Influence of production parameters on the superconducting properties of NbTi and Nb3Sn wires

The commercial specification of superconducting NbTi and Nb3 Sn composite wires is normally given by parameters such as the critical current (which is dependent on conductivity, temperature, and magnetic field), an empirically deduced parameter for which the effective resistivity is about 10-14 Ωm, wire and filament diameter, and twist length. To some extent their values cannot be chosen independently, nor do they guarantee proper operation of the system in all aspects. It is argued that for Nb3Sn composite, depending on the production process, an extra set of parameters describing the stress sensitivity seems to be needed to specify the quality of the composite

New developments on calculating and measuring ac losses in composite superconductors

A method for the complete numerical solution of the Maxwell equation for a multifilamentary wire carrying a transport current and subject to applied fields of arbitrary direction, where both current and applied fields have arbitrary time dependence, has been developed. First results show unexpected differences from analytical models used in the past. From both approaches current degradation effects can be estimated and loss contributions resulting from the combined action of applied field and current can be calculate

A.c. stability and a.c. loss in composite superconductors

Two methods of loss calculations are reviewed. The first method, for loss calculations in wires, uses a numerical solution of the Maxwell equations. The second method makes use of Kirchhoff's equations and is much better suited to cables, including braids. Both methods require a knowledge of the constitutive equations relating E and j or V and l in the composite conductor. Experimental results regarding the stability of large cables are presented and a way of improving the stability of a single strand is suggested

Electrodynamic sources of non-uniform heat production in composite superconductors causing instabilities

Model calculations of the electrodynamic properties of superconducting composites are usually carried out assuming that the material constants, such as critical current density and resistivity, are uniform over the cross-section of the composite, or at least rotationally symmetric. Also, the applied field is usually considered to be uniform over a distance compared to the composite diameter. In this paper the possibility will be discussed that non-uniformity in field and material properties may cause significant non-uniformity in heat production so to disturb the local temperature pattern and form sources of instabilities and quenches. The influence of the cooling conditions on the transport current-carrying capacity in the a.c. regime is also discussed

A macroeconomic two-country model with price-discriminating monopolists

Macroeconomic Models

Anomalous skin effect in cylindrical samples

A description is given of the anomalous skin effect in a cylinder placed in an a.c. magnetic field parallel to the cylinder axis. The necessary nonlocal relation between current density and electric field inside the sample is established with the aid of Boltzmann's transport equation. Results are presented in terms of the current density in the sample and its magnetic susceptibility