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Seth Zenz | Imperial College London | UK

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Growing Pains

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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20 Responses to “Growing Pains”

  1. [...] current in the magnet suddenly starts heating it up, causing huge internal mechanical stresses. As pointed out elsewhere, quenches are expected to happen quite often in the LHC. The magnets are designed to withstand [...]

  2. David Parker says:

    Thanks for the update Seth.
    Are magnet quenches potentially dangerous? Surely 2000A suddenly finding an increase in resistance due to a rise in temp is potentially explosive? It would be in the PA in my radio transmitter anyway!!

  3. [...] current in the magnet suddenly starts heating it up, causing huge internal mechanical stresses. As pointed out elsewhere, quenches are expected to happen quite often in the LHC. The magnets are designed to withstand [...]

  4. Seth Zenz says:

    Hi David. I’ve never heard of any possibility of an explosion per se, but quenches are certainly potentially dangerous for the magnets. There’s enough stored energy to fuse the wires together and stop them from working. Under ordinary circumstances, as I explained, the LHC is designed to survive quenches without difficulty. (In fact, part of the task of preparing the magnets includes “training” them by quenching them on purpose, which puts the wires into more stable configurations for future quenches.)

    In this case, it seems reasonable to infer that something went wrong, either in the way the systems responded to the quench or in something else–obviously leaking helium into the tunnel is not a design feature! But no matter what, quenches and other LHC problems are never dangerous to humans: in the worst case, the energy is dissipated in the tunnel and the surrounding earth, and there’s over three hundred vertical feet of that earth between the tunnel and the nearest people!

  5. LHC wurde abgeschaltet…

    Wegen eines Zwischenfalls muss der LHC für ein paar Wochen abgeschaltet werden….

  6. [...] US LHC Blog has very informative [...]

  7. Popolou says:

    Heard on the local news that downtime will be approx 2 months – commiserations to the team and best of luck in getting things back up and running as swiftly as possible.

  8. Tara says:

    Dear Seth.

    Thank you for writing this blog.

    The day the LHC started was really weird for me. I woke up and read the message a friend of mine has sent me “maybe in 2 minutes we are all dead”. I was near to an heartattack or similar, really really bad shocked. Thoughts in my head of atombombs or anything like that. Than i watched news on TV and nevertheless it was getting worse. the media’s talked about “end of the world” and so on and i was three days in panic.

    well i started reading plenty of information in the net i found on google.

    maybe you can explain me the risks of the LHC colliding – could you handle it if any black holes would be generated? is it possible that something really worse can happen? maybe a bigger atomreaction for example?

    my email adress is up in the contact infos so it would be a great thing for me if you could send me an answer soon.

    last i will tell you that i am really impressed on your works up in the CERN – the internet and many more things are great – so just hold on finding more ways of making our lives easier – but never forget the risks and never do anything which has no reason (i think finding a “god particle” … what good for should it be? – it is always the next question “what was before!” …

    maybe we should use all our knowledges we got at this moment – to make our live more livable …. saving our nature – getting away from “money money money” … eyplain the world how to love ….

    many thanks for reading
    best wishes

    Tara

  9. Dear Tara,

    Besides all other entries on this blog on LHC safety, I also recommend you read a recent post on the Cosmic Variance blog. I think that explains with a very nice analogy why we think the LHC is safe, the short answer is because it is doing something that has been done millions and millions of times before.

    Freya

  10. Seth Zenz says:

    Hi Tara. The LHC cannot make black holes: Click here to see why we’re sure it can’t. The very worst thing that can happen from the LHC running, or from it malfunctioning, is damage to the accelerator itself.

    I’m sorry to hear that the TV news and other media frightened you so badly. They emphasized the “end of the world” angle in order to improve their ratings, not because they had any serious reason to believe it was true.

    Some of your other comments can be addressed by reading my responses in the comments section of this entry.

    Oh, and one other thing. I’m fully aware that particle physics isn’t much good for explaining how to love — if it were, I’d be a lot more popular in bars.

  11. Tara says:

    Dear Freya,

    Thank you for answering.
    I really don’t understand why the media’s make such a panic so … really really bad for the thoughts of the people.

    I wish that we could find new energy forms in this experiment and making our world better … thanks at all for your work.

    Sunny week for you
    Tara

  12. Didi Mousse says:

    Seth,
    This too shall pass… There was bound to be a gremlin or two throwing his shoes in the works. It certainly isn’t going to keep me off the edge of my seat.This project will probably be the greatest fundamental research done in my lifetime -I can wait a few months. Besides, there’s always the science channel (pale substitute as it is :-)

    Keep up the good work (including the public education stuff) and be sure to toss us any interesting, gory details on the progress of the hardware and repairs. Perhaps this is a good time to find some data for the LHC@Home folks to crunch?

    God bless.
    Didi

  13. reila says:

    Hi Seth,

    i’m very pleased about your posting here. For me, it is the only source for latest news from LHC. Better than the short comments on the operator web site. So, if you have any new status of the repairs, please let us know.
    I hope, we will see mini black holes, because I think it is a hint to the string theory. How is ATLAS prepared for this?

    many thanks and best wishes
    reila

  14. Tim J says:

    Really technical question for anyone who knows that bit of the physics: I know that according to relativity, a black hole as seen from our reference frame takes infinitely long to form (because time stops at the event horizon). So we can never observe an actual black hole (short of falling into one so we experience a different reference frame).

    I’ve seen several references now to the idea that some theories involving extra dimensions …

  15. Tim J says:

    … allow black holes to form (in principle). How does this work? Is the idea that the infinite time needed for formation passes in an extra timelike dimension, or something like that? Just curious.

    Oh and wouldn’t any black hole produced simply look like the disappearance of a lot of energy, followed almost instantaneously by the same energy’s reappearance as a burst of very high temperature black-body radiation as the hole evaporated?

  16. reila says:

    i think we can determine a mini black hole in ATLAS only indirect, perhaps by means of energydifference.
    The reason why mini black holes can form is the extra dimensions. Gravity in subatomic area takes effect in every dimension, so it is quite stronger than in three dimensions. The possibility for building a mini black hole is likely.
    I think Seth can explain better.

    reila

  17. Seth Zenz says:

    Okay, let me tackle those questions about black holes.

    Tim’s first. Classical General Relativity isn’t my best subject, but my understanding is that black holes do form in a finite time. You may be thinking of dropping an object into an existing black hole, which takes forever from the perspective of an outside observer.

    However, to segue into Reila’s question, a key point here is that at the LHC we wouldn’t be dealing with classical black holes, but rather quantum mechanical ones. Nobody knows exactly how quantum mechanics and gravity work together, but it’s expected when gravity is strong, the interactions will look a lot more like the usual particle collisions than the formation of a large black hole from a collapsing star. The black hole will be formed and then decay essentially instantly.

    As Tim said, that will be “as a burst of very high temperature blackbody radiation.” (This is Hawking radiation, which we have very good reasons to expect even if we don’t rely on it to prove that the LHC is safe.) What that means is that many different Standard Model particles will be produced. The heavy ones (e.g. top quarks, W bosons, and Z bosons) will be produced in about equal quantities to all the others as long as they’re much lighter than the black hole; this will make for a very unique (and crowded!) signature in the detector.

  18. reila says:

    Thank’s Seth.
    I have another question. I wonder about the sector temperature profile of sector 34. I think it is unchanged since days. Shouldn’t we see a slowly drift to higher temperatures or is the cooling of the magnets still going on?

    reila

  19. Seth Zenz says:

    Hi Reila. On the dedicated Sector 34 webpage, you can see that the sector as a whole is warming over time. However, the plot in the lower right (which is also on the cryo main page) seems to be missing information; I don’t know why that is.

  20. reila says:

    Hi Seth,

    again thanks.
    Today we have another picture for sector temperature profile of sec 34. It seems as if the quenched magnet was cooled down.
    reila

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