Under pressure: Foundations of stellar physics and nuclear fusion
investigated

Date:
May 31, 2023
Source:
University of Warwick
Summary:
Research using the world's most energetic laser has shed light
on the properties of highly compressed matter -- essential to
understanding the structure of giant planets and stars, and to
develop controlled nuclear fusion, a process that could harvest
carbon-free energy.


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FULL STORY ========================================================================== Research using the world's most energetic laser has shed light on the properties of highly compressed matter -- essential to understanding the structure of giant planets and stars, and to develop controlled nuclear
fusion, a process that could harvest carbon-free energy.

Matter in the interior of giant planets and some relatively cool stars
is highly compressed by the weight of the layers above. The extreme
pressures generated are strong enough to charge of atoms and generate
free electrons, in a process known as ionisation. The material properties
of such matter are mostly determined by the degree of ionisation of
the atoms. While ionisation in burning stars is primarily determined
by temperature, pressure-driven ionization dominates in cooler stellar
objects. However, this process is not well understood, and the extreme
states of matter required are very difficult to create in the laboratory limiting the predictive power required to model celestial objects.

Extreme conditions also occur in laser-driven fusion experiments where
hydrogen atoms are fused under high pressures and temperatures to helium,
a heavier element. This process has been heralded as an unlimited,
carbon free energy source -- by using large excess energy generated by
the fusion reactions to generate electricity. Progress in this grand
scientific challenge relies heavily on numerical modelling and the
ionisation balance in high-pressure systems is of central importance.

The only way to study this complex process in the laboratory is
to dynamically compress matter to extreme densities which requires
very large energy inputs in a very short time. In a new experiment
published today in Nature, scientists have done just that using the
largest and most energetic laser in the world, the National Ignition
Facility (NIF). Through their research at the Lawrence Livermore
National Laboratory (LLNL), US, the team provide new insights on the
complex process of pressure-driven ionisation in giant planets and
stars. They investigated the properties and behaviour of matter under
extreme compression, offering important implications for astrophysics
and nuclear fusion research.

The international research team used NIF to generate the extreme
conditions necessary for pressure-driven ionisation. They focused 184
laser beams on a cavity, converting the laser energy into X-rays that
heated a 2mm metal shell placed in the centre. As the outside of the shell rapidly expanded due to the heating, the inside was driven inwards --
reaching temperatures around two million kelvins (1.9m degrees Celsius)
and pressures up to three billion atmospheres -- creating a tiny piece
of matter as found in dwarf stars for just a few nanoseconds.

The highly compressed metal shell (made of beryllium) was then
analysed using X-rays to reveal its density, temperature, and
electron structure. The findings revealed that, following strong
heating and compression, at least three out of four electrons in
beryllium transitioned into conducting states, that is, they can move independent from the nuclear cores of the atoms. Additionally, the study uncovered unexpectedly weak elastic X-ray scattering, indicating reduced localization of the remaining electron, that is a new stage shortly
before all electrons become free and thus revealing the pathways to a
fully ionised state.

LLNL physicist Tilo Do"ppner, who led the project, said: "By recreating
extreme conditions similar to those inside giant planets and stars,
we were able to observe changes in material properties and electron
structure that are not captured by current models. Our work opens new
avenues for studying and modeling the behavior of matter under extreme compression. The ionization in dense plasmas is a key parameter as it
affects the equation of state, thermodynamic properties, and radiation transport through opacity." Associate Professor Dirk Gericke, University
of Warwick, Department of Physics, added: "Having created and diagnosed
these extreme pressures in the laboratory gives an invaluable benchmark
for our theoretical models. Improved predictive capabilities are urgently needed not only for astrophysics but also for further progress toward controlled nuclear fusion which would allow to harvest the energy source
of the stars for humanity." The pioneering research was the result
of an international collaboration to develop x-ray Thomson scattering
at the NIF as part of LLNL's Discovery Science program. Collaborators
included scientists from University of Rostock (Germany), University of
Warwick (U.K.), GSI Helmholtz Center for Heavy Ion Research (Germany), University of California Berkeley, SLAC National Accelerator Laboratory, Helmholtz-Zentrum Dresden-Rossendorf (Germany), University of Lyon
(France), Los Alamos National Laboratory, Imperial College London (U.K.),
and First Light Fusion Ltd. (U.K.).

* RELATED_TOPICS
o Space_&_Time
# Astrophysics # Dark_Matter # Stars
o Matter_&_Energy
# Physics # Nuclear_Energy # Quantum_Physics
o Earth_&_Climate
# Energy_and_the_Environment # Renewable_Energy # Weather
* RELATED_TERMS
o Nuclear_fusion o Stellar_nucleosynthesis o Nucleosynthesis
o Effects_of_nuclear_explosions o Nuclear_fission o Astronomy
o Supernova o Atom

========================================================================== Story Source: Materials provided by University_of_Warwick. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. T. Do"ppner, M. Bethkenhagen, D. Kraus, P. Neumayer, D. A. Chapman,
B.

Bachmann, R. A. Baggott, M. P. Bo"hme, L. Divol, R. W. Falcone,
L. B.

Fletcher, O. L. Landen, M. J. MacDonald, A. M. Saunders,
M. Scho"rner, P.

A. Sterne, J. Vorberger, B. B. L. Witte, A. Yi, R. Redmer,
S. H. Glenzer, D. O. Gericke. Observing the onset of
pressure-driven K-shell delocalization. Nature, 2023; DOI:
10.1038/s41586-023-05996-8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230531150055.htm

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