Technological applications of superconductivity

Some of the technological applications of superconductivity include the production of magnetometers based on SQUIDs, digital circuits (including those based on Josephson junctions and rapid single flux quantum technology), Magnetic Resonance Imaging (MRI) and Nuclear magnetic resonance (NMR), control magnets in particle accelerators and fusion reactors (tokamaks), power cables, and RF and microwave filters (e.g., for mobile phone base stations, as well as, military ultra-sensitive/selective receivers).

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The biggest application right now for superconductivity is in producing the large volume, stable magnetic fields required for MRI and NMR. This represents a multi-billion US$ market for companies such as Oxford Instruments, Siemens etc. The magnets typically use low temperature superconductors (LTS). These need to be cooled to liquid helium temperatures to superconduct. LTS is also used in high field scientific magnets because copper has a limit to the field strength it can produce.

The commercial applications so far for high-temperature superconductors (HTS) have been limited. HTS superconduct at temperatures up to that of liquid nitrogen which makes them cheaper to cool. The problem with HTS technology is that the currently known high-temperature superconductors are brittle ceramics which are expensive to manufacture and not easily turned into wires or other useful shapes.

Therefore the applications have been where HTS has some other intrinsic advantage i.e. in low thermal loss current leads for LTS devices (low thermal conductivity), RF and microwave filters (low resistance to RF), and increasingly in specialist scientific magnets, particularly where size and electricity consumption are critical (while HTS wire is much more expensive than LTS in these applications this can be offset by the relative cost and convenience of cooling).

Commercial quantities of HTS wire based on BSCCO are now available at around five times the price of the equivalent copper conductor (this wire is referred to as Generation 1 conductor). BSCCO wire requires an expensive batch production process and relatively high quantities of silver (but less than 10% of the cost). Pilot plants have been developed that use YBCO to produce coated conductors in a semi-continuous process (Generation 2). Manufacturers are claiming the potential to reduce the price in volume to 50% to 20% of BSCCO. If the latter occurs HTS wire will be competitive with copper in many large industrial applications, putting aside the cost of cooling.

Promising future industrial and commercial HTS applications include transformers, fault current limiters, power storage, motors, fusion reactors (see ITER) and magnetic levitation devices. For a relatively technical and US-centric view of state of play of HTS technology in power systems and the development status of Generation 2 conductor see Superconductivity for Electric Systems 2007 US DOE Annual Peer Review.

HTS also has a future in scientific and industrial magnets, including use in NMR and MRI systems. Also one intrinsic attribute of HTS is that it can withstand much higher magnetic fields than LTS, so HTS at liquid helium temperatures are being explored for very high-field inserts inside LTS magnets.

Magnesium diboride is a much cheaper superconductor than either BSCCO or YBCO in terms of dollars per current carrying capacity times length ($/kA.m) and in the same ballpark as LTS. Most manufactured wires are already substantially cheaper than copper. Furthermore MgB₂ superconducts at temperatures higher than LTS (below 39K compared with below 4K for LTS). However MgB₂ is limited in the strength of the field it can tolerate at these higher temperatures so applications will be similarly limited unless significant improvements can be made to the field it can withstand. Research is ongoing into this.