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Critical current density and strain effects of Fe/MgB 2 tapes with different particle sizes Université de Genève Paola Lezza Co-workers:H. L. Suo V. Abächerli D. Uglietti N. Clayton C. Senatore N. Musolino R. Flükiger Département de Physique de la Matière Condensée, Université de Genève, 24, quai Ernst Ansermet, 1211 Genève, Switzerland

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Université de Genève Present state of critical current density in MgB 2 Tapes preparation Critical current density J c for 3 h and 100 h ball milled tapes n-values Inductive and transport measurements on 100 h ball milled tape Irreversibility fields B irr Strain Effect on 100 h ball milled tape Conclusion Outline

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Université de Genève Present state, wires and tapes Wang Giunchi Gümbel Unige Dhallé Goldacker Wire Tape Bulk Tape Bulk Fe Soft S. Fe R. Flukiger et al., « Superconducting properties of MgB 2 tapes and wires », Physica C 385 (2003) 286-305

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Université de Genève Present state, films Bu Kang Komori Unige Film YSZ Tape Film Al 2 O 3 None Al 2 O 3 R. Flukiger et al., « Superconducting properties of MgB 2 tapes and wires », Physica C 385 (2003) 286-305

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Université de Genève Present state, effect of additives Dou Zhao Wang Unige Wire Ti Y2O3Y2O3 Tape Bulk SiC None R. Flukiger et al., « Superconducting properties of MgB 2 tapes and wires », Physica C 385 (2003) 286-305

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Université de Genève Preparation Ball milling under Ar P. I. T. Swege Draw Flat rolling in = 5 mm out = 8 mm = 3.85 mm = 2 mm Tape 4 x 0.38 mm 2 P.I.T. Flat rolling Final Tape MgB 2

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J c at 4.2 K for different powder grain sizes Université de Genève 0.1 1 10 60 3 h ball milled 100 h ball milled 100 90 80 70 60 50 40 30 20 10 0 100 90 80 70 60 50 40 30 20 10 0 0.1 1 10 60

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n values for Fe/MgB 2 tape Université de Genève 0.1 V/cm 1 V/cm I n=148, 4.5 T n>30, 9.5 T 0.1 V/cm 1 V/cm I log-log

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Transport measurements on annealed Fe/MgB 2 tape 100 h ball milled Université de Genève

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Irreversibility field as a function of grain size Université de Genève Definitions: R. Flukiger et al., « Superconducting properties of MgB 2 tapes and wires », Physica C 385 (2003) 286-305 1) A frequently used definition is based on the resistively measured superconducting transition, the criterion being the 10% of R N or the intersection of the extrapolated linear part of R(T) with R=0 2) The field at which the the inductively measured critical current vanishes 10% R N R(T) T T JcJc B M H

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Irreversibility field as a function of grain size Université de Genève Third Definition: 3) The onset of the third harmonic susceptibility, in presence of a magnetic field H dc >> H ac results from a crossover between a regime in which the system response is flux low dominated (no harmonic signal) and one which is pinnig dominated. The onset of the third harmonic thus corresponds to a non-zero critical current density J c

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Strain Effect on MgB 2 long tape 100 h ball milled Université de Genève Strain gauges Modified Walter s Spiral (WASP) MgB 2 Tape d=26 cm

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Université de Genève Conclusion The actual state of the critical current densities has been presented, and compared with our latest data. The critical current densities J c and the n-values of the Fe/MgB 2 tapes, 3 h and 100 h ball milled have been compared. An enhancement is obtained for the smaller particle size. The critical current densities J c in the two configurations with the tape surface parallel and perpendicular to the magnetic field direction have been measured. A strong difference has been obtained, reflecting a partial texture of the grains. The various criteria of the irreversibility field B irr have been discussed. Strain effects on 100 h ball milled tape have been measured on 80 cm length with a modified Walters Spiral. The degradation of the critical current and the n-values confirming the pre-stress model.

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n values for Fe/MgB 2 tape Université de Genève

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