TARDIS Experiments Boost NIF Discovery Science and Stockpile Stewardship

On the morning of July 10, a team of researchers completed an experiment on Lawrence Livermore National Laboratory (LLNL)’s National Ignition Facility (NIF) that marked the 200th use of NIF’s workhorse TARDIS (target diffraction in situ) experimental platform.

The experiment kicked off a series of three NIF shots over two days that underscored the value of TARDIS to the NIF Discovery Science program.

TARDIS experiments, the first to include a target and diagnostic on a single, integrated platform, enable a technique known as x-ray diffraction, which determines the crystal structure of solids. The platform has allowed researchers to collect x-ray diffraction patterns to document the atomic structure of a variety of materials laser-compressed to extreme pressures of up to 20 megabars (Mbar), or 20 million Earth atmospheres—more than six times the pressure at Earth’s center.

“The NIF TARDIS platform is unparalleled worldwide,” said LLNL physicist Marius Millot, a frequent user. “It allows us to determine the atomic structure of materials compressed to unprecedented extreme conditions of pressure and temperature that we can only create in a controlled way with NIF’s world-leading laser performance and diagnostics. TARDIS opens up fantastic opportunities for fundamental science and programmatic applications.”

The July 10 experiment, led by Millot along with principal investigator Ivan Oleynik from the University of South Florida, concluded a campaign to investigate the synthesis of novel carbon phases under extreme pressures. The team is now actively working on deciphering the resulting trove of unique experimental data.

A Multiple-Use Platform

NIF conducts about 400 experiments each year, using its 192 high-energy lasers to support the National Nuclear Security Administration’s science-based Stockpile Stewardship Program, including the inertial confinement fusion research that has repeatedly achieved fusion ignition on NIF.

About 8 percent of NIF’s highly competitive shot time is set aside for Discovery Science. The experiments bring together the best scientific minds from both outside and inside the Lab, nationally and internationally, to take advantage of NIF’s unique ability to conduct high-energy laser experiments in nuclear physics, plasma physics, materials science, and astrophysics.

As its 192 high-energy laser beams converge inside its 10-meter-diameter Target Chamber, NIF can simulate conditions found inside stars, giant planets, and thermonuclear reactions. NIF’s basic science experiments probe the makeup and inner workings of stars, planets, plasmas, and materials placed under extreme conditions of pressure, density, and velocity.

"We can reach just about any pressure anywhere in the interior of any planet that we’re aware of," said Discovery Science Program Leader Bruce Remington. "The discovery of exoplanets has greatly amplified interest in this science."

"Discovery Science has played a significant role in the development and visibility of TARDIS experiments since the platform's inception” said LLNL physicist Jon Eggert, who originally designed the TARDIS platform along with LLNL physicist Ray Smith. “In fact,” he said, “the third TARDIS experiment, conducted on September 19, 2013, was performed for Discovery Science just 52 days after the inaugural TARDIS shot.”

Along with its use in Discovery Science campaigns, the TARDIS platform has been employed to study the properties of uranium and plutonium for stockpile stewardship experiments. Eggert noted that of the 202 TARDIS experiments conducted to date, 69 have supported Discovery Science, while nine have been related to inertial confinement fusion and 124 have been supported by the Lab’s Strategic Deterrence directorate. Of those, 52 experiments have collected classified data “that has been highly valuable to the strategic mission of LLNL," Eggert said.

Over the years, TARDIS has been used in Discovery Science campaigns that have produced groundbreaking results, such as how the compression of iron at pressures ranging from five to 10 Mbar can provide insights into the cores and the mass-radius relation of large Earth-like exoplanets; and experimentally determining for the first time if magnesium transforms into a series of exotic “electride” structures under the extremely high pressures generated by NIF’s lasers.

Solid Ice Ramp Compression

The second of the three TARDIS Discovery Science experiments in July investigated the formation of novel phases of ice under extreme pressure and temperature conditions, such as those found in the cores of ice-giant planets and other extreme astrophysical environments.

This campaign, led by LLNL physicist Federica Coppari, explores the fundamental physics of water under these conditions, seeking to validate theoretical predictions of new complex solid ice phases that exist beyond the experimentally explored phase diagram boundaries. The experiments use laser-driven ramp compression to compress and heat liquid water in the 3-10 Mbar range while maintaining temperatures below 2,000 Kelvin — accessing the thermodynamic regime where theoretical calculations predict the formation of new solid ice phases.

NIF ramp-compression experiments apply a carefully tailored laser pulse shape that more “softly” compresses a material without forming a shock. NIF’s ability to tweak pulse-shaping keeps temperatures low enough to preserve the sample’s solid state.

By achieving these specific pressure-temperature conditions, the experiment aimed to synthesize and characterize previously unobserved ice structures, providing direct experimental validation of computational predictions and expanding our knowledge of water’s phase behavior under extreme conditions.

New Challenges and Opportunities

“This Discovery Science campaign leverages previous technical development and research conducted at the OMEGA Laser” at the University of Rochester, Coppari said. That work led to the discovery of an exotic phase of water ice called “superionic.”

“Going from experiments at the OMEGA Laser facility to the NIF presented new challenges and also new opportunities,” Coppari said. “Challenges include how to confine a thin layer of liquid water in an environment that is compatible with the TARDIS platform. The ‘liquid cell’ developed for diffraction experiments at OMEGA cannot directly be used with the TARDIS diagnostic because of the slightly different size and shape of the diagnostic, as well as tolerances and beam- clearance requirements that are different in the two facilities.”

A key advancement in the NIF shots was the use of an improved liquid cell design—a 3D-printed container engineered by the NIF Target Fabrication team—which has demonstrated significantly enhanced robustness and reliability compared to previous versions, enabling more consistent experimental conditions for water containment and compression.

Silicon Dioxide Ramp Compression

The final Discovery Science experiment in July investigated the structural evolution of silicon dioxide (SiO₂) under extreme pressures relevant to planetary science.

This campaign, led by physicist Michelle Marshall of the Laboratory for Laser Energetics at the University of Rochester, addresses fundamental questions about the atomic arrangement of geoscience-relevant materials under the extreme pressures found in the deep interiors of super-Earth planets. Silicon dioxide is one of the most abundant materials in rocky planets, and understanding its behavior under extreme compression is crucial for modeling planetary formation, evolution, and internal structure.

Super-Earth exoplanets, which can be significantly more massive than Earth, subject their constituent materials to pressures far exceeding those in Earth's interior, potentially creating entirely new mineral phases and structures that have never been observed or characterized.

The shot’s primary objective was to use laser-driven ramp compression with simultaneous x-ray diffraction to measure the evolution of the crystalline structure of SiO₂ between 6 and 12 Mbar of pressure. This pressure range encompasses conditions predicted to exist in super-Earth interiors, where theoretical models suggest the formation of novel high-pressure phases of silica that could fundamentally alter our understanding of planetary composition and dynamics. The results will provide critical experimental validation for theoretical predictions and inform models of super-Earth interior structure and evolution.

The shot used ramp compression to gradually compress 60-micron-thick SiO₂ samples to 8 Mbar using 16 NIF beams and a tailored 30-nanosecond laser pulse. The TARDIS platform employed nanosecond-resolution x-ray diffraction to probe the crystal structure of the compressed solid throughout the compression process, enabling real-time observation of structural phase transitions as they occur under these extreme conditions.

“Celebrating the 200th NIF experiment with the TARDIS platform is a good opportunity to recognize the large number of people involved in making these experiments possible,” Millot said, “from the User Office and the Expert Groups to Target Fabrication, Target Diagnostics, NIF Operations, and the Physics teams.”

More Information:

“Imaging velocity interferometer system for any reflector (VISAR) diagnostics for high energy density sciences,” Review of Scientific Instruments, January 18, 2023

“Iron Under Extremes,” Science & Technology Review, December 2022

“A Shot Like No Other,” Science & Technology Review, January/February 2022

“NIF’s TARDIS Featured in Review of Scientific Instruments,” NIF & Photon Science News, June 3, 2020

“X-ray diffraction at the National Ignition Facility,” Review of Scientific Instruments, April 21, 2020

“Gently Compressing Materials to Record Levels,” Science & Technology Review, September 2019

“Searching for an Exotic Phase of Magnesium,” NIF & Photon Science News, March 2018

“Probing the Possibility of Life on ‘Super-Earths,’” NIF & Photon Science News, May 2017

“A Growing Family of Targets for the National Ignition Facility,” Science & Technology Review, January/February 2016

“NIF’s TARDIS Aims to Conquer Time and Space,” NIF & Photon Science News, December 10, 2014

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