An Assessment of the Department of Energy's Office of Fusion Energy Sciences Program (2001) / Chapter Skim
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Plasma Confinement Configuration
Plasma Confinement Configuration
Pages 45-61
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From page 45... ...
Plasma behavior is determined in large part by the spatial structure of the confining magnetic field. The experimenter can manipulate the magnetic field to vary crucial properties such as curvature, field line pitch, field strength (relative to plasma pressure)
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From page 46... ...
The four physics challenges that the committee has selected are neither exhaustive nor necessarily optimal for planning purposes; rather, they are illustrative, and the actual development of a complete set of physics issues is left to the research community. Understand the Stability Limits to Plasma Pressure All plasma configurations possess an upper limit on the pressure (product of plasma density and temperature)
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From page 47... ...
to stabilize the plasma while using a poloidal field created by a toroidal plasma current to confine the particles. The final configuration includes a large vacuum vessel to isolate the hot plasma from the surrounding environment (bottom)
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From page 48... ...
The continuing challenge is to develop a quantitative understanding of the nonlinear evolution of instabilities, of the relationship of stability to properties of the magnetic field (such as magnetic curvature and shear) , and of additional effects on stability that cannot be treated within the MHD fluid model (such as the effects of large particle orbits, separate electron and ion dynamics, and energetic particles)
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Understand Classical Plasma Behavior and Magnetic Field Symmetry The transport of particles through the plasma arising only from collisional interactions between particles (two-particle correlations) is referred to as classical transport.
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The magnetic topology includes a reversal of the toroidal field inside the plasma owing to plasma currents. Under normal inductive current drive, the magnetic field lines can readily become chaotic, as indicated by a puncture plot of the field lines as they traverse a poloidal plane (bottom left)
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In a plasma containing fusion reactions, a state can be reached in which the plasma is self-sustaining: the alpha particles produced in the fusion reaction deposit their energy back into the plasma at a rate sufficient to keep the plasma at a fixed temperature. In such a burning plasma, the external heating can be turned off and the plasma will undergo fusion burn continuously until the fuel is exhausted.
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has relatively simple helical symmetry and multiple harmonics in the field strength along a field line (b) , which in turn gives rise to large particle losses.
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Thus, the United States must soon explore options for pursuing alpha-particle physics issues, possibly as a part of an international team. REACTOR DESIGN FEATURES MOTIVATING FUSION CONCEPT DEVELOPMENT In the last section, physics questions were discussed that motivate research employing a variety of plasma configurations and that can serve as organizing elements for a program of multiple confinement configurations.
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54 AN ASSESSMENT OF THE DEPARTMENT OF ENERGY'S OFFICE OF FUSION ENERGY SCIENCES PROGRAM OFIGURE 3.5 Improvements in plasma stability and confinement obtained in magnetic confinement configurations should allow the study of burning fusion plasmas in the near future. The Lawson fusion parameter is the product of the plasma density, ion temperature, and average confinement time and represents a simple figure of merit for proximity to conditions for fusion ignition.
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· Understand classical plasma behavior and the role of magnetic field symmetry. The magnetic field within plasmas that lack symmetry can be produced without externally driven current.
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As mentioned earlier, the United States should begin to reestablish its international leadership role by defining an affordable burning plasma experiment that could be constructed with financial contributions from several international partners. ENABLING TECHNOLOGIES FOR PLASMA CONFIGURATION DEVELOPMENT This report focuses on the scientific aspects of fusion concept development.
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CURRENT METRICS FOR FUSION CONCEPT DEVELOPMENT FESAC has defined three stages for the experimental development of a fusion concept, beginning with the concept exploration stage (initial experiments to investigate, at a small scale, isolated physics features of a concept) , the proof-of-principle stage (with medium-sized experiments aimed at investigating the broad range of key physics issues)
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However, the categories mainly relate to the progress of individual confinement concepts toward a fusion power reactor and not to progress on understanding fundamental, cross-cutting science issues. Thus, alongside these FESAC categories of concept development, a parallel set of scientific questions should be developed, as was proposed earlier in this chapter.
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The present set of categories (concept exploration, proof of principle, performance extension) describes the progress of individual fusion concepts towards a fusion power reactor but does not reflect progress in cross-cutting scientific issues.
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Determining the optimal route to a burning plasma experiment is beyond the scope of the committee' s charge; rather, the route should be decided in the near future by the fusion community. Resources above and beyond those for the present program will be required.
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