C波段小型化高功率微波输出窗的设计

为了满足高功率微波系统对微波输出窗高功率容量和紧凑化的应用需求,以传统盒型窗的设计理论为基础,通过优化窗体结构和添加过渡段等手段,设计了一种C波段小型化高功率微波输出窗。通过增大窗体表面积、改变矩形波导-圆波导过渡段的连接方式可提高功率容量并缩小微波输出窗的纵向尺寸;采用“I”型的窗体结构可有效抑制三相点（真空-介质-金属）附近的次级电子倍增效应对输出窗性能的影响。在电磁仿真的基础上采用粒子模拟（Particle-in-Cell）的方法研究了微波输出窗三相点附近的次级电子倍增效应,从微观角度进一步证实了“I”型窗体结构可使三相点位置发生移动,减小三相点发射的电子在窗片表面产生次级电子倍增效应的概率,降低微波输出窗的击穿风险。设计结果表明,微波输出窗在中心频点处的主模反射系数低于0.01,传输效率高于99.9%,功率容量可达47.9 MW。     

高功率盒形窗内次级电子倍增效应

以S波段高功率盒型窗为对象,采用Monte Carlo模拟方法对盒型窗内的次级电子倍增效应进行研究,探索次级电子的倍增规律。模拟得到了盒型窗内TE11模和TM11模共同作用下,两种陶瓷窗片表面次级电子倍增活跃的区域随传输功率的变化特点。在低传输功率下,次级电子仅在未镀膜窗片表面被激励,并以双面倍增的方式在金属法兰与镀膜窗片相对应的区域增长;在较高的传输功率下,窗片表面的次级电子将以单面倍增的方式活跃在窗片表面与波导口相对的区域。传输功率的升高使得镀膜窗片表面的次级电子倍增活跃区域转移到矩形波导窄边对应的区域,并加剧了未镀膜窗片表面的局部倍增效应。     

金属壁与介质窗之间次级电子倍增效应的研究

高功率盒形窗内的TM11模法向电场对次级电子倍增现象具有较大的影响,特别是在介质窗片与金属波导壁相对的区域,易发生双面次级电子倍增.采用蒙特卡罗粒子模拟方法,研究了法向电场作用下氧化铝陶瓷窗片与铜波导壁之间的双面倍增敏感曲线、倍增阈值电压、粒子数量的演变过程以及粒子运动轨迹.通过对相关参数的分析,获得了金属壁与陶瓷窗片之间双面谐振倍增和非谐振倍增的规律以及双面倍增向单面倍增转变的特点.此研究可为分析窗片失效机理提供理论依据.     

圆柱盒型窗的连续波功率容限问题的研究

 运用精确的解析推导方法对圆TE₁₁模微波窗的额定平均功率公式做了修正，给出了圆柱盒型窗中介质窗片温升的具体计算方法，并结合实际问题对圆柱盒型窗用于传输高功率连续波时的功率容限和鬼模振荡的特殊危害性以及排除方法进行了详细的讨论。研究结果表明：在L波段，只要排除工作频带内的鬼模，普通圆柱盒型窗用于传输120~150kW的连续波不成问题，并且可以得到14%左右的相对带宽。     

S波段高功率径向线输出窗的设计

为进一步改进和优化高功率径向线阵列天线的拓扑结构,提高功率容量水平,并满足馈源的真空密封需求,提出并设计了一种适用于高功率径向线阵列天线的微波输出窗。该高功率径向线输出窗采用圆环形陶瓷,材料介电常数为9.4,窗片厚度为3 mm,内径为36 mm,可实现径向线阵列天线馈电系统的输入同轴波导与输出同轴波导间的真空密封。设计结果表明:在中心频率为2.856 GHz下,该径向线输出窗驻波比为1.03,插入损耗为0.17 dB,设计功率容量约150 MW。     

高功率微波高斯馈源口面场分析

 用波导本征模展开方法对用于高功率微波发射系统的方角锥高斯馈源口面场进行分析，提出结合馈源远场辐射特性和避免高功率击穿折衷选定相应的高斯模注腰半径，进而确定多个波导模幅值，从而为运用模匹配或耦合波理论设计高斯馈源提供依据。     

速调管矩形波导窗的研究

 运用微波等效电路（微波网络）的方法，研究了大功率速调管矩形波导输出窗的转移矩阵，根据微波无反射条件求解窗的最佳尺寸。利用3维电磁场计算软件ISFEL3D进行精确模拟。将微波等效电路方法的计算结果与ISFEL3D的模拟结果和实验结果相比较，得出结论：运用微波等效电路方法对矩形波导输出窗进行设计，理论较为简单，编程容易实现，计算速度很快，便于参数调整，且计算结果与实际测量误差较小，适合应用于速调管矩形波导输出窗设计的初步阶段。     

真空高功率微波介质窗表面击穿破坏现象的研究进展

综述了国内外真空中高功率微波(HPM)下介质窗表面击穿问题的研究现状和进展。在介质窗表面击穿实验研究方面,介绍了国外最具代表性的研究成果,给出了介质窗材料表面及内部的破坏发展规律,并提出相应的理论模型。在理论仿真方面,重点介绍了国外在运用蒙特卡罗(Monte Carlo)程序和PIC模型对认识HPM下介质窗表面倍增放电机理上做出的突出贡献,给出了HPM下介质窗表面电子在不同影响因素下的运行状态,并提出了一个理论模型,从本质上解释了倍增电子数目和表面静电场以微波频率的2倍振荡的原因。介绍了目前几种可有效抑制介质窗表面微波击穿的技术手段。     

脊波导在速调管输出组件中的应用

在新型L波段多注速调管的研制中,为了降低电磁聚焦系统的设计难度,需要减小输出波导的截面尺寸。为此,提出了在速调管输出组件中应用脊波导的方案。针对该型速调管的要求,设计了完整的脊波导输出组件并进行验证。计算结果表明,这种采用了脊波导的速调管输出组件,能够在10%的带宽内达到1.2以下的驻波比,理论功率容量达到490 MW。采用了该方案的组件尺寸紧凑,加工方便,调试容易。     

刻周期半圆弧槽窗片对次级电子倍增效应的抑制

为了抑制高功率盒形窗内的次级电子倍增效应,研究了一种刻周期半圆弧槽窗片结构. 通过对槽内电场进行分析,证明了半圆弧状槽可以有效避免尖锐边界的局部场增强效应. 利用蒙特卡罗随机算法对槽内的次级电子倍增效应进行数值模拟,跟踪次级电子的轨迹及发展趋势,获得了不同槽宽所对应的抑制次级电子倍增最低电场强度. 讨论了法向电场对半圆弧槽抑制次级电子倍增的影响. 该结构有望在高功率速调管中获得应用. 关键词： 盒形窗 半圆弧槽 次级电子倍增 蒙特卡罗模拟     

Design and high-power test of 800-kW UHF klystron for CEPC

To reduce the energy demand and operation cost for circular electron positron collider (CEPC), the high efficiency klystrons are being developed at Institute of High Energy Physics, Chinese Academy of Sciences. A 800-kW continuous wave (CW) klystron operating at frequency of 650-MHz has been designed. The results of beam-wave interaction simulation with several different codes are presented. The efficiency is optimized to be 65% with a second harmonic cavity in three-dimensional (3D) particle-in-cell code CST. The effect of cavity frequency error and mismatch load on efficiency of klystron have been investigated. The design and cold test of reentrant cavities are described, which meet the requirements of RF section design. So far, the manufacturing and high-power test of the first klystron prototype have been completed. When the gun operated at DC voltage of 80 kV and current of 15.4 A, the klystron peak power reached 804 kW with output efficiency of about 65.3% at 40% duty cycle. The 1-dB bandwidth is ±0.8 MHZ. Due to the crack of ceramic window, the CW power achieved about 700 kW. The high-power test results are in good agreement with 3D simulation.     

低能二次电子对微波输能窗击穿现象的影响

在微波输能窗次级电子倍增效应的模拟研究中，往往忽视低能电子的作用。基于Monte Carlo算法，模拟输能窗次级电子倍增规律，研究了经典的Vaughan模型、Vincent模型和Rice模型三种二次电子发射模型下次级电子倍增效应的差异，通过拟合倍增敏感曲线，获得了低能电子对切向和法向电场作用下输能窗次级电子倍增效应的影响。模拟结果表明，当切向电场作用时，三个发射模型得到的敏感曲线几乎重合，低能电子对敏感曲线的影响甚微，其中Rice模型的敏感区域最大。当法向电场作用时，由Vincent模型拟合得到的敏感区域远大于其他两个模型。     

RF system for VEPP-5 damping ring

This paper presents the RF system of VEPP-5 damping ring created at BINP Novosibirsk. The RF system operates at 700 MHz and consists of a generator based on KU-393 klystron, a transmitting waveguide with wave-to-coax adapters, an accelerating cavity, and a control system. Cavity HOMs are damped with resistive loads to eliminate the beam instability. Parameter results of cold measurement tests and high-power level tests are presented.     

Window breakdown caused by high-power microwaves

Physical mechanisms leading to microwave breakdown on windows are investigated for power levels on the order of 100 MW at 2.85 GHz. The test stand uses a 3-MW magnetron coupled to an S-band traveling wave resonator. Various configurations of dielectric windows are investigated. In a standard pillbox geometry with a pressure of less than 10^-6 Pa, surface discharges on an alumina window and multipactor-like discharges starting at the waveguide edges occur simultaneously. To clarify physical mechanisms, window breakdown with purely tangential electrical microwave fields is investigated for special geometries. Diagnostics include the measurement of incident/reflected power, measurement of local microwave fields, discharge luminosity, and X-ray emission. All quantities are recorded with 0.21-ns resolution. In addition, a framing camera with gating times of 5 ns is used. The breakdown processes for the case with a purely tangential electric field is similar to DC flashover across insulators, and similar methods to increase the flashover field are expected to be applicable     

X波段高功率高增益多注相对论速调管放大器设计

针对器件工程应用中的高功率高增益需求，设计了工作在X波段的高功率高增益多注相对论速调管放大器，建立了带输入、输出波导结构的三维整管模型。设计双边对称耦合孔输入腔结构，降低了输入波导对输入腔间隙电场均匀性的影响以抑制非均匀干扰模式；设计采用多腔多间隙群聚结构，降低了输入微波功率的需求，提高了器件放大增益；并且分析设计了多间隙扩展互作用微波提取结构，提高了器件的功率转换效率以及降低输出结构表面电场强度。通过优化设计，粒子模拟仿真实现X波段多注相对论速调管放大器输出微波功率达到3.2 GW，器件放大增益约为60 dB，功率转换效率约为40%。器件验证实验在电子束电压550 kV，电流5.1 kA的情况下，输出功率为0.99 GW，放大增益约为53 dB，转换效率约为35%。     

环形电子束X-波段相对论速调管实验研究

 相对论速调管放大器试验中，采用强流环形电子束，可提供器件更大的脉冲功率，虽然电子束—微波转换效率有所降低，但可望获得更大的辐射功率。另外，研究表明由于采用环形电子束，相互作用间隙中出现静电绝缘现象，有助于提高腔的功率容量而避免打火现象。我们利用为实心束而设计的相对论速调管放大器，适当改变有关参数，获得大于5MW的微波输出，电子束参数为550keV,500A。     

BEPCⅡ直线加速器速调管的反射保护

为了使速调管陶瓷窗免受大功率微波反射信号的损伤,延长速调管使用寿命,要求当前反射信号功率超过阈值后,系统能够在下一个脉冲到达之前发出报警信号,进而切断触发信号,实现对速调管的保护。提出了3种较高性价比、易实施的方案,即PicoScope虚拟示波器的遮罩报警方案、基于自带检波和报警输出功能的芯片制作反射保护插件以及原功率计的升级改进。创新性地提出“3+1”反射保护响应时间测试法,并对上述3种方案进行详细测试。最终后两种方案取得较好的结果,综合考虑后,将改进型功率计作为最终实施方案。目前该改进型功率计已稳定可靠地上线运行超过1年。     

Super-reltron theory and experiments

A highly efficient, high-power microwave tube called super-reltron is reported. The authors have achieved operation at >400 MW with ~50% efficiency at 1 GHz, and 250 MW with 40% efficiency at 3 GHz. The RF pulse durations are typically a few hundred nanoseconds. These compact lightweight tubes do not require an external magnetic field. The RF output coupling is straightforward and delivers the power directly via the fundamental TE₁₀ wave in a rectangular waveguide without a mode converter. The key features of the tube include (i) generation of a well-modulated electron beam by periodic virtual cathode formation, (ii) postacceleration of the modulated beam to reduce the relative electron energy spread, and (iii) a multicavity output section that efficiently extracts power without RF breakdown. Various theoretical aspects of the device are discussed and the experimental results are summarized     

Microwave magnetic field effects on high-power microwave windowbreakdown

Microwave window breakdown in vacuum is investigated for an idealized geometry, where a dielectric slab is located in the center of a rectangular waveguide with its normal parallel to the microwave direction of propagation. An S-band resonant ring with a frequency of 2.85 GHz and a power of 60 MW is used. With field enhancement tips at the edges of the dielectric slab, the threshold power for breakdown is observed to be dependent on the direction of the microwaves; i.e., it is approximately 20% higher for the downstream side of the slab than it is for the upstream side. Simple trajectory calculations of secondary electrons in an RF field show a significant forward motion of electrons parallel to the direction of microwave propagation. Electrons participating in a saturated secondary avalanche on the upstream side are driven into the surface, and electrons on the downstream side are driven off the surface, because of the influence of the microwave magnetic field. In agreement with the standard model of dielectric surface flashover for dc conditions (saturated avalanche and electron-induced outgassing), the corresponding change in the surface charge density is expected to be proportional to the applied breakdown threshold electric field parallel to the surface