by Lewis Page
November 5, 2009

from TheRegister Website

A bird dropping a piece of bread onto outdoor machinery has been blamed for a technical fault at the Large Hadron Collider (LHC) this week which saw significant overheating in sections of the mighty particle-punisher's subterranean 27-km supercooled magnetic doughnut.

According to scientists at the project, had the LHC been operational - it is scheduled to recommence beaming later this month - the snag would have caused it to fail safe and shut down automatically.

This would put the mighty machine out of action for a few days while it was restarted, but there would be no repeat of the catastrophic damage suffered last September. On that occasion, an electrical connection in the circuit itself failed violently, causing a massive liquid-helium leak and knock-on damage along hundreds of meters of magnets.

Reg readers alerted us yesterday to the temperature rises in the LHC's Sector 81, which began in the early hours of Tuesday morning: most of the collider's operational data can be viewed on the web for all to see. Initial enquiries to CERN press staff led to assurances that the rises were the result of routine tests.

However Dr Mike Lamont, who works at the CERN control centre and describes himself as "LHC Machine Coordinator and General Dogsbody" later confirmed that there had indeed been a problem.

Lamont, briefing reporters at the control room yesterday, told the Reg that machinery on the surface - the LHC accelerator circuit itself is buried deep beneath the Franco-Swiss border outside Geneva - had suffered a fault caused by "a bit of baguette on the busbars", thought perhaps to have been dropped by a bird.

As a result, temperatures in part of the LHC's circuit climbed to almost 8 Kelvin - significantly higher than the normal operating temperature of 1.9, and close to the temperature at which the LHC's niobium-titanium magnets are likely to "quench", or cease superconducting and become ordinary "warm" magnets - by no means up to the task imposed on them.

Dr Tadeusz Kurtyka, a CERN engineer, told the Reg that this can happen unpredictably at temperatures above 9.6 K.

An uncontrolled quench would be bad news with the LHC in operation, possibly leading to serious damage of the sort which crippled the machine last September.

At the moment there are no beams of hadrons barreling around the huge magnetic doughnut at close to light speed, but when there are, each of the two beams has as much energy in it as an aircraft carrier underway. If the LHC suddenly lost its ability to keep the beam circling around its vacuum pipe, all that energy would have to go somewhere - with results on the same scale as being rammed by an aircraft carrier.

About to get hit by an aircraft carrier? You need a Dump

But there's no cause for concern, according to Lamont. The LHC's monitoring and safety systems have always been capable of coping with an incident of this sort, and have been hugely upgraded since last September.

Had this week's feathered baguette-packing saboteur struck in coming months, with a brace of beams roaring round the LHC's magnetic motorway, the climbing temperatures would have been noted and the beams diverted - rather in the fashion that a runaway truck or train can be - into "dump caverns" lying a little off the main track of the LHC.

In these large artificial caves, each beam would power into a "dump core", a massive 7m-long graphite block encased in steel, water cooled and then further wrapped in 750 tonnes of concrete and iron shielding. The dump core would become extremely hot and quite radioactive, but it has massive shielding and scores of meters of solid granite lie between the cavern and the surface.

Nobody up top, except the control room staff, would even notice.

This whole process would be over in a trice, well before the birdy bread-bomber's shenanigans could warm the main track up to anywhere near quench temperature. Should the magnets then quench, no carrier-wreck catastrophe would result.

According to Lamont, provided the underlying fault didn't take too long to rectify, the LHC could be up and beaming again "within, say, three days" following such an incident.

We asked if more such incidents would occur, once the Collider is up and running for real from later this month.

"It's inevitable," the particle-wrangling doc told the Reg. "This thing is so complicated and so big, it's bound to have problems sometimes."

Meanwhile, it would seem that this particular snag has been solved, as the Sector 81 temperatures are now headed back down to their proper 1.9 K.