Instead of taking a late-morning coffee today, Lyn Evans hopes to raise a glass of champagne in triumph. For the past 14 years, the Welsh engineer has been leading tens of thousands of the world’s finest minds in the construction of the biggest machine ever built. And this morning, he will finally get the chance to switch it on.

Starting at around 8am UK time, Dr Evans’s team will begin to fire particles around the 17-mile (27km) ring of the Large Hadron Collider (LHC), the world’s most powerful atom-smasher. By about 11am, he hopes to have a beam circulating, to start a set of experiments that should reveal many of the most elusive mysteries in physics. “Then we can all go for lunch,” he says.

“It will be a great relief, though I will be even more relieved when I see the first collisions at high energy,” Dr Evans told The Times. “People expect me to be a kind of nervous wreck at the moment, but I’m absolutely certain that we’ve put everything we know, our best ideas into this machine.

“There will always be some surprises, but there will be no fundamental surprises. And it’ll be just great to see this thing finally operating after such a long project. You know it’s been 14 years, that’s a lot of your life to invest in such a thing. I’ve been privileged. There’s not many people get a chance of building a thing such as this, and I think there will be a certain sense of pride as well I’m sure.”

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Today’s “first beam” ceremony at the CERN laboratory near Geneva will not directly answer any of the great questions that the LHC has been built to ask. But it will prove that the “Big Bang machine”, which will recreate conditions that last existed in the first trillionth of a second after the dawn of time, actually works.

It is designed to accelerate two streams of protons to within 99.9999991 per cent of the speed of light, so they complete 11,245 17-mile circuits per second. At four points, these beams will collide inside vast detectors, which will look for clues to the nature of the Universe in the sub-atomic debris that is created.

The collisions will not start until later this month, and it will be next year before the particle accelerator is running at full power. The first challenge, which begins today, is to use superconducting magnets to guide the two beams around the ring’s vacuum tubes. Only once the beams are circulating properly can scientists use them to hunt for the so-called “God particle” – the fabled Higgs boson which is believed to give matter its mass, but which has yet to be detected.

“The first big day is always when you get the first beam around,” Professor Evans said. “We’ll be injecting the beam and getting it all around, getting it circulating, many thousands of turns. If we can do more, we will start on the other beam.

“That’ll be the first point at which I can start to breathe a sigh of relief – that there aren’t any obstacles in the vacuum chamber. We’re pretty sure it’s clear, but you can’t know until you get a beam around. It’s the beam in the end that decides.”

Getting the beam to circulate will not be simple, especially as preparations were disrupted by a thunderstorm at the weekend. Bursts of protons will be fired first through one of the LHC’s eight sectors, and if the beam fails to pass through the engineers will then use magnets to correct their aim. The biggest challenge will be to get the beam around three sectors in which it is impossible to

“We will have a stopper in at one eighth of the way round,” Dr Evans said. “Then we’ll remove that and get to one quarter. Then we have nothing and we have to go 10km without anything. That’s when we’re most likely to lose the beam. It’ll might the wall and then dissipate.

“It’s called threading the beam. The vacuum pipe is about the size of a 50p coin. This is the aperture we have to take the beam around for 27km, and bring it around to close in on itself within millimetres. The beam is a few millimetres in diameter. It’s pretty small when compared to the size of a 50p coin, and getting it around without losing it is not trivial.

“I would optimistically think the first step will go rather quickly in 15 minutes, then as we go around this very long section maybe an hour. I would hope to be around by midday (Swiss time) if everything goes fine.

“It relies on the quality of the alignment of the magnets. And when we get through, it’ll be the surveyors who did that for whom I’ll buy the first glass of champagne.”

He likened the task to playing with a buzzer toy, in which you must thread a metal loop along a curvy wire without touching it. “That would be a good analogy, that’s perfect. Of course, we might set the buzzer off a few times as we go around, but then we will know where, we’ll make a correction, and then the next shot will go further. It’s like threading the eye of a needle, you know?”

The first beam will be the culmination of 14 years of work for Dr Evans, 63, who as the LHC project leader has been the man in charge of its planning and construction.

“I’m not a particle physicist, I’m an accelerator builder,” he said. “It’s been enormous, I’ve been the project leader for 14 years, from the conception through the prototype to the construction. And you know, when we started we didn’t even have a prototype that worked of the most crucial elements, which are the superconducting magnets.”

The task of building these magnets, which bend the beams and accelerate them, was a “technological marvel” that took five years. “Each one has been tested at -271 degrees Centigrade, and installed with an exquisite precision, at least I hope it’s going to be exquisite. And now we’re operating the whole thing as an ensemble. Thousands of people have been involved all over the globe, and now it’s coming together and I think we’ve got enormous excitement from all over the globe.”

The LHC is the last accelerator that Dr Evans will build. He will retire in a year and a half, by which time he hopes his machine will be running at full power and transforming science. “It’s a fantastic job that’s been done to build it, an enormous effort of thousands of people in numerous laboratories,” he said. “It’s a triumph as far as I’m concerned, and now we’ve got to get it to work.”

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