2-million-degree matter reveals the structure of stars

Ashley N. Paddock, ashley.paddock@photonics.com

Using the world’s most powerful x-ray laser, scientists have created and probed a 2-million-degree piece of “hot, dense matter” in a controlled way for the first time. This is a significant step forward in understanding the most extreme matter found at the center of giant planets and stars, and it could help experiments aimed at recreating the nuclear fusion process that powers the sun.

Researchers at the SLAC National Accelerator Laboratory conducted experiments using its Linac Coherent Light Source (LCLS), which produces laser pulses 1 billion times brighter than those of any earlier x-ray source. They used its pulses to flash-heat a small piece of aluminum foil, generating solid plasma with a temperature of about 2 million degrees. The whole process took less than one-trillionth of a second.

The interior of a Linac Coherent Light Source SXR experimental chamber, set up for an investigation to create and measure a form of 2-million-degree matter. The central part of the frame contains the holder for the material that will be converted into hot, dense matter. To the left is an extreme-UV spectrometer, and to the right is a small red laser set up for alignment and positioning. Courtesy of University of Oxford/Sam Vinko.

“Making extremely hot, dense matter is important scientifically if we are ultimately to understand the conditions that exist inside stars and at the center of giant planets within our own solar system and beyond,” said Sam Vinko, a postdoctoral researcher at Oxford University and lead author of the paper, which appeared in Nature (doi: 10.1038/nature10746).

Scientists have long been able to create plasma from gases and study it with conventional lasers, said co-author Bob Nagler of SLAC, an LCLS instrument scientist. But no tools were available for doing the same at solid densities that cannot be penetrated by conventional laser beams.

Now, with its ultrashort wavelengths of x-ray laser light, the LCLS can penetrate a dense solid to create a uniform patch of plasma – in this case, a cube one-thousandth of a centimeter on a side – and probe it at the same time, Nagler said.

The resulting measurements, he said, will feed back into theories and computer simulations of how hot, dense matter behaves. This could help scientists analyze and recreate the nuclear fusion process that powers the sun.

The Oxford-led research team included scientists from SLAC (a multiprogram laboratory operated by Stanford University for the US Dept. of Energy’s Office of Science) and from Lawrence Berkeley and Lawrence Livermore national laboratories, as well as from five other international institutions.