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Report CopyRight/DMCA Form For : Nb3sn Wire Technology For High Field Superconducting Magnet
of the materials made by different production formation of Cu Sn alloy during the Nb3Sn making. processes the details of which will be described step which minimizes the adverse effect of the work. later hardening that occurs during the wire drawing A. The characteristics required of superconducting direct reaction occurs between Nb and Sn without. wires depend on the apparatuses and applications involving any Cu matrix resulting in a high rate of. including among others factors the critical electric Nb Sn diffusion Hence the powder in tube process. current density hereinafter Jc residual resistance has the advantage that the volume fraction of Nb3Sn. ratio hereinafter RRR mechanical strength can be increased and a high critical current density. and alternate current loss This paper focuses on Jc can be obtained. Jc which is the most important characteristic of The use of Nb alloy tube however results in a. superconducting wires used for high magnetic Nb3Sn core that is larger than that produced by the. field superconducting magnets and provides bronze routed process or by the internal tin process. improvement guidelines for each manufacturing which increases the hysteresis loss when used for. process AC applications, 1 1 Bronze routed process 1 3 Internal tin process. The bronze routed process the bronze means The internal tin process was devised based on. a Cu Sn alloy in this article is a production method the bronze routed process to resolve the limitation. comprising the following making a bundle of a of Sn concentration required for increasing Jc 7 The. multiplicity of hexagonal Cu Sn alloy rods each resulting wire has a cross section with multiple. having a Nb filament core Fig 1 a inserting the Nb cores and Sn alloy embedded in a Cu matrix. bundle into a sheath of oxygen free copper to create Various types of internal tin processes have hitherto. a composite wire drawing the composite and heat been devised and they all commonly use the three. treating the wire drawn composite at 650 750 materials Sn Nb and Cu One of the several wire. thereby producing Nb3Sn compound on the surface making methods includes assembling modules each. of the Nb filament by diffusion reaction 4 This integrating Cu Nb core and Sn alloy in advance. process involves no as is use of Sn which has a low Another method involves assembling together a. melting point and thus enables the extrusion of module combining a Cu and Nb core and another. the billets at high temperatures each billet having module combining Cu and Sn alloy Fig 1 c As in. a large size and weight Hence the bronze routed the case of the bronze routed process heat treatment. process has the advantage of mass productivity is applied such that Nb3Sn is formed on the surfaces. Although historically speaking this is the earliest of Nb cores by diffusion reaction The solid. process to have become industrially feasible issues solubility limit of Cu Sn alloy places no limitation. remain with regards to the cost and Jc characteristic on the supply of Sn which enables the amount of. The Cu Sn alloy used as raw material is more Nb3Sn formation to be increased in order to achieve. expensive than pure metal Sn and Cu Also the alloy high Jc Moreover this production method processes. exhibits significant work hardening during the wire the Cu Nb core and Sn alloy independently without. drawing step requiring frequent annealing to soften involving any material such as Cu Sn alloy that. it In addition the supply of Sn to the diffusion would cause a rapid increase in work hardening and. reaction is limited by the solid solubility limit of thus eliminates the need for frequent intermediate. Sn in the alloy 15 8 This limits the amount of annealing which is the factor increasing the cost. Nb3Sn produced making it difficult to improve the of the bronze routed process It should be noted. Jc characteristic however that hot extrusion cannot be applied due. to the low melting point of Sn hence the process, 1 2 Powder in tube process requires a newly devised technology for volume. production,The powder in tube process for making Nb3Sn. wires comprises the following filling a tube of Nb 2 Improvement of critical current density Jc. alloy with powder containing Sn e g Sn Sn alloy, Sn compounds and Cu placing the tube in a sheath Various Nb 3Sn wires have been developed. of copper and bundling a hexagonal column Fig 1 for apparatuses applying superconductivity. b forming the Cu sheathed composite no figure each having improved characteristics such as Jc. Nb3Sn is formed by Sn contained in the Nb alloy mechanical properties and alternate current loss. tube diffusing into Nb This method results in the depending on the intended purpose The critical. 73 KOBELCO TECHNOLOGY REVIEW NO 34 MAR 2016, current density Jc is the most basic characteristic. of high magnetic field superconductor magnets, since it determines the magnetic field generated by. superconducting magnets,There are three aspects involved in improving. Jc namely i the amount of the Nb3Sn compound,formed ii grain size grain boundary and iii. stoichiometric composition Among them increasing,the amount area ratio of Nb3Sn occupying the. cross section of a wire is the most basic approach. for improving Jc In the case of the bronze routed,process for example the amount of Nb3Sn generated. can be increased by increasing the concentration,of Sn in the Cu Sn alloy and adjusting the area. ratio of the Nb core Fig 2 shows the relationship,between the concentration of Sn in the bronze and. Jc It is revealed that increasing the Sn concentration. increases Jc, Fig 3 SEM images of Nb 3Sn crystals using 13 wt Sn. Next the crystalline structure of the Nb3Sn phase bronze top and 15 wt Sn bronze bottom. which has a significant effect on Jc is considered. Nb3Sn is a type II superconductor which upon, the application of an external magnetic field exceeding 18 T the composition of the Nb 3Sn. allows the magnetic field to penetrate into the phase affects Jc significantly To improve the Jc. superconductor The penetrating magnetic field characteristic in the high magnetic field range. turns into a quantized state called magnetic several measures have been taken including the. fluxes When an electric current flows through the addition of a third element into the Nb3Sn phase and. superconductor the Lorentz force is applied to the the high temperature heat treatment for making the. magnetic fluxes Any movement of magnetic fluxes composition close to stoichiometry 2. in this state generates voltage in the energizing The next section describes the development of. direction causing energy loss Hence practical Nb3Sn wires by the Kobe Steel group. superconducting wires have mechanisms to, suppress the movement of or to fix the magnetic 3 Development of Nb3Sn wires by Kobe Steel group. flux to avoid the loss The fixing of magnetic, fluxes in a superconductor is called magnetic flux As a Kobe Steel group company JASTEC. pinning this function is carried out at pinning manufactures as one of its main products the. centers 10 The major pinning centers for Nb3Sn are superconducting magnets of NMR apparatuses for. its grain boundaries and fine and isotropic crystal chemical analysis and focuses also on the business. grains provide a high Jc characteristic 11 The grain of the Nb3Sn superconducting wires used for this. size changes with the concentration ratio of Nb and application The detection sensitivity of NMR. Sn heat treatment and the like Fig 3 measurement increases proportionally to the 3 2. Moreover in the high magnetic field range power of the magnetic field used The resolution also. increases in proportion with the magnetic field,NMR has been used mainly in the field. of chemistry including the synthesis of organic,compounds however with the recent development. of biotechnology the demand for it is increasing in. the structural analysis of large biomolecules like. proteins Proteins have complicated structures with. large molecular weights hence analyzing their,structures requires NMR apparatuses with high. resolution As a result there is a strong demand for. magnets with a high magnetic field 12 Currently,the superconducting magnets most commonly used. Fig 2 Non Cu Jc versus magnetic field curves of Nb3Sn for NMR have a magnetic field of 9 4 T at median. conductors with shown Sn amount in bronze alloy while the NMR apparatuses for biomolecules use. KOBELCO TECHNOLOGY REVIEW NO 34 MAR 2016 74, superconducting magnets each can generate a resulted in higher Jc at magnetic fields up to the. magnetic field of 14 T or higher The demand for vicinity of 18 T Superconducting magnets designed. high field NMR is strong and a 1 GHz class high contemplating the Jc characteristics at these magnetic. field NMR magnet central magnetic field 23 5 T is fields will have an excellent balance of cost and. being developed The magnetic field to be generated performance The following describes the details of. is close to the upper critical magnetic field Hc2 of each process. Against this background and with application 3 1 Bronze routed process Development of Nb3Sn. to superconducting magnets for high field NMR as wire based on high Sn bronze. a goal JASTEC has tested several superconducting, wires made by the bronze routed process powder The first industrial Nb3Sn wire was produced. in tube process TS PIT and internal tin process by the bronze routed process Kobe Steel group. DT Fig 4 includes cross sectional photographs adapted this process first and continued its. of wires produced by the respective processes and development As a means for increasing Jc the. Fig 5 shows their Jc characteristics Compared with company aimed at increasing the amount of Nb3Sn. the bronze routed process the powder in tube generated in wires and conducted development. process TS PIT resulted in Jc at higher magnetic based on Cu Sn alloy bronze with a high Sn. fields in excess of 18 T while the internal tin process concentration As described above increasing the. Sn concentration in the Cu Sn alloy results in a large. amount of intermetallic compound rendering the,processing difficult To this end the Kobe Steel. group focused on the design of cross sections,that are less susceptible to working and on the. optimization of the process steps including the,wire drawing and heat treatment As a result the. company successfully developed a Nb 3Sn wire,on the basis of a Cu Sn alloy containing 16 Sn. and achieved a Jc of 194 A mm2 at 18 5 T 4 2 K,The superconducting magnet based on this wire. succeeded in generating a high magnetic field,of 22 T in 2000 This magnet was used for NMR. measurement at 930 MHz and the NMR apparatus, achieved the highest central magnetic field at the. 3 2 Powder in tube process Nb3Sn wire made by,TS PIT process. Fig 4 SEM images of Nb 3Sn conductors developed by. Kobe Steel A bronze routed process B power in In order to achieve a high magnetic field for. tube process C internal tin process distributed tin. an NMR apparatus it is particularly important,to improve Jc at high magnetic fields JASTEC. conducted development adapting a type of powder,in tube process called TS PIT 9 In the TS PIT. process powders of Ta and Sn are heat treated for,molten diffusion to produce a Ta Sn compound. which is ground to powder The powder is used,to fill a sheath of Nb Ta alloy to be wire drawn. The idea behind this was that the addition of Ta, would increase the diffusion rate of Sn in Nb which. would increase the amount of Nb3Sn that would be,formed As seen above the powder in tube process. is characterized by the fact that elemental addition is. Fig 5 Non Cu Jc versus magnetic field curves of Nb 3Sn. relatively easy Moreover this process is not limited. conductors with three types of manufacturing by the supply of Sn as in the case of the bronze. processes routed process which enables the Nb3Sn phase to be. 75 KOBELCO TECHNOLOGY REVIEW NO 34 MAR 2016, formed in a large amount resulting in an excellent 3 3 Internal tin process Development of Nb3Sn. Jc characteristic at a magnetic field of 20 T or higher wire based on dispersed tin process. It should be noted however that this process, involves the handling of powder which requires In the case of superconducting magnets for. dedicated facilities Also required are technologies super high magnetic fields the amount of wire used. that are different from the wire drawing of ordinary for an intermediate layer coil located outside the. composite wires innermost layer coil is much greater than that of. In order to demonstrate that the excellent the innermost layer coil affecting the cost more. magnetic field characteristics of Nb3Sn wires made significantly Using a wire based on the powder. by the TS PIT process can be realized on a practical in tube process for these coils is not desirable. scale a prototype 50 kg wire was produced which from the aspect of market competitiveness The. verified a significant improvement of Jc in the high intermediate layer coils require Nb3Sn wires that. magnetic field region cost less than those made by the TS PIT process. The Jc characteristic has improved by 52 and have Jc values higher than that achieved by the. Jc 295 A mm2 at 18 5 T and 4 2 K compared bronze routed process in the high magnetic field. under the same condition with the wires region of approximately 16 18 T JASTEC has been. produced by the bronze routed process used conducting technology development based on the. for the superconducting magnet for NMR at 930 concept that the distributed tin process a type of. MHz previously described Another challenge for internal tin process is suitable for this purpose and. practical applications was the uniformity of the so far has completed prototype production on a. characteristics over the entire length of the wires volume production scale The distributed tin process. since this production method employs powder for is a method involving wire drawing in which an. raw material For evaluating the uniformity of Jc Nb module an array of Nb cores disposed in a Cu. characteristic samples were taken at intervals of 50 matrix and Sn module Sn alloy embedded in a. m from a 500 m long prototype material and the Cu matrix are combined This process allows the. samples were subjected to Jc measurement The amount of Cu matrix to be reduced below that of the. results are shown in Fig 6 The average value of conventional process incorporating Nb and Sn into. Jc was 295 A mm2 while the standard deviation the same module and enables the improvement of Jc. was 10 A mm2 This value is as good as the values That is the one module of Nb and Sn requires a Cu. for the bronze routed process used in practical matrix that promotes the diffusion reaction of Nb3Sn. applications verifying that a uniform Jc was while the distributed tin process allows Nb and Sn. obtained over the entire length In addition a Jc to be distributed which decreases the amount of Cu. of 170 A mm2 was achieved in a high magnetic matrix enabling a high Jc to be obtained. field region 21 5 T Although this value falls Another prototype 50 kg wire was produced. slightly short of 190 A mm2 which is required for using the distributed tin process to verify its. an NMR superconducting magnet for 1 000 MHz performance The resulting Jc was 373 A mm2 at. the results appear promising for the improvement 18 5 T and 4 2 K indicating an improvement in the. of characteristics by the future optimization of the Jc characteristic of 70 or greater compared with the. production process bronze routed process,3 4 Summary. Nb3Sn wires based on three different processes,have been developed for application to magnets. with a high magnetic field As shown in Fig 6, the relationship between Jc and the magnetic field. varies depending on the production processes,Each process has pros and cons and an optimal one. must be selected with reference to specifications,and economy for example Table 1 summarizes. the features of these processes When designing a, magnet with a high magnetic field care is taken to. selectively exploit the wire performance for the most. Fig 6 Jc distribution by PIT process in 500 m long Nb3Sn. conductor economical generation of a high magnetic field. KOBELCO TECHNOLOGY REVIEW NO 34 MAR 2016 76, Table 1 Featured aspects of Nb 3Sn conductors made by References. different processes and design consideration for, NMR magnets 1 Denkigakkai Tsushinkyoiku CHOUDENDOU KOUGAKU. Ohmsha 1988 p 233,2 K Tachikawa TEION KOUGAKU 2009 Vol 44 No 10. 3 K Egawa et al TEION KOUGAKU 2004 Vol 39 No 9,4 M Sugimoto et al TEION KOUGAKU 2012 Vol 47 No 8. 5 A Godeke et al Cryogenics 2008 Vol 48 p 308,6 K Tachikawa TEION KOGAKU 2010 Vol 45 No 3 p 88. 7 T Takeuchi National Institute for Materials Science NIMS. http www nims go jp smcMetal,kinzokuchoudenndoutainoayumi 5 S1 2 pdf. reference date 2015 03 10, Conclusions 8 T Miyazaki et al TEION KOUGAKU 2004 Vol 39 No 9. In order to develop a superconducting magnet 9 K Zaitsu et al R D Kobe Steel Engineering Reports 2007. that generates a high magnetic field it is imperative Vol 57 No 3 p 58. that the Nb3Sn wires have a high Jc The wires 10 T Matsushita et al CHOUDENDOU KOUGAKU NO KISO. Yoneda Shuppan 2004 p 23, must also be made at low cost to increase market 11 M Konuma et al CHOUDENDOU ZAIRYOU TO. competitiveness With consideration to these SENZAIKA GIJUTSU Kougakutosho 1995 p 181. two aspects we will strive to contribute to the 12 H Maeda et al TEION KOUGAKU 2002 Vol 37 No 1 p 2. superconductivity business of the Kobe Steel group 13 T Kiyoshi TEION KOUGAKU 2002 Vol 37 No 1 p 10. through the development of Nb3Sn wires,77 KOBELCO TECHNOLOGY REVIEW NO 34 MAR 2016.
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