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The critical current density (Jc) of hot isostatic pressed (HIPed) MgB2 wires, measured by d.c. transport and magnetization, is compared with that of similar wires annealed at ambient pressure. The HIPed wires have a higher Jc than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field (Hirr). The HIPed wires are promising for applications, with Jc>106 A/cm2 at 5 K and zero field and >104 A/cm2 at 1.5 T and 26.5 K, and Hirr ~ 17 T at 4 K. The improvement is attributed to a high density of structural defects, which are the likely source of vortex pinning. These defects, observed by transmission electron microscopy, include small angle twisting, tilting, and bending boundaries, resulting in the formation of sub-grains within MgB2 crystallites.Comment: 13 pages,3 figure

We report dc transport and magnetization measurements of J c in MgB 2 wires fabricated by the powder-in-tube method, using commercial MgB 2 powder with 5 %at Mg powder added as an additional source of magnesium, and stainless steel as sheath material. By appropriate heat treatments, we have been able to increase J c by more than one order of magnitude from that of the as-drawn wire. We show that one beneficial effect of the annealing is the elimination of most of the micro-cracks, and we correlate the increase in J c with the disappearance of the weak-link-type behavior.

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Abstract. We present the fabrication and test results of Hot-Isostatic-Pressed (HIPed) Powder-in-Tube (PIT) MgB 2 coils. The coils properties were measured by transport and magnetization at different applied fields (H) and temperatures (T ). The engineering critical current (J e ) value is the largest reported in PIT MgB 2 wires or tapes. At 25 K our champion 6-layer coil was able to generate a field of 1 T at selffield (I c > 220 A, J e ∼ 2.8 × 10 4 A/cm 2 ). At 4 K this coil generated 1.6 T under an applied field of 1.25 T (I c ∼ 350 A, J e ∼ 4.5 × 10 4 A/cm 2 ). These magnetic fields are high enough for a superconducting transformer or magnet applications such as MRI. A SiC doped MgB 2 single layer coil shows a promising improvement at high fields and exhibits J c > 10 4 A/cm 2 at 7 T.