Beam Schedule
Posted by Monica Dunford on 23 Apr 2008 at 11:24 am
The beam schedule. It is a constant source of anxiety at CERN. If you are interested in the latest-minute fluctuation in the beam schedule, I am not the person to ask. As a principle I refuse to worry about it because there is absolutely nothing that I can do to change it. The beam schedule will be what the beam schedule is regardless of whether I worry or not.
Instead I prefer to lose sleep over preparing ATLAS for beam readiness. Because it would be quite embarrassing with all the hype about the beam schedule to then not have a working detector. And preparing ATLAS for beam is something that at least I can contribute directly to.
The other reason I don’t try to determine the beam schedule on a daily basis is because then I would have to interpret charts like this.
But there are some major announcements worth noting. First the current schedule plans that the machine will be cold (to superconducting temperatures) by mid-June. And that we could expect single beam in July. The first physics run in 2008 will be at an energy of 10TeV. (The machine design is 14TeV and for comparison the Tevatron accelerator in Chicago is 1.96 TeV).
There is disappointment from some that the first run will not be at the full design power. But for me, any beam will do. We have been building and testing this detector for so long. We all want to take it for a test drive. Even a ‘little’ 10 TeV one.
What does “single beam” mean? Will you need a dual beam to create the first proton collisions and if so when could that be?
The LHC has two 7 TeV proton beams traveling in opposite directions around the ring. These beams are focused to collide within the detectors on the ring. In single beam running, only one beam is sent around the ring. Single beam is used for tests of the accelerator and is of limited use to the detectors (because there are no collisions). Collisions are expected around August/September.
Hi Monica,
I’m surprised to hear anyone is upset about running at “only” 10 TeV. I would expect the biggest obstacles to interesting physics measurements in 2008 to be the total number of collisions and an adequate understanding of detector calibration — not the available energy. Of course, it’s a great opportunity to work on that calibration, and the sooner we start the better; so agree 100% with you on wanting to take a test drive.
For the general reader, I should clarify the issue with the total number of collisions. We don’t expect the beams to be as well-focused early on as they will be later; it will take time to tune everything so the machine reaches its design precision. This means that the same number of protons will occupy a much wider area, and thus fewer collisions. (Also, I believe there will be many fewer bunches of protons in the machine at first.)
By the way, hi everyone! I’m scheduled to become a regular writer on this blog starting in a couple of weeks.
Does anybody remember how long it was between beam-on and PRL for CDF/D0? I’m just curious at what point people shift their mindset from detector-centric to analysis-centric, not that they are completely unrelated.
There are many factors which determine the time from turn-on to publication. As Seth points out, one of those factors is the number of collisions. The fewer collisions, the longer we must run to gather decent statistics. Additionally before reaching the publication stage we have to have a good understanding of the detector calibration. And how long this takes depends on how smoothly each of the steps along the way go. There are two many unknown factors right now, such as how stable the beam will be in the beginning, how straightforward the calibration will be, to really be able to predict the time to publication.
Just to answer the question, the first Run II measurement was received on March 19 and published on Oct 29 2003 in PRD. It was based on 11.6 1/pb taken between February and May of 2002. The tougher question is “when did Run II start”? In the first year, the data taking rate was about 100 1/pb pre year, whereas over the last year it has been about 10 times that rate.
This mass measurement was exactly a by-product of what Monica says- a calibration of the detector in terms of momentum resolution (which is partly how much material the particles interact with, and partly understanding the magnetic field) and the new trigger mechanism for Run II which is a fancy way of saying a smarter way of keeping the interesting 1% of events and throwing away the boring 99% of the events.
Over the past 40 years I have worked on implementing some of the largest Commercial Computing systems in the US.
Looking at the Infrastructure of the LHC just “blows my mind”. It is truly something that the CERN group can be proud of.