Click for live LHC status.
The LHC is continuing studies to reach higher beam intensities. There was a “technical stop” the past few days to turn on more of the machine protection system so that the they can safely operate at higher intensities.
A 3.5 TeV beam of protons can cause plenty of damage if there’s uncontrolled beam loss!
Yesterday I (virtually) attended the CMS “physics operations” meeting, the first meeting of this sort in the 7 TeV era. We’ll be having a few of these per week for the foreseeable future (but I probably won’t attend all of them). The goal of the meeting is to check in on how everyone is doing in the day-to-day, hum-drum work of getting our physics business done. This includes everything from checking the reconstruction of the basic objects (leptons, jets, etc.) in the detector through full analyses that lead to publishable measurements. Does everyone have the simulation samples that they need? Have we learned enough about the data that it seems useful to reprocess all it with our new knowledge applied? What sort of problems are they running into with accessing the data or using the distributed computing system? (I came to get the word on the latter, which falls in my purview.) This meeting should be useful in helping us get work done efficiently, especially given the crush of activity that is occurring in the enthusiasm to study and understand our early data, and to prepare our first results from 7 TeV collisions.
That being said, the concept of “physics operations” sort of turns my stomach. Poking around on the Web, I found a definition of “operations management,” which was “the maintenance, control, and improvement of organizational activities that are required to produce goods or services for consumers. Operations management has traditionally been associated with manufacturing activities but can also be applied to the service sector.” This suggests the idea of physics as a factory — there is an assembly line, you put some raw materials into it, you make sure that all the machines run smoothly, and out come publishable papers at the other end. Of course this isn’t how physics research actually works — throughout the process of making a measurement, we need to apply plenty of human judgment and creativity, at least if we want to advance the field in a real way.
But perhaps this is just the way things have to be these days — when you have hundreds of humans being creative at the same time, you want to make sure that they don’t all collide with each other, that they are getting the resources that they need, and that the systems and tools that we have provided don’t hamper anyone’s creativity. And perhaps this was a natural evolution: I have certainly been among the people who talk about “physics commissioning,” the work you need to do to get data analyses up and going, in analogy to getting a detector up and going. And once you’ve commissioned a detector, you operate it, of course.
In other news: I’m supposed to be going to CERN in a week for the semi-annual CMS software and computing week, but the eruption of Eyjafjallajokull (pronounced EY-ya-fyat-lah-YO-kut) volcano in Iceland and its impact on trans-Atlantic air traffic has me spooked. Apparently when the volcano last erupted, about two hundred years ago, it did so on and off for about two years. Will I make it over there? Will I be able to come home? Answers in my next post.
KB
These past few weeks have gone by in a blur. The LHC provided us with the first collisions, then it became the highest energy accelerator, and for a few minutes last night, the LHC became highest energy collider.
Crazy.
It’s been busier than usual at CERN, with people in a rush to examine the first collision data to try and learn as much as possible. But tonight, at least some of us, took a little time to celebrate. Our detector, CMS, held a Christmas Party near Prévessin-Moëns, with food, drink, and music. 800 people showed up: physicists, engineers, post-docs, students, and their friends and family. Everyone has been working so hard, putting in extra time, they deserve it.
It is an exciting time to be here.
It was reported last week by Dennis Overbye at the New York Times that the LHC is only going to reach a center-of-mass energy of 2.2 TeV (i.e. an energy of 1.1 TeV per beam) before the winter shutdown. I was asked about this previously, and at the time I thought it was “in a schedule somewhere.” After looking around, though, it’s much less clear to me where the information actually come from — maybe I heard it from people who had read the New York Times blog, and maybe Overbye originally learned it from magical time-traveling Higgs Bosons! So we might have to demote the whole thing to the category of rumor — but it’s a rumor that appeared in the news, so I can certainly say what I’d think about it if it were true.
If indeed the LHC only achieves an energy of 2.2 TeV by the time it’s shut down in mid-December, some might be tempted to characterize it as a serious setback or defeat; in fact, it’s nothing of the kind. Here’s what’s really going on: the LHC is in the middle of an ongoing start-up process, and has to take a quick break in December and January, but will then pick up where it left off. That means that the point the accelerator startup happens to reach before shutdown doesn’t mean anything special at all — the really important thing is where it gets to when the process continues next year.
What we do know from CERN is that there are three stages of LHC magnet commisionning: to 2000, 4000, and 6000 amps of current. We also know that reaching 2000 amps “allow[s] the passage and guidance of beams at about 1.2 TeV” (which sounds close enough to the 1.1 TeV figure to be rounding uncertainty). So if there were only time to commission to 2000 amps before the end of the year, that could certainly explain the limited beam energy.
Is running at 2.2 TeV good for the physics program? Oddly enough, if we only have a few days of running, there are two lower energies that would be more fun for physicists. The best option might be to continue at the energy at which the center-of-mass energy achieved by the previous accelerator stage, 0.9 TeV. This is the energy that the first collisions will happen at, and longer running at a single energy would let those of us who work on the detectors get a better handle on how our data looks. (For example, I could attempt to do an early, quick version of my track jet analysis. In fact, I’ll try to do that no matter what; it will be good practice, if nothing else.) Another option might be to run at exactly 1.96 TeV, which is the energy of the Tevatron accelerator at Fermilab; that would give us a rare chance to look at the differences between proton-proton and proton-antiproton collisions at the same energy.
But the physics program isn’t the top priority this year, it’s getting the LHC fully up and running. Whatever the rumors say, we don’t yet know how far accelerator commissioning will get this year. Even 2.2 TeV would be enough to make the LHC the highest-energy collider in the world, which is an accomplishment to be proud of. No matter what, there will be much more to do next year, and we can start making discoveries! — Seth
Currently I am sitting at Geneva airport waiting for my plane to finally leave for Amsterdam. Looking east I see something the average cernoise is always happy to see: First snow on the Jura.
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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.
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.
This morning, at about 9:55 CERN time, the LHC beam was dumped on a
collimator just upstream of CMS. This is when we first saw for the
first time the beam activity in the detector, a picture is attached.
What you see is the debris of the beam particles hitting the collimators. The resulting shower then produced a lot of activity in our hadron calorimeter (blue) and some hits in our muon system (small green rectangles). And all of those dirty messy particle showers from three different angles, which is why we have three different figures for the same events. The inner detector was turned off due to the beam still being very unstable and it can actually be damaged easily by randomly flying particles.
I am so excited! I am currently in the CERN media center where things are buzzing with journalists from all over the world! Before I forget to brag about the fact that the google home page is LHC themed today!
I’m usually fairly reserved about my enthusiasm, but I have to admit that now even I am getting excited about first beam.
The ATLAS pixel detector is up and running in the pit, and I’ve been working hard this week on looking at the data from calibration scans. Since I wrote a lot of the tools for looking at large quantities of pixel calibration data in a systematic way, I’m the most up-to-speed on using them; and since we have to be calibrated and ready to run very soon, there’s a lot of demand for those skills. Being useful, and having a lot to do, makes me happy. I get up early in the morning ready to come to work, and leave only reluctantly in the evening when I’m too tired to get anything done.
I’ve also been trying hard to get all the training I need to run pixel detector shifts, and it looks like my efforts have borne fruit. I have “training shifts” on Friday and Monday, and hopefully after that I’ll be able to do things on my own. The only downside is that the day shifts now start at 7 AM—it’s a good thing I’ve been getting up early ready to come to work!
The LHC startup is getting closer and closer. A few previous blog entries already informed you that there was a successful insertion of beam into the LHC. This is of course great news, but means that the testing and final preparations of the detectors has now become serious business. As the CMS pixel detector was planned to be installed as one of the final components before the first beam was delivered, we are very much under pressure to be ready in time. 
You can read that as ‘continuously on shift until things are stable enough to be run by non-experts’. This also explains the lack of blog entries by me and some of the other people working closely on the detector, at the moment the pressure is really on and the detector comes first!
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