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Archive for September, 2008

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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That is how it goes…

Sunday, September 21st, 2008

Hi All-

Welcome to the occasionally exasperating world of pushing the limits of science.  Yes, transformers break (and are repaired within days) and problems occur which also could be fixed in days were it not that they are in parts that operate at about 1 degree above absolute zero, which means repair requires some care and some time.  If you don’t know what I am talking about, have a look at Seth’s blog which does a nice play-by-play.  This sort of thing makes it very hard to plan on the beam, but those of us who have been there before (like at the Tevatron for 8 years) know that this is how it goes.  So do not despair and think the LHC is dead on arrival, it’s just going to take a little while longer.   In fact, for me it means an opportunity to be present at first collisions, which is a bit like icing on the cake in that I’m not crucial for operations, still, icing tastes good!

So what happens now?  Well, that is what the experimental teams are discussing, but essentially we’ll keep refining our own operational procedures using cosmic rays, take the opportunity to shore up the weak links in our systems, like fans that are affected by the magnetic fields, or failing electronic components, etc – turns out even the elevator at CMS is somewhat susceptible to the stray magnetic field – there are stairs for backup, but it is a long way up.

I hope (and expect) we’ll get a debriefing on what went wrong in the accelerator, and why it wasn’t caught in testing before the turn on, but right now they have to wait until the arcs are warm before they can go find out.  Anyway, one of the most remarkable things we’ve learned so far is that people are genuinely excited about what is happening, which enourmously gratifying – keep asking questions, we’ll keep answering, and try to fill you in on what to expect in the next few months.

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Yes We Can !!

Friday, September 19th, 2008

I happened to log in to Yahoo News last night around midnight and, to my surprise, the top story, again, was the LHC. This time due to the late reported transformer failure at CERN. But first the positive: this was the third time this week that we were the lead story on Yahoo. First the actual turn-on, then the hacker attack and now the transformer failure. You could turn that into the negative by saying that when we didn’t destroy the Earth we were at least fodder for the internet because of hacker attacks and equipment failure, but to all those naysayers I say: the word ‘atom smasher’ is by now engrained in everybody’s brain and that is a mighty good thing. First year undergraduate students come up to me after class and tell me that they have heard that I am working on this enormous physics enterprise, the world’s largest accelerator, and that we might unravel some major science mysteries. That is a great start, because we can capture them even further by telling them the details of our exciting field, and because we are professionals who know how to deal with the negative publicity. Equipment failures are common in the startup phase of such highly sophisticated machines and hacker attacks are our speciality. So we will find you, buddy ! And besides, our hack attack paled in terms of news coverage in comparison to the people who got access to Sarah Palin’s e-mail account. 

In a time of wall-to-wall political coverage, a major financical crisis, a war and two political campaigns spending several hundred Million Dollars each to capture your vote, it is reaffirming to see what human beings are are capable of when it comes to creative applications of their strength. So let’s celebrate the purpose and resolve and ingenuity of this project in this time of wastefulness. Yes we can. 

 

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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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CERM Start-up

Thursday, September 18th, 2008

No, that isn’t a typo; I’m talking about the activation of a completely different machine. This one is cheaper, and the practical applications are more obvious, but you can see it doesn’t work quite as quickly as the LHC did:

It has exactly the same probability of destroying the earth that the LHC does.

This excellent video was pointed out to me by someone from the Accelerator and Beams department; his enthusiasm should come as no surprise, because coffee is a major part of the institutional culture here at CERN. We’re powered by it when we’re tired. We drink it when we have informal chats with our colleagues. There are many machines and kinds of coffee to suit all different tastes and nationalities — and yes, you’d better believe there are international coffee issues. For example, if you’re buying coffee and an Italian asks for an espresso, you have to know to buy what the cafeteria coffee machines call a “ristretto” — which apparently just means “small, dense espresso” — because that’s how they make espresso in Italy. As an American, I miss my Venti Double Chip Mocha Frappes, but alas, the coffee machines don’t make those under any name.

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The Waiting is the Hardest Part

Wednesday, September 17th, 2008

After the sprint out of the gate by the LHC and even rumors of collisions coming much sooner than expected, things have slowed down here for the last few days.  I am in the ATLAS control room on shift from 3pm-11pm, Monday-Thursday this week, and I had dreams that the LHC would collide some low energy beams during that time and I could celebrate again in the control room.  Instead it is Wednesday night, I just ate a terrible “Poulet Curry” sandwich from the cafeteria, and the LHC hasn’t had any beams at all in the last few days.

In the meantime, everyone here has been working with their piece of the detector.  The other 2 people and me who are at the liquid argon calorimeter desk have been learning a lot about the various procedures which are still new to us, updating/improving documentation, recording calibration data, and responding to small problems here and there.

Last night we recorded calibration data for most of the shift.  Then, we tried to record some cosmic muons data, but had several problems reading out our detector that stopped us.  After several hours of trying, we finally started recording data just as the shift ended.  Tonight, we have taken only about 20 minutes of data due to various problems, the last being a magnet quench.  And we are back to waiting.

The accelerator folks keep moving the time for putting some beam back into the LHC back every few hours.  It was estimated at 7pm when we got here at 3pm.  The current estimate at 10pm is no beam before 2am.  Maybe tomorrow night during my shift there will at least be one beam circulating through ATLAS.  And then hopefully only a few more days until collisions.  Just have to wait and see.

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The new particle data book is here!

Tuesday, September 16th, 2008

OK, it may not be quite as exciting as the arrival of the new phone books in that Steve Martin movie, but I was still pleased to receive my copy of the 2008 Review of Particle Physics this week.  This year’s edition clocks in at somewhere around a thousand pages; not easy to tote around, but fortunately the summary booklet, formerly known as the “wallet card,” will soon be in the mail too.

What is this thing, anyway?  It’s a compendium of all of our knowledge of particle physics, and that is an amazing resource.  My colleagues in other disciplines, and even in other fields of physics, have a hard time knowing what is actually known in their field.  It can be hard to make an exhaustive search of the literature.  But in particle physics, we have a big book (and Web site) which records everything — every published measurement of every measured quantity out there, plus statistical analyses that provide world-average values that serve as reference points.  (Actually, that is no longer strictly speaking true; very obsolete measurements have been removed from the review, to save space.)  If you want to work on some measurement, this is the first place to go to find out what has already been done.

It doesn’t come for free, of course.  There is a hard-working team based at Lawrence Berkeley National Laboratory that produces the review every two years, collaborating with partners from around the world.  This year they sifted through 645 new publications from which they gathered 2,778 measurements that they have added to the 24,559 that were already in the previous review.  In addition, there are numerous in-depth reviews of specific topics, written by experts on those particular topics.  Mad props to all of those people.

The big question for this blog: what impact will the LHC have on the 2010 Review of Particle Physics?  The cutoff date for published data to be included in the next review will probably be in January 2010, which doesn’t really give us much time, especially given that we will have a limited amount of data in the next year and it will take us a while to analyze it.  But of course our goal, over time, is to completely re-write that book.  Stay tuned.

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First ATLAS Pixel Tracks!

Sunday, September 14th, 2008

I’m on my 18th hour on training shift since Saturday morning, getting in as much time in the control room as I can, and it’s been a very exciting time. One of my colleagues has just discovered that, last night, we recorded the first cosmic ray tracks in the ATLAS pixel detector!

First ATLAS Pixel Detector Track!

This is very exciting news for us; we’re working right up to the wire to make sure our pixel detector is able to run stably along with the rest of the detector. Collisions are coming soon soon soon!

Update (Sept 15): In response to two excellent questions in the comments, I wrote in a little more detail what you’re looking at in the picture. I figure the explanations might as well go in the entry:

1. What’s the perspective? Where’s the LHC?

You’re looking at the inner part of the ATLAS detector, which is wrapped around one of the collision points of the LHC. The large image in the upper left is a cross-section of the detector; the white dot in the very center is where the LHC beam pipe is. The image along the bottom shows the same tracks from the side; the LHC beam pipe isn’t shown, but it would run horizontally (along the Y’ = 0 cm line).

2. What do the dot colors mean? What’s the line?

All the dots are the actual points at which we have a signal from our detector. The red dots represent the signal that we think was left by a charged particle when it passed through, and the red line is the path we think that particle took (i.e. the “track”). The green dots are also signals in the detector, but we think they’re random firings in our electronics, because we can’t make any tracks out of them.

It may look like a lot of electronic noise, because there are more hits from random firings than from the track. But remember that there were only one or two tracks to be found, whereas we have over eighty million pixels in our detector. Thus the fraction of noisy pixels was actually quite small, and certainly didn’t interfere with finding the track. We also have a list of especially noisy pixels that we can “mask” (i.e. ignore), which will bring down the noise by quite a lot but which we haven’t begun to use yet.

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Night and Day

Friday, September 12th, 2008

It’s Saturday morning, and I’m up at 6 AM again for my fourth training shift in eight days.  I’m tired.  I’ve not only being dealing with getting up very early, but also with staying up late: on Wednesday, I was the “live from the control room” connection for a San Francisco Bay Area party to celebrate the start of the LHC.  The party was in the evening there, which meant the middle of the night here, and so for me, Circulation Day stretched from 9 AM until 6 AM the following morning, when I finally left work.  That made for a very abbreviated Thursday, because I had a shift yesterday (Friday) at 7 AM as well.

Anyway, I’ve actually had it easy with the shifts so far, because training shifts are all day shifts.  I’m (probably) almost done with them though, and ready to start running the station on my own. (There are experts on call if something happens that I’ve never seen, thankfully!)  I’ve just been asked to submit my shift availability for October, and here it is:

Seth's shift availability for October

Green means I’m willing to take a shift at that time, red means I can’t; the horizontal axis is the 31 days of the month, while the three vertical entries are the 7-3 day shift, the 3-11 evening shift, and the 11-7 night shift.  There are two things you should note:

  1. You can probably guess which weekend I’m meeting a friend in Zagreb, Croatia.
  2. I’m willing to take as many night shifts as day shifts — which means that I can be put on as many night shifts as the shift scheduler thinks is reasonable.  Three or four nights in a row is not unusual as all.

Fortunately, as a new shifter I’ll still be on the day shift for a bit, so I at least won’t be waking the experts up when I screw up and have to call them.  But there’s work to be done, and I have to be willing to work (almost) all the time.  And you know what?  I’m thrilled to be doing it.

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Now the Fun Starts

Thursday, September 11th, 2008

If the LHC folks had managed to get one proton to go around the 17-mile tunnel once yesterday, CERN would have declared it a huge success.  Well, by the end of the day they sent a beam of protons around the ring hundreds of times.  I’d say they blew away expectations!

At ATLAS today, everyone was gushing about yesterday’s success, and about the data we had in our hands.  The LHC people decided to put a collimator in front of ATLAS yesterday for several hours, resulting in numerous showers of particles lighting up our detector like a christmas tree.  In the calorimeter data, we see energy in these events in just about every one of the independent 200,000 cells (each makes its own measurement of energy in a small region).  Other detectors have similar luck.  With this we can do a lot of work fine tuning and calibrating our detector, to be ready to take full advantage of proton-proton collisions, whenever they come.  This by the way was supposed to be maybe a month or two, but with the way the LHC is working, we better be ready by about next week.

Also, here are some cool event displays from ATLAS.

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