Dec 21, 2009

The Large Hadron Collider Is Cool

What a machine!




After becoming the world’s highest energy particle accelerator, the LHC is now making progress in commissioning stable beams and providing more collisions at the four points for several hours at a time. For the first time, beams have circulated with more than one bunch of protons, thus increasing the intensity.



Nothing is really ordinary when one operates a prototype: ups and downs are possible, adjustments are certainly necessary and a reasonable amount of time is needed to understand the system’s behaviour. The LHC is no exception. With all its achievements since it was switched on a few weeks ago, it has made the headlines in the world’s press several times. The first beams circulated smoothly, the first low-energy collisions happened very quickly, and the first ramp up to record energy was exceptionally good.

Since then the focus has been on increasing the number of protons in the circulating beams. In the first tests, the operators used a ‘pilot’ beam, containing only one bunch of protons, but on the evening of Friday, 4 December, a beam circulated with more than one proton bunch for the first time. Then, in the early hours of Sunday morning, operators succeeded in circulating four bunches in both directions around the LHC and announced stable beams.

During the following days, work focussed on making sure that each step towards higher intensities can be safely handled and that stable conditions can be guaranteed during collisions first at 450 GeV and then at 1.18 TeV per beam. On the evening of Tuesday, 8 December, two bunches per beam circulated for the first time at 1.18 TeV for a short period and ATLAS recorded its first collisions at the record energy of 2.36 TeV (centre of mass).

Over the same period, cryo-experts have intervened a few times to correct some parameters, vacuum experts have quickly repaired some imperfections in the pre-injector chain and operators have injected and dumped the beams to test the behaviour of the various components of the machine and to measure its performance – which is proving to be excellent.

With four bunches per beam and more protons per bunch, the LHC is providing more and more collisions and all six experiments are recording as much data as possible. During the stable beam periods, they can gather a great deal of useful information about their sub-detectors as well as about the whole chain from collisions to data distribution and analysis. On 28 November, the ALICE collaboration submitted its first paper based on the reconstruction and analysis of the 284 collision events at 450 GeV per beam. The results of the ALICE study are consistent with measurements performed by previous experiments, in particular with those at the SPS when it worked as a proton-antiproton collider with the same beam energy as the LHC in this first phase of commissioning.

Over the final few days before the LHC turns off on 16 December, the operators will continue to increase the beam intensity, delivering further good quantities of collision data to the experiments before Christmas.

When the LHC starts up again in 2010, the operators will aim at gently increasing the intensity and energy of the beams until the planned 3.5 TeV for each beam is reached, marking the beginning of the physics programme.

LHC sets new world record

Geneva, 30 November 2009. CERN1’s Large Hadron Collider has today become the world’s highest energy particle accelerator, having accelerated its twin beams of protons to an energy of 1.18 TeV in the early hours of the morning. This exceeds the previous world record of 0.98 TeV, which had been held by the US Fermi National Accelerator Laboratory’s Tevatron collider since 2001. It marks another important milestone on the road to first physics at the LHC in 2010.

“We are still coming to terms with just how smoothly the LHC commissioning is going,” said CERN Director General Rolf Heuer. “It is fantastic. However, we are continuing to take it step by step, and there is still a lot to do before we start physics in 2010. I’m keeping my champagne on ice until then.”

These developments come just 10 days after the LHC restart, demonstrating the excellent performance of the machine. First beams were injected into the LHC on Friday 20 November. Over the following days, the machine’s operators circulated beams around the ring alternately in one direction and then the other at the injection energy of 450 GeV, gradually increasing the beam lifetime to around 10 hours. On Monday 23 November, two beams circulated together for the first time, and the four big LHC detectors recorded their first collision data.

Last night’s achievement brings further confirmation that the LHC is progressing smoothly towards the objective of first physics early in 2010. The world record energy was first broken yesterday evening, when beam 1 was accelerated from 450 GeV, reaching 1050 GeV (1.05 TeV) at 21:48, Sunday 29 November. Three hours later both LHC beams were successfully accelerated to 1.18 TeV, at 00:44, 30 November.

“I was here 20 years ago when we switched on CERN’s last major particle accelerator, LEP,” said Accelerators and Technology Director Steve Myers. “I thought that was a great machine to operate, but this is something else. What took us days or weeks with LEP, we’re doing in hours with the LHC. So far, it all augurs well for a great research programme.”

Next on the schedule is a concentrated commissioning phase aimed at increasing the beam intensity before delivering good quantities of collision data to the experiments before Christmas. So far, all the LHC commissioning work has been carried out with a low intensity pilot beam. Higher intensity is needed to provide meaningful proton-proton collision rates. The current commissioning phase aims to make sure that these higher intensities can be safely handled and that stable conditions can be guaranteed for the experiments during collisions. This phase is estimated to take around a week, after which the LHC will be colliding beams for calibration purposes until the end of the year.

First physics at the LHC is scheduled for the first quarter of 2010, at a collision energy of 7 TeV (3.5 TeV per beam).

1. CERN, the European Organization for Nuclear Research, is the world's leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. India, Israel, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer status.

LHC accelerator at CERN

End of the world? The Large Hadron Collider ( LHC )