Neutron Irradiation of SiC Doped and Magnesium Rich MgB$_{2}$ Wires

Abstract

Monofilamentary SiC doped wires and multifilamentary wires made from magnesium-rich powders were exposed to thermal neutrons. The induced defects enhance the field, up to which the resistivity is zero ("irreversibility field") at 4.2 K (by about 1-2 T), and, therefore, reduce the field dependence of the critical current density. On the other hand, the transition temperature decreases from about 35 K to 32.5 K, thus restricting the beneficial effect of neutron irradiation to low temperatures. Changes of the critical current density are discussed in terms of changes of the fundamental superconducting parameters (condensation energy, upper critical field, anisotropy) and changes of the flux pinning properties.

Magnetic properties and critical currents of MgB2

“…p(J ) denotes the fraction of grains with critical current densities above J . Good agreement with experimental data was obtained [253,393,426,427] with a simple power law…”

Influence of crystalline boron powders on superconducting properties of C-doped internal Mg diffusion processed MgB2wires

“…By decreasing the wire diameter to 0.63 mm, the J c -B properties are further improved. The highest layer J c of 4.8×10 4 A cm −2 at 10 T is achieved for the IMD-processed C-doped MgB 2 wire heated at 650 °C for 5 h, which is 37% higher than that of the 1.75 mm diameter wires at the same heating conditions. Besides, the 0.63 mm diameter wire sintered at 650 °C for 3 h has a similar layer J c to that sintered at 700 °C for 1 h. We calculated the non-barrier J c for I11 with the largest layer J c in order to compare to the PIT-processed MgB 2 fairly.…”

“…superconducting properties, especially the upper critical field (B c2 ), vortex pinning and intergranular connectivity, still need to be optimized to make MgB 2 suitable for power applications [3]. Various methods have been used to improve the J c -B properties, such as irradiation with heavy ions [4], processing in an external magnetic field [5], mechanical alloying [6][7][8][9] and chemical doping [10][11][12][13][14][15][16][17][18][19]. An unacceptable problem of the in situ PIT process is the low mass density, which is caused by the reduction of volume and the introduction of voids during the reaction process of Mg and B powders.…”

Calculation of the volume pinning force inMgB2superconductors

“…6,41 The percolation threshold mainly depends on the number of connections between the grains; thus, clean dense samples have a comparatively small p c and porous or dirty samples with a large amount of secondary phases have a larger p c . 21,42 The peak field only changes from 0.09 for p c = 0.2 to 0.103 for p c = 0.3 in the case of a typical anisotropy of 4 ͑inset in Fig. 3͒.…”