Degree matter mimics stars

The experimental set-up at LCLS used by the team. Photo: Oxford University

Extreme conditions of temperature and pressure found in stars have been recreated on Earth using the world's brightest X-ray source.

An international team, led by Oxford University scientists, studied how solid matter responded to X-ray laser pulses produced by the Linac Coherent Light Source (LCLS) based in Stanford, California. The team focused the X-rays onto a spot 30 times smaller than the width of a human hair, heating a metal foil to two million degrees Celsius within a fraction of a trillionth of a second.

They found that the metal was heated to high temperatures so quickly that the atoms hardly had time to move and the thin foil did not get the chance to expand and ‘blow up’: producing in a laboratory the kind of extreme conditions that, within our solar system, can only be found inside the Sun.

The researchers report their results this week in Nature.

‘Making hot, dense, matter is important scientifically if we are to understand the sort of conditions that exist inside stars and at the centre of giant planets, within our own solar system and beyond,’ said Sam Vinko of Oxford University's Department of Physics, lead author of the paper. ‘The LCLS X-ray laser is a truly remarkable machine and the sort of hot plasma (an ionized gas containing free electrons and positive ions) we created and observed has implications for many other fields of science LCLS is being used to study; for instance materials science and biological research.’

Vinko is part of a larger research group led by Professor Justin Wark of Oxford University’s Department of Physics. Professor Wark said: ‘We feel extremely privileged to have been given access to the world’s first true hard X-ray laser. The machine will, in our view, be ‘game-changing’ in many areas of science. The 60 hours of machine time we were allocated just over a year ago, when we were the first team to focus down the world’s most intense X-ray source onto solid matter to see how it responded, was the most exciting 60 hours of my scientific career.’

The 2-km long LCLS free-electron laser, based at the SLAC National Accelerator Laboratory, is capable of generating intense bursts of X-ray radiation which are over a billion times brighter than any other X-ray source in the world. The peak power of these pulses can, for an instant, even exceed the power production of a small country, such as Belgium.

The Oxford University team was complemented by researchers from nine other institutions, including Lawrence Berkley National Laboratory, SLAC National Accelerator Laboratory, and Lawrence Livermore National Laboratory.

A report of the research, ‘Creation and diagnosis of solid-density plasma with an X-ray free-electron laser’, is published as an advance online publication (AOP) paper in Nature.