Exclusive 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 metres 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 barrelling 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.