Local strain / stress and their influence to mechano - electromagnetic properties of in composite superconducting wires

Abstract

Practical superconducting wires are designed with a composite structure to meet the desired engineering characteristics by expert selection of materials and design of the architecture. In practice, the local strain exerted on the superconducting component influences the electromagnetic properties. Here, recent progress in methods used to measure the local strain in practical superconducting wires and conductors using quantum beam techniques is introduced. Recent topics on the strain dependence of critical current are reviewed for three major practical wires: $Nb_3Sn$, BSCCO-2223 and REBCO tapes.

Fig. 1. Principle of strain measurement by diffraction method.

Fig. 2. Low temperature apparatus for strain measurement under tensile strain at RESA, JRR-3.

Fig. 3. Setup for strain measurement on Nb₃Sn wires, where 1: three Nb₃Sn wires, 2: dummy wire under no applied strain, 3: Nb₃Sn powder, 4: Ni powder, 5: strain gauges and 6: thermometer.

Fig. 4. Low temperature apparatus at BL19 TAKUMI of J-PARC.

Fig. 5. Detail of the sample holder.

Fig. 6. Room temperature apparatus at BL46XU SPring-8.

Fig. 7. Two types of sample holder for diffraction experiments.

Fig. 8. Open cryostat system for I_c measurements under tensile and compressive uniaxial load.

Fig. 9. Cross section of the Nb₃Sn wires.

Fig. 10. Applied strain dependence of normalized critical current for ITER Nb₃Sn strand fabricated by Hitachi cable.

Fig. 11. Applied strain dependence of local strain exerted on Nb₃Sn filaments at 9.3 K.

Fig. 13. Applied strain dependence of the normalized critical current for BSCCO tapes laminated with and without SS sheet.

Fig. 14. Applied strain dependence of local strain exerted on BSCCO filaments for DI-BSCCO tapes.

Fig. 15. Stress - strain curve at room temperature for four DI - BSCCO tapes laminated with SS sheet and one bare tape.

Fig. 16. Change of three kinds of strains as a function of pretension, where A95 is the strain to retain 95% Ic , Ay is the yielding strain and Ar is the relaxation strain of BSCCO filaments.

Fig. 17. Normalized critical currents, I_c/I_c0 and I_cr/I_c0 as a function of applied strain for Superpower tape free standing.

Fig. 19. Change of local strain exerted on REBCO layer as a function of applied strain at RT for the tape free standing and the tape mounted on SB for Superpower tape.

Fig. 20. Normalized critical currents obtained by two techniques as a function of local strain exerted on REBCO layer for Superpower tape.

Fig. 12. Record of stress – strain data during the neutron diffraction measurements.

Fig. 18. Normalized critical currents, I_c/I_c0 and I_cr/I_c0 as a function of applied strain for Superpower tape mounted on SB.

TABLE I NUMERICAL COMPARISON FOR USUAL NEUTRON AND X-RAY DIFFRACTION EXPERIMENTS FOR COPPER.