1 / 24

  MgB 2  superconductor processed in  high magnetic fields 

  MgB 2  superconductor processed in  high magnetic fields . Yanwei MA Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100080, China. Background. Candidate HTS for large scale applications. Commercial production: Bi2223 / silver tape - 1 st Generation HTS

teleri
Download Presentation

  MgB 2  superconductor processed in  high magnetic fields 

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1.   MgB2 superconductor processed in high magnetic fields   MgB2 superconductor processed in high magnetic fields  Yanwei MA Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100080, China

  2. Background Candidate HTS for large scale applications • Commercial production: • Bi2223/ silver tape - 1st Generation HTS • Industrial laboratory: • YBCO 2nd Generation HTS “coated conductor” • Pre-commercial: • MgB2 D. C. Larbalestier et al., Proceedings of the IEEE, vol. 92, 2004, 1639

  3. Benefits of SC Materials Merits of superconductors: 1. Low losses, 2. Small volume, 3. Light weight, 4. High efficiency.

  4. Structure of HTS superconductors Bi2223 YBCO MgB2

  5. Magnetic aligning technique • The principal limitation to technological applications of high-Tc polycrystalline oxide superconductors is the low critical current density (Jc) found in these materials. • This limitation is strongly correlated with the misorientation among the grains. Hence, to minimize the number of intergranular weak links, a high degree of crystallographic texture must be obtained. One possible route by which a strong crystallographic texture can be produced is to melt-process the HTS material under the effect of an elevated magnetic field.

  6. First report in Nature, in 1991 • Effect of magnetic field: > kT c-axis alignment is strongly preferred. V:volume of particle H:external magnetic field D: magnetic anisotropy (-//) • For YBCO superconductors: = 6.1 x 10-7 emu/g  =4.3 x 10-7 emu/g At 1000C, 10 T, orientation takes place for grains with the size of 40 nm. P. de Rango et al., Nature 349 (1991) 770

  7. Present situation Bi-oxide superconductors (Bi2212 and Bi2223) and YBCO exhibit strong anisotropy in magnetic susceptibility. Many studies reported enhancements in texture for HTS superconducting bulks and tapes, by magnetic-melt processing (MMP) , and showed that uniform high texture is achieved throughout the thickness. • Bi-2223 tapesYanweiMa, et al., Physica C282 (1997) 2619. • Bi-2212 tapesH. B. Liu, et al., Physica C 303 (1998) 161. S. Awaji, Yanwei Ma, et al., CurrentAppl. Phys. 3 (2003) 391. • Bi-based bulksH. Maeda, et al.,Physica C 386 (2003) 115. W. Chen, et al., J. Crystal Growth 204 (1999) 69. • YBCO bulksS. Awaji, et al., IEEE Appl. Supercond. 9 (1999) 2014. • YBCO filmsYanwei Ma, et al., Appl. Phys. Lett. 77 (2000) 3633. Yanwei Ma, et al., Phys. Rev. B 65 (2002) 174528.

  8. Hot topic: Superconductors synthesized in high magnetic fields In 1991, Rango et al. at Grenoble reported the effect of magnetic field on the growth of YBCO bulk samples. In 1997 Ma, et al. Bi-2212 tape In 1999 Liu, et al. Bi-2212 tape In 2000年 Maeda, Awaji, et al. Bi-bulk,YBCO bulk In 2000年 Ma, et al., YBCO film Improved the degree of texture and enhanced Jc by MMP! ？ MgB2 processed in fields Motivation

  9. Introduction-MgB2 The recent discovery of magnesium diboride (MgB2) with its superconducting transition temperature at 39 K has generated much interest in both fundamental research and applications. J. Akimitsu et al., Nature (London) 410, 63 (2001). a=3.086 Å; c=3.524 Å

  10. Experimental procedure Tape Characterization MgB2 Powder Heated in magnetic fields Pressing Bulk

  11. Temperature profile for processing of MgB2 in magnetic fields Temp. 600-800C in vacuum Magnetic field 0.5 h 1 h Furnace cooling Time

  12. Group Sample type Sintering temperature/ time Applied field during sintering Sample surface and field direction during sintering Tc Group I Fe clad tape 600C/1 h 10 T Parallel 35.2 Fe clad tape 600C/1 h 0 T 35.5 Group II Fe clad tape 700C/1 h 14 T Perpendicular  Fe clad tape 700C/1 h 0 T  Group III Pellet 800C/2h 14 T Perpendicular 37 K pellet 800C/1 h 8 T 36.9 K pellet 800C/1 h 0 T 37.1 K Description of samples used in this work

  13. XRD patterns for tapes with and without filed Broadening of the FWHM indicates inferior MgB2 crystallinity and lattice distortion of the core MgB2, closely related to the enhanced flux pinning.

  14. Transport critical current density Jc (Tapes) 600  C Ha is parallel to the tape surface

  15. Magnetc critical current density Jc measured by magnetization (Tapes) 700  C Ha is perpendicular to the tape surface

  16. Microstructure (SEM)-Tapes 0 T 14 T Clearly, well-developed grains can be seen in both samples. However, the core of the 0T sample is quite porous and loose. In contrast, with the application of strong magnetic field, densification of the MgB2 core obviously occurred, resulting in the quite uniform microstructure and the better connectivity between the MgB2 grains.

  17. Comparison between Group I and II tapes • It is interesting to note the effect of a magnetic field seems different between Group I (Ha // the tape plane) and II (Ha the tape surface) tapes. • For Group I, although the enhanced Jc-B characteristic was observed in high field region due to induced poor crystallinity, the Jc improvement in low field area is small. • The improved Jc by more than a factor of 2 for the field tapes of Group II was achieved. This indicates that the magnetic field works more effectively to enhance the Jc-B properties for Group II during processing.

  18. XRD patterns for different bulks XRD results also reveal a larger FWHM of the MgB2 peaks for the pellet samples processed in the fields, implying that the pinning centers effective in a high-field region were possibly introduced by the applied magnetic field during processing.

  19. Critical temperature Tc (Bulk) The magnetic fields hardly affect Tc!

  20. Magnetc critical current density Jc measured by magnetization (Bulk)

  21. Conclusions The effect of high magnetic fields on the current carrying properties of both MgB2 bulks and Fe-sheathed tapes was investigated following different thermal sequences. It is found that application of a large magnetic field during processing not only results in the quite uniform microstructure and the better connectivity between the MgB2 grains, but also induces the flux pinning centers effective in high-field region. As a result, the Jc of these samples has showed much higher value than that of the MgB2 samples in the absence of magnetic field. A magnetic field is a more effective method to enhance Jc for MgB2 superconductors.

  22. Acknowledgements Thanks to the Chinesisch-deutsches Zentrum fuer Wissenschaftsfoerderung. This work is supported by the NSFC, “Bairen” program of CAS, and also “973” national program. • G. Nishijima, S. Awaji, K. Watanabe IMR, Tohoku Univ. • K. Togano NIMS, Tsukuba • Aixia Xu, Xianping Zhang IEE, CAS, China Collaborators:

  23. Thank you for your attention!

  24. Barrier for applications Many groups have already demonstrated powder-in-tube (PIT) conductors for applications. The key problem of MgB2 superconductors for large-scale applications is the irreversibility field (17 T) is less than for Nb3Sn (27 T). D. C. Larbalestier, et al., Nature411 (2001) 368

More Related