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The Large Hadron Collider Fires Up... Again

11/28/2009 09:12AM

The Large Hadron Collider Fires Up... Again
This week, the Large Hadron Collider (LHC) circulated two beams simultaneously for the first time, allowing the operators to test the synchronization of the beams and giving the experiments their first chance to look for proton-proton collisions. With just one bunch of particles circulating in each direction, the beams can be made to cross in up to two places in the ring. From early in the afternoon, the beams were made to cross at points 1 and 5, home to the ATLAS and CMS detectors, both of which were on the look out for collisions. Later, beams crossed at points 2 and 8, ALICE and LHCb.

“It’s a great achievement to have come this far in so short a time,” said CERN Director General Rolf Heuer. “But we need to keep a sense of perspective – there’s still much to do before we can start the LHC physics programme.”

Beams were first tuned to produce collisions in the ATLAS detector, which recorded its first candidate for collisions at 14:22 this afternoon. Later, the beams were optimised for CMS. In the evening, ALICE had the first optimization, followed by LHCb.

“This is great news, the start of a fantastic era of physics and hopefully discoveries after 20 years' work by the international community to build a machine and detectors of unprecedented complexity and performance," said ATLAS spokesperson, Fabiola Gianotti.

“The events so far mark the start of the second half of this incredible voyage of discovery of the secrets of nature,” said CMS spokesperson Tejinder Virdee.

“It was standing room only in the ALICE control room and cheers erupted with the first collisions” said ALICE spokesperson Jurgen Schukraft. “This is simply tremendous.”

“The tracks we’re seeing are beautiful,” said LHCb spokesperson Andrei Golutvin, “we’re all ready for serious data taking in a few days time.”

These developments come just three days after the LHC restart, demonstrating the excellent performance of the beam control system. Since the start-up, the operators have been circulating beams around the ring alternately in one direction and then the other at the injection energy of 450 GeV. The beam lifetime has gradually been increased to 10 hours, and today beams have been circulating simultaneously in both directions, still at the injection energy.

Next on the schedule is an intense commissioning phase aimed at increasing the beam intensity and accelerating the beams. All being well, by Christmas, the LHC should reach 1.2 TeV per beam, and have provided good quantities of collision data for the experiments’ calibrations.

“It’s great to see beam circulating in the LHC again,” said CERN Director General Rolf Heuer. “We’ve still got some way to go before physics can begin, but with this milestone we’re well on the way.”

The LHC circulated its first beams on 10 September 2008, but suffered a serious malfunction nine days later. A failure in an electrical connection led to serious damage, and CERN has spent over a year repairing and consolidating the machine to ensure that such an incident cannot happen again.

“The LHC is a far better understood machine than it was a year ago,” said CERN’s Director for Accelerators, Steve Myers. “We’ve learned from our experience, and engineered the technology that allows us to move on. That’s how progress is made.”

Recommissioning the LHC began in the summer, and successive milestones have regularly been passed since then. The LHC reached its operating temperature of 1.9 Kelvin, or about -271 Celsius, on 8 October. Particles were injected on 23 October, but not circulated. A beam was steered through three octants of the machine on 7 November, and circulating beams have now been re-established. The next important milestone will be low-energy collisions, expected in about a week from now. These will give the experimental collaborations their first collision data, enabling important calibration work to be carried out. This is significant, since up to now, all the data they have recorded comes from cosmic rays. Ramping the beams to high energy will follow in preparation for collisions at 7 TeV (3.5 TeV per beam) next year.

Particle physics is a global endeavour, and CERN has received support from around the world in getting the LHC up and running again.

“It’s been a herculean effort to get to where we are today,” said Myers. “I’d like to thank all those who have taken part, from CERN and from our partner institutions around the world.”

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