Plasma Science Enabling Technology, Sustainability, Security, and Exploration (2021) / Chapter Skim
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5 Low-Temperature Plasmas: A Unique State of Matter for Addressing Societal Needs
5 Low-Temperature Plasmas: A Unique State of Matter for Addressing Societal Needs
Pages 208-263
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From page 208... ...
Those plasma-enabled e societal transformations will continue into the future. A strategic and new opportunity for LTP science and technology is to help enable the electrification of the chemical industry -- that is, to drive chemical processing by electrical means facilitated by plasmas.
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The electric fields in the sheaths accel erate positive ions to surfaces which then provide activation energy for material changing reactions on surfaces. Low temperature radical generation coupled with normal incidence positive ion bombardment at surfaces has enabled a tre mendous range of industrial applications based on LTP processing of material surfaces and thin films; and in particular has enabled industrial scale fabrication of microelectronics.
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HTs (3-4.5 kW) have been flown on commercial communica tions satellites in the past decade, significantly reducing the propellant needed for orbit raising and station keeping, and similar thrusters are planned for upcoming deep space missions.
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LTP has been shown to stimulate subcutaneous blood flow and blood O2 content; cell-cell communication; and elements of both innate and adaptive immunity. Another important LTP-associated mechanism is the biological effects of pulsed electric fields.
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Keidar, 2018, A prospectus on innovations in the plasma treatment of cancer, Physics of Plasmas 25:083504, with the permission of AIP Publishing. Plasma-Materials Interactions Major developments in plasma materials processing have included the continu ing progress in applying LTPs to manufacturing of integrated circuits.
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and atomic layer etching (ALE) processes have been developed to meet these needs.
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Localized heating and radicals produced by nanosecond pulsed plasmas were found to be effective for triggering combustion processes. Nanosecond pulsed plasmas that produce high electric fields efficiently channel energy deposi tion into electronically excited states of the molecules in air-fuel mixtures, resulting in rapid oxygen dissociation by electron impact and in excitation transfer from other electronically excited atoms and molecules.
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Thagard, 2017, Plasma-based water treatment: Efficient transformation of perfluoroalkyl substances in prepared solutions and contaminated groundwater, Environmental Science and Technology 51:1643, copyright 2017 American Chemical Society. different pollutants has been investigated.
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This enhanced capability in LTP will benefit multiple sectors of society. Controlling plasma-surface interactions at the atomic level will enable the next generation of materials for quantum computing, combating anti-microbial resistance, improving agriculture efficiencies and food safety, enabling new energy storage technologies and devel oping plasma-based propulsion capable of taking mankind to Mars and beyond.
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The funding landscape is therefore highly dispersed and with a primary focus on applications and translational research. There is relatively little inter agency coordination of LTP research with the exception of the NSF/DOE Partner ship in Basic Plasma Science and Engineering.
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However, given that fundamental LTP research underpins several industries that are critically to our national economy and national security, the applied-to-fundamental research ratio appears to be significantly out of balance. The central role of LTP is often hidden from public view, creating hidden value to the United States and world economy.
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From page 219... ...
It is important to note that whereas LTP research involving applications continues to grow, fundamental research in LTP appears to be declining. There is concern that if this trend continues, within the next 10 years, fundamental research in LTP that has historically been the basis of the development of LTP applications will, with a few exceptions, no longer be practiced in the United States.
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RELEVANCE AND BENEFITS OF LTP RESEARCH In most LTP applications, control of the plasma to achieve the desired effects is the ultimate goal. Designing the plasma device entails making decisions on par ticulars of the power supply (e.g., radio frequency, pulsed)
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Hall thrusters are also planned for the upcoming NASA science mission to the asteroid Psyche. LTP Enabling Long-Mission Human Space Science and Exploration One of the unsolved challenges for long mission human space flight is life support-systems.
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Semiconductor Industry Association entitled Winning the Future. A Blueprint for Sustained U.S.
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LTP research will play a crucial role in some of the key science challenges in this area including: • Lightning inception: It is now roughly understood how a lightning discharge can start near one graupel particle (soft hail or snow pellets) due to the local enhancement of the rather low background electric field in the cloud.
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Producing high micro wave-energy-density systems requires addressing issues of intense beam generation, dense charged-particle confinement, extreme-environment-compatible materials, intense radiation and particle diagnostic development, and the development of compact pulsed power. HPM research and development requires advances in plasma physics theory, computation, experimental diagnostics, and the integration of ad vanced electronics (sensors, system control, pulsed power)
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Controlling surface breakdown of both distributed and spatially periodic discharges would enable longer HPM pulses. Plasmas for Optics and Wave Manipulation The field of "plasma metamaterials and plasma photonic crystals" involves LTP science in which plasma elements (individual plasmas, plasma gratings or plasma ar rays)
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The image shows an example of a plasma photonic crystal setup that is completely formed by plasma elements that are individually controllable.
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LTPs are being investigated as in-water sources of oxidizing species such •OH, O•, and H•, and for the emission of UV light for disinfection. Plasma based water treatment is especially attractive since there is no input required other than electricity.
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LTP IN ECONOMIC DEVELOPMENT LTP science and technology have long addressed critical societal problems and have created significant economic impact through the interplay between basic sci ence, applied science, and technological challenges. Since plasma technologies are primarily enabling technologies, their contribution to a specific product or method often remains hidden or even unknown and their direct impact, especially their economic impact, is often difficult to assess.
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Plasma etching, alone ("trimming") , or in conjunction with atomic layer deposition (ALD)
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Another major application includes plasma deposition on glass substrates for reflection and antireflection coatings. Materials Processing: Additive Manufacturing Metallic additive manufacturing is an increasingly important process, enabling prototyping, production of custom-designed parts and production of complex structures not possible using traditional methods.
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L ow - T e m p e r at u r e P l a s m a s 231 FIGURE 5.7 Plasma additive manufacturing. Two robotic welding machines are fabricating steel aluminum aircraft wing ribs using a wire + arc additive manufacturing process (WAAM)
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Ozone Generation LTPs, as ozone generators, have for many decades served as the basis of water purification in municipal water systems. The global ozone generation market was valued at $880 million in 2016 and is expected to reach $1.5 billion by 2023.
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This discourages their use for rural point-of-use water treatment far from municipal systems. A recent development is using microplasmas for rural point-of-use water treatment.
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The driving focus for LTP science is the following: Controlling the nonequilib rium energy deposition and dissipation in collisional LTPs to enable plasma-produced selectivity. This is an extremely challenging topic that has a common science base -- that being plasma kinetics and collision physics.
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Crossed Electric and Magnetic Fields Transport Anomalously high transport of plasma across magnetic field lines is pervasive, spanning many branches of plasma physics from fusion to astrophysical plasmas. In LTPs, crossed electric and magnetic fields, E×B, transport is most commonly associated with magnetrons used to sputter in materials fabrication and in electric propulsion (EP)
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Expanded experimental efforts combined with new diagnostics will need to be able to measure energy coupling across several scale lengths, the phase relation between microscale electric field and density, and particle distributions. Plasma Surface Interactions In most cases, LTPs are bounded and the bounding interface dominates plasma properties.
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Three dimensional simulations of ionization waves and streamers have been performed in the gas phase whereas surface ionization waves have only been recently modeled and intrinsic 3D phenomena have not yet been addressed. We currently do not have a general understanding of the mecha nisms responsible for self-organization in atmospheric pressure plasmas interacting with surfaces.
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of the type used for microelectronic processing, is independent control of the flux and the energy of ions impinging on a substrate. This implies a requirement of direct control of the spatial distribution of plasma properties and ionization.
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(Translational research refers to a smooth continuum that begins with fundamental studies and leads to applications.) The translational nature of LTP science is a tremendous strength, but it also places an implied obligation on LTP science to perform that science in regimes that will produce results that quickly convert to applications.
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From page 240... ...
Trans lating fundamental studies of particle distributions to activating a desired surface modality is at the forefront of LTP science. • There remain significant theoretical and experimental challenges to under standing the correlation between a plasma treatment "dose" (the sum of all reactant species incident on the target)
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and atmospheric pressure LTP research. For more compact LTS setups, the use of volume Bragg gratings (in place of triple grating spectrometers)
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the most fundamental plasma properties (electron densities and temperatures, and electric fields) also continues to be challenging at atmospheric pressure.
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This could be accomplished by developing new surface diagnostics or adapting, where pos sible, surface science techniques. Modeling and Simulation Predictive computational modeling capabilities are critically important in advancing LTP science and technologies.
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Given the translational nature of LTP research, models are required that are fully fundamentally physics based, but also have the robustness to be used for design and optimization of de vices. For example, complex plasma chemistries may include a hundred individual gas phase species (ions and neutrals)
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The devel opment of validated predictive capabilities requires a large team and long-term efforts that are currently not in place for the U.S. LTP community.
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Trieschmann, 2019, Machine learning plasma-surface interface for coupling sputtering and gas-phase transport simulations, Plasma Sources Science and Technology 28:035002. Copyright IOP Publishing, reproduced with permission, all rights reserved.
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FUTURE OPPORTUNITIES IN LTP SCIENCE -- STRATEGIC CHALLENGES Given the great diversity of science areas and applications in LTPs, future op portunities that cross the area may best be expressed in terms of high-level Strategic Challenges. Here are four strategic challenges that, while not exhaustive, encompass the breadth of the field.
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Plasma has been shown to effectively inactivate biofilms including MRSA. The figure illustrates the ac tive plasma components possibly involved in the inactivation and the complex structure of the biofilm.
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In each of the potential applications listed above, there are corresponding chal lenges, opportunities and needs to expand and extend LTP science. Challenge 2: Controlling plasma-surface interactions at the atomic level to enable the next generation of materials for quantum computing, new communication, sensor, energy storage and harvesting technologies.
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Challenge 3: Electrification of the chemical industry based on renewable electricity to enable a sustainable society. LTP science could be crucially important to enable the vision of a future based on renewable electricity.
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L ow - T e m p e r at u r e P l a s m a s 251 FIGURE 5.15 Plasma catalysis. Plasma catalysis provides possible new exciting opportunities for selective and enhanced chemical transformations, however, the underlying mechanisms are not clear.
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From Europe, the committee received input on the status of LTP research in Germany, Belgium, France and the Netherlands. From Asia, the committee received input from South Korea, Japan, and China.
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HT use a cross field E×B plasma to ionize and accelerate gaseous propellant. When spacecraft reenter the atmosphere at hypersonic speeds, an enveloping plasma produces a complex chemically reacting LTP.
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Self-Assessment of International Research Activities In Europe, the LTP community is very active, but the level of activity varies among the different countries. Across Europe, the total number of researchers involved in LTP research activities seems to have remained relatively constant in the last 10 years with fluctuations across the different countries: Germany reports relatively stable numbers, while the Netherlands is experiencing a slight increase, but France and Belgium are possibly experiencing a slight decrease.
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publication rate (as a percentage of first authorship) has generally remained stable around 25 percent in a selection of journals publishing LTP research, including the Journal of Applied Physics, Plasma Sources Science and Technology, and Journal of Physics D: Applied Physics.
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The vast majority of laboratory facilities for the study of low pressure to at mospheric pressure LTPs are in the tabletop scale of devices -- often surrounded by a suite of advanced diagnostic tools. The major investments for a typical LTP laboratory are often complex power supplies including nanosecond pulsed power capabilities and modulated multifrequency RF plasma sources, coupled with vari ous probe, optical, surface and mass spectrometry-based diagnostics.
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Needs and Opportunities Most of the U.S. LTP research community does not utilize the kind of central ized facilities that are more common in other areas of plasma physics -- facilities that are few in number, high in cost, and take years to plan and build.
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Future IC device technologies will depend more than ever on plasma-based processing. The IC industry needs advances in LTP science to meet their diverse and extreme challenges, demanding a deeper understanding of the physics, chem istry and materials-modifying characteristics of LTP used in IC manufacturing as described above.
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The extremely successful Low Temperature Plasma Science Center program sup ported by the DOE Office of Fusion Energy Science has had a tremendous impact. Finding: The success of the DOE Low Temperature Plasma Science Center program underlines that there is a need to sustain LTP research directions for a sufficient period of time (5 to 10 years)
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Finding: The fundamental research performed in LTP is intrinsically interdis ciplinary with societal benefits occurring most rapidly when that fundamental research is guided by applications. Finding: Although the NSF/DOE Partnership in Basic Plasma Science and Engineering is a strong supporter of LTP research, the translational and con vergent nature of LTP research often transcends the scope of the NSF/DOE partnership.
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The establishment of the Low Temperature Plasma Science Center program at DOE since the 2010 Decadal study has benefited fundamental LTP research. Finding: Continuing initiatives like the DOE Low Temperature Plasma Science Center program will help sustain an internationally competitive LTP commu nity in the United States.
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Finding: The demographics in the LTP field show that the leadership class will retire within the next decade with an insufficient number of early career faculty available to assume leadership positions. LTP research is multidisciplinary and the model for hiring university faculty in multidisciplinary fields has produced too few early career faculty with a focus on the fundamentals of LTP science.
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Recommendation: NSF and DOE should expand opportunities to devel op and acquire diagnostics, plasma sources, numerical models, and reac tion mechanisms in support of low-temperature plasmas science, perhaps through the NSF/DOE Partnership in Basic Plasma Science. This effort could be configured similarly to LasernetUS, with support for both equipment and use of the diagnostics, sources, numerical codes and reaction mechanisms.
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