The most powerful laser in the world reveals the secrets of ionization resulting from pressure in stars and nuclear fusion

Scientists at Lawrence Livermore National Laboratory have successfully used the world’s most powerful laser to simulate and study pressure ionization, a process vital to understanding the structure of planets and stars. The research has revealed unexpected properties of highly compressed matter and has important implications for astrophysics and nuclear fusion research.

Scientists have conducted laboratory experiments at Lawrence Livermore National Laboratory (LLNL) that provide new insights into the complex process of pressure-induced ionization in giant planets and stars. Their research was published May 24 in naturereveals the properties of materials and the behavior of matter under extreme pressure, offering important implications for astrophysics and nuclear fusion research.

“If you can recreate the conditions that occur in an astral body, you can actually tell what’s going on inside it,” said collaborator Siegfried Glenzer, director of the High Energy Density Division at the DOE’s SLAC National Accelerator Laboratory. “It’s like putting a thermometer into a star and measuring its temperature and what those conditions do to the atoms within matter. It can teach us new ways to process matter for fusion energy sources.”

The international research team used the world’s largest and most energetic laser, the National Ignition Facility (NIF), to generate the extreme conditions needed for pressure ionization. Using 184 laser beams, the team heated the interior of the cavity, converting the laser energy into X-rays that heat a 2-millimeter-diameter beryllium shell positioned in the center. As the outer surface of the shell rapidly expanded due to heat, the interior accelerated inward, reaching temperatures of about two million Kelvins and pressures of three billion atmospheres, creating a tiny sliver of matter as found in dwarf stars for a few nanoseconds in a lab.

The highly compressible beryllium sample, with up to 30 times its density as the surrounding solid, was investigated using Thomson X-ray scattering to infer its density, temperature and electron structure. The results revealed that after strong heating and pressure, at least three out of every four electrons in beryllium transitioned into conductive states. In addition, the study revealed an unexpectedly weak elastic scattering, indicating low residual electron localization.

The material in the interiors of giant planets and some relatively cool stars is being compressed tightly by the weight of the layers above. At such high pressures, due to high pressure, the proximity of the atomic nuclei leads to interactions between the electronic bonding states of neighboring ions and eventually their complete ionization. While ionization in burning stars is primarily determined by temperature, ionization due to pressure dominates in cooler objects.

Although important for the structure and evolution of celestial bodies, pressure ionization as a pathway for highly ionized matter is poorly understood theoretically. Moreover, the required extreme states of matter are difficult to create and study in the laboratory, said LLNL physicist Tilo Dubner, who led the project.

“By recreating extreme conditions similar to those found inside giant planets and stars, we were able to observe changes in material properties and electron structure that are not captured by current models,” Dubner said. “Our work opens new horizons for studying and modeling the behavior of matter under extreme pressure. Ionization in dense plasma is a key factor because it affects equation of state, thermodynamic properties, and radiation transport through opacity.”

The research also has important implications for self-confinement fusion experiments at NIF, where X-ray absorption and tunability are key factors for optimizing high-performance fusion experiments. A comprehensive understanding of ionization due to pressure and temperature is essential to modeling compressed materials and ultimately to developing an abundant, carbon-free energy source via laser-driven nuclear fusion, Dubner said.

“The unique capabilities of the National Ignition Facility are unparalleled. There is only one place on Earth where we can create, study and monitor the intense compression of planetary cores and stellar interiors in the laboratory, and that’s on the world’s largest laser,” said Bruce Remington, NIF Discovery Science programme. And the most active. leader. “Building on the foundation of previous research at NIF, this work extends the boundaries of laboratory astrophysics.”

Reference: “Observation of the onset of K-shell delocalization due to pressure” by T. Döppner, M. Bethkenhagen, D. Kraus, P. Neumayer, DA Chapman, B. Bachmann, RA Baggott, MP Böhme, L. Divol, and RW Falcone, LB Fletcher, OL Landen, MJ MacDonald, AM Saunders, M. Schörner, PA Sterne, J. Vorberger, BBL Witte, A. Yi, R. Redmer, SH Glenzer and DO Gericke, May 24, 2023, Available here. nature.
DOI: 10.1038/s41586-023-05996-8

Led by Dubner, the LLNL research team included co-authors Benjamin Bachmann, Laurent Devol, Otto Landin, Michael McDonald, Alison Saunders, and Phil Stern.

The pioneering research was the result of an international collaboration to develop Thomson X-ray scattering at NIF as part of the Science Discovery Program at LLNL. Collaborators included scientists from the SLAC National Accelerator Laboratory, University of California Berkeley, University of Rostock (Germany),[{” attribute=””>University of Warwick (U.K.), GSI Helmholtz Center for Heavy Ion Research (Germany), 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.).