Nano-SiC doped MgB2 tapes were prepared by the in situ powder-in-tube method. Heat treatment was performed at 650℃ for 1 h. XRD data indicate that SiC particles had reacted with the MgB2 during sintering process. MgB2 core seemed to be denser after SiC doping, and the critical temperature was slightly depressed. The critical current density Jc of the SiC doped tapes was significantly enhanced in magnetic fields up to 14 T compared to the undoped ones. For the 5% SiC doped samples, Jc was in- creased by a factor of 32 at 4.2 K, 10 T. The enhancement of Jc-B properties in SiC doped MgB2 tapes is considered to be due to the enhancement of grain linkages and the introduction of effective flux pining centers. The substitution of B by C in MgB2 grains is thought to be the main reason for the improve- ment of the flux pinning ability in SiC doped MgB2 tapes.
由于铁的磁化特性,对于铁包套的MgB_2线材来说,线材的截面形状和铁包套的厚度都会影响到MgB2超导芯的磁场,进而影响到MgB_2线材的载流能力。文中将建立几种典型的单芯及多芯MgB_2线材模型,并利用有限元方法(finite element method,FEM)分析铁包套对这些模型中超导芯的最大磁场B_(max)和临界电流密度J_c,经过对这几种典型结构的载流能力进行比较,可以得到一些有益于改善铁包套MgB_2线材的载流能力的合理性建议。
The amplitude-dependent ac susceptibility of high-temperature superconductors is shown to obey some empirical scaling relations. We try to analyze this behavior by extending a dc nonlinear response function of mixed state to the ac cases. The derived equations for critical current and ac susceptibility x(T) agree with the scaling relations of experimental data.
CHEN Kaixuan NING Zhenhua XU Hengyi QI Zhi LU Guo WANG Furen YIN Daole
