New tabletop device that produces high energy X-rays at lower costs

Monday, October 25, 2010

LONDON - Scientists have suggested a new tabletop instrument that would make producing tightly focused beams of high energy X-rays-cheaper and simpler.

Researchers from Imperial College London, the University of Michigan and Instituto Superior Technico Lisbon described a tabletop instrument that produces synchrotron X-rays, whose energy and quality rivals that produced by some of the largest X-ray facilities in the world.

Although high power, high quality X-ray sources are typically very large and very expensive, the researchers have demonstrated that they can replicate much of what these huge machines do, but on a tabletop.

Their micro-scale system uses a tiny jet of helium gas and a high power laser to produce an ultrashort pencil-thin beam of high energy and spatially coherent X-rays.

“We have taken the first steps to making it much easier and cheaper to produce very high energy, high quality X-rays. Extraordinarily, the inherent properties of our relatively simple system generates, in a few millimetres, a high quality X-ray beam that rivals beams produced from synchrotron sources that are hundreds of metres long,” Nature quoted Stefan Kneip, lead author on the study, as saying.

“Although our technique will not now directly compete with the few large X-ray sources around the world, for some applications it will enable important measurements which have not been possible until now,” he said.

The X-rays produced from the new system have an extremely short pulse length.

They also originate from a small point in space; about 1 micron across, which results in a narrow X-ray beam that allows researchers to see fine details in their samples.

These qualities are not readily available from other X-ray sources and so the researchers’ system could increase access to, or create new opportunities in, advanced X-ray imaging.

To create their new X-ray system, the research team shone the very high power laser beam, named Hercules, into a jet of helium gas to create a tiny column of ionised helium plasma.

In this plasma, the laser pulse creates an inner bubble of positively charged helium ions surrounded by a sheath of negatively charged electrons.

Due to this charge separation, the plasma bubble has powerful electric fields that both accelerate some of the electrons in the plasma to form an energetic beam and also make the beam ‘wiggle’.

As the electron beam wiggles it produces a highly collimated co-propagating X-ray beam, which was measured in these experiments.

The acceleration and X-ray production happens over less than a centimetre with the whole tabletop X-ray source housed in a vacuum chamber that is approximately 1 metre on each side.

This miniaturisation leads to a potentially much cheaper source of high quality X-rays. It also results in the unique properties of these short bright flashes of X-rays.

The findings were reported in Nature Physics. (ANI)

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