Preliminary Design of a Harmonic-doubling Gyrotron Traveling Wave Amplifier

This study proposes a Ka-band harmonic-doubling gyrotron traveling-wave amplifier (gyro- TWT), using distributed wall losses in the input stage and mode-selective interaction circuit in the output stage, to improve the stability of the amplification. Based on a large signal simulation code, a saturated peak power of 163 kW with an efficiency of 15.5%, a gain of 31.1 dB, and a 3 dB bandwidth of 0.9 GHz is predicted for the gyro-TWT driven by 70 kV, 15 A electron beam with a velocity ratio of 1.2 and velocity spread 5% at 33.2 GHz.     

回旋行波放大器输出端反射对注-波互作用的影响

基于回旋行波放大器的非线性自洽理论,研究渐变输出端反射对回旋行波放大器注-波互作用的影响.数值模拟结果表明,对于Ka波段TE₀₁模基波工作回旋行波放大器,渐变输出端渐变角的变化以及互作用长度的改变将导致不同的反射系数幅度和相位,从而影响注-波互作用过程,改变功率演化过程.在输出饱和功率不变的情况下,合理选择输出渐变角,可能可以减小注-波互作用长度,展宽互作用频带. 关键词： 回旋行波放大器 注-波互作用 反射系数     

Reflections Influence on the Gyrotron Oscillation Regimes

Influence of some types of reflections on oscillatory processes in gyrotrons has been studied. Estimations of the conditions for oscillation stability in the presence of a reflected signal are given. The processes in a gyrotron with a fixed structure of the RF field have been modeled numerically, and enhancement of the spectrum signal in the presence of reflections has been studied.     

回旋行波放大器输出端反射对其稳定性的影响

 基于回旋行波放大器的线性理论和反射边界条件,建立了渐变输出端存在反射时回旋行波放大器模型,分析了TE₀₁圆电模基波回旋行波放大器输出端反射对其增益、返波起振长度、返波起振电流和返波起振频率的影响。结果表明,随着反射增强,线性增益降低,返波起振长度和起振电流减小,返波起振频率的变化较小;反射增强将在一定程度内影响放大器的稳定性。     

Chaotic Behavior in the Raman Interaction of a Trapped Ultracold Ion with Two Traveling Wave Lasers

By means of the Bloch-Maxwell equation,the Raman interaction of a trapcd ultracold ion with two traveling wave lasers is treated semiclassically.As the model works without limitation of the Lamb-Dicke limit and the weak excitation regime,we study chaotic behavior of the system in the wide range of the parameters,It is shown that the chaotic behavior is more and more pronounced with the increase of the Lamb-Dicke Parameter and Rabi frequency,and can e exhitited experimentally by using quantum jump technique.     

Dependence of Output Power on Cavity Length in a Gyrotron Backward Wave Oscillator

A relativistic electron beam (500 keV, 200 A, 10 ns) generated magnetically tunable microwave radiation in a frequency range of 9-13 GHz when it is injected into an X-band rectangular waveguide immersed in a uniform axial magnetic field (4-10 kG). The mechanism of the microwave radiation was identified as the gyrotron backward wave interaction. The output power of the radiated microwave increased exponentially with the increase of the cavity length.     

Temporal Dynamics of Mode Interaction in Submillimeter-Wave Second-Harmonic Gyrotron

Competition of the operating modes at the second cyclotron harmonic with spurious modes at fundamental is studied numerically for the cases of gyrotron and traveling opposite spurious modes in the gyrotron FU II. This competition limits significantly the output power at the second harmonic. The results are in good agreement with experiments.     

CW Operation of a Submillimeter Wave Gyrotron (Gyrotron Fu IV) for High Stability of the Output Frequency

The first cw operation of our submillimeter wave gyrotron (Gyrotron FU IV) using a 12 T superconducting magnet has been successfully carried out. Output power is more than 20 W at a frequency of 301 GHz in the TE₀₃₁ resonant cavity mode. Time-resolved frequency measurement s shows that the frequency fluctuation of the gyrotron output is smaller than 2 MHz. This frequency fluctuation is mainly due to the fluctuation in the output voltage of the power supply.     

Development of Submillimeter Wave Catheter Transmitting a Gyrotron Output for Irradiation on Living Bodies

The development of a millimeter and submillimeter wave catheter for irradiation on living bodies using a gyrotron as the radiation power source is described. The GYROTRON FU-IV, optimized for such applications was used in the development. It was operated in both CW and pulsed regime at TE₀₃ and TE₃₂ modes with frequencies 302 GHz and 238 GHz respectively. Irradiation tests were made on thermal papers, beefs and liver of living rats.     

Analysis of a Disc-Loaded Circular Waveguide for Interaction Impedance of a Gyrotron Amplifier

A rigorous electromagnetic analysis of a circular waveguide loaded with axially periodic annular discs was developed in the fast-wave regime, considering finite axial disc thickness and taking into account the effect of higher order space harmonics in the disc-free region and higher order modal harmonics in the disc-occupied region of the structure. The quality of the disc-loaded circular waveguide was evaluated with respect to its azimuthal interaction impedance that has relevance to the gain of a gyrotron millimeter-wave amplifier (gyro-traveling-wave tube) in which such a loaded waveguide finds application as a wideband interaction structure. The results of electromagnetic analysis of the structure with respect to both the dispersion and azimuthal interaction impedance characteristics were validated against the commercially available code: high frequency structure simulator (HFSS). The analysis predicts that the value of the interaction impedance at a given frequency decreases with the increase of the disc hole radius and disc periodicity. The change of the axial disc thickness does not significantly change the value of the interaction impedance though it shifts the frequency range over which appreciable interaction impedance is obtained. Out of the three disc parameters, namely the disc hole radius, thickness and periodicity, the lattermost is most effective in controlling the value of the azimuthal interaction impedance. However, the passband of frequencies and the center frequency of the passband both decrease with the increase of the disc periodicity. Moreover, the disc periodicity that provides large azimuthal interaction impedance would in general be different from that giving the desired dispersion shape for wideband interaction in a gyro-TWT, suggesting a trade-off in the value of the disc periodicity to be chosen.     

Analysis and Numerical Calculations of the Beam-Wave Interaction for Gyroklystron Amplifiers

A four-cavity gyroklystron was designed and optimized after analysis and calculation of RF system and magnetron injection gun, numerical simulations showed that the TE₀₁₁ mode gyroklystron achieved 280kW peak output power, 38% efficiency, 35dB saturated gain with 250Mhz bandwidth centered at 34GHz for a 68 kV, 11A electron beam. The numerical simulation results were used to build a Ka band high power gyroklystron amplifier. In this paper, analysis and numerical calculation results of the beam-wave interaction are presented. The influences of electron beam, RF system parameters, magnetic field, and input RF signal on output power, efficiency, bandwidth and gain are discussed.     

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采用三支节液态调配器使离子回旋加热(ICRH)天线系统达到阻抗匹配,在阻抗匹配的条件下结合频率调制技术来减小由天线输入阻抗变化所引起的反射功率。数值模拟了频率调制前后天线负载与反射系数的变化关系,用来验证频率调制对ICRH天线中阻抗匹配装置的影响。模拟结果表明:三支节液态调配器结合频率调制方法,能更好地降低天线传输系统的反射系数,使得发射机的功率通过天线辐射更加有效地耦合到等离子体中去。     

频率调制对ICRH 天线阻抗匹配的影响研究

采用三支节液态调配器使离子回旋加热(ICRH)天线系统达到阻抗匹配,在阻抗匹配的条件下结合频率调制技术来减小由天线输入阻抗变化所引起的反射功率。数值模拟了频率调制前后天线负载与反射系数的变化关系,用来验证频率调制对ICRH 天线中阻抗匹配装置的影响。模拟结果表明：三支节液态调配器结合频率调制方法,能更好地降低天线传输系统的反射系数,使得发射机的功率通过天线辐射更加有效地耦合到等离子体中去。     

Nonstationary Behavior of a Gyrotron in the Presence of Reflections

Nonstationary behavior of a gyrotron in the presence of reflections is investigated by means of our time-dependent self-consistent code. It is shown that the traditionally accepted scenario of the transition from the single-frequency stationary operation regime to the chaotic nonstationary regime due to an increase in the magnitude of the reflection coefficient is not correct if a realistic non-fixed field profile is used in the simulations. In this case, the increase of the reflection coefficient above a certain threshold value (R 0.4) leads to an excitation of a number of modes of the mismatched gyrotron cavity. Then the gyrotron shows a very complicated periodic or quasiperiodic behavior. For higher reflection coefficients (R 0.85), the competition between the modes of the mismatched cavity leads to the suppression of the main mode by another one operating at higher frequency. The influence of the distance to the reflecting load on the gyrotron behavior is also demonstrated.     

表面波布拉格声光互作用耦合波方程的研究

定义了压电晶体的增劲声光系数,它反映压电晶体中声光、电光和压电效应共同作用的结果。从参量互作用基本理论出发,同时考虑声光效应、电光效应和压电效应三个因素,用一个压电增劲声光系数来表示三种因素的共同作用,导出表面波声光布拉格互作用的耦合波方程。并求解得出相应衍射效率的计算公式。该式说明在弱声光互作用条件下,衍射导光波强度与超声功率成正比。表面波声光器件具有体积小、工作稳定、能耗小、易于集成等优点。可以用作光偏转器、光调制器、滤光器。在光通信以及各类实时信号处理,如相关、卷积、频谱分析、矩阵光计算等领域具有广泛的应用前景。     

Quick Estimation of Mode Content in a Submillimeter-Wave Gyrotron Output

An inexpensive and quick method for the approximate estimation of the mode content of the output of a submillimeter-wave gyrotron requires a thermographic pattern measurement in one cross section only.     

Simulation of Mode Interaction in the Gyrotron FU CW I

A series of experiments carried out in order to study the operational performance and oscillation characteristics of a 300 GHz/3.5 kW gyrotron FU CW I have demonstrated a complicated behaviour which is attributed to multimoding phenomena. In this paper we present and discuss some initial results from computer simulation of mode interaction in this tube. They give a better insight in the underlying processes, possible excitation conditions of various competing modes and suggest some directions for continuation of this investigation.     

Observation of Frequency Down-Shift in a Submillimeter Wave Gyrotron

Frequency down-shift in the initial stage of CW or long pulse operation of a submillimeter wave gyrotron, Gyrotron FU IV, is observed. The shift occurs in a few minutes after turning on the operation and the amount of the shift attains even 0.1 GHz. The observation results are analyzed on the basis of a simple model for heat conduction in the region of a resonant cavity. The frequency shift is explained consistently by expansion of the cavity.     

Nonlinear Eulerian Analysis of Harmonic Generation in Traveling-Wave Tubes

A third-order nonlinear Eulerian hydrodynamic formulation was developed for the analysis of harmonic generation in helix traveling-wave tubes. The analysis was simple and computationally fast compared to Lagrangian analysis, and contrary to the existing belief, the theory could as well demonstrate the saturation behavior of the device. The performance of the theory was also found to be in close agreement with that of the Lagrangian analysis. The theory is expected to be useful as a first-hand design and simulation tool for microwave and millimetric wave traveling-wave tubes.     

Conversion of Gyrotron Output into a Gaussian Beam Using the Far-Field

A compact system to convert gyrotron output into an intense gaussian beam has been designed by introducing an intermediate focusing element into the quasi-optical system. The design is significantly simplified by applying gaussian optics and confirmed by application of the Huygens equation. The beam quality is improved by truncating the sidelobes of the far-field. In spite of the beam truncation, only a small fraction (11 %) of the beam power is sacrificed.