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Chamonix Summary @ CERN

Cosmic Variance
By JoAnne Hewett
Feb 25, 2009 3:05 AMNov 5, 2019 8:18 AM


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During the week of February 6, a workshop on the LHC performance was held in Chamonix, France. All of the main LHC machine folks gathered there, in one room, and discussed their strategy for the start of operations of the LHC, for all aspects of the accelerator. Reports have appeared on the blogosphere, for example here and here.

What’s new is that this afternoon at CERN, a 3 hour summary of the workshop was given in the main auditorium. And I was there. The auditorium was packed, and the audience peppered the speakers with questions. The CERN staff certainly appreciated the opportunity to hear the summaries and to ask questions. I know I did. It’s one thing to sit in California and read the slides and perhaps watch the video stream, but it’s another thing to be there in person, listen to the discourse, and to ask questions myself. The talks ranged from safety issues, to what they learned with and without their few days of beam in 2008, to their plans for the next run. And here is the official schedule for the 2009/2010 run:

For me, the most interesting part of the talks was information on the next run: The accelerator physicists presented the lab management with two options for the 09/10 run, depending on how many of the pressure relief valves in the arcs would be installed before the run. It’s worth noting that the full quench system will be operational in either scheme and that the pressure relief valves only serve to stem possible damage, i.e., they are not preventive. The accelerator guys were split on which plan was better. Management opted for the plan which gave beam in 2009. The schedule is tight with no room for contingency in case of slippage. Today, they are 1.5 weeks behind schedule, which is actually very good! They will have a short run (few days?) with collisions at injection energy (450 GeV per beam). This is at the request of the general purpose experiments (ATLAS and CMS) in order to aid in the calibration of their detectors. They will then run at 4 TeV per beam for a limited time (I asked specifically about this afterwards and was given various answers about the length of time at 4 TeV). Clearly, they will ramp up the beam when (and not before) they feel it is safe to do so. Then they will run at 5 TeV per beam with the goal of collecting 200 inverse picobarns of luminosity. To do this, they must run during the winter months December 09 – February 2010. CERN accelerators do not normally run during the winter months as the cost of electricity is 3 times higher than for the rest of the year. The additional electric bill for running the LHC during these months is $8M Euros. It’s not clear how the lab is going to pay the additional electricity costs and the lab staff is clearly concerned about cuts, but management thinks it is manageable. It’s not clear that the LHC will ever run at the design energy of 14 TeV. There is a problem with the number of expected magnet quenches as one tunes the beam from 6.5 to 7 TeV. Namely, it’s alarmingly high. They don’t know why yet, but are working on it. It is possible that the maximum energy the machine will ultimately reach is 13 TeV in the center of mass. All in all, the news is good. They are expecting a reasonable set of good quality data at high energies with good discovery potential. Colliders are always slow to start up (just ask Fermilab), and the LHC will get to design parameters in good time.

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