High energy density (HED) science is all about extremes. Imagine the temperature and pressure found in stars, at the centers of giant planets, and associated with nuclear reactions.
Materials under these conditions exhibit properties not observed in our everyday environment: nonmetals become metals, crystals take on surprisingly complex structures, and normal mass can be converted into energy.
HED science is a wide-ranging, rapidly evolving research frontier that focuses on matter where external forces, like pressure and temperature, begin to overwhelm the chemical forces of ordinary matter on Earth. Experts from astrophysics, condensed-matter and plasma physics, materials chemistry, high-pressure research, and planetary science join together to address topics ranging from security to sustainability.
Hot Matter Matter at high enough temperatures to sustain nuclear fusion.
Warm Matter Matter typically at “classical” conditions. Warm Dense Matter is the subregime of this type where methods used in plasma or condensed matter physics may not be reliable in this regime.
Quantum Matter Matter exhibiting quantum behavior, often characterized by the atom or electron wavelengths exceeding the separation between atoms.
Cold Matter Matter that is not ionized by temperature. Typically solids or fluids. Often have quantum properties.
Spectacular breakthroughs in fundamental science and technology, experimental and theoretical capabilities, and potential impacts to society motivate today’s work in the field.
In December 2022, the National Ignition Facility at Lawrence Livermore National Laboratory used the world's highest energy laser system to crush tiny pellets containing a form of hydrogen fuel to enormous temperature and pressure.
Accessing deep, inner electrons
Chemistry on Earth at ambient conditions is usually defined by the bonding of an atom’s outer electrons. However, the intense temperatures and pressures involved in HED science allows interactions with inner electrons (as depicted above showing unusual electron transitions between ions due to extreme conditions). This unexplored realm known as “kilovolt chemistry” is now accessible to theoretical and experimental study in HED science.
HED science involves uncommon conditions, such as extremely high pressures. At high enough pressures, common materials like the metal sodium—normally opaque to visible light at ambient conditions—can become transparent. Visible light can be seen passing through the transparent metal (shown above) and even reflecting back at the camera.
The next decade of HED science will be instrumental to growing our understanding and in the development of new technologies and processes.
HED science can develop the technologies and processes required for controlling nuclear fusion in the laboratory, taking current experiments that are documenting the onset of nuclear ignition to the point of fully exploiting the output of nuclear reactions. More effective means of achieving fusion will offer a unique platform for characterizing new states of matter through experiment, simulation, and theory.
Due to the extreme nature of the HED science, developments in the field are dependent on cutting-edge scientific facilities.
To strengthen its global leadership in high energy density (HED) science and address future national needs, the National Nuclear Security Administration (NNSA) should exploit and enhance the capabilities of its flagship HED facilities (e.g., the National Ignition Facility, Z Pulsed Power Facility, and Omega Laser Facility) by establishing plans over the next 5 years for
VIEW RELATED RECOMMENDATIONS
Beyond a focus on facilities, much can be done to advance HED science with appropriate focus. Below is a list of topics and associated recommendations the committee believes will help advance the field and overcome current challenges.
Benchmarking, in general, refers to establishing an independent standard that can be relied on to characterize the accuracy of any given model or experiment. HED science can greatly benefit from a dedicated effort to establish combined experimental and theoretical standards and benchmarks in both measurement and computation, along with robust verification and validation procedures.
A major challenge has been that input energy to start nuclear fusion is required to be higher than the energy keeping apart the positively charged hydrogen ions that make up fusion fuel. To make things more difficult, hot plasmas undergoing fusion—or “burning plasmas”—are hard to confine, like steam in a kettle. Recent progress (noted earlier under “Key Discoveries and Accomplishments”) makes the next decade a crucial time for improved understanding, control, and use of burning plasmas made from Inertial Confinement Fusion (ICF).
There is an opportunity for the NNSA to develop partnerships with private industry in order to strengthen and broaden the HED science workforce. Doing so will also develop new technologies that are mutually beneficial for both fundamental-science and industrial applications. Without greater partnership, leadership, and strategic planning with industry, the NNSA is risking increased competition for the top-caliber workforce and decreased capability to meet the technology needs for the future.
In order to ensure a robust HED science workforce, appropriate investment and support is needed from an early stage to ensure diversity and build a broad and engaged community.
An overarching challenge that NNSA faces is retention and recruitment of the expert workforce that carries out HED science. The exploding influence of the private sector, developments in other nations, and challenges to the workplace climate put at risk the approach and laboratories in HED research that have served the nation well since World War II.
Therefore, it is of crucial importance to broaden the number of sources for HED science candidates, as well as the number of career pathways one might take into HED science. The committee makes this the focus of its second leading recommendation:
To enhance career pathways for high energy density science research at NNSA facilities, the NNSA should
VIEW RELATED RECOMMENDATIONS
Below is a list of recommendations the committee believes will help address current issues faced by the HEDS workforce.
HED science is a collaborative field in nature and maintaining strong national and international collaborations facilitates retaining and recruiting a global workforce.
While the United States is a leader in traditional HED science with high energy lasers and pulsed power Z-pinches, changes are occurring that could alter that situation. Materials science under extreme pressure can now also be studied at smaller facilities, and the current and planned high-intensity lasers in Europe and Asia far exceed the power of those in the U.S.
International collaborations strengthen collaborations within the HED science workforce, and thus enhance the utilization of HED science facilities. Increased usage of these facilities remotely (i.e., with remote access) would also enhance their utilization by both domestic and international users.
The nation will also need to find ways to attract domestic students and retain international students in relevant domains of science and technology, and to work out solutions allowing those students trained in the U.S. to remain in the country.
VIEW RELATED RECOMMENDATIONS
The National Defense Authorization Act for Fiscal Year 2020, Congress directed the National Nuclear Security Administration to sponsor this study, specifying an emphasis on basic science.
HED science is a wide-ranging, rapidly evolving research frontier seeking to understand and control material at extreme conditions. (For example, the domain of HED science is defined by pressures exceeding one million times atmospheric pressure.) Materials under these conditions exhibit properties not observed in our everyday environment: nonmetals become metals, crystals take on surprisingly complex structures, and normal mass can be converted into energy. Experts from several other fields—such as astrophysics, condensed-matter and plasma physics, materials chemistry, high-pressure research, and planetary science—join together to address topics ranging from security to sustainability.
Selection of appropriate committee members is essential for the success of a study. One of the strengths of the National Academies is the tradition of bringing together recognized experts across many disciplines and facilitating collaboration. Careful steps are taken to convene diverse committees that have an appropriate range of expertise and represent a balance of perspectives. Stakeholders will have the opportunity to nominate potential committee members at the beginning of the study, and all nominations are carefully considered. Provisional committee members are screened for possible conflicts of interest. All committee members serve as individual experts, not as representatives of organizations or interest groups.
The final report of the study will be directed at policy makers, industry, NGOs, the public, and the scientific community. These groups, including the U.S. Congress and the executive branch, will be briefed on the key messages of the report. The committee and Academies staff will also work to communicate the report’s findings to stakeholders and non-specialist audiences.
Key Discoveries (Fusion): LLNL; Key Discoveries (Chemistry): S.X. Hu, V.V. Karasiev, V. Recoules, P.M. Nilson, N. Brouwer, and M. Torrent, 2020, “Interspecies Radiative Transition in Warm and Superdense Plasma Mixtures,” Nature Communications 11:1989; CC BY 4.0.; Key Discoveries (Un-Metallization): Reprinted by permission from Springer Nature: Y. Ma, M. Eremets, A. Oganov, et al., 2009, “Transparent Dense Sodium,” Nature 458:182-185; © 2009; Astrophysical Jet: NASA/CXC/SAO (x-ray image), NASA/STScI (visible light image), NSF/NRAO/AUI/VLA (radio waves image); Science Investments: LLNL