrictions between -90° and 90°. Comparing with the curve of the locking bandwidth obtained by Adler’s equation, the simulated result is slightly asymmetrical due to the field concentration near beam entrance. Finally an efficiency enhancement on the injection-locked gyro-BWO is found and will be discussed.
15
Huang, Yi-Chen, and 黃易辰. "Study of Efficiency Enhancement of the W-Band Gyro-Backward Wave Oscillator." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/01277808031774664673.
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碩士國立清華大學
物理系
101
The gyro-BWO(gyrotron backward wave oscillator) is a promising source of coherent millimeter-wave based on the ECM(Electron Cyclotron Maser) interaction. The facts that oscillation is formed by an internal feedback loop enables a gyro-BWO to use a non-resonant structure, hence the frequency of a gyro-BWO can be tuned broadly and continuously. However, the facts that the field profile tends to concentrate in front of the interaction structure when a gyro-BWO is working, strongly affects the interaction between electrons and wave, and this usually ruins the efficiency of a gyro-BWO. Hence the main idea of this study is to realize the basic characteristic and enhance the efficiency of a gyro-BWO. W-band gyro-BWO is the main target of this study, and all the working parameters of this study is based on our W-band MIG gun, which has been designed and fabricated by Dr. C.P. Yuan, and the result is compared with our previous study on Ka-band gyro-BWO. In small-signal operation, the behavior of the gyro-BWO is linear. The number of axial modes is strongly related to the times of energy deposition between electrons and wave. On the other hand, in nonlinear operation, the efficiency saturates with growing current or interaction length, which is result from the contraction of the internal feedback loop and hence contracts the field profiles. Last of all, according to previous paper, we do some optimize to enhance the efficiency of W-band gyro-BWO by tapering our interaction structure quiet smoothly. The result shows that our by-tapering structure gives about 23%~30% in efficiency from 94GHz to 99GHz in oscillation frequency.
16
CJIAMG, PO-YI, and 江柏儀. "A low-voltage fourth-harmonic reflective large-orbit gyrotron backward-wave oscillator." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/yy9hnb.
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碩士南臺科技大學
光電工程系
107
Frequency-tunable gyrotron is urgently needed by many emerging applications, such as electron spin resonance, sensitivity enhancement of nuclear magnetic resonance by the technology of dynamic nuclear polarization, and accurate measurement of hyperfine splitting of positronium.The most appealing characteristic of the reflected gyrotron backward-wave oscillator (gyro-BWO) is that its frequency can be tuned by adjusting the magnetic field. In addition, a reflected gyro-BWO does not require a mode converter. Harmonic operation in a reflected large-orbit (LOG) gyro-BWO is able to greatly suppress lower harmonic mode to alleviate mode competition in harmonic gyrotrons. In this paper, we study investigates the electron dynamics of gyrotron interaction in a tapered waveguide and proposes a 200-GHz low-voltage fourth-harmonic TE_4,1-mode reflective LOG gyro-BWO. In addition to the characteristics of large-orbit gyrotron, this paper includes the introduction for gyrotrons, nonlinear theory, boundary condition, and simulation model. It also show the oscillation characteristics of different axial modes transverse modes, including the relationship between the start-oscillation current and the applied magnetic field, and the influence of the output power and frequency of oscillation on the applied magnetic field. The simulation results indicate that cut-off section of the reflective gyro BWO reflects the backward propagating wave and is extracted from the downstream. However, an initial resonance mismatch leads to low interaction efficiency in the reflective gyro-BWO. The reflective gyro-BWO with the tapered structure can significantly enhance the output power, but narrow the frequency-tuning range. By increasing the waveguide's length, we can increase the frequency-tuning range of the reflective gyro-BWO. A stable TE41S4-mode large-orbit gyrotron at the fourth axial mode is predicted to yield peak output power of 2.8 kW at 200.2 GHz with an efficiency of 2.8% and a 3-dB frequency-tuning range of 3 GHz for a 50-kV, 2-A electron beam with an axial velocity spread of 3%.
17
Lee, Hsun, and 李勳. "Study of Efficiency Enhancement of 400GHz TE41 Forth-Harmonic Gyro-Backward Wave Oscillator." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/27426693993595016443.
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Lin, Po Nien, and 林柏年. "Study of Efficiency Enhancement of the Gyrotron Backward-wave Oscillator with Nonlinear Tapered Waveguide." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/34009466327842975432.
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Liao, Chih-Wei, and 廖志偉. "A Study of Operating Regimes of a Gyrotron Backward-Wave Oscillator Driven by an External Signal." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/58704496548410596295.
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碩士南台科技大學
光電工程系
96
A gyrotron backward wave oscillator is a promising source of coherent millimeter wave radiation based on the electron maser instability on a backward waveguide mode. However, the requirement on phase coherence is strict for applications. Controlling the phase and frequency of a gyrotron backward-wave oscillator (gyro-BWO) by means of injection-locking techniques is of practical importance. Using a nonlinear self-consistent time-independent code and analyze of stability to delineate the drive curve. The simulation results of gyro-BWO driven by an external signal show that there are three roots exist. The operating regimes of a gyro-BWO driven by an external signal are analyzed using nonlinear oscillation theory, linear theory, nonlinear code, and Adler’s curve. When the beam current is below free-running start oscillation current, the results of the nonlinear simulation are consistent with the results of the amplifier’s linear theory. This is an amplifier regime. When the beam current is above start oscillation current, there are three different operating regimes, amplifier regime, mode competing regime and phase-locking oscillation regime in a gyro-BWO driven by an external signal. There are three possible mode, amplifier mode, unstable mode and phase-locking oscillation mode in the mode competing regime. Due to nonlinear oscillation theory the solutions of the unstable mode are the steady-state solutions, but aren’t stable solutions.
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Chung, Ping Hsueh, and 鍾秉學. "A study on the efficiency and the tunability of the coaxial-waveguide gyrotron backward-wave oscillator." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/64343321608994169371.
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碩士國立澎湖科技大學
電資研究所
100
The oscillation frequency of a gyrotron backward-wave oscillator (gyro-BWO) can be continuously tuned by changing the beam voltage or the magnetic field, so the gyro-BWO is characterized mainly by its superior frequency tunability. The coaxial waveguide has mode selective properties. The wall losses on the inner cylinder and the outer cylinder of a coaxial waveguide can attenuate different oscillation modes. However, little research has been done on the gyro-BWO with a coaxial interaction structure. In a recent study, the coaxial gyro-BWO, which used an axial uniform magnetic field and a uniform cross-section waveguide with distributed losses for suppressing oscillations, achieved an output power of 137 kW with an efficiency of 9.1 % and a 3dB continuously tunable bandwidth 1.32 GHz (4.2%). This paper intends to adopt a waveguide tapering method to remove the limit of the gyro–BWO efficiency and bandwidth. A steady-state, particle tracking code, which can be applied to the problem of small and large signals, is used to analyze the beam-wave interaction. The axial field distribution can be solved by a set of nonlinear self-consistent equations for the electron beam and electromagnetic waves. Simulation results show that single-stage tapered structure only enhance the power of the gyro-BWO, but can not effectively increase the bandwidth. The gyro-BWO with a two-stage tapered structure can achieve an output power of 316 kW with an efficiency 27% and a bandwidth of 2.3% (2.3 times the uniform structure), or a bandwidth of 8.4% (2.1 times the uniform structure) with an output power of 129 kW and an efficiency of 8.6%. Thus, the output power and the bandwidth of a coaxial gyro-BWO can be greatly enhanced by optimize the circuit parameters of the two-stage tapered structure.
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Chang, Pei-Che, and 張培哲. "Theoretic and Experimental Investigation of Gyrotron Backward-wave Oscillator with High Efficiency and Broad-Band Capabilities." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/92791024161107688499.
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博士國立臺灣大學
物理研究所
103
The gyrotron is a coherent radiation source based on the electron cyclotron maser (ECM) instability and capable of generating unprecedented power levels in the millimeter to terahertz (THz) region of the electromagnetic spectrum. The focus of the present study in my paper is gyrotron backward-wave oscillator (gyro-BWO) simulation and experiment. Gyro-BWO is the only version of four basic embodiments of gyrotron with continuous frequency tunability The simulation has provided the highest efficiency about 30% without taper magnetic field. After optimized the efficiency by taper magnetic field, the 3dB bandwidth can achieve up to 35% which implied frequency tuning in different currents almost reach the highest efficiency, while it is also the least exploited version although many applications require frequency tunable broadband sources. The gyro-BWO employs a nonresonant interaction structure (basically a waveguide section). This makes the interaction dynamics fundamentally different from that of the cavity-based gyro-monotron. The existence of gyro-BWO oscillating modes and their field profiles must then depend entirely upon the beam-wave interaction. As it turns out, the field profiles of different axial modes are asymmetric in different ways, which in turn determines their competitive advantages. Moreover we can do the continuous frequency operation by tuning the magnetic field so optimized efficiency can be achieved through magnetic field and taper magnetic field in different current. In practical, we can also reach higher efficiency and bandwidth from low current to high current. A single-mode, stationary code and a multimode, time-dependent, particle-in-cell code are employed for electron dynamics and wave stability studies.
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Chih, Hsiao Ming, and 蕭明志. "Stability Analysis of Gyrotron Backward-Wave Oscillators." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/26623424906393652145.
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碩士南台科技大學
電機工程系
94
The gyrotron backward wave oscillator (gyro-BWO) is a promising source of coherent millimeter wave radiation based on the electron maser instability on a backward waveguide mode. In this study, distributed wall losses and shortening the interaction length have adopted to enhance the stability of a W-band and Ka band gyrotron backward-wave oscillators (gyro-BWO). Simulation results reveal that distributed wall losses can effectively suppress high-order axial modes and do not significantly degrade the performance of a gyro-BWO operating at the fundamental axial mode. In contrast, shortening the interaction length can increase start-oscillation for all axial modes. In this study, the stationary nonlinear simulation code is employed to analysis, including the interaction length saturation characteristic, oscillation conditions of axial modes and transverse modes and frequency tuning range. Meanwhile, tapering waveguide structure is used for optimizing output power and bandwidth of gyro-BWO and increasing distributed wall losses is employed to enhance the stability of gyro-BWO. The stable gyro-BWO W-band is predicted to yield a peak output power of 100 kW at 96 GHz with an efficiency of 20 %, a half-power frequency tuning bandwidth of 1.8 GHz for a 100 kV, 5 A electron beam with an axial velocity spread of =5 %, and the stable gyro-BWO operating in the Ka band mode, is predicted to yield a peak output power of 233.7 kW at 36.32 GHz with an efficiency of 13 %, and a 3 dB frequency tuning ranges 0.82 GHz for a 120 kV, 15A electron beam with an axial velocity spread of. =8 %.
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Huang, Wei-yang, and 黃煒揚. "Effects of Long-line Reflection on the Dynamical Behavior of Gyrotron Backward-wave Oscillators." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/34248260516420332188.
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碩士國立中央大學
物理研究所
99
The gyrotron backward-wave oscillator (gyro-BWO) is a coherent microwave or millimeterwave radiation source based on the electron cyclotron maser instability. The backward wave oscillation occurs in an internal feedback loop which consists of a forward moving electron beam and a backward propagating wave. Since the gyro-BWO employs a non-resonant structure, the frequency can be tuned continuously by varying the beam voltage or magnetic field. However, discontinuous tuning induced by external reflection was observed in experiments. In this study, the effects of external reflections on the gyro-BWO were examined by using the stationary code and the particle-in-cell simulation code. The numerical results show that the dynamical behavior of the gyro-BWO is sensitive to the length of the external reflection circuit (Lext). As Lext is increased, the discontinuity in frequency tuning becomes more severe. The hysteresis phenomenon is also observed while varying the voltage or current. The mode selection in the gyro-BWO was achieved by adjusting the external reflection circuit. The gyro-BWO can be stably operated in the second axial mode by properly adjusting Lext and the height of the iris (Delta r). Moreover, the output power of the second mode is two times of the oscillating power of the fundamental mode. Nonstationary oscillations are also observed at some settings of of Lext and , and the main cause is mode competition.
24
Chen, Yen-Cheng, and 陳彥誠. "Fourth-harmonic reflective large-orbit gyrotron backward-wave oscillators at different high-order transverse modes." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/6nykd6.
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碩士南臺科技大學
光電工程系
107
In recent years, Terahertz (THz) gyrotrons have been applied to nuclear magnetic resonance (NMR), electron spin resonance, outer space research, military radar and other related applications. The gyrotrons in harmonic operation offer the magnetic-field reduction, but the considerably weak harmonic interactions in harmonic gyrotrons lead to serious mode-competition problems. An axis-encircling electron beam for the gyrotron is able to greatly avoid lower harmonic mode to alleviate mode competition in harmonic gyrotrons. In this paper, we study the fourth-harmonic large-orbit reflective gyrotron backward-wave oscillators (gyro-BWOs) operating at the transverse modes TE4,ns4 with different radial numbers. We discuss the characteristics of the dispersion relations, start-oscillation conditions, 3-dB frequency-tuning ranges and the efficiencies using the nonlinear simulation code for the gyro-BWOs. Tapering the waveguide radii and increasing the interaction lengths are employed to enhance the 3-dB frequency tuning ranges and the efficiencies for the gyro-BWOs. When the beam current is 2 A, the simulated results show that the TE4,1s4-mode gyro-BWO yields the peak output power of 3 kW with an efficiency of 3% at 200.22 GHz, the 3-dB frequency-tuning range of 3 GHz for a 50-kV and axial velocity spread of 3%. Similarly, the TE4,2s4-mode gyro-BWO yields the peak output power of 2.1 kW with an efficiency of 2.1% at 193.6 GHz, a 3-dB frequency-tuning range of 1.8 GHz and the TE4,3s4-mode gyro-BWO yields the peak output power of 2.1 kW with an efficiency of 2.1% at 190.55 GHz, a 3-dB frequency-tuning range of 1.25 GHz.