Plasma Science Advancing Knowledge in the National Interest (2007) / Chapter Skim
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4 The Plasma Science of Magnetic Fusion
4 The Plasma Science of Magnetic Fusion
Pages 115-151
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From page 115... ...
Understanding and controlling burning plasmas is an essential step in developing fusion as a source of electricity. In addition to its scientific importance, ITER is expected to be the first magnetic fusion device to generate substantial levels (as much as 500 MW)
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From page 116... ...
The nonplasma fusion sciences and enabling technologies needed to develop an electricity-producing fusion power system are beyond the scope of this report; they are discussed in the report of the Burning Plasma Assessment Committee. Magnetic Fusion: A Brief Description The design and proposed operation of ITER illustrates the key principles, phys ical processes, and terminology involved in magnetic fusion. To introduce these basic ideas and give a context for recent developments, we will refer to the ITER design.
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From page 117... ...
For the size scale, note the small blue standard person shown in the lower left portion of the figure. The hot plasma is enclosed in a magnetic doughnut, whose dominant magnetic field coils encircle the plasma.
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From page 118... ...
magnetic fusion concept improvement experiments in decreasing order of plasma self-organization.
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From page 119... ...
Reducing the plasma turbulence would decrease heat loss and allow for smaller burning plasmas. Research is focused on (1)
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From page 120... ...
Such initiatives would allow the United States to retain its leading role in plasma science within the international magnetic fusion program. ITER needs a deeper understanding of these key plasma physics issues; the party that comes to the ITER table with this expertise will have a strong position in the international magnetic fusion program for at least 15 years.
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From page 121... ...
These concept improvements must develop further during the ITER era and provide a basis for going beyond ITER to commercial fusion power. The goal is to be in a position to define an optimal fusion energy system for the post-ITER phase of magnetic fusion energy development -- a demonstration electricity-producing power plant.
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From page 122... ...
The critical long-term goal of the concept improvement program is to identify and develop a more efficient magnetic configuration for the post-ITER phase of magnetic fusion research. But, the burning plasma and concept improvement parts of the fusion program are not, of course, separate in a scientific sense.
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From page 123... ...
Wang, and H Yuh, "Scaling of electron and ion transport in the high-power spherical torus NSTX," Physical Review Letters 98: 175002 (2007)
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From page 124... ...
However, magnetic fusion research does contribute to the national scientific enterprise in three ways that are not directly part of the primary goal: • Plasma physics: Magnetic fusion relies upon and drives plasma science. The most critical science for fusion is plasma physics. Thus the fusion research program has been the primary driver for development and support of plasma physics, a new discipline of physics, over the past 50 years.
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From page 125... ...
The fusion research program continues to train many young scientists who then move into other areas of plasma science such as space plasma physics, stockpile stewardship, inertial confinement fusion, and plasma processing of microprocessors. The NRC report An Assessment of the Department of Energy's Office of Fusion Energy Sciences Program (2001)
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From page 126... ...
form in the magnetic fields, bringing hot plasma into contact with relatively cool material surfaces and/or dilut ing the hot central plasma with cool plasma from closer to the edges of the device. Boxes 4.1 and 4.2 describe two important examples of success in understanding, calculating, and suppressing important macroscopic instabilities.
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From page 127... ...
If energy diffused from the hot, central tokamak plasma to the relatively cool periphery via particle collisions alone, then the projected energy confinement time in ITER plasma would be hundreds of seconds, not three. However, this is not expected since at fusion temperatures energy diffusion across the magnetic field in a nearly collisionless magnetized plasma is dominated by small-scale microturbulence.
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From page 128... ...
McGuire, M.C. Zarnstorff, and TFTR group, "Observation of nonlinear neoclassical pressure-gradient-driven tearing modes in TFTR," Physical Review Letters 74: 4663 (1995)
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The Plasma Science of Magnetic Fusion 129 (c) Threshold reached Island width (cm)
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Courtesy Unstable of General Atomics and Princeton Plasma Physics Laboratory.
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From page 131... ...
at much higher pressure and fusion power than is otherwise achievable. For the low plasma rotation values expected on ITER, RWM stabilization may B.42c require active magnetic feedback control and is presently being prototyped on several devices.
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From page 132... ...
. The perturbed magnetic field lines no longer isolate the plasma from the boundary, and charged particles traveling along the field lines can wander out of the device.
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Such full-body diagnostics will reveal the global structure and the mesoscale correlations. Boundary Plasma Properties and Control In a magnetic confinement device, the bulk of the plasma is kept away from material structures for two distinct reasons.
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NOTE: PCI, phase contrast imaging; AU, atomic units. the plasma and the plasma facing components come into conflict as never before.
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From page 135... ...
PCI Viewing Geometry Spectrum of Density Fluctuations Integration over parts of flux tube viewed by PCI due to Trapped Electron Modes 0.5 PCI laser chords 3 10 kθ [A.U.]
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From page 136... ...
Such a liquid wall may act like a sponge soaking up particles exiting from the plasma without returning any cold particles. This raises the possibility of hotter plasma edges and vastly improved plasma performance.
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From page 137... ...
(d) Opportunities in Boundary Plasma Properties and Control The chief goal of research in boundary plasma properties is to find a stable regime where plasma and heat can be removed from the plasma and collected fig B.4.4 a,b,c,d without damage by material surfaces.
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From page 138... ...
Such magnetic chaos occurs in a toroidal laboratory plasma, the reversed-field pinch, as illustrated in the field line puncture plot (a) inferred from scaled computer modeling of the experiment.
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From page 139... ...
The Plasma Science of Magnetic Fusion 139 8 Overlap parameter 6 (c) 4 2 0 0.0 0.2 0.4 0.6 0.8 1.0 Radius 10000 Thermal diffusivity (m2/s)
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From page 140... ...
(c) Photograph and theoretical model of an unstable edge mode that has coalesced into singular plasma filaments aligned along and carrying a magnetic field line.
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From page 141... ...
(d) Wave–Particle Interactions in Fusion Plasmas Hot magnetized plasma supportsB.4.6 variety of waves that can exchange fig a huge a,b,c,d energy and momentum with the plasma particles.
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High-k MC waves are predicted to be capable of gen erating sheared plasma flows and could ultimately provide a powerful tool for efficiently controlling plasma microturbulence and therefore the fusion gain in burning plasmas.
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The Plasma Science of Magnetic Fusion 143 1.0 MC Waves FW ñ eL (AU)
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VanZeeland, and L Zeng, "Multitude of core-localized shear Alfvén waves in a high-temperature fusion plasma," Physical Review Letters 96: 105006 (2006)
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The Plasma Science of Magnetic Fusion 145 (b)
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From page 146... ...
Conclusions and Recommendations FOR THIS TOPIC The U.S. decision to rejoin ITER is recent, and the magnetic fusion program is beginning to evolve into the burning plasma era.
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From page 147... ...
Taking advantage of this opportunity to significantly advance plasma measurements should be a key priority of the magnetic fusion program. Most of the advances in modeling plasmas originated from the development of tractable reduced models, helped by the astonishing increase in computational power.
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From page 148... ...
The next large step in magnetic fusion research is to measure and explore the properties of burning plasmas. This step has been greatly facilitated by the U.S.
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From page 149... ...
Conclusion: To ensure that the magnetic fusion program can progress be yond ITER to electricity-producing fusion power, it is essential that research in concept improvement and innovation continue. To hasten fusion energy development, a demonstration reactor must follow the completion of the burning plasma research mission on ITER.
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From page 150... ...
The committee notes that the U.S. magnetic fusion science community has made several efforts to develop plans for the future, most recently in two reports of the Fusion Energy Science Advisory Committee: Scientific Challenges, Opportu nities, and Priorities for the U.S.
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From page 151... ...
utilization of the major magnetic fusion research facilities is expected to continue. These projections make it difficult for the United States to close the growing gap between newer, more capable intermediate-scale facilities being built abroad and the aging U.S.
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