Correlation between the critical-current anisotropy and the microstructure of ex situ powder-in-tube processed MgB2 tapes

The MgB2 superconductor is a promising material for the coil conductors in the superconducting magnets. The anisotropy of the upper critical field of MgB2 is one of the limiting factors to the critical current density especially in the high magnetic field. The correlation between the critical current density and the microstructure of the MgB2 core part in the tape processed by the ex situ powder-in-tube method was investigated to obtain a clue for improving the critical current density values. The anisotropy in the field dependence of the critical current density was observed with respect to the angle between the applied magnetic field and the tape surface. Both the pole figure data in the x-ray diffraction analysis and the grain orientation map data in the electron back scattering pattern analysis indicated that the texture of the (001) plane occurred in the MgB2 core part of the tape quantitatively. This result suggests that the critical current density can be enhanced through the control of the microstructure of the MgB2 superconductor tapes.