Thursday, September 25, 2008

Hadron Collider to be turned off for two months

Large Hadron Collider to be turned off for two months following damage

A faulty connection between two magnets has triggered a meltdown which will delay the world’s biggest science experiment by two months, the Cern laboratory has admitted.

The fire brigade was called to the Large Hadron Collider after the fault, which sent temperatures soaring by 100 degrees celsius in a section of the 17-mile underground circuit on the Swiss-French border.

The first protons circulated in the huge collider on September 10 before an estimated television audience of one billion, and initial progress seemed to be smooth.

Last week the Welshman in charge of the collider, Dr Lyn "the Atom" Evans, told the Telegraph that he expected to collide the first particles next week, much earlier than thought. But the breakdown, at 11am UK time on Friday morning, led to the release of a ton of helium used to cool the magnets that guide subatomic particles around the machines’s circuit. Engineers had to wait for oxygen levels to return to normal before they were able to weigh up the damage.

When they did, their verdict came as a major blow. The failure will delay the process of commissioning by at least two months, said James Gillies, spokesman for Cern, the European particle physics laboratory.

"This kind of incident was always a possibility with such a unique and demanding project, that’s why we were so tense on the 10th," commented Prof Jonathan Butterworth of University College London, the UK head of the Atlas detector, which will study collisions.

"Having seen those tantalising first signs of beam in our detectors, everyone is raring to go. So it’s really disappointing, and hard for us to keep in perspective right now. "But a delay like this in a 20-year project isn’t an utter disaster and I’m sure the team at Cern will fix it, and make it more robust as they go." The explanation for the delay lies in how the giant machine relies on both the lowest temperature and the highest vacuum to collide particles – protons – at a shade under the speed of light. Liquid helium is used to cool the LHC’s so-called "superconducting magnets".

These are built from coils of special electric cable that operates in a superconducting state, efficiently conducting electricity without resistance or loss of energy, and thus offering the ability to generate vast magnetic fields. There was a faulty connection between two magnets, explained Gillies. As a result, during a power test, the high current melted the connection and helium leaked out from the magnet, which is located under the Jura mountains, and the vacuum was lost. This change, called a quench, releases stored energy.

"It seems to be the faulty connection that quenched. It stopped superconducting, which led it to heat up and melt, which in turn seems to have caused the mechanical failure that released helium," said Gillies. The massive quench took place between two focusing "quadrupole" magnets in sector 3-4 of the accelerator, which lies between the Alice and CMS detectors, the "eyes" of the machine that study collisions. As a result of the quench, the temperature of about 100 of the magnets in the machine’s final sector rose by around 100C.

One of the eight sectors of the giant machine will now have to return to room temperature and pressure for the magnet to be repaired, or even replaced, if necessary. While a repair of the magnet itself would take no more than two days, it will take "several weeks" to warm up the sector and then another "several weeks" to cool it down again, explained Gillies.

The magnets in that sector will have to be pre-cooled to -193.2°C (80 K, or 80 deg above absolute zero ) using 10,080 tons of liquid nitrogen, before they are filled with nearly 60 tons of liquid helium to bring them down to -271.3°C (1.9 K). The setback came just a day after the LHC’s beam was restored after engineers replaced a faulty transformer that had hindered progress for much of the past week.

Prof Brian Cox of Manchester University said: "It's disappointing of course to have to wait another couple of months for the physics to begin, but with a machine as complex as the LHC these things will happen in the commissioning stage.

"When we do wonderful and difficult things at the very edge of our capability we can't expect everything to go smoothly, but this is the price we must pay to make the most profound discoveries about our Universe."

Jad Marrouche, Imperial College London, who works on the CMS detector, said: "Having been so close to taking the first data from collisions, we are all disappointed that we will have to wait just that little bit longer.

"Preparations were gathering pace, especially with the very fast progress made by the collider team of late, so it feels a bit like there has been a false start at the 100m finals."

1 comment:

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