Investigation of local current flow in polycrystalline, anisotropic superconductors using finite element simulation

A finite element program was used to calculate current distributions in superconductors, assuming a nonlinear (power-law or percolation-type) local dependence of the electrical field on current density. A bicrystal geometry, which forms the basic building block of (Bi,Pb)2Sr2Ca2Cu3Ox powder-in-tube tapes and other polycrystalline conductors, was studied. Current–voltage curves and critical currents were calculated for different geometrical and electromagnetic parameters. Bicrystals of “brick-wall” and “railway-switch” geometry were compared, and it was found that in both cases anisotropy is the dominating factor determining the overall critical current. Strong anisotropy leads to current concentration around grain boundaries, thereby reducing the critical current. Addition of a grain boundary with finite resistance does not significantly change the current distribution within the grains.

[1]  B. Glowacki,et al.  Current transfer at superconducting Bi2Sr2CaCu2O8+δ–Ag joints , 1999 .

[2]  Peter P. Silvester,et al.  Finite Elements for Electrical Engineers , 1983 .

[3]  C. P. Bean,et al.  Magnetization of High-Field Superconductors , 1964 .

[4]  J. Evetts,et al.  A model for the V-I characteristics in brick-wall-like structures , 1993, IEEE Transactions on Applied Superconductivity.

[5]  P. Anderson,et al.  HARD SUPERCONDUCTIVITY: THEORY OF THE MOTION OF ABRIKOSOV FLUX LINES , 1964 .

[6]  D. Larbalestier,et al.  Current-limiting mechanisms in individual filaments extracted from superconducting tapes , 1998, Nature.

[7]  Grasso,et al.  Limits to the critical transport current in superconducting (Bi,Pb)2Sr2Ca2Cu3O10 silver-sheathed tapes: The railway-switch model. , 1995, Physical review. B, Condensed matter.

[8]  Charles M. Lieber,et al.  Nanorod-Superconductor Composites: A Pathway to Materials with High Critical Current Densities , 1996, Science.

[9]  S. Dou,et al.  Recrystallization effects and grain size in Bi-2223 tapes , 1998 .

[10]  Fisher,et al.  Thermal fluctuations, quenched disorder, phase transitions, and transport in type-II superconductors. , 1991, Physical review. B, Condensed matter.

[11]  Y. Yan,et al.  Structure of grain boundaries: Correlation to supercurrent transport in textured Bi_2Sr_2Ca_n−1Cu_nO_x bulk material , 1997 .

[12]  Coulter,et al.  Limits to the critical current in high-Tc superconducting tapes. , 1993, Physical review. B, Condensed matter.

[13]  J. Mannhart,et al.  Superconducting and normal-state properties of YBa2Cu3O7−δ -bicrystal grain boundary junctions in thin films , 1998 .

[14]  Gurevich.  Electromagnetic instabilities and current structures in anisotropic superconductors. , 1992, Physical review. B, Condensed matter.

[15]  S. Dou,et al.  Experimental assessment of the current-limiting mechanisms in BSCCO/Ag high-temperature superconducting tapes , 1997 .

[16]  J. Vargas,et al.  The Nature of Grain Boundaries in the High-Tc Superconductors , 1995 .

[17]  A. Gurevich.  NONLINEAR FLUX DIFFUSION IN SUPERCONDUCTORS , 1995 .

[18]  L. Méchin,et al.  Observation of viscous flux flow in YBa 2 Cu 3 O 7 − δ low-angle grain boundaries , 1998 .

[19]  L. Méchin,et al.  EVIDENCE FOR VORTEX PINNING BY DISLOCATIONS IN YBA2CU3O7-DELTA LOW-ANGLE GRAIN BOUNDARIES , 1998 .

[20]  A. Gupta,et al.  Flux creep characteristics in high‐temperature superconductors , 1990 .

[21]  Prester.  Dynamical exponents for the current-induced percolation transition in high-Tc superconductors. , 1996, Physical review. B, Condensed matter.

[22]  R. Yoshizaki,et al.  Ni-doping effect on the anisotropic resistivity in Bi2Sr2Ca(Cu1−xNix)2Oy single crystals , 1996 .

[23]  Malcolm McCulloch,et al.  Computer modelling of type II superconductors in applications , 1999 .