Pub Date : 2024-06-04DOI: 10.1088/1361-6668/ad541f
Sijian Wang, H. Yong, Youhe Zhou
The finite element method (FEM) provides a powerful support for the calculations of superconducting electromagnetic responses. It enables the analysis of large-scale high-temperature superconducting (HTS) systems by the popular H formulation. Nonetheless, modeling of contact resistivity in three-dimensional (3D) FEM is still a matter of interest. The difficulty stems from the large aspect ratio of the contact layer in numerical modeling. Nowadays, an available solution is to model the contact layer with zero thickness but requires the discontinuity conditions of the magnetic field. In this paper, the energy variational method is utilized to incorporate the contribution of contact resistivity into the H formulation. From the perspective of energy transfer, the contact resistivity is related to the energy dissipation of the radial current flowing through the contact interface. In terms of applications, this method can be employed to calculate the charging delay of no-insulation (NI) coils and the current sharing behaviors of CORC cables. One advantage of this model is that the magnetic field is continuous and hence can be easily implemented in FEM. Additionally, it requires fewer degrees of freedom and hence presents advantages in computational efficiency. Moreover, this method can be employed to simplify the 3D H homogeneous model for insulated coils. The above discussions demonstrate that the proposed model is a promising tool for the modeling of contact resistivity.
有限元法（FEM）为超导电磁响应的计算提供了强大的支持。它可以通过流行的 H 公式分析大规模高温超导 (HTS) 系统。然而，在三维（3D）有限元中建立接触电阻率模型仍然是一个令人感兴趣的问题。困难在于数值建模中接触层的高宽比较大。目前，一种可用的解决方案是建立零厚度接触层模型，但需要磁场的不连续条件。本文利用能量变分法将接触电阻率的贡献纳入 H 公式中。从能量传递的角度来看，接触电阻率与流经接触界面的径向电流的能量耗散有关。在应用方面，这种方法可用于计算无绝缘（NI）线圈的充电延迟和 CORC 电缆的分流行为。该模型的一个优点是磁场是连续的，因此可以在有限元模型中轻松实现。此外，它所需的自由度较少，因此在计算效率方面具有优势。此外，这种方法还可用于简化绝缘线圈的三维 H 均质模型。上述讨论表明，所提出的模型是一种很有前途的接触电阻率建模工具。
{"title":"Modeling of contact resistivity and simplification of 3D homogenization strategy for the H formulation","authors":"Sijian Wang, H. Yong, Youhe Zhou","doi":"10.1088/1361-6668/ad541f","DOIUrl":"https://doi.org/10.1088/1361-6668/ad541f","url":null,"abstract":"\u0000 The finite element method (FEM) provides a powerful support for the calculations of superconducting electromagnetic responses. It enables the analysis of large-scale high-temperature superconducting (HTS) systems by the popular H formulation. Nonetheless, modeling of contact resistivity in three-dimensional (3D) FEM is still a matter of interest. The difficulty stems from the large aspect ratio of the contact layer in numerical modeling. Nowadays, an available solution is to model the contact layer with zero thickness but requires the discontinuity conditions of the magnetic field. In this paper, the energy variational method is utilized to incorporate the contribution of contact resistivity into the H formulation. From the perspective of energy transfer, the contact resistivity is related to the energy dissipation of the radial current flowing through the contact interface. In terms of applications, this method can be employed to calculate the charging delay of no-insulation (NI) coils and the current sharing behaviors of CORC cables. One advantage of this model is that the magnetic field is continuous and hence can be easily implemented in FEM. Additionally, it requires fewer degrees of freedom and hence presents advantages in computational efficiency. Moreover, this method can be employed to simplify the 3D H homogeneous model for insulated coils. The above discussions demonstrate that the proposed model is a promising tool for the modeling of contact resistivity.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"3 5","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141266199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.1088/1361-6668/ad5382
P. Huslage, David Kulla, J. Lobsien, Tristan Schuler, Eve V Stenson
We designed and constructed two non-planar coils with high-temperature superconductors (HTS) based on shapes from the Wendelstein 7-X stellarator. Tape track orientation of the HTS was optimized to reduce the coil size as much as possible while staying within the strain limits of the Gadolinium Barium Copper Oxide (GdBCO) superconductor. This resulted in average coil radii of 0.23 m and 0.48 m at strain limits of up 0.45 % to for the coil shapes that were chosen. The coils were produced by winding the GdBCO tapes onto 3D-printed plastic frames. We confirmed the integrity of the superconducting layer after winding by spatially resolved measurement of the critical current and by energizing the coils in liquid nitrogen. Coil 1 showed a resistance of 1.75 µΩ and did not have any critical current degradation, while coil 5 had a resistance of 195 µΩ and showed only one dropout, attributable to a handling error. We measured the magnetic field of the coil with a 3-axis Hall probe system and found good agreement with predictions. This work demonstrates the manufacturing of small-scale, non-planar magnetic coils from commercially available HTS.
{"title":"Winding angle optimization and testing of small-scale, non-planar, high-temperature superconducting stellarator coils","authors":"P. Huslage, David Kulla, J. Lobsien, Tristan Schuler, Eve V Stenson","doi":"10.1088/1361-6668/ad5382","DOIUrl":"https://doi.org/10.1088/1361-6668/ad5382","url":null,"abstract":"\u0000 We designed and constructed two non-planar coils with high-temperature superconductors (HTS) based on shapes from the Wendelstein 7-X stellarator. Tape track orientation of the HTS was optimized to reduce the coil size as much as possible while staying within the strain limits of the Gadolinium Barium Copper Oxide (GdBCO) superconductor. This resulted in average coil radii of 0.23 m and 0.48 m at strain limits of up 0.45 % to for the coil shapes that were chosen. The coils were produced by winding the GdBCO tapes onto 3D-printed plastic frames. We confirmed the integrity of the superconducting layer after winding by spatially resolved measurement of the critical current and by energizing the coils in liquid nitrogen. Coil 1 showed a resistance of 1.75 µΩ and did not have any critical current degradation, while coil 5 had a resistance of 195 µΩ and showed only one dropout, attributable to a handling error. We measured the magnetic field of the coil with a 3-axis Hall probe system and found good agreement with predictions. This work demonstrates the manufacturing of small-scale, non-planar magnetic coils from commercially available HTS.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"44 40","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141270200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-03DOI: 10.1088/1361-6668/ad5383
Xiaofang Ouyang, Zeyi Song, Yuzhong Zhang
Inspired by the parabolic trend of the superconducting transition temperature(Tc) of bulk FeSe under hydrostatic pressure, we investigated the effect of magnetism and hydrostatic pressure on the electron-phonon coupling (EPC) in FeSe using density-functional perturbation theory. We found that both magnetism and hydrostatic pressure enhanced EPC. The enhancement of the EPC is mainly attributed to phonon softening and deformation potential induced by magnetism, rather than Fermi surface nesting. Furthermore, we investigated the effect of spin fluctuations on superconductivity by applying the random phase approximation method (RPA). A possible application of our results to the phase diagram of FeSe under hydrostatic pressure was discussed, and we demonstrated that when EPC and spin fluctuations are both considered, a parabolic superconducting Tc may be obtained, providing a plausible explanation for the phase of FeSe under hydrostatic pressure.
{"title":"Enhancement of electron-phonon coupling due to increased magnetism and applied hydrostatic pressure in FeSe","authors":"Xiaofang Ouyang, Zeyi Song, Yuzhong Zhang","doi":"10.1088/1361-6668/ad5383","DOIUrl":"https://doi.org/10.1088/1361-6668/ad5383","url":null,"abstract":"\u0000 Inspired by the parabolic trend of the superconducting transition temperature(Tc) of bulk FeSe under hydrostatic pressure, we investigated the effect of magnetism and hydrostatic pressure on the electron-phonon coupling (EPC) in FeSe using density-functional perturbation theory. We found that both magnetism and hydrostatic pressure enhanced EPC. The enhancement of the EPC is mainly attributed to phonon softening and deformation potential induced by magnetism, rather than Fermi surface nesting. Furthermore, we investigated the effect of spin fluctuations on superconductivity by applying the random phase approximation method (RPA). A possible application of our results to the phase diagram of FeSe under hydrostatic pressure was discussed, and we demonstrated that when EPC and spin fluctuations are both considered, a parabolic superconducting Tc may be obtained, providing a plausible explanation for the phase of FeSe under hydrostatic pressure.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"19 18","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141270912","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-28DOI: 10.1088/1361-6668/ad4a32
P K Meena, M Mandal, P Manna, S Srivastava, S Sharma, P Mishra and R P Singh
Recently, the emergence of superconductivity in kagome metals has generated significant interest due to its interaction with flat bands and topological electronic states, which exhibit a range of unusual quantum characteristics. This study thoroughly investigates largely unexplored breathing kagome structure C14 Laves phase compounds XOs2 (X = Zr, Hf) by XRD, electrical transport, magnetization, and specific heat measurements. Our analyses confirm the presence of the MgZn2-type structure in ZrOs2 and HfOs2 compounds, exhibiting type-II superconductivity with critical temperature ( ) values of 2.90(3) K and 2.69(6) K, respectively. Furthermore, specific heat measurements and electron–phonon coupling constants for both compounds indicate weakly coupled fully gapped superconductivity.
{"title":"Superconductivity in breathing kagome-structured C14 Laves phase XOs2(X = Zr, Hf)","authors":"P K Meena, M Mandal, P Manna, S Srivastava, S Sharma, P Mishra and R P Singh","doi":"10.1088/1361-6668/ad4a32","DOIUrl":"https://doi.org/10.1088/1361-6668/ad4a32","url":null,"abstract":"Recently, the emergence of superconductivity in kagome metals has generated significant interest due to its interaction with flat bands and topological electronic states, which exhibit a range of unusual quantum characteristics. This study thoroughly investigates largely unexplored breathing kagome structure C14 Laves phase compounds XOs2 (X = Zr, Hf) by XRD, electrical transport, magnetization, and specific heat measurements. Our analyses confirm the presence of the MgZn2-type structure in ZrOs2 and HfOs2 compounds, exhibiting type-II superconductivity with critical temperature ( ) values of 2.90(3) K and 2.69(6) K, respectively. Furthermore, specific heat measurements and electron–phonon coupling constants for both compounds indicate weakly coupled fully gapped superconductivity.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"38 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141168818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-22DOI: 10.1088/1361-6668/ad4f5d
N. Strickland, Shen V Chong, Chiheng Dong, Xianping Zhang, Yanwei Ma, Zhenan Jiang
Ba1-xKxFe2As2 superconductors have strong potential for magnet applications through their very high upper critical field, relatively high superconducting transition temperature and manufacturability through the powder-in-tube (PIT) route. However, the critical current density in PIT tapes is still low compared to the incumbent technologies, so a greater understanding of the limiting factors is required. We have measured in-field critical currents (Ic) of stainless steel and silver double-sheathed monofilament Ba0.6K0.4Fe2As2 superconductor tapes at elevated temperatures from 15 K to 35 K. At 20 K the critical current density is up to 140 kA/cm2 in low (optimal) field and 22 kA/cm2 in 8 T. In the low-field region we observe an anomalous and sharp suppression of Ic centred at zero field. This feature is non-hysteretic for lower temperatures and perpendicular field, but becomes hysteretic for higher temperatures in perpendicular field and all temperatures in parallel field. The low-field suppression is reflected also in the n-values which can otherwise be very high, in excess of 100, in optimal field. Magnetic-field hysteresis of Ic is generally attributed to flux exclusion / flux trapping in granular superconductors and this is likely to be the case also in the present conductors. The low-field Ic anomaly also likely has its origin in the planar granularity, while magnetic phases in grains or grain boundaries may also play a role.
Ba1-xKxFe2As2 超导具有很高的上临界磁场、相对较高的超导转变温度以及通过管内粉末（PIT）工艺制造的可制造性，因此在磁体应用方面具有很强的潜力。然而，与现有技术相比，PIT 磁带的临界电流密度仍然较低，因此需要进一步了解其限制因素。我们测量了不锈钢和银双鞘单丝 Ba0.6K0.4Fe2As2 超导带在 15 K 至 35 K 高温下的场内临界电流 (Ic)。在 20 K 时，临界电流密度在低（最佳）磁场下高达 140 kA/cm2，在 8 T 时为 22 kA/cm2。这一特征在较低温度和垂直磁场下是非滞后的，但在温度较高的垂直磁场和所有温度的平行磁场下则变得滞后。低磁场抑制也反映在 n 值上，否则在最佳磁场中，n 值会非常高，超过 100。Ic 的磁场滞后通常归因于颗粒状超导体中的磁通排斥/磁通捕获，而目前的导体很可能也是这种情况。低磁场 Ic 异常也可能源于平面粒度，而晶粒或晶粒边界中的磁相也可能起作用。
{"title":"Low field anomaly in the critical current of Ba1‑xKxFe2As2 tapes","authors":"N. Strickland, Shen V Chong, Chiheng Dong, Xianping Zhang, Yanwei Ma, Zhenan Jiang","doi":"10.1088/1361-6668/ad4f5d","DOIUrl":"https://doi.org/10.1088/1361-6668/ad4f5d","url":null,"abstract":"\u0000 Ba1-xKxFe2As2 superconductors have strong potential for magnet applications through their very high upper critical field, relatively high superconducting transition temperature and manufacturability through the powder-in-tube (PIT) route. However, the critical current density in PIT tapes is still low compared to the incumbent technologies, so a greater understanding of the limiting factors is required. We have measured in-field critical currents (Ic) of stainless steel and silver double-sheathed monofilament Ba0.6K0.4Fe2As2 superconductor tapes at elevated temperatures from 15 K to 35 K. At 20 K the critical current density is up to 140 kA/cm2 in low (optimal) field and 22 kA/cm2 in 8 T. In the low-field region we observe an anomalous and sharp suppression of Ic centred at zero field. This feature is non-hysteretic for lower temperatures and perpendicular field, but becomes hysteretic for higher temperatures in perpendicular field and all temperatures in parallel field. The low-field suppression is reflected also in the n-values which can otherwise be very high, in excess of 100, in optimal field. Magnetic-field hysteresis of Ic is generally attributed to flux exclusion / flux trapping in granular superconductors and this is likely to be the case also in the present conductors. The low-field Ic anomaly also likely has its origin in the planar granularity, while magnetic phases in grains or grain boundaries may also play a role.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"34 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141109346","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-21DOI: 10.1088/1361-6668/ad4e76
Shengchen Xue, Yi Li, Lingfeng Zhu, Bhabesh Sarangi, Jithin sai sandra, Jian Rong, Nghia Mai, Siwei Chen, Atik Chavda, Umesh Sambangi, Jithin Peram, Prakash Parthiban, V. Selvamanickam
Current sharing between RE-Ba-Cu-O (REBCO, RE=rare earth) tapes within a high-temperature superconducting (HTS) coil or cable is important to avoid damage from uncontrolled quench of superconducting devices operating at high currents. Current sharing between REBCO tapes is found to be limited by contact resistivity between the adjacent tapes, which is about 20x higher in the REBCO-facing-substrate (face-to-back) configuration that is commonly used in devices compared to a REBCO-facing-REBCO (face-to-face) configuration. Double-sided REBCO tapes always offer face-to-face contacts between adjacent tapes, and this benefit for excellent current sharing has been validated in experiments wherein an artificial defect is introduced in one tape in a 2-ply tape stack. Additionally, current sharing between the two REBCO layers within one double-sided REBCO tape has also been investigated. Slotting of the double-sided tapes, wherein slots through the insulating buffer stack are filled with a conductive material, has been found to significantly enhance the current sharing from one REBCO layer to the opposite layer.
{"title":"Current sharing in double-sided REBCO tapes","authors":"Shengchen Xue, Yi Li, Lingfeng Zhu, Bhabesh Sarangi, Jithin sai sandra, Jian Rong, Nghia Mai, Siwei Chen, Atik Chavda, Umesh Sambangi, Jithin Peram, Prakash Parthiban, V. Selvamanickam","doi":"10.1088/1361-6668/ad4e76","DOIUrl":"https://doi.org/10.1088/1361-6668/ad4e76","url":null,"abstract":"\u0000 Current sharing between RE-Ba-Cu-O (REBCO, RE=rare earth) tapes within a high-temperature superconducting (HTS) coil or cable is important to avoid damage from uncontrolled quench of superconducting devices operating at high currents. Current sharing between REBCO tapes is found to be limited by contact resistivity between the adjacent tapes, which is about 20x higher in the REBCO-facing-substrate (face-to-back) configuration that is commonly used in devices compared to a REBCO-facing-REBCO (face-to-face) configuration. Double-sided REBCO tapes always offer face-to-face contacts between adjacent tapes, and this benefit for excellent current sharing has been validated in experiments wherein an artificial defect is introduced in one tape in a 2-ply tape stack. Additionally, current sharing between the two REBCO layers within one double-sided REBCO tape has also been investigated. Slotting of the double-sided tapes, wherein slots through the insulating buffer stack are filled with a conductive material, has been found to significantly enhance the current sharing from one REBCO layer to the opposite layer.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"16 11","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141114567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-21DOI: 10.1088/1361-6668/ad4e77
Shahin Alipour Bonab, Yiteng Xing, Giacomo Russo, Massimo Fabbri, A. Morandi, Pierre Bernstein, Jacques G Noudem, M. Yazdani-Asrami
The advent of superconducting bulks, because of their compactness and performance, offers new perspectives and opportunities in many applications and sectors, such as magnetic field shielding, motors/generators, NMR/MRI, magnetic bearings, flywheel energy storage, Maglev trains, among others. The investigation and characterization of bulks typically relies on time-consuming and expensive experimental campaigns; hence the development of effective surrogate models would considerably speed up the research progress around them. In this study, we have first produced an experimental dataset with the levitation and lateral forces between different MgB2 bulks and one permanent magnet under different operating conditions. Next, we have exploited the dataset to develop surrogate models based on Artificial Intelligence (AI) techniques, namely Extremely Gradient Boosting (XGBoost), Support Vector Machine Regressor (SVR), and Kernel Ridge Regression (KRR). After the tuning of the hyperparameters of the AI models, the results demonstrated that SVR is the superior technique and can predict levitation and lateral forces with a worst-case accuracy scenario 99.86% in terms of goodness of fit to experimental data. Moreover, the response time of these models for prediction of new datapoints is ultra-fast.
{"title":"Estimation of magnetic levitation and lateral forces in MgB2 superconducting bulks with various dimensional sizes using artificial intelligence techniques","authors":"Shahin Alipour Bonab, Yiteng Xing, Giacomo Russo, Massimo Fabbri, A. Morandi, Pierre Bernstein, Jacques G Noudem, M. Yazdani-Asrami","doi":"10.1088/1361-6668/ad4e77","DOIUrl":"https://doi.org/10.1088/1361-6668/ad4e77","url":null,"abstract":"\u0000 The advent of superconducting bulks, because of their compactness and performance, offers new perspectives and opportunities in many applications and sectors, such as magnetic field shielding, motors/generators, NMR/MRI, magnetic bearings, flywheel energy storage, Maglev trains, among others. The investigation and characterization of bulks typically relies on time-consuming and expensive experimental campaigns; hence the development of effective surrogate models would considerably speed up the research progress around them. In this study, we have first produced an experimental dataset with the levitation and lateral forces between different MgB2 bulks and one permanent magnet under different operating conditions. Next, we have exploited the dataset to develop surrogate models based on Artificial Intelligence (AI) techniques, namely Extremely Gradient Boosting (XGBoost), Support Vector Machine Regressor (SVR), and Kernel Ridge Regression (KRR). After the tuning of the hyperparameters of the AI models, the results demonstrated that SVR is the superior technique and can predict levitation and lateral forces with a worst-case accuracy scenario 99.86% in terms of goodness of fit to experimental data. Moreover, the response time of these models for prediction of new datapoints is ultra-fast.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"129 19","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141115094","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-20DOI: 10.1088/1361-6668/ad44ea
J V J Congreve, Y Shi, N C Tutt, R W Taylor, C Bumby, A R Dennis, H Druiff, D Weerakonda Arachchilage, J H Durrell and D A Cardwell
The fabrication of large (RE)–Ba–Cu–O single grains [(RE)BCO], where RE = Y, Gd, Eu or Sm, with the complex geometries required for many practical applications is currently limited by the time intensive, complex nature of the grain growth process. In addition, the shapes achievable using established melt processing techniques, such as top seeded melt growth, are constrained significantly by the limited number of post-processing techniques readily available. Machining of these materials is also difficult given their ceramic-like mechanical properties, which makes them both brittle and hard. A potential alternative to the slow and inflexible melt growth processes is to join many small, single grains to form one large composite grain, connected by electrically and mechanically high-performance joints. A reliable joining technique would also greatly reduce the need for post-growth machining processes. In this work we extend our previous investigation of the use of single grain YBCO-Ag as an intermediate joining material to achieve effective and reliable superconducting joints between EuBCO-Ag bulk, single grain superconductors. The technique reported in the earlier studies requires limited specialist equipment and does not require tight process parameter control, since there is no need to re-grow the joining material at the intergrain interface. This technique is of particular interest given that the difference between the peritectic temperatures of the bulk superconductor and the intermediate joining material is large. We report the properties of seven joints engineered at different joining temperatures. The trapped field properties of the resulting joined samples were measured and the microstructure at the position of the joint examined. We demonstrate that this simple and the rapid joining technique makes it possible to manufacture composite grains in an industrially important (RE)BCO bulk superconductor with comparable superconducting properties to those of a single grain of similar dimensions.
{"title":"A route to fabricate low resistance joints between Eu–Ba–Cu–O bulk, single grain superconductors","authors":"J V J Congreve, Y Shi, N C Tutt, R W Taylor, C Bumby, A R Dennis, H Druiff, D Weerakonda Arachchilage, J H Durrell and D A Cardwell","doi":"10.1088/1361-6668/ad44ea","DOIUrl":"https://doi.org/10.1088/1361-6668/ad44ea","url":null,"abstract":"The fabrication of large (RE)–Ba–Cu–O single grains [(RE)BCO], where RE = Y, Gd, Eu or Sm, with the complex geometries required for many practical applications is currently limited by the time intensive, complex nature of the grain growth process. In addition, the shapes achievable using established melt processing techniques, such as top seeded melt growth, are constrained significantly by the limited number of post-processing techniques readily available. Machining of these materials is also difficult given their ceramic-like mechanical properties, which makes them both brittle and hard. A potential alternative to the slow and inflexible melt growth processes is to join many small, single grains to form one large composite grain, connected by electrically and mechanically high-performance joints. A reliable joining technique would also greatly reduce the need for post-growth machining processes. In this work we extend our previous investigation of the use of single grain YBCO-Ag as an intermediate joining material to achieve effective and reliable superconducting joints between EuBCO-Ag bulk, single grain superconductors. The technique reported in the earlier studies requires limited specialist equipment and does not require tight process parameter control, since there is no need to re-grow the joining material at the intergrain interface. This technique is of particular interest given that the difference between the peritectic temperatures of the bulk superconductor and the intermediate joining material is large. We report the properties of seven joints engineered at different joining temperatures. The trapped field properties of the resulting joined samples were measured and the microstructure at the position of the joint examined. We demonstrate that this simple and the rapid joining technique makes it possible to manufacture composite grains in an industrially important (RE)BCO bulk superconductor with comparable superconducting properties to those of a single grain of similar dimensions.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"140 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141149008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-05-20DOI: 10.1088/1361-6668/ad44df
Chukun Gao, Pin-Hui Chen, Nicholas Alaniva, Snædís Björgvinsdóttir, Ioannis Pagonakis, Alexander Däpp, Michael Urban, Ronny Gunzenhauser and Alexander Barnes
We present a compact 23 T no-insulation (NI) magnet that was wound with 60 m of 10 mm wide high temperature superconducting (HTS) tape. The magnet consists of only one pocket-sized double pancake (DP) coil with an inner diameter of ∼6 mm, a height of 20 mm, and an outer diameter of 41.6 mm. Another NI coil of similar size but with a larger inner diameter of 8 mm reached a slightly lower magnetic field of 21 T. We also present a smaller coil which was wound with only 20 m of HTS tape and still achieved a magnetic field of 16 T. During the experiments in liquid helium, each coil was charged to a current between 690 A and 850 A, corresponding to a high current density of 1500–1900 A mm−2. The small bore size and high current density contributed to the high fields generated by these coils. We present the fabrication details, helium tests and repeatability analysis of these ‘pocket’ magnets.
我们展示了一种用 60 米宽的 10 毫米高温超导（HTS）带缠绕而成的 23 T 紧凑型无绝缘（NI）磁体。该磁体仅由一个袖珍型双薄饼（DP）线圈组成，其内径为 6 毫米，高度为 20 毫米，外径为 41.6 毫米。我们还展示了一个更小的线圈，它只缠绕了 20 米长的 HTS 磁带，但仍然达到了 16 T 的磁场强度。在液氦实验中，每个线圈的充电电流介于 690 A 和 850 A 之间，相当于 1500-1900 A mm-2 的高电流密度。小孔径和高电流密度是这些线圈产生高磁场的原因。我们介绍了这些 "袖珍 "磁体的制造细节、氦气测试和重复性分析。
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Pub Date : 2024-05-19DOI: 10.1088/1361-6668/ad4a35
Zhi-Hao He, Zi-Yan Han, Kuang-Hong Gao, Zi-Wu Wang and Zhi-Qing Li
The electrical transport properties of Pbx(TiO2) (x being the Pb volume fraction and ranging from ∼0.45 to ∼0.72) granular films are investigated experimentally. The charging energy of the Pb granules is reduced to less than the superconducting gap of Pb granules for the low temperature insulating films by using high-k dielectric TiO2 as the insulating matrix. For the insulating films in the vicinity of the superconductor-insulator transition, Cooper-pair hopping governs the low-temperature hopping transport. For these films, the low-temperature magnetoresistance is positive at low field and the resistivity vs temperature for Cooper-pair hopping obeys an Efros–Shklovsii-type variable-range-hopping law. A crossover from Cooper-pair-dominated hopping to single-electron-dominated hopping is observed with decreasing x. The emergence of single-electron-dominated hopping in the more insulating films is due to the causation that the intergrain Josephson coupling becomes too weak for Cooper pairs to hop between adjacent Pb granules.
实验研究了 Pbx(TiO2)（x 为 Pb 体积分数，范围为 ∼0.45 至 ∼0.72）颗粒薄膜的电传输特性。在低温绝缘薄膜中，通过使用高 K 介电体 TiO2 作为绝缘基体，铅颗粒的充电能被降低到小于铅颗粒的超导间隙。对于超导体-绝缘体转变附近的绝缘薄膜，库珀对跳变控制着低温跳变输运。对于这些薄膜，低温磁阻在低磁场时为正，库珀对跳变的电阻率与温度的关系遵循 Efros-Shklovsii- 型变程跳变定律。随着 x 值的减小，出现了从库珀对主导跳变到单电子主导跳变的交叉。在绝缘性较强的薄膜中出现单电子主导跳变的原因是晶粒间的约瑟夫森耦合变得太弱，库珀对无法在相邻的铅颗粒之间跳变。
{"title":"Crossover from Cooper-pair hopping to single-electron hopping in Pb x (TiO2) 1−x granular films","authors":"Zhi-Hao He, Zi-Yan Han, Kuang-Hong Gao, Zi-Wu Wang and Zhi-Qing Li","doi":"10.1088/1361-6668/ad4a35","DOIUrl":"https://doi.org/10.1088/1361-6668/ad4a35","url":null,"abstract":"The electrical transport properties of Pbx(TiO2) (x being the Pb volume fraction and ranging from ∼0.45 to ∼0.72) granular films are investigated experimentally. The charging energy of the Pb granules is reduced to less than the superconducting gap of Pb granules for the low temperature insulating films by using high-k dielectric TiO2 as the insulating matrix. For the insulating films in the vicinity of the superconductor-insulator transition, Cooper-pair hopping governs the low-temperature hopping transport. For these films, the low-temperature magnetoresistance is positive at low field and the resistivity vs temperature for Cooper-pair hopping obeys an Efros–Shklovsii-type variable-range-hopping law. A crossover from Cooper-pair-dominated hopping to single-electron-dominated hopping is observed with decreasing x. The emergence of single-electron-dominated hopping in the more insulating films is due to the causation that the intergrain Josephson coupling becomes too weak for Cooper pairs to hop between adjacent Pb granules.","PeriodicalId":21985,"journal":{"name":"Superconductor Science and Technology","volume":"55 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141149027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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