Glossary

1G

First generation HTS wires, formed by extrusion of BSCCO with a metal sheath.

2G

Second generation HTS wires, formed by depositing YBCO onto a metal substrate.

A/cm

Unit of critical current, Ic, for superconducting wire per 1 cm width. Used especially for YBCO because it is a tape form and the Ic depends on its width.

$/kAm

Unit of price in $ of superconducting wire per 1000 A of critical current, Ic, and per 1 meter length of the wire. Common measure for comparison of the price, especially of YBCO wire.

$/m

Unit of price in $ of superconducting wire per 1m length of the wire.

AC loss

Thermal heat loss by AC current transporting in superconductor.

Artificial pinning center

Oxide fine particle or columnar structure to pin flux lines in the superconductor. Only used in 2G HTS wire. See Pinning Center.

Bi2223

Its molecular formula is (Bi,Pb)2Sr2Ca2Cu3O10-x also known as BSCCO, which is used in 1G HTS wire.

Biaxially textured

Textured along two axes of the crystal lattice directions. Used in 2G HTS wire.

BSCCO

HTS compound composed of Bi, Sr, Ca, Cu, O, and sometimes Pb. Used in 1G HTS wire. See Bi2223.

Buffer layer

Material put in place between metal substrate and superconductor material to prevent contamination and provide texturing. Used in 2G HTS wire.

Closed system

Cooling system in which the cooling substance is recycled through the system and re-used.

Coated conductor

Also known as 2G, YBCO HTS wire. The name is derived from the form of the YBCO wire where a superconducting YBCO film layer is deposited on a substrate.

COP

Co-efficient of performance used for cryogenic system efficiency. The ratio of the cooling power and the input power. The value varies from 0 to 1.0.

Critical current (Ic)

Maximum current through a material that allows it to remain in the superconducting state.  See Ic.

Cryogenics

A branch of physics and engineering that studies and produces very low temperatures and the behavior of materials at those temperatures.

Cu stabilizer

Cu layer or matrix in the superconducting wire to absorb the heat generated in the wire during the transition to a normal state, which protects the wire from burning. It stabilizes the superconducting current transport.

Current density

Electrical current per cross-sectional area. Measured in A/cm2 (Amps/cm2) or A/m2, A/mm2. See Jc.

Distribution voltage

Electric power grid classification for voltage, 10-66 kV.

Epitaxial

A thin film with the same crystal structure as the substrate it was grown on. The property of superconductor materials to grow this way is used to get films with good grain alignment. Used in in 2G wire.

Ex-situ

In the wire fabrication process, first the superconducting material is formed, and then put into a metal tube to form a superconductor. Example: MgB2 superconducting powders are prepared, put in to a metal tube, cold-worked and then heat-treated to form a wire. Compare In-situ.

Fault Current Limiter (FCL)

Device to reduce a fault current in an electrical power system.

Filament

In the wire, superconductor is sometimes divided into filament form of fine strips, which is continuous for whole length of the wire.

GM (Gifford McMahon)

One of the most widespread types of cryogenic systems used with superconducting devices such as MRI or Maglev. The cold head part of the system is cooled by the expansion of inert He gas to around 4 K.

Hastelloy

Trade name of commercial Ni-based high temperature alloys. A substrate metal used in 2G wire.

HTS

Ceramic materials that are superconducting with a Tc of 30 K or greater. Some examples are YBCO, BSCCO and MgB2.

Ic

Critical current of a superconductor, the maximum amount of current that can flow below a fixed electric field or resistivity criterion.

Ic-B property

Critical current property against the applied magnetic field (B) to the wire.

In-situ

In the wire fabrication process, when the precursors are put into place before being reacted to form the superconducting compound. Example: Mg and B powders themselves are put in to a metal tube and then heat-treated to form MgB2 superconductor. Also see Ex-Situ.

I-V

Current-voltage

Jc

Critical current density. Maximum current density (Ic per superconducting or total wire cross-sectional area) in a material that allows it to remain in the superconducting state.

Kelvin (K)

A scale of temperature measurement that starts at "absolute zero", the coldest theoretical temperature attainable. 0 K equals -273°C.

Liquid Helium, LHe

Coolant with the boiling point of 4.2 K; it is used for LTS superconductors and devices.

Liquid Hydrogen, LH2

Coolant with the boiling point of 20 K; it can potentially be used in MgB2 applications.

Liquid Nitrogen, LN2

Coolant with the boiling point of 77 K; it can be used for HTS superconductors and devices.

LTS

Low Temperature Superconductor: Metallic materials with a Tc of less than 30 K. Typically, NbTi and Nb3Sn.

Maglev

Magnetic levitation trains. Strong magnetic field generated by superconductor can levitate and propel the train at a high speed.

MgB2

Magnesium diboride becomes superconducting at 39 K, which is a much higher Tc than other metallic superconductors. Mg and B are relatively inexpensive and lightweight.

MRI

Magnetic resonance imaging. In MRI, the human body is exposed to a strong, homogeneous and stable magnetic field by a superconducting coil. It displays the cross-sectional images of the human body and helps medical diagnosis.

Nb3Sn

Typical metallic LTS superconductor made of Nb and Sn.

NbTi

Typical metallic LTS superconductor made of Nb and Ti.

NMR

Nuclear Magnetic Resonance. Its stable, homogeneous high field created by a superconducting magnet can precisely analyze medical, chemical or biochemical materials like proteins.

Offshore wind turbine

Turbine used in large windmills that operate at sea, where the wind is strong and stable. These turbines are expected to generate large amounts of power.

Pinning

Preventing the movement of flux lines within a superconductor. This suppresses destruction of superconductivity and increases a critical current.

Pinning center

A defect to pin the flux line movement.

Pinning property

The ability to pin the flux line movement. The higher pinning property, the larger Ic.

Pulse tube refrigerator

A kind of refrigerator developed in early 1980s based on thermo-acoustics. It is a closed system that uses an oscillating pressure at one end to generate an oscillating gas flow in the rest of the system. This gas flow can carry heat away from a low temperature point. The prime advantage is that they have no moving parts, resulting in high reliability for long time operation.

Quench

The phenomenon where superconductivity in a material is broken especially for a superconducting coil, usually by exceeding the maximum current the material can conduct (Ic or Jc) or exceeding the Tc.

RE

Rare earth element (such as La, Nd, Sm, Eu, Gd, etc.). Often used in YBCO replacing Y for RE element to improve the flux pinning ability.

REBCO

123 compounds formed with a rare earth instead of yttrium. See YBCO.

Roebel conductor

In this report, a transposed combined superconductor composed of a few bundles of YBCO wires to reduce AC loss.

SFCL

Superconducting Fault Current Limiter. See FCL.

SMES

An acronym for Superconducting Magnetic Energy Storage. Superconducting current circulates without any ohmic loss in the coil of SMES and then SMES can store the electric energy. The only method to store energy in the form of electricity.

Stirling cryogenic system

A kind of system consisting of a piston, compression space, regenerator, heat exchanger, and expansion space. The working fluid is gaseous He, which is compressed and expanded. This cycle is used to reduce the temperature.

Striation

Dividing YBCO film into thin parts using a laser. The divided parts are called filaments. See filament.

Substrate

The base (normally metal tape form) on which a superconducting HTS film layer is grown.

Tc

The critical transition temperature below which a material is superconducting.

Tesla (T)

Unit for magnetic flux density. Equal to one weber per square meter.

Texturing

Crystal grain alignment. A textured buffer layer that is used to grow an aligned superconductor layer.

Three cores in one cable

A kind of structural configuration of an HTS power cable with each core transporting each phase of AC.

Three phase coaxial type cable

A kind of structural configuration of an HTS power cable with a single core with three concentric layers of AC phase.

Transmission voltage

Electric power grid classification for voltage, 66-275 kV.

Turbo Brayton system

A kind of cryogenic system comprising a turbo pump compressor, expansion turbine and heat-exchanger especially for large power applications of more than 1 kW.

Winding

Superconducting wire used in part of a coil for generating a magnetic field.

Wire

"Wire" is used, in a broad sense, for "round wire" (Bi2223, MgB2 wires) and "flat tape" (YBCO wires).

YBCO

A well-known HTS superconductor composed of Yttrium, Barium, Copper and Oxygen. Its actual molecular formula is YBa2Cu3O7-x also known as 123 compounds. Used in 2G wires.