Technological applications of superconductivity
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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, control magnets in particle accelerators and fusion reactors (tokamaks), power cables, and microwave filters (e.g., for mobile phone base stations).
Many promising applications of superconductivity have been stalled by the impracticality of maintaining large systems (e.g. long stretches of cable) at cryogenic temperatures. These problems may soon be alleviated with the continued development of high temperature superconductors (HTS), as these can be cooled by using liquid nitrogen rather than liquid helium (which is much more expensive and difficult to handle) or by using cryocoolers. However, the currently known high-temperature superconductors are brittle ceramics which are expensive to manufacture and not easily turned into wires or other useful shapes.
Commercial quantities of HTS wire based on BSCCO are now available at around 5 times the price of the equivalent copper conductor. BSCCO wire requires an expensive batch production process and relatively high quantites of silver, but even so the silver is only a small part of the cost (less than 10%). Pilot plants have been developed that use YBCO to produce coated conductors in a semi-continuous process. 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.
Right now HTS wire is used in current leads for low temperature superconducting devices. Early markets for the wire are emerging in replacing low temperature superconductors (LTS) in powerful magnets (copper has a limit to the field strength it can produce, and while HTS wire is much more expensive than LTS this can be offset by the relative cost and convenience of cooling). Also, HTS can withsand much higher magnetic fields than LTS can, so HTS at liquid helium temperatures are used for high-field inserts inside LTS magnets.
Promising future industrial and commercial applications include transformers, power storage, motors, fusion reactors (see ITER) and magnetic levitation devices. Most applications employ the well-understood conventional superconductors, but it is expected that high-temperature superconductors will soon become more cost-effective in many cases.
A new manufacturing process has been discovered that will make YBCO as cheap as copper [1] but this is partly because the price of cuopper has increased substatially recently. The comparison is flawed because the cryogenic cooling for superconducting machines is still required, and this can be half the capital cost of the machine when cheap superconductors are used.
Magnesium Diboride is a much cheaper superconductor than either BSCCO or YBCO in terms of dollars per current carrying capacity times length ($/kA.m). Most manufactured wires are already substantially cheaper than copper. However, this material must be operated at temperatures below about 30K; so the cost of cryogenic equipment is very significant.
