Echoes drift up from the huge white cavern far below the surface, and a flurry of activity can be seen 100m down at the bottom of the wide circular shaft.
Beneath tonnes of glacial deposits and then solid rock, a narrow tunnel stretches away from the cavern as far as the eye can see, looping for tens of kilometres under the Geneva suburbs and Jura Mountains. Back at ground level is the overbearing red bulk of a machine the
size of a five-storey building. It is one of a series of giant detectors to spot the tiniest of particles and will soon be lowered into the cave where it will connect to a chain of thousands of superconducting magnets.
This is the Large Hadron Collider — a massive £1.3bn experiment at particle physics hub CERN in Geneva that will help us better understand our universe by accelerating sub-atomic particles around a 27km tube and smashing them together at energies not seen since the
Big Bang. Among other weird effects like creating mini-black holes, it should prove the existence of the elusive Higgs Boson, the so-called ‘God particle’ that physicists think interacts with all matter to give it mass. It is no hyperbole to suggest that we will see some of the century’s biggest scientific discoveries when the experiments begin in 2007.
It is science at its most way-out and abstract, but behind the complex particle physics experiment is the biggest international collaboration of engineers and technicians ever formed. Nearl 40 countries have come together in an unprecedented collaboration — arguably no single engineering project in history has involved such a diverse mix of nations and industry. The colossal instruments of the LHC are garnered with flags and names indicating each component’s provenance, and next to the Europeans there are some unlikely bedfellows: Iran and the US, Taiwan and China, India and Pakistan.
A pot-pourri of countries has put aside strained political relations and jealousies to improve mankind’s collective knowledge, according to CERN’s Prof Jim Virdee, co-ordinating work on one of the main detectors. ‘It’s fostering relationships instead of conflict between countries,’ he said. ‘These experiments are so large that the future of our field depends on the collaboration. We almost have an obligation to allow people to work on this if they want to.’ The collider and vast detectors are the most complicated piece of apparatus that science has ever seen, he said.
Nations have realised that international partnerships are the only way to make further discoveries with ambitious research projects like this. The US experienced the folly of going it alone in the 1990s, when after spending $2bn (£1bn) digging the early stages of a tunnel for its Superconducting Super Collider, Congress pulled funding as costs spiralled out of control. It is probably the world’s most expensive empty hole. So as countries squabble over their roles in future projects like fusion experiment ITER, important lessons can be learnt by looking to the work going on in Geneva.
The Engineer was granted rare access inside the LHC before it fires up in two years’ time and saw how a fertile collaboration of the world’s industry and researchers has overcome a series of engineering challenges that will lead to groundbreaking discoveries and fresh technology.
The Large Hadron Collider will accelerate sub-atomic particles around a 27km tube and smash them together at energies not seen since the Big Bang.
In a key milestone for the project, the first of the 1,232 superconducting magnets to guide the huge energy beams along the LHC tunnel was installed earlier this month. But this is the easy part: when the machine fires up, the full 27km length of the accelerator will need to be held at just two degrees above absolute zero if the beams are to reach the enormous energies needed. While normal superconducting magnets operate at six tesla, the LHC needs to operate at magnetic fields of 9T. But the cheaper superconductor chosen to achieve this only works at a chilly 1.9 kelvin.
The tunnel will therefore be one of the coldest places in the universe, according to Dr Lyn Evans, LHC’s UK project leader, and it takes an esoteric substance called superfluid helium to reach that very low temperature. ‘Superfluid helium is a very interesting engineering material if you can handle it. It can take heat out of the magnets very efficiently,’ he said. ‘It’s a spectacular effect. Suddenly the thermal conductivity becomes huge. The temperature goes down like a stone because the heat is going out so fast.’ Cryogenic plants will pump the material through the magnets every 3.3km on the ring.
One hundred tonnes of superfluid helium is difficult to store, however, and the team has yet to decide on a way of keeping the material when the LHC is dormant. The material also has zero viscosity, meaning it could flow through the smallest of holes in a ‘superleak’. So one major challenge was to ensure that there were no weaknesses in the cryogenic system.
The team faced significant problems last year when a plastic component showed cracks, leading to a major refit which cost six months. ‘We’ll never know what would have happened if we hadn’t found the component. If we’d switched it on it may well have had no effect, but we don’t know that for sure,’ said Evans.
The magnets themselves have also posed engineering challenges. The narrow tunnel, which previously hosted a less-powerful particle collider (called the Large Electron Positron (LEP), dictated a strict design. Two separate parallel tubes had to be incorporated into one unit to make it fit in the tunnel and also keep costs down. Dual vertical dipole fields carry the beam in opposite directions, and extra steering magnets are needed to guide the beam because of this.
The main magnets are strong enough to blow the whole structure apart without careful construction. ‘The mechanical forces when the magnet is at full power are huge. The coils are trying to push outwards at 500 tonnes — that’s one jumbo jet— per metre,’ said Evans. The superconducting wires — copper-coated filaments of niobium-titanium alloy called Rutherford cable, invented in the UK — can also shift disastrously under very strong fields, he said. ‘They only have to move microns and they will generate heat, which will take the superconductor above its transition point and the magnet will quench.’ This refers to a loss of superconductivity of the current carrying coils.
A radio frequency system will accelerate the beam through the magnetsfrom one point in the ring. ‘Every time the beam goes around it gets a kick by RF waves,’ said Evans. ‘It’s a tricky business because as the beam energy increases, the magnetic field has to rise synchronously to keep the beam in the middle of the vacuum chamber.’
The beam energy is equivalent to 80kg of TNT, so at the end of experiments or in emergencies it is fed down a 700m-long exit tunnel and spread over an absorber block.
At very high energy the beams can emit problematic synchrotron light, which can desorb molecules from the liner and produce an ‘outgassing’ effect that can hamper the proton beam’s path in the vacuum. Engineers designed a perforated inner tube in the chamber to prevent this. ‘Gas molecules come off and go through the perforations and stick on the cold surface outside. It’s like a distributed pumping system,’ said Evans.
Now all the key design problems have been solved, the pressure is on to ensure the LHC is in place and working reliably for 2007 — if just one component fails, the whole project could be delayed. As Evans acknowledges, installing 6,000 magnets, 7,000km of superconducting cable and a cryogenic system capable of cooling 50,000 tonnes of material is clearly no simple task.
Behind the congeniality among researchers and engineers at CERN is a growing sense of competition. The two main detector teams will go head to head in an attempt to make the most exciting discoveries first, and both have to make sure that their devices are up and running in 2007, otherwise they risk squandering 15 years of development time — and losing the glory.
As parts arrive from companies and universities all over the world, engineers on both sides are racing to install the detectors in huge underground caverns at separate points of the 27km ring. The beams will collide inside the instruments, which look like cylindrical onions with several detector layers, and researchers will pick through the resulting debris of smashed particles to test their theories.
The group behind the Compact Muon Solenoid (CMS) detector is building its instrument on the surface, after which it will be lowered in 15 slices down a 100m shaft to the cavern. The other main team, making the ATLAS detector (abbreviated from A Toroidal LHC ApparatuS), is building its device straight into another cavern further round the ring that is big enough to hold Canterbury Cathedral. Both instruments need a magnetic field strong enough to bend the paths of the charged particles, but the teams have chosen different routes to achieve that. The CMS team went for a cylindrical solenoid magnet — the largest magnet in the world — whereas the ATLAS team chose a riskier toroidal magnet that looks like radiating stretched doughnuts.
Mark Hatch, ATLAS technical co-ordinator, said toroidal magnets have never been built on this scale before. ‘We don’t know fully whether the toroidal magnet will work until it is assembled,’ he said. ‘There are eight together in the structure. It’s our biggest challenge to put them in and all working.’
Once completed, the caverns will be shut off because of high radiation levels, so the teams know they have to get it right now. A key problem has been making the electronics inside the detectors radiation-hardened. The CMS team tweaked the design of IBM’s mass-produced quarter-micron chips and found they were more resistant to radiation than the expensive technology originally planned. Prof Virdee, who is heading the international collaboration on CMS, said that CERN’s specific demands throughout the LHC design have yielded benefits for the manufacturers involved.
We’re trying to push companies so hopefully they’re learning a lot,’ he said. 'Industry is happy to work with us. It gets a lot of intellectual know-how at little cost. Companies listen to us and then apply what they hear to their own problems.’
International involvement has also allowed smaller countries with less expertise to work under the umbrella of experienced nations, said Virdee. The CMS detector team illustrates just how diverse the whole LHC collaboration has become, with 36 nations and 159 institutions involved. The main superconducting magnet was joint-funded by all partners including Japan, Europe and the US. But some sections like the crystals in the calorimeters to measure particle energy came from Russia and China, while many other parts came from even further afield, be it Pakistan, Bulgaria, Iran or even Uzbekistan.
In fact the CMS team has already won the race for the most unusual component: the brass in one Belarus-built section was melted down from decommissioned Russian Navy ordnance shells
Particle physics experiments at CERN have already generated many potential technology transfers to everyday life such as medical imaging tools, but perhaps the most useful application emerging from Geneva is the LHC Computing Grid.
Researchers will pioneer one of the world’s biggest computer grids to process the flood of data produced by each collision, as a single computer would not be able to cope with so much information. The physicists hope to harness the collective processing power of institutions worldwide, and it was announced last week that 100 sites in 31 countries have now signed up, including the Rutherford Appleton laboratory here in the UK and Fermilab in the US.
Grid computing has been predicted to grow in a similar way to the world wide web, which also originated at CERN, and could lead to a variety of applications from managing an electricity power grid to allowing companies to buy processing power only when needed.
As the LHC readies to power up in 2007, plans are already underway to build a more powerful £3bn atom smasher called the International Linear Collider, which would accelerate the particles down two 15km straight pipes. The final location has yet to be decided but the favourites are the US, Japan or Germany.
In the longer term researchers at CERN are studying the possibility of building an even bigger linear collider in Geneva, and a team at Fermilab in the US are investigating the feasibility of building a VLHC (or Very Large Hadron Collider) which would need to be housed in a tunnel 200km long.
Progress is slow in the early stages of large international science projects like these — and often acrimonious, as seen in the recent disputes over where the fusion reactor experiment ITER should be built. But as the work going on beneath the Geneva suburbs has shown, a collective endeavour of the world’s engineers and researchers is the only way to make the big discoveries that will bear the fruits of