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Abstract: A methodology of synchronous optimization design of magnets under construction according to original design scheme is put forward in this paper, and it has been successfully used for refining design of a superconducting magnet on Lanzhou Penning Trap (LPT). This paper expounds the necessity of tracking optimization of magnet coil in the process of traditional manufacturing, and optimization design of magnet coils by particle swarm optimization is proposed. Particle swarm optimization is turned out to be an effective design method for magnet optimization. The expected homogeneity of the magnet is improved to 200ppm from 1150ppm through the refining optimizing, which provides important guarantee for required homogeneity of the whole magnet. [Copyright &y& Elsevier]

Magnetic hysteresis loops are measured on Bi2Sr2CaCu2O8+δ (Bi-2212) single crystal with different surface states and shapes. The result obtained on Bi-2212 single crystals with dirty and clean surfaces demonstrates that variation of surface state does not result in the disappearance of anomalous magnetization peak H2p and has only an influence on the width of magnetic hysteresis loops. The result obtained on Bi-2212 single crystals with elongated and circular shapes shows that the variation of shape also does not give rise to the disappearance of H2p. The origin of H2p of Bi-2212 single crystal is suggested to originate from other intrinsic reasons and should not be attributed to the surface state and surface shape. [Copyright &y& Elsevier]

Bi2−xPbxSr2CaCu2Oy ((Bi,Pb)-2212) single crystals with a large doping range up to x=0.8 have been grown by the conventional self-flux method. The resistivity anisotropy of (Bi,Pb)-2212 single crystals and their transport properties under applied magnetic fields with H∥c have been systematically studied. In-plane resistivity (ρab), out-plane resistivity (ρc) and anisotropy (γ) of (Bi,Pb)-2212 are significantly reduced by heavy Pb doping. The dissipation behavior of (Bi,Pb)-2212 single crystals in the mixed state can be well described by the thermally activated flux creep model and flux creep is obviously suppressed for heavily Pb-doped single crystals. The origin of the improved flux pinning is suggested to stem mainly from the reduced anisotropy and the improved coupling strength between Cu–O layers due to Pb-doping. [Copyright &y& Elsevier]

MgB2/Cu tapes were fabricated by power-in-tube technique using MgB2 superconducting powder and no post-annealing treatment was performed for the prepared tapes. Both X-ray diffraction and scanning electron microscopy results indicate that there is no obvious texture of grains for the tape samples. However, compared with the bulk sample, evident shifting and broadening of diffraction peaks is observed and Tc is reduced for the tape samples. In addition, it is found that there exists a remarkable difference in flux pinning ability for tapes prepared using wires with different diameters. The difference seems to originate from the different strain and microstructure defects of MgB2 grains caused by cold working. [Copyright &y& Elsevier]

Anomalous magnetization is investigated on a heavily Pb-doped Bi2Sr2CaCu2O8+δ as-grown single crystal [(Bi,Pb)-2212] with Tc=92 K. Both the anomalous magnetization peak H2p and the onset of the anomalous magnetization peak Hon are detected in temperature region from 0.3Tc to 0.9Tc based on the descending field branch of magnetic hysteresis loops. At low temperatures below 20 K, the magnetic hysteresis loop behaves as an obvious asymmetry. The double magnetic hysteresis behavior is observed at high temperatures close to Tc. The temperature dependence of H2p can be described according to the thermal disorder induced decoupling theory. The double magnetization behavior may be ascribed to the existence of intra-grain granularity due to the inhomogeneity of oxygen distribution induced by heavily Pb-doping. [Copyright &y& Elsevier]

Y-deficient Y1-xBa2Cu3O7-δ films (x=0, 0.05, 0.1) are fabricated on LaAlO3 (0 0 1) single crystal substrates using trifluoroacetate-based metalorganic deposition (TFA-MOD). X-ray diffraction patterns show that all films are highly c-axis oriented. The measurement of the resistance transition broadening under the applied magnetic field perpendicular to the surfaces of YBCO films indicates that a slight Y-deficiency (Y0.95Ba2Cu3O7-δ) in YBCO films is favorable to improve flux pinning. However, a further increasing of Y-deficiency (Y0.9Ba2Cu3O7-δ) leads to the degeneration of flux pinning abilities. The improvement of flux pinning may be related to the BaCuO2 phase particles with submicrometer scale or the defects induced by slight Y-deficiency. [Copyright &y& Elsevier]

The resistive transitions of (Bi, Pb)2Sr2Ca2-xPrxCu3Oy silver sheathed tapes with x=0.0, 0.001, 0.002 have been measured under applied magnetic fields oriented perpendicular to tape plane (Hǁc) from 0 to 7 T. The transitions can be well agreed with the thermally activated flux creep model by Anderson: R(T,H)=R0exp[-U(H)/kBT] in the low resistance range. Under lower applied magnetic field the calculated activation energies U(H) of flux motion increased drastically in the samples with proper amount of Pr-ion defects, for example, U is about 29,000 K for tape with x=0.001 at 0.025 T while that is 4200 K for that without ion defects. For our samples, U are all well fitted with the law of U/(1-Tirr/Tc0)∝1/Hα. With the doped Pr-ion defects, the data α are obviously increased from 0.67 to 1–1.22. The markedly changed α indicated the flux creep according to varied manners in different samples. [Copyright &y& Elsevier]

Bi-2223/Ag tapes with nominal chemical compositions of Bi1.8Pb0.4Sr2Ca2.2Cu3−xNixOy (x=0, 0.003 and 0.005) were prepared by powder-in-tube method. The XRD and SEM analysis of their phases and microstructures show that a proper amount of Ni doping at Cu sites does not impede the formation of Bi-2223 phase. The measurements of magnetic field dependence of critical current density Jc and resistance transition broadening under magnetic fields oriented along c-axis indicate that the Ni doping at Cu site can improve the flux-pinning ability of Bi-2223/Ag tapes significantly. The improvement of flux pinning is suggested to originate from the introduction of flux pinning centers due to the destruction of local superconductivity caused by Ni doping at Cu sites because of the ferromagnetism of Ni. [Copyright &y& Elsevier]

(Bi,Pb)2.2Sr2Ca2.2Cu3−xCrxOy silver sheathed tapes with x=0.0 (un-doped), 0.0005, 0.001, 0.002 and 0.004 (Cr-doped) have been investigated. X-ray diffraction analyses and transmission electron microscopy observation manifest that partial Cr substitution for Cu may introduce a lot of fine Cr-ion defects into the samples. The different performances of critical current densities (at 77 K) under applied magnetic fields, the irreversibility lines and activation energies of flux motion indicate that their flux pinning has been enhanced by induced Cr-ion defects obviously. Their pinning forces have also been analyzed, and the results imply that the flux pinning in Cr-doped tapes enhanced mainly originate from the fine normal-like Cr-ion defects. [Copyright &y& Elsevier]

The samples of Mg deficiency with different Mg nominal content (Mg1−xB2) are prepared by the solid-state reaction method at the sintering temperatures of 900 and 640 °C. The effects of Mg deficiency on the structure and superconducting properties are investigated by the Rietveld refinement of X-ray powder diffraction and the resistance measurement, respectively. The results show that the lattice parameters of the samples sintered at different temperatures are of a similar variation, i.e., a decreasing and c increasing with increasing x, respectively. Tc of the samples decreases with increasing x and the maximum Tc variation of ΔTc(Tcmax−Tcmin)∼2 K is observed for samples sintered at high temperature. It is concluded that the nominal Mg content reduction does not give rise to serious Mg deficiency and slight Mg deficiency does not result in a remarkable change of Tc and normal state properties of the samples. [Copyright &y& Elsevier]