fyi & historically doubling time of L is 10 days.
---------- Forwarded message ----------
Date: Fri, 24 Sep 2010 16:39:03 +0200
From: Rolf Heuer <[log in to unmask]>
To: "cern-personnel (CERN Personnel - Members and Associate Members)"
<[log in to unmask]>
Subject: A game-changing fill for the LHC - Une exploitation qui change la
donne pour le LHC
Version française ci-dessous
A game-changing fill for the LHC
A long period of machine development paid dividends last night with a
game-changing fill in the LHC. As I write this, the fill, which started
colliding at 19:00 yesterday evening, has just wound down. Both ATLAS and
CMS have posted integrated luminosities of over 680 inverse nanobarns, and
the initial luminosity for the fill doubles the previous record at
2•1031cm-2s-1.
But it’s not the records that are important this time – it’s normal that
in the start-up phase of a new machine, records will fall like autumn
leaves – what’s significant here is that the LHC’s performance this fill
significantly exceeded some crucial design parameters, opening up the path
to much better still to come.
Last night’s fill was the first with 56 bunches arranged in trains of
eight bunches per train. The significance of bunch train running is that
we can configure the orbits such that more bunches collide in the
experiments, so even though the number of bunches may not be much higher,
the collision rate is. For example, last night’s 56-bunch fill had 47
bunches colliding at ATLAS, CMS and LHCb, with 16 colliding in ALICE,
whose needs are lower. This compares to a maximum of 36 colliding bunches
out of 48 total before we introduced bunch trains.
A big jump in luminosity was clearly expected in moving to bunch trains
and colliding more bunches. What came as a pleasant surprise is that it
was accompanied by an exceptional beam lifetime of 40 hours, and less
disruption to the beams caused by packing more protons into a smaller
space (in technical terms, the beam-beam tune shift was much less
destructive to the beams than anticipated). This result means that the LHC
operators have more leeway in operational parameters in the quest for
higher luminosity.
The plan for today and the weekend is to run for one more fill with 56
bunches in trains of eight before moving on to 104 bunches in 13 trains of
eight, with 93 bunches colliding in ATLAS and CMS. Ultimately, the LHC
will run with 2808 bunches in each beam, so there’s still a long way to
go. We’ll get there slowly but surely by adding bunches to each train
until the trains meet in a single machine-filling train. That will take
time, but for the moment, last night’s fill puts us well on the way to
achieving the main objective for 2010: a luminosity of 1032cm-2s-1.
Rolf Heuer
