冷却高温超导磁体的大冷量单级G-M制冷机

随着高温超导磁体在电工技术方面日益广泛的应用，如高温超导限流器、高温超导变压器、高温超导储能系统等。对工作在30K～40K、并可提供50W～100W制冷量的低温制冷机提出了需求。常规的单、双级G-M制冷机产品不能满足高温超导磁体的冷却要求，本文初步得到了提高单级G-M制冷机性能、增大40K温度以下制冷量的方法，并在一台常规单级G-M制冷机上验证，获得了30W/40K制冷量的好结果，指明了研制这种大冷量G-M制冷机的方向，为成功研制冷却高温超导磁体的大冷量单级G-M制冷机走出了第一步。     

高温超导磁储能(SMES)磁体直接冷却热输运过程研究

随着高温超导材料与低温技术的发展，采用制冷机直接冷却已经成为高温超导应用的发展方向，而界面热阻则直接影响着超导器件的冷却效率和运行可靠性，因此减小和控制低温界面热阻是实现超导系统直接冷却的技术关键。对直接冷却高温超导磁体从室温冷却到49K低温的热输运过程进行了理论分析和实验研究，磁体冷却实验结果和理论分析符合较好，通过直接冷却实验所达到的最低温度特性和过程分析，证实从微结构低温工程学的角度研究界面热阻、探索超导直接冷却最佳热耦合机制是高温超导应用基本而重要的科学问题之一。     

直接冷却中高温超导电流引线的传热研究

降低高温超导电流引线向低温环境的漏热,以及实现电流引线与制冷机冷头导热不导电的直接接触冷却,是制冷机直接冷却超导系统走向应用的关键技术之一。本文提出了高温超导电流引线的基本结构,并对进入制冷机一、二级冷头的漏热进行了理论推导和数值模拟计算。     

高温超导SMES磁体直接冷却的热分析

用G-M制冷机(5W/20K)将Bi2223带材绕制的SMES超导磁体,在10-3Pa真空度下,从常温300K左右冷却到25K,得到了磁体冷却过程速率和磁体温度分布.在实验研究超导磁体降温特性的基础上,对SMES磁体的冷却过程进行了热分析,实验研究表明为使超导磁体有效地冷却和稳定运行,除了减小磁体漏热和其内部发热,有效控制热传导部件间的接触界面热阻是高温超导直接冷却磁储能装置研发应用中的关键技术问题.     

制冷机直接冷却高温超导磁体电流引线优化设计

针对制冷机直接冷却高温超导磁体电流引线的传热特性进行理论分析,对其在不同结构模式下进行漏热计算和比较,找到了大通流(kA级)电流引线结构优化设计方法和电流引线漏热与通电电流的关系式.     

深冷文献消息(国内部分)

20 0 2 310 1　冷却高温超导磁体的大冷量单级Ｇ—Ｍ制冷机龚领会等　《低温工程》　 2 0 0 2　№ 1　 1～ 6随着高温超导磁体在电工技术方面日益广泛的应用 ,对工作在 30～ 40Ｋ、并可提供 5 0～ 10 0Ｗ制冷量的低温制冷机提出了需求。文章初步得到了提高单级Ｇ—Ｍ制冷机性能、增大 40Ｋ温度以下制冷量的方法 ,并在一台常规单级Ｇ—Ｍ制冷机上验证 ,获得了 30Ｗ/Ｋ制冷量的好结果 ,指明了研制这种大冷量Ｇ—Ｍ制冷机的方向 ,为成功研制冷却高温超导磁体的大冷量单级Ｇ—Ｍ制冷机走出了第一步。2 0 0 2 310 2　 4Ｋ以下温区脉管制冷性能的…     

高熵合金凝固用高精度低温超导磁体的研制

根据高熵合金凝固用高精度低温超导磁体的技术要求,研制1套磁场可达10 T,室温直径为100 mm的高精度传导冷却超导磁体。该超导磁体由1组Nb3Sn和4组Nb Ti线圈组成,同时设计并制造了直径650 mm、高612 mm的杜瓦。为降低磁体运行过程中漏热,采用1对150 A高温超导电流引线为磁体供电。磁体总质量388 kg,通过1台1.5 W@4.2 K的G-M制冷机作为冷源,经过62 h,将超导磁体冷却至2.92 K,磁体正常运行电流119.95 A,工作磁场10.001 T,励磁过程中未发生失超,运行稳定。同时,对强磁场下高熵合金的凝固进行实验研究,详细介绍了该超导磁体装置的设计、制造和测试过程。     

我国研制成功首台3．2T传导冷却高温超导磁体系统

中科院电工所研制成功了我国第一台传导冷却高温超导磁体系统。高温超导磁体采用Bi2223高温超导带材制造，系统采用GM制冷机传导冷却，系统的充电速率达到5Ms，在运行电流120A的条件下，产生的中心磁场达到了3．23T。目前，该超导磁体系统已在实验室顺利通过了各种性能的测试，系统运行稳定。     

ITER 10kA高温超导电流引线测试装置低温系统的研究

为ITER CC 10 kA高温超导电流引线服务的低温性能测试装置已研制完成,并成功运行。其低温系统主要由500W/4.5 K氦制冷机,真空杜瓦,低温组件(低温阀门,过冷槽,管道加热器,热防护层),汽化器及低温传输管线等部分组成。本文对真空杜瓦和过冷槽进行设计,并讨论该低温系统的冷却流程方案,最后通过电流引线10 kA稳态实验结果对低温系统的运行效果进行分析,结果表明该低温系统运行稳定,能满足ITER CC电流引线的测试需要。     

50 kA超导变压器杜瓦及高温超导电流引线的设计与优化

CICC超导导体性能测试用50 kA超导变压器由初级线圈和次级线圈组成,初级线圈浸泡在4.2 K液氦低温杜瓦中,次级线圈为CICC导体采用4.2 K/354 637 Pa超临界氦迫流冷却,液氦和超临界氦均由500 W/4.5 K制冷机提供,变压器低温杜瓦的理论液氦蒸发率为1.52 L/h。为减少电流引线漏热,超导变压器采用B i-2223/AgAu高温超导(HTS)二元电流引线,并且在颈管中部设计了一个新型的直接用液氮冷却的热截流装置来截断电流引线高温端的热流;最后对铜电流引线部分进行了尺寸优化计算,得到最佳截面积和直径分别为28 mm2和6 mm。     

制冷机直接冷却的超导磁体系统

研制了制冷机直接冷却的５Ｔ,ＮｂＴｉ超导磁体系统。使用国产４Ｋ级制冷量有０．５Ｗ的ＧＭ制冷机。国产Ｂｉ２２３高温超导体电流引线和国产ＮｂＴｉ超导线。针对传导冷却超导磁体系统的特性,在磁体结构,环氧浸渍,电流引线与制冷机联结结构等做了特殊设计。为了尽量缩短整个系统的冷却时间和解决制冷机的一级制冷量不足,使用了液氮冷却的辐射屏和用液氮预冷磁体的方案。     

Experimental investigation on the detachable thermosiphon for conduction-cooled superconducting magnets

A detachable thermosiphon, as a transient thermal switch for conduction-cooled superconducting magnet, is designed, fabricated and tested. A thermosiphon between the first and second stages of a cryocooler can reduce the cool-down time of a conduction-cooled superconducting magnet by using the large cooling capacity of the first stage. The thermosiphon is a very efficient heat transfer device until all the working fluid in it freezes (off-state). After the working fluid freezes and the second stage temperature becomes lower than that of the first stage, however, the thermosiphon then becomes a conduction heat leak path between two stages of the cryocooler. Considering a very small cooling capacity of the second stage of the cryocooler around 4.2 K, the conduction heat loss is not negligible. Therefore, a detachable thermosiphon, made of a metal bellows, is considered to be able to eliminate such a conduction heat leak. The mock-up magnet is cooled down with the thermosiphon and the thermodynamic states of the thermosiphon and the mock-up magnet are precisely examined during the whole cool-down process. At off-state, the thermosiphon is detached mechanically from the magnet. In this way, the conduction heat leak path through the thermosiphon wall is completely eliminated. This paper describes the detailed transient operation of the detachable thermosiphon using nitrogen as the working fluid.     

Quench protection tests of a cryocooler cooled 6 T NbTi superconducting magnet by an active power method

When a quench occurs in a superconducting magnet, excessive joule heating may damage the magnet. We have presented the quench protection system based on an active power method. Our previous quench protection tests have been carried out for small superconducting magnets whose self inductances are less than several hundred mH to verify principles of our proposed system. In this paper, we present experimental results of quench protection tests of a cryocooler cooled 6 T NbTi superconducting magnet (self inductance 15.5 H), which is a commercial size magnet made by Tamakawa Co., Ltd. We confirmed that our proposed system could inhibit the maximum temperature of the superconducting magnet (initial temperature 4.3 K) after the quench to less than about 44 K at operation magnetic field 5.5 T. Experimental results suggest that our proposed system is useful for practical used superconducting magnets.     

The cryogenic system for ITER CC superconducting conductor test facility

This paper describes the cryogenic system of the International Thermonuclear Experimental Reactor (ITER) Correction Coils (CC) test facility, which consists of a 500 W/4.5 K helium refrigerator, a 50 kA superconducting transformer cryostat (STC) and a background field magnet cryostat (BFMC). The 500 W/4.5 K helium refrigerator synchronously produces both the liquid helium (LHe) and supercritical helium (SHe). The background field magnet and the primary coil of the superconducting transformer (PCST) are cooled down by immersing into 4.2 K LHe. The secondary Cable-In-Conduit Conductor (CICC) coil of the superconducting transformer (SCST), superconducting joints and the testing sample of ITER CC are cooled down by forced-flow supercritical helium. During the commissioning experiment, all the superconducting coils were successfully translated into superconducting state. The background field magnet was fully cooled by immersing it into 4.2 K LHe and generated a maximal background magnetic field of 6.96 T; the temperature of transformer coils and current leads was reduced to 4.3 K; the inlet temperature of SHe loop was 5.6 K, which can meet the cooling requirements of CIC-Conductor and joint boxes. It is noted that a novel heat cut-off device for High Temperature Superconducting (HTS) binary current leads was introduced to reduce the heat losses of transformer cryostat.     

Development of 3kA conduction cooled HTS current lead system

The research and development of superconducting magnet energy storage (SMES) system, a national project, began in 1999. One of the purposes of this project is investigation concerning the application of high-temperature superconducting (HTS) SMES. As a part of this project, the 3 kA class HTS small model coil was manufactured in order to verify the possibility of realizing conduction cooled HTS SMES. Therefore, it is important to develop the conduction cooled current lead system for applying this coil. We developed a kA class conduction cooled HTS current lead system. This current lead system consists of the copper current lead and the YBaCuO (YBCO) HTS current lead. The YBCO bulk manufactured by Nippon Steel Corporation was applied to the HTS current lead. The YBCO bulk keeps high critical current density (J_c > 10,000 A/cm²) in the magnetic field (1 T) at 77 K compared with Bi2223 superconductor. The experiment of this HTS current lead system was carried out, and rated current of 3000 A was achieved successfully.     

Design,fabrication techniques and test results of 1.2 kV/80 A inductive fault current limiter by using conduction-cooled system

An inductive superconducting fault current limiter protects power system by limiting the amplitude of fault current by the inductance of its dc reactor. Therefore, it is very important to design the dc reactor of high critical current prior to fabrication. At first, the optimal design parameters were calculated by using finite element method and then the superconducting dc reactor for 1.2 kV/80 A_rms inductive superconducting fault current limiter was designed by considering the conduction-cooling characteristics. Moreover, the design, fabrication and conduction-cooling method of the superconducting dc reactor were introduced. Actually, the superconducting dc reactor was fabricated and cooled down to 20 K by using GM cryocooler. Finally, the short-circuit test was performed and the experimental results were discussed.     

Development of a Superconducting Magnet System with Zero Liquid Helium Boil-off

A homogeneous magnetic field superconducting magnet with a cold bore of 250 mm and a central field of 4.3 T has been designed, manufactured, and tested with zero liquid helium boil-off. As a result of magnetic field homogeneity considerations, the magnet is composed of three coaxial coils: one main coil and two compensation coils. All coils are connected in series and can be charged with a single power supply. The magnetic field homogeneity is about ±3.0 % from ?200 mm to 200 mm in axial direction with 86 mm in diameter. The magnet can be operated in persistent mode with a superconducting switch. A two-stage GM cryocooler with a capacity of 1.5 W at 4.2 K was used to cool the superconducting magnet. The cryocooler prevents the liquid helium from boiling off and leads to zero helium loss during static operation. The magnet can be operated in liquid helium circumstance by cooling the gas helium with the cryocooler without additional supply of liquid helium. Under this condition, the magnet is successfully operated up to 4 T without quench. The magnet system can be generating 0.25 L/h liquid helium with the cryocooler by supplying the gas helium without loading the magnet. In this paper, the magnet design, manufacture, mechanical behavior analysis, and the performance test results of the magnet are presented.     

Numerical optimization of conduction cooled current leads for low current applications

The basic design principles of current leads for superconducting magnets are well established but HTS materials and conduction cooled systems call for new numerical methods. In this paper the design of current leads was formulated as an optimization problem. Both time integration and finite differencing were examined as possible ways to compute the temperature distribution inside the leads. Three examples about optimization of conduction cooled as well as gas cooled systems are presented. First, the design of tubular normal conducting gas cooled current leads was studied. Second, normal conducting leads cooled with a two-stage cryocooler were examined. Third, the optimization was applied to current leads consisting of HTS tapes at the low temperature end of a normal conducting bar. The study took into account the magnetic field and temperature dependent voltage-current characteristics of the anisotropic Bi-2223 material. The results are compared with traditional analytical ones and the numerical optimization is shown to be an efficient design tool for both normal conducting and HTS current leads.     

Optimal cool-down time of a 4 K superconducting magnet cooled by a two-stage cryocooler

A cool-down time is one of the major factors in many cryocooler applications, especially for the design of conduction-cooled superconducting devices. Cool-down time means a time cooling a thermal mass from a room-temperature to cryogenic-temperature within a stipulated amount of time. The estimation of cool-down time seeks the elapsed time to cool the thermal object by a cryocooler during initial cool-down process. This procedure includes the dimension and properties of thermal object, heat transfer analysis for cryogenic load, thermal interface between cold mass and cryocooler, and available refrigeration capacity of cryocooler. The proposed method is applied to the specific cooling system for 3 T superconducting magnet cooled by a two-stage GM cryocooler. The result is compared with that of experiment, showing that proposed method has a good agreement with experiment. In addition, the initial cool-down time can be shortened by employing thermal link between the cold mass and first-stage of cryocooler. Through a rigorous modeling and analysis taking into account the effect of thermal link size, it is concluded that there exists an optimal cool-down time during initial cooling in conduction-cooled superconducting magnet system.     

Generation of 1 T, 0.5 Hz alternating magnetic field in room temperature bore of cryocooler-cooled Bi-2212 superconducting magnet

Alternating magnetic fields have been stably generated at frequencies up to 0.5 Hz in a room temperature (RT) bore of a Bi-2212 superconducting magnet cooled by a Gifford-McMahon (G-M) cryocooler. The magnet has generated alternating magnetic fields with peak magnetic fields up to 1.0 T. The present Bi-2212 superconducting coil heat-treated in an oxygen partial pressure (pO₂) of 1 atm has shown an alternating current (a.c.) loss characteristic, reducing the intergranular hysteresis loss compared with the heat treatment in pO₂ of 0.2 atm.