Looks like the LHC will miss its run this year.
Every once in a while, one of the 1232 superconducting dipole magnets that bend the beam can heat up to above the critical temperature, causing it go from being superconducting to normal conducting. This rise in temperature is usually caused by some small misalignment in the beam, causing a few stray particles to hit a magnet. Once this happens, the current passing through the magnet’s now significant resistance causes it to heat up like crazy – parts of the magnet can be heated up from -271 to 700 deg C in under a second! This is known as quenching, and it comes as no surprise to particle physicists, who have been dealing with it since superconducting magnets where first used in the Tevatron. They’ve come up with effective ways of dumping the heat and dealing with the problem – the LHC has failsafes built in to deal with quenches effectively, and they should normally be back online after a quench in a matter of hours.
However, in this case it seems that the quench was caused due to a faulty electrical connection between two magnets that likely melted at high current, resulting in mechanical failure and a leakage of liquid helium into the tunnel. The sector (number 23) of the ring will have to be warmed up for repairs, and the cooled down after. The process, which would take a few days to fix in a normally conducting machine, will delay the LHC by two months!
This news comes as a bit of a disappointment, as the experimentalists were hoping to use this years run with a lower energy beam to calibrate the detectors. It looks like they’ll now probably have to wait until the LHC runs at full energy in 2009. However, as long as next years run is not delayed, this should hopefully not be a setback to physics.
For more thorough coverage:
The US LHC Blog has very informative coverage
Last december’s issue of symmetry has an excellent fact-filled article on quenching
CERN has put up a press release
CV is a good place to find some thoughtful reporting. John Conway has already posted about the incident.
And you can see the incident and the progress of the warmup for yourself here
The clock is ticking to the imminent startup of the LHC. (that link is now my new home page!)
As usual, the good folks at CV are on the ball.
This is the last of my 5 days at PASCOS, and it’s been an enthralling past week. I feel like I’m at an awesome festival of science – I had a great time, everything was superbly organized, and I got to witness some great science in action! I hope that next year it’s held somewhere that I can visit, because I’m already looking forward to it!
One of the talks that I found most exciting was given by James Wells at CERN, and he spoke about ‘The Fragility of Higgs Boson Predictions for the LHC’. The talk was exceptionally clear and well delivered, it was an great example of how to give an impressive scientific talk! He spoke about how it is an act of human-centric hubris on our part to think that the only particles out there are the kind that make us up (plus their superpartners). Anthropocentric lines of thought have not got us far in the science in the past (he showed us a picture of Copernicus).
In particular, there is no reason to discount the idea of the SM being coupled to a hidden sector that interacts with the Higgs. The particles of this sector would be invisible to our detectors but can be detected by their missing energy. Such an idea seems to be a recurring theme in many of the talks in this conference, and is increasingly becoming an active area of research in phenomenology. His conclusion was that such a hidden sector could easily complicate our lives by making Higgs phenomenology more difficult, and it’s not hard for it to rule out the favored light Higgs altogether! He presented ways for the LHC to find evidence for such a hidden sector.
Nathan Seiberg is no longer working on string theory, and is now working full time on LHC related physics. He considers supersymmetry to be the most conservative possibility for physics to be discovered in the LHC, and also the most concrete. In terms of making predictions, he says that “nothing else comes close”.
He gave an excellent clear talk on ‘Gauge mediation of SUSY breaking’, a topic which is of particular interest for those (like myself) interested in LHC phenomenology.
He summarized on the order of 10,000 papers on SUSY in one slide! The mechanism for supersymmetry breaking consists of coupling a ‘hidden sector’ where supersymmetry is broken, to the minimal supersymmetric standard model (MSSM) via some kind of mediator particles.
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