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news release:
World’s Largest
Superconducting Magnet Switches On
Geneva, 20 November: The largest superconducting magnet ever built has
successfully been powered up to its nominal operating conditions at the first
attempt. Called the Barrel Toroid because of its shape, this magnet provides a
powerful magnetic field for
ATLAS, one of the major particle detectors being prepared to take data at
CERN’s
Large Hadron Collider (LHC), the new particle accelerator scheduled to turn on
in November 2007.
The ATLAS Barrel Toroid consists of eight superconducting coils, each in the
shape of a round-cornered rectangle, 5m wide, 25m long and weighing 100 tonnes,
all aligned to millimetre precision. It will work together with other magnets in
ATLAS to bend the paths of charged particles produced in collisions at the LHC,
enabling important properties to be measured. Unlike most particle detectors,
the ATLAS detector does not need large quantities of metal to contain the field
because the field is contained within a doughnut shape defined by the coils.
This increases the precision of the measurements it can make.
At 46m long, 25m wide and 25m high, ATLAS is the largest volume detector ever
constructed for particle physics. Among the questions ATLAS will focus on are
why particles have mass, what the unknown 96% of the Universe is made of, and
why Nature prefers matter to antimatter. Some 1800 scientists from 165
universities and laboratories representing 35 countries are building the ATLAS
detector and preparing to take data next year.
The ATLAS Barrel Toroid was first cooled down over a six-week period in
July-August to reach –269oC . It was then powered up step-by-step to higher and
higher currents, reaching 21 thousand amps for the first time during the night
of 9 November. This is 500 amps above the current needed to produce the nominal
magnetic field. Afterwards, the current was switched off and the stored magnetic
energy of 1.1 GigaJoules, the equivalent of about 10 000 cars travelling at
70km/h, has now been safely dissipated, raising the cold mass of the magnet to
–218oC.
“We can now say that the ATLAS Barrel Toroid is ready for physics,” said Herman
ten Kate, ATLAS magnet system project leader.
The ATLAS Barrel Toroid is financed by the ATLAS Collaboration and has been
built through close collaboration between the French CEA-DAPNIA laboratory
(originator of the magnet’s design) , Italy’s INFN-LASA laboratory and CERN.
Components have been contributed in-kind by national funding agencies from
industries in France (CEA), Italy, Germany (BMBF), Spain, Sweden, Switzerland,
Russia, and the Joint Institute for Nuclear Research (JINR), an international
organization based near Moscow. The final integration and test of the coils at
CERN, as well as assembly of the toroid in the ATLAS underground cavern, was
done with JINR providing most of the manpower and heavy tooling.
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