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Researchers
working at the U.S. Department of Energy’s (DOE) SLAC National
Accelerator Laboratory have used the world’s most powerful X-ray laser
to create and probe a 2-million-degree piece of matter in a controlled
way for the first time. This feat, reported today in Nature,
takes scientists a significant step forward in understanding the most
extreme matter found in the hearts of stars and giant planets, and could
help experiments aimed at recreating the nuclear fusion process that
powers the sun.
The
experiments were carried out at SLAC’s Linac Coherent Light Source
(LCLS), whose rapid-fire laser pulses are a billion times brighter than
those of any X-ray source before it. Scientists used those pulses to
flash-heat a tiny piece of aluminum foil, creating what is known as “hot
dense matter,” and took the temperature of this solid plasma—about 2
million degrees Celsius. The whole process took less than a trillionth
of a second.
“The
LCLS X-ray laser is a truly remarkable machine,” said Sam Vinko, a
postdoctoral researcher at Oxford University and the paper’s lead
author. “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.”
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.
“The
LCLS, with its ultra-short wavelengths of X-ray laser light, is the
first that can penetrate a dense solid and 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.
“Those
60 hours when we first aimed the LCLS at a solid were the most exciting
60 hours of my entire scientific career,” said Justin Wark, leader of
the Oxford group. “LCLS is really going to revolutionize the field, in
my view.”
The
Oxford-led research team included scientists from U.S. Department of
Energy’s SLAC, Lawrence Berkeley and Lawrence Livermore national
laboratories as well as five other international institutions.
Portions
of this research were carried out on the SXR instrument at the LCLS, a
division of SLAC National Accelerator Laboratory and an Office of
Science user facility operated by Stanford University for the U.S.
Department of Energy (DOE). The SXR instrument and the Resonant Coherent
Imaging endstation are funded by a consortium whose membership includes
the LCLS, Stanford University through the Stanford Institute for
Materials & Energy Sciences, Lawrence Berkeley National Laboratory,
the University of Hamburg and the Center for Free Electron Laser Science
(CFEL). Further support was provided by the UK Engineering and Physical
Sciences Research Council, the DOE Basic Energy Sciences contract, the
DOE Stewardship Science Academic Alliances program contract, and the
German Ministry for Education and Research (BMBF), as well as other
grant funding.
