The biggest science facility to be built in the UK for 30 years - the Diamond Light Source synchrotron - has opened its doors for business.
The vast machine, which covers the area of five football pitches, generates intense light beams to probe matter down to the molecular and atomic scale.
The South Oxfordshire-based facility will be used by many fields, including medicine and environmental science.
Researchers have now commenced their experiments at its "beamline" stations.
Gerhard Materlik, chief executive of Diamond, said: "The first users possess an extensive knowledge of synchrotron science and bring a range of research projects to Diamond, from cancer research, to advancing data storage techniques, to unravelling the mysteries of the Solar System."
Within the machine, which is sometimes described as a "super microscope", electrons are accelerated into a thin, doughnut-shaped vacuum chamber, which measures 562.6m (1,846ft) in circumference.
As the particles whizz around and around, almost reaching the speed of light, they lose energy in the form of synchrotron light.
This intense light, which falls in the range of x-ray, ultra-violet and infra-red, is then channelled off into beamlines, where it passes through samples of material, probing deep into their fine-structure.
HOW DIAMOND WORKS
Electrons fired into straight accelerator, or linac
Boosted in small synchrotron and injected into storage ring
Magnets in large ring bend and focus electrons accelerated to near light-speeds
Energy lost emerges down beamlines as highly focused light at X-ray wavelengths
On completion of phase one of its construction, Diamond has seven beamlines, each designed to carry out different kinds of experiments.
Professor Chris Binns, a physicist from the University of Leicester and one of the first researchers to use the facility, said: "We are looking at methods for making new high-performance magnetic materials for the future by assembling nanoparticles.
"The problem is, to understand them, we need to understand the magnetic structure at nanometre scales. The beamline we have been using for the last six days has a special microscope that can image magnetic structures at these very small scales."
His work, he said, was key to storing greater amounts of data on ever-shrinking devices.
Other beamlines are dedicated to studying materials under intense pressure; looking at the chemical make-up of complex materials, such as moon rocks and other geological samples; and understanding diverse biological samples.
Professor Dave Stuart, a structural biologist from the University of Oxford, is about to begin using one of the beamlines to investigate the structure of protein molecules found in human cells, to understand the molecular basis of diseases such as cancer.
He told BBC News: "It is wonderful that Diamond has opened in the UK. Over the last two years I have made about 50 trips to the European synchrotron in Grenoble, France.
"It will be a revelation for us to have this here and it is great to be one of the first users.
"It will also affect the science we will do; our samples are sometimes not very stable and often the experiments don't work first time, so if we have to make an aeroplane trip or long drive it can be very difficult."
The team running the facility says on average another four to five new beamlines will added every year until 2011.
The project has cost about £300m, funded by the Central Laboratory of the Research Councils (CCLRC) and the Wellcome Trust.
Dr Mark Walport, director of the Wellcome Trust, said: "This is a monumental occasion and represents the culmination of a huge amount of work by a large number of people."
The Diamond synchrotron will be replacing the Synchrotron Radiation Source (SRS) in Daresbury, Cheshire. The SRS was the world's first dedicated source of synchrotron radiation but is due to close at the end of 2008.
Many countries have their own synchrotrons, and new ones are being built in France, the US, Australia and China.