Critical current density and strain effects of Fe/MgB 2 tapes with different particle sizes

1. Université de Genève Critical current density and strain effects of Fe/MgB2 tapes with different particle sizes 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 Outline Present state of critical current density in MgB2 Tapes preparation Critical current density Jc for 3 h and 100 h ball milled tapes n-values Inductive and transport measurements on 100 h ball milled tape Irreversibility fields Birr Strain Effect on 100 h ball milled tape Conclusion

3. Université de Genève Wang Wire Fe Giunchi Wire Soft S. Goldacker Tape Fe Gümbel Bulk Unige Tape Fe Dhallé Bulk Present state, wires and tapes R. Flukiger et al., « Superconducting properties of MgB2 tapes and wires », Physica C 385 (2003) 286-305

4. Université de Genève Bu Film Al2O3 Kang Film Al2O3 Komori Film YSZ Unige Tape None Present state, films R. Flukiger et al., « Superconducting properties of MgB2 tapes and wires », Physica C 385 (2003) 286-305

5. Université de Genève Present state, effect of additives Dou Wire SiC Zhao Bulk Ti Wang Bulk Y2O3 Unige Tape None R. Flukiger et al., « Superconducting properties of MgB2 tapes and wires », Physica C 385 (2003) 286-305

6. Université de Genève Swege Flat rolling F = 3.85 mm Tape 4 x 0.38 mm2 P. I. T. Fin= 5 mm Fout= 8 mm Draw Ball milling under Ar P.I.T. F = 2 mm Final Tape MgB2 Flat rolling Preparation

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

8. Université de Genève n values for Fe/MgB2 tape n=148, 4.5 T 1 mV/cm 0.1 mV/cm n>30, 9.5 T I log-log 1 mV/cm 0.1 mV/cm I

9. Université de Genève Transport measurements on annealed Fe/MgB2 tape 100 h ball milled

10. Université de Genève R(T) T M Jc H B Irreversibility field as a function of grain size Definitions: 1) A frequently used definition is based on the resistively measured superconducting transition, the criterion being the 10% of RN or the intersection of the extrapolated linear part of R(T) with R=0 R(T) 10% RN T 2) The field at which the the inductively measured critical current vanishes R. Flukiger et al., « Superconducting properties of MgB2 tapes and wires », Physica C 385 (2003) 286-305

11. Université de Genève Irreversibility field as a function of grain size Third Definition: 3) The onset of the third harmonic susceptibility, in presence of a magnetic field Hdc>> Hac 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 Jc

12. Université de Genève Modified Walters Spiral (WASP) MgB2 Tape Strain gauges d=26 cm Strain Effect on MgB2 long tape 100 h ball milled

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 Jc and the n-values of the Fe/MgB2 tapes, 3 h and 100 h ball milled have been compared. An enhancement is obtained for the smaller particle size. The critical current densities Jc 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 Birr 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. Université de Genève n values for Fe/MgB2 tape