Hamburg  - The most intense X-ray beam of its type in the world was switched on Thursday in a 2,300-metre circular tunnel under the German city of Hamburg, the Desy research institute said.

The new machine, known as a synchrotron, has been remodelled from an earlier particle accelerator at the site and is named Petra III.

Bookings are already being taken from chemists and biologists who need short-wavelength X-ray light to study minuscule material samples and determine the arrangement of their atoms, or check out the atomic structure of protein crystals.

Desy, which is mainly funded by the German government, said the rebuilding work had cost 225 million euros (297 million dollars).

In a previous life, the Petra ring was used to discover an atomic particle called the gluon.

The synchrotron keeps a beam of up to 10 billion positrons - the anti-particles to electrons - going round a circle permanently at almost the speed of light. Desy said the synchrotron was more effective for its job than a similar machine at Grenoble, France.

To ensure that vibrations do not disturb the high-precision measuring equipment, the experiments will be installed on the biggest single slab of concrete in the world, a 300-metre-long block which is insulated from the ground around it.

Test runs with synchrotron radiation are planned this summer and regular user operation by scientists will start next year, Desy said. (dpa)