LHC repairs almost complete
February 16, 2009 | 2:42 am
Engineers at CERN are installing the last component necessary to fix the Large Hadron Collider, LHC production manager Lyn Evans said at the AAAS conference in Chicago.
In about a month, they will begin the process of cooling the accelerator’s eight sectors, one by one. And by late September, “we’ll be ready to be back where we were last September,” Evans said.
The LHC saw first beams in September 2008, but shortly afterward a flaw in one of its electrical components brought the accelerator to a halt.
Researchers at CERN are in fact working to be in an even better position for collisions this time around. They’re spending their downtime training new physicists and practicing using the worldwide computer grid that will process the information the detectors collect. They have taken data from naturally occurring cosmic rays with the detectors in preparation for recording actual collisions. Once the machine is cooled, experimentalists will make partial beam runs to test pieces of the detector they have improved since the last run.
Researchers at the LHC had originally scheduled a yearly shut-down of the machine between November and April because of the high cost of electricity during the winter months. But this year, they plan to run for 10 months through the winter to make up for lost time.
Once they have the machine running, they will probably need about five years to gradually turn the energy of the LHC’s beams up to 7 TeV. After five or six years, the LHC will have a scheduled upgrade, which should improve its luminosity by a factor of three or four, Evans said.
The scientists at CERN cannot start running the LHC at full power right off the bat because they’re still learning how to drive it, Evans said. One of the next big challenges for experimentalists working at the LHC will be learning how to discriminate between useful information and the large amount of extraneous data that proton-proton collisions generate.
Protons are made up of quarks and gluons. Physicists are interested in collisions between quarks. But when gluons collide, they create distracting debris in the detectors.
“The noise in enormous in these machines,” Evans said. “Imagine building an orange collider. Very occasionally there will be a collision between two pips [seeds]. But every time there will be pulp.”
Kathryn Grim
Posted in AAAS 2009, LHC updates |
9 Comments »
February 16th, 2009 at 4:02 am
The LHC saw its first beams in September 2008, not first collisions.
February 16th, 2009 at 6:16 am
“The LHC saw first collisions in September 2008″ is not exactly describing what happened: we saw “beam splash” events (beam against a closed collimator just before the detector area, just like in a fixed target experiment). Unfortunately, real collisions remained a wish.
February 16th, 2009 at 10:32 am
@Seth&Marco: Quite right, Seth and Marco. I’m putting that mistake down to it getting toward the end of a long tiring conference! I’ve fixed it above.
February 16th, 2009 at 10:55 am
“Protons are made up of quarks and gluons. Physicists are interested in collisions between quarks. But when gluons collide, they create distracting debris in the detectors.”
This is also not necessarily true. Most physicists (i.e. those interested in new physics) are interested in high-transverse momentum collisions, independent of whether they are quarks or gluons.
The ‘distracting debris’ can come from both quarks and gluons. Both can radiate gluons/quarks which manifest themselves as hadronic jets. Both also contribute to the soft-scattering ‘qcd junk’ along the beamline.
February 16th, 2009 at 1:49 pm
Since it sounds like there are some knowledgeable folks here, could any one explain more fully what actually caused the failure, and was heat the damaging effect? From the pictures, the damage seemed to be from a somewhat powerful force.
February 17th, 2009 at 6:47 am
Basically it was bad solder joints between the tube/magnet assemblies that had an ever so slightly elevated resistance to current flow. This caused the joints to heat up. The cooling medium then warmed above its critical temperature, causing the superconducting coils to become resistive. The large amount of energy had no way of dissipating fast enough.
February 18th, 2009 at 11:17 am
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February 19th, 2009 at 12:27 pm
So, the large amount of energy released ended up causing the cooling containment to rupture? If I understand correctly, there are relief valves that weren’t large enough to handle the volume of escaping cooling medium, and these valves were replaced with larger ones? Also I read somewhere that new circuit boards were added to monitor the solder joints to give advanced warning of a similar event in the future.
November 14th, 2009 at 4:33 pm
The LHC control center was slowly raising the current in the magnets in the LHC region called sector 3-4. This is where the failure occurred.
Monitor screens lit up with alarms that more than 100 magnets had “quenched” which means they lost their superconductivity.
It was known that uncontrolled quenches like this could be disastrous, so it was immediately realized that something serious had happened. It turns out that the magnet quenching was by design. LHC automatically brought the magnets out of their superconducting state to protect them.
Investigation showed that a single “busbar” connection on one of the magnets was improperly attached. Each dipole magnet is 15 meters long with a .5 meter diameter. The busbar is a small ribbon of niobium-titanium alloy, about as wide as a finger. The busbar supplies current to the magnet.
The bad braze of the busbar came undone when 8,700 amps of current vaporized a .5 meter length of the ribbon.
This punctured the LHC’s heavy vacuum insulation.
The liquid helium the insulation protected boiled immediately.
The outer shell gave the gas boiling off nowhere to go and in places the pressure built up to 20 atmospheres. A leak formed with helium escaping into the tunnel.
This pried magnets loose of their steel anchors and all told, 53 magnets were affected.
Not only do the magnets have to be replaced, but relief valves need to be designed throughout LHC to prevent busbar bursts