Studying Warm Dense Matter on NIF

Category Physics

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The National Ignition Facility has developed a new experimental platform designed to use colliding planar shocks to produce warm dense matter. This platform uses X-ray Thomson scattering and X-ray radiography to measure density, temperature and ionization state. Studying WDM is important for understanding the formation and evolution of the universe and helping to find extraterrestrial life.

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Obtaining x-ray scattering and radiography data in a single NIF shot is another distinctive feature of the CPS platform, said NIF Discovery Science program leader Bruce Remington. "You get density and temperature and ionization state," he said. "You measure almost everything that we care about" without having to rely so much on simulations to supply missing information.

Studying WDM, an exotic state of high-temperature, high-density material that makes up the cores of giant planets and brown dwarf stars, helps scientists gain a better understanding of the nature and evolution of the universe. It can also shed light on the chaotic conditions that can occur in high energy density (HED) and ICF experiments on NIF and other facilities, including studies in support of LLNL’s stockpile stewardship mission.An experimental platform developed at the National Ignition Facility will use colliding planar shocks to produce warm dense matter with uniform conditions and enable high-precision equation of state measurements. The platform uses simultaneous x-ray Thomson scattering and x-ray radiography to measure the density, electron temperature, and ionization state in warm dense matter. The experimental platform is designed to create a large volume of uniform plasma (approximately 700×700×150 cubic microns) at pressures approaching 100 Mbar and minimize the distribution of plasma conditions in the x-ray scattering volume, significantly improving the precision of the measurements. This experimental design of the platform and compare hydrodynamic simulations to x-ray radiography data from initial experiments studying hydrocarbons, producing uniform densities within ±25% of the average probed condition. They show that the platform creates a homogeneous plasma that can be characterized using x-ray Thomson scattering. Thus, the new platform enables accurate measurements of plasma conditions necessary to test models for the equation of state and ionization potential depression in the warm dense matter regime.

WDM accounts for about half of the volume of planets and is considered an important part of astrophysical systems, like stars

Astrophysicists are keen to learn more about WDM because it could help shed light on the dynamics of planetary formation and the search for extraterrestrial life, Remington said. More than 5,000 exoplanets have been discovered, a subset of which are similar to Earth.

"If you have a terrestrial planet, even if it’s bigger than ours," he said, "and you understand the warm dense matter conditions well enough to say, ‘The interior must look like the following,’ then you can predict if it has a magnetic field or not. If you don’t have a magnetic field, you won’t have biology." .

An important research goal of the NIF platform is to allow researchers to measure the equation of state of WDM material to sufficient accuracy to improve models significantly

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