LHC Ready for 248 Bunches

The Large Hadron Collider is now ready for its next step up to 248 bunches which should raise the peak luminosity to 85/μb/s. That will be one more step away from this years target of 100/μb/s which will require 296 bunches.

To progress at each step when they add another 48 bunches, they need three fills and 20 hours of stable beams. At 152 bunches they had a rough time and ended up with only 16 hours, but they decided that was OK because that’s 20 in octal (I’m not making it up). The latest run at 200 bunches has gone very well with one run of 14 hours delivering 2/pb. Two shorter runs take the total time to over 20 hours so they are preparing for the next step.

To inject 248 bunches they need to switch to injecting 24 bunches in one go. If all goes well they should be ready to set the new record tonight. There is no sleep for the LHC.

The plot above shows the delivered luminosity for each experiment which is now between 12/pb and 13/pb for the big three. However, the experiments do not collect everything that is delivered. The plot below shows that ATLAS has collected 11.5/pb. I don’t have the equivalent plot for the other but it is likely that CMS and LHCb are also past the 10/pb mark at least.

Update (8 Oct 2010): 248 bunches now running with peak luminosity in ATLAS of around 88/μb/s

In case you want to see what 248 bunches per beam looks like here is a picture taken from the LHC filling schemes page. The current fill pattern is 150ns_248b_233_16_233_3x8bpi15inj.txt 

update (11 Oct 2010): There was a three day interuption to LHC opperations due to a problem with cryogenics and other niggles. They are now back up and have increase luminosity to 94/μb/s for the second run with 248 bunches. Remember,  the target for this year is 100/μb/s, so nearly there!

update (12 Oct 2010): In a surprise move they have switched to a new filling scheme with 256 bunches giving 3% more collisions for ATLAS and CMS. If they get a good fill they might just reach 100/μb/s which means party time! If they don’t get there with this fill but they keep it going for a few hours they will be able to add 48 more bunches and that will certainly do it. Of course that might be someone elses shift :)

7 Responses to LHC Ready for 248 Bunches

  1. Luboš Motl says:

    If I understand the charts well, collisions at 248 bunches began around 2:40 am, Friday morning, October 8th, 2010, and the luminosity went above 80/ub/s for the big three, and above 85/ub/s for the big two.

    • Philip Gibbs says:

      From the plots it looks like ATLAS hit the best peak at around 88/μb/s. Now they have 1.5/pb after just 5 hours and still going strong.

  2. Luboš Motl says:

    Yes, it was 88/ub/s. Atlas.CH now also shows over a trillion, 1.03 trillion, of collisions! That means 14.4/pb.

    • Philip Gibbs says:

      They need two more good runs with 248 bunches before they can go to 296 bunches which should surpass this year’s official target of 100/μb/s. They have lost a day to cryo problems this weekend and with only three weeks left they probably wont get to the full 384 bunches.

      I know they have a long list of other tests and fixes they want to do, including some setup tasks for heavy ions. It will be a case of sorting priorities that determines how much further they try to push it this year.

  3. Bill K says:

    A trillion collisions! Finding the Higgs will mean a lot of work for some graduate student: “Nope, that’s not it. Nope, that’s not it…”

    • Lawrence B. Crowell says:

      A lot of sophisticated track finding programs from the calorimeter and muon detector counts will filter out most of the data which constitutes noise. Marjorie Shapiro has a reasonable lecture overviewing the algorithms used to perform some of this

      So things are a bit more convenient than the old bubble chamber days where people counted tracks by eyeballing them.


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