Analytical and finite element investigations of shear/compression test fixtures

Insulation systems are critical components of the international thermonuclear experimental reactor (ITER). They must meet the super conducting magnets design requirements, including mechanical strength under combined shear and compressive stresses at cryogenic temperatures. Past cryogenic magnet systems often relied on woven glass/epoxy materials for insulation. An important point is to find a reliable shear/compression test method for these materials. The present work investigates a commonly used shear/compression setup and aims at measuring the reliability of the obtained test results. Therefore, the stress and failure analysis is performed analytically and numerically using the finite element method. The model is based on woven glass fiber reinforced materials which are subjected to combined shear and compressive stresses as well as to thermal loading, that results from cooling from 293 K to the test temperature of 77 K. A short analytical section shows the problems of common failure criteria which are used to describe the interaction of the shear and compression stresses. The numerical—finite element—section is based on three-dimensional linear elastic finite element models under thermo-mechanical loading. The locations of high stress gradients are investigated using an average stress criterion. Three different model geometries (15°, 45°, and 70°) are analyzed and finally compared with respect to their reliability.     

磁体用Nb3Sn超导体研究进展

Nb3Sn是典型的低温超导材料,主要应用于高能物理(HEP)和热核聚变(ITER)以及高场核磁共振(NMR)等磁体领域.Nb3Sn材料在2K时的上临界场Hc2达到30T,为其在高场磁体的应用提供了契机.综述了Nb3Sn的发展现状与研究成果,以及近年来其制备工艺的改进和存在的问题.     

运行核电设施在爆破振动激励下新安全标准探讨

针对我国核电基地即将或正在扩建、而前端基础开挖所用爆破产生的振动危害效应会威胁核电设施安全问题,基于分形理论开展核电扩建工程中爆破振动新安全标准探讨,研究成果对进一步规范、约束在运行核电设施附近实施工程爆破方法具有指导意义,为制定国家核电安全规划及确保我国核电安全、高效发展奠定重要基础。     

Development of a lightweight low-current 10 K 4 T magnet for space-flight ADRs

Future space missions will include detectors and other components cooled to cryogenic temperatures by adiabatic demagnetization refrigerators (ADRs) coupled with mechanical cryocoolers. In such systems the ADRs require lightweight, low-current superconducting magnets. At least one of an ADR’s magnets must operate at the cryocooler’s coldest stage temperature. This temperature should be as high as possible in order to improve operating efficiency and design flexibility. We previously reported the development of a lightweight (1 kg) low-current (8 A) Nb₃Sn magnet which produces a 3 T central field at 10 K. We now report our progress in developing a new 10 K magnet of similar size made with smaller diameter Nb₃Sn wire which will produce a 4 T central field with approximately 5 A.     

Investigation of two different types of displacement transducers in the cryogenic environment

This paper presents the investigation of two different types of conventional displacement sensors applied in the cryogenic environment for instrumentation of superconducting fusion magnets and its test facilities. The first one is a wire-wound potentiometer and the second one is a strain gauge displacement sensor. These sensors were tested at different temperature levels between 300 and 6 K. Another test at high magnetic fields between 0 and 9 T was performed as well. The most important sensor properties such as sensitivity, linearity and hysteresis were derived and calculated.     

Superconducting magnet development for fusion at JAERI

The development of superconducting magnets for fusion at the Japan Atomic Energy Research Institute (JAERI) is described. The objective of the project is the Fusion Experimental Reactor (FER) which will be constructed with superconducting toroidal and poloidal coils. For toroidal coils, JAERI has already developed the 8 T Japanese LCT coil and five other large coils (one NbTi and four Nb₃Sn coils, from 7 T to 11 T) for the Cluster Test Programme. For poloidal coils, JAERI has developed three 30–50 kA pulsed conductors. In addition to coil development, cryogenic technology and structural material development are also in progress.     

Recent progress of applied superconductivity in China

China has been involved for many years in the development of superconducting magnets for high energy physics, fusion research, magnetohydrodynamic power generation, magnetic separator, magnetic resonance imaging and other applications. The research activity in superconducting magnets has been intensified and diversified at the Institute of Electrical Engineering, Academia Sinica and other laboratories. This paper reviews the recent progress of applied superconductivity in China. A possible future programme is also outlined in this paper.     

Soviet research in cryogenic technology and applied superconductivity

This paper reviews the achievements of forty years of Soviet research in cryogenic technology and applied superconductivity, including air fractionation, helium liquefaction, refrigeration, superconducting magnet systems, composite conductors, dipole magnets, saddle winding magnets, electrical insulation properties, power transmission, and liquid helium storage and transmission.     

Electrical Conductance of Bolted Copper Joints for Cryogenic Applications

We present the results of electric contact resistance measurements at low temperatures on copper-to-copper bolted joints. Our accurate and systematic data display a rather small dispersion, and may be a useful tool for cryogenic applications like pulse-tubes, dilution refrigerators and nuclear refrigerators.     

A lightweight low-current 10 K magnet for space-flight ADRs

Future space missions will include detectors and other components cooled to cryogenic temperatures by adiabatic demagnetization refrigerators (ADRs) coupled with mechanical cryocoolers. In such systems the ADRs require lightweight, low-current superconducting magnets. At least one of an ADR’s magnets must operate at the cryocooler’s coldest stage temperature. This temperature should be as high as possible in order to improve operating efficiency and design flexibility. Until now all space-flight compatible magnets have been made with NbTi wire, which has limited their operating temperatures to below about 5 K. We have developed a lightweight (1 Kg) low-current (8 A) Nb₃Sn magnet which produces a 3 T central field at 10 K. We explain the choice of this magnet’s specifications and describe its performance testing.     

Miniature Stirling cryocoolers: trends in development

Following a lengthy period of development, Stirling refrigerators have emerged as the preferred system for the miniature cryocoolers used in infrared night-vision, missile guidance systems and other low capacity cryogenic sensors. Single stage expansion integral and split-Sterling refrigerators having capacities of 0.25-1 W at 80 K are in series volume production. They are characterized by increasing reliability (multithousand hours operation). Future preference is anticipated for split-Stirling systems with close tolerance seals replacing rubber contact seals and linear electric motors increasingly preferred as the compressor drive. Present difficulties with the cooler—sensor interface and of fluid leakage will be overcome by manufacture of integrated cooler—sensor units welded leak-proof and having no provision for field servicing. Eventual production is anticipated of throw-away, radio tube like, cryocooler-sensor units capable of plugging in to ambient temperature circuits. Control of compression speed in accordance with load demand will be routine. The use of multistage expansion Stirling cryocoolers for superconducting electronics is anticipated with the development of the high temperature superconducting materials having critical temperatures ≈ 20 K and operating temperatures ≈ 10 K. Availability of a reliable, compact, relatively low cost, 10 K refrigerator would eliminate the need for liquid helium cooling and open possibilities for application of superconducting electronics on a broad front for diverse military and civil purposes.     

Experimental tests and modeling of the optimal orifice size for a closed cycle He sorption refrigerator

Closed cycle ⁴He sorption refrigerators are an increasingly popular choice for remote cryogenic operations. The presence of a superfluid film on the inner walls of the evaporation pot limits their performance. We present a simple model of the gas, film, and heat flow in a ⁴He sorption refrigerator, taking into account the effects of an orifice to limit superfluid film flow. The model serves as a useful guideline for optimizing cryogenic performance. We also present a diagram of hold time vs. steady state temperature as a function of the radius of the orifice and compare the model to measurements.     

Magnet-Technology Development at the Dresden High Magnetic Field Laboratory

The Dresden High Magnetic Field Laboratory (HLD) is a user facility which provides scientists with the possibility to perform a broad range of experiments in pulsed magnetic fields. Recent progress in the magnet-technology development at the HLD has led to significant advances in achieving non-destructive pulsed magnetic fields close to the megagauss mark. Using 9.5 MJ dual-coil magnets with 16 mm bore, in 2011 a world-record field of 91.4 T has been achieved. Later 94.2 T have been reached. We report on the magnet design and performance of these magnets as well as on the design for the next generation of dual-coil magnets characterized by interchangeable inner sub-coils and improved control of the axial preload.     

Worldwide cryogenics — United Kingdom Superconductivity at IRD

Activities associated with superconductivity at the International Research and Development Company are described. The development of superconducting machines is followed and their installation in ships is predicted for 1980. The company's involvement with magnets for fusion research is mentioned together with a project to manufacture and test a fault current limiter.     

Cryogenic system design of the next generation infrared space telescope SPICA

The Japanese infrared space telescope SPICA mission, following the successful Akari mission, has been studied at the concept design phase in international collaboration with ESA under the framework of the ESA Cosmic Vision 2015-2025. The SPICA spacecraft is to be launched in 2018 and transferred into a halo orbit around the Sun-Earth L2 to obtain a stable thermal environment where the IR space telescope’s large mirror of 3 m-class in diameter can be cooled to <5.5 K with mechanical coolers and effective radiative cooling with no use of stored cryogen. The SPICA’s large and cold telescope is expected to provide unprecedented scientific observation optimized for mid-IR and far-IR astronomy with ultra-high sensitivity and excellent spatial resolution during a nominal mission life of 3 years (goal 5 years). Thermal and structural analyses show that the obtained design of the SPICA cryogenic system satisfies the mission requirement. Mechanical coolers for the 4.5 K stage and the 1.7 K stage, which have been continuously developed, have a sufficient cooling capacity with low power consumption to lift the heat loads from instruments and parasitic heat loads. As a result, it is concluded that the concept design of the SPICA cryogenic system is confirmed for the initial cooling mode after launch and the nominal operation mode.     

US Navy programme in small cryocoolers

If superconducting and cryogenic electronic instrumentation are to be deployed in future US Naval operational systems, there is a strong need for compact, highly reliable cryogenic refrigerators. Accordingly, several years ago, a programme was initiated to develop fractional-watt cryocoolers capable of operating below 10 K. Several varieties of Stirling coolers have been built and are under evaluation. In addition, helium gas compressors designed for use with small, closed cycle Joule- Thomson coolers are under development. An overview of the technical aspects of the programme are presented.     

Effect of different treatments of copper surface on its total hemispherical absorptivity bellow 77 K

Total hemispherical absorptivity of copper surfaces treated with standard industrial methods was measured in dependence on the temperature of thermal radiation, varying from 25 K to 300 K. The sample temperature was typically from 5 K to 40 K and did not exceed 70 K. Usability of chemical and mechanical Cu surface finishing as well as Cu plating with Ni and Au for cryogenic design is discussed. As an example of practical application of our results, the cryogenic design of a LN₂ trap is presented.     

斯特林低温制冷机的研究与发展

介绍了近40年来斯特林循环低温制冷机从整体式到分置式结构、从旋转式压缩机到直线式驱动、从普通轴承到板弹簧柔性支承、从机械驱动排出器到气动控制等一系列变化和发展,叙述了中国低温斯特林制冷机从无到有、从仿制国外产品到自主创新、从单件研制到批量生产的历程,展示了中国近年取得的最新成就,指出建立和发展一支具有国际前沿水平的研究队伍和研究基地的重要性.在新世纪,为了满足中国空间和地面红外技术不断增长的需要,研制各种类型的高质量线性驱动压缩机、开发低温制冷机用的精密电子控制技术、批量生产长寿命的微型斯特林制冷机,是一项重要任务.     

低温工程领域的新机遇

简要介绍和讨论了低温工程领域3个令人兴奋的进展。首先描述了提高电-燃气轮机混合驱动飞机性能的两个机会:采用超导电机或定子实现超过30kW/kg的推重比,或者使用含液化天然气的混合燃料。第二个机遇是基于氢燃料电池汽车,扼要给出了氢燃料电池汽车在商业部门的快速发展情况,液氢的供应和运输是氢燃料电池汽车相关基础设施的重要组成部分。第三探讨了小型等离子体热核反应装置的新兴发展情况,等离子体热核反应将在未来10到15年成为人类重要的清洁能源来源。由于小型等离子体热核反应装置依赖于工作在超高磁场强度的高温超导磁体,所以它将为低温工程领域带来一系列创新的机会。