New Luminosity Milestone for LHC

The Large Hadron Collider has today surpassed 2000/μb/s in peak luminosity for both ATLAS and CMS. This was achieved during the Adjust phase of fill number 1992 using 1380 bunches per beam, just before stable beams were declared this morning.

Luminosity has been gradually increased above the 1280/μb/s limit reached before the technical stop at the end of last month. So far only emittance has been used to enhance the luminosity. This does not increase the overall intensity of the beams so there is no increased risk or extra demand on the cryogenics. At the recent mini-chamonix meeting it was predicted that emittance could provide an extra 35% luminosity but now they are 55% above where they were before.   This extra is probably just due to the fact that the final runs before the technical stop suffered from some emittance blowup or injection losses that meant they were not as good as they could have been.

It was intended that further luminosity improvements would be attempted by increasing bunch intensity. This has the potential to double the peak luminosity again. This plan has been held back because of the technical difficulties of running at the high intensities they are now using. This can effect the vacuum and cryogenics leading to premature dumping of the beams and increasing times for returning to stable beams. Indeed the current rate of luminosity delivery is around 35/pb per day, just slightly better than the 30/pb per day when they ran with 1092 bunches during June. The proportion of time in stable beams recently has only been about 30% but there are signs that this is getting better.

There are just 24 days left before they break for the next Machine Development slot and the beam operation groups will be keen to make further progress with both stability and luminosity during that time. With 1.75/fb now delivered they are already on target to reach 2.6/fb at the next technical stop. After that there will be a final run lasting eight weeks before they switch from proton physics to heavy ions for they last part of the year. It is not yet clear at what point the experiment collaborations will decide to update their analysis but clearly this level of data is guaranteed to have enormous impact, especially on the Higgs searches.

7 Responses to New Luminosity Milestone for LHC

  1. […] LHC 2011 – latest news, 30th July. También se ha hecho eco del logro Philip Gibbs, “New Luminosity Milestone for LHC,” viXra log, July 30, […]

  2. Clara says:


    is there an update of the slide


    There is much more data available now…

  3. Bill K says:

    “.. technical difficulties of running at the high intensities they are now using. This can effect the vacuum and cryogenics..”

    Phil, can you explain this a bit more? How does high beam intensity put a strain on the cryogenics? I understand that heat will be generated during transient stages like injection and ramp, but properly a stable beam should not be a significant heat source.

    We are still running at half power. Presumably these effects will be much more at 7 TeV, and ability to handle them must be part of the design.

    • Philip Gibbs says:

      Bill, it’s likely that you know more than me about this, but there is heating of the magnets that goes up with beam intensity and it has to be dissipated by the cryogenics. I am not sure if this heating arises through beamstralung or EM induction or what, but all that energy from the RF being used to keep the protons moving must go somewhere.

      The cryogenics should be fine up to nominal spec and they are only at half that, but there is extra heat load caused by the e-cloud. I don’t know if this is the main issue.

      There are probably other effects at play. At some point the accelerator physics gets to a higher level of detail than I am interested in studying and this is about there. If anyone else can explain better though I would be happy to hear about it.

      • carla says:

        Upto now, the cryogenic’s main problems seem to be with loss of communication.

        The main unresolved problem are increased vacuum activity with increased bunch intensity and erratic triggering of the thratrons in the MKI-B1.

      • Bill K says:

        Thanks Carla. It sounds from what you said that the problems haven’t been with the cryogenics so much as with the instrumentation. Maybe it’s connected to SEU’s (Single Event Upsets) which they’ve been talking a lot about lately. An SEU can happen when radiation strikes a critical electronic component.

        Meanwhile the last two runs have been excellent! Around twelve hours each. Although CMS has been down for part of the time.

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