C波段能量倍增器的研制

C波段(5712 MHz)能量倍增器——SLED是我国研制的首台C波段能量倍增器。简述了利用三维电磁场仿真软件HFSS和CST对C波段能量倍增器的高品质因数储能腔、耦合孔、3 dB桥等进行优化设计的情况,对加工的能量倍增器做了射频低功率测试,实验测试和理论计算的一致性很好,测试结果表明所有技术参数指标均达到了设计要求。     

基于同轴波导的1分16功分器的设计与实验

针对高功率固态源多路功率分配技术的需要,设计并研究了一种基于同轴波导的多路功率分配器件。通过分析同轴波导传输特性与阻抗匹配理论,利用电磁仿真软件设计了一种S波段1分16功分器模型,并加工出实物进行实验测试。实验结果表明：该功分器在2.28～2.86 GHz,相对带宽约23%频率范围内,输入端反射系数S11≤-15 dB;在2.37～2.57 GHz,相对带宽约8.1%频率范围内,输入端反射系数S11≤-20 dB;输出幅度不平衡度±0.1 dB,相位不平衡度±5°。该功分器满足输出幅度与相位一致性要求,可应用于S波段百瓦级连续波功率分配。     

S波段多路径向线功率分配器的设计与实验

为了实现高功率微波的多路等幅同相功率分配,提出了一种新型的使用单圈探针耦合的多路径向线功率分配器。通过对新型探针耦合特性的分析,设计了一个S波段的16路功率分配器模型,并对该模型进行了数值模拟和实验测量。实验结果表明:该功率分配器在2.55~3.15 GHz的频带范围内,驻波比小于1.4,插入损耗小于0.3 dB,输出幅度不平衡度小于±0.5 dB,输出相位不平衡度小于±5°,可以在较宽的频带内实现微波的等幅同相功率分配。     

一种新型的能量倍增器解调谐系统

在北京正负电子对撞机(BEPC)直线加速器工程中,参考美国SLAC微波脉冲压缩技术,成功地研制了能量倍增器(SLED).该装置自1988年运行以来,一直存在一个隐患,解调谐系统设计有问题,不能随便解谐.BEPCⅡ经常需要长脉冲束流,这就要求能量倍增器能够方便地进行解调谐.为此,参考日本KEK的资料,对目前能量倍增器解调谐系统进行了彻底的改进,完成了新的SLED解调谐系统的研制任务,并在加速器上成功地进行了高功率试运行.     

BEPCⅡ直线加速器的误差和抖动效应

为达到BEPCⅡ 直线加速器的设计指标,系统地研究了误差和抖动(Jitter)效应对束流性能的影响。误差效应包括束流的初始偏轴和聚焦透镜偏轴导致的色差效应;束流的初始偏轴和加速结构偏轴导致的尾场效应等。主要的抖动效应包括相位漂移抖动和高频功率源中调制器电压的抖动影响等。确定了在BEPCⅡ直线加速器上对误差和抖动的限制,如来自电子枪的束流的初始偏轴应小于等于0.3 mm,加速结构和聚焦磁铁的安装误差应小于等于0.2 mm,相位漂移抖动误差应小于等于2°,调制器的电压抖动误差应小于等于0.1%。并进一步确认了必须采用相位控制系统和束流轨道校正系统,以抑制这些误差效应的影响,达到正、负电子束流能散度小于等于0.5% 和电子束束流发射度小于等于0.25 mm·mrad,正电子束束流发射度小于等于1.60 mm·mrad 的设计目标。     

能量倍增器法微波脉冲压缩

为了开展S波段能量倍增器脉冲压缩实验,对能量倍增器进行了冷测和热测工作,主要包括对能量倍增器的指标、参数的测量以及在高功率下对能量倍增器的输出功率、功率增益等参数的测量。实验中,完成了微波固态源系统的改造,研制了同步信号控制器,研究了输入输出脉冲宽度对输出峰值功率的影响,并对实验中可能的射频击穿问题进行了研究。在输入功率5 MW时,得到了功率增益7.122,输出脉宽260 ns,输出峰值功率35.35 MW。     

基于FPGA的能量倍增器相位翻转系统的研制

介绍了基于可编程逻辑门阵列(FPGA)的能量倍增器(SLED)相位翻转系统。该系统主要由微波IQ调制器、FPGA和高速DAC组成。在FPGA的控制下,DAC输出两路双极性脉冲电平信号,加载于调制器的IQ端,将微波连续波输入信号转变为4μs脉冲输出信号,并且在3μs时刻微波相位发生180°跳变。经测试,相位翻转精度为180°±2°,翻转相位的长期稳定度优于±0.5°;相位翻转系统驱动的6台SLED的输出功率增益均超过7dB,最高达到7.54dB,增益的长期稳定度达到±0.1dB。     

大随机相位误差下条带模式合成孔径激光雷达成像实验

为了探索大随机相位误差条件下合成孔径雷达(SAL)成像特点和规律,本文采用波长为1 550 nm的线性调频激光器建立了能够产生大的共模随机相位误差的条带模式SAL成像实验装置。利用此装置获得了不同目标回波强度下条带模式SAL成像实验数据,结合条带模式相位梯度自聚焦(PGA)多次迭代处理,获得了高分辨率SAL图像。实验发现在[-6. 45π,6. 45π]范围的大随机相位误差下,通过简单的距离压缩和方位匹配滤波,无法实现SAL图像聚焦,图像信噪比仅为3 dB。进一步采用PGA处理,就能很好地校正相位误差,得到聚焦良好的SAL图像,图像信噪比达到43 dB。实验还发现,当存在大共模随机相位误差时,PGA处理展现出非常强的鲁棒性,在回波弱到10-15W的情况下依然有效。在大相位误差存在的SAL系统(如机载SAL)中,PGA处理能有效消除相位误差,实现图像聚焦;另外,增大探测激光功率以提高成像数据信噪比,将有助于提升PGA处理效果。     

BEPCⅡ直线加速器微波系统

BEPCⅡ直线加速器微波系统要求的技术指标比旧系统有了大幅度的提高, 为此老系统的许多部件需要重新研制和改造. 本文首先介绍了关键部件的改造研制情况, 它包括能量倍增器、加速管、大功率波导阀门、大功率干负载及其中功率和高功率波导衰减/移相器; 其次简要介绍了微波系统高功率运行情况.     

基于人工传输线的小型微带Wilkinson功分器

提出了一种基于人工传输线的小型微带Wilkinson功分器,该器件使用由LC元件构成的人工传输线取代传统传输线,并使用交指电容和贴片电阻进行端口隔离。设计制作的Wilkinson功分器中心频率为915MHz的微带3dB功分器,等幅同相地将输入功率分配到2个输出端口,尺寸仅有传统Wilkinson功分器的25%,端口幅度平衡度±0.2dB,相位平衡度±1°。实验结果表明:功分器带宽为0.49～1.20GHz,插入损耗小于3.2dB,回波损耗大于10dB,仿真结果和测量结果吻合较好。     

Error and jitter effect studies on the SLED for the BEPC Ⅱ-linac

An RF pulse compressor is a device used to convert a long RF pulse to a short one with a much higher peak RF magnitude. SLED can be regarded as the earliest RF pulse compressor to be used in large-scale linear accelerators. It has been widely studied around the world and applied in the BEPC and BEPC linac for many years. During routine operation, error and jitter effects will deteriorate the performance of SLED, either on the output electromagnetic wave amplitude or phase. The error effects mainly include the frequency drift induced by cooling water temperature variation and the frequency/Q 0 /β unbalances between the two energy storage cavities caused by mechanical fabrication or microwave tuning. The jitter effects refer to the PSK switching phase and time jitters. In this paper, we re-derive the generalized formulae for the conventional SLED used in the BEPC linac, and the error and jitter effects on SLED performance are also investigated.     

Compact multimode interference coupler with tapered waveguide geometry

In this paper, a novel MMI coupler, based on general interference, with tapered waveguide geometry has been proposed for reduction of coupling length. The coupling characteristics and power imbalance of the proposed structure are compared with conventional MMI structures by using a mathematical model based on sinusoidal modes. It is seen that the beat length for tapered MMI coupler with angle of taper ∼1.05° is reduced by ∼24% of that of conventional MMI coupler and the coupling characteristics obtained with the mathematical model, match well with those obtained by more sophisticated BPM computer aided design software. The power imbalance for tapered 3 dB MMI coupler is more sensitive to the wavelength than that for conventional 3 dB MMI coupler and variation of power imbalance with fabrication tolerance for both the MMI coupler is almost same.     

一种耦合度可调节的微波脉冲压缩装置设计及实验

针对有源能量倍增器法(SLED)脉冲压缩实验中对储存能量阶段和释放能量阶段耦合度调节的需求,利用支臂短路波导H-T的调配功能,设计了一种耦合度可调节的SLED脉冲压缩装置。基于散射矩阵理论,分析了支臂短路波导H-T对SLED脉冲压缩装置耦合度的调节能力。利用大功率波导环形器代替3 dB耦合器,进行了基于单储能腔的无源SLED脉冲压缩实验,实验结果表明,支臂短路波导H-T对耦合度的调节能力与理论分析相吻合。     

A New Type of Detuning System of RF Compressors (SLED)

In our SLAC type of RF pulse compressor (SLED), the detuning device works not as well as expected. It happend that the detuning needles sticked to the sleeves when working at detuning mode. Due to this reason, we can not measure its energy multiplication factor. To solve the sticking problem of SLED needles, a prototype of the new SLED detuning system has been developed and it has been operated with high power successfully on BEPC Linac.     

Estimation of the performance of a 3-dB Y-junction optical coupler with a channel profile of proton-exchanged lithium niobate

A 3-dB optical coupler (power splitter) based on a Y-junction waveguide with a channel profile of proton-exchanged lithium niobate has been modeled. Finite difference beam propagation method has been used to investigate light wave propagation in axially varying waveguides. It is found that the structure splits the input power equally at the Y-junction with an efficiency of 99% and an average excess loss ?0.04 dB. The novelty of the coupling structure proposed is its capability to function as a wavelength-independent 3-dB coupler while maintaining very low-power imbalance for widespread optical communication wavelengths of 1.3 and 1.55 µm.     

Microwave System for BEPCⅡ-Linac

Specifications of microwave system for BEPCⅡ-Linac were enhanced by a wide margin in comparison with those of the microwave system for BEPC-Linac. For this reason many RF components must be developed and improved. This paper introduces the developments of SLED detuning system, accelerating section, high power waveguide valve, high power dummy-load, and medium & high power waveguide attenuator/phase shifters. High power operation of the microwave system has been carried out.     

Design and simulation of a C-band SLED with mode converter

The transient response analysis of the SLED based on the equivalent circuit is described. Then, a C-band SLED using TE0,1,15 mode cylindrical cavity with TE10-TE01 mode converter has been designed. According to the main RF parameters of the accelerator, the coupling coefficient is optimized to obtain the maximum multiplication factor. The key components of the pulse compressor include a 3 dB directional coupler, a TE10-TE01 mode converter,and a cylindrical cavity, which are simulated and optimized using 3D electromagnetic field simulation software. In addition, the function defining the relation between the coupling factor and aperture size is derived by a mathematical fitting method.     

Calculation of the external quality factor of the high power input coupler for the BEPC Ⅱ superconducting cavity

It is very important to predict the coupling between the cavity and the high power input source in the coupler design. In this paper, a time domain method is used to calculate the external quality factor Qext for the BEPC Ⅱ superconducting cavity. A comparison between simulation results and experimental results is presented. The results of simulation and measurement of Qext have a good agreement within an error of 10%.The geometry parameters related with Qext are also studied.