The effects of external reinforcement on the mechanical property and the axial tensile stress/strain dependence of the critical current Ic in Bi (2212) superconducting tapes were evaluated at a temperature of 4.2K and a magnetic field of 14T. The monocore and 19-core superconducting tapes with three kinds of sheath-Ag, Zr-reinforced Ag, and Ag/Zr-reinforced Ag double layer-were incorporated with reinforcing CuAg tape. As a result of this reinforcement, the 0.2% proof stress of superconducting tapes increased markedly without significant degradation of the Ic. The limiting value in strain for Ic degradation in Ag-sheathed tape was slightly improved, and that in stress was markedly improved. The improvement in the limiting value in strain or stress for the degradation was more evident in tapes with Zr-reinforced Ag sheath, compared with those with pure Ag sheath.
A new method is proposed to carry out numerical calculations on the shape of field-free core, current distribution, and AC transport losses in self-fields as a function of current amplitude I0 for high-Tc superconducting tapes with arbitrary cross-sectional geometry. Its validity can be confirmed by verifying that calculated results of AC losses for elliptic tapes agree with the prediction advanced by the theory of Norris. An application to rectangular tapes leads to the finding that the AC losses for them behave as a thin-strip superconductor in high I0 values near critical current Ic, but gradually deviate from this behavior with decreasing I0. A decrease in the aspect ratio of width to thickness for rectangles makes the deviation more remarkable. By using this method, the AC transport losses for two kinds of the 7-filamentary tapes with different filament arrangements are calculated, and the results are compared with the experimental behaviors of losses for tapes fabricated by a powder-in-tube method using the Ag sheath. The measured losses can be explained neither by the prediction for an elliptic tape nor by that for a thin strip based on the theory of Norris. Furthermore, the loss values depend on the filament arrangement, which is explained by the calculated results of loss-density distribution. The influence of filament arrangement on the loss behaviors is suppressed as the number of filaments increases to 37, from 7.
A stray field from a superconducting coil restricts the use of SMES at a demand site, though SMES has an attractive potential for power management and quality control. The stray field outside a solenoid is analyzed by a series of Legendre polynomials, and the results are then applied to various coil configurations. The summation of magnetic moments from all coils must be zero, which leads the stray field decreasing as Rp-3 to vanish, where Rp is distance from the coil. The higher order of the stray field can be cancelled out if the coil arrangement is optimized. In this paper, we treat a single solenoid as a reference, and active shield coil, axially displaced coil, multipole coil and toroidal coil configurations to reduce the stray field. It is shown that the stray field from the active shield coil configuration decreases as Rp-7. On the other hand, the stray field from an axially displaced coil drops as a function of Rp-5. The multipole coil configuration has high potential to reduce the stray field because the stray field behaves like Rp-(n/2+3), where n is the coil number. The toroidal coil configuration has the stray field decreasing as Rp-(n+2), though it has alarge volume facility.
The two-fluid model explains the unique features of flow and heat transfer in superfluid helium, of He II. In the multidimensional analysis with a two-fluid model, much CPU time will be necessary because this model consists of four complicated equations. Thus we propose a new numerical model, called the simplified model, which is derived from the two-fluid model. It consists of a conventional continuity equation, a momentum equation for total fluid in the form of a modified Navier-Stokes equation, and an energy equation in the form of a conventional temperature-based energy equation in which the heat flux resulting from the Gorter-Mellink internal convection is properly incorporated. To verify the validity of the simplified model, its results are compared with results of the two-fluid model in the analysis of one-dimensional heat transfer in a vertical He II duct heated at the bottom boundary. To demonstrate the capability of the present model to deal with multidimensional problems, a two-deimensional analysis is performed for internal-convection heat transfer in an He II pool with one wall partially heated. Our purpose was to verify the validity of the simplified model in multidimensional analysis, so we compared the analytical results obtained by use of the simplified model with those obtained by the two-fluid model in a two-dimensional analysis. The validity of the analytical method, which obtained was adopted by Ramadan and Witt, is also discussed.