Magneto-Optical Imagine (MOI) Technique as a

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Magneto-Optical Imagine (MOI) Technique as a Powerful Tool for Study of Superconductivity in. Different Superconducting Forms. A. A. Polyanskii (NHMFL), A.

NATIONAL HIGH MAGNETIC FIELD LABORATORY 2008 RESEARCH REPORT

Magneto-Optical Imagine (MOI) Technique as a Powerful Tool for Study of Superconductivity in Different Superconducting Forms A. A. Polyanskii (NHMFL), A. Yamamoto (NHMFL), A. Malagoli (CNR-INFM LAMIA, Genova, Italy), D. Abraimov (NHMFL), P.J. Lee (NHMFL), and D.C. Larbalestier (NHMFL) Introduction Magneto-Optical Imaging (MOI) technique is a powerful tool for studying the magnetic flux patterns in different forms of superconductor. In this year MOI together with different electromagnetic technique and such as SEM, TEM and Laser Scanning Confocal Microscope (LSCM) were successfully applied to many forms of superconductors: a) YBCO thin films patterned for reduction of AC losses, b) MgB2 tapes with cores treated so as to enhance critical current and upper critical field, c) Nb3Sn strands deformed to different sizes to simulate damage produced during cabling and d) the newly discovered family of oxypnictides where the connectivity of polycrystals is under debate. Five papers on the work were published and one is in preparation.

Experimental The MOI technique uses the strong magneto-optical Faraday effect in in-plane magnetized Bi-doped garnet film placed on the sample surface, to measure the vertical component of the magnetic field above the sample.

Results and Discussion Fig.1 is the example of MOI of the 1111 Sm oxypnictide 40% showing granular b b e e behavior (left) and 0.6 mm the deduced bulk 40% Jc(T) taken from MO and c Fig. 1 c Trapped flux at 6K magnetization Fig. 2 measurements [1]. Fig. 2 shows IT-RRP Nb3Sn strands rolled to 40%. Left column: a,b,c-the cross sections. Due to the 12 mm twist pitch in IT-RRP applies different geometric distortions (a,b). Right column: d,e- MO images of trapped flux at T=12 K (FC). MOI reveals the shearing open of filament sub-elements (light arrows) and unreacted Nb in low Tc sub-elements (black circles). Two sub-elements also fused together (b,c,e- black arrows) and as result increase the effective filament diameter and decrease magnet stability [2]. a a

d d

0.6 mm

Conclusions Different types defects were locally recognize in deformed Nb3Sh strands. The global and local current in new Sm and Nd oxypnictides were quantitatively evaluated by remnant magnetization and local MOI. The granularity of MgB2 wires was revealed.

Acknowledgements Work at the NHMFL was supported by NSF, ITER contract (ITER-CT-07-012), DOE Office of HEP, and AFOSR.

References [1] Yamamoto A., et al., Supercon. Science and Techn. 21 (2008) 095008 (11 pp) [2] Polyanskii A.A., et al., Paper in progress for Supercon. Science and Techn. [3] Kametani T., et al., Supercon. Science and Techn. 22 (2009) 015010 (6 pp) [4] Malagoli A., et al., J. Appl. Phys. 104, 103908 (2008) (7 pp) [5] Yamamoto A., et al., Appl. Phys. Letts. 92, 252501 (2008) (3 pp) [6] Abraimov D. et al., Supercon. Science and Techn. 21 (2008) 082004 (4 pp)