|
New
Release -- Superconductor Week does not edit or endorse the following
news release:
For the first time the LHC reaches temperatures colder than outer space
Geneva, Switzerland, 10 April 2007: The first sector of
CERN’s
Large Hadron Collider (LHC)
to be cooled down has reached a temperature of 1.9 K (-271°C), colder than deep
outer space! Although just one-eighth of the LHC ring, this sector is the
world’s largest superconducting installation. The entire 27-kilometre LHC ring
needs to be cooled down to this temperature in order for the superconducting
magnets that guide and focus the proton beams to remain in a superconductive
state. Such a state allows the current to flow without resistance, creating a
dense, powerful magnetic field in relatively small magnets. Guiding the two
proton beams as they travel at nearly the speed of light, curving around the
accelerator ring and focusing them at the collision points is no easy task. A
total of 1650 main magnets need to be operated in a superconductive state, which
presents a huge technical challenge. “This is the first major step in the
technical validation of a full-scale portion of the LHC,” explained LHC project
leader, Lyn Evans.
There are three parts to the cool down process, with many tests and intense
checking in between. During the first phase, a sector is cooled down to 80 K,
slightly above the temperature of liquid nitrogen. At this temperature the
material will have seen 90% of its final thermal contraction, a 3 millimetre per
metre shrinkage of the steel structures. Each of the eight sectors is about 3.3
kilometres long, which means shrinkage of 9.9 metres. To deal with this amount
of shrinkage, specific places have been designed to compensate, including
expansion bellows for piping elements and cabling with some slack. Tests are
done to make sure no hardware breaks as the machinery is cooled.
The second phase brings the sector to 4.5 K using enormous refrigerators. Each
sector has its own refrigerator and each of the main magnets is filled with
liquid helium, the coolant of choice for the LHC because it is the only element
to be in a liquid state at such a low temperature.
The final phase requires a sophisticated pumping system to help bring down the
pressure on the boiling Helium and cool the magnets to 1.9 K. To achieve a
pressure of 15 millibars, the system uses both hydrodynamic centrifugal
compressors operating at low temperature and positive-displacement compressors
operating at room temperature. Cooling down to 1.9 K provides greater efficiency
for the superconducting material and for the helium’s cooling capacity. At this
low temperature helium becomes superfluid, flowing with virtually no viscosity
and allowing greater heat transfer capacity.
“It’s exciting because for more than ten years people have been designing,
building and testing separately each part of this sector separately and now we
have a chance to test it all together for the first time,” said Serge Claudet,
head of the Cryogenic Operation Team. For more information and to see regular
updates, see
http://lhc.web.cern.ch/lhc/.
The conditions are now established to allow testing of all magnets in this
sector to their ultimate performance.
[1] CERN, the European Organization for Nuclear Research, is the world's leading
laboratory for particle physics. It has its headquarters in Geneva. At present,
its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark,
Finland, France, Germany, Greece, Hungary, Italy, Netherlands, Norway, Poland,
Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. India,
Israel, Japan, the Russian Federation, the United States of America, Turkey, the
European Commission and UNESCO have Observer status.
Return
to industry news releases |
