• John
  • Felde
  • University of Maryland
  • USA

Latest Posts

  • USLHC
  • USLHC
  • USA

  • James
  • Doherty
  • Open University
  • United Kingdom

Latest Posts

  • Andrea
  • Signori
  • Nikhef
  • Netherlands

Latest Posts

  • CERN
  • Geneva
  • Switzerland

Latest Posts

  • Aidan
  • Randle-Conde
  • Université Libre de Bruxelles
  • Belgium

Latest Posts

  • TRIUMF
  • Vancouver, BC
  • Canada

Latest Posts

  • Laura
  • Gladstone
  • MIT
  • USA

Latest Posts

  • Steven
  • Goldfarb
  • University of Michigan

Latest Posts

  • Fermilab
  • Batavia, IL
  • USA

Latest Posts

  • Seth
  • Zenz
  • Imperial College London
  • UK

Latest Posts

  • Nhan
  • Tran
  • Fermilab
  • USA

Latest Posts

  • Alex
  • Millar
  • University of Melbourne
  • Australia

Latest Posts

  • Ken
  • Bloom
  • USLHC
  • USA

Latest Posts

Posts Tagged ‘calibration’

The Joys of Submission

Tuesday, November 3rd, 2009

A couple of months ago I blogged about how at ATLAS we’re using cosmic rays to study the detector.  Well with data impending, the work that my group and I have been doing was submitted to become internal ATLAS document last week. This process was new to me… so I thought I’d share. Not every plot we make is available for public viewing. Our “notes” (ATLAS documents) come in two flavors: one that is available for public view, and one that isn’t. The ones that aren’t for public view don’t really have any special information – for ATLAS eyes only – they just don’t require that all the plots included are approved by the group they’re associated with. For example, the study I did was on the uniformity of the Liquid Argon (LAr) Calorimeter, so the LAr group has to approve the plots (in other words, make sure they aren’t confusing, that things are labeled properly, that it’s relevant… etc). The process of writing this note took about 5 months. There were at least 5 direct authors and about 10 total people reading and giving input (relatively small group for ATLAS standards 🙂 ). However, with every plot, and with every paragraph we had to make sure we understood exactly what we were implying. From new questions came more cross-checking and new understanding. There was one point where we were comparing numbers of events in a specific region of the detector because I wrote my code separately than the other members of the group (which is also standard.. being able to check independently).

We had several plots approved, but wanted to include a couple of additional plots for clarity – which means that it’s internal only. So finally after all this – months and months of back and forth, editing and re-editing, we submitted… as a “communications” note. This means that it hasn’t been reviewed yet. Before it can be an “internal” note, it has to be checked by an independent group. Then we make changes as suggested, and it can finally be approved. This whole process reminds me of that old school house rock song about how a bill becomes a law. See there’s me waiting for the note to be approved.

There we are waiting for our note to become official

There we are waiting for our note to become official

So Tuesday was a day for celebration (ok, so we don’t need too much of an excuse to celebrate). But some of the plots we worked on are going to go into another publication, which will be public and I’ll definitely share when it’s available. That is a whole other process though for another time.

-Regina

Share

Why are you still doing night shifts?

Thursday, November 13th, 2008

This is a question I’ve received recently from a couple of my friends in the theory community.  Theoretical particle physicists are pretty smart people, and they do know a little something about particle detectors — so if they’re wondering, then I’m sure some of you will be curious too!  This is also a chance to see a snapshot of my psychological state at the end of a night shift: I wrote all of this to explain what I was doing between 6:20 and 6:45 in the morning a couple weeks ago.  My only edits are two places where I wrote something incorrect and replaced it with a new explanation in brackets.

To summarize: I’m busy this week and getting an easy entry out of cutting and pasting from my gChat log.

Again, the question was (more or less), “Why are you still doing night shifts when the accelerator, and large parts of the ATLAS detector, are off?”  Here’s my answer:

06:22 calibrate the detector
the pixel detector has 80 million channels (i.e. pixels, 400 x 50 microns)
06:23 they actually live, physically, on about 1700 modules, which talk to various hierarchically-organized computers
06:24 [to transmit the data the 100 meters to the counting room without high voltage or repeaters] we have optical links for transmitting the data from inside the detector until it gets outside
thus we need lasers to turn digital signals into optical light, and then we also need to convert the light back
the lasers have to be timed and powered correctly, as does whatever reads the information
06:25 at the moment, the ATLAS pixel detector isn’t using some fraction like [3%] of its modules, because they aren’t set correctly. in some cases, they may be impossible to set correctly until we can open the detector and replace components — which may be many years
but in other cases, the automatic-setting didn’t work, and we have to take a closer look.
06:26 some experts were in here today to try to recover a few such modules by taking that closer look; now I’m running scans that tell us if they were succesful or not.
06:27 that’s only one example of the kind of thing we do. there are a lot of things you can set on every module, and we have to get them all set right.
06:38 [My friend asks why we run all night, and if we run all the time]
06:43 me: yes, we have finite time, and lots of work to do
and clearly more people than pixel detectors.
06:44 once the cooling goes off, in a few weeks, we have to turn the modules off. then there’s only a few kinds of calibration scans/studies we can do

It’s worth noting that now, two weeks later, all the optical links are working well, except for a very few that are hard-core unrecoverable — thanks to the work of the experts who looked at the tuning and the very small contribution I made by running scans for them overnight.  Our night shifts continue, with a few nights each from over a dozen people in this month alone.   Although the details of the work at the moment are different, but the overall plan is the same: to have our subdetector, the last one installed, be as ready as the rest of ATLAS when data finally arrives next year!

Share

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.
(more…)

Share

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.

Share

Getting Ready

Wednesday, September 3rd, 2008

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!

Share