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Posts Tagged ‘quench’

The dice have been cast

Tuesday, September 23rd, 2008

This just came in from the CERN directorate:

LHC re-start scheduled for 2009

Geneva, 23 September 2008. Investigations at CERN following a large helium leak into sector 3-4 of the Large Hadron Collider (LHC) tunnel have indicated that the most likely cause of the incident was a faulty electrical connection between two of the accelerator’s magnets. Before a full understanding of the incident can be established, however, the sector has to be brought to room temperature and the magnets involved opened up for inspection. This will take three to four weeks. Full details of this investigation will be made available once it is complete.

“Coming immediately after the very successful start of LHC operation on 10 September, this is undoubtedly a psychological blow,” said CERN Director General Robert Aymar. “Nevertheless, the success of the LHC’s first operation with beam is testimony to years of painstaking preparation and the skill of the teams involved in building and running CERN’s accelerator complex. I have no doubt that we will overcome this setback with same degree of rigour and application.”

The time necessary for the investigation and repairs precludes a restart before CERN’s obligatory winter maintenance period, bringing the date for restart of the accelerator complex to early spring 2009. LHC beams will then follow.

Particle accelerators such as the LHC are unique machines, built at the cutting edge of technology. Each is its own prototype, and teething troubles at the start-up phase are therefore always possible.

“The LHC is a very complex instrument, huge in scale and pushing technological limits in many areas,” said Peter Limon, who was responsible for commissioning the world’s first large-scale superconducting accelerator, the Tevatron at Fermilab in the USA. “Events occur from time to time that temporarily stop operations, for shorter or longer periods, especially during the early phases.”

CERN has received similar words of support from several laboratories, including Germany’s DESY, home of the HERA superconducting particle accelerator, which ran from 1992 to 2007.

“We at DESY have been following the commissioning of the LHC with great excitement and have been very impressed with the success of the first day,” said Albrecht Wagner, DESY Director. “I am confident that our colleagues at CERN will solve the problem speedily and we will continue to support them as much as we can.”

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What Now?

Monday, September 22nd, 2008

Good morning! I’m back at work here at CERN, and I can assure you that there is no pall of doom over the laboratory. Yes, it’s a bummer that collisions won’t happen for a while, but everyone I know still has plenty of work to do to get ready — heck, the only reason I even have time to blog is that I’m waiting for code to compile!

There are plenty of sources for what exactly went wrong, and how long it will officially take to repair; you can see some links in the updates of my last entry. The bottom line is that the needed repair is not a huge one, but it will be very time consuming because of the necessity of warming up the magnets to do it. Why do we need to warm the magnets up? Well, because they’re filled with liquid helium, and you can’t do much work on the magnets while the helium inside. And, as someone asked in a comment, why does it take so long anyway? Didn’t the magnets warm up by a hundred degrees rather quickly during Friday’s malfunction? Yes, they did, but they did it by venting a large amount of helium into the tunnel — and, although helium isn’t dangerous unless there’s so much of it that it crowds out the air, it sure is expensive. The accelerator experts need to slowly warm up, remove, and store the helium; this will save it for future use and prevent damage to the magnets.

So what are we going to do with the next few months? Well, no high-level decisions have been made, and obviously graduate students don’t get to vote on them anyway, but I doubt that there will be collisions in 2008. The old schedule was to slowly get the machine working, and hopefully achieve 5 TeV on 5 TeV collissions sometime in October. If everything went well, this would have allowed maybe a month of physics running before the winter shutdown. (The winter shutdown is CERN’s typical time to do maintenance because electricity is more expensive due to everyone using it for heating; accelerators in places with a lot of air conditioning often shut down in the summer for similar reasons.) After that, the plan was to have a long shutdown during which the machine would be prepared for full energy 7 TeV on 7 TeV collisions, after which it would come online again in Spring 2009. It doesn’t make any sense to shut down the accelerator for repairs, run it for a short while, and then shut it down again for upgrades — so I expect the planned work for the shutdown will begin in parallel with the repairs. Perhaps that means that the LHC will come online at full energy even a bit sooner than it would have otherwise, but bear in mind that that’s speculation based more on my hopes and guesses than on my (non-existent) accelerator-commissioning expertise.

For me and my colleagues working on the ATLAS pixel detector, there is a lot of work still to be done. Our sub-detector is now taking data, but we have a long list of things still to be achieved before it’s operating at its best. We have been doing our utmost to get things ready, but realistically, if the first full energy LHC collisions had been in October, there would have been more work to do: there would still have been a few pieces of our detector shut down because of electronics problems, and the accuracy of our measurements would have been reduced because we didn’t yet know the alignment between different parts of the detector very well. Obviously we would have welcomed that collision data, and used it to continue our improvements, but there was plenty more calibration and commissioning work to do over the winter shutdown. Now we’ll just do that work before we see first collisions instead of after, and hopefully we’ll be in great shape by the time the accelerator is back.

For me personally, the news is not a big setback. I had already decided (by coincidence, last week) that it would be better to stay at CERN and help with the pixel comissioning work in the winter and early spring, even if it meant forgoing the chance to use 2008 data to write my thesis. The downside of this decision was that it committed me to probably being in graduate school until 2011, for a total of seven years — but the upside was that I would learn more about the detector, and be able to do a more thorough job on my thesis as well. Because of the incident last Friday, it turns out that I didn’t really have a choice after all; but since I had already made the decision, it doesn’t feel like much of a loss.

But certainly this is bad news for a lot of people. Many graduate students and postdocs were counting on 2008 data, and they will now be spending quite a bit longer in their present positions than they had hoped, or making other difficult decisions. And everyone working in particle physics, or interested in particle physics, will now have to wait a few months longer to see what the LHC has in store.

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Growing Pains

Friday, September 19th, 2008

Yesterday CNN reported on a transformer failure that temporarily shut down the LHC.  This happened over this past weekend, and the issues continued into this week.  What you should know about it, from our perspective here at CERN, is that it was absolutely not a big deal.  The LHC isn’t a big magic experiment machine, it’s actually made of a huge number of components.  We expect that some of those components will have problems as the accelerator gets going, because turning on the complex is nothing like switching on a light switch: we’ve never built an LHC before.  Swapping out these components is generally pretty easy; the transformer may have weighed forty tons, but replacing it was straightforward enough and only took a day or two.  So here at the experiments, we’re a tiny bit annoyed about the delay, but we really think it’s par for the course.

Today we’ve had another delay with the machine itself, which as far as I know hasn’t made the news yet.  According to one of the status pages for LHC, there has been a magnet quench in LHC sector 34; at this moment, it reads, “Investigating quench in S34, more news as available.” A magnet quench is when the temperature of a magnet section goes too high for it to be superconducting; when that happens, the resistance goes higher, and the current going through the magnet heats it up rapidly.  This leads to further loss of superconductivity, and more heat, which could damage the (very thin) wires that ultimately make up the LHC electromagnets.  The solution, oddly enough, is to install heaters that can spread the energy of a quench more uniformly over a larger area; thus puts the magnets out of action for a number of hours but prevents damage to the accelerator.  Quenches are expected to happen pretty routinely, and to be dealt with without any permanent damage; you can learn more about them in this article from Symmetry.

You can see the effect of the quench on the sector 34 section of the LHC cooldown status page, and get additional details from this page on S34.  I have no inside information, and I’m no more of an accelerator expert than you are, so the details aren’t entirely clear to me; but it is pretty clear that around 11 AM today, the temperature in S34 went up by quite a bit, and it still isn’t recovered completely.  Past that, we don’t know yet what is going on; I expect that the accelerator experts will make more details available once they have a handle on the situation.

A problem with the accelerator is potentially more serious than a problem with a transformer.  Transformers are big and expensive, but compared with the LHC they are small potatoes and quick to replace.  Damage to the LHC magnets can be a more serious business, because replacing and repairing them involves heating a large portion of the accelerator up to room temperature, which can take months.  However, let me stress: I’m not worried.  I have absolutely no reason to believe that any maintenance is needed which would require warming the machine, and it’s far more likely that this is a minor glitch than a major one.  We still have a lot to do to prepare the detectors for data taking, and we are continuing to work.   Collisions will happen when they happen: probably not as soon as we hope, but soon enough in any case.

Update:The CERN users’ page has a brief official statement:

During the commissioning of the final LHC sector (sector 3-4) for 5 TeV operation, an incident occurred at 12:05 today resulting in a large helium leak into the tunnel. Further details are not yet known. Investigations will continue over the weekend and more information will be made available as soon as possible.

That means the incident is more complicated than I realized when I was writing, and that there will certainly be a delay of a few days because of the incident.  Past that, I’d say we’re still waiting for information.

Update 2: The Times has an article about this.  It has an unidentified “CERN source,” vanishing logbook entries, and other intrigue–so it’s definitely worth a read if you’re into that sort of thing.

Update 3 (Sept 20): The BBC is now reporting that the magnets in sector 34 will have to be warmed for repairs, which will indeed take months.  I suspect this means that the work planned for the winter shutdown, in particular preparing for the full 7 TeV on 7 TeV collisions, will begin earlier than planned, as much as possible in parallel with the repairs.  Hopefully we’ll come online and go quickly to full energy a few months into 2009 — so in the long term, this may not end up being such a large delay in the physics program.  It’s obviously a short-term disappointment, though, and a lost opportunity to calibrate our detectors with physics data prior to the 2009 run.

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