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LOW-TEMPERATURE PLASMAS 40 generation community is mostly industrial, and much of this work has been performed by Textron Defense Systems (formerly the Avco Everett Research Laboratory). There is some university involvement, such as the work at the University of Tennessee Space Institute. Workers in the field are generally engineers with plasma and fluid, thermoscience, mechanical engineering, or electrical engineering backgrounds. There are several technological opportunities for applications, including electric power plants; multimegawatt portable power supplies for land, air, or space uses; high-enthalpy test facilities for testing high-speed propulsion systems; magnetoplasmadynamic (MPD) thrusters for space vehicles; and MHD boost of oxygen-fuel jets in coating applications. The ultimate users of MHD power generation technology may be the utilities and independent power producers who generate electric power and who seek economic and environmentally benign methods of generating it. Major achievements during the past 10 years include the development of equipment capable of operating for long durations and a greater understanding of the physical phenomena associated with the corrosion and erosion of plasma- facing surfaces. Industry has played a key role in the engineering development of components and subsystems of power-generating systems for proof-of- concept demonstrations. The ultimate objective of this work is commercialization of the technology. The science community involved in this area is small. There is a need for a better understanding of basic MHD phenomena. Specific needs include a detailed understanding of conditions that lead to plasma instabilities at high power densities; better understanding and analysis of electric discharges in flowing, reacting gases; analysis and experiments to better understand electrode and boundary layer phenomena in the presence of strong magnetic fields, slag- layer shorting effects, and associated electrical nonuniformities; and a better understanding of scaling laws. Additional research could also foster the development of high-temperature, nonslagging channel walls and high- temperature direct-fired air preheaters. PLASMAS FOR POLLUTION CONTROL AND REDUCTION With the increased concern for the environment, the use of plasmas for pollution control and reduction is predicted to be an area of considerable growth in the next decade. In particular, American industry is beginning to realize the importance of low-temperature plasmas for pollution control (e.g., flue gas treatment, air toxics treatment), while international efforts at pilot-plant scale are much more advanced. At present, researchers in this community are focusing mainly on studies of the plasma chemistry and discharge physics of nonequilibrium plasmas. The plasmas are usually created by electrical or electron-beam-driven discharges. This field is very old in terms of the phenomenological un
LOW-TEMPERATURE PLASMAS 41 derstanding of the phenomena involved and the identification of potential practical applications. Modern research in this field is highly applications oriented, with basic research focused primarily on the measurement and computer-based modeling of transient events. Applied research in this area is divided between a fundamental approach, involving basic discharge physics and plasma chemistry, and an Edisonian approach, centered on plasma-based pollution control devices. Nonequilibrium plasma technology has been applied to the chemical processing of gaseous media for more than a century. Two major applications are chemical synthesis, exemplified by ozone generation, and the removal of undesirable compounds from flue gases, exemplified by the electrostatic precipitator. During the past two decades, interest in applying nonequilibrium plasmas to the removal of hazardous chemicals from gaseous media has been growing, particularly because of heightened concerns over the pollution of our environment and a growing body of environmental regulations. These more recent applications have involved efforts to destroy toxic chemical agents, to remove harmful acid rain gases such as sulfurous and nitrous oxides, and to treat other environmentally hazardous hydrocarbon and halocarbon compounds. Major contributions in the last 10 years include the decontamination of wastewater, flue/stack gas processing for SO2 and NOx reduction, military applications (nerve agent destruction), and toxic chemical/vapor processing. Industry is a potential user and market for plasma technology for pollution control. The utility industry is faced with more stringent environmental regulations, which demand improved technology for effluent cleanup (both for power plants and for utility customers). Industry can play a strong role as an advocate for technology development and as a technical contributor by working cooperatively with researchers in the field on applications. Many institutions are actively involved in this area, including Lawrence Livermore National Laboratory, Los Alamos National Laboratory, Sandia National Laboratories, and several universities and industrial laboratories. To date, funding in this area has been small, but given the increasing concern about environmental issues, it could increase dramatically in the next decade. There is much that has to be learned before low-temperature plasmas can be used in the cleanup and preservation of the environment. This includes developing a better database for plasma chemical processes, reaction-rate constants, and the resulting products, and developing diagnostics to determine the physics and chemistry of the cleanup process. There are many scientific and technical opportunities, including developing basic plasma data on the reaction of excited states and radicals with various contaminants and sophisticated modeling of the physics and chemistry of plasmas they apply to the cleanup problem. Fortunately, there are many facilities in the various national laboratories, universities, and industry that can be used to perform the initial proof-of-principle experiments. There is a strong synergism between environmental applications and the many other disciplines that also depend on low-temperature plasmas.
