One of the world's most powerful "atom smashers", at the leading edge of scientific discovery for a quarter of a century, is about to shut down.

The Tevatron facility near Chicago will fire its last particle beams on Friday after federal funding ran out.

Housed in a 6km-long circular tunnel under the Illinois prairie, the Tevatron leaves behind a rich scientific legacy.

This includes finding nature's heaviest elementary particle: the top quark.

Since 1985, engineers have been accelerating bunches of proton and antiproton particles around the Tevatron's main ring at close to the speed of light, then smashing them together in a bid to unlock the secrets of the Universe.

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TEVATRON TIMELINE


1983 - Tevatron switched on
1985 - Collides its first proton-antiproton beams
1995 - Discovers the top quark particle
1996 - Detects simplest form of antimatter atom
1998 - Discovers last undetected meson particle
2000 - First direct evidence for the tau neutrino
2008 - Starts narrowing search area for Higgs
2011 - Shut down after funding runs out
Interactive Timeline (Fermilab)
But the Tevatron has been superseded by the Large Hadron Collider (LHC) - located on the French-Swiss border - which is capable of getting to much higher energies than the US machine.

Shortly after 1400 local time on Friday, the Tevatron's designer Dr Helen Edwards will push a button in the control room that diverts the last beam of particles into a solid metal block, closing the book on an era in American big physics.

The particle accelerator is run by the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, which is now likely to shift its emphasis to projects that - for example - rely on particles at high intensities, rather than high energies.

"People like me, who have been here for many years, are very attached to the Tevatron. The Tevatron has really defined this laboratory over the last 30 years," said Dr Roger Dixon, head of the laboratory's accelerator division, who nevertheless said he was enthusiastic about future projects at Fermilab.

For many, the closure will be a solemn occasion, at a time when US budgets for science are increasingly being squeezed.

"If you ask me whether I'm confident the country can keep doing things, it's hard to read the newspaper everyday and believe it's going to work out, but we have to trust that it will," Dr Dixon explained.