The diffusion process of Sn in the transformation of Nb_6Sn_5 to Nb_3Sn has been studied.The experimental results show that the growth of Nb_3Sn laver is controlled by two processes,i.e. the short range diffusion of S...The diffusion process of Sn in the transformation of Nb_6Sn_5 to Nb_3Sn has been studied.The experimental results show that the growth of Nb_3Sn laver is controlled by two processes,i.e. the short range diffusion of Sn which is responsihle for the inner layer with large grains,and the long,range diffusion of Sn which results in the outer layer with fine grains.It was found thai grain size depends on the reaction temperature.A model of Nb_3Sn growth based on the above processes was established and its solution was found to be in good agreement with ex- perimental results.展开更多
The element diffusion process of Nb_3Sn superconductors by bronze route was studied using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The critical current of superconductors was...The element diffusion process of Nb_3Sn superconductors by bronze route was studied using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The critical current of superconductors was measured by four-point method. The results show that a diffusion layer has formed around the boundaries between the filaments and bronze matrix after 15 h heat treatment. The diffusion layer thickness keeps stable after heat treatment duration of 50~75 h. The stable and solid Nb 3 Sn layer is obtained in the sample after 100 h heat treatment. Excessive heat treatment would induce superconductivity degeneration because of superconductor grain coarsening. The characteristics of the element diffusion process were discussed. The diffusion of tin atom is the governing factor in diffusion. In this study, Nb_3_Sn superconductors with good superconducting property were fabricated successfully at 670 °C after 100h heat treatment.展开更多
Boundary conditions constructed by two typical geometrical configurations related to the manufacturing methods of bronze process and tin-rich Nb tube method have been considered in a diffusion model in which the diffu...Boundary conditions constructed by two typical geometrical configurations related to the manufacturing methods of bronze process and tin-rich Nb tube method have been considered in a diffusion model in which the diffusion of Sn in CuSn matrix plays a major role is as- sumed.The dependence of thickness of Nb_3Sn layer on reaction time has been derived.It is shown that the growth rate of Nb_3Sn relates to the configuration of the superconductor,the geometrical parameters of Nb filaments and CuSn matrix.The theory is qualitatively con- sistent with the experimental results.展开更多
Low‐temperature superconducting(LTS)wires are of significant importance in high‐field magnet applications.Current developments of the LTS wires are attributed to many studies.Particularly,Nb_(3)Sn is an attractive s...Low‐temperature superconducting(LTS)wires are of significant importance in high‐field magnet applications.Current developments of the LTS wires are attributed to many studies.Particularly,Nb_(3)Sn is an attractive superconductor with substantial potential for performance improvement in view of an ideal microstructure that maximizes flux pinning properties.To date,various reviews have been reported on the physical properties of low‐temperature superconductors.Therefore,this review focuses on understanding the fundamental phase formations and microstructural controls of low‐temperature superconductors from the perspectives of growth kinetics,nucleation theory,and chemical potentials to facilitate the syntheses of these superconductors and advancement of wire production.Taking Nb_(3)Sn as an example,the effect of Cu addition to Nb_(3)Sn on Nb/Sn reactive diffusion is briefly described.Then,representative Nb_(3)Sn formations are schematically summarized to broaden our understanding of the development behaviors of Nb_(3)Sn.These behaviors are qualitatively reviewed in terms of Sn chemical potential.After mentioning the potential for performance improvement of Nb_(3)Sn,the influences of element additions,specifically those of Zr and Hf additions,resulting in breakthrough microstructural refinements,on Nb/Sn diffusion are investigated.Subsequently,strengthening of the matrix via element additions is reviewed.Thereafter,taking Nb_(3)Al as an example,the features of Nb_(3)Al formation and basic development processes,including low‐temperature processes,metastable phase transformations,and microstructural control,are described.Strain sensitivity,one of the most important properties of Nb_(3)Al,is also briefly reviewed.Then,taking Nb alloy as an example,α‐Ti precipitation in a binary Nb–Ti system is concisely summarized.Subsequently,recently reported new artificial pin incorporation based on a powder method is introduced,followed by a unique study of the application of high‐temperature‐tolerable Nb superco展开更多
In order to verify the feasibility of applying high-Jc Nb_(3)Sn strand in fusion magnet,a full-size cable-in-conduit conductor(CICC)with short twist pitch(STP)cable pattern was manufactured and tested in SULTAN facili...In order to verify the feasibility of applying high-Jc Nb_(3)Sn strand in fusion magnet,a full-size cable-in-conduit conductor(CICC)with short twist pitch(STP)cable pattern was manufactured and tested in SULTAN facility at SPC,Switzerland.Three levels of cyclic electromagnetic(EM)load were applied on the sample stepwise,no visible decrease of current sharing temperature(TcsT was observed until the EM load increased to 80 kA×10.8 T,after that the Tcs decreased dramatically with the EM cycles,which suggested that irreversible deformation,causing a change in the strain state,or even damage has occurred in the superconducting strands.For investigating the reason which caused the conductor performance degradation,the tested conductor was dissected for metallographic observation.Eight segments which subjected to different EM loads were extracted from one of the legs,the geometric feature changes of the cable cross-sections were analyzed and compared.A good correlation was found between the decrease of the Tcs and deformation of the cable cross section.A mass of cracks were found on the sub-elements of strands in the segment which subjected to highest EM load,but the amount of crack is much lower in other segments.Combining the analyses,it is speculated that the critical EM load which causes irreversible degradation is between 850 kN/m and 870 kN/m for this conductor.The results could be a reference in high-Jc Nb_(3)Sn CICC design.展开更多
High-field superconducting magnets are poised to revolutionize technologies,including particle accelerators,magnetic resonance imaging(MRI)machines,and fusion reactors.They stand at the frontier of superconductor inno...High-field superconducting magnets are poised to revolutionize technologies,including particle accelerators,magnetic resonance imaging(MRI)machines,and fusion reactors.They stand at the frontier of superconductor innovation.Nb_(3)Sn wires,which operate at cold temperatures,along with rare-earth barium copper oxide(REBCO)coated conductors that include rare earth elements like Y,Gd,and Dy,are gaining preference.Their high electrical efficiency in strong magnetic fields makes them particularly attractive for such advanced applications.展开更多
Nb_(3)Sn triple‐helical structure is the elementary structure in the superconducting cable of ITER magnets and undergoes prolonged fatigue loading in extreme environments leading to serious damage degradation.In this...Nb_(3)Sn triple‐helical structure is the elementary structure in the superconducting cable of ITER magnets and undergoes prolonged fatigue loading in extreme environments leading to serious damage degradation.In this paper,the fatigue behaviors of the Nb_(3)Sn triple‐helical structure have been investigated by the strain cycling fatigue experiments at liquid nitrogen temperature.The results indicate that Nb_(3)Sn triple‐helical structures with short twist‐pitches possess excellent fatigue damage resistance than that of long twist‐pitches,such as longer fatigue life,slower damage degradation,and smaller energy dissipation.Meanwhile,a theoretical model of damage evolution has been established to reveal the effects of twist‐pitches on fatigue properties for triplehelical structures,which is also validated by the present experimental data.Furthermore,one can see that the Nb_(3)Sn superconducting wires in a triple‐helical structure with the shorter twist‐pitches have a larger elongation of helical structure and less cyclic deformation,which can be considered as the main mechanism of better fatigue damage properties for the triple‐helical structures during the strain cycling processes.These findings provide a better understanding of the fatigue properties and damage mechanisms for Nb_(3)Sn triple‐helical structures in superconducting cables of ITER magnets.展开更多
The composite multi‐filamentary Nb_(3)Sn wire with a high critical current density is a preferred option for fabricating the superconducting magnet beyond the limit of NbTi wire(9–16 T).However,one crucial issue ste...The composite multi‐filamentary Nb_(3)Sn wire with a high critical current density is a preferred option for fabricating the superconducting magnet beyond the limit of NbTi wire(9–16 T).However,one crucial issue stems from the fact that electromagnetic force in superconducting coils is very strong,and the critical physical properties of Nb_(3)Sn,such as Jc,are more sensitive to mechanical strain than those of other possible low‐temperature superconductors.We theoretically investigated the impact of mechanical strain on the thermomagnetic instabilities such as the flux jump(FJ)and quenching of Nb_(3)Sn wire exposed to a static magnetic field and transport current.The good agreements with H formulation or H‐φformulation implemented on COMSOL software confirm the validity of our numerical simulations using home‐made codes.It is discovered that mechanical strain can trigger flux jumps even in a static magnetic field.Furthermore,the threshold value of mechanical strain to trigger the first flux jump is a monotonic function of the static magnetic field in the case of high transport currents,while it is a non‐monotonic function in the case of low transport currents.It is attributed to the fact that flux can be released by the mechanical strain,causing smooth flux penetration before triggering the flux jump.We also present the stable/unstable regions by applying mechanical strain by varying transport current,magnetic field,and working temperature,which helps in avoiding thermomagnetic instabilities while designing the superconducting magnet.展开更多
文摘The diffusion process of Sn in the transformation of Nb_6Sn_5 to Nb_3Sn has been studied.The experimental results show that the growth of Nb_3Sn laver is controlled by two processes,i.e. the short range diffusion of Sn which is responsihle for the inner layer with large grains,and the long,range diffusion of Sn which results in the outer layer with fine grains.It was found thai grain size depends on the reaction temperature.A model of Nb_3Sn growth based on the above processes was established and its solution was found to be in good agreement with ex- perimental results.
基金supported by the National Natural Science Foundation of China(No.50925726)
文摘The element diffusion process of Nb_3Sn superconductors by bronze route was studied using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The critical current of superconductors was measured by four-point method. The results show that a diffusion layer has formed around the boundaries between the filaments and bronze matrix after 15 h heat treatment. The diffusion layer thickness keeps stable after heat treatment duration of 50~75 h. The stable and solid Nb 3 Sn layer is obtained in the sample after 100 h heat treatment. Excessive heat treatment would induce superconductivity degeneration because of superconductor grain coarsening. The characteristics of the element diffusion process were discussed. The diffusion of tin atom is the governing factor in diffusion. In this study, Nb_3_Sn superconductors with good superconducting property were fabricated successfully at 670 °C after 100h heat treatment.
文摘Boundary conditions constructed by two typical geometrical configurations related to the manufacturing methods of bronze process and tin-rich Nb tube method have been considered in a diffusion model in which the diffusion of Sn in CuSn matrix plays a major role is as- sumed.The dependence of thickness of Nb_3Sn layer on reaction time has been derived.It is shown that the growth rate of Nb_3Sn relates to the configuration of the superconductor,the geometrical parameters of Nb filaments and CuSn matrix.The theory is qualitatively con- sistent with the experimental results.
基金supported by the National Institute for Materials Science.
文摘Low‐temperature superconducting(LTS)wires are of significant importance in high‐field magnet applications.Current developments of the LTS wires are attributed to many studies.Particularly,Nb_(3)Sn is an attractive superconductor with substantial potential for performance improvement in view of an ideal microstructure that maximizes flux pinning properties.To date,various reviews have been reported on the physical properties of low‐temperature superconductors.Therefore,this review focuses on understanding the fundamental phase formations and microstructural controls of low‐temperature superconductors from the perspectives of growth kinetics,nucleation theory,and chemical potentials to facilitate the syntheses of these superconductors and advancement of wire production.Taking Nb_(3)Sn as an example,the effect of Cu addition to Nb_(3)Sn on Nb/Sn reactive diffusion is briefly described.Then,representative Nb_(3)Sn formations are schematically summarized to broaden our understanding of the development behaviors of Nb_(3)Sn.These behaviors are qualitatively reviewed in terms of Sn chemical potential.After mentioning the potential for performance improvement of Nb_(3)Sn,the influences of element additions,specifically those of Zr and Hf additions,resulting in breakthrough microstructural refinements,on Nb/Sn diffusion are investigated.Subsequently,strengthening of the matrix via element additions is reviewed.Thereafter,taking Nb_(3)Al as an example,the features of Nb_(3)Al formation and basic development processes,including low‐temperature processes,metastable phase transformations,and microstructural control,are described.Strain sensitivity,one of the most important properties of Nb_(3)Al,is also briefly reviewed.Then,taking Nb alloy as an example,α‐Ti precipitation in a binary Nb–Ti system is concisely summarized.Subsequently,recently reported new artificial pin incorporation based on a powder method is introduced,followed by a unique study of the application of high‐temperature‐tolerable Nb superco
基金supported by the National Key R&D Program of China(Grant No.2017YFE0301404)the Comprehensive Research Facility for Fusion Technology Program of China under Contract No.2018-000052-73-01-001228。
文摘In order to verify the feasibility of applying high-Jc Nb_(3)Sn strand in fusion magnet,a full-size cable-in-conduit conductor(CICC)with short twist pitch(STP)cable pattern was manufactured and tested in SULTAN facility at SPC,Switzerland.Three levels of cyclic electromagnetic(EM)load were applied on the sample stepwise,no visible decrease of current sharing temperature(TcsT was observed until the EM load increased to 80 kA×10.8 T,after that the Tcs decreased dramatically with the EM cycles,which suggested that irreversible deformation,causing a change in the strain state,or even damage has occurred in the superconducting strands.For investigating the reason which caused the conductor performance degradation,the tested conductor was dissected for metallographic observation.Eight segments which subjected to different EM loads were extracted from one of the legs,the geometric feature changes of the cable cross-sections were analyzed and compared.A good correlation was found between the decrease of the Tcs and deformation of the cable cross section.A mass of cracks were found on the sub-elements of strands in the segment which subjected to highest EM load,but the amount of crack is much lower in other segments.Combining the analyses,it is speculated that the critical EM load which causes irreversible degradation is between 850 kN/m and 870 kN/m for this conductor.The results could be a reference in high-Jc Nb_(3)Sn CICC design.
文摘High-field superconducting magnets are poised to revolutionize technologies,including particle accelerators,magnetic resonance imaging(MRI)machines,and fusion reactors.They stand at the frontier of superconductor innovation.Nb_(3)Sn wires,which operate at cold temperatures,along with rare-earth barium copper oxide(REBCO)coated conductors that include rare earth elements like Y,Gd,and Dy,are gaining preference.Their high electrical efficiency in strong magnetic fields makes them particularly attractive for such advanced applications.
基金the National Natural Science Foundation of China(Grant Nos.11602185,11972271,and 12322208)the Young Elite Scientists Sponsorship Program by CAST(Grant No.2020QNRC001)the Fundamental Research Funds for the Central Universities.
基金the National Natural Science Foundation of China(Grant Nos.11427904,12025506,and 12172357)the Key Scientific Instruments Development Program of CAS(Grant No.GJJSTD20210007)the Key Projects of Guangdong Basic and Applied Basic Research Fund Joint Fund(Grant No.2022B1515120051).
文摘中国科学院近代物理研究所正在研发第四代ECR(电子回旋共振)离子源FECR(first 4th generation ECR ion source).以20 kW/45 GHz微波加热运行为目标,需要研制Nb_(3)Sn超导磁体以实现对所加热等离子体的有效磁场约束.作为首台采用Nb_(3)Sn超导磁体技术的ECR离子源,FECR的主磁场线圈由4套独立的轴向螺线管线圈与1套径向六极线圈所构成,且均采用单股Nb_(3)Sn线绕制而成,这给线圈的加工、冷体装配、磁体的失超保护等环节带来一系列挑战.为使磁体能在高场、高应力作用下安全稳定运行,项目采用基于铝壳体结构与bladder&key的预紧应力控制技术,完成了一套半尺寸冷体样机的研发.该样机已完成4.2 K低温测试.本项研究的核心关键问题与挑战是如何在复杂的高精度机械装配与高电流强磁场励磁过程中实现对易碎Nb_(3)Sn导线的有效保护.本篇文章中,我们将阐述如何设计、研制、装配及测试工作于复杂磁场与应力环境的高性能Nb_(3)Sn六极磁铁.针对于单个六极线圈的测试,我们设计研发了一种称为“Mirror”结构的测试工装.论文中会详细论述基于壳层结构与bladder&key的装配预紧技术在半尺寸样机上的应用效果.同时,论文对在半尺寸样机上观察到的强烈磁通跳跃现象和它对失超探测保护的严峻挑战问题及相关解决或规避方案进行相关论述.
基金supported by the National Natural Science Foundation of China(Nos.12232005,U2241267)the Natural Science Foundation of Gansu Province of China(No.23JRRA1118).
文摘Nb_(3)Sn triple‐helical structure is the elementary structure in the superconducting cable of ITER magnets and undergoes prolonged fatigue loading in extreme environments leading to serious damage degradation.In this paper,the fatigue behaviors of the Nb_(3)Sn triple‐helical structure have been investigated by the strain cycling fatigue experiments at liquid nitrogen temperature.The results indicate that Nb_(3)Sn triple‐helical structures with short twist‐pitches possess excellent fatigue damage resistance than that of long twist‐pitches,such as longer fatigue life,slower damage degradation,and smaller energy dissipation.Meanwhile,a theoretical model of damage evolution has been established to reveal the effects of twist‐pitches on fatigue properties for triplehelical structures,which is also validated by the present experimental data.Furthermore,one can see that the Nb_(3)Sn superconducting wires in a triple‐helical structure with the shorter twist‐pitches have a larger elongation of helical structure and less cyclic deformation,which can be considered as the main mechanism of better fatigue damage properties for the triple‐helical structures during the strain cycling processes.These findings provide a better understanding of the fatigue properties and damage mechanisms for Nb_(3)Sn triple‐helical structures in superconducting cables of ITER magnets.
基金support from the National Natural Science Foundation of China(Grant Nos.11972298).
文摘The composite multi‐filamentary Nb_(3)Sn wire with a high critical current density is a preferred option for fabricating the superconducting magnet beyond the limit of NbTi wire(9–16 T).However,one crucial issue stems from the fact that electromagnetic force in superconducting coils is very strong,and the critical physical properties of Nb_(3)Sn,such as Jc,are more sensitive to mechanical strain than those of other possible low‐temperature superconductors.We theoretically investigated the impact of mechanical strain on the thermomagnetic instabilities such as the flux jump(FJ)and quenching of Nb_(3)Sn wire exposed to a static magnetic field and transport current.The good agreements with H formulation or H‐φformulation implemented on COMSOL software confirm the validity of our numerical simulations using home‐made codes.It is discovered that mechanical strain can trigger flux jumps even in a static magnetic field.Furthermore,the threshold value of mechanical strain to trigger the first flux jump is a monotonic function of the static magnetic field in the case of high transport currents,while it is a non‐monotonic function in the case of low transport currents.It is attributed to the fact that flux can be released by the mechanical strain,causing smooth flux penetration before triggering the flux jump.We also present the stable/unstable regions by applying mechanical strain by varying transport current,magnetic field,and working temperature,which helps in avoiding thermomagnetic instabilities while designing the superconducting magnet.
