Light-weight years ahead

US researchers are developing a strong and lightweight superconductor magnet made from carbon fibre that could provide engine thrust for the next generation of spacecraft.

The US military is backing the technology as a means of propulsion for a satellite or deep space probe. Powerful electromagnets can be used to confine plasma, then direct and expel the very high-energy hot gas for thrust.

A carbon fibre magnet would be significantly lighter and stronger than conventional high-power superconductor electromagnets made from niobium or titanium in a copper matrix.

Prof. David Young and colleagues at the Department of Physics and Astronomy at Louisiana State University can synthesise a layer of superconductor directly on to carbon fibres which are seven microns wide.

‘It makes for a very lightweight, strong and thin superconducting wire,’ said Young. It could potentially be wound into a coil to create a large magnetic field. ‘You can get carbon fibre of an indefinite length, so in principle we could make superconducting fibres that are miles long,’ he said.

Superconductor material transports electric current with zero resistance and no loss of energy if it is cooled below a certain temperature, its ‘transition temperature’.

‘Once you start a current flowing, it will stay there forever,’ said Young. ‘You could energise the magnet then get rid of the power supply.’

Young said lightweight carbon fibre magnets will be easier to transport into orbit. The carbon fibre coils will also be stronger once in space.

‘The coils will experience very large forces in space,’ said Young. ‘In order to keep the coils of a conventional magnet together, you have to have a pretty substantial support structure. This tends to add large amounts of weight. If you make these magnets with carbon fibre you already have that structure.’

However the superconductor material used so far, magnesium carbon nickel compound, is unsuitable for space travel. This is because the material’s transition temperature, below which it becomes a superconductor, is cooler than the space environment.

The researchers are currently attempting to synthesise a wire using magnesium boron compound that will function at the appropriate temperature. But sticking a semiconductor to the carbon fibre surface is difficult. ‘To get them to react, you have to heat to a very high temperature,’ said Young.

Another application for superconducting microfibres could be smaller and lighter MRI machines. Young said: ‘Since the wires are very thin, the same number of turns on a superconducting coil would fit in a much smaller volume.’