Study of multipacting effect in superconducting cavity

A number of superconducting cavities of axis-symmetric geometry have been considered to study the effect in order to achieve the desired performance.It is shown that the multipacting effect is strongly dependent on the condition of the RF surface and can be suppressed with reconsideration of the geometry.The simulation result is compared with the result of the semi-analytical model in the end.     

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.     

射频超导腔加速性能的改进

为提高超导加速腔的加速梯度和Q值,改进了薄膜型超导腔的加速性能。研究证明,对于铜铌溅射腔,在无氧铜衬底和铌膜之间加入NbN 层可以提高铌膜的超导转变温度,改善晶格结构;对纯铌超导腔提出了改进方法,在传统的纯铌超导腔表面制备多层的超导-绝缘-超导复合膜可以屏蔽Nb腔表面的界面场,提高超导腔的临界磁场,从而提高了铌腔的加速梯度。     

Multipacting simulation and analysis of a taper quarter wave cavity by using Analyst-PT3P

Since the tapered quarter wave resonator (QWR) cavity is proven to have a much lower peak surface magnetic field in the short plate and a lower peak surface electric field near the beam tube compared with the straight outer conductor QWR, it has been recommended for the separated sector cyclotron linac injector system in the heavy ion research facility in Lanzhou. This paper is focused on the multipacting (MP) analysis for the tapered QWR with a frequency of 80.5 MHz and beta of 0.085. Using the Analyst program, MP bands can be simulated and analyzed with the Particle Tracking module to identify potential problems in the cavity design. This paper will present the simulation results of MP for the tapered QWR cavity.     

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.     

Multipacting phenomenon at high electric fields of superconducting cavities

Recently multipacting (MP) recalculation of the TeV Energy Superconducting Linear Accelerator (TESLA) resonator was performed. In addition to the normal MP which occurs at a peak electric field of around 40MV/m for the TESLA cavity, another type of multipacting with resonant electron trajectory that is far from the equator is also seen.It occurs at a gradient around 60MV/m to 70MV/m. This result seems to explain some experimental observations.     

Study of multipacting effect in sub-harmonic buncher of SSRF linac

During the design process, multipacting effect has been taken into consideration using a 2D simulation code MultiPac and all of the corners are rounded to suppress the multipacting effect in the pill-box cavity. However, unexpected multipacting effect prevents the increase of the input power when the magnetic field of focusing coils is added after adequate conditioning and a novel method is adopted to suppress it by introducing extra coils to counteract the field. This paper focuses on the simulation of multipacting effect in different magnetic field configurations. The experimental observations and simulation results of multipacting effect are presented and details of the multipacting process are also analyzed.     

Analysis of superconducting cavity quench events at SSRF

Quench is important and dangerous to superconducting RF cavities. This paper illustrates the mechanism of quench and how a quench detector works, and analyzes the quench events happening during beam operations and cavity conditioning. We find that the quench protection is mostly triggered by some reasons such as fluctuation of cavity voltage, multipacting or arc, rather than a real cavity thermal breakdown. The results will be beneficial to optimize the operation parameters of superconducting cavities, to discover the real reasons for beam trip by quench interlock, and to improve the operation stability of superconducting RF systems.     

Study of multipacting effect in sub-harmonic buncher of SSRF linac

During the design process, multipacting effect has been taken into consideration using a 2D simulation code MultiPac and all of the corners are rounded to suppress the multipacting effect in the pill-box cavity. However, unexpected multipacting effect prevents the increase of the input power when the magnetic field of focusing coils is added after adequate conditioning and a novel method is adopted to suppress it by introducing extra coils to counteract the field. This paper focuses on the simulation of multipacting effect in different magnetic field configurations. The experimental observations and simulation results of multipacting effect are presented and details of the multipacting process are also analyzed.     

Analysis of superconducting cavity quench events at SSRF

Quench is important and dangerous to superconducting RF cavities. This paper illustrates the mechanism of quench and how a quench detector works, and analyzes the quench events happening during beam operations and cavity conditioning. We find that the quench protection is mostly triggered by some reasons such as fluctuation of cavity voltage, multipacting or arc, rather than a real cavity thermal breakdown. The results will be beneficial to optimize the operation parameters of superconducting cavities, to discover the real reasons for beam trip by quench interlock, and to improve the operation stability of superconducting RF systems.     

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.     

1.3 GHz超导腔磁通排出效应研究

设计并搭建了一套高精度的磁场测量和补偿系统,并结合中国科学院高能物理研究所（IHEP）的2K超导腔垂直测试平台对1.3 GHz 单加速间隙超导腔的磁通排出效应开展了实验研究：利用研制的磁场测量和补偿系统能够精密地测量超导腔赤道位置磁场,并能够将磁场补偿至小于5.0×10⁻⁸ T;并对超导腔不同表面温度梯度下的磁通排出效应进行了测量分析;对钉扎了磁场的超导腔进行了射频性能测试,研究了超导腔电阻对磁通钉扎的敏感度,以及在不同电场梯度下超导腔的表面电阻变化情况。结果表明,研制的高精度磁场测量和补偿系统能够满足超导腔磁通排出研究的需求;高的超导腔表面温度梯度有利于磁通的排出;磁通钉扎电阻的敏感度随着加速电场梯度的增加而增大,导致超导腔的性能下降。此实验研究也为后续超导腔的研制奠定了一定基础。     

The design of a five-cell high-current superconducting cavity

Energy recovery linacs are promising for achieving high average current with superior beam quality. The key component for accelerating such high-current beams is the superconducting radio-frequency cavity. The design of a 1.3 GHz five-cell high-current superconducting cavity has been carried out under cooperation between Peking University and the Argonne National Laboratory. The radio-frequency properties, damping of the higher order modes, multipacting and mechanical features of this cavity have been discussed and the final design is presented.     

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     

超导腔垂直测试数字化自激励环路研制

介绍北京大学垂直测试系统的数字化自激励环路系统,重点分析了实际测试中避免多单元（cell）超导腔模式串扰的方法以及偏离四倍频采样对信号幅度和相位的影响。该系统运行稳定可靠,可有效区分1.3 GHz 9-cell超导腔$ {\rm{{\text{π}}}} $模与$ 8{\rm{{\text{π}}}}/9 $模,解决了多cell超导腔测试中模式串扰问题。分析了超导腔自激励环路在垂直测试中的应用,介绍了北京大学垂直测试系统的数字化自激励环路,采用上下变频方案的射频前端和包括有限脉冲响应滤波器的数字算法,系统简洁扩展性强。重点分析了实际测试中避免多cell超导腔模式串扰的方法以及偏离四倍频采样对信号幅度和相位的影响。在多种不同频率超导腔的垂直测试中该系统运行稳定可靠,可有效区分1.3 GHz 9-cell超导腔$ {\text{π}} $模与$ 8{\rm{{\text{π}}}}/9 $模,解决了多cell超导腔测试中模式串扰问题。     

Design and study of a high-current 5-cell superconducting rf cavity

The Advanced Photon Source (APS) at Argonne National Laboratory is considering the development of a superconducting linac-based fourth-generation hard X-ray source to meet future scientific needs of the hard X-ray user community. This work specifically focuses on the design of an optimized 5-cell superconducting radio-frequency structure well suited for a high-energy, high-beam-current energy recovery linac. The cavity design parameters are based on the APS storage ring nominal 7 GeV and 100 mA beam operation. A high-current 5-cell cw superconducting cavity operating at 1.4 GHz has been designed. In order to achieve a high current, the accelerating cavity shape has been optimized and large end-cell beam pipes have been adopted. The beam break-up threshold of the cavity has been estimated using the code TDBBU, which predicts a high threshold beam current for a 7 GeV energy recovery linac model. A copper prototype cavity has been fabricated that uses half-cell modules, initially assembled by clamping the cells together.     

射频超导腔加速性能的改进

 为提高超导加速腔的加速梯度和Q值，改进了薄膜型超导腔的加速性能。研究证明，对于铜铌溅射腔，在无氧铜衬底和铌膜之间加入NbN 层可以提高铌膜的超导转变温度，改善晶格结构；对纯铌超导腔提出了改进方法，在传统的纯铌超导腔表面制备多层的超导-绝缘-超导复合膜可以屏蔽Nb腔表面的界面场，提高超导腔的临界磁场，从而提高了铌腔的加速梯度。     

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.     

Design and study of a high-current 5-cell superconducting rf cavity

The Advanced Photon Source （APS） at Argonne National Laboratory is considering the development of a superconducting linac-based fourth-generation hard X-ray source to meet future scientific needs of the hard X-ray user community. This work specifically focuses on the design of an optimized 5-cell superconducting radio-frequency structure well suited for a high-energy, high-beam-current energy recovery linac. The cavity design parameters are based on the APS storage ring nominal 7 GeV and 100 mA beam operation. A high-current 5-cell cw superconducting cavity operating at 1.4 GHz has been designed. In order to achieve a high current, the accelerating cavity shape has been optimized and large end-cell beam pipes have been adopted. The beam break-up threshold of the cavity has been estimated using the code TDBBU, which predicts a high threshold beam current for a 7 GeV energy recovery linac model. A copper prototype cavity has been fabricated that uses half-cell modules, initially assembled by clamping the cells together.