Sep 21 2006
The world’s largest superconducting solenoid magnet has reached full field. Weighing in at over 10,000 tonnes, the CMS experiment’s magnet is built around a 6-metre diameter, 13-metre long superconducting solenoid coil. It generates a field of 4 teslas, some 100,000 times higher than that of the Earth, and stores 2.5 gigajoules of energy, sufficient to melt 18 tonnes of gold.
CMS is one of the experiments preparing to take data at CERN ’s Large Hadron Collider (LHC) particle accelerator, which is scheduled to switch on in November 2007. CMS physicists will address some of nature’s most fundamental questions, such as why particles have mass and what the so-far unexplored 96% of the Universe is made of. Some 2000 scientists from 155 institutes in 36 countries are working together to build the CMS particle detector, which is currently undergoing tests prior to installation in an experimental hall 100 metres underground. These tests are being carried out with a full slice of the CMS detector, including all its subsystems. “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 is a marvel of modern technology. When it was designed in the early 1990s, it was beyond the state-of-the art at the time. What makes it remarkable is not just its high magnetic field, but also the fact that the field is maintained with high uniformity over such a large volume. New techniques have had to be developed, allowing the solenoid coil to be more compact than 1990s technology could have achieved.
CMS magnet construction was approved in 1996, and began in earnest in 1998. By 2002, fabrication of the superconducting wire was complete. Winding the cable to produce the solenoid coil began in 2000 and took five years to achieve. By the end of 2005, the solenoid was ready for testing, and in February this year, it was cooled down to its operating temperature of around -269 degrees Celsius. Following the insertion of particle detectors, testing started at the end of July.
The magnet is a common project to which all of CMS’s 155 institutes have contributed financially. Major innovative and technical contributions have been made by the French Atomic Energy Commission in Saclay (CEA) for the original concept and general engineering, CERN for the project coordination, all ancillaries, and the magnet yoke and assembly, the Swiss Federal Institute of Technology (ETH Zurich) for the development and production of the compound superconductor and organization of major magnet procurement including the barrel yoke, the US Department of Energy's Fermi National Accelerator Laboratory near Chicago for the superconducting wire and field mapping, the Italian National Institute of Nuclear Physics (INFN) in Genoa for the design and execution of the winding operation, the Russian Institute for Theoretical and Experimental Physics (ITEP) in Moscow and the University of Wisconsin for the endcap yoke.