An introduction to Superconductors

First discovered in 1911 when Dutch Physicist Heike Onnes submerged mercury in liquid helium which he had prepared. Astonishingly, the mercury’s electrical resistance dropped to zero – a state which he eventually called superconductivity.

For every superconductor material, when cooled below a certain temperature, the Critical Temperature the electrical resistance becomes zero. In this state the current flows in the circuit indefinitely even without an applied voltage – this is like a circuit without a battery!

Superconductors have two main obvious applications: magnetic levitation and efficient power solutions. The former utilises interesting magnetic phenomena, such as the repulsion of all magnetic fields by the superconductor. This means that objects, such as trains or cars, could in the future be levitated above the road, reducing the friction caused by wheels and tyres (N.B this is not quite the same as electromagnetic levitation, which requires coils of wire). The other main use involves using superconducting tapes or wires which, when cooled, can transmit very large amounts of power because they have no resistance. Unfortunately, in modern power lines, about 7% of produced power is lost through resistance. Reducing the resistance of the cable, therefore, is an extremely worthwhile venture.

The current scientific goal is to create superconductors that can retain their conductive properties at temperatures closer to room temperature. This means that less energy needs to be spent cooling the system to make it superconducting.

Lots of methods involve the calcination and sintering of solid powders/oxides. The mixture, which often contains a careful ratio of elements, is eventually formed into a disk or other shape.

Some examples of the materials used in modern superconductors are:

Niobium-titanium

Used in superconducting magnets at CERN

Must be cooled using expensive liquid Helium

BSCCO (Bismuth strontium calcium copper oxide)

A  good original contender for superconducting wires

Can be coated and extruded into a wire

YBCO (Yttrium Barium Copper Oxide)

The American Superconductor Corporation replaced BSCCO with this in their R&D

Can operate with liquid nitrogen

Formed into a conducting ‘tape’

(Tl5Pb2)Ba2Mg2Cu9O18 and others

Show lots of promise for near room temp superconductors

The list goes on – superconductors are an expotic field and this list is barely representative

Nexans and AMSC are two companies that are working on the development of superconducting cables for energy transmission. A test piece carrying 138 Kilovolts was powered up in 2008 near Long Island by AMSC (American Superconductor). Currently maintenance, cost-per-length and implementation costs are high, however many predict that these costs will go down.