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Superconducting wire

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Title: Superconducting wire  
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Subject: Furukawa Electric, Superconducting magnetic energy storage, Wire, Superconductivity, Superconductors
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Superconducting wire

An example of a wire (V3Ga alloy) used in a superconducting magnet.

Superconducting wire is wire made of superconductors. When cooled below its transition temperature, it has zero electrical resistance. Most commonly, conventional superconductors such as niobium-titanium are used,[1] but high-Tc 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 helium or liquid nitrogen), 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.[2] Its main application is in superconducting magnets, which are used in scientific and medical equipment where high magnetic fields are necessary.

Often the superconductor is in filament form in a copper or aluminium matrix which carries the current should the superconductor quench for any reason. The superconductor filaments can form a third of the total volume of the wire.

Contents

  • Important parameters of SC wires/tapes/conductors 1
  • Types of Wire 2
    • LTS(Low Temperature Superconductor) Wire 2.1
    • HTS(High Temperature Superconductor) Wire 2.2
  • Preparation 3
    • Wire drawing 3.1
    • Surface diffusion 3.2
    • Chemical vapor deposition 3.3
    • Hybrid Physical-Chemical Vapor Deposition 3.4
    • Powder-in-tube 3.5
  • See also 4
  • References 5

Important parameters of SC wires/tapes/conductors

The construction and operating temperature will typically be chosen to maximise :

  • Current density (see images below for examples).

Types of Wire

LTS(Low Temperature Superconductor) Wire

LTS wires are made from superconductors with low critical temperature, such as Nb3Sn(niobium-tin) and NbTi(niobium-titanium).

HTS(High Temperature Superconductor) Wire

HTS wires are made from superconductors with high critical temperature(high-temperature superconductivity), such as YBCO and BSCCO.

Preparation

Wire drawing

The normal wire drawing process can be used for malleable alloys such as niobium-titanium.

Surface diffusion

Vanadium-gallium (V3) can be prepared by surface diffusion where the high temperature component as a solid is bathed in the other element as liquid or gas.[3] When all components remain in the solid state during high temperature diffusion this is known as the Bronze Process.[4]

Chemical vapor deposition

CVD is used for YBCO coated tapes.

Hybrid Physical-Chemical Vapor Deposition

HPCVD can be used for magnesium diboride.

Powder-in-tube

Simplified diagram of the PIT process

The powder-in-tube (PIT, or oxide powder in tube, OPIT) process is often used for making electrical conductors from brittle superconducting materials such as niobium-tin[5] or magnesium diboride,[6] and ceramic cuprate superconductors such as BSCCO.[7][8] It has been used to form wires of the iron pnictides.[9] (PIT is not used for YBCO (Yttrium barium copper oxide) as it does not have the weak layers required to generate adequate 'texture' (alignment) in the PIT process.)

This process is used because the high-temperature superconductors are too brittle for normal wire forming processes. The tubes are metal, often silver. Often the tubes are heated to react the mix of powders. Once reacted the tubes are sometimes flattened to form a tape-like conductor. The resulting wire is not as flexible as conventional metal wire, but is sufficient for many applications.

There are 'in situ' and 'ex situ' variants of the process, as well a 'double core' method that combines both.[10]

See also

References

  1. ^
  2. ^
  3. ^
  4. ^
  5. ^
  6. ^
  7. ^ Sheathed or Powder-in-Tube Conductors
  8. ^
  9. ^
  10. ^
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