Properties of superconducting MgB_2 wires: "in-situ" versus "ex-situ" reaction technique

Abstract

We have fabricated a series of iron-sheathed superconducting wires prepared by the powder-in-tube technique from (MgB_2)_{1-x}:(Mg+2B)_x initial powder mixtures taken with different proportions, so that x varies from 0 to 1. It turned out that "ex-situ" prepared wire (x = 0) has considerable disadvantages compared to all the other wires in which "in-situ" assisted (0 < x < 1) or pure "in-situ" (x = 1) preparation was used due to weaker inter-grain connectivity. As a result, higher critical current densities J_c were measured over the entire range of applied magnetic fields B_a for all the samples with x > 0. Pinning of vortices in MgB_2 wires is shown to be due to grain boundaries. J_c(B_a) behavior is governed by an interplay between the transparency of grain boundaries and the amount of "pinning" grain boundaries. Differences between thermo-magnetic flux-jump instabilities in the samples and a possible threat to practical applications are also discussed.

arXiv commentTo be published in Supercond. Sci. Technol. (2003), in press

References in corpus (9)

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• High critical current density and improved flux pinning in bulk MgB2 synthesized by Ag addition
• Overcritical state in superconducting round wires sheathed by iron
• Increases in the Irreversibility Field and the Upper Critical Field of Bulk MgB2 by ZrB2 Addition
• The effect of sample size on field dependence of Jc for MgB2 superconductor
• Superconducting screening on different length scales in high-quality bulk MgB2 superconductor
• Transport and magnetic Jc of MgB2 strands and small helical coils
• Enhancement of flux pinning and high critical current density in graphite doped MgB2 superconductor
• Impact of strain and field ramp functional form on thermomagnetic instabilities in composite Nb3Sn wires with multi-filaments inside the superconducting coil