The near-term plans for LHC repairs and commissioning are a common topic for lunchtime conversations these days. I don’t really know much beyond the very basics, but a recent post at the US LHC Blog motivated me to put up a post in the hope of generating some discussion.
Last Friday Robert Aymar (the CERN Director General) gave a presentation on the `status of CERN,’ the image that caught my eye was this one on page 18:
By now we’re all familiar that the LHC had some problems on 19 September 2008, the “S34 Incident.” Here’s Aymar’s summary of the event:
Within the first second, an electrical arc developed and punctured the helium enclosure, leading to release of helium into the insulation vacuum of the cryostat.
The spring-loaded relief discs on the vacuum enclosure opened when the pressure exceeded atmospheric, thus relieving the helium to the tunnel. They were however unable to contain the pressure rise […] thus resulting in large pressure forces acting on the vacuum barriers separating neighboring subsectors, which most probably damaged them. These forces displaced dipoles in the subsectors affected from their cold internal supports, and knocked the Short Straight Section cryostats housing the quadrupoles and vacuum barriers from their external support jacks at positions Q23, Q27 and Q31, in some locations breaking their anchors in the concrete floor of the tunnel. The displacement of the Short Straight Section cryostats also damaged the “jumper” connections to the cryogenic distribution line, but without rupture of the transverse vacuum barriers equipping these jumper connections, so that the insulation vacuum in the cryogenic line did not degrade.
Phew. That was a slide-ful. (I still think the image above tells the story more descriptively.) Aymar goes on to say that no more than 5 quadrupole and 24 dipole magnets need to be repaired, but up to 57 magnets have to be removed to be cleaned.
Aymar says that the experiments should be ready next spring.
There was no mention of the “Plan A/Plan B” from Jorg Wenninger’s report a few days earlier, in which he outlined two paths for LHC running in 2009:
- (A) Low-intensity, low-energy running in late 2009 with an upgrade of the pressure relief system during the 2009-10 Winter shutdown
- (B) Complete upgrade of pressure relief system, no beam until 2010.
Both reports mention the ‘busbar,’ which seems to have something to do with the magnet interconnections (whatever that means). Wenninger suggests that during the S34 incident, there was an electric arc (whatever that means) due to the rupture of an interconnect. I don’t understand the significance of this, but he says that,
Unfortunately this is difficult to prove, since the whole dipole interconnect was ‘vaporised’ during the event!
These all sound like neat lunchtime talking-points next time I get to chat with experimentalists. Does anyone have any thoughts?