高能加速器中的低温超导技术

 高能物理与低温物理本是两个独立的研究领域,在各自的能量区域里并没有重叠.然而低温制冷和低温超导技术在高能物理和高能加速器中,显示了相当高的应用价值.     

超导及其军用前景

 1911年荷兰科学家昂内斯(Ｈ.Ｋ.Ｏｎｎｅｓ)在测量汞电阻实验中发现了超导,从此,超导走进人类社会。超导体处于超导态时电阻率为零,且具有完全抗磁性,正由于它这不同寻常的特性,潜藏着无比广阔的应用前景,几十年来吸引着大批科学家孜孜不倦地探索它的奥秘。近年来超导研究飞速发展,不少国家在实用化超导技术的开发应用中取得累累硕果,大批超导产品纷纷问世。据国际超导产业技术研究中心等机构预测,到2020年,超导产业在电子和医疗等领域将发挥重要作用,会发展成1500亿美元的巨大国际市场。     

超导质子直线加速器的分段研究

对超导直线加速器的分段进行了详细的研究.包括超导加速器的分段原则的讨论,对称性分段和非对称性分段的讨论.超导加速腔的加速单元数及设计值β_G的确定,加速器的能量增益的确定.     

230MeV质子回旋加速器超导线圈拉杆结构研究

该院承研的230Me V质子回旋加速器是中核集团在研的质子治疗系统的核心装置。230Me V质子回旋加速器具有常温铁轭与4叶片螺旋扇磁极结构,采用超导线圈励磁,具有结构紧凑、运行功耗低的特点。230Me V质子回旋加速器的超导线圈通过拉杆在低温恒温器中进行定位和位置调节。拉杆按照周向位置分4组共12根,每组包括轴向向上、轴向向下、径向3个方向的拉杆。分析了拉杆结构以确保拉杆中各零件满足强度要求,研究了拉杆的调节方法和步骤,并在超导线圈降温过程中对拉杆进行了调节。通过对拉杆结构的研究,保证了超导线圈与常温主磁铁的相对位置关系,为回旋加速器质子束流的顺利引出提供条件。     

20T混合磁体超导线圈的研制和性能试验

我国第一个稳态强磁场装置——合肥20T 混合磁体系统正在建造中.装置中的超导线圈已经绕制完成并作了性能试验.这是一个口径为320mm 的密绕线圈,其中心磁均高于8.3T,储能超过2MJ.本文报道了线圈的设计,绕制和实验结果.     

美妙的超导应用

 超导态是物质的一种独特状态,它的新奇性,立刻使人想到将它用到技术上。自20年代起,人们对超导应用的热情总比对超导机理研究要高;到80年代高温超导材料问世后,这种热情就更为炽烈。目前超导的应用正在许多领域里迅速发展,其景况十分美妙和诱人。     

超导Wiggler磁体实验

本给出了超导Ｗｉｇｇｌｅｒ磁体的初步实验结果，讨论了的心对磁场的贡献，提出了磁体性能改善的措施。     

直线加速器超导段故障补偿的人工智能算法研究

强流直线加速器的长时间稳定运行是该领域的难点和前沿课题之一。以加速器驱动嬗变研究装置(CiADS)的加速器为例,利用TraceWin软件模拟的虚拟加速器数据,提出了基于人工智能算法的超导腔失效的分段故障补偿方法。当有腔体故障时,故障腔的相邻器件将用于重新匹配束流包络,而所有下游腔均可用于补偿束流能量。与传统的优化方法相比,该方法可实现低能耗的超导腔段的故障补偿,具有计算速度快、普适性强等优点,为实际应用器件故障补偿提供了新的可行性。     

国内外加速器低温系统近况

超导腔和超导磁体是现代加速器的重要组成部分, 伴随着加速器技术的发展和更高束流能量和亮度的要求, 低温超导技术在加速器中得到了广泛的应用. 本文在对国内外几个典型的加速器上采用的低温超导技术进行了调研的基础上, 介绍了国内外加速器低温系统的近况.     

Superconducting linac and associated accelerator development at NSC

There has been significant progress in the programme to develop a superconducting linear accelerator as a booster for the Pelletron accelerator at the Nuclear Science Centre. This paper presents the current status of the development in all the major components of the accelerator.     

国内外加速器极高真空技术进展

介绍了国内外要求在极高真空条件下运行的部分粒子加速器概况; 极高真空系统材料选择和处理工艺方面的进展; 真空获得设备的选择和抽气方法的创新性进展; 极高真空条件下的检漏方法研究及极高真空度的测量和校准现状.     

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.     

Some experiences with BEPCII SRF system operation

The Superconducting Radio Frequency(SRF) system of the upgrade project of the Beijing Electron Positron Collider(BEPCII) has been in operation for almost 8 years.During operation,many problems have been encountered,such as excessive heating of the power couplers,frequent beam trips during high intensity colliding,false arc interlock trigger and so on.Among them,some has been solved successfully,some have been alleviated.This paper will describe some experiences with BEPCII SRF system operation,including the symptoms,causes and solutions of problems.     

拓扑材料中的超导

近来,人们在凝聚态体系中发现了由拓扑不变量定义的物相,其中最重要的有拓扑绝缘体、拓扑半金属和拓扑超导体等.这些物相的拓扑性质由非平凡的拓扑数描述,相应的材料被称为拓扑材料,具有诸多新奇的物理特性.其中拓扑超导体由于边界上有满足非阿贝尔统计的Majorana零能模,成为实现拓扑量子计算的主要候选材料.除了探索本征的拓扑超导体外,由于拓扑性质上的相似性,在不超导的拓扑材料中调制出超导自然成为了实现拓扑超导的重要手段.目前,人们发展了栅极调制、掺杂、高压、近邻效应调制和硬针尖点接触等多种技术,已经成功地在许多拓扑绝缘体和半金属中诱导出了超导,并对超导的拓扑性和Majorana零能模进行了研究.本文回顾了本征拓扑超导候选材料,以及拓扑绝缘体和半金属中诱导出超导的代表性工作,评述了不同实验手段的优势和缺陷、分析了其超导拓扑性的证据,并提出展望.     

射频超导腔的研究新进展

射频超导谐振腔已经大规模地应用到粒子加速器领域,其优越之处在于它可以在CW模式或长宏脉冲模式下,提供高的加速梯度。射频超导已经成为自由电子激光和能量回收直线加速器的关键技术。经过30多年的研究发展,解决了超导腔的热崩溃、场致发射等诸多关键问题,目前加速梯度已经超过40 MV/m。高加速梯度的获得是射频超导领域的前沿热点,电抛光＋低温热处理技术使射频超导腔的加速梯度提高3～4 MV/m。最新发展起来的超导腔的干式处理可以改善超导腔的表面状况,提高超导腔的Q值,抑制次级电子发射效应,有可能成为提高超导腔性能的又一有效手段。     

Effects of the Next Nearest Neighbor Hopping on Superconductivity and Antiferromagnetism of Gossamer Superconductivity

The two dimensions hole-doped t-t '-J-U model was studied based on the Gutzwiller approach and the renormalized mean-field theory.The phase diagrams of gossamer superconductors and the effects of the next-nearestneighbor hopping(t ') on superconductivity and antiferromagnetism based on the t-t '-J-U model were investigated.The results show that the qualitative feature of the phase diagrams in the t-t '-J-U model is the same as in the case of the t-J-U model.The antiferromagnetic order coexists with the d-wave superconductivity(dSC) in the underdoped region below the doping δ≈ 0.1 and is enhanced by the t '.The dSC order is slightly suppressed by t ' in the underdoped region and greatly enhanced in the overdoped region.The dSC order is pushed to a larger doping region and the coexistence region of the AF and dSC extends to higher doping.     

Superconductivity in ultrasmall metallic grains

We review recent experimental and theoretical work on superconductivity in ultrasmall metallic grains, i.e. grains sufficiently small that the conduction electron energy spectrum becomes discrete. The discrete excitation spectrum of an individual grain can be measured by the technique of single‐electron tunneling spectroscopy, and reveals parity effects indicative of pairing correlations in the grain. After introducing the discrete BCS model that has been used to model such grains, we review a phenomenological, grand‐canonical, variational BCS theory describing the paramagnetic breakdown of these pairing correlations with increasing magnetic field. We also review recent canonical theories that have been developed to describe how pairing correlations change during the crossover, with decreasing grain size, from the bulk limit to the limit of few electrons, and compare their results to those obtained using Richardson's exact solution of the discrete BCS model.     

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.