The MAX IV storage ring project.
The MAX IV storage ring project.
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DOI：
10.1107/s1600577514011503
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发表时间：
2014-09
影响因子：
2.5
通讯作者：
Andersson A
中科院分区：
文献类型：
--
作者：
Tavares PF;Leemann SC;Sjöström M;Andersson A
介绍了MAX IV 3 GeV超低发射度存储环的设计，并描述了如何解决紧凑的多弯消色差晶格带来的技术挑战。目前正在瑞典隆德建造的MAX IV设施配备了两个电子存储环，分别工作在3 GeV和1.5 GeV，分别针对硬X射线和软X射线/真空紫外线光谱范围进行了优化。3 GeV直线加速器既是两个环的全能量注入器，也是短脉冲装置的驱动器，在短脉冲装置中，波荡器产生短至100 f的X射线脉冲。3 GeV环采用多弯消色差(MBA)晶格，在528 m的较短圆周内实现了0.33 nm rad的裸晶格发射度，随着插入器件的增加，发射度降低到0.2 nm rad。MBA格子的工程实现带来了几个技术问题。每个消色差者都有大量的强磁铁，这就需要一个紧凑的设计，其特点是将小间隙的组合功能磁体组合成单元，并共享一个共同的铁轭。小孔导致了低电导真空室的设计，这种设计依赖于真空室本身作为分布式铜吸收器来吸收由同步辐射沉积的热量，而非蒸散性吸气剂(NEG)涂层提供了减少的光解吸产率和分布式泵浦。最后，为产生长束的射频系统选择了较低的主频(100MHZ)，这些长束被被动操作的三次谐波朗道腔进一步拉长，从而减轻了集体效应，既有相干的(例如，阻性壁不稳定性)，也有非相干的(束内散射)。本文以MAX IV 3 GeV环为研究对象，给出了晶格设计以及解决这种设计所带来的挑战的工程方案。作为第一个基于MBA概念的光源实现，MAX IV 3 GeV环提供了一个验证概念的机会，这些概念很可能是未来衍射限制光源的基本成分。
The design of the MAX IV 3 GeV ultralow-emittance storage ring is presented and the implementation of solutions to the technological challenges imposed by the compact multi-bend achromat lattice are described. The MAX IV facility, currently under construction in Lund, Sweden, features two electron storage rings operated at 3 GeV and 1.5 GeV and optimized for the hard X-ray and soft X-ray/VUV spectral ranges, respectively. A 3 GeV linear accelerator serves as a full-energy injector into both rings as well as a driver for a short-pulse facility, in which undulators produce X-ray pulses as short as 100 fs. The 3 GeV ring employs a multibend achromat (MBA) lattice to achieve, in a relatively short circumference of 528 m, a bare lattice emittance of 0.33 nm rad, which reduces to 0.2 nm rad as insertion devices are added. The engineering implementation of the MBA lattice raises several technological problems. The large number of strong magnets per achromat calls for a compact design featuring small-gap combined-function magnets grouped into cells and sharing a common iron yoke. The small apertures lead to a low-conductance vacuum chamber design that relies on the chamber itself as a distributed copper absorber for the heat deposited by synchrotron radiation, while non-evaporable getter (NEG) coating provides for reduced photodesorption yields and distributed pumping. Finally, a low main frequency (100 MHz) is chosen for the RF system yielding long bunches, which are further elongated by passively operated third-harmonic Landau cavities, thus alleviating collective effects, both coherent (e.g. resistive wall instabilities) and incoherent (intrabeam scattering). In this paper, we focus on the MAX IV 3 GeV ring and present the lattice design as well as the engineering solutions to the challenges inherent to such a design. As the first realisation of a light source based on the MBA concept, the MAX IV 3 GeV ring offers an opportunity for validation of concepts that are likely to be essential ingredients of future diffraction-limited light sources.