Minimum heat pulse to quench a superconducting magnet

The minimum energy required to quench a fully impregnated superconducting winding has been measured at a constant field of 5 T for various currents. Great care has been taken to match the experimental conditions with those presumed in the minimum propagating zone (MPZ) treatments of the situation. In particular the winding has been designed so that the MPZ is smaller than the heat source thus satisfying the requirement for a point disturbance. The adiabatic requirement has been met with an inductive heating technique in place of the usual resistive heating. As a consequence of these features the minimum quench energies are much smaller than those obtained in previous experiments and agree well with Wilson's theoretical treatment for a point disturbance.     

A NbTi 10T 388mm bore magnet working at 1.8K in pressurized superfluid helium

A new high field test facility has been constructed for overall property measurements of the conductors developed for the superconducting coils of the TORUS II Tokamak project proposed by the EURATOM-CEA Association. This facility features a dc background field of 10 T in a useful volume of 338 mm in diameter and super-imposed pulsed fields of various configurations.The present paper describes the design, construction and operation of the 10 T field coil system in its pressurized superfluid helium cryostat.     

Quench back in thin superconducting solenoid magnets

Superconducting magnets with well coupled, low resistance, secondary circuits have been observed to become fully normal faster than quench propagation in the coil would permit. This process is referred to as ‘quench back’. Quench back observed at the Lawrence Berkeley Laboratory (LBL) was caused by heating the secondary circuit from the current induced from the primary circuit as normal region in the superconducting coil propagated. This paper develops the theory for thermal quench back in thin solenoid magnets and compares this theory with measurements made in two one-meter diameter superconducting solenoid magnets.     

Sweeping a persisting superconducting magnet with a transformer

A method for sweeping a persisting superconducting magnet is described. The field sweep is achieved by including in the superconducting loop of the magnet a coil which acts as the secondary coil of a transformer. Variation of the current in the primary coil of the transformer, controlled from outside the cryostat, causes the field-sweeping action through flux-linking with the superconducting loop. Compared by the ratio of the magnet's inductance to the transformer's inductance. The advantages of using an all-metal vacuum-tight superconducting feedthrough are discussed.     

Fabrication experiences and performance tests of the coal-fired flow facility superconducting dipole magnet

The Argonne National Laboratory has designed, constructed and tested a large aperture superconducting MHD magnet for use in the coal-fired flow facility at Tullahoma, Tennessee. The magnet generates a peak on-axis field of 6 T in a MHD warm bore of 80 cm diameter at inlet, 100 cm diameter at outlet, and 300 cm effective length. The stored energy of the magnet is 210 MJ, the cold mass (4.2 K) is 131 metric tons and the ampere-turns, 13.7 × 10⁶. The final design of the magnet will be briefly introduced. Described in detail are the experiences of coil winding and coil assembly, the assembly of force-containment superstructure, assembly of magnet cryostat and results of magnet performance tests.     

Application of the acoustic emission technique to the react and wind processed Nb3Sn superconducting magnet

A technique combining acoustic emission and voltage measurement is applied to quench experiments conducted on a newly fabricated Nb₃Sn superconducting magnet. Based on the results, the training mechanism, epoxy potting effect and conductor degradation due to the electromagnetic force are discussed.     

11 T liquid helium-free superconducting magnet

An 11 T liquid helium-free superconducting magnet designed at 6 K in vacuum using high temperature superconducting current leads was developed. The coil was conductively cooled down from room temperature to 4.1 K in 40 h by two 4 K GM-cryocoolers. In a performance test, the coil temperature rose to 6.8 K for the inner Nb₃Sn coil and 5.9 K for the outer NbTi coil, while sweeping the field at 5 A min⁻¹. A central field of 10.7 T in a 52 mm room temperature bore was generated at an operating current of 149 A. Holding the field at 10.5 T was achieved continuously for 24 h at a constant coil temperature of 4.8 K.     

Development of a variable quench pressure relief valve for superconducting magnet system

A new variable quench pressure relief valve (VQRV) for a superconducting magnet system has been developed at the High Energy Accelerator Research Organization (KEK). The VQRV is designed that the setting of the blowout pressure can be freely controlled and be maintenance-free for long-term operation.A prototype VQRV was tested under a high radiation environment up to 2.5 MGy. The heat load of 1.5 W at 4.2 K and a seat leakage rate of 4.5 × 10⁻⁷ kg/s at 4.2 K of the VQRV were confirmed. It has enough performances for the cryogenic system operation in the Japan Proton Accelerator Research Complex (J-PARC) neutrino beam line.The design and test results of the VQRV are described in this technical note.     

The mechanism of frictional motion and its effects at 4.2 K in superconducting magnet winding models

Frictional sliding occurs on both a microscopic and a macroscopic scale. Sliding on a microscopic scale appears as discrete events called microslips. Microslips are inherent in all sliding events and are quite different from macroscopic instabilities such as stick-slips. It is thought that the training effect observed in quench current data from a superconducting braid may be caused by microslips.The mechanisms of sliding motion and its effects at 4.2 K were studied in detail for a number of metal/insulator pairs that model superconducting magnet windings; the results impact the performance of superconducting magnets. Organic surface coating materials are generally effective in eliminating macroscopic instabilities. Instrumentation used in these experiments includes a high-resolution extensometer and an acoustic emission sensor, both with sensitivities capable of detecting microslips (～ 1 μm).     

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.     

Design,development and fabrication of indigenous 30 kA NbTi CICC for fusion relevant superconducting magnet

The fusion relevant superconducting magnet is under development in India using a cable-in-conduit-conductor (CICC) with operating current of 30 kA at 5.5 T and 4.5 K. The 30 kA NbTi based CICC is designed on the basis of desired critical design parameters as well as mechanical fabrication considerations. The 30 kA CICC has been designed having square cross-section (30 mm × 30 mm) consisting NbTi as superconducting cable, SS316LN as jacket material and SS304 foil as wrapping around the cabled strands. The design configuration of 30 kA NbTi CICC has been discussed in this paper. The NbTi base high current carrying strands have been fabricated indigenously using direct extrusion and cold drawing process. The 100 m long NbTi–Cu strands twisting, insertion of cabled strands into a circular conduit has been developed with pull through technology. The welding process qualification and effects of cold work on jacket material at room temperature have been elaborated in this paper. The manufacturing parameters and quality procedures for development of CICC have been successfully established and demonstrated with fabrication of 100 m NbTi based CICC without any technical difficulties.     

传导冷却超导磁体系统真空问题的试验研究

成功研制了6T NbTi 传导冷却超导磁体系统,制冷机为二级GM-制冷机.磁体冷却到4 K需用74 h左右,目前磁体系统已分别完成了115 A(6T),45 h和95 A,264 h的无间断运行实验.制冷机可在长达15天(359 h)的时间里,对系统抽真空并维持系统真空在1.5×10-2 Pa左右,其间不再使用扩散泵对超导磁体系统抽真空.     

35 kJ高温超导磁储能(SMES)的热输运实验研究

研制了中国首台高温超导磁储能直接冷却系统,该系统不使用低温液体(液氦、液氮).在10-3Pa的真空度下,高温超导磁体线圈由1台单级GM制冷机从室温293 K冷却到19 K,Bi2223电流引线由另一台制冷机冷却到77 K以下.整个系统在通140 A直流电流的时候产生了4.5 T的磁场.系统连续运行480 h(20 d),磁体和低温系统各参数动态特性良好.实验研究表明,控制系统的漏热,优化磁体内部导冷结构,有效减少热传导部件的接触界面热阻是制冷机直接冷却高温超导磁体的关键技术.     

Design analysis of a solid nitrogen cooled “permanent” high-temperature superconducting magnet system

Potential performance advantages of a solid nitrogen cooled “permanent” high-temperature superconducting (SN2/HTS) magnet system over a liquid helium cooled low-temperature superconducting (LHe/LTS) system are explored. The SN2/HTS system design includes a second solid heat capacitor that cools a radiation shield. Recooling of the heat capacitors is performed with a demountable cryocooler. The SN2/HTS system offers both enhanced stability and improved portability over a LHe/LTS system.Design codes are constructed to compare the SN2/HTS system design with a LHe/LTS design for a general permanent superconducting magnet system employing a room temperature bore. The codes predict the system volume and mass that should be expected for a given set of design requirements, i.e. field strength and bore size, and a given set of conductor properties. The results indicate that present HTS conductor critical current and index are not yet sufficient for producing SN2/HTS systems of a size that is comparable with that expected for a LHe/LTS system; however, the conductor properties of Bi2223/Ag have been consistently improving, and new HTS conductors are expected to be developed in the near future. The codes are used to determine the minimum Bi2223/Ag conductor performance required for a SN2/HTS system to be competitive with a LHe/LTS system.     

基于液氮冷源超导磁体氦气循环预冷系统设计

为了提高超导磁体300-80 K预冷过程中的降温效率和安全性,开发了一种新的预冷方法.设计了一台以液氮为冷源、氦气为循环介质的可控温预冷装置,对其内部结构进行了优化设计,包括低温风机、板式换热器、气动调节阀、翅片换热器等主要组成部分,整个装置与磁体构成一个闭合循环系统.在预冷装置的作用下,该超导磁体从300 K到80 ...     

A magnetic levitation rotating plate model based on high-Tc superconducting technology

With the wide requirements of the training aids and display models of science, technology and even industrial products for the public like schools, museums and pleasure grounds, a simple-structure and long-term stable-levitation technology is needed for these exhibitions. Opportunely, high temperature superconducting (HTS) technology using bulk superconductors indeed has prominent advantages on magnetic levitation and suspension for its self-stable characteristic in an applied magnetic field without any external power or control. This paper explores the feasibility of designing a rotatable magnetic levitation (maglev) plate model with HTS bulks placed beneath a permanent magnet (PM) plate. The model is featured with HTS bulks together with their essential cryogenic equipment above and PMs below, therefore it eliminates the unclear visual effects by spray due to the low temperature coolant such as liquid nitrogen (LN₂) and additional levitation weight of the cryogenic equipment. Besides that, a matched LN₂ automation filling system is adopted to help achieving a long-term working state of the rotatable maglev plate. The key low-temperature working condition for HTS bulks is maintained by repeatedly opening a solenoid valve and automatically filling LN₂ under the monitoring of a temperature sensor inside the cryostat. With the support of the cryogenic devices, the HTS maglev system can meet all requirements of the levitating display model for exhibitions, and may enlighten the research work on HTS maglev applications.     

40T混合磁体低温分配阀箱真空系统设计

根据40 T稳态混合磁体低温分配阀箱对真空的要求,对低温分配阀箱真空系统进行了设计,设计结果如下:选择阀箱真空室的壳体形状,通过计算确定出真空室壳体壁厚为12 mm;选择封头形状,对封头强度进行校核,确定封头壁厚为16 mm;对整个真空系统抽真空泵机组进行选型,选出粗抽泵机组由一套ZJ-150罗茨泵和2XZ-30旋片式真空泵组成,主抽泵由一套F-100/110分子泵和2X-4旋片式机械泵组成,可达到阀箱对真空度的要求。     

Design, development and experiment of a 1.5 T MgB2 superconducting test magnet

Superconducting magnets using MgB₂ tapes are potentially applicable in many areas, such as medical magnetic resonance imaging and fault current limiting. Under conduction cooling environments, the magnets can work at 15-20 K. In this work, a solenoid structured magnet with ∅ 100 mm bore is designed, built and tested. The maximum field at its center is up to 1.5 T. The field homogeneity, the thermal stability and the quench characteristics in the magnet are also investigated.     

A 17.5 Tesla superconducting concentric Nb3Sn and V3Ga magnet system

A superconducting magnet system has been designed and constructed; it now operates to a field of 17.5 Tesla. The system consists of an outer Nb3Sn solenoid with a 160 mm bore producing 13.5 T, and an inner V3Ga solenoid with a 31 mm bore producing an incremental 4 T. Electrical transients were monitored in the outer magnet during normal transition and compared with predictions. The inner magnet operates close to the critical current of the V3Ga as measured in small coil tests. The magnet system was driven normal several times at a stored energy level of approximately 1.8 Megajoules, activating protective circuitry, designed to safely dissipate the energy released.