London: A senior scientist who helped to build the Large Hadron Collider (LHC) is claiming that the cause of the shutdown of the giant particle accelerator in 2008 was not a freak accident, but a crucial flaw in the machine`s design.
Running more than a year behind schedule and at half its intended energy, the world`s most powerful particle accelerator is slated to begin its first full scientific run this week. But, according to a report in Nature News, Lucio Rossi, a physicist who oversaw the production of the accelerator`s super conducting magnets, is claiming that the cause of the delay - a major accident in 2008 - could have been avoided.
"Any technical fault is a human fault," said Rossi. Rossi said that the catastrophic failure of a splice between two magnets was not a freak accident, but the result of poor design and lack of quality assurance and diagnostics.
On September 19, 2008, just weeks before the LHC was first scheduled to start colliding protons, an electrical short caused massive damage. A connection between two super conducting cables developed a small amount of resistance, which warmed the connection until the cables - cooled by liquid helium to super conducting temperatures - lost their ability to carry current.
Thousands of amps arced through the machine, blowing a hole in its side and releasing several tonnes of liquid helium. The expanding helium gas created havoc, spewing soot into the machine’s ultra clean beam line and ripping magnets from their stands.
Repairs took more than a year, and the LHC successfully restarted last November. An investigation revealed that technicians had not properly soldered the cables together. "With tens of thousands of such connections, it is perhaps inevitable that some were faulty, but design flaws worsened the problem," Rossi said.
The silver-tin solder that was used melted at high temperatures and did not flow easily into the cable joints. Moreover, workers did not adequately check to see if each connection was electrically secure.
Sensors to detect an overheating circuit, which might have helped prevent the accident, were not installed until after it happened. When the wires were originally joined, the same silver-tin solder was used to connect them to an adjacent copper stabilizer, meant to provide an escape route for current in the event of a failure, according to Rossi.
"That step risked reheating and destroying the original connection," he said. Making the second connection to the stabilizer with a different type of solder that had a lower melting point could have avoided the problem. The project, according to Rossi, will be coping with the consequences for many months to come. "What we have to do is learn from our mistakes and make it better," he said.