CERN tests largest superconducting solenoid magnet

Brussels, 21 Sep 2006

CERN's Compact Muon Solenoid (CMS) - the world's largest superconducting solenoid magnet - has reached full field in testing. The instrument is part of the proton-proton Large Hadron Collider (LHC) project, located in a giant subterranean chamber at Cressy on the Franco-Swiss border. The vast device is not only a remarkable piece of technology and engineering, but also a giant piece of apparatus - tipping the scales at more than 10,000 tonnes. The CMS is essentially a huge detector, and will be used to measure particles generated during high energy collisions from the Large Hadron Collider.

The CMS uses magnetic fields to track subatomic particles and then lead tungstate crystals to create a scintillation, which can be captured using photography.

After collision, the magnet bends the subatomic particles towards millions of silicon detectors to 'spot' subatomic particles in a way analogous to light in a digital camera. Because the subatomic particles are charged, their interaction with the huge magnets in the CMS generates a 'Lorentz force', which can be 'seen' by some 80 million silicon detectors, allowing researchers to deduce the momentum of particles, as well as trajectory.

This is not the end of the detection, as the particles then hit the lead tungstste crystals, inside the 'electromagnetic calorimeter'. The interactions cause a tiny but observable burst of light. Photographs capturing this light burst can then be used to reconstruct the paths of the particles, and so determine their energy.

The CMS will be used to help determine not so much whether certain particles have or do not have any mass, but why, and what the dark matter and dark energy - together making 96 per cent of the known universe - actually are.

So far the CMS has been used to track the high-energy cosmic rays during its testing phase. 'After recording 30 million tracks from cosmic ray particles, said CMS spokesman Michel Della Negra, 'all systems are working very well, and we're looking forward to first collisions in the LHC next year.'

The CMS magnet required specialised input from experts from around Europe, the US and Russia. When initially designed, the CMS was simply beyond human technical capabilities. Simply winding the six metre diameter solenoid coil took five years, but the resulting magnet is exceedingly uniform.

The CMS will have to be cooled to minus 269&#deg;Celsius - only four degrees above absolute zero - when working. The solenoid generates an energy field of four teslas - 100,000 times the Earths own magnetic field, and enough to melt 18 tonnes of gold. The CMS will finish testing and begin service in late 2007.

The CMS project involves 2000 researchers from 155 institutes in 36 countries, making it a blueprint for the European Research Area.

Further information:
http://public.web.cern.ch/Public/Welcome.html

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