1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

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

10. 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

11. 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

12. 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

13. 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.

14. n values for Fe/MgB 2 tape Université de Genève