Relation between critical current and exponentnin Bi(2223)/Ag tapes

Abstract

Transport critical currents I c at 1 µV cm −1 and exponents n of the power law characteristics (E ∼ j n ) of single-filament Bi(2223)/Ag tapes were measured at 77 K in the self-field and in external magnetic fields up to 1.2 T. The effects of tape orientation in a transverse magnetic field from −120 • to +120 • (related to the basic state at B c-axis) were investigated as well. The values of the transport critical current I c and exponent n as well their mutual relation reflect the quality of the Josephson-linked current network connectivity at B < B * (B * is the cross-over field at which the weak-link currents cease to contribute to the transport current) and the ability of pinning centres to pin flux lines in the whole magnetic field region. The weak-link connectivity and the pinning potential are directly related to the structural state of the samples resulting from their different thermomechanical treatments. The better the structural quality, the higher the I c /n ratio. This ratio seems to reflect the effective number of intergrain connections and pinning centres.

Behaviour of filamentary MgB2wires subjected to tensile stress at 4.2 K

“…An attempt to find a relation between the n-value and an average value of the effective pinning potential has been made for BSCCO/Ag [28]. Fabbricatore et al [29] analysed pinning energy in MgB 2 wires following the theory of Thinkham for the temperature dependence g(t = T/T c ) [30] and determined n(B, t) = U 0 (B)g(t)/k B T, (11) where U 0 is the averaged value of the pinning potential and k B the Boltzmann constant.…”

“…18-30 filament MgB 2 wires from three producers-HyperTech (HyT), IFW-Dresden (IFW) and IEE-Bratislava (IEE)-have been selected for the tensile stress testing at 4.2 K. The name of each presented wire consists of the short name of producer, the number of filaments (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) and the material of outer sheath (M-Monel, G-GlidCop R , S-stainless steel). Table 1 summarize the wire's diameter, composition and heat treatment (HT) conditions and figure 1 shows typical cross-sections.…”

MgB2 cables made of thin wires manufactured by IMD process

“…The determination of n(B,t) was done from the I-V curves measured MgB 2 wires at a constant temperature [20]. The ratio of I c /n was also analyzed in details for Bi-2223/Ag superconductors and it was shown that the higher the I c /n ratio the better structural quality reflecting the effective number of inter-grain connections and pinning centers [21]. Consequently, n values of presented samples represent intrinsic pinning energy and also extrinsic quality e.g.…”

Current Estimation of an HTS BSCCO Magnet Having Multiple Power Sources Based on the Field Dependent $E{\hbox{–}}J$ Relation

“…4. The profile of field dependent value had been reported to be similar with that of the curve provided that was replaced by [8], [9]. and were the critical current and value at self field.…”