LHC: The Beams are Back

Particle beams are once again circulating in the Large Hadron Collider (LHC), 14 months after an electrical failure caused serious damage to the world’s most powerful particle accelerator, which straddles the borders of France and Switzerland and is hosted by CERN, the European Organization for Nuclear Research.

“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.”

Scientists at CERN react to the Large Hadron Collider restart on Friday, Nov. 20. (CERN photograph by Claudia Marcelloni)

The machine was handed over for operation on the morning of Nov. 18, and a clockwise circulating beam was established Nov. 20 at 10 p.m. This is an important milestone on the road toward the first physics at the LHC, expected in 2010, scientists said.

The ultimate goal of LHC is high-energy beams colliding in the centers of its particle detectors. Beyond revealing a new world of unknown particles, the LHC experiments could explain why those particles exist and behave as they do. They could reveal the origins of mass, shed light on dark matter, uncover hidden symmetries of the universe and possibly find extra dimensions of space. (For an explanation of how the LHC works, see the video below.)

The LHC circulated its first beams on Sept. 10, 2008, but suffered a serious malfunction nine days later (See Collider Beams Up at CERN and Quench Latest LHC Setback). A failure in an electrical connection led to serious damage and a large release of helium, and CERN spent the next year repairing and consolidating the machine to ensure that such an incident won’t happen again.

“The LHC is a far better understood machine than it was a year ago,” said Steve Myers, CERN director for accelerators. “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 last summer. The LHC reached its operating temperature of 1.9 K, or about –271 °C, on Oct. 8. Particles were injected on Oct. 23, but not circulated. A beam was steered through three octants of the machine on Nov. 7, and circulating beams have now been re-established.

A cross-section image of CMS showing debris (or “splash”) of particles entering the detector when the LHC beam was steered into the collimator (tungsten block) at point 5, at around 9:50 a.m. on Sept. 10, 2008. The energy deposits in the electromagnetic (pink) and hadronic (blue) calorimeters are visible. Hits in the resistive plate chamber muon (RPC) system in green and drift tube (red) also are seen. (Image ©CERN)

The collider made headlines around the world earlier this month when a power outage in an electrical substation that supplied part of the LHC’s cryogenic systems reportedly was caused by a piece of bread dropped by a passing bird.

While news outlets all over the world jumped on the story of how the “bird and the baguette” could bring down the world’s mightiest machine, the truth, according to a CERN news bulletin, is that, “to this day, we do not know what caused the power cut, but it is true that feathers and bread were found at the site.

“The truth about birds and baguettes is that two sectors of the LHC warmed by a few degrees while the substation was repaired and were then cooled back to 1.9 K. There was no damage and no delay,” CERN said. “Had we been running, we’d have lost a day or two’s worth of beam time, which is nothing unusual when operating a frontier research machine like the LHC. Power cuts are, of course, something that the LHC has been designed to cope with, as have all its predecessors.”

The next important milestone will be low-energy collisions, expected in about a week. These will give the experimental collaborations their first collision data, enabling important calibration work to be carried out. This is significant, because up to now, all the data they have recorded comes from cosmic rays.

“We will systematically go through all the measurements, put all the systems through their tests, and when we’re sure everything’s safe, we will increase the beam intensity,” Myers said. “During some shifts, we will try to accelerate beam to the maximum energy for this year – 1200 GeV per beam. Then we will decide about collisions. Two possibilities are to collide at the 450 GeV injection energy or at 1200 GeV per beam. That is our program until just before Christmas.”

Over the next year, the energy will be ramped to 3.5 TeV (3500 GeV) per beam, and then possibly to a maximum of 5 TeV.

“With 3.5 TeV per beam, we will open new windows to new physics,” Heuer said.

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

An estimated 10,000 people from 60 countries have helped design and build the accelerator and its massive particle detectors, including more than 1700 scientists, engineers, students and technicians from 94 US universities and laboratories supported by the DoE’s Office of Science and the NSF, which invested a total of $531 million in the construction of the accelerator and its detectors.

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

For more information, visit: www.cern.ch