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Concept
Superconducting wire
Résumé
Superconducting wires are electrical wires made of superconductive material. When cooled below their transition temperatures, they have zero electrical resistance. Most commonly, conventional superconductors such as niobium–titanium are used, but high-temperature superconductors such as YBCO are entering the market.
Superconducting wire's advantages over copper or aluminum include higher maximum current densities and zero power dissipation. Its disadvantages include the cost of refrigeration of the wires to superconducting temperatures (often requiring cryogens such as liquid nitrogen or liquid helium), the danger of the wire quenching (a sudden loss of superconductivity), the inferior mechanical properties of some superconductors, and the cost of wire materials and construction.
Its main application is in superconducting magnets, which are used in scientific and medical equipment where high magnetic fields are necessary.
The construction and operating temperature will typically be chosen to maximise:
Critical temperature Tc, the temperature below which the wire becomes a superconductor
Critical current density Jc, the maximum current a superconducting wire can carry per unit cross-sectional area (see images below for examples with 20 kA/cm2).
Superconducting wires/tapes/cables usually consist of two key features:
The superconducting compound (usually in the form of filaments/coating)
A conduction stabilizer, which carries the current in case of the loss of superconductivity (known as quenching) in the superconductoring material.
The current sharing temperature Tcs is the temperature at which the current transported through the superconductor also starts to flow through the stabilizer. However, Tcs is not the same as the quench temperature (or critical temperature) Tc; in the former case, there is partial loss of superconductivity, while in the latter case, the superconductivity is entirely lost.
Low-temperature superconductor (LTS) wires are made from superconductors with low critical temperature, such as Nb3Sn (niobium–tin) and NbTi (niobium–titanium).
Source officielle
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