The Shanghai High Repetition Rate XFEL and Extreme Light Facility (SHINE), under construction, will use 40 vacuums superconducting undulators (SCU) to generate linearly polarized free-electron lasers. Its magnetic field measurement system relies on the Hall probe method, featuring components like a Hall probe sledge, laser positioning, vacuum chambers, motion control, and data acquisition. At 4K, as the sledge moves, the system performs precise magnetic measurements. The paper discusses the magnetic field measurement system, the low-temperature calibration of the Hall probe and recent experimental data.

In order to provide hard X-rays with a 1.5 GeV electron ring, a new superbend-magnet will be used in middle of each standard cell at Wuhan Advanced Light Source (WALS). Design, assembly, and detailed magnetic measurement of the prototype have been finished. The results of magnetic measurement show that central magnetic field reaches 3.67 T in a gap of 14.72 mm, and the range of high field region (>3.5 T) is larger than 40 mm in the longitudinal direction. The uniformity of the magnetic field integrals is below 5 × 10 −4 within the good field region.

上海硬X射线自由电子激光装置（SHINE）的一台磁体长度为4 m、周期长度16 mm、磁气隙为5 mm的超导波荡器样机目前已完成集成和测试。本文针对这种超小间隙的超导波荡器，提出了一种基于双霍尔探头的磁场点测量方法，描述了其测量原理，并对样机做了磁场测量和优化实验。通过分段调节其2 m段超导磁体的激磁电流对磁场进行优化，使该段在100 A激磁电流下的相位误差小于5°满足设计要求。实验结果表明了本文提出的磁场测量和优化方法是有效的。

A superconducting undulator (SCU) prototype with a magnet length of 4m is being developed for the SHINE (Shanghai High Repetition Rate XFEL and Extreme Light Facility) project. The period length of the undulator is 16mm, the period number is 250, and the pole gap is 5mm. A point measurement system with three Hall probes will be used to measure the magnetic fields in the gap. The Hall probes fixed on a sledge will experience temperatures of about 4.2K to 50K when they move through the undulator gap. A temperature-dependent calibration system for these hall probes is necessary. The paper introduces the configuration of the cryogenic calibration system, and the result for the sensitivity and nonlinearity of one Hall probe from 2.8K to 300K over a magnetic field range of ±1.9T.

Starting in the autumn of 2022, the Shanghai soft X-ray Free-Electron Laser User facility (SXFEL-UF) is open for users. SXFEL-UF has two undulator lines: a SASE line and a Seeding line, which generate FEL radiation with the shortest wavelength of about 2 nm and 3 nm, respectively. A total of 31 undulators of diverse types have been installed, including eighteen hybrid permanent magnet undulators (PMU), ten hybrid in-vacuum undulators (IVU), two APPLE II elliptically polarized undulators (EPU), and an electromagnet wiggler (EMW). An Apple III EPU is under development and scheduled for installation in the spring of 2024. This paper presents an overview of various types of undulators at SXFEL, encompassing their main parameters, design, and magnetic field performance.

The accelerators of Wuhan Advanced Light Source (WALS) consist of a 1.5 GeV Linac, a 1.5 GeV storage ring (SR), and a single beam transport line. Due to the limited longitudinal space, the SR lattice incorporates many combined function magnets to optimize beam optics and minimize emittance. These magnets include horizontal and longitudinal gradient dipoles (LGB), electromagnetic and permanent hybrid dipoles (HYB), and anti-bending single-sided dipole-quadrupole magnets (ABM). This paper introduces the key designs and challenges of these magnets, and it also presents the field measurement results of prototypes for the HYD and ABM.

BackgroundIn the Shanghai High Repetition rate XFEL (X-ray free electron laser) and Extreme Light (SHINE) facility, the vertical linear polarization laser is generated by using 40 planar superconducting undulators (SCUs) with a period length of 16 mm, length of 4 m, and a gap of 4 mm. At present, the Hall probes are the most reliable method for measuring the undulator magnetic field whilst the positioning accuracy of the sensitive center of the Hall probe is one of the main factors affecting the accuracy of magnetic field measurement.PurposeThis study aims to calibrate the position of the Hall probes' sensitive region for magnetic field measurements of SCU with high-precision.MethodsThe experimental platform for magnetic field point measurement of SCUs was introduced in details, a sledge with three mounted Hall probes and a retro-reflector were applied for magnetic field measurement. By flipping the sledge, the lateral distance between the sensitive centers of the Hall probe and each other were obtained, so did the lateral distance between the sensitive centers of the Hall probe and the apex of the pyramid prism. Therefore, the position of the Hall probes' sensitive region and center of the retro-reflector were calibrated.Results & ConclusionsThe positional calibration of the Hall probes has an accuracy higher than ±10 μm, which meets the requirements for magnetic field measurement.

针对目前多极磁铁孔径越来越小的发展趋势,搭建了一种基于单根伸展线法(Single Stretched Wire Method,SSWM)的磁测系统,该系统的主要优势是测量域所需空间小且运动模式灵活.基于该系统的优势及四极磁铁磁场分布的特点,尝试使用双曲线轨迹对四极磁铁靠近其四个极头的区域进行了扫描测量,并根据矢势在测量点分布的特性,提出了一种全新的数据分析方法,用以分析四极磁铁的梯度积分和高阶场误差.用该系统对一孔半径为11 mm、梯度大于100 T·m?1的四极磁铁进行测量,测量结果表明高阶场误差测量重复性好于±1.5×10?4,能满足小孔径高梯度四极磁铁的磁场测量要求.

A planar superconducting undulator (SCU) prototype with the magnetic length of 4 m and the magnetic gap of 5 mm is being developed for Shanghai High Repetition rate XFEL and Extreme Light facility (SHINE) to generate vertical linear polarization FELs. The magnetic field measurement device based on Hall probes has been built for the SCU. Three Hall probes mounted on a sledge are used to measure the magnetic field in the undulator gap. The three-dimensional positioning system based on the Gaussian laser beam for the sledge and the Hall probes is presented in detail in this paper.

High gradient quadrupoles are key components for advanced synchrotron radiation light sources. This paper presents the magnet design, the mechanical structure and the magnetic field measurements of a novel high gradient quadrupole magnet. This high gradient quadrupole magnet with a gradient greater than 100 T/m uses permanent magnets (PMs) on the poles to improve the excitation efficiency. The magnetic field measurement results show the feasibility of this magnetic design.

针对斯特林制冷循环内膨胀腔与压缩腔温度差异较大导致采用闭口系统分析与实际情况偏差较大的问题,本文将产生实际制冷能力的膨胀腔视为开口系统,并对其进行制冷能力分析.结果表明,工质的制冷能力可用气缸内工质体积对压力的积分表示,膨胀腔的实际制冷能力可用工质的制冷能力减去工质进出膨胀腔的焓差表示;影响工质体积对压力积分的主要因素为活塞面积比n、膨胀腔相位领先角ψ与膨胀腔温度Te;当压缩腔温度为320 K、膨胀腔温度为80 K时,活塞面积比在4左右时会获得最优的制冷效率.所得结果可为斯特林制冷循环的设计与优化提供依据.

BackgroundSuperconducting undulator (SCU) prototype with small magnet gap of 5 mm, long magnet length of 4 m and high magnet field of 1.58 T was being developed at Shanghai High Repetition rate XFEL and Extreme light facility (SHINE). Compared to any other superconducting undulator, there is no cryocooler being installed on the cryostat in this SCU prototype.PurposeThis study aims at the cooling design for the binary current leads for SCU's normal operating.MethodsBinary current leads composed of normal conductive copper leads and high temperature superconducting current leads (HTS) were adopted for SCU to connect superconducting coils inside the cryostat and outer cables. Low-temperature helium gas was used to transport independent refrigerator system to the cooling tubes inside the prototype, hence the binary current leads were cooled. Thermal conduction components installed on the middle of the thermal shield were employed to transfer heat load of normal conductive copper leads, and heat load of copper leads was optimized by simulation. Auxiliary superconducting rods were designed for connecting cold ends of HTS in the cryostat test.ResultsThe temperature difference between hot ends of HTS and low-temperature helium gas is less than 20 K from the result of cryostat test, all binary current leads is operating normally with full current.ConclusionsIt is practicable to use cooling tubes with low-temperature helium gas to cool binary current leads of the SCU prototype by thermal conduction, which is different from cooling solution for current leads in any other SCU being developed presently.

为解决超导波荡器磁体采用G-M制冷机传导冷却温度不均匀的问题,采用以G-M制冷机为冷源、将氦为传热工质冷却超导波荡器.通过采用两台E415制冷机预冷氦气并积液冷却磁体的方式,将氦槽内压力调节至1.6 bar-1.9 bar的工况下,可在制冷机开启55 h后将磁体从室温冷却至4.5K,在75 h后在氦槽内完成积液50％的目标,并在87 h后将磁体冷却至3.8K下稳定,磁体与冷头的温差约0.3K,验证了系统利用氦气冷凝积液作为传热工质并冷却超导波荡器磁体的功能.

为进一步研究斯特林循环内回热器换热过程对系统性能的影响,建立气缸的等温换热过程模型,以容积为1 L、初始压力为500 kPa的理想气体为工质,计算分析了循环内工质经等容回热过程对系统内参数和各部件的影响.结果表明,在工质从303 K等容吸热升温至973 K的过程中,系统压力升高,压缩腔内工质密度从5.75 g/m3增加至18.5 g/m3,膨胀腔内工质密度从1.75 g/m3增加至5.75 g/m3,压缩腔与膨胀腔需对外释放的热量分别为364和824 J;回热器在工质等容吸热前后的换热量为工质的焓差,而不是工质的内能差.

为消除在线运行时超导波荡器内束流热负荷对超导磁体的影响,并给储存环提供高真空环境,为波荡器安装了一套束流室并对其隔热效果进行研究.通过将波荡器安装至储存环内,实验对比测试了带束流与不带束流时波荡器内束流室与磁体的温度变化情况.结合G-M制冷机的工作特性,利用热平衡法测出了 200 mA流强的束流对束流室和磁体产生的热负荷.实验结果显示,通束流后,束流室温度从17.2 K上升至28.3 K,磁体温度从4.3 K上升至4.4 K,束流在束流室上产生的热负荷为17.4 W,在磁体上产生的热负荷为0.2 W.表明束流室可有效屏蔽束流热负荷对磁体的影响,并使磁体工作在4.5 K以下.

The Shanghai soft X-ray Free-Electron Laser facility (SXFEL), which is the first X-ray FEL facility in China, is being constructed in two phases: the test facility (SXFEL-TF) and the user facility (SXFEL-UF). The test facility was initiated in 2006 and funded in 2014. The commissioning of the test facility was finished in 2020. The user facility was funded in 2016 to upgrade the accelerator energy and build two undulator lines with five experimental end-stations. The output photon energy of the user facility will cover the whole water window range. This paper presents an overview of the SXFEL facility, including considerations of the upgrade, layout and design, construction status, commissioning progress and future plans.

BackgroundHigh gradient quadrupole magnet has become a key element with the development of diffraction-limited storage ring for the fourth generation light source. The gradient of magnetic field of a quadrupole magnet depends on the inscribed radius, ampere-turns per pole and magnetic efficiency. However, the radius and ampere-turns per pole cannot be reduced or increased indefinitely. Improving magnetic efficiency has become an effective method to improve the gradient of magnetic field.PurposeThis study aims to design a novel magnetic circuit to improve magnetic efficiency and verify the effectiveness by simulation.MethodsPermanent magnets were installed on both sides of the poles face to improve the efficiency of saturated magnets, so as to improve the magnetic field gradient of the quadrupole magnet. A novel high gradient quadrupole magnet, targeted 100 T·m-1, was designed to verify the theory by simulation calculation using Poisson for 2D analysis and OPERA for 3D analysis. The effect to the magnetic field quality of the novel magnetic circuit was optimized to achieve good field region.ResultsSimulation results show the magnetic field gradient of designed novel high gradient quadrupole magnet reaches to 100 T·m-1 when the ampere-turns per pole is about 5400AT. The magnetic efficiency is about 91%. All of the multipole components of magnetic field meet the requirements.ConclusionsThe design of the new quadrupole magnet provides a feasible and effective solution for the design of high gradient quadrupole magnet in the future.

Further reducing the period length will be a very attractive direction for the future development of undulators, and it is one of the effective ways to realize the miniaturization of free-electron laser facilities and obtain short wavelengths. In this paper, a novel planar hybrid permanent magnet undulator is proposed which can obtain a higher peak field with a short period length. The dimensions of the magnet blocks and the poles are numerically optimized for a sample undulator with a period length of 16 mm and a gap of 5 mm. Compared to the conventional hybrid undulator, the effective peak field can be enhanced by about 48%. An eight-period model is built and the result of the magnetic field measurement by a pulsed wire system shows a good consistent with the simulation result.

Shanghai soft X-ray free-electron laser (SXFEL) test facility is the first coherent X-ray light source in China, and its output wavelength is shorter than 9 nm. This free-electron laser (FEL) facility is based on a 0.84 GeV linear accelerator, and its main goal is to develop FEL related technologies and test new FEL schemes, especially the cascaded seeding FEL and short wavelength EEHG FEL. This facility already achieved its design goal and passed the national acceptance in November 2020. Status and main achievements of the SXFEL test facility are introduced in this article.