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Posts Tagged ‘startup’

I know what you are thinking. The LHC is back in action, at the highest energies ever! Where are the results? Where are all the blog posts?

Back in action, yes, but restarting the LHC is a very measured process. For one thing, when running at the highest beam energies ever achieved, we have to be very careful about how we operate the machine, lest we inadvertently damage it with beams that are mis-steered for whatever reason. The intensity of the beams — how many particles are circulating — is being incrementally increased with successive fills of the machine. Remember that the beam is bunched — the proton beams aren’t continuous streams of protons, but collections that are just a few centimeters long, spaced out by at least 750 centimeters. The LHC started last week with only three proton bunches in each beam, only two of which were actually colliding at an interaction point. Since then, the LHC team has gone to 13 bunches per beam, and then 39 bunches per beam. Full-on operations will be more like 1380 bunches per beam. So at the moment, the beams are of very low intensity, meaning that there are not that many collisions happening, and not that much physics to do.

What’s more, the experiments have much to do also to prepare for the higher collision rates. In particular, there is the matter of “timing in” all the detectors. Information coming from each individual component of a large experiment such as CMS takes some time to reach the data acquisition system, and it’s important to understand how long that time is, and to get all of the components synchronized. If you don’t have this right, then you might not be getting the optimal information out of each component, or worse still, you could end up mixing up information from different bunch crossings, which would be disastrous. This, along with other calibration work, is an important focus during this period of low-intensity beams.

But even if all these things were working right out of the box, we’d still have a long way to go until we had some scientific results. As noted already, the beam intensities have been low, so there aren’t that many collisions to examine. There is much work to do yet in understanding the basics in a revised detector operating at a higher beam energy, such as how to identify electrons and muons once again. And even once that’s done, it will take a while to make measurements and fully vet them before they could be made public in any way.

So, be patient, everyone! The accelerator scientists and the experimenters are hard at work to bring you a great LHC run! Next week, the LHC takes a break for maintenance work, and that will be followed by a “scrubbing run”, the goal of which is to improve the vacuum in the LHC beam pipe. That will allow higher-intensity beams, and position us to take data that will get the science moving once again.


Running with Scissors

Wednesday, February 3rd, 2010


We are at the stage now where the ability to crank up the intensity and energy of the LHC beams to full power is at hand.  We’re like a toddler that just learned to walk: the urge to run is present and exciting, but the probability of banging our head would be high!

It has been decided through many meetings, and with considerations of experts on the front lines, that the highest, safest energy the beams can be run at without major repairs is 3.5 TeV per beam with an instantaneous luminosity of 2*1032/cm2/sec. (The LHC was designed for 7 TeV per beam and an intensity of 1034/cm2/sec.)

More intensity means more proton collisions, and more energy means high probability of interesting collisions.  Unfortunately, high intensity and high energy also means high risk of accidents – like the one in Sep 2008.

With that in mind, management decided to balance safety of the machine with the drive to explore and make discoveries.  So, the current plan sets a goal of collecting a specific amount of data, 1 fb-1, before shutting down for one or two years starting around the beginning of 2012 for repairs and upgrades.

If nature is hiding secrets in areas we now expect them, then this should provide enough data for discovering some of them, or at least allow ruling out some theories – and all without hurting ourselves.



LHC Collisions Playlist

Thursday, November 12th, 2009

The first LHC collisions won’t be for at least a few weeks, but there’s a critical question I’m sure you’re already asking: what music should I listen to for the big event? Here are some suggestions:

Collide – Howie Day
Key lyrics: “Out of the back you fall in time / I somehow find you and I collide”

Surfin Bird (Bird is the Word) – The Trashmen
Key lyrics: “A-well-a everybody’s heard about the bird / B-b-b-bird, bird, bird, b-bird’s the word.”

If You Don’t Cry – The Magnetic Fields
Key lyrics: “Another five years off your life / If you don’t cry, it isn’t love.”

Collider – Les Horribles Cernettes
Key lyrics: “You never spend your nights with me / You don’t go out with other girls either / You only love your collider”

Still Alive – GLaDoS and Jonathan Coulton
Key lyircs: “This was a triumph / I’m making a note here: huge success”

Have more song ideas? You know what to do: comment here, on Facebook, or on Twitter — with enough good suggestions, there might be another post!


Much Ado About 2.2 TeV

Thursday, November 5th, 2009

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


The Beam is Back!

Tuesday, October 27th, 2009
Beam in the LHC!

First beam in the LHC since last year!

As reported by the BBC, last weekend particles were injected into the LHC for the first time in over a year.  This confirms what we’ve known all along — the scientists, engineers, and technicians working on the LHC are making steady progress toward restarting the machine — and it’s an excitingly concrete reminder of how close we are to taking data!

Last year’s big startup event was focused on circulating a beam around the entire ring, which hasn’t happened again yet.  This year’s really exciting milestone will be when beams are not only circulating in both directions, but actually colliding: that’s when we can start to do physics.


Schedule Disappointments

Wednesday, November 19th, 2008

As Adam noted yesterday, the date now being cited by the CERN Press Office for the restart of the LHC is early summer.  Unfortunately, there are two reasons why I’m personally not inclined to take this new estimate too seriously.

First, CERN has an increasingly long history of being over-optimistic on LHC start-up times.  At one time it was scheduled to run in 2005. Even into 2007, the official schedule said there would be a low-energy run that year; but in the end, it didn’t start running until almost a year later.  After the accident on September 19, CERN initially announced that the incident would lead to minor delays, then that it would take several months because of the winter shutdown, and now we have the revision that the repairs will push into the summer. Obviously some of these delays were due to unforeseen circumstances, for example the recent accident itself.  But even if all the schedule changes are due to equally-unforeseeable (if less dramatic) issues, the sheer number of revisions seems to suggest that CERN ought to take a step back and consider how it does contingency planning and the certainty with which it expresses its scheduling announcements.

Second, this new announcement is not accompanied by a new detailed schedule.  What would be useful for the experiments is more information about the damage and a full discussion of how the repairs will proceed, along with a range of possible start times depending on how well still-unknown factors turn out; this would let us do better contingency planning for our own maintenance work, not to mention our careers.  It’s very possible that CERN doesn’t yet have all the information about what repairs will be necessary, but then why the new announcement?  What use can it have beyond publicity, and what meaning can anyone possibly extract from it?

I should be clear here what I mean when I talk about “CERN” making announcements.  Obviously I’m not talking about the technicians, engineers, and physicists who work on the LHC; I’m sure they’re doing a great job, and of course they don’t write the press releases or talk to the media.  I’m also not referring to anyone in particular in the CERN Press Office or Management; the Press Office does a lot of good work on outreach, including putting forth an extraordinary effort for First Circulation Day, and the folks who write the press releases aren’t necessarily the ones who decide what they say.  The truth is that I simply don’t know how decisions about these announcements are made, or who makes them.  But somehow the official system for disseminating information is falling short of providing what the physicists working here need or what the public deserves.


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.”


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.


from the media center…

Wednesday, September 10th, 2008

I was just handed an ATLAS postcard with a graphical display of one of the first debris events on it.

All I could think was: Wow, those guys are fast!


first CMS beam event

Wednesday, September 10th, 2008

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!

First CMS beam event