Approach for the fabrication of MgB2 superconducting tape with large in-field transport critical current density

Abstract

The paper reports the first successful fabrication of MgB 2 superconducting tape using a flexible metallic substrate as well as its strong pinning force, which was verified by direct measurement of transport critical current density. The tape was prepared by depositing MgB 2 film on a Hastelloy tape buffered with an YSZ layer. The J c of the tape exceeds 10 5 A/cm 2 at 4.2K and 10T, which is considered as a common benchmark for magnet application. The J c dependence on magnetic field remains surprisingly very small up to 10T, suggesting that the tape has much better magnetic field characteristic than conventional Nb-Ti wires in liquid helium.The newly discovered MgB 2 superconductor 1 is expected to be useful for various electric power applications as well as electronic device applications because its transition temperature is much higher than those of conventional metallic superconductors such as Nb-Ti and Nb 3 Sn. In order to evaluate the potentiality for p ower applications, the development of wire processing techniques is essential. The first attempt at wire fabrication was the magnesium vapor diffusion to boron fibers presented by Canfield et al 2 . Recent efforts at wire fabrication have centered on developing the powder-in-tube (PIT) process due to its greater easiness of scaled up production [3][4][5][6][7] . The transport critical current density J c at 4.2K and in self-field of the PIT processed tapes has already exceeded the practical level of 10 5 A/cm 2 . However, the J c rapidly decreases in an applied magnetic field due to its weak pinning force. The J c values at 4.2K and 10T reported so far for PIT processed wires and tapes remain as low as the order of 10 3 A/cm 2 , although the values are being steadily improved.In contrast to the relatively poor in-field J c values of the tapes and bulks, there are several papers on MgB 2 thin films, which reported very much higher Hc 2 values and J c values in applied magnetic fields than those of tape and bulk samples 8,9 . Kim et al 9 reported a large transport J c value of 10 5 A/cm 2 at 5T and 15K for the c-axis oriented MgB 2 film prepared on an Al 2 O 3 substrate. Those results suggest to us that the MgB 2 phase formed by vapor deposition techniques has extremely strong pinning force. However, all experiments on the thin films have been performed using ceramic substrates, which are not suitable for long length production of flexible conductor. This paper reports a successful new approach to fabricate MgB 2 tape that is the combination of the high critical current density achieved by vapor deposition and the use of flexible metallic substrate tape. The technique is similar to the so-called coated conductor techniques developed for YBa 2 Cu 3 O y (Y-123), where Y-123 thin films are deposited on various buffer layers on a metallic substrate 10 -12 . The MgB 2 tape obtained in this work has an excellent transport J c of 1.1x10 5 A/cm 2 at 4.2.K and 10T. It is also surprising that the J c dependence on the magnetic field remains extremely small up to 10T, ...

Mechanically reinforced MgB2 wires and tapes with high transport currents

“…In a quite recently reported thin film sample extraordinary high current densities of J c > 10 5 Acm -2 at 4.2 K, 10 T, and an irreversibility field of 21 T (4.2 K) was measured and H c2 = 40 T was confirmed [12]. Investigations on single crystals confirmed the anisotropic superconductivity in MgB 2 [13].…”

“…thin films with textured MgB 2 [11,12] demonstrated the potential for the achievable critical current densities of J c > 10 7 Acm -2 (4.2 K, self field) and had as expected anisotropic superconducting properties with upper critical fields H c2 up to 40 Tesla (H || a, b). In a quite recently reported thin film sample extraordinary high current densities of J c > 10 5 Acm -2 at 4.2 K, 10 T, and an irreversibility field of 21 T (4.2 K) was measured and H c2 = 40 T was confirmed [12].…”

Unusual effects of anisotropy on the specific heat of ceramic and single crystal MgB2

“…9). As discussed in the Section V, the contribution at low field (< 0.5 T) and low temperature mostly comes from the isotropic π- H obtained by irradiation, as well as by other types of disorder [78,79], shows that this is not a definitive limit.…”

Microscopic role of carbon on MgB2 wire for critical current density comparable to NbTi

“…Two important ways to increase critical current density are by the enhancement of the pinning force 30,31 and/or by increasing the crosssectional area fraction. 7 First, we consider the area fraction.…”