TESLA式高阶模衰减器的改进与设计研究

为了消除超导加速腔中高阶模场对加速粒子的影响, 在DESY的高阶模耦合器结构的基础上本文提出了改进的耦合器. 用HFSS程序针对1.5cell腔设计优化了高阶模耦合器, 得到高阶模耦合器对几种主要模式的吸收. 研究结果表明, 采用新型结构后, 衰减器对主要有害模的衰减由－40dB提高到－15dB, 使原有高阶模衰减器的性能明显提高. 该高阶模衰减器也适用于国产2cell超导腔的使用.     

高阶模高斯光束整形方法研究

研究了高阶模高斯光束的整形方法.在高阶模高斯光束和平顶光束理论模型的基础上,分别选择了平项洛仑兹函数和费米狄拉克函数作为平顶光分布函数,利用能量守恒定律,分别推导针对拉盖尔-高斯光束和厄米特-高斯光束整形系统中入射光与出射光的映射函数.最后利用ZEMAX软件设计了针对TEM01模高斯光束进行整形的非球面透镜元件.结果表...     

带高阶模谐振腔反射器的过模高功率毫米波源

针对过模系数为2.3的高功率毫米波发生器设计了工作于高次模的谐振腔反射器。谐振腔反射器工作模式为TM035模式,在58~62 GHz频带内对TM01模式的反射系数大于0.9。运用2.5维全电磁粒子程序模拟分析了器件中束波相互作用过程,通过调整慢波结构与谐振腔反射器间的漂移段长度得到了器件在570 kV,6.0 kA电子注量驱动下,在引导磁场为4 T时,能辐射出功率1.06 GW、频率为60.2 GHz的毫米波,主要工作模式为TM01模,效率约为31%,起振时间为3.3 ns。     

带高阶模谐振腔反射器的过模高功率毫米波源

针对过模系数为2.3的高功率毫米波发生器设计了工作于高次模的谐振腔反射器。谐振腔反射器工作模式为TM035模式,在58~62 GHz频带内对TM01模式的反射系数大于0.9。运用2.5维全电磁粒子程序模拟分析了器件中束波相互作用过程,通过调整慢波结构与谐振腔反射器间的漂移段长度得到了器件在570 kV,6.0 kA电子注量驱动下,在引导磁场为4 T时,能辐射出功率1.06 GW、频率为60.2 GHz的毫米波,主要工作模式为TM01模,效率约为31%,起振时间为3.3 ns。     

光纤Mach-Zehnder干涉仪中的高阶模干涉现象

利用Hermite-Gauss函数、模式干涉理论以及电场矢量线性叠加方法,分析了高阶模经光纤Mach-Zehnder干涉仪后的输出光场的空间干涉现象,得出了两个高阶模之间干涉光场的公式,计算出了双模光纤中各模式之间空间干涉的光场.数值仿真结果表明二阶模之间的干涉光场是两个相同的圆形光斑,而基模和二阶模之间的干涉光场是两个不等大的圆形光斑.     

超导加速器CW模式的高阶模初步分析

超导加速器由于具有极高的Q值,因此表现出较强的腔束相互作用,尤其是在以CW模式运行下,严重时会产生束流崩溃(BBU)效应。德国TESLA式的9-cell超导串腔在束流负载为1 mA,束团重复频率为81.25 MHz情况下,对其高阶模的产生及相应的功率水平进行了分析。结果表明：对于该腔的主要高阶模,谐振偏差值在π/4以上,束流没有发生谐振,高阶模功率在mW量级。     

超导加速器CW模式的高阶模初步分析

 超导加速器由于具有极高的Q值,因此表现出较强的腔束相互作用,尤其是在以CW模式运行下,严重时会产生束流崩溃(BBU)效应。德国TESLA式的9-cell超导串腔在束流负载为1 mA,束团重复频率为81.25 MHz情况下,对其高阶模的产生及相应的功率水平进行了分析。结果表明：对于该腔的主要高阶模,谐振偏差值在π/4以上,束流没有发生谐振,高阶模功率在mW量级。     

β=0.45,f=350MHz spoke腔高阶模的研究

质子或者离子在中低能段的加速结构是目前研究的热点, 其中许多实验结果表明spoke腔是连接RFQ加速结构和椭球腔加速结构的最具潜力的桥梁. 但是这种新型结构仍然存在许多问题有待解决, 为此, 北京大学开展了spoke型质子加速腔的研究, 完成了β=0.45, 频率为350MHz spoke腔的设计和铜模型腔的加工. 重点对spoke腔高阶模进行了分析, 模拟计算找出了几种危害模式, 并完成了实验测量, 取得了实验测量与模拟计算相一致的结果.     

矢量有限元方法精确计算轴对称?谐振腔高阶模

采用矢量有限元方法计算了任意轴对称谐振腔高阶模的本征频率.这种方法能够将数学模型和物理理论很好地结合起来,避免了一般有限元方法计算谐振腔本征模式中可能出现伪根的问题,并且可以通过采用二阶标量和矢量基函数,在较少的网格数的情况下得到很高的计算精度.基于该方法的程序Cafe为进一步精确研究下一代直线对撞机失谐结构的尾场奠定了基础.     

2-cell超导腔的高阶模分析

 阐述了2-cell Telsa腔的设计。用3维程序HFSS分析了其高阶模的特点，给出了高阶模的主要参数频率、品质因数、分路阻抗以及模式的电场分布，并且π模的电场分布与Superfish的模拟结果相比较，两者是一致的。最后，简要分析了各高阶模对电子加速的影响，分析表明高阶模降低了电子加速效率和束流的稳定性。     

Stop band characteristics of a TESLA cavity coaxial-type HOM coupler

A TTF-type coaxial higher order modes (HOM) coupler has been used in a TESLA 9 cell cavity. It is impossible to measure the stop band characteristics of the HOM coupler with the cavity. A measurement device for the coaxial transmission line type for the HOM coupler has been designed at Peking University. Experimentally it was shown that the average voltage standing wave ratio of the coaxial transmission line is smaller than 1.08. The experimental results of the stop band characteristics of the TTF-type HOM coupler have been fitted for the simulation. This paper describes the design of the measurement device and discusses the experimental and simulation results of stop band characteristics of the HOM coupler.     

Stop band characteristics of a TESLA cavity coaxial-type HOM coupler

A TTF-type coaxial higher order modes (HOM) coupler has been used in a TESLA 9 cell cavity. It is impossible to measure the stop band characteristics of the HOM coupler with the cavity. A measurement device for the coaxial transmission line type for the HOM coupler has been designed at Peking University. Experimentally it was shown that the average voltage standing wave ratio of the coaxial transmission line is smaller than 1.08. The experimental results of the stop band characteristics of the TTF-type HOM coupler have been fitted for the simulation. This paper describes the design of the measurement device and discusses the experimental and simulation results of stop band characteristics of the HOM coupler.     

A coaxial HOM coupler for a superconducting RF cavity and its low-power measurement results

A resonant buildup of beam-induced fields in a superconducting radio frequency(RF)cavity may make a beam unstable or a superconducting RF cavity quench. Higher-order mode(HOM)couplers are used for damping higher-order modes to avoid such a resonant buildup. A coaxial HOM coupler based on the TTF (TESLA Test Facility)HOM coupler has been designed for the superconducting RF cavities at the Proton Engineering Frontier Project(PEFP)in order to overcome notch frequency shift and feed-through tip melting issues. In order to confirm the HOM coupler design and finalize its structural dimensions, two prototype HOM couplers have been fabricated and tested. Low-power testing and measurement of the HOM couplers has shown that the HOM coupler has good filter properties and can fully meet the damping requirements of the PEFP low-beta superconducting RF linac.     

A coaxial HOM coupler for a superconducting RF cavity and its low-power measurement results

A resonant buildup of beam-induced fields in a superconducting radio frequency (RF) cavity may make a beam unstable or a superconducting RF cavity quench. Higher-order mode (HOM) couplers are used for damping higher-order modes to avoid such a resonant buildup. A coaxial HOM coupler based on the TTF (TESLA Test Facility) HOM coupler has been designed for the superconducting RF cavities at the Proton Engineering Frontier Project (PEFP) in order to overcome notch frequency shift and feed-through tip melting issues. In order to confirm the HOM coupler design and finalize its structural dimensions, two prototype HOM couplers have been fabricated and tested. Low-power testing and measurement of the HOM couplers has shown that the HOM coupler has good filter properties and can fully meet the damping requirements of the PEFP low-beta superconducting RF linac.     

Measuring the performance of the coaxial HOM coupler on a 2-cell TESLA-shape copper cavity

Coaxial High Order Mode （HOM） couplers have been fabricated at Peking University and their RF performance has been measured on a test device consisting of a coaxial transmission line and a 2-cell TESLA-shape copper cavity. The test results on the 2-cell TESLA-shape copper cavity with HOM couplers indicate that the coupler can cut off the fundamental mode TM010 and absorb HOMs effectively after a careful adjustment. The optimal angle of the HOM coupler with the beam tube is found. The initial test results of HOM couplers are presented in this paper.     

Measuring the performance of the coaxial HOM coupler on a 2-cell TESLA-shape copper cavity

Coaxial High Order Mode (HOM) couplers have been fabricated at Peking University and their RF performance has been measured on a test device consisting of a coaxial transmission line and a 2-cellTESLA-shape copper cavity. The test results on the 2-cell TESLA-shape copper cavity with HOM couplers indicate that the coupler can cut off the fundamental mode TM010 and absorb HOMs effectively after a careful adjustment. The optimal angle of the HOM coupler with the beam tube is found. The initial test results of HOM couplers are presented in this paper.     

GaAs非对称X结波导混合耦合器的研究

本文报道了ＧａＡｓ非对称Ｘ结波导耦合器的工作原理。该器件制作在ｎ＾－／ｎ＾＋ＧａＡｓ外延材料上。文中采用有效折射率法分析了这个耦合器的分离角、波导脊高及其两个非对称波导传播常数差之间的关系。器件在λ＝１．１５μｍ下测量，得到了小于－２．９ｄＢ的分光性能和小于－２０ｄＢ的串音比。