A view of Atlas. Higgs Boson, extra dimensions, dark matter, look here. Photo by Ellen Wallace

Geneva, Switzerland (GenevaLunch) – The Large Hadron Collider (LHC) at Cern (European Centre for Nuclear Research) will be switched on this weekend 21-22 November after its year-long repairs. The LHC, the world’s most expensive  machine, smashes atoms into each other at very high energies in order to recreate the conditions at the very beginning of the universe. The LHC will start up very slowly at first, probably at no more than 45o GeV, says James Gillies, head of communications. Energy levels will slowly be increased to about 3.5 TeV by mid-January.

GenevaLunch asked Gillies why the LHC, designed to run at 7 TeV, was going to go at only half-steam. He explained that the LHC’s breakdown in September 2008 required a series of careful checks on the machine before it could ramp up to full power.

But even at 3.5 TeV scientists will still be able to conduct new physical research. The maximum power of the repaired LHC right now is 5 TeV, and Gillies says that the choice of only 3.5 TeV puts the LHC at a level where new research can usefully be conducted.

LHC will gear up slowly but surely

At 3.5 TeV the collider’s operation will fulfill two objectives: calibration and research. The machine has to be carefully calibrated in order for its results to make sense. Cern’s scientists will conduct a series of tests on the LHC and compare the results to known particle physics results, so that when they turn their attention to new discoveries they can feel confident that the LHC’s readouts are reliable.

The scientists also need time to get used to the complexity of the machine. There are 100 million detectors, or channels of information, within the 27km long tunnel, capturing information from up to 40 million collisions per second. The detectors have to be carefully checked so that the information running off them onto the centre’s computers is reliable and useful.

The 1,600 massive magnets, supercooled by nitrogen, which make up the LHC are “trained”, or broken in slowly until they reach their maximum capacity.

Cern’s CHF40 million “magnet quench”

Scientists want to be extra careful this time to avoid a repeat of the explosion that resulted in damages that cost more than CHF40 million to repair. The explosion was caused when the energy flowing through the super-cooled, super-conducting series of magnets met resistance at the joints between the magnets. The energy stored in one of the LHC’s sectors is similar to the kinetic energy of a passenger jet at cruising speed. This sudden resistance, known as a “magnet quench”, occurs when part of the super-conductor suddenly becomes normal conducting. It releases a lot of energy, and last September it heated up the super-cooling nitrogen, and caused it to explode.

The repairs include the addition of thousands of new detectors capable of sensing a quench almost before it happens. If it does, the stored energy is safely “dumped” into special resistors.

Energy intensive physics

Cern uses 230 megawatts of electricity with the LHC running. The LHC alone consumes 120 megawatts of electricity, roughly half the consumption of the canton of Geneva. Cern is on the border between France and Switzerland, and it has two substations, one in each country, and contracts with Swiss and French suppliers. In summer, Cern is supplied by relatively cheap electricity from France, the source of which is mostly nuclear. Since the supply of nuclear-sourced electricity is inelastic, because it is impossible to add additional capacity to a nuclear power plant, EDF, the French electricity supplier, reduces electricity to Cern if it needs to, in a hurry, in return for good electricity rates.

• Damage done in explosion: Guardian
• Repairs necessary: Popular Science
• A TeV is a Teraelectronvolt, a measure of energy. The thermal energy at room temperature is about 1/40^th of an electron-volt (eV). Seven TeV is 280,000,000,000,000 times the energy in the room you’re reading this in.

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