Superconducting filaments

Correlating the electrical and mechanical data, it appears that mechanical failure was due to damage of the copper matrix, rather than the NbTi superconducting filaments. NbTi is nearly elastic up to the point of fracture and, electrically, no damage was measured. Copper, on the other hand, has a very low yield stress and deforms plastically, starting at about 0.2% strain, which, as expected, is about half the above-measured peak-to-peak endurance strain limit [% This can be observed in both the stress-strain curves and the resistivity of the matrix. 

The FEA simulation revealed that high tensile stress is applied to the core of a wire under the conditions under which filament breaks are likely to occur. For this reason, to prevent filament breaks, brittle superconducting filaments should not be placed at the center of a wire. 

Koza, J. A., E. W. Bohannan, and J. A. Switzer. 2013. Superconducting filaments formed during nonvolatile resistance switching in electrodeposited fl-BijOj. ACS Nano 7 9940-9946. 

It is widely used as filaments for mass spectrographs and ion gauges. Rhenium-molybdenum alloys are superconductive at 10 K. 

Single or multifilament wire with a matrix of Cu or CuNi is commonly available in several diameters. Single-filament wire is usually reserved for low current applications. Multifilament wire has a higher critical current, since supercurrents flow only in the surfaces of superconductors, and in multifilamentary wire there is more superconducting surface. 

Beltrami fields have been advanced [4] as theoretical models for astrophy-sical phenomena such as solar flares and spiral galaxies, plasma vortex filaments arising from plasma focus experiments, and superconductivity. Beltrami electrodynamic fields probably have major potential significance to theoretical and empirical science. In plasma vortex filaments, for example, energy anomalies arise that cannot be described with the Maxwell-Heaviside equations. The three magnetic components of 0(3) electrodynamics are Beltrami fields as well as being complex lamellar and solenoidal fields. The component is identically nonzero in Beltrami electrodynamics if is so. In the Beltrami... 

This is a very unique situation for superconductivity, since in the previous experience inhomogeneity is almost always harmful to superconductivity. Why is the superconductivity in the cuprates so different While further research is clearly required to answer this puzzle, one possibility is that the spatial confinement produces the vibronic resonant state of phonon and charge that enhances HTSC [15,23], The benefit of spatial confinement on HTSC has been strongly advocated for some time by Phillips with the idea of filamental superconductivity [24] and more recently by Bianconi [25] as the shape resonance effect. In both cases the effect arises due to the enhancement of the local density of states (DOS). An additional, and possibly more central, effect of confinement is to reduce the group velocity of electrons and bring it comparable to the phonon velocity, thus... 

HTS materials, becanse of their ceramic nature, are quite brittle. This has introduced problems relative to the winding of superconducting magnets. One solution is to first wind the magnet with the powder-in-tube wire before the ceramic powder has been bonded and then heat treat the desired configuration to form the final prodnet. Another solution is to form the superconductor into such fine filaments that they remain sufficiently flexible even after the powder has been heat treated. 

Many authors have discussed the excitonic mechanism (36-37.) of superconductivity, in which the effective attractive interaction between conduction electrons originates from virtual excitations of excltons rather than phonons. The basic idea of the models proposed is that conduction electrons residing on the conducting filament (or plane) induce electronic transitions on nearby easily polarizable molecules (or complexes), which result in an effective attractive interaction between conduction electrons. As perhaps a striking realization of the excitonic mechanism of superconductivity,... 

Gilli and Kamaye went on to build the analogy with type II superconductors into their models of filaments. Firstly they noted that the coexistence of vortices in the bulk of the superconducting volume results from the existence of small regions that make possible a partial penetration of the magnetic flux... 

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