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G. Grasso, A. Malagoli, M. Modica, V. Braccini, A. Tumino, S. Roncallo, E. Bellingeri, C. Ferdeghini, A.S. Siri INFM -LAMIA, Corso Perrone 24, 16152 Genova.

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Presentation on theme: "G. Grasso, A. Malagoli, M. Modica, V. Braccini, A. Tumino, S. Roncallo, E. Bellingeri, C. Ferdeghini, A.S. Siri INFM -LAMIA, Corso Perrone 24, 16152 Genova."— Presentation transcript:

1 G. Grasso, A. Malagoli, M. Modica, V. Braccini, A. Tumino, S. Roncallo, E. Bellingeri, C. Ferdeghini, A.S. Siri INFM -LAMIA, Corso Perrone 24, Genova -Genova, Via Dodecaneso 33, Genova Preparation and properties of MgB 2 superconducting tapes

2 tube filling PIT Processing routes for the fabrication of MgB 2 wires + BMg a) IN-SITU b) + BMg MgB 2 EX-SITU wire drawing wire rolling Cold Working long lengths of tape

3 Cu-sheathed tape transverse cross section Tube filling with MgB 2 reacted powders Wire drawing and/or rolling Flat rolling Long lengths can be now fabricated irregular cross section No sintering is necessary! APL 79 (2001) 230 Alfa-Aesar or homemade precursors ex-situ PIT processing High critical currents are achieved even without any sintering process! I-V characteristics vs. sheath material 4.2 K.25x3 mm 2 strength

4 Harder sheath material larger j c Less sausaging + higher powder compactionLow powder compaction => lower I c and j c 240A 10 5 A/cm x 4 mm 2 f. f. 17% V-I characteristics at 4.2 K, self field strength f.f.

5 Mechanical properties of unsintered tapes Unsintered SUS316 MgB 2 tape Kitaguchi et al. submitted to Phys. C Preliminary bending strain experiment Tape double bent on diameter 30 mm No reduction of I c Mechanical properties are already sufficient for applications!

6 Transport j c (B,T) measurements on unsintered MgB 2 tapes Kramer plot J c (B,T) 0.5 B 0.25 B Thanks to ENEA-Frascati Lab, Rome, Italy (M. Spadoni, P. Gislon) B//tape plane T c lower than expected for MgB 2 Magnetoresistance measurements B tape plane

7 IL of Ni-sheathed tape presents a larger slope than for MgB 2 powders Irreversibility lines from R, I c (B,T) Superconducting irreversibility line and XRD of unsintered MgB 2 tapes A new source of pinning centers is present in ex-situ MgB 2 tapes XRD peaks are broader in the Nickel- sheathed MgB 2 filament; some level of c -axis texture is also present XRD of Ni-sheathed tape large lattice distortion: a / a = 0.3%

8 What if we heat? Treatment of 1 h in Ar Too large I c in low-T heated tapes quench Magnetic measurement of MgB 2 core Assuming M=2/3 j c d Magnetic and transport j c coincide

9 Argon Anisotropy of the critical current density at 4.2 K Correlation between magnetic and transport j c => extrapolation of 20K behavior New transport I c data: 27 K, s. f. > 500A 1 T ~100 A 1.5 T ~ 20 A 20K, 1.5T 4.2K, 3 T Tape dimensions: 3.5 mm x 0.35 mm Filling factor 20% Treated at 900°C for 2 hours in Ar Transport properties of ex-situ tapes reacted in Argon atmosphere

10 IL of unsintered, 800ºC and 900°C tapes Irreversibility lines from magnetoresistance measurements At 800°C the initial T c is recovered Pinning centers induced by cold working are partly removed at 900 °C

11 Neutron diffraction experiments ILL D1A facility – Grenoble (F) MgB 2 MgO In-situ analysis of Ni-sheathed tapes confirms: a)Lattice strain increases during cold working b)Lattice strain progressively relaxes during the heat treatment

12 880°C 900°C 920°C 940°C Reaction layer between Ni and MgB 2 900°C Ni MgB 2 MgB 2 Ni °C Ni MgB 2 MgB 2 Ni 2.5 The reaction layer increases with increasing temperature

13 Optimal conditions for j c are different for low & high fields J c after heat treatment mainly results from the compromise between: - MgB 2 packing density - residual lattice strain - increase of T c - reaction layer with Ni sheath

14 Critical strain Transport j c and critical strain measurements (NIST) Tape dimensions: 3.5 mm x mm Filling factor 16% Superconducting cross section mm 2

15 First test of an MgB 2 pancake MgB 2 BSCCO Pancake coil

16 Ex-situ Nickel-sheathed MgB 2 tapes have been fabricated by the Powder-In-Tube method in lengths up to 25 meters Critical current densities in excess of 1000 A/mm 2 have been achieved at 4.2 K and magnetic fields up to 3 Tesla A direct correlation has been observed between MgB 2 lattice strain induced by cold deformation and the irreversibility field A relevant reaction layer between MgB 2 and Nickel sheath has been observed Conclusions


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