Plasma Science Advancing Knowledge in the National Interest (2007) / Chapter Skim
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6 Basic Plasma Science
6 Basic Plasma Science
Pages 184-216
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From page 184... ...
Of particular interest, for example, are the six fundamental processes highlighted in Chapter 1: multiphase effects in plasmas; explosive instabilities; particle acceleration mechanisms; turbulence and turbulent transport, magnetic reconnection and magnetic self-organization; and the effects of strong particle correlations in plasmas. These and many other important plasma effects manifest themselves in a wide range of situations, from dusty plasmas to HED plasmas.
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From page 185... ...
Understanding the fundamentals of plasma behavior over such enormous ranges of parameters presents huge challenges. Here the committee discusses progress and future opportunities in eight topics: • Nonneutral and single-component plasmas, • Ultracold plasmas, • Dusty plasmas, • Laser-produced and HED plasmas,
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From page 186... ...
. Whether a plasma is strongly or weakly coupled is determined by the ratio, BOX 6.1 The Dynamic Forefront of Research -- New Opportunities Many of the current forefront areas in basic plasma research (dusty plasmas, HED plasmas, micro plasmas, and ultracold plasmas)
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From page 187... ...
Examples in which strongly coupled plasma phenomena are important and frequently dominant include pure ion plasmas, ultracold plasmas, dusty plasmas, and laser-produced HED plasmas. A further distinction is the regime in which quantum mechanical effects are important.
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From page 188... ...
FIGURE 6.1 Evolution of vortex turbulence in a pure electron plasma. These magnetically confined plasmas flow across the magnetic field in direct analogy to the flow of an incompressible fluid with an unusually small viscosity.
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From page 189... ...
The spectacularly successful test of this theory is shown in Figure 6.2 for a cold ion plasma at a temperature ~3 mK and Γ > 500. Other important recent results include the creation of antiproton and positron antimatter plasmas, studies of energy transport through long-range collisions, and studies of the intrinsic thermodynamics of these systems.
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From page 190... ...
For example, plasma rotation, which is a zeroth-order effect in single-component plasmas owing due to their space charge, is known to play an important role in confinement in tokamak plasmas. Ultracold Neutral Plasmas Ultracold plasmas provide qualitatively new opportunities for plasma science, ranging from the study of spatial ordering in new plasma regimes, to the study of novel atomic physics processes, to the development of techniques to produce and study antihydrogen.
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From page 191... ...
Dusty Plasmas Dusty plasmas are ionized gases containing small (i.e., micron-size) particles of solid material.
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From page 192... ...
Techniques making use of the new understanding of dusty plasmas were developed to control this contamination. Another area of great practical importance is dust in tokamak fusion plasmas, where sputtered materials can condense to form dust particles.
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From page 193... ...
Another important issue is the nature of waves and transport in dusty plasmas of astrophysical interest. Finally, study of dusty plasmas in large magnetic fields would enable tests of theoretical predictions for new classes of dusty plasma phenomena.
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From page 194... ...
This section describes recent progress and the wealth of opportunities that exist for future research. Several of these examples illustrate the synergistic relationship between pure and applied research -- for one thing, novel plasma phenomena are frequently being used as innovative research tools in many areas of science and engineering: • Beam physics. Whereas plasmas in thermal equilibrium are Maxwellian distributions, relativistic beams are typically non-Maxwellian in that dif ferent temperatures exist in the perpendicular and parallel directions.
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From page 195... ...
Note the dramatic narrowing of the beam energy distribution in (B)
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From page 196... ...
Gases of nanoplasmas could be used to study radiation transport under optically thick conditions relevant to solar, astrophysical, FIGURE 6.6 Simulation of a cluster nanoplasma and subsequent femtosecond timescale explosion due to Coulomb repulsion of the highly charged ions. Spatial distribution of the plasma ions (in units of the initial ion spacing ∆ = 1.6 nm)
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From page 197... ...
The associated gigagauss magnetic fields help to confine the plasma. Estimates indicate positron densities ~10–3 of the background electron density (i.e., ~1022 cm–3)
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From page 198... ...
198 FIGURE 6.7 Ultrafast laser-accelerated protons used as a plasma diagnostic. Left: The experimental setup.
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From page 199... ...
The challenge for basic plasma science is to isolate the underlying physical mechanisms and develop predictive theories of the turbulence. Considerable progress has been made recently in understanding important aspects of plasma turbulence, and new computational, theoretical, and experimental tools offer great opportunities for progress in the coming decade.
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From page 200... ...
They propagate in the direction perpendicular to the magnetic field and perpendicular to the gradients in plasma density and temperature. Early experiments elucidated the linear and weakly nonlinear properties of these waves.
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From page 201... ...
Shown in Figure 6.10 are data from a recent laboratory study of this phenomenon. Zonal Flows and Transport Barriers In magnetically confined plasmas, the magnetic field inhibits the flow of heat from the hot core of the plasma to the edge.
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From page 202... ...
Dynamo Action, Reconnection, and Magnetic Self-Organization Magnetic fields play a critical role in many plasmas, so understanding their behavior is a central issue in basic plasma science. This subsection describes stud ies of three key questions: How can magnetic fields be generated through dynamo action?
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From page 203... ...
6.11 right FIGURE 6.11 Observation of dynamo action in the laboratory, with a magnetic field generated spontaneously by a helical flow pattern in liquid sodium. Left: Schematic diagram of the experiment.
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From page 204... ...
At small spatial scales, the motions of the electrons and ions in the presence of a magnetic field cause charge separation and decoupling of the motions of the electrons and ions, which now act as two interpenetrating fluids and render MHD models invalid. The smoking gun signature of fast reconnection is the self-generated, out-of-plane, quadruple component of magnetic field.
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From page 205... ...
Courtesy of M Yamada, Princeton Plasma Physics Laboratory.
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From page 206... ...
Plasma Waves, Structures, and Flows The focus of this section is recent studies of fundamental plasma processes such as particle acceleration and plasma instabilities, which can drive plasma waves, structures, and flows. Experiments can now provide measurements of relevant quantities, including the electrical potential, density, magnetic field, and particle distribution functions -- all at thousands of spatial locations and at very high data acquisition rates to allow comparison with new theories and a new generation of plasma simulations.
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From page 207... ...
Applications include understanding the aurora, the solar wind, coronal mass ejections from the Sun, and fusion plasmas.
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From page 208... ...
(b) Magnetic field of expansion-driven Alfvén waves downstream.
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From page 209... ...
Improved Methodologies for Basic Plasma Studies A number of developments over the past decade hold much promise for future progress. Experimental and technical capabilities continue to expand.
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From page 210... ...
Conclusions and Recommendations FOR THIS TOPIC Many important new research opportunities in basic plasma science come about from progress and new discoveries in the last decade. Such opportunities ex ist for studies in dusty plasmas, a new generation of laser-driven and HED plasmas, and micro- and ultracold plasmas, in addition to studies of new and fundamental aspects in areas such as Alfvén-wave physics and magnetic reconnection and self organization.
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From page 211... ...
The program has become a critical source of funding for basic plasma research and is responsible for much of the progress described in this chapter. In parallel, OFES created a General Science Program to fund basic research at DOE laboratories and a very successful Young Investigator Program to fund research by junior faculty at colleges and universities.
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From page 212... ...
Conclusion: The collaborative partnership for basic plasma science and engineering between the National Science Foundation and Department of Energy has been critical to progress in basic plasma science. Focusing on single-investigator and small-scale research and aided by an effective sys tem of peer review, it is an efficient and effective instrument to fund basic plasma research.
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From page 213... ...
There is much forefront, fundamental plasma science research that requires intermediate-scale facilities -- experimental facilities larger than can be easily fielded by a single investigator but smaller than those at the larger national research installations. A recent and successful example of such an intermediate-scale experimental research effort is the creation of a national facility to study basic plasma problems that require large volumes of magnetized plasma.
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From page 214... ...
This project can be regarded as a model for addressing basic plasma science problems that require facilities larger than required by the typical effort of a single principal investigator. During the course of the committee's work, the plasma community indicated that other scientific problems would benefit from intermediate-scale facilities of this type.
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From page 215... ...
Recommendation: The plasma community and the relevant federal gov ernment agencies should initiate a periodic evaluation and consultation process to assess the need for, and prioritization of, new facilities to address problems in basic plasma science at the intermediate scale.
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