Updatelink interview; What's up with the LHC Big Bang machine ?

The fault that has shut down the Large Hadron Collider (LHC) will be hugely disappointing for scientists and engineers following the successful "start-up" of the experiment. It is now over a week since the first beams were fired around the accelerator's 27km (16.7 miles) underground ring. The crucial next step is to collide those beams head on.

But hopes that the first trial collisions would be carried out before the machine's official inauguration on 21 October now seem to have been dashed. It even looks uncertain whether this can be achieved before 2009. The failure on 19 September - described as a "massive" magnet quench - certainly seems dramatic: it caused the temperatures in about 100 of the LHC's super-cooled magnets to soar by as much as 100C. The fire brigade had to be called after a tonne of liquid helium leaked out into the LHC tunnel.

'MAGNETS'

Chilling them to -271C – where even helium gas is turned into a liquid - makes them "superconducting".

This allows the magnets to conduct electrical current without resistance, thereby generating the large magnetic fields required to steer the beams while at the same time consuming relatively little power.

A quench occurs when part of a superconducting magnet heats up and becomes resistant to electrical current; the magnet essentially starts to lose its superconducting properties.

Engineers have a system in place to deal with this issue, but in this case, the quench created a hot spot in the magnet which got out of control and damaged hardware. The current problem appears to have affected the "bus bar" – a cable that carries current between the two magnets.

'Helium leak'

"What appears to have happened... is that there was a faulty connection in the bus bar," Mr Gillies told BBC News. He described this connection as a hi-tech version of a soldering joint to link the two stretches of cable together.

"The bus bar quenched, and that connection seems to have melted. The melting appears to have caused the helium leak.

"It seems to be a badly made connection – but this all has to be confirmed once we have had the chance to take a look at it."

The incident occurred during the final test of the last of the LHC's electrical circuits to be commissioned.