双间隙输出腔开放腔的高频特性分析

 建立了S波段相对论速调管放大器双间隙输出腔开放腔的3维模型。采用时域有限差分法，通过监测激励电流源的响应计算了该双间隙输出腔的谐振频率、有载Q值、场分布以及特性阻抗，并分析了腔体结构尺寸对谐振频率、有载Q值和特性阻抗的影响。研究表明：腔体半径对开放腔的谐振频率影响很大，耦合孔尺寸对腔体谐振频率的影响较小；随着耦合孔张角增加，有载Q值逐渐减小；随着腔体半径增大、间隙的减小，腔体特性阻抗降低。研究结果可为S波段强流相对论速调管放大器双间隙输出腔的设计提供理论依据。     

微波脉冲与不同形状带矩形孔缝腔体耦合的数值模拟

 利用时域有限差分法对微波脉冲与带矩形孔缝的矩形和圆柱形腔体两种系统的线性耦合过程进行了研究。首先用数值方法分析了耦合过程中的场增强现象、脉宽展开现象和腔体调制现象,并发现了耦合过程中微波脉冲存在频谱分离现象。当微波脉冲的电场与孔缝窄边平行时,借助耦合函数对两个系统内部耦合场的分布特性进行了研究,结果表明在与孔缝窄边垂直的平面内,越靠近腔体壁,耦合场越弱。此外,两种腔体内部的耦合场在腔体截面内均呈现准周期振荡分布,矩形腔体内部耦合场振荡的幅值较均匀,而圆柱形腔体内部耦合场幅值在其截面中心附近区域最大;除了孔缝附近区域外,圆柱腔体轴线两端的耦合场远大于矩形腔体相应的耦合场。最后,研究了孔缝耦合共振频率与孔缝尺寸的关系,结果表明系统耦合共振频率不只与孔缝尺寸有关,而是由孔缝尺寸和腔体形状及其对微波脉冲的反射特性共同决定。     

渐变段倾角对渐变复合腔特性影响的分析

 利用模式耦合理论，在考虑多模耦合的情况下，对渐变结构复合腔进行了冷腔分析，计算了H₅₁-H₅₂模式对下，各个模式的耦合及场幅值分布情况，分析了渐变段的倾角对渐变复合腔的Q值及场幅值分布的影响。研究表明：渐变段的倾角对渐变结构复合腔的高频特性有很大的影响，特别是各模式的场分布及Q值，合适地选择渐变角度，能使场幅值放大率比较大，这将有利于提高注-波互作用效率。     

含有吸收介质的突变结构腔体场匹配分析

采用分区求解场及边界场匹配方法推导出含有吸收介质波导的色散方程及突变结构高频腔体混合模式的场匹配方程。将解析分析与数值计算结合，对回旋速调管放大器高频腔体进行了数值计算，研究了吸收层对波导传播、衰减特性及谐振腔的谐振特性、损耗特性、Q值、场分布的影响。给出了数值模拟主要结果。 关键词： 吸收介质 场匹配 混合模 谐振腔 高功率微波     

大耦合孔同轴输出腔的3维解析分析

 在高功率微波器件中，通常采用大耦合孔的同轴微波输出腔，该腔为3维结构。采用场等效原理将腔体、耦合孔及其输出负载(行波边界)进行分区,每个区域中的场由界面上的磁流密度决定。采用格林函数积分法可得每个区域中的3维场,再由各个区域的场匹配方程求得腔体的谐振频率、特性阻抗、有载品质因数、模式分布等参数。为腔体的计算和设计提供一种计算模型。     

SSC新高频腔设计与分析

简要分析了HIRFL SFC与SSC之间的束流匹配关系, 给出了新高频腔的频率范围。 利用经典三维电磁场数值模拟软件MAFIA对SSC新高频腔体进行了模拟计算, 得出了SSC新高频腔体的相关物理参数, 并对频率范围、Q值、 并联阻抗和电压分布等参数进行了分析。 高频腔体的模拟计算结果完全符合SSC回旋加速器改造的物理设计及空间结构要求。     

二维等离子体填充金属光子晶体腔体特性

设计了等离子体填充的二维金属光子晶体特殊开放腔体结构,并采用粒子模拟技术(PIC)建立了基于等离子体填充腔体结构物理模型,分析了等离子体填充下二维腔体的各模式场分布特性,以及等离子体的引入对腔体内各模式工作频率、电场幅值的影响。结果表明:腔体内各模式的电场强度随等离子体密度的增加而减弱,模式频率随背景等离子体归一化频率的提高而增加,工作模式的产生与激励方式密切相关。     

同步辐射用高频腔的性能研究实验

基于合肥光源提供的铜制有源高频腔和上海光源提供的铌制超导无源高频腔,设计了可以测量高频腔性能参量的实验装置.以探针将微波信号馈入高频腔体中,通过网络分析仪接收到的信号分析微波在腔体中的谐振情况,从而测量腔体的特性.利用该实验装置测量了2个高频腔的谐振频率、品质因数和腔体中心轴线上的电场分布.     

估算双层屏蔽腔体窄缝耦合的混合方法

 用混合方法计算双层屏蔽腔体窄缝耦合时,外腔体的窄缝耦合用传输线模型计算,内腔体的用磁偶极子模型计算。混合法可以求出双层屏蔽腔体内的场分布和屏蔽系数的分布规律,避免了传输线模型只能计算腔体中心线上的屏蔽系数而不能分析腔内横截面上耦合场分布规律的缺点。将得到的窄缝耦合的传输线模型和磁偶极子模型的计算结果与实测值和Micro-Stripes软件仿真值进行对比,验证了传输线和磁偶极子模型的有效性。混合方法给出了窄缝数量及腔体内不同观测点对屏蔽系数的影响,结果表明：双层屏蔽腔体的屏蔽效能明显优于单层屏蔽腔体;随着相同尺寸的窄缝数量的递增,腔体内的屏蔽系数递减;在与双层屏蔽腔体中心线垂直的横截面上,观测点屏蔽系数以中心线上点为中心,沿窄缝方向向两边递增,也就是离中心线越远,腔体内的耦合电场越弱,且混合法的速度明显快于软件计算速度,适合于高频范围的分析。     

二次电子倍增对射频平板腔建场过程的影响

建立了射频平板腔动态建场等效电路以及腔体双边二次电子倍增的混合物理模型,利用自主编制的1D3V-PIC二次电子倍增程序和射频平板腔动态建场全电路程序,研究分析了不同腔体Q值情况下二次电子倍增对射频平板腔动态建场过程的影响.数值模拟表明：射频平板腔建场过程中不存在二次电子倍增的情况下,腔体Q值越高,建场时间越长,注入能量等于腔体储能和腔体耗能,建场前期腔体储能速度快于耗能速度,建场后期腔体耗能速度快于储能速度,建场成功后平均腔体消耗功率与平均注入功率相等.射频平板腔建场过程中存在二次电子倍增情况下,腔体Q值越高,进入二次电子倍增的时刻越晚,二次电子倍增作用时间越长;二次电子发射面积越大,二次电子电流峰值越高.二次电子倍增的持续加载,最终会导致射频平板腔建场过程的失败;腔体Q值越高或二次电子发射面积越大,射频平板腔建场成功的概率越低.相关模拟结果可为工程设计提供一定的参考.     

高功率毫米波圆波导半径微扰模式变换器的优化设计

从半径渐变波导的耦合波方程出发,利用龙格-库塔法进行优化数值迭代,得到在3 mm波段,TE03-TE02, TE02-TE01高效率模式变换器的设计参数。通过优化程序,设计出了6周期TE03-TE02和3周期TE02-TE01模式变换器优化尺寸。利用CST微波工作室电磁仿真软件对结构尺寸进行优化仿真,仿真结果与优化程序计算结果基本一致。以此数据设计中心频率94 GHz的TE03-TE02,TE02-TE01模式变换器功率转换效率可以达到98.5%以上,90%功率转换的绝对带宽分别达到3.5和7.0 GHz以上,优于设计要求。     

Experimental study of efficiency optimization in a three-cavitygyroklystron amplifier

An experimental study quantifying the effects of both penultimate cavity tuning and magnetic field profiling on the saturated efficiency of a three-cavity gyroklystron amplifier has been performed at a frequency of 4.5 GHz. As predicted by theory, it is observed that the penultimate cavity detuning in the gyroklystron is in the opposite direction from a conventional klystron for enhanced efficiency operation. This is a result of the opposite energy dependence of the bunching mechanism for the two interactions. Magnetic field profiling has also been shown to have a very strong effect on the amplifier efficiency, both through beam loading effects in detuning the penultimate cavity and through enhanced energy extraction in the output cavity. The measured efficiency of the gyroklystron is observed to improve from 5% to 21% by profiling the magnetic field along the device, and then from 21% to 29% by penultimate cavity detuning with an optimized magnetic field profile     

The study of wavelength modulation off-axis integrated cavity output spectroscopy in the case of Lorentzian absorption profile

According to the property of optical cavity and the principle of signals and systems, the mathematical derivations for wavelength modulation off-axis integrated cavity output spectroscopy (WM-OA-ICOS) are presented. And based on the analytical method, the function expression of WM-OA-ICOS signal from Lorentzian absorption profile is obtained. To validate the analyses and deductions, some special cases in 2f-harmonic detection of WM-OA-ICOS are studied and experimented with a built compact WM-OA-ICOS apparatus. It is found that the measured results can coincide with the deduced conclusions. The works can provide some references for the application of WM-OA-ICOS in the case of Lorentzian absorption profile.     

S波段大间隙速调管放大器输出腔的3维模拟

 利用3维高频软件设计了一种用于S波段大间隙速调管的膜片加载大间隙单重入输出腔,建立了带大耦合孔的输出腔3维全结构模型,采用3维PIC程序对输出腔的提取效果进行了粒子模拟。研究结果表明：膜片加载的大间隙单重入输出腔开大耦合孔后,其所有谐振频点的场分布都不再是TM ₀₁₁模式,因此,在设计此类输出腔时不能以工作频点是否谐振为优化目标。提出了大间隙输出腔设计原则,根据设计原则优化后的输出腔可稳定提取1.07 GW的平均功率,提取效率约35.7%。     

Self-consistent field theory and calculation for gyromonotron

A self consistent field large signal theory of gyromonotron is studied in this paper. The RF field profile function satisfies a wave equation. The field is determined by cavity geometry and AC electron beam current. The RF field not only satisfies the boundary conditions at the ends of the cavity but also obeys conservation of energy for steady state interaction between electron beam and field. The parameters of a particular gyrotron are calculated numerically using present theory. Effect of some factors on gyrotron characteristic is discussed. Comparison is made between the results of the self consistent field calculations with and without conservation of energy.     

Particle Simulation of a 35-GHz Third-Harmonic Low-Voltage Complex Cavity Gyrotron

A self-consistent particle simulation code has been developed for the research of a 35-GHz third-harmonic Low-voltage complex cavity gyrotron. Aided with microcomputer we use FORTRAN to simulate the process of interaction between electron beam and electromagnetic field. About 7000 macro particles are included at the same time. In the program many useful physical graphs are accessible for the further research of this kind of gyrotron such as the field profile, electrons distribution in various spaces, output power, efficiency and et al. Such simulation results may be helpful to the optimization of devices operation parameters     

The study of diffraction radiation oscillation

Theoretical and experimental study of Diffraction Radiation Oscillator (DRO) is reported in this paper, it is the first work done in P. R. China. The sphere-cylindrical open cavity used in the DRO has been analysed, the method for testing the field profile and the cold measurement of the open cavity have been worked out. The experimental device was manufactured in our lab. and the theoretical analysis and experimental study of the device have been carried out. The main experimental results are: from 2000 V to 4000 V, the tube operates in the 60–87 GHz band, and the maximum output power is about 800 mW.     

Multistability,intermittency and remerging Feigenbaum trees in an externally pumped ring cavity laser system

We study a Fabry-Pérot cavity containing a saturable absorber and driven by an external laser. It is shown that the output field as a function of the input field and bistability parameter exhibits multistability, intermittency and remerging Feigenbaum trees.     

Coherence phenomena in the phase-sensitive optical parametric amplification inside a cavity

We theoretically and experimentally demonstrate coherence phenomena in optical parametric amplification inside a cavity. The mode splitting in the transmission spectra of a phase-sensitive optical parametric amplifier is observed. Especially, we show that a very narrow dip and peak, which are the shape of a delta function, appear in the transmission profile. The origin of the coherence phenomenon in this system is the interference between the harmonic pump field and the subharmonic seed field in cooperation with dissipation of the cavity.     

Numerical simulation of dynamic processes in gyrotrons with low-Q cavities

We study theoretically models of gyrotrons having fixed and self-consistent axial structures of the high-frequency field in the cavity with an actual profile. The limits of applicability of the model with a given field structure are determined during the study of competition of the operating and parasitic modes. It is shown that for the regimes which are optimal in terms of efficiency, the influence of the nonfixed nature of the high-frequency field structure on the starting current, the stability of stationary generation of the operating mode, the efficiency, the output power, and the thermal ohmic load of the cavity is insignificant. As the beam current and the mismatch between the cutoff frequencies of the operating and parasitic modes increase, significant qualitative differences between the models with given and self-consistent axial structures of the high-frequency field are observed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 4, pp. 307–320, April 2006.