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Powerful collider set to smash protons

LHC to begin collisions soon, but will be limited to half power

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2:45pm, February 13, 2010
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Editor's note:
On February 20, Steve Myers, CERN's director of accelerators and technology, told Science News that regular collisions at the Large Hadron Collider are now not expected until about March 1. However, the mid-March goal for ramping up the energy of each of the collider's twin proton beams to 3.5 TeV remains the same, he said. (Note added February 22, 2010.)

After more than a year of delays, the most powerful atom smasher on Earth will finally begin regular collisions of its two proton beams around February 20. But to help safeguard CERN’s Large Hadron Collider from further electrical problems, the accelerator will run at only half its maximum energy for the next 18 months to two years, said Steve Myers, CERN’S director for accelerators and technology.

That decision all but guarantees a new and major delay in discovering new elementary particles — including the long-sought Higgs boson, whose existence would account for why subatomic particles have mass.

Starting in mid-March, each of the twin beams of protons accelerated by CERN’s Large Hadron Collider are expected to carry an unprecedented energy of 3.5 trillion electron-volts. But that’s just half the 7 TeV per beam that the particle accelerator is designed to have, Myers noted. The collider won’t run at full power until 2013, he said on February 13 during a talk at a meeting of the American Physical Society in Washington, D.C.

The lower-than-designed operating energy will ensure that the collider won’t suffer any additional electrical problems. In September 2008, an electrical short in the system powering some of the collider’s superconducting magnets forced a shutdown of the accelerator for more than a year. The short caused a thermal runaway in a section of the superconducting magnetic system, not only damaging magnets but also flooding part of the 27-kilometer accelerator with helium gas.

After a yearlong set of repairs during which 106 magnets were either refurbished or replaced and 6,500 new detectors were added to the system’s magnetic protection system along with 250 kilometers of new cable, that particular problem “can never happen again,” said Myers. But during tests in April 2009, scientists discovered another set of problems. Electrical flaws were found in copper bus bars housing superconducting cables.

The copper problem is not a complete showstopper but means that the LHC can operate safely only at 3.5 TeV per beam. At higher energies, the faulty connection could vaporize the copper and cause further damage to the collider. After 2011, the Collider will shut down for a year of upgrades and then is expected to finally achieve its maximum energy in 2013, Myers said.

Late last year, the LHC achieved what was then the highest energy of any accelerator  — 1.18 TeV per beam, beating out the Fermilab’s Tevatron in Illinois. Because of all the delays with the LHC, the Tevatron’s operating life has already been extended two years, to 2011, and Fermilab scientists are closely watching the LHC’s progress to determine whether it might keep the Tevatron working until 2012, said Joseph Incandela of the University of California, Santa Barbara.

In the meantime, even operating the LHC at 3.5 TeV per beam takes physicists “into new territory” where discovery of new physics, including a search for signs of a new theory of elementary particles known as supersymmetry, is still possible, he added.

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