【作者】 白现臣；

【导师】 张建德； 杨建华；

【作者基本信息】 国防科学技术大学 ， 电子科学与技术， 2012， 博士

【摘要】 单个高功率微波源（HPM）输出功率的继续提高受到了腔内强场击穿等物理机制的限制。为进一步提高HPM系统的输出功率，研究人员提出了多个HPM源空间相干功率合成的方案，这要求多个HPM源必须是频率一致和相位锁定的。与高功率微波振荡器相比，高功率微波放大器如相对论速调管放大器具有频率、相位稳定的优点，因此成为了HPM空间相干功率合成的首选器件之一。但在向更高的频段发展时，大型的速调管放大器功率合成阵列的商用大功率种子源面临着输出功率不足的问题。鉴于此，本文提出了利用高功率微波源作为种子源，注入锁定多台速调管放大器进行功率合成的思路。作为该思路的初步验证工作，本文开展了利用一台S波段相对论返波振荡器（RBWO）作为种子源，驱动并锁定一台高注入功率、两腔、大间隙相对论速调管放大器（WKA）频率和相位的研究。论文的研究内容和主要结论如下：基于电路理论和粒子模拟程序，系统研究了金属膜片-回流杆结构对WKA谐振腔高频特性及WKA基本工作特性的影响。分析结果表明：WKA谐振腔的间隙宽度是相同工作频率常规RKA的2倍以上，能够承受更强的电场而不发生击穿，因而允许数十MW的高注入功率；在抑制WKA谐振腔空间电荷效应中起主导作用的是回流杆而非金属膜片，一旦加载了回流杆，只需要填充少量的金属膜片就能够把间隙附近的空间电势压力抑制到较低的水平；回流杆的尺寸对间隙电场分布特征和电子负载电导的影响较小，因此回流杆的加载并不会明显影响WKA的基本工作特性如束流调制和微波提取效果等。在物理分析方面，研究了高注入功率条件下大间隙速调管的微波注入和束流群聚特征。根据等效电路模型得到了谐振腔与电子束及外电路的阻抗匹配条件，为WKA输入腔的设计打下了理论基础；随着注入功率的增加，WKA的束流群聚过程由小信号线性区过渡到大信号非线性区，这分别和小信号的Webster去聚理论以及考虑到电子超越现象的Roe理论的预言结果基本一致；在高注入功率条件下出现的第二峰值电流与多重电子超越现象密切相关，利用电子多重超越效应可把WKA输入腔的群聚电流深度由第一峰值电流的饱和值80%继续提高到92%，从而获得更高的群聚束流功率。在粒子模拟方面，对RBWO种子源驱动的高注入功率、两腔WKA进行了优化设计和三维粒子模拟研究。采用优化结构模型，在二极管电压595kV、电流4.9kA、导引磁场约1.5T、净注入功率约36MW、工作频率3.6GHz时，束流群聚深度达92%，两腔WKA的输出功率约为1.05GW，功率效率超过36%。在此基础上，获得了两腔WKA输出功率对RBWO种子源的注入频率、净吸收功率以及二极管电压的依赖关系，研究了WKA对以上输入参数的容忍度。模拟结果指出：两腔WKA的输出频率被RBWO种子源的注入频率线性锁定；高注入功率条件下电子束调制的强烈非线性效应，显著提高了两腔WKA输出功率对高功率种子源RBWO注入功率变化的容忍度；由于省去了品质因数较高的中间腔，两腔WKA的3dB相对工作带宽达到了2.5%，在一定程度上提高了对RBWO种子源注入频率变化的容忍度。同时，分析了加速器二极管电压变化对RBWO-WKA系统锁相效果的影响。分析结果显示：在RBWO种子源初始相位、注入频率以及电子直流渡越效应等三种与二极管电压变化有关的因素中，RBWO种子源初始相位的变化对两腔WKA锁相效果的影响最为显著；然而无论如何，只要二极管电压的变化量足够小，就能利用RBWO种子源锁定两腔WKA的相位，这要求在实验中对加速器的主开关实施外部触发措施。在实验研究方面，详细阐述了RBWO-WKA实验系统的设计思想，以及关键设备的准备情况。利用电子束直流冲击法检验了两腔WKA的工作机制，结果说明在150ns的电脉宽下，所设计的两腔WKA工作在放大机制。研究了RBWO-WKA的基本工作特性：两腔WKA的输出频率被RBWO种子源的注入频率线性锁定；在注入功率约22.5MW，注入频率3.55GHz，二极管电压530kV，电流4.1kA，约束磁场1.6T时，两腔WKA的检波功率约229MW，半高宽70ns，功率效率10.9%，功率增益约10dB；结合粒子模拟结果，分析了两腔WKA实验功率和效率偏低的原因。同时，观察了加速器主开关的触发特性对RBWO-WKA系统锁相效果的影响。在主开关工作于电触发模式时，二极管电压稳定在530kV，工作频率稳定在3.55GHz左右，单炮次时RBWO注入信号和WKA输出信号的实时相位差稳定在±16°之内，多炮次时的相对相位差则锁定在±11°之内，保持锁相的时间超过40ns。理论计算结果表明，两个采用类似锁相技术的两腔WKA具有实现高效率相干功率合成的潜力。更多还原

【Abstract】 Due to the characteristics of high power, high efficiency, stable frequency andphase, the relativistic klystron amplifier has been proved to be one of the promisingcandidates for the high-power microwave coherent power combining. However, therelativistic amplifier devices always require the external injection source to supply tensof or hundreds of kilo-watts power. It means that RF power up to10MW is needed forlocking dozens of amplifiers. This is beyond the output capacity of the external sourcewhich is, commonly, a commercial magnetron of MW levels, particularly as attemptingto scale the system to the higher operation frequency. One potential solution for thisissue is employing a high power external source of GW-class to replace the commercialmagnetron. Because of the plenteous output power of the external source, there is nolimitation on increasing the number of the amplifiers.In this dissertation, the mentioned idea is preliminarily validated at a relativelylower frequency by using an S-band relativistic backward wave oscillator (RBWO) asan external source to drive a high power injection two-cavity wide-gap klystronamplifier (WKA) for frequency and phase locking. The related theoretical analyses, PICsimulations and initial experiments are carried out on such a RBWO-WKA system. Thedetailed contents and main conclusions are presented as following.In part one, influences of the washers/rods structure of the WKA on the highfrequency characteristics and the basic operation of the amplifier are investigated. Theanalyses show that the return current rods play the more important role in depressing thespace-charge potential of the wide-gap cavity than the metallic washers. Once the rodsare employed, the potential effect can be greatly suppressed even a fewer of washers areused. Moreover, only if the wide-gap cavities are properly tuned, influences of the rodsize on the basic operation of the WKA, such as the beam current modulation and theRF power extraction, are believed to be very weak.In part two, to further understand the essential operation process of the WKA underthe high power inspiring case, the external RF signal injection and beam currentbunching are inspected. The impedance matching condition between the electron beamand the external load is obtained according to the circuit model. Considering theelectron bunching theory and the PIC simulation results together, the formationmechanism of the second peak current in the case of high voltage modulationcoefficient is discussed. The results indicate that the second peak current has a closerelation with the electron multiple-overtaking phenomenon.In part three, the two-cavity WKA with high power injection is researched in detailthrough the three dimensions electromagnetic particle-in-cell (PIC) code. Basing on theoptimized configuration, the WKA output power of about1.5GW with the conversion efficiency of36%and power gain of14.6dB is achieved under diode voltage of595kV,beam current of4.9kA, input power of36MW and working frequency of3.6GHz.Furthermore, dependences and sensitivities of the output power on the diode voltage,the injection power and frequency of the RBWO source are attained. Benefited from thehigh power injection condition and the two-cavity structure, affects of the injectionpower and frequency on the WKA output power are alleviated. The phase locking effectof the WKA with regard to the diode voltage is also discussed. It demonstrates thatoutput frequency of the WKA is linearly locked by the input frequency of the RBWO.However, for practical application in a power combining system, frequency and phaselocking are supposed to be satisfied simultaneously. In order to restrict the phasedifference of the two-cavity WKA within a narrow enough range, the external RBWOsource should have good frequency reproducibility and stability from pulse to pulse. Itrequires excellent voltage stability in the experiment.In part four, the initial experimental studies on the two-cavity WKA driven by theRBWO are accomplished. Preparations of the dual-beam accelerator, the dual-cathodediode, the RBWO external source, the solenoid of the WKA and the time-delay triggersystem are introduced. Under the injection power of~22.5MW, injection frequency of3.55GHz, diode voltage of530kV, beam current of4.1kA and confinementmagnetic-field of1.6T, the WKA output power is about229MW with RF pulse widthof70ns, conversion efficiency of10.9%and power gain of about10dB. Theseexperimental results are compared with that of the PIC simulation cases. Moreover, theperformance of the triggered gas-gap switch of the accelerator is examined and theinfluence of the diode voltage on the phase-locking effect of the RBWO-WKA systemis observed. While the gas-gap switch is externally triggered, the diode voltage and theinjection frequency from the RBWO are maintained around530kV and3.55GHzrespectively within a series of shots. Phase difference between the external source andthe two-cavity amplifier is less than±16°in a single shot, and phase jitter within±11°isgained from shot to shot, with locking duration of about40ns.更多还原