RF characters study of a pick-up parallel-setting HOM coupler

A pick-up parallel-setting high order mode coupler(pps-HOM coupler)has been fabricated at Peking University.It has been tested on a coaxial transmission line and a 2-cell TESLA-shape copper cavity.The test result of the 2-cell TESLA cavity shows that the coupler can cut off the fundamental mode TM010 and absorb HOMs electively.As its RF properties are insensitive to the probe dip length,there is no need to adjust the probe repeatedly during practical operation.     

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。     

Design of a 450 MHz β=0.2 single spoke cavity at PKU

The design of a 450 MHz β=0.2 superconducting single spoke cavity has been finished at Peking University. A theoretical model and a numerical simulation are used to study the relationship between the RF performance and the geometric parameters of the cavity. In this paper, the optimization of the spoke cavity is described in detail. The RF simulation gives the optimum parameters Epk/Eacc of 2.65 and Epk/Eacc of 5.22 mT/(MV/m). The mechanical properties of the cavity are also studied. Two stiff ribs are used to offer a credible mechanical stability.     

Preliminary study of the higher-harmoni ccavity for HLS-Ⅱ

A higher-harmonic cavity will be used to increase the beam lifetime and suppress coupled-bunch instabilities for Hefei Light Source-Ⅱ. In this paper, results simulated by the particle-tracking model confirm that tuning in the harmonic cavity may suppress the parasitic coupled-bunch instabilities. The factors calculated for lifetime improvement are larger than 2.5. The 3rd and 4th harmonic cavities have been designed. In particular, the absorbers and antenna couplers are applied in harmonic cavities to damp the higher order modes. Finally, the 4th harmonic cavity similar to the Duke's RF cavity will be used for HLS-Ⅱ.     

β=0.45, f=350 MHz Spoke腔的设计

近几年来,低b超导腔(例如spoke型,re-entrant 型,CH型)作为质子或者离子在中低能段的加速结构成为研究的热点.许多实验结果表明spoke腔在低能段是很好的选择,在中能段跟椭球腔相比也很具有竞争实力,为此,北京大学开展了β=0.45,频率为350MHz的spoke型质子超导加速腔研究. 本文详细阐述了这种腔的结构及电磁场的设计,从射频参数Q,r/Q,最大表面电磁场和加速效率的计算结果来看,它具有很好的加速性能.     

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.     

Study on the Lorentz detuning and tuning of β=0.3, 352 MHz spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of the high power proton linac for the Accelerator Driven Sub-critical System in China. In this paper, the basic geometric and RF parameters of a β=0.3, 352 MHz spoke cavity are given, and the Lorenz detuning and tuning are presented.     

A preliminary quadrupole asymmetry study of a β=0.12 superconducting single spoke cavity

An Accelerator Driven System(ADS) has been launched in China for nuclear waste transmutation. For the application of high intensity proton beam acceleration, the quadrupole asymmetry effect needs to be carefully evaluated for cavities. Single spoke cavities are the main accelerating structures in the low energy front-end. The single spoke cavity has small transverse electromagnetic field asymmetry, which may lead to transverse RF defocusing asymmetry and beam envelope asymmetry. A superconducting single spoke resonator(PKU-2 Spoke) of β=0.12 and f =325 MHz with a racetrack-shaped inner conductor has been designed at Peking university. The study of its RF field quadrupole asymmetry and its effect on transverse momentum change has been performed. The quadrupole asymmetry study has also been performed on a β=0.12 and f =325 MHz ring-shaped single spoke cavity. Our results show that the quadrupole asymmetry is very small for both the racetrack-shaped and the ring-shaped single spoke cavity.     

Study on the Lorentz detuning and tuning of β=0.3, 352 MHz spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of the high power proton linac for the Accelerator Driven Sub-critical System in China. In this paper, the basic geometric and RF parameters of a β=0.3, 352 MHz spoke cavity are given, and the Lorenz detuning and tuning are presented.     

深度抑制的超导高频腔研究

参照KEKB 509MHz超导腔,同时考虑到许多方面因素的影响,为北京正负电子对撞机改造工程改频设计了一个500MHz超导腔,并且对腔的一些性能进行了模拟计算,同时利用铝模型腔对一些主要参数进行了测量和校核.     

Design of a 450 MHz β=0.2 single spoke cavity at PKU

The design of a 450 MHz β=0.2 superconducting single spoke cavity has been finished at Peking University. A theoretical model and a numerical simulation are used to study the relationship between the RF performance and the geometric parameters of the cavity. In this paper, the optimization of the spoke cavity is described in detail. The RF simulation gives the optimum parameters Epk/Zacc of 2.65 and Bpk/Eacc of 5.22 mT/（MV/m）. The mechanical properties of the cavity are also studied. Two stiff ribs are used to offer a credible mechanical stability.     

Analysis of the impacts of mechanical errors on the RF performance of a single spoke cavity

Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.     

325 MHz spoke腔的二次电子倍增效应

采用CST软件的粒子工作室模块, 对spoke超导腔中可能发生的二次电子倍增效应进行了分析研究,并采用二次电子倍增效应发生后形成稳定状态时的粒子数增长率来表征其强度。模拟计算表明：该腔存在两处二次电子倍增效应,spoke柱两端的两点一阶倍增; spoke腔两端侧壁与中心圆筒交界处的单点一阶倍增;二次电子倍增在加速腔压为0.65 MV时的增长率最高,而腔压大于1 MV时,增长率均为负,即无倍增发生。