Washington: The Large Hadron Collider (LHC), or the ‘Big Bang Machine’, as it is popularly called, is fizzling out, as many of the magnets meant to whiz subatomic particles around the 17-mile underground machine outside Geneva have mysteriously lost their ability to operate at high energies. According to a report in New York Times, after 15 years and USD 9 billion, and a showy “switch-on” ceremony last September, the LHC, the giant particle accelerator outside Geneva, has to yet collide any particles at all, thanks to thousands of bad electrical connections.
The collider’s own prodigious energies are in some way its worst enemy.
In order to carry enough current, the collider’s superconducting magnets are cooled by liquid helium to a temperature of 1.9 degrees above absolute zero, at which point the niobium-titanium cables in them lose all electrical resistance and become superconducting.
Any perturbation, however, such as a bad soldering job on a splice, can cause resistance and heat the cable and cause it to lose its superconductivity in what physicists call a “quench”, which is what happened on September 19 last year, when the junction between two magnets vapourised in a shower of sparks, soot and liberated helium.
Technicians have spent most of the last year cleaning up and inspecting thousands of splices in the collider.
About 5,000 will have to be redone, according to Steve Myers, head of CERN’s accelerator division.
Before the superconducting magnets are installed, engineers “train” each one by ramping up its electrical current until the magnet fails, or “quenches”. Thus, the magnet gradually grows comfortable with higher and higher current.
According to Dr Myers, all of the magnets for the collider were trained to an energy above seven trillion electron volts before being installed, but when engineers tried to take one of the rings’ eight sectors to a higher energy last year, some magnets unexpectedly failed.
Lucio Rossi, head of magnets for CERN, said that 49 magnets had lost their training in the sectors tested and that it was impossible to estimate how many in the entire collider had gone bad.
He said the magnets in question had all met specifications and that the problem might stem from having sat outside for a year before they could be installed.
Experts say that retraining magnets is costly and time consuming, and it might not be worth the wait to get all the way to the original target energy.
“It looks like we can get to 6.5 relatively easily,” Dr Myers said, but seven trillion electron volts would require “a lot of training.”
First Published: Tuesday, August 4, 2009, 12:02