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Plasma Science: Enabling Technology, Sustainability, Security, and Exploration

A SOCIETY WITH PLASMA SCIENCE

How does plasma science impact today’s society?

• The Internet, computers, cell-phones, jet turbines, medical implants, lighting, solar cells, nanomaterials, advanced batteries, and spacecraft exploring our solar system are all enabled by plasmas.
• Stockpile stewardship, hypersonic flight, space weather, indeed our very national security, relies on our understanding and mastering the complexities of plasmas.
• From magnetic fields generated throughout the universe to the earthly creation of states of matter that otherwise exist only in the center of stars, to exploring whether life can exist on exoplanets—all are enabled by plasma science.

Perhaps our greatest present and future challenge is sustainability. How do we sustainably use the planet’s resources while having ever more prosperous societies? How do we generate the power we need? How do we produce the essential chemicals and materials society needs? Plasma science can be a large part of addressing those challenges. We can envision a future in which plasma science, aggressively stewarded, can use its potential toward achieving a sustainable society by providing

• Nearly unlimited sources of carbon-free electricity;
• Compact particle accelerators for imaging and cancer treatment;

• New materials, green chemical production, new modalities for medicine and agriculture;
• Secure management of our nation’s most strategic weaponry; and
• Fundamental knowledge about the creation of the solar system and worlds beyond.

Enabling this vision of the future through the support of plasma science is the topic of this report.

Plasma is often called the fourth state of matter—gases, liquids, solids, and plasma. Plasmas are ionized gases in which electrons have been removed from neutral atoms to make a collection of negatively charged electrons and positively charged ions, sometimes including negative ions and neutral atoms and molecules. Plasmas are perhaps the most abundant form of matter, accounting for 99.9 percent of the visible universe. Stars are made of plasmas—the Sun is a plasma. Life on Earth may have started from amino acids formed by lightning, a plasma, in the primordial atmosphere. A huge array of technologies that define modern society rely on the chemical activation of atoms and molecules enabled by plasmas, from lighting to the fabrication of microelectronics devices. Plasmas are increasingly being used to benefit human health and well-being, from plasma-based medical devices for wound healing and cancer treatment to the use of plasmas to enhance the growth rate and yield of agriculturally important crops. Plasmas are a source of electromagnetic radiation and, when combined with intense lasers, could act as compact particle accelerators for medical and security imaging, and exploration of the frontiers of high-energy physics. U.S. national security relies on plasmas, from our strategic weapons to the high-energy-density experiments needed to steward our nuclear deterrent. Plasmas are the basis of one of the most ambitious experiments ever attempted: controlled thermonuclear fusion reactions that one day will provide sustainable electricity. Understanding the most fundamental processes in planetary ionospheres and magnetospheres, in interstellar space, and in the matter falling into black holes requires that we first understand the dynamics of plasmas. Spacecraft powered by plasma propulsion are now visiting asteroids and distant planets and may propel astronauts to Mars. The existence of life and habitability on planets and moons in the solar system, and the much larger collection of exoplanets, will in large part be determined by space weather, a plasma phenomenon.

In many ways, plasmas are the technological and scientific success story of the 20th century, with the potential to completely redefine the 21st century. During the 20th century, plasma-based technologies enabled efficient lighting, new materials, welding, internal combustion and jet engines, medical implants, and water purification. Plasmas, through microelectronics fabrication by etching and deposition of materials, are singularly responsible for the information technology revolution. We came to understand the plasma processes that power the stars, how the dynamics of the Sun’s surface affect Earth’s atmosphere, and how dusty plasmas in the laboratory can teach us about the atmospheres of comets.

In the 21st century, translating fundamental research in plasma science and engineering (PSE) into practice will produce controlled fusion, an entirely new paradigm for chemical processing, compact accelerators for medical and security imaging, warning systems for extreme space weather events, agricultural and medical advances, propulsion sending spacecraft and astronauts to the planets, an expansion of our knowledge of extreme states of matter that govern astrophysical phenomena, and experiments that reproduce those conditions for study on Earth.

The potential of fundamental research in PSE to translate to societal benefit is captured in the vision of a future based on renewable electricity where societies are powered by nonpolluting, renewable, and sustainable electricity.¹ The source of that electricity will be largely plasma-enabled, from plasma fusion reactors to solar cells that are produced by plasma materials processing. That electricity will be stored in batteries made with plasma-synthesized materials. The electrical infrastructure will be protected by predictions of space weather events resulting from advanced understanding of the plasma processes connecting the Sun to the surface of Earth. Plasma-based processes will use the potential energy in that electricity to convert waste products to the chemicals upon which society depends, and to recover resources and protect public health by cleaning polluted water. Agriculture and the food cycle will become electricity based, through plasma-based production of fertilizer, enhancement of plant growth, and ensuring food safety. New modalities in health care will become electricity based by taking advantage of plasma-based patient-specific treatments and imaging.

Plasma science and engineering is perhaps the most interdisciplinary of the major fields of physics. With rare exceptions, there are no departments of plasma physics or plasma engineering in U.S. universities. However, some form of plasma science, from fundamental investigations to technological applications, is found in nearly every engineering, life science, and physical science department in colleges and universities. The impact of PSE is due to its interdisciplinary nature since fundamental advances in plasma science can rapidly transition to societal benefit. That impact is felt across U.S. federal agencies and departments. “Plasma” formally appears in the titles of research and technology programs at the the Department of Energy (DOE), the National Science Foundation (NSF), the Department of Defense (DoD), and the National Aeronautics and Space Administration (NASA). However, the technologies and science enabled by plasmas are critical to the the National Institutes of Health (NIH), the Environmental Protection Agency (EPA), the National Institute of Standards and Technology (NIST), the U.S. Department of Agriculture (USDA), the Food and Drug Administration (FDA), the National Security Agency (NSA), and the Department of Homeland Security (DHS), and across the law enforcement agencies. As a result, the impact of the interdisciplinary nature

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¹ S. Mededovic Thagard, M. Sankaran, and M.J. Kushner, 2019, “Science Challenges in Low Temperature Plasma Science and Engineering: Enabling a Future Based on Electricity through Non-Equilibrium Plasma Chemistry,” http://arxiv.org/abs/1911.07076.

of PSE can be found in how plasmas enable current and proposed federal initiatives. Advances in artificial intelligence, machine learning, and quantum-based computing are made possible by plasma materials processing of microelectronics devices. Exploration of the solar system is propelled by plasma-fueled electric engines. The National Nuclear Security Administration’s (NNSA’s) stockpile stewardship is singularly dependent on high-energy-density plasmas.

This decadal study, Plasma 2020, reviews the scientific advances and societal benefits brought by PSE over the past decade; and discusses the scientific challenges that must be addressed to continue and expand upon those societal benefits.

AN INTELLECTUALLY DIVERSE FIELD UNITED BY SCIENCE CHALLENGES

PSE is perhaps one of the most intellectually diverse of the physical sciences. Plasmas exist over more than 10 orders of magnitude in pressure (or energy density) and more than 10 orders of magnitude in spatial scale. At one extreme of spatial scale are the micron-size cathode-spot plasmas that sputter metals to place thin metal films on materials. At the other extreme are the plasma jets that emanate from galaxies and the diffuse plasmas permeating galactic clusters. Plasmas with temperatures rivaling and exceeding that of the center of the Sun are being investigated to sustain fusion in the laboratory, while plasmas gentle enough to touch human tissue are being investigated for biomedical therapies.

In spite of these vastly different spatial scales, pressures, power levels, and applications, common themes and scientific challenges do bring cohesiveness to the field. These common challenges may not apply universally to every subfield and application of PSE, but there is continuity throughout the field. Common scientific challenges that unite the field include:

• Complexity arising from multiple scales and phenomena.
• Controlling synergistic exchanges in plasma-surface interactions.
• Understanding and leveraging how complex phenomena can self-organize into coherent structures.
• Controlling the flow of power through plasmas as means of energy and chemical conversion.
• Developing ever more capable diagnostics, theories, and computations to characterize this complexity.

Even with these common themes, the intellectual diversity and breadth of applications in PSE is enormous. As a result, the subfields of PSE are supported by several federal agencies whose missions align with those subfields. In many ways, this diverse base of relevance and support among federal agencies is a strength and testament to the value of PSE to the nation. In other ways, this highly mission-driven support of

PSE has led to fragmentation of the field, lack of an identifiable home agency, and reduced ability to capitalize on interdisciplinary opportunities. This is particularly the case in those areas of PSE that involve the life sciences and materials.

While acknowledging that there are common scientific challenges, this report is structured around the subfields of PSE. This choice was made to enable federal agencies to optimally receive the findings and recommendations that are most relevant to their missions. At the same time, our high-level recommendations propose actions to mediate that fragmentation of the field, to work toward a more cohesive discipline, to enable more plasma-related collaboration between agencies and between programs in single agencies, and to jointly support initiatives between plasma-focused agencies and those benefiting from plasma science and technology.

This proposed coordination and collaboration has great potential to advance both PSE as a discipline and to advance the missions of agencies. For example, dozens of low-temperature plasma projects at the various NASA Centers span many different areas important to NASA missions, ranging from plasma technologies for waste gasification, remediation and sterilization to devices such as plasma contactors and electric thrusters. These projects tend to be led by engineers and research scientists in different mission areas who are not necessarily plasma specialists, without significant leveraging of expertise from other plasma-focused projects within NASA and without the input of plasma experts in other federal agencies. The outcomes of these efforts would certainly benefit from improved coordination of plasma-focused activities within NASA, and from outreach by NASA to other agencies to provide plasma expertise to the projects. The likely outcome is a better end result and reduction in the time to deployment or flight.

PSE ACCOMPLISHMENTS AND OPPORTUNITIES

The advances in PSE during the past decade have been outstanding in their contributions to scientific knowledge, economic vitality, and national security. As discussed below and in the chapters, impressive progress has been made on several challenges highlighted in Plasma Science: Advancing Knowledge in the National Interest² (hereafter “Plasma 2010 report”). For example, Plasma 2010 cited the inability “to place a satellite at the right place and time to study reconnection.” The 4 satellite Magnetospheric MultiScale mission (MMS), launched in 2015, has enabled just such measurements. Plasma 2010 cited opportunities to use HED to study astrophysical plasmas. Outstanding progress has occurred in laboratory astrophysics, an example being measurements of opacity of iron for studies of stellar

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² National Research Council. 2007. Plasma Science: Advancing Knowledge in the National Interest. Washington, DC: The National Academies Press. https://doi.org/10.17226/11960.

interiors. Plasma 2010 recognized the importance of understanding “multiscale” processes in magnetized plasmas. Impressive insights into these processes have come from simulations and experiments—such as interactions between global magnetohydrodynamics (MHD) instabilities and microturbulence. The opportunities to control plasma-chemical processes were highlighted in the Plasma 2010 report. Major advances have been made in our understanding and use of ns pulsed power to selectively produce reactive species for combustion and chemical conversion. Plasma 2010 cited the need for plasma accelerators, then a nascent field, to be scaled to much longer plasmas and achieve higher energies. This has been realized, with particle bunches close to 10 GeV and sequencing of plasma stages.

Fundamental Plasma Science

Plasma processes occur in nature, laboratories and in industrial settings over a vast range of space and time scales. Despite this great diversity of plasmas, there are unifying themes and processes, such as magnetic reconnection, waves, turbulence, charged particle acceleration, and self-organized structures. The past decade has seen tremendous progress in understanding these underlying, unifying principles. This progress was enabled by controlled and reproducible laboratory experiments; observations of solar and astrophysical processes and missions to space and advanced computer simulations (see Figure 1.1). This progress was also enabled by the development of theories that account for these observations and simulations while explaining regimes not yet accessible by either observations or simulations. Research and education in fundamental plasma science are essential to the entire PSE enterprise. In spite of its great importance, the link between basic plasma science and its many applications is not always appreciated. As a result, support for fundamental plasma research is sometimes deemed of secondary importance to supporting applications. Furthering discovery of fundamental plasma processes is in fact at the root of and essential to applications, and so can be transformational for PSE.

In the following the committee describes an extremely broad range of plasmas, which span an enormous range of plasma densities, temperatures, composition, and magnetic fields, and which are vital to our economic competitiveness and national security. The opportunity, the challenge, for basic plasma science is to make new discoveries and breakthroughs that help unify the field so that advances in one subfield of plasma science benefit another, and that those fundamental advances translate quickly to applications and societal benefit.

High-Energy Density Plasmas and Inertial Confinement Fusion

High-energy density (HED) plasma physics is the study of matter whose energy content exceeds any natural phenomenon on Earth. HED physics often describes the

behavior of space and astrophysical plasmas, and the systems on which the United States relies for national security. HED physics is a field with broad, cross-cutting applications in plasma physics. Understanding the dynamics of HED plasmas addresses many fundamental questions relevant to the broader plasma communities, including space science, material science and quantum materials, nuclear physics, atomic physics, and the generation and transport of hard radiation. Major new facilities have had a great impact on the HED field, helping it flourish over the past decade. These facilities include the LCLS (Linac Coherent Light Source at the SLAC National Accelerator Laboratory), NIF (National Ignition Facility at Lawrence Livermore National Laboratory), Z (the Z-pulsed power machine at Sandia National

Laboratories), and Omega/Omega EP (lasers at the Laboratory for Laser Energetics at the University of Rochester). Experiments on NIF and Z, and supported by other facilities, as demonstrated in Figure 1.2, have produced essential data for stockpile stewardship and national security. Experiments on LCLS and Omega, and supported by the fundamental science programs at NIF and Z, have enabled extraordinary improvements in our understanding of extreme states of matter.

HED physics encompasses inertial confinement fusion (ICF), which is the pursuit of controlled fusion in the laboratory by the compression of matter to the densities found at the center of stars. The ICF community is pursuing several options to achieve fusion, including magneto-inertial confinement, direct laser illumination to compress small pellets of deuterium and tritium (D-T), and indirect laser drive. Ignition of a controlled fusion event in the laboratory is only one of the most visible challenges to HED plasma science. Significant new understanding of the plasma physics required for ignition and data essential to our national security have been gained on NIF even without ignition. While the existing major facilities are expected to continue to produce scientific advances for at least the next decade, planning for the next generation of ICF and HED facilities, both laser- and pulsed-power-driven, is beginning. LCLS II is under construction, and proposals to upgrade the MEC (Matter in Extreme Conditions) facility at SLAC are in progress. If the United States is to continue as the international leader in ICF, the next HED facility intended for ignition must be designed and built.

High-Intensity Laser-Plasma Interactions and Accelerators

Laser and particle-beam control of intense electromagnetic fields that can be sustained and organized in plasmas, far beyond the intensities accessible in ordinary matter, has produced new fields and capabilities in plasma optics and particle acceleration. Combining plasmas with laser and particle beams enables focusing, guiding, and amplification of those beams to unprecedented high intensities, as demonstrated in Figure 1.3. Electrons and positrons can be accelerated in plasmas by resonant plasma wakefields created by these lasers or particle beams with rates of acceleration that can be thousands of times those of conventional accelerators. These plasma-driven accelerators are maturing as a technology and will improve the performance of future High-Energy-particle Physics (HEP) colliders and enable compact, short pulse and high-intensity X-ray sources. The field is on the verge of creating precise low-dose X-ray imaging systems for medical science and national security in the next decade. Ultrafast, high-gradient acceleration has produced ion beams in excess of 100 MeV, with potential applications ranging from medical therapy to probes of HED plasmas. These outcomes will be enabled by high average power, high repetition rate, shaped-pulse laser systems, and a new understanding of their interactions with plasma. The high-intensity electromagnetic fields produced in these systems are

enabling, for the first time, experiments in nonlinear high-field Quantum ElectroDynamics (nQED), the fundamental theory of how light and matter interact. The electric fields being produced in plasmas are approaching the intensities capable of producing matter from the pure electro-magnetic energy of photons.

High intensity laser-plasma interactions (HILPI) and accelerations are strongly linked to other areas of plasma science in the underlying physics, in applications and enabling capabilities. With advances in laser technology, the coupling of lasers and plasma phenomena can be controlled, providing the ability to manipulate and measure states in plasmas with unprecedented accuracy. Understanding and controlling these new processes are pushing the frontiers of exascale computing while requiring new computational algorithms. Continued advances in HILPI supported by new facilities with higher precision and repetition rate have the potential to enable revolutionary new capabilities for society and to support fundamental studies across the field of plasma science.

Space and Astrophysical Plasmas

Space is perhaps the final frontier for plasmas. Space and astrophysical plasmas (SAPs) reach regimes inaccessible to Earthbound laboratory experiments, enabling deep insights into fundamental plasma processes. Some of these fundamental phenomena can be sampled directly by spacecraft, while others can only be studied by spectroscopy, imaging, polarimetry, and other remote sensing techniques. New observations by ground- and space-based instruments continually challenge theorists and computational scientists to decipher the underlying plasma physical processes, while increasingly sophisticated numerical simulations guide the requirements and choice of targets for the next generation of observing platforms and space missions (see Figure 1.4).

The societal benefits of understanding SAPs range from the practical to the inspirational. Over the past decade, research into the origins and effects of space

weather—disturbances throughout the solar system, including Earth, driven by solar eruptions—has brought us ever closer to linking together the complex chain of phenomena that connect our Sun to Earth and beyond. However, we are far from being able to predict space weather events and impacts from start to finish—an ambitious grand challenge for PSE in the next decade. Deeper investigations into the adverse effects of space weather on spacecraft, instruments, and humans in space, as well as our electric power grids and other vulnerable infrastructure on Earth, are essential for both national security and protection of our upcoming robotic and human explorations of the Moon and Mars.

The pioneering detection of gravity waves from a neutron star merger was accompanied by observations of radio, X-ray and visible plasma emission that produced unprecedented insights into the nature of and conditions within this cosmic event. The future of gravitational wave astronomy is inextricably linked to improving our understanding of these exotic events through SAP research. The explosion of discoveries of planets orbiting distant stars (exoplanets) over the past decade has driven a parallel effort to apply our knowledge of plasma-produced space weather in our own solar system to those distant systems, in order to determine whether some exoplanets may be hospitable to life. SAP science therefore plays a key role in the formidable challenge of searching for extraterrestrial life.

SAPs are also fascinating and exotic—from solar flares to active galactic nuclei and black hole accretion disks—giving plasma physics high public visibility and recognition. The importance of the public appeal of SAPs cannot be overstated in motivating the study of science in general and plasma physics in particular. We are now experiencing the retirement of an entire generation of researchers who were inspired to pursue careers in science by our first ventures into space—Explorer, Mariner, Apollo. The images brought to us by the Hubble Space Telescope and the Solar Dynamics Observatory have been equally motivational. We can only expect that continuing and expanding our intellectual reach in SAPs will continue to bring new generations of researchers into science and plasma science in particular.

SAP studies rely heavily on other areas of plasma science, from laboratory experiments on magnetic reconnection and dynamos to atomic and nuclear calculations of opacities, involving HED physics, basic plasma science, particle acceleration physics, computational plasma physics, and radiative hydrodynamics. In turn, SAPs serve as unique windows into a vast range of plasma conditions that can test fundamental theories, motivate novel laboratory experiments, and answer critical questions about particle acceleration, atomic and molecular spectroscopy, and turbulence. Plasma engineering is essential for the design and construction of state-of-the-art instruments on spacecraft, capitalizing on the latest techniques and materials to obtain the spatial and spectral resolution and sensitivity needed to probe ever deeper into SAPs throughout the universe.

Magnetic Confinement Fusion Energy

Nuclear fusion, the process whereby lighter elements fuse into heavier elements and release energy, is the power source of stars. In stars, self-gravity confines plasmas hot and dense enough to produce fusion reactions that are the source of their enormous power. In the laboratory, strong magnetic fields are used in lieu of gravity to confine hot plasmas to produce fusion—magnetic confinement fusion energy (MFE), as demonstrated in Figure 1.5. The societal benefit of this research is clear and enormous—fusion energy can provide a carbon-free source of power for generating electricity, utilizing an abundant and essentially limitless source of fuel. The fusion reaction that most MFE research focuses on uses two isotopes of hydrogen: deuterium and tritium (D-T). Tritium is radioactive but can be produced from lithium. Both deuterium and lithium are abundant in sea water, ensuring there is a sufficient supply of both to use fusion power to provide the energy needs of our planet for many hundreds of thousands of years. (The amount of lithium

that might be used in fusion reactors is a tiny fraction of that currently expended in batteries.) Newly investigated approaches to fusion power could directly produce highly energetic charged particles that can generate electrical current without also producing unwanted neutrons. However, their energy requirements for break-even (generating more energy than expended in making the reactions) are more stringent than for D-T processes.

Progress in fusion research over the past decade has placed MFE on the brink of creating the first burning plasma—a plasma where self-heating from fusion reactions dominates external heating. The goal of the international ITER project is to demonstrate a burning plasma. ITER is under construction and is on schedule to produce first plasma by 2026. A recent National Academies of Sciences, Engineering, and Medicine study (A Strategic Plan for U.S. Burning Plasma Research³) endorsed U.S. participation in ITER, and made the case that knowledge gained from the burning plasma experiments to be conducted on ITER will be essential in realizing commercial fusion power in the United States. The study also recognized that while the ITER design is a low-risk route to a burning plasma, it is also a high-cost route to commercial fusion power. A fusion-based electrical power network using ITER concepts may be simply too expensive. The study recommended that U.S. researchers learn from ITER and apply that learning to the development of a compact fusion pilot power plant that would lead the way to more economical fusion power. To achieve this goal, the field must address challenges at the forefront of PSE and take advantage of advancements in technology (e.g., high-temperature superconducting magnets) that are only now beginning to mature.

Low-Temperature Plasmas

Low-temperature plasmas (LTPs) are partially ionized plasmas that contain electrons energetic enough to collisionally break apart molecules to produce chemically reactive species while also keeping the overall gas temperature near ambient—low enough to contact living tissue. The ability of LTPs to produce chemically reactive environments in gases, on surfaces, and in liquids has already made society-wide transformations in our quality of life—from lighting, materials synthesis, and water purification to enabling the information technology revolution through plasma-enabled fabrication of microelectronics. Plasmas are now being used to remove harmful substances from water, such as perfluoroalkyl carboxylate, that have defied other economic means of remediation. Plasma methods that etch a single layer of atoms from semiconductor devices have enabled the microelectronics

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³ National Academies of Sciences, Engineering, and Medicine, 2019, Final Report of the Committee on a Strategic Plan for U.S. Burning Plasma Research, The National Academies Press, Washington, DC, https://doi.org/10.17226/25331.

industry to make ever smaller and more capable devices. Clinical trials and medical practice are now using plasmas to treat human cancer and promote wound healing. There are many opportunities to advance these applications further, for example, in the anticipated future growth of the integrated circuit industry associated with intelligent machines, autonomous vehicles, and other innovative technologies; protecting the food chain; and addressing pandemic spread of bacteria and viruses through plasma sterilization of materials and tissues.

A strategic opportunity for LTP science is to assist in the electrification of the chemical industry—that is, to drive chemical processing by electrical means facilitated by plasmas. The key enabling science will be controlling the flow of energy through LTPs to produce predictable chemical transformations in gases, on solids, and in liquids (see Figure 1.6). The electrification of the chemical industry is a

grand science and engineering challenge that will enable an economically viable and sustainable future based on renewable electricity.

To achieve this goal, we first need to deepen our understanding of how energy flows through plasmas, in order to produce more selective and efficient chemical transformations. This challenge will require investigations of kinetic and collisional processes, plasma self-organization, transport and plasma-surface interactions under highly nonequilibrium conditions. This new understanding will also augment plasma-aided technologies across the board, thereby benefiting nearly every sector of our society. Examples include controlling plasma-surface interactions at the atomic level to enable the next generation of materials for quantum computing, combating anti-microbial resistance, improving nitrogen fixation and food safety, creating new energy storage technologies, and developing plasma-based propulsion capable of taking humankind to Mars and beyond.

Computational Plasma Science and Engineering

Computations are one of the four main methods of scientific investigation—the others being theoretical, experimental, and observational. However, computations merit special attention due to its growing number of uses, including prediction, diagnosis, and experimental design; the rapidly changing nature of the field, the emergence of artificial intelligence (AI) and machine learning (ML) as computational disciplines, and the opportunities for PSE to leverage computations to address its research challenges. Over the past decade, computational capabilities have increased by many orders of magnitude, in large part by increasing the number of central processing units (CPUs, also called cores) on a single microprocessor chip and by very efficiently linking together many microprocessors. These advances have taken computing from Gigascale (10⁹ floating point operations [flops] per second) to Petascale (10¹⁵ flops/s), making use of tens or hundreds of thousands of CPU and Graphics Processing Unit (GPU) cores. In the next decade, computational capabilities will likely increase another 3 orders of magnitude to reach the Exascale (10¹⁸ flops/s) level. The coming advances will impact every scale of computing. High-performance computing (HPC) will become affordable by small research groups, allowing them to tackle computational analyses several orders of magnitude larger than they could just a few years ago. Breakthroughs in computational capabilities make it possible not only to speed up large simulations, but also to discover new realms in the underlying science.

Specialized computational plasma science and engineering (CPSE) software capable of utilizing the emerging highly concurrent and heterogeneous hardware is under development for specific applications related to the research missions of federal agencies. However, these efforts are not affecting nor are they accessible to all areas of PSE. Indeed, even in areas of agency-supported research, critical soft-

ware is not accessible. For example, PSE does not have the range of software that is available in computational fluid dynamics (CFD) or structural mechanics, which includes both commercial codes and well-supported, more research-oriented, open-source codes. This situation is exacerbated by the increasing array of potential computational devices, including quantum based. The multiscale, multi-physics and multi-applications nature of PSE makes it difficult to develop broadly applicable and accessible codes, a condition that is also exacerbated by segmentation of the field. Concerted effort is therefore needed to better unify computational efforts across the realm of PSE, particularly for implementing new computational approaches, such as AI and ML. To date, AI/ML has shown encouraging results in prediction through pattern recognition, but the possibilities for discovery in PSE using AI/ML, particularly in deriving underlying fundamental parameters, have not yet been fully developed.

Efforts that will enable the development of more broadly applicable, high-performance, and easily implemented software for PSE, with the goal of achieving the robustness of CFD software, clearly deserve support. Major thrusts include education, to develop the next generation of computational PSE practitioners in both software development and scientific discovery, and ensuring that algorithm development continues in both the mathematical and computer sciences. Even within a single computation, PSE phenomena are often multiscale and multiphysics, which makes it difficult to develop efficient algorithms for machines that require extremely high levels of concurrency. Ultimately, developing efficient computational platforms for PSE may require codes that take advantage of heterogeneity (computing across multiple devices of different architectures). This goal becomes even more challenging when it is also necessary to make these codes accessible to the broader community—noncomputer experts should not need to become expert code developers to utilize computations. As new devices become available, such as quantum computers, plasma theorists and computer scientists should jointly develop new algorithms that account for the multi-physics nature of PSE from the start, as opposed to trying to make existing incompatible algorithms fit new architectures.

VALUE OF PSE TO THE NATION

Grand Challenges of Plasma Science and Engineering

Plasma science and engineering holds rich science challenges while being extremely relevant to the economic vitality and security of the nation. Addressing these challenges is part of the continuum of translational research that begins with fundamental scientific understanding and culminates in societal benefit. In most fields of PSE, it is not possible to investigate plasma science challenges in isolation

without focusing on some aspect of the science that is motivated by, and whose findings will translate to, an application.

Underpinning these challenges is the need to develop a predictive understanding of plasmas over a vast range of accessible parameters: from weakly ionized, low temperature atmospheric pressure plasmas, through high-temperature, high-density plasmas, to the extreme plasma conditions that can only be accessed on earth by ultra-intense lasers. Plasmas are complex physical entities that can exist in states that range from weakly coupled to strongly coupled and from nonmagnetized to magnetized states. Plasmas also exhibit a wide variety of self-organized behaviors. These rich scientific topics all motivate the study of plasmas as a distinct scientific discipline. Deep, predictive understanding of plasmas will provide the fundamental knowledge upon which future applications can be built. There should be continued investments in theoretical, computational, and experimental exploration of the fundamental processes of plasmas, not only to advance the science of the discipline, but also as a necessary prelude to applications.

The translational continuum from fundamental science to applications is an outstanding strength of PSE, and is captured in the following PSE Grand Challenges—high-level goals in which mastery of the complexities of plasma science benefits society.

• Understanding the behavior of plasmas under extreme conditions will enable energy conversion by plasmas to be predicted and efficiently controlled, to address the challenges of sustainability, economic competitiveness, and national security, and expand our knowledge of the most fundamental processes in the universe.

  When astrophysical objects undergo disruptive events, such as the violent ejection of material from the Sun that influence space weather or the formation of relativistic jets of material from the black holes at the centers of galaxies, it is the abrupt reconnection of magnetic fields that produces massive plasma outflows and energetic particles. Inside plasma processing reactors, oscillating electric fields heat plasmas that produce new materials. Powerful lasers generate plasmas that compress matter to densities found in the center of stars. Mitigating disruptive events in fusion plasmas will be an important achievement in helping to realize the economical production of fusion power, satisfying the energy demands needed for national security. These are all examples of energy conversion from one form to another that occurs in plasmas. This conversion empowers societies with beneficial applications and is the basis of nearly all astrophysical and space plasma phenomena. Understanding the complexities of these plasma-enabled energy conversions will require new theoretical, computational, and experimental approaches. At one extreme, controlling and predicting these complexities will improve economic competitiveness and national security. At another

• extreme, increasing our knowledge of how our universe operates will enable us to answer fundamental questions about the birth and death of stars while protecting astronauts on their journeys to the planets.

• Mastering the interactions of the world’s most powerful lasers and particle beams with plasmas will enable precision X-ray imaging for medical science, advances in national security, compact particle accelerators, advanced materials and sustainable energy sources, while opening new regimes for high-energy and quantum physics.

  The coupling of intense, high-repetition-rate lasers with plasmas will produce conditions that have never before existed on Earth, and the resulting physical phenomena will expand our knowledge of how matter behaves under intense electric fields. Mastery of that knowledge will enable creation of plasma optics that control light with unprecedented intensities, new compact particle accelerators, conditions accessing nonlinear Quantum ElectroDynamics (nQED) regimes, and opportunities for precision plasma physics and control of particle-wave interactions. With the development of petawatt-class (10¹⁵ W), high-repetition-rate lasers, new technologies will emerge ranging from compact particle accelerators and coherent X-ray imaging to remote detection for national security. These capabilities will provide transformational improvements in resolution and capability for medicine, biology, materials science, and the investigation of fundamental meso- and nanoscale physics. They will extend the reach of high-energy particle physics, and improve our understanding of the fundamental forces that shape the universe.

• Accelerating the development of fusion generated electricity, tapping the virtually unlimited fuel in sea-water, to bring the benefits of carbon-neutral power to society, through economical, deployable, and sustainable fusion systems enabled by advances in experimental and computational plasma physics.

  Perhaps society’s greatest challenge is sustainability—a vision that will in part be enabled by a transition to carbon-free and carbon-neutral sources of electricity. Having such sources provides for a future based on renewable and sustainable electricity. Controlling fusion reactions will provide nearly limitless clean power by converting hydrogen into helium in star-like plasmas on Earth, and holds the promise of providing sustainable electricity. To meet that goal, science and technology challenges must be addressed using the most advanced computational and experimental techniques. The significant investments already made in main-line magnetic fusion energy (MFE) concepts should continue to determine how to create steady state, disruption-free fusion burning plasmas and how to engineer the plasma-facing materials to withstand the intense heat generated by fusion reactor plasmas. At the same time, alternative MFE concepts and innovative technologies must be explored

• and exploited to achieve economical fusion power that will help enable a future based on renewable and sustainable energy. Pursuit of main-line and alternative concepts will require investments in and leveraging of computational and experimental investigations of the fundamental yet complex plasma transport occurring in MFE systems, while partnering internationally to develop the technologies and demonstration systems required to transition fusion power into a practical source of unlimited carbon-free electricity.

• Demonstrating that lasers and pulsed-power devices can produce inertially confined fusion ignition by creating plasma-based extreme states of matter to support stockpile stewardship, further the goal of sustainable energy, and expand our understanding of high-energy-density physics.

  The compression of matter by lasers and pulsed power will produce inertial confinement fusion (ICF), one of the most scientifically and technologically complex projects ever attempted. High-energy-density physics, the basis of ICF, involves extreme states of matter that occur naturally only in astrophysical objects. Understanding these extreme states is absolutely essential to the stewardship of our nuclear stockpile and to understanding supernovae, some of the largest releases of energy in the universe. Advancing that stewardship and understanding cosmic phenomena require the most sophisticated computer simulations ever attempted, advanced pulsed-power and laser facilities, ever more refined diagnostics, and support for new methods to produce and analyze the fundamental experimental and computational data produced by and required by these efforts. The states of matter produced by HED plasmas in pursuit of ICF have never before controllably existed on earth, have never before been directly studied, and have nearly defied being described computationally from first principles.

• Electrification of the chemical industry by controlling the flow of power through low-temperature plasmas will produce predictable chemical transformations in gases, on solids, and in liquids, on scales capable of economically establishing a future based on renewable and sustainable electricity.

  The ability of low-temperature plasmas (LTPs) to induce desired chemical transformations in gases, on surfaces, and in liquids has already been exploited to improve our quality of life—from lighting, materials synthesis and water purification, to enabling the information technology revolution through plasma-based fabrication of microelectronics. An improved ability to control chemical transformations through electricity-driven LTPs has tremendous potential to meet a wide range of current and future societal challenges, including the transformation of the chemical industry from fossil-fuel-driven to electricity-driven. This enhanced capability enabled by LTPs will broadly benefit society by controlling plasma-surface interactions at the atomic level to create the next generation of materials for quantum

• computing, combating anti-microbial resistance, helping to prevent pandemic outbreaks of pathogens through plasma sterilization of materials and tissue, improving agricultural efficiencies and food safety, enabling new energy-storage technologies, and developing plasma-based propulsion capable of taking humankind to Mars and beyond.

• With life, technology, and space travel at risk from damaging solar plasma activity, developing the capability for timely and actionable space-weather observations and predictions will mitigate the potential effects of extreme solar plasma storms on spacecraft, humans, power grids, and infrastructure.

  Living with a star means enjoying its benefits and dealing with its disruptive behavior. The Sun, itself a plasma, steadily emits the solar wind while intermittently producing coronal mass ejections and flares in which intense electromagnetic radiation and massive clouds of magnetized plasma can be directed toward Earth. The high-speed plasmas and energetic particles produced by these extreme eruptions can collide with and potentially damage spacecraft and harm human passengers, and interact with Earth’s magnetic field and atmosphere, producing electrical transients that affect communications, power grids, and infrastructure. Our aspirations to explore the Moon, Mars, and the rest of our solar system are also endangered by adverse space-weather. Although humankind cannot prevent extreme solar plasma eruptions from occurring, being able to predict those events many days in advance can provide the time to take protective measures. Achieving this predictive capability will require substantial advances in our theoretical and computational abilities to model solar eruptions, the acceleration of highly energetic particles, and the interaction of these energetic particles and magnetized plasmas with spacecraft and planetary magnetospheres. Achieving this capability will require a new generation of space-based constellations and ground-based observatories. The Space Weather Operations, Research, and Mitigation (SWORM) subcommittee of the National Science and Technology Council is leading a community-wide conversation on benchmarking of extreme space weather events based on studies, data acquisition, and research. Global efforts to develop metrics for model validation are underway under the aegis of the COSPAR (Committee on Space Research) International Space Weather Action Team program. Continued interagency and international cooperation will be key to meeting the grand challenge of accurate and timely space-weather prediction.

In addressing these Grand Challenges, the humanities and social sciences provide an important lens through which all scientific advances can be viewed.

Because PSE is integral to so many of the technological developments of the last several decades, it is important for the field to be introspective about the impact of those technologies. Furthermore, because of the great potential for areas such as LTPs to impact important societal needs such as water purification and waste cleanup, it will be important to contemplate topics such as social justice in order to ensure that such critical societal needs can benefit all of society.

Critical Support from Other Science Areas

PSE is an intellectually broad and interdisciplinary field that benefits nearly every other field of science and engineering. For example, the biotechnology and material disciplines have made and continue to make advances based on the ability of plasmas to synthesize, modify, and functionalize surfaces and materials. At the same time, PSE is exceedingly dependent on allied disciplines for the fundamental data utilized in analyzing experiments and needed for model development. As PSE focuses on translational research that involves plasma surface interactions, there are critical data needs for how plasma produced activation energy (electrons and ions, chemically active species, UV/VUV radiation) interact with hard solids, liquids and soft and organic materials, including living tissue. These data are best produced by experts in those disciplines, in collaboration with PSE researchers as needed. We often find that generation of fundamental data that is used by other disciplines sometimes falls out of favor with funding agencies as that work is perceived as being a service. It is the committee’s experience that these data needs are often at the leading edge of science challenges in allied disciplines; and so should be strongly and robustly supported.

This need for critical and robust support from allied sciences is nowhere more true than in the synergistic relationship of PSE with atomic, molecular, and optical physics (AMOP) and chemical physics (CP). The most basic processes in PSE involve electron and ion impact on atoms, molecules, and surfaces (solid and liquid) to produce excited states and new functionality, to generate electromagnetic radiation and energetic particles, and to catalyze chemical reactions between multiple phases. Describing and analyzing these processes require a wide range of fundamental data, including electron impact cross sections for excitation, dissociation, and ionization of atoms and molecules; optical absorption cross sections; oscillator strengths and opacities; charge exchange cross sections; and reaction probabilities of plasma-produced radicals, ions, and photons with gases, solids and liquids. The importance of these fundamental data cannot be overstated—they are essential to the health and advancement of PSE. Well supported programs in AMOP and CP not only advance the science of those disciplines but also enable advances in other disciplines, and PSE in particular.

Diversity, Equity, and Inclusion and the Plasma Science and Engineering Workforce

The principle of diversity, equity, and inclusion (DEI) broadens a discipline to the betterment of that discipline and to the betterment of the society the discipline serves. Regrettably, plasma science and engineering is among the least diverse STEM fields, for historical and current reasons. For example, data from the annual Survey of Earned Doctorates in 2013-2017 shows that the percentage of women annually earning doctorates in plasma physics averaged 14 percent (below the approximately 20 percent average for physics), while the percentages of PhDs obtained by Hispanic and African-American students fluctuated around 3 percent (with several years reporting zero). These data are consistent with statistics from the American Institute of Physics. A 2017 assessment from the University Fusion Association has shown that the fusion community (which represents a large portion of the overall PSE community) is aging, with an average age of 56. At the same time, STEM fields that may utilize plasmas, such as chemical engineering and bioengineering, are significantly more diverse.

The committee notes that federal agencies funding research in PSE have greatly differing expectations for grantees to produce broader impacts in their research and conduct outreach activities. The committee endorses the premise that the primary focus of these agencies should be addressing the science and technology challenges in PSE that will lead to societal benefit. However, the committee also feels that a more consistent set of expectations among these agencies would deliver a stronger message of the importance of diversifying PSE.

A professional workforce cannot reflect society if the student pipeline entering PSE is not diverse. There are many causes for lack of diversity in the pipeline and many remedies being proposed to diversify the pipeline. Early exposure to plasma science (e.g., the APS-DPP Plasma Expo, science museum exhibits, and university outreach activities) is important for building an appreciation of plasma science on the part of students and the general public. A more direct method for increasing interest in PSE and in diversifying the pipeline is to increase the numbers of undergraduate students exposed to PSE through research experiences. Such research experiences are more readily available at universities with PhD programs in physics and engineering than at primarily undergraduate institutions (PUIs). Yet, the highest degree in more than two-thirds of physics departments in the United States is the bachelor’s degree, and approximately half of all physics bachelor’s degrees are awarded by departments that do not offer a PhD. Therefore, the majority of U.S. physics students and potential plasma physics graduate students are likely not exposed to plasma physics as undergraduates. A significant portion of the future PSE workforce relies on prospective graduate students encountering plasma research only in graduate school, and only if a plasma program exists at that institution.

PSE research programs in PUIs could have a disproportionately large influence in developing the PSE workforce by exposing undergraduates to plasma physics and engineering, thus increasing the pipeline of students entering graduate school with the goal of studying plasma physics. PUIs tend to be liberal-arts-focused institutions with broader curricula and more diverse student bodies. Their smaller student-to-faculty ratios enable closer mentoring of research experiences involving students who would not otherwise have research opportunities. Smaller colleges and institutions also have a history of serving underrepresented minorities and first-generation college students, thereby helping to introduce PSE to precisely the audience needed to diversify the pipeline.

The committee acknowledges and is concerned about the lack of diversity in the core areas of PSE. The goal of the PSE community should be to improve the diversity of PSE to reflect the society it serves by increasing the participation of women, ethnic and religious minorities, gender-preference and gender-identity minorities including members of the LGBTQ+ community, and persons with disabilities, while recognizing that this list may not be fully inclusive of all underrepresented communities in PSE. Addressing this persistent problem of under-representation should be a high priority in the PSE community. The committee strongly believes in the benefits that will result from improving that diversity, and strongly encourages community leaders throughout the PSE enterprise to carefully consider and assess the DEI practices within their own organizations. Even more critically, individual members of the PSE community should be involved in DEI activities at the most primary levels in their institutions.

The committee acknowledges and supports the DEI activities that have been initiated since the Plasma 2010 report,⁴ and the committee encourages continued community-wide discussions and actions that will produce a more diverse PSE discipline. Professional societies, universities, national academies, national laboratories, and federal agencies are now actively engaged in addressing DEI issues in STEM, and in PSE in particular. Given the demographics of the field, the next decade will likely see significant turnover in the PSE workforce, providing ample opportunities for improving the diversity of the field. Although the committee is not formally endorsing a particular organization’s DEI activities, the committee strongly endorses the importance of and efforts of the field to diversify.

FINDINGS AND RECOMMENDATIONS

The PSE community in the United States has had an enormous impact since publication of the Plasma 2010 report.⁴ Internationally leading research has been performed in all fields of PSE, with landmark contributions having been made

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⁴ National Research Council, 2007, Plasma Science: Advancing Knowledge in the National Interest, The National Academies Press, Washington, DC, https://doi.org/10.17226/11960.

to the advancement of the science of plasmas, national security, and economic competitiveness. These advances confirm the value and need for discipline-centric research on the basic plasma science challenges, the interdisciplinary research that will translate that learning to applications, and support for that translational process. To expand upon that progress in the next decade, the discipline needs greater interdisciplinary coordination between federal agencies (and programs within agencies) in their approach to PSE, an activity that would be in their own benefit as well as that of the discipline. The committee notes that the National Research Council Plasma Science Committee (PSC) at one time helped to heighten awareness of these opportunities and be a spokes-group for the field. Unfortunately, the PSC has been inactive for several years. Expanding the impact of research in PSE also needs an ecosystem of facilities, diagnostics, computations, and, importantly, renewal of the PSE workforce through education and career enhancement programs. The high-level, findings and recommendations from this study are discussed below. These high-level recommendations, as well as more specific individual chapter-based recommendations, are collected in Appendix B.

Stewardship and Advancement of Interdisciplinary Research

Finding: PSE is inherently an interdisciplinary field of research. While the underlying science has common intellectual threads, the community is organized into sometimes isolated subdisciplines.

At the same time, examples of initiative-driven and long-term collaborations between federal agencies in PSE are rare. The recently enacted Space Weather Research and Forecasting Act that mandates joint activities by NASA, NOAA, NSF, DoD, and FAA, and the NSF/DOE Partnership in Basic Plasma Science and Engineering, are notable exceptions. This isolation is in part driven by the extreme diversity of applications that motivates the fundamental research. It is also occasionally reinforced by narrow, mission-driven support at the federal level.

Several program managers contacted by the committee were cautious about participating in interdisciplinary programs in PSE due to the risk of being perceived as duplicating research priorities of other agencies, a practice which has been historically discouraged. The committee and the PSE field have a different perspective.

During review and final preparation of Plasma 2020, the committee was in the midst of the Covid-19 pandemic (beginning in March 2020). The areas of plasma medicine and plasma biotechnology encompass the use of plasmas for sterilization of materials and living tissue such as skin, and address the need to physically kill pathogens without risking antimicrobial resistance. Plasma medicine and plasma biotechnology are examples of interdisciplinary fields that have fallen between

the cracks of the perceived responsibilities of individual funding agencies. Plasma focused agencies are reluctant to sponsor projects that involve biological systems and biologically focused agencies are reluctant to sponsor projects that have a focus on plasma physics. As a result, we may have missed an opportunity to have another tool at our disposal to aid in the current health crisis.

Finding: What may be narrowly perceived as duplication is actually critically necessary collaboration needed to address the complex science challenges in PSE while rapidly translating results to society-benefiting outcomes.

Finding: Institutional barriers between subdisciplines of PSE make mutually advantageous interactions difficult, yet interactions between subdisciplines have led to important advances that would have been difficult to produce otherwise.

Finding: A more unified voice for the field would create opportunities for interdisciplinary and translational research, and initiate activities that exploit synergies among different subdisciplines of PSE.

Recommendation: Federal agencies directly supporting plasma science and engineering (PSE) and those federal agencies benefiting (or potentially benefiting) from PSE should better coordinate their activities extending into offices and directorates within larger federal agencies.

One mechanism to facilitate this coordination is to establish an Interagency Working Group (IWG) with representatives from agencies that investigate plasmas as part of their mission (e.g., NSF [MPS, GEO, ENG], DOE [SC, NNSA, ARPA-E], NASA [SMD, HEOMD], DOE [FES, NNSA, HEP, BES, ARDP, ARPA-E], NOAA, DoD [AFOSR, ONR, ARO, DTRA]) and those agencies that benefit from (or could benefit from) plasma applications (e.g., EPA, NIH, DHS, FDA, NSA, and USDA). The IWG would identify feasible areas of collaboration and build upon current programs that contribute to the missions of the agencies in basic and applied PSE areas. In this regard, those agencies performing research in basic plasma science (e.g., NSF, DOE, DoD) could reach out to agencies that benefit or could benefit from plasma applications (e.g., NIH, USDA, EPA), while mutually soliciting community input on possible areas of collaboration. Given the breadth of the IWG, this effort would best be coordinated by the National Science Foundation, perhaps in partnership with the National Science and Technology Council (NSTC) and the Office of Science and Technology Policy (OSTP). (NSTC/OSTP have experience in organizing such working groups, for example, in HED.) Several potential interagency collaborations on topics across the field of PSE are listed in Table 1.1 located at the end of this chapter. The collaborations listed in Table 1.1 are intended

to be examples of potential partnerships that would meet many of the needs and priorities of the field and nation. The committee intends these suggestions as starting points for discussions.

Finding: Fundamental research in PSE can and does rapidly translate to the development of societally relevant technologies, the benefits of which cut across the missions of many federal agencies.

In fact, the majority of PSE research is motivated by the final application, from producing electricity using controlled fusion and protecting information technology assets from errant space weather, to plasma synthesis of new materials and medical diagnostics using table-top laser-accelerators. In some areas of PSE, such as MFE and ICF, the motivating application is contained within the same agency or program that funds the fundamental plasma research. In these situations, the translational research is well leveraged toward the intended application. In other areas of PSE, such as plasma materials processing, the motivating application is the primary mission of an agency or program other than that funding the fundamental plasma research. For example, plasma-based accelerators benefit broad interests outside the agencies principally responsible for their development. The DOE High Energy Physics Accelerator Stewardship Program is an example of such a program.

Finding: The interdisciplinary and multidisciplinary strengths of PSE are not being fully utilized. This situation is to the detriment of the fundamental plasma research and to the detriment of the intended applications.

Although inter-agency and intra-agency collaborations that jointly fund PSE activities exist, these efforts are largely ad-hoc and not in the form of proposal-driven initiatives. Notable exceptions include the recurring NSF/DOE Partnership in Basic Plasma Science and Engineering, an outcome of the 1995 Plasma Decadal Study, and the recently announced NSF/NASA Next Generation Software for Data-driven Models of Space Weather with Quantified Uncertainties. Another successful example is the 2007 Interagency Task Force on High Energy Density Physics, with membership from the DOE Office of Science (SC) and NNSA, NASA NIST, NSF and DoD, which had a significant impact on the high energy density field. A recent RFI (request for information) issued by the DOE-SC to support research in advanced microelectronics, a component of which is plasma materials processing, involves multiple programs within DOE-SC. Increased collaboration between agencies to support fundamental research, translational research, and applications-focused research in PSE would benefit all partners. The barriers to

such collaboration should be reduced. Examples of beneficial cross-agency linkages are listed in Table 1.1.

Finding: Interagency (and inter-program) initiatives would fully exploit the interdisciplinary and multidisciplinary potential of PSE in both fundamental and translational research if properly stewarded.

Recommendation: Federal agencies and programs within federal agencies that are separately focused on fundamental plasma research, and those that are focused on science and technologies that utilize plasmas, should jointly coordinate and support initiatives with new funding opportunities.

There are extraordinary opportunities for such jointly sponsored initiatives in, for example, materials, biotechnology, medicine, agriculture, accelerators, energy, environment, propulsion, manufacturing, space weather, security, and computations. Some of these opportunities and potential agency partnerships are listed in Table 1.1. These initiatives will significantly advance fundamental plasma science while accelerating the translational outcomes of those advances. One of the goals of the recommended IWG would be to address the scope, feasibility, and possible implementation of these initiatives, an activity best organized by NSF. Within federal agencies whose programs are highly mission-driven, coordination of such initiatives may best come from higher levels—for example, at the level of the DOE Office of Science.

Finding: The potential is enormous for PSE to contribute to one of society’s greatest challenges—sustainability. The contributions that PSE could make extend from fusion-based, carbon-free electrical power generation to electrification of the chemical industry.

As the needs for sustainability become clearer, the plasma science challenges will become more focused and more tied to the applications. Although the research will remain fundamental, the research will also become more translational. At NSF, this research would best be performed in the Engineering Directorate (ENG). However, support for PSE in ENG has been inconsistent, and particularly so since the Plasma 2010 report.⁵ As the priorities of programs in the ENG change, PSE is added and removed from program descriptions. Programs in the ENG also choose to participate or not in the NSF/DOE Plasma Partnership depending on

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⁵ National Research Council, 2007, Plasma Science: Advancing Knowledge in the National Interest, The National Academies Press, Washington, DC, https://doi.org/10.17226/11960.

the changing priorities. With this inconsistent record of support for PSE in the Engineering Directorate, it is difficult to develop long term PSE strategies to address critically important challenges such as sustainability.

Finding: The translational nature of fundamental research in PSE needs to be formally recognized at NSF.

Recommendation: The Engineering Directorate of NSF should, as a minimum, consistently list plasma science and engineering in descriptions of its relevant programs and consistently participate in the NSF/DOE Plasma partnership.

Recommendation: More strategically, NSF should establish a plasma-focused program in the Engineering Directorate that would further engineering priorities across the board, including advanced agricultural systems, energy and environment, chemical transformation, advanced manufacturing, electronics, and quantum systems.

These efforts would complement the more fundamental plasma physics program in the Mathematical and Physical Sciences Directorate. The PSE program in ENG could follow the recommendations of the NSF workshop “Science Challenges in Low Temperature Plasma Science and Engineering: Enabling a Future Based on Electricity through Non-Equilibrium Plasma Chemistry.”⁶

Finding: Public-private partnerships (PPP) have long been a benefit to PSE, largely in the form of SBIR (Small Business Innovative Research) and STTR (Small Business Technology Transfer) programs.

SBIR/STTR programs have been highly successful in translating fundamental science toward commercialization. Although PSE industries have long funded fundamental research focused toward developing their own products, the emergence of venture-capital-funded fusion research and international competition in industries reliant on plasma science have significantly changed the landscape for PPPs. One recent development acknowledging the new landscape is the DOE Office of Science Innovation Network for Fusion Energy (INFUSE), whose goal is to accelerate fusion energy development in the private sector by opening resources at DOE laboratories and reducing barriers to collaboration. In another example,

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⁶ S.M. Thagard, M. Sankaran, M.J. Kushner, 2019, “Science Challenges in Low Temperature Plasma Science and Engineering: Enabling a Future Based on Electricity through Non-Equilibrium Plasma Chemistry,” arXiv preprint arXiv:1911.07076.

an increasing number of small companies that specialize in space-weather plasma data and models tailored primarily to aviation, aerospace, and defense needs have been responding to SBIR/STTR calls by several federal agencies, broadening the commercial space-weather sector.

There are challenges in leveraging PPP for economic and national security benefits for both small and large companies. The requirements to make breakthroughs in translational research and commercialization in multidisciplinary fields such as PSE may exceed the resources and know-how of many small businesses. These requirements then fit poorly within the traditional SBIR/STTR structure. For large businesses, there are extreme pressures from international competition, in large part resulting from strong foreign government support for fundamental and translational research in key plasma-based industries. For example, South Korea and China have aggressive national programs to address fundamental research vital to the plasma-based microelectronics industry.

Finding: With there being few U.S. governmental programs designed to translate industrially relevant fundamental science to practice, U.S. industries are at a competitive disadvantage internationally.

Recommendation: Federal agencies focused on plasma research, and DOE in particular, should develop new models that support the translation of fundamental research to industry. Programs that support vital industries depending on plasma science and engineering should be developed through relevant interagency collaborations.

Examples of translational research that would benefit plasma enabled industries include development of diagnostics that could be used for real-time control of plasma processes, understanding and optimizing the production of plasma generation of precursors used in materials processing and developing industrially relevant modeling platforms. The United States is well known for being a hotbed for entrepreneurship but it is unclear whether the PSE research infrastructure is properly configured to meet entrepreneurial needs. For example, many biotechnology startups use plasma processes for biocompatible coatings, yet are more likely to seek and receive support from NIH than FES. As a result, a needed plasma focus may be absent.

The committee acknowledges that this is a multifaceted recommendation with many avenues for implementation. Certainly, the PSE community could take advantage of existing resources to engage with the private sector, such as the National Academies Government-University-Industry Research Roundtable (GUIRR). One implementation could be encouraging or requiring more collaborative research between universities and small companies, both for commercialization and to

meet the needs of national laboratories. In parallel, INFUSE-like programs could be extended through partnerships to support the science needs of industries and companies, large and small, in areas of national importance that depend on PSE. Another implementation would be to sponsor translational research to bring plasma-based capabilities to a level where private research and development can continue. A particularly valuable implementation would be to regularly convene an advisory board of technical leaders from industries that rely on or could utilize advanced PSE capabilities to articulate the needs of industry in fundamental research. Such an advisory board would guide federal agencies in how best to support translational and multidisciplinary research, including selection of SBIR/STTR topics that have a high probability for industrial impact. This could be coordinated by the recommended IWG, with a more mission, outcomes focused agency, such as the DOE, leading the effort.

The Plasma Science and Engineering Community

Plasma science and engineering is a highly multidisciplinary field, a quality that is reflected by the large number of federal agencies with interests in plasmas, and the diverse array of university departments in which plasma faculty and researchers can be found. At any given university, one is likely to find plasma-focused faculty in physics, chemistry, geophysics, space sciences, astronomy and astrophysical sciences, climate sciences, and many engineering fields (e.g., aerospace, agriculture electrical, nuclear, chemical, biomedical, and mechanical).

Finding: The multidisciplinary approach has been at the heart of the success of the PSE field, while simultaneously working against the long-term viability of the field in academia.

Since plasma physics is a minority discipline in nearly every department containing plasma-focused faculty, maintaining faculty expertise is becoming progressively more challenging. Universities provide thought leadership and drive innovation, while also training the workforce for the field, and that leadership and training requires a robust faculty in PSE.

Finding: Lack of a critical mass of faculty in PSE inevitably will lead to an erosion of U.S. capability in PSE. At the same time, the university leadership in PSE is rapidly aging and will need renewal in the coming decade.

There are great opportunities for new PSE university faculty to address sustainability, investigate laser-plasma produced quantum effects, make space weather predictions, and investigate exotic states of matter. However, the

committee is gravely concerned that poor PSE demographics and current hiring practices are eroding the ability of the field to meet national priorities, from security to the economy. There are simply too few early-career faculty to renew the field. Opportunities for scientific leadership are also essential for healthy university programs. This is particularly true for those faculty members whose primary focus is investigating the fundamentals of plasma science as opposed to their applications.

Recommendation: Federal agencies—for example, DOE, NSF, NASA, and DoD—should structure funding programs to provide leadership opportunities to university researchers in plasma science and engineering areas and to directly stimulate the hiring of university faculty.

These leadership opportunities are critical to all areas of PSE. Examples of implementing this recommendation include soliciting major new facilities or missions with leadership teams composed in part or wholly by university researchers. Major activities in the field could be organized around centers that are led by university researchers. Specific programs could be implemented to provide funds for the creation of faculty positions, following the model of the NSF Faculty Development Program in Space Sciences.

Finding: Plasma-specific educational and research programs that also provide opportunities to diverse and less advantaged populations are needed to ensure a critically populated PSE workforce.

As discussed earlier in this chapter, increased emphasis on PSE undergraduate research and internships, particularly at primarily undergraduate institutions (PUIs), will improve awareness of our field among all undergraduates, and women and underrepresented students in particular, thus enabling a more heavily populated and a more diverse discipline. Stronger links between PUIs and research institutions would also improve the pipeline.

Finding: Plasma-specific intern programs and summer schools are needed for undergraduate and graduate students, as are programs supporting students with incomplete preparation to progress in plasma physics, such as the American Physical Society Bridge Program.

The past DOE National Undergraduate Fellowship program in plasma physics, now a Science Undergraduate Laboratory Internship (SULI) program at Princeton Plasma Physics Laboratory, and the American Physical Society Division of Plasma Physics outreach events for students, are two successful examples. Physics curricula

are traditionally sequential, with plasma physics typically covered toward the end of the sequence (if at all).

Finding: Requiring students to know early in their undergraduate years that plasma physics is a career goal has limited the number of students continuing in plasma physics in graduate school and has excluded less advantaged populations.

Finding: Support for junior faculty for course development, and for curricula enhancement (e.g., inclusion of plasma physics in other courses), is necessary to enable students from a wide range of institutions to enter the field.

Federally funded programs to support undergraduate education, graduate fellowships, postdoctoral fellowships, and early-career awards have been essential in attracting and supporting a talented and diverse population of junior scientists to PSE. However, recent policy changes have eliminated many of these programs in important areas of PSE within the DOE Office of Science. While the policy changes were intended to prevent duplication of educational efforts across agencies, the programs that were eliminated have no equivalents in other agencies. Consequently, their loss has significantly affected the ability to attract and retain new talent and university faculty in PSE.

Finding: The committee regards multiagency investment in education—whether through directly supporting undergraduate and graduate students or programs or through faculty and resource development—as being critical. “Duplication” of effort in these areas can only further strengthen PSE.

Recommendation: Federal agencies (e.g., DOE, NSF, NASA, DoD) should structure funding to support undergraduate and graduate educational, training, and research opportunities—including faculty—and encourage and enable access to plasmas physics for diverse populations.

To implement this recommendation, federal agencies supporting PSE research could be allowed to establish domain-specific educational and outreach programs, reversing recent changes that were intended to reduce duplication in educational programs across the federal enterprise. New opportunities for undergraduate research in PSE at smaller PUIs would increase exposure of diverse populations to plasma physics and engineering, thus increasing both the population and the diversity of the pipeline into graduate school and the profession. This activity could be built on the model of the NSF program in Facilitating Research at Primarily Undergraduate Institutions. Stronger links between PUIs and research institutions

could be established by postdoctoral or graduate fellowships for researchers to work at PUIs or jointly with larger plasma institutions, and by broadening REUs (Research Experiences for Undergraduates) beyond NSF.

The Research Enterprise in Plasma Science and Engineering

The research enterprise in PSE has had tremendous impact over the past decade. Plasma science has opened opportunities across a remarkably diverse range of areas, including semiconductor processing, new accelerators, understanding astrophysical and planetary states of matter, new energy sources, and enhancing national security. Although the progress has been impressive, it has also been made in an environment of tremendous competing international investments across the spectrum of PSE. These investments challenge and may potentially usurp U.S. leadership in PSE. International investments in large fusion devices, powerful lasers and research networks over the past decade have generally exceeded that of the United States.

Finding: Given these strong international investments, incremental progress in facilities in the United States is insufficient to maintain leadership.

Finding: A spectrum of facility scales is required by the subfields of PSE to address their science challenges and translational research.

Finding: Midscale facilities (e.g., in the $1 million to $40 million range, depending on agency) offer particularly good opportunities for broadening participation within academia.

Recommendation: Federal agencies (e.g., DOE, NSF, NASA, DoD) should support a spectrum of facility scales that reflect the requirements for addressing a wide range of problems at the frontiers of plasma science and engineering.

In some cases, advancing the state of the art requires significant investments in large facilities built over many years, while in other areas, better equipping the laboratories of single investigators with advanced diagnostics as part of a distributed network best serves the field. However, research facilities cannot function efficiently without the support of experienced scientific staff, and significant operations cannot proceed efficiently without the procurement of increasingly costly essential materials, such as liquid helium.

Finding: Investment in facilities without the concurrent support of research and operations is not optimum.

Recommendation: Federal agencies whose core missions include plasma science and engineering—for example, DOE, NSF, NASA, and DoD—should provide recurring and increased support for the continued development, upgrading, and operations of experimental facilities, and for fundamental and translational research in plasma science. A spectrum of facility scales should be supported, reflecting the requirements for addressing different problems at the frontiers of plasma science and engineering.

Finding: Computational plasma science and engineering (CPSE) has become essential across PSE for experiment and mission design and diagnosis, idea exploration, probing of fundamental plasma physics processes, and prediction.

For computations to continue to progress in PSE, the next generation of researchers critically needs to be better educated through the development of plasma-focused computational textbooks and courses, and through participation in funded computational research projects. At the same time, the computational landscape is rapidly evolving, with increasing heterogeneity in devices, languages, and coding practices. GPU computing is just now under development, and new devices, such as quantum computers, are on the horizon. As a result, writing computational plasma software now requires mastery of multiple technologies, all of which are swiftly changing, leading to crises whereby small development teams cannot build performant software. Simultaneously, new methodologies for prediction, including machine learning and artificial intelligence, are becoming increasingly possible with new, high-throughput computing devices.

Recommendation: Federal agencies should support research into the development of computational algorithms for plasma science and applications for the heterogeneous device computing platforms of today and upcoming platforms (e.g., quantum computers), while also encouraging mechanisms to make advanced computational methods, physics-based algorithms, machine learning, and artificial intelligence broadly available.

Stronger cooperation between programs within NSF, DOE, NASA, and DoD that support computer science, applied mathematics, and physical sciences and engineering is encouraged. Several possible partnerships are listed in Table 1.1. Proposals should be solicited and supported that include, at least as a component, the development of plasma-focused computational educational materials, and in particular graduate-level texts.

Better Serving the Community

Following the recommendations of the Plasma 2010 report,⁷ the DOE Office of Fusion Energy Science (FES) broadened the scope of its programs to better serve the plasma science community. This broadened mission, contained primarily within the Discovery Plasma Science (DPS) program of FES, has increased its support of research on LTPs, basic plasma physics, and high-energy-density plasmas. FES continues to be a vital member of the NSF/DOE Partnership in Basic Plasma Science and Engineering. The committee gratefully acknowledges the response of FES to the Plasma 2010 recommendations to broaden its mission.

Finding: Although the majority of the FES budget is still devoted to supporting fusion science, the present office title does not now accurately reflect its broader mission. The present title may, in fact, impede the ability of FES to collaborate with other offices within DOE and with other federal agencies, including impeding its ability to garner support for nonfusion plasma research.

Finding: The national interest as a whole would be better served by renaming the office to better reflect the broader mission of FES, maximize its ability to collaborate with other agencies and to garner nonfusion plasma support.

Recommendation: Consistent with our recommendations to broaden the impact of plasma science, the DOE Office of Fusion Energy Science should be renamed to more accurately reflect its broader mission, and so maximize its ability to collaborate with other agencies and to garner nonfusion plasma support. A possible title is Office of Fusion Energy and Plasma Sciences.

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⁷ National Research Council, 2007, Plasma Science: Advancing Knowledge in the National Interest, The National Academies Press, Washington, DC, https://doi.org/10.17226/11960.

TABLE 1.1 Examples of Interagency and Interoffice Collaborative Initiatives