CERN tests LHC computing grid

By Leon Engelbrecht, ITWeb senior writer

Johannesburg, 20 Mar 2008

CERN, the European organisation for nuclear research, is conducting final tests on the Large Hadron Collider (LHC) computing grid.

The testing is being undertaken as the facility readies to switch on the LHC for a series of physics experiments that could change humanity's understanding of the atom, as well as the vast reaches of space.

The LHC is a large particle collider, buried under the Franco-Swiss border, just outside Geneva, that generates charged sub-atoms to power a number of experiments. These are expected to generate petabytes of data that will be distributed worldwide for processing, including to SA.

"Final tests are under way to show that [the computing grid] can sustain the expected data from all four experiments at once, and we expect to make a major press announcement about this in June, once the tests are completed," says CERN spokesman Francois Grey.

The Wikipedia notes that, in April 2005, a trial successfully streamed 600MB per second to seven different sites across the world. But if all the data generated by the various LHC experiments is to be analysed, "then scientists must achieve 1 800MB per second before 2008," the online encyclopaedia notes.

The physical construction of the LHC ended in ceremony last month, with the lowering into the accelerator cavern of the last large detector element for the ATLAS (A Toroidal LHC ApparatuS) experiment. Assembly of ATLAS commenced in 2003 and that of the LHC in 2005 - after the cavern that now houses it was cleared of an older collider.

Facts and figures

The ATLAS detector is the world's largest general-purpose particle detector at 46m long, 25m high and 25m wide. It weighs 7 000 tonnes and consists of 100 million sensors that measure particles that will be produced in proton-proton collisions once the LHC is switched on.

Known as the "small wheel", this final ATLAS element is itself 9.3m in diameter and weighs 100 tonnes. The "small wheel", of which there are two, are covered with sensitive detectors to identify and measure the momentum of particles that will be created in the proton collisions.

The entire ATLAS muon spectrometer system is equal in area to three football fields and includes 1.2 million independent electronic channels. It has the ability to accurately track particles passing through the magnetic field produced by the LHC's superconducting magnets to the width of a human hair.

"These fragile detectors comprise the largest measuring device ever constructed for high-energy physics," said ATLAS muon project leader George Mikenberg at a ceremony last month to market the lowering of the "small wheel" into the LHC cavern. The "small wheel" has a substantial shielding element and Mikenberg noted this had been constructed in Armenia and Serbia.

What it is all for

Experiments at the LHC will allow physicists to jump ahead on a journey that started with British physicist Sir Isaac Newton and his description of gravity. CERN says gravity is ubiquitous since it acts on mass, "but so far science is unable to explain why particles have the masses they have".

Experiments such as ATLAS may provide the answer. LHC experiments will also probe the mysterious dark matter and energy of the Universe, they will investigate the reason for nature's preference for matter over antimatter, probe matter as it existed close to the beginning of time and look for extra dimensions of space-time.

Another CERN spokesman, James Gillies, adds: "We know about 4% of the universe. The LHC might teach us about what the remaining 96% of the universe is made of..."

Once the LHC starts running, it is likely to take a year for "new physics" to emerge, he says. Useful science is expected to continue unfolding for up to 20 years.

Before the LHC can be started up, some 38 000 tonnes of equipment must be cooled to minus 271^0C for the magnets to operate in a superconducting state. This is to be done using many tonnes of liquid nitrogen and liquid helium.

"That is actually colder than outer space," says Gillies, making the interior of the LHC the coldest place in the known universe.