Zhang Pingxiang

Magnetization study of ITER-type internal-Sn Nb3Sn superconducting wire

Through magnetization measurement with a SQUID magnetometer the heat treatment optimization of an international thermonuclear experimental reactor (ITER)-type internal-Sn Nb3Sn superconducting wire has been investigated. The irreversibility temperature T*(H), which is mainly dependent on A15 phase composition, was obtained by a warming and cooling cycle at a fixed field. The hysteresis width ΔM(H) which reflects the flux pinning situation of the A15 phase is determined by the sweeping of magnetic field at a constant temperature. The results obtained from differently heat-treated samples show that the combination of T*(H) with ΔM(H) measurement is very effective for optimizing the heat reaction process. The heat treatment condition of the ITER-type wire is optimized at 675°C/128 h, which results in a composition closer to stoichiometric Nb3Sn and a state with best flux pinning.

Influence of Nb Diffusion Layer on Superconductivity of MgB2/Nb/Cu Wires

Abstract The MgB 2 wires were prepared by in-situ Powder-in-Tube (PIT) method with Nb/Cu compounds tube as the sheath and then were heat treated at various temperatures for 2 h in flowing argon. The resistivity ( R-T ), magnetic moment ( M-T ), transport critical current ( I c - B ) and magneto optical (MO) properties of MgB 2 wires were analyzed. The results show that there is a diffusion layer between MgB 2 superconducting core and Nb barrier layer when the heat-treatment temperature is higher than 750 °C, and this diffusion layer obstructs the current transfer into MgB 2 superconductor core from the Cu sheath. This indicates that the best heat-treatment temperature for the MgB 2 wires with Nb as the barrier layer should be lower than 750 °C.

Influence of Cu Content in Precursor Powders on the Phase Evolution and Superconducting Properties of Bi-2212 Superconductors

Abstract Precursor powders of Bi 2.1 Sr 1.96 CaCu x O 8+δ (Bi-2212) high temperature superconductors with different nominal Cu ratios of x =2.0, 2.1, 2.2, 2.4 were fabricated by a modified co-precipitation process. The influences of Cu ratios on the phase evolution process during sintering were investigated. Bi-2212 thick films and single filament tapes were fabricated with dip-coating process and powder in tube process, respectively. Obvious influences of Cu ratios on the phase compositions, microstructures and superconducting properties were discussed. Results show that the initial Cu ratio can affect the thermodynamic properties of Bi-2212 phase, thus changing phase evolution process. With the increase of Cu ratio, the phase content of Bi-2201 decreases, while the content of AEC phase increases. The maximum critical current density is obtained in the x =2.2 film and tape simultaneously due to the proper phase composition and better texture structures.

Influence of Amorphous Carbon Doping on Superconductivity of MgB2/Nb/Cu Wires

Abstract The effects of amorphous carbon doping on superconducting properties of MgB 2 /Nb/Cu wires fabricated by the in-situ powder-in-tube (PIT) method have been investigated. Using Nb as the barrier and Cu as the stabilizer, the MgB 2 wires were fabricated by cold drawing. The wires of MgB 2- x C x ( x = 0.0, 0.05, 0.08, 0.10, 0.15) have been investigated to realize the effect of amorphous carbon doping on the phase formation, microstructure and superconducting properties. Characterization of MgB 2 /Nb/Cu wires was carried out using XRD, SQUID, SEM/EDS, and I c measurements. XRD result shows that the high purity MgB 2 phase is acquired after heat-treatment at 700 °C. The microstructure observation for wires shows that the MgB 2 /Nb/Cu wires have better grain connectivity after doping amorphous carbon, and Energy Dispersive X-ray (EDS) analysis confirms the uniform distribution of carbon in the MgB 2 superconducting phase. The critical current density ( J c ) of wires was measured in different magnetic fields by a standard four probes method, and the transport J c values as high as 1.4 × 10 5 A/cm 2 (4.2 K, 5 T) and 3.3 × 10 4 A/cm 2 (4.2 K, 10 T) have been achieved.