溅射方法干式处理超导加速腔表面的研究与分析

详细研究了利用超高真空氩离子清洗技术发展的一种超导铌腔表面的“干式”处理方法,从微观和宏观角度分析了溅射处理对铌的表面特性和对超导腔性能的影响.与传统的“湿式”处理方法(化学抛光BCP和电抛光EP)相比,干式处理方法具有结构简单、容易控制、没有污染等优点,是一种很有潜力的超导腔处理方法,可以提高超导腔的性能. 关键词： 超导加速腔 溅射 形貌分析 残留电阻比RRR     

射频超导谐振腔中的电磁场研究

由高纯铌制成的射频超导谐振腔在高场时会出现Q值下降现象，这是高场下超导腔表面局部磁场增强所致. 为研究高场下超导腔表面的电磁场特性，用单cell超导腔设计了腔表面峰值磁场的研究实验. 通过对单cell超导腔表面峰值磁场的测量，可以确定超导腔焊缝及iris附近表面是否存在缺陷，以便进一步进行腔的处理来改进腔的性能.     

Status of the IHEP 1.3 GHz superconducting RF program

The 1.3 GHz superconducting radio-frequency (SRF) technology is one of the key technologies for the ILC and future XFEL and ERL projects in China. With the aim to develop 1.3 GHz SRF technology, IHEP has started a program to build an SRF Accelerating Unit. This unit contains a 9-cell 1.3 GHz superconducting cavity, a short cryomodule, a high power input coupler, a tuner and a low level RF system. This program also includes the SRF laboratory upgrade, which will permit the unit to be built and tested at IHEP. The unit will be used for the 1.3 GHz SRF system integration study, high power horizontal test and possible beam test in the future. In this paper, we report the recent R&D status of this program. The first large grain low-loss shape 9-cell superconducting RF cavity made by IHEP reached 20 MV/m in the first vertical test in July, 2010. The prototype tuner and low level RF (LLRF) system are under test. The high power input coupler and cryomodule are under fabrication. Several key SRF facilities for 9-cell cavity surface treatment and pre-tuning were successfully commissioned and are in operation.     

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.     

The First Nine-Cell TESLA Cavity Made in China

A totally home-made 9-cell TESLA type superconducting cavity is mane at Peking University. The cavity abrication is according to DESY specification. The cavity is made of high purity niobium from OTIC, Ningxia. The electron beam welding is carried out at Harbin Institute of Technology, Harbin. By the cooperation, the cavity is tested at Thomas Jefferson National Accelerator Facility, USA. The preliminary result shows the acceleration gradient Eacc is 23 MV/m without quench and has potential for improvement.     

超导腔数字自激垂直测试系统

基于数字自激算法设计并实现的超导腔垂直测试系统提高了超导腔的垂直测试效率,为先进光源技术研发与测试平台(PAPS)的超导腔批量化生产提供了重要保障;垂直测试系统的射频前端和时钟分配系统采用了二次上下变频方案,可以在一定范围内灵活设置测试系统自激环路的工作频率,增大了该测试系统的工作带宽。利用此系统完成了1.3 GHz 9-cell超导腔的通带频率测试,结果表明,该测试系统能有效避免不同模式之间的串扰,具备较强的频率分辨能力(<800 kHz),保证多单元超导腔性能验证的进行。     

Study on the 1.3 GHz low loss shape superconducting cavities at IHEP

As part of the international research program on the superconducting cavity for the International Linear Collider (ILC) R&D on the 1.3 GHz low loss superconducting cavities has been carried out at the Institute of High Energy Physics (IHEP) since 2005. A design of 1.3 GHz low loss cavity shape was proposed and six single-cell cavities of different niobium material were successfully fabricated with standard technology. In this study our priority was on large grain (LG) cavities. The two LG cavities were treated with complete procedures of surface treatments based on chemical polishing (CP) without electro polishing (EP) at IHEP. The two LG cavities and a fine grain cavity were sent to KEK for vertical testing. All the three cavities reached accelerating gradients higher than 35 MV/m and the maximum gradient of 40.27 MV/m was achieved in the LG cavity. This paper presents the process of the vertical RF tests and the comparison of the LG and fine grain cavities's performance.     

Multi-pass,multi-bunch beam breakup for 9-cellTesla cavities in the ERL

Generally, the Energy Recovery Linac (ERL) needs specially designed high current superconducting RF cavities. In this paper, the threshold current of beam breakup for compact ERL facilities with 9-cell Tesla type cavities are investigated. The results show that it is feasible to adopt the 9-cell Tesla cavity for compact ERL test facilities with just a few cavities and beam current around 10 mA.     

Researches and Preliminary Experiments on Copper-Niobium Sputtered Low-β Superconducting Resonator

Superconducting resonator is the important component of a superconducting accelerator. The best choice of the acceleration cavity for heavy ion superconducting accelerator is quarter wave resonator (QWR). By sputtering a layer of niobium films of several microns on the OFHC copper substrate, good superconducting properties and acceleration properties of the cavity can be obtained. However, it is very difficult to get uniform niobium films by sputtering because the inner surface of the QWR is complicated. To deal with this problem, we developed a multiparameter adjusting method to control the sputtering process of different parts of the QWR. A layer of uniform niobium film with nice superconducting performance is obtained. The low temperature experiments with liquid helium show that the Cu Nb QWR has good superconducting characters. The Q value of the cavity is about 5×10⁸.     

北京大学国产大晶粒铌材超导腔的性能研究

大晶粒铌材是射频超导领域的研究热点之一. 采用大晶粒铌材的射频超导谐振腔, 其后处理工艺可以大大简化. 北京大学对此进行了深入细致的研究, 自主研制了采用国产大晶粒铌材的射频超导腔, 对这些超导腔进行了简单的表面处理, 包括标准的化学抛光(BCP)和120℃低温烘烤处理, 未进行非常复杂的电抛光处理, 低温性能测试结果表明其低温超导性能优越, 大晶粒1.3GHz超导腔的加速梯度达到了43.5MV/m, 为我国超导加速器的国产化打下了基础.     

Amplitude and phase stability studies in a DC superconducting injector

The DC superconducting injector will be used in the PKU-THz facility which consists of a DC-gun and a 3+1/2-cell superconducting cavity. The cavity must accelerate the electron beam to 5.82 MeV which is susceptible to perturbations because of its narrow bandwidth. In this paper, the sources and influences of the perturbations in the 3+1/2-cell cavity are discussed. It is shown that the control system is essential for the cavity. The design of a feedback based digital RF low level control system for the 3+1/2-cell cavity is accomplished.     

Thermal simulation and analysis of the STF cryomodule

STF is a superconducting RF test facility constructed at the high energy accelerator research organization of Japan (KEK), as a main part of a R&;D project for the proposed International Linear Collider (ILC) in Asia. Thermal study of the STF 1.3 GHz 9-cell cavity cryomodule was carried out within a collaboration between China and Japan. Static and dynamic thermal behaviors of the STF cryomodule were simulated and analyzed with the FEM method, and some simulation results were compared with the available experimental data. This paper presents the details.     

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.     

Study on the RF performance of 2-cell superconducting cavity

The physical design of the 2-cell superconducting cavity is presented.The RF parameters of the cavity and HOMs (high order modes) are reported.In this paper,we put the emphasis on the analysis of the HOMs and interaction between beam and cavity.     

Study on the RF performance of 2-cell superconducting cavity

The physical design of the 2-cell superconducting cavity is presented. The RF parameters of the cavity and HOMs （high order modes） are reported. In this paper, we put the emphasis on the analysis of the HOMs and interaction between beam and cavity.     

Thermal simulation and analysis of the STF cryomodule

STF is a superconducting RF test facility constructed at the high energy accelerator research orga-nization of Japan (KEK), as a main part of a R&D project for the proposed International Linear Collider (ILC) in Asia. Thermal study of the STF 1.3 GHz 9-cell cavity cryomodule was carried out within a collaboration between China and Japan. Static and dynamic thermal behaviors of the STF cryomodule were simulated and analyzed with the FEM method, and some simulation results were compared with the available experimental data. This paper presents the details.     

超导在加速器中的应用概况

文中简要回顾了世界上已建造的大型超导加速器,重点介绍未来的超导加速器方案,对超导新材料在加速器中的应用研究以及我国超导在加速器中的应用研究情况作了简要介绍.     

Low-Loss NbTiN Films for THz SIS Mixer Tuning Circuits

Recent results at 1 THz using normal-metal tuning circuits have shown that SIS mixers can work well up to twice the gap frequency of the junction material (niobium). However, the performance at 1 THz is limited by the substantial loss in the normal metal films. For better performance superconducting films with a higher gap frequency than niobium and with low RF loss are needed. Niobium nitride has long been considered a good candidate material, but typical NbN films suffer from high RF loss. To circumvent this problem we are currently investigating the RF loss in NbTiN films, a 15K Tc compound superconductor, by incorporating them into quasi-optical slot antenna SIS devices.     

超导腔垂直测量系统中的磁屏蔽

简要介绍空间磁场对纯铌超导加速腔性能的影响,以及在超导腔垂直测量时对空间磁场进行有效屏蔽的方法.由于多数磁性材料对应力和温度变化非常敏感,而且国内缺乏在低温下相关磁屏蔽材料性能的数据,为此对8种国产铁磁和软磁材料在低温下的初始磁导率进行了测量,并给出了相应的测试结果.最后介绍了作者研制的1.3GHz超导腔垂直测量低温恒温器内置式磁屏蔽装置及其性能.