Particle physics experiments

Shock-Free Compression Experiments Set New Extreme Pressure Scales


Using the world’s most energetic laser and the world’s most powerful pulsed power plant, an international research team has derived new pressure scales for gold and platinum at 1 teapascal.

To test the Standard Model of particle physics, scientists often collide with particles using gigantic underground rings. Likewise, high-pressure physicists compress materials to ever-increasing pressures to further test condensed matter quantum theory and challenge predictions made using more powerful computers.

Pressures in excess of 1 million atmospheres are capable of dramatically distorting atomic electronic clouds and altering the way atoms are grouped together. This led to new chemical bonds and revealed extraordinary behaviors such as helium rain, the transformation of sodium into a transparent metal, the emergence of superionic water ice, and the transformation of hydrogen into a fluid. metallic.

With new techniques constantly pushing the frontier of high pressure physics, once-inaccessible terapascal pressures (TPa) can now be achieved in the laboratory using static or dynamic compression (1 TPa equals approximately 10 million atmospheres).

However, the precise and precise determination of pressure adds yet another level of complexity to experiments under extreme conditions. Many of these techniques rely on a calibrated pressure standard. Until now, most experiments have relied on extrapolations from low pressure calibration measurements or theoretical models to determine pressure under such extreme conditions.

Scientists at Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories and Hyogo University have turned the game around by performing experiments on the world’s most energetic laser – the National Ignition Facility (NIF) at LLNL in Livermore , California – and the world’s most powerful pulsed laser – power plant – Sandia’s Z Machine in Albuquerque, New Mexico.

Using a new approach, called shock-free or ramping compression, the team determined how gold and platinum compress when compressed to 1 TPa with extremely high precision. Then, they used their data to derive new pressure scales at 1 TPa. The research was published on June 4, 2021 in Science and presented in a special section “Perspectives”.

“The NIF and the Z machine are unique installations. We really pushed their ability to do the most accurate measurement possible, ”said Dayne Fratanduono, LLNL physicist and lead author of the publication. “To perform shock-free compression, we use either multiple laser beams or the pulsed power source to gradually squeeze our sample. But the key is to control very carefully how quickly we increase the pressure on the sample, to avoid forming a shock wave that would ruin the experiment. And you have to keep in mind that the whole experience lasts much less than a millionth of a second.

“The trick is that most materials get stiffer as they are compressed, so all we have to do is guess by how much and then find a machine that will not only provide enough power but also enough power. control to perform the experiment, ”added Marius Millot, LLNL physicist and co-author.

According to Fratanduono, several other areas were essential to achieve the high level of precision: an incredible level of precision in the machining of steps of the order of a micron on the targets; the measurement of these steps; and ultrafast velocimetry measurements that allowed the research team to determine how the sample is compressed.

“It is truly the culmination of decades of technological developments,” said Fratanduono. “It took several years of development to reach this level of maturity in the experiments and combining the individual advantages of NIF and Z, the two best high energy density facilities, was also essential to constrain the material response of gold very tightly. and platinum. . “

The team predicts that these new pressure scales will allow other scientists around the world to easily, but precisely, determine the pressure in their experiments by simply measuring the density of a piece of gold or platinum compressed with their sample. of interest.

“This is a huge step forward because with a much better determination of the pressure in the experiments, we will be able to really test the theoretical predictions and compare the quantum simulations performed with the most powerful computers in the world,” said Fratanduono. “This will provide a solid foundation for future discoveries using static and dynamic compression as we continue to test our understanding of quantum condensed matter theory, an area of ​​active research at the conjunction of condensed matter physics, materials science and quantum chemistry. Because our work will allow more precise measurements of the properties of planetary constituents at the relevant TPa pressures, we also hope to attract the interest of geophysicists, planetologists and astronomers.

The references:

“Establishing gold and platinum standards at 1 teapascal using shock-free compression” by DE Fratanduono, M. Millot, DG Braun, SJ Ali, A. Fernandez-Pañella, CT Seagle, J.-P. Davis, JL Brown, Y. Akahama, RG Kraus, MC Marshall, RF Smith, EF O’Bannon III, JM McNaney and JH Eggert, June 4, 2021, Science.
DOI: 10.1126 / science.abh0364

“Calibration of experiments at atom– crushing pressures ”by Raymond Jeanloz, June 4, 2021, Science.
DOI: 10.1126 / science.abi8015

In addition to Fratanduono and Millot, co-authors include David Braun, Suzanne Ali, Amalia Fernandez-Pañella, Richard Kraus, Michelle Marshall, Raymond Smith, Earl O’Bannon, James McNaney and Jon Eggert of LLNL; Christopher Seagle, Jean-Paul Davis and Justin Brown of Sandia National Laboratories; and Yuichi Akahama from Hyogo University.