Study on the HOMs coupler design of spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of high power proton linac for an Accelerator Driven Sub-critical System (ADS). Considering that the High Order Modes (HOMs) in the superconducting cavity have far reaching influence on power dissipation and beam stability, the analysis of HOMs of the spoke cavity is needed. In this paper, we put emphasis on the analysis of HOMs of the spoke cavity and the HOMs coupler design.     

Design study on very low Beta spoke cavity for China-ADS

Very low Beta superconducting spoke cavity is one of the key challenges for the China-ADS project. In this paper, a new structure of 3βλ/2 spoke cavity is first studied in detail. Its RF and mechanical properties are simulated using CST-MWS and ANSYS, and compared with the traditional βλ/2 spoke structure.     

Low beta spoke cavity multipacting analysis

The simulation and analysis for electron multipacting phenomenon in a low β spoke superconducting cavity in ADS proton accelerator are proposed. Using both CST and Track3P codes, the electron multipacting calculation for β=0.12 spoke superconducting cavity is implemented. The methods of multipacting calculation on both codes are studied and described. With the comparison between the calculation results and the cavity vertical test result, the accuracy and reliability of different codes on calculating multipacting are analyzed. Multipacting calculation can help to understand the results of vertical test and also can help to do the optimization in cavity design.     

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.     

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。     

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.     

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.     

Study of medium beta elliptical cavities for CADS

The China Accelerator-Driven Sub-critical System(CADS) is a high intensity proton facility to dispose of nuclear waste and generate electric power.CADS is based on a 1.5 GeV,10 mA CW superconducting(SC) linac as a driver.The high energy section of the linac is composed of two families of SC elliptical cavities which are designed with geometrical beta 0.63 and 0.82.In this paper,the 650 MHz β=0.63 SC elliptical cavity is studied,including cavity optimization,multipacting,high order modes(HOMs) and generator RF power calculation.     

Study and design of RF coupler for Chinese ADS HWR superconducting cavity

An RF power coupler is a key component of the superconducting accelerating system in Chinese ADS proton linac injector I, which is used to transmit 15 kW RF power from the power source to the superconducting HWR cavity. According to the requirement of working frequency, power level, transmission capability and cooling condition, the physics design of coupler has been finished, which includes RF structure optimization, thermal simulation, thermal stress analysis and so on. Based on this design, the prototype of HWR coupler has been fabricated, and it has successfully passed the high power test.     

Study and design of RF coupler for Chinese ADS HWR superconducting cavity

An RF power coupler is a key component of the superconducting accelerating system in Chinese ADS proton linac injector I, which is used to transmit 15 kW RF power from the power source to the superconducting HWR cavity. According to the requirement of working frequency, power level, transmission capability and cooling condition, the physics design of coupler has been finished, which includes RF structure optimization, thermal simulation, thermal stress analysis and so on. Based on this design, the prototype of HWR coupler has been fabricated, and it has successfully passed the high power test.     

Directional coupler design based on coupled cavity waveguides in photonic crystals

We propose a directional coupler design based on coupled cavity waveguide in photonic crystals. The plane wave expansion is used to give the dispersion of the coupled cavity waveguides and two parallel such waveguides. The couple length is got from the dispersion curves. Based on the research of the dispersion, we present a directional coupler and the transmission property is given. This structure is potentially important for highly efficient directional coupler in integrate optical circuit.     

HOMs simulation and measurement results of IHEP02 cavity

In accelerator RF cavities, there exists not only the fundamental mode which is used to accelerate the beam, but also higher order modes(HOMs). The higher order modes excited by the beam can seriously affect beam quality, especially for the higher R/Q modes. 1.3 GHz low-loss 9-cell superconducting cavity as a candidate for ILC high gradient cavity, the properties of higher order mode has not been studied carefully. IHEP based on existing low loss cavity, designed and developed a large grain size 1.3 GHz low-loss 9-cell superconducting cavity(IHEP02cavity). The higher order mode coupler of IHEP02 used TESLA coupler's design. As a result of the limitation of the mechanical design, the distance between higher order mode coupler and end cell is larger than TESLA cavity.This paper reports on measured results of higher order modes in the IHEP02 1.3 GHz low-loss 9-cell superconducting cavity. Using different methods, Q e of the dangerous modes passbands have been obtained. The results are compared with TESLA cavity results. R/Q of the first three passbands have also been obtained by simulation and compared with the results of the TESLA cavity.     

Tuner control system of Spoke012 SRF cavity for C-ADS injector I

A new tuner control system for spoke superconducting radio frequency(SRF) cavities has been developed and applied to cryomodule I of the C-ADS injector I at the Institute of High Energy Physics, Chinese Academy of Sciences. We have successfully implemented the tuner controller based on Programmable Logic Controller(PLC)for the first time and achieved a cavity tuning phase error of ±0.7?(about ±4 Hz peak to peak) in the presence of electromechanical coupled resonance. This paper presents preliminary experimental results based on the PLC tuner controller under proton beam commissioning.     

Design of a 325 MHz SC Spoke040 cavity at IHEP

A spoke cavity is a TEM-class superconducting resonator with particular advantages: compact structure and high shunt impedance. The 325 MHz β =0.40(β =v/c, v is the velocity of particle and c is the velocity of light)single spoke cavity(Spoke 040) is adopted for the Chinese ADS(Accelerator Driven Sub-critical System) project. The physics and mechanical design has been accomplished, and the fabrication of a prototype is currently in progress. In this paper, the optimization processes for the main radio frequency(RF) and mechanical parameters are analyzed in detail. Two kinds of cavity end-walls(flat and convex) are compared. The convex end-wall is preferred in order to improve mechanical performance of the cavity. Two prototypes of the Spoke 040 cavity are in the machining stage,and should be finished in early 2014.Vertical testing is also under preparation.     

1+1/2 Cell超导加速腔的本征高阶模场分布研究

为实现高平均流强加速, 需要有效地消除超导加速腔中的高阶模场. 为研制有效的高阶模耦合器, 本文对北京大学DC-SC光阴极超导注入器的核心部件—1+1/2 cell超导加速腔中高阶模场进行了分析研究, 用HFSS程序计算给出前31个高阶模场参数, 与实验测量较为符合. HFSS计算与Superfish计算结果比较符合很好, 验证用HFSS计算可靠, 为以后超导腔的升级研究提供有效的手段.     

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.     

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.     

High power conditioning of the input coupler for BEPCⅡ superconducting cavity

High power conditioning of the input coupler for BEPCⅡ supercOnducting cavity has been performed.After room temperature conditioning,the RF power of 150 kW with continuous wave at standing wave mode passed through the coupler without any problem.Meanwhile,a series of methods have also been studied to improve the performance of the coupler during the beam operation.Up to now,the input coupler can feed a RF power up to 100 kW stably with high current of 250 mA at 2.5 GeV.     

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.