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.     

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.     

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.     

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.     

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.     

提高射频超导加速腔性能的表面干式处理研究

射频超导谐振腔以其优越性在加速器领域起到了常温加速腔无法替代的作用. 超导腔的表面 特性直接影响到加速腔的性能. 为进一步提高超导腔的加速性能，北京大学利用超高真空氩 离子清洗技术发展了一种超导腔表面的干式处理方法. 与传统的湿处理方法(化学抛光BCP和 电抛光EP)相比，干式处理方法具有其特有的优点，有可能成为一种新的超导腔表面处理方 法，对提高加速腔的性能起到推动作用. 进一步的研究正在进行之中. 关键词： 射频超导 表面处理 溅射 抛光     

Analysis of a teleportation scheme involving cavity field states in a linear superposition of Fock states

We analyse a teleportation scheme of cavity field states. The experimental sketch discussed makes use of cavity quantum electrodynamics involving the interaction of Rydberg atoms with superconducting (micromaser) cavities as well as with classical microwave (Ramsey) cavities. In our scheme the Ramsey cavities and the atoms play the role of auxiliary systems used to teleport a field state, which is formed by a linear superposition of vacuum |∅〉 and the one-photon state |1〉, from a micromaser cavity to another.     

Great progress in developing 500 MHz single cell superconducting cavity in China

Superconducting cavities have been adopted in many kinds of accelerator facilities such as synchrotron radiation light source, hard X-ray free electron laser linac, colliders and energy recovery linacs (ERL). The 500 MHz superconducting cavities will be a candidate to be installed in the high current accelerators and high current ERLs for their large beam aperture, low higher order modes impedance and high current threshold value. This paper presents great progress in the whole sequence of developing 500 MHz superconducting cavity in China. It describes the first in-house successful development of 500 MHz single cell superconducting cavity including the deep-drawing of niobium half cells, electron beam wielding of cavity, surface preparations and vertical testing. The highest accelerating gradient of the fabricated cavity #SCD-02 higher than 10 MV/m was obtained while the quality factor was better than 4×10⁸ at 4.2 K, which has reached the world level of the same kind of cavities.     

Field emission and x-ray effect on RAON half-wave resonator (HWR) superconducting cavity performance

Performance of superconducting cavities are investigated with field emission effect and x-ray detection. Conducting particles and surface curvature can cause field emission from the surface of the superconducting Nb cavity. The field emission makes the local temperature increase and the quality factor decrease. Vertical test is performed for half-wave resonator (HWR) cavities. The vertical test facilities are introduced and the quality factors are measured for the half-wave resonator (HWR) cavities. The quality factors of the cavities decrease as the x-ray are increased. The surface resistance and x-ray generation of the cavity can be fitted well with the field emission theory. The quality factor for the half-wave resonator (HWR) cavities decreases linearly with the field enhancement factor for x-ray generation.     

STF数字微波低电平系统研究

STF是KEK为国际直线对撞机(ILC)建立的试验装置. 在STF中, 数字微波低电平系统用于控制超导腔的RF相位和幅度. 在没有实际腔运行的情况下, 设计了一个基于FPGA技术的实时超导腔模拟器, 用于测试微波低电平系统的硬件和算法. 超导腔的数字控制器用FPGA实现, 其中采用了PI反馈控制和前馈控制算法. 测试表明, 超导腔模拟器和控制器都工作良好, 可用于STF微波低电平系统的进一步开发.     

Physical design of superconducting magnet for ADS injection Ⅰ

A superconducting solenoid prototype magnet for Accelerator Driven Subcritical System (ADS) Injection Ⅰ has been designed and fabricated, which has also been tested in a liquid Helium state inside a vertical Dewar in the Haerbin institute of Technology in November 2012. The design current was 210 A, when the test current reached 400 A no quench occurred so the solenoid magnet was forced to quench by the embedded heaters. The integral field strength, leakage field at the nearby upstream and downstream superconducting spoke cavities all meet the design requirements. At the same time, it also checked the reliability of the vertical test Dewar and the quenched detection system. The superconducting prototype magnet has accumulated valuable experiences for the coming batch magnets production and cryogenic test.     

CiADS超导直线加速器超导腔失效的分段补偿与冗余设计

加速器驱动次临界装置（ADS）对加速器运行稳定性和失束指标提出了前所未有的要求。对于超导直线加速器的研究发现,超导腔失效是失束的一个较大的来源,故针对超导腔的失效情况,本文提出分段补偿新方法,以提高高功率超导直线加速器的运行稳定性。提出的分段补偿方法与已有的全局补偿和局部补偿的方法相比,在保证加速器出口束流品质与无束损束流传输的同时,分段补偿束流能量,优化了参与能量补偿的超导腔数量,降低超导腔的备份功率源需求。论文最后针对CiADS的超导直线加速器的物理设计,做了分段补偿的多粒子模拟。结果表明,采用了分段补偿方法实现超导腔失效补偿的前提下,参与补偿过程中改变腔压的超导腔数量比例为48%,对功率源总的功率备份冗余需求小于20%。The accelerator driven subcritical system (ADS) has put forward unprecedented demands on the stability and beam trip of the accelerator operation. Depending on analysis, failure of the superconducting cavities is a major cause for beam trip of the superconducting cavity. Therefore, a new method of piecewise compensation is proposed to improve the stability of high power superconductivity linac. The piecewise compensation scheme proposed in this paper is compared with the existing global compensation and local compensation technology. While guaranteeing the beam quality of the accelerator and without beam loss transmission, the piecewise compensation method can optimize the number of superconducting cavities involved in energy compensation and reduce the demand for the backup redundancy of power sources of the superconducting cavities. At the end of the paper, the multi-particle simulation of piecewise compensation aims at the physical design of CiADS superconducting linac. The result shows that 48% of superconducting cavities modify the cavity's Epeak during the compensation process and the demanded redundancy of total power sources is less than 20% under the premise of successful compensation for the failure of superconducting cavities through the piecewise compensation method.     

1.3 GHz超导腔的掺氮实验

为了大幅度提高纯铌超导腔的品质因数,从而降低其使用功耗,选择对超导腔进行高温氮掺杂处理。立足国内外大型加速器的需求,中国科学院高能物理研究所首先开展了1.3 GHz 1-cell超导腔的研究,包括常规处理以及氮掺杂实验,并且对掺杂前后的结果进行了分析、对比。结果表明,通过掺氮,两只1.3 GHz 1-cell细晶粒纯铌超导腔的品质因数均获得了显著提升,同时在超导腔低温垂直测试中观察到了比较明显的反常的品质因数随加速梯度变化的曲线,即"anti-Q-slope"现象。     

RF超导腔低温测量原理

本文依据能量守恒,就RF超导腔低温测量方法和原理进行了推敲.指出:由于在超导腔中存在场致电子发射(FE)效应,高功率腔和低功率腔在测量方法上是有区别的.并系统地推导了获得超导腔物理参数,比如空载Q₀、最大表面电场和最大加速梯度等的准确公式.     

A vertical test system for China-ADS project injector Ⅱ superconducting cavities

To test superconducting cavities, a vertical test system has been designed and set up at the Institute of Modern Physics (IMP). The system design is based on VCO-PLL hardware and the NI Labview software. The test of the HWR010#2 superconducting cavity shows that the function of this test system is satisfactory for testing the low frequency cavity.     

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.     

低温二次电子产额测试系统设计与研究

在合肥先进光源（HALF）建设中,由低温超导材料组成的真空部件被大量使用,尤其是超导高频腔。超导腔以高加速梯度、低束流阻抗、高无载品质因数和低运行成本等特点,成为21世纪国际上拟建的大型加速器的首选。而超导腔和低温真空室内表面的二次电子发射可能会引发电子云（EC）现象。超剂量的二次电子倍增功率沉积会引起低温区域热负载增加、超导腔失超等现象,因此降低超导高频腔内二次电子发射成为合肥先进光源设计过程中的巨大挑战。在常温材料二次电子产额（SEY）测试系统的基础上,作者自主研发设计低温样品架结构,使液氦流经样品台并通过热传导冷却样品,计算漏热来反推所需要的制冷量和液氦的消耗速率。在系统集成调试后进行降温性能测试,搭建了低温材料二次电子测试系统。