Plasmas and Fluids (1986) / Chapter Skim
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1. Introduction and Executive Summary
1. Introduction and Executive Summary
Pages 1-35
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Plasma physics combines concepts from electromagnetism, fluid physics, statistical mechanics, and atomic physics into a unified methodology for the study and practical use of the nonlinear collective interactions of charged particles with one another and with electric and magnetic fields. · The most important applications of plasma physics are to fusion and space research, which have stimulated many recent advances in plasma science.
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. · The concepts and techniques of fluid physics find widespread use In plasma physics, atmospheric science, oceanography, solid-earth geophysics, astrophysics, biology, and medicine; in problems in laser physics, combustion, and pollution control; and in the engineering of transportation and defense systems, among others.
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An adequate level of basic research, free from short-term, applicationoriented goals, should be established in order to provide the foundations for future scientific advances and new technologies. In addition, the Panel makes the following recommendation to the academic community: · In view of the increasing precision of the experimental and theoretical techniques of plasma and fluid physics, and their many applications, we strongly recommend that senior-level courses in plasma physics and fluid physics become a required part of university physics curricula.
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Two powerful motivations stimulated the growth of plasma physics after 1960. Fusion research seeks a source of energy accessible to human use that will last for a time comparable with the present age of the Earth.
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However, the energy confinement time was orders of magnitude lower than that required for net energy production. The simultaneous achievement of high temperatures, densities, and confinement times similar to the plasma conditions at the centers of stars required significant improvements in forming and understanding plasmas confined by magnetic fields or by inertial techniques.
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Not only does plasma physics describe both solar-system and astrophysical phenomena, but the solar system has become a laboratory in which astrophysical processes of great generality can be studied in situ. The study of plasmas beyond the solar system has developed more slowly than space plasma physics for a fundamental reason: the microscopic plasma processes that regulate the behavior of distant astrophysical systems cannot be observed directly, as they can in space and in the laboratory.
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RELATIVIST I C PLASMA Magnetic Fusion Solar Co rona Solar Wind IDEAL CLASSICAL PLASMA Inertial Fus ion kBT~E ~Discharges ~i ~nX3 = I NO NOTICEABLE IONIZATION 1~1 1 , , , 1 , , /EF = kBT / DEGENERATE QUANTUM PLASMA lo, ,, Electron ,, Gas in Metals EF=e2/n l/3 Wh its Dwa rfs _ ~ 1 103° pulsars to the extremely dense, cold, degenerate quantum electron plasmas in white dwarfs. As a guide to Figure 1.1, we consider a plasma with average number density n and mean kinetic energy (3/2)
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, the correlations due to Coulomb interactions are strong, and such systems are modeled by numerical simulation on high-speed computers. Fluid Physics*
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The pacing element for advances in many applications such as the efficiency of flight, the effectiveness of heat engines, and the productivity of chemical processing systems is our understanding of the fundamentals of fluid motion. There are striking examples in the machines of engineering as they exist today, compared with even the recent past, that measure the magnitude of the advances in our understanding of fluid physics.
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A striking example is the minimal support for basic research in laboratory plasmas by the National Science Foundation. · Because fundamental understanding of plasma properties precedes the discovery of new applications, and because basic plasma research can be expected to lead to exciting new discoveries, increased support for basic research in plasma physics is strongly recommended.
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· The impact of plasma physics on related sciences and on technology has continued to grow since the birth of modern plasma physics in the late 1950s and will continue to grow for the foreseeable future, provided a strong research base for plasma physics is maintained by an adequate level of support. Fusion Plasma Confinement and Heating We divide the major findings and recommendations into those that pertain to magnetic confinement, in which strong externally applied magnetic fields are used to confine a high-temperature fusion plasma, and those that pertain to inertial confinement, in which a solid pellet is imploded to ultra-high densities.
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* Magnetic Fusion Advisory Committee Recommendations on the Tokamak Fusion Core Experiment, Department of Energy (July 1984)
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INERTIAL CONFINEMENT The United States has maintained world leadership in inertialconfinement fusion research since its inception in the late 1960s. Its near-term applications are military, with promising long-term applications to energy production.
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Plasma processes in this environment also influence and even disrupt important ground-based systems over local and regional scales. · The solar system, including the Sun itself, is the primary laboratory in which astrophysical processes of great generality can be studied in situ; these processes include magnetic reconnection, plasma heating and particle acceleration, magnetohydrodynamic wave generation and propagation, magnetoconvection, magnetoturbulence and turbulent magnetic-field diffusion (including spatially intermittent magnetic fields)
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· In view of the increasing precision of its experimental and theoretical techniques, and in view of its wide applicability to space physics, astrophysics, and technology, we recommend that plasma physics become a regular part of the university science curriculum. · In view of the many common processes underlying both laboratory and space plasmas, such as reconnection of magnetic field lines and particle acceleration by plasma waves, there should be an expanded effort to simulate space- and astrophysical-plasma processes in the laboratory.
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· Access to major computational and experimental research facilities in fluid physics is limited. The computer has emerged as a significant tool whose applications range from the rapid organization of data and its subsequent analysis and display to the direct numerical simulation of the major features of limited volumes of turbulent flow.
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· Funding for basic research in fluid physics comes from a wide variety of sources, but the field lacks an individual national identity. Despite the common technical threads that bind fluid physics as a scientific discipline, its basic research support is poorly organized and lacks quantity, continuity, and the early recognition of significant new opportunities.
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General Plasma Physics SIGNIFICANT RECENT ACCOMPLISHMENTS Selected significant accomplishments in general plasma physics during the past decade include the following: · Major advances in understanding the physics of nonlinear (i.e., large-amplitude) plasma phenomena.
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FUTURE RESEARCH OPPORTUNITIES Particularly promising research areas are summarized below: · Development of new particle accelerators of two types: first, high-current accelerators that necessarily involve collective effects, that is, electric and magnetic fields generated by charged particles; second, accelerators employing the intense electromagnetic fields generated by high-power lasers to achieve ultrahigh particle energies. · Further development of free-electron radiation sources, to produce tunable radiation sources, some of exceptionally high-power output.
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Fusion Plasma Confinement and Heating SIGNIFICANT RECENT ACCOMPLISHMENTS MAGNETIC CONFINEMENT The last decade saw greater progress than any previous decade in fusion's history. Many of the most significant accomplishments were achieved within the U.S.
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· The successful use, in accordance with theoretical prescriptions, of radio-frequency waves to drive plasma currents in tokamaks, thereby permitting confining magnetic fields to be steady state, a property of importance to the practicality of tokamak reactors. Experiments on radio-frequency current drive have exhibited a hot-electron population of current carriers in agreement with theory and have verified the predicted dependence of current-drive efficiency on plasma density.
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. FUTURE RESEARCH OPPORTUNITIES MAGNETIC CONFINEMENT Now that magnetic confinement has been shown to be a viable fusion concept, at least qualitatively, the future emphasis of magnetic fusion research will be on quantitative questions: What are the precise laws governing the fine-scale stability and rate of transport of hot plasma from practically configured magnetic confinement systems, and how are such systems to be optimized?
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All of these advances depend critically on improved understanding of the dynamics of confined plasmas. · Increased fundamental understanding of hot plasmas made possible by, and contributing to, these advances in fusion research.
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Pellet shells must be uniformly imploded at high speeds and yet remain cold to compress the fuel properly. · Deuterium-tritium fuel in laser-irradiated pellets was heated to thermonuclear temperatures early in inertial fusion research.
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FUTURE RESEARCH OPPORTUNITIES INERTIAL CONFINEMENT Many scientific and technological issues will be addressed with the hundred-kilojoule drivers that will be available in the mid-1980s, while others await megajoule systems. Future research opportunities in inertial fusion include the following: · Detailed tests of the improved laser-plasma coupling with shortwavelength light will be made.
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· Detailed observations of the solar surface have forced a reevaluation of our current theoretical understanding of hydrodynamic and magnetohydrodynamic flows: in consequence, sophisticated analytical and numerical models that aim to describe the observed highly intermittent magnetic fields on the solar surface have been initiated. · The detection by the Einstein Observatory spacecraft of stellar coronal x rays proved that solarlike magnetohydrodynamic and plasma processes are central to the physics of the atmospheres of all stars that have convecting outer layers.
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· Detection of an x-ray line, plausibly at the electron cyclotron frequency, provided the first experimental indication that neutron stars have superstrong magnetic fields, of order 10~2 gauss a fundamental hypothesis of pulsar and galactic x-ray source theories. · Energetic plasma jets were found to occur in a wide range of astronomical objects, from compact stars to active galaxies and quasars.
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Such models will likely make plasma physics central to the interpretation of many astronomical observations and motivate new and different kinds of observations. Fluid Physics SIGNIFICANT RECENT ACCOMPLISHMENTS During the past decade, significant research accomplishments in fluid physics included the following: · The revolutionary development of computational fluid dynamics, which has made possible the solution of problems that previously defied theoretical analysis and experimental simulation, such as convection and circulation within the Sun and planetary atmospheres, and the nonequilibrium flow surrounding the Space Shuttle on re-entry.
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· Dimensional analysis and recent theoretical understanding of jet noise, acoustic damping, and turbulent flows led to a thousandfold reduction in the energy of acoustic emissions from aircraft, resulting in major reductions in perceived noise levels. · An accelerated pace of accomplishment in understanding highspeed flows has been made possible by improved analytical tools, numerical simulation, and new experimental techniques.
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FUTURE RESEARCH OPPORTUNITIES During the next decade, the expected research opportunities and accomplishments in fluid physics include the following: · Rapid advancement in the basic understanding of the characteristics and origins of turbulence, including investigations of the connection between the routes to chaos found for systems with a finite number of degrees of freedom and the continuous instability that is fluiddynamic turbulence. · Improvements in the ability to control turbulent flows will lead to novel drag and noise-reduction techniques; increased combustion efficiency; and control of separation, spreading, and mixing.
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· We expect to see major advances in the understanding of multiphase flow systems, including the macroscopic and microscopic interface phenomena of interest in both industrial and geological processes, for example, the stability of the liquid-liquid interface leading to fingering in oil recovery, convective processes in the ocean, and the formation of layered structures in magma chambers. · There will be increased interest in denser particulate systems, from the multiparticle interaction of finite clouds of particles to, more generally, the flow through porous media and filters based on the hydrodynamic interaction with their microstructure.
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The incremental funding and manpower required to carry out the recommended research programs over the next 5 years are delineated in subsequent chapters. Specific areas in which there is a critical manpower shortage are also identified (e.g., coherent radiation generation, atomic physics, basic experimental plasma physics, computational plasma physics and fluid dynamics, and plasma astrophysics)
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Magnetic471 - - 47 lb (b) Inertial170 - l70C Space and astrophysical2 30 5 100 2 1394 plasmas Fluid physics25 80e 170 110 42 427f a DOD funding total includes: $4 million, ONR; $36 million, DARPA; $6 million, AFOSR; $1.6 million, ASD (Wright-Patterson)
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in magnetic fusion research. Similarly, the major part of inertial confinement research is carried out at national laboratories (Livermore, Los Alamos, and Sandia)
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Fluid Physics Fluid physics, consistent with the unusual breadth of its applications (aeronautics, weather, and oceanography, for example) , derives its support from a variety of agencies, notably NSF, NASA, the Air Force Office of Scientific Research, the Office of Naval Research, the National Oceanic and Atmospheric Administration (NOAA)
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