Burning Plasma Bringing a Star to Earth (2004) / Chapter Skim
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4 Program Structure and Balance
4 Program Structure and Balance
Pages 88-132
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From page 88... ...
On the basis of these considerations, and given the centrality of a burning plasma experiment to the development of fusion energy, the committee affirmed in December 2002 in its interim report and reaffirms here its recommendation that the U.S. fusion program participate in a burning plasma experiment.
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From page 89... ...
The Department of Energy's fusion pro gram must be designed both recognizing this timescale and addressing the impor tance of balancing the pursuit of the other critical issues of fusion science needed to establish the basis for fusion energy. In its interim report, the committee listed some minimal level of participation in the ITER program to which the U.S.
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From page 90... ...
fusion science program, including a burning plasma experiment, the committee presents in this chapter a discussion of the domestic fusion science research program. The outstanding compelling scientific issues fac ing the program are considered in the following major section, entitled "Fusion Science Issues and Research Portfolio," and how elements of the program will address these issues is discussed in the section after that, "Research Opportunities and Science and Technology Goals for the Domestic Fusion Program." Developing any energy source is a long and difficult task.
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From page 91... ...
fusion program, this requires advances in the fusion science of plasma confinement and fusion technol ogy. For magnetic confinement, the key overarching goals for achieving attractive fusion energy are these: · Maximize the plasma pressure, · Maximize the plasma energy confinement, · Minimize the power needed to sustain the plasma configuration, and · Simplify and increase reliability of the overall system.
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From page 92... ...
. A burning plasma experiment is a crucial step for the development of fusion science and technology.
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From page 93... ...
The ST and advanced tokamak experiments use geometrical variations and increasingly sophis ticated active control tools to optimize the performance and confinement efficiency of the plasma. These two types of devices are stabilized by relatively strong external magnetic fields, but also include significant plasma current and some self-organiz ing features of plasma behavior.
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From page 94... ...
Some efforts- referred to as advanced tokamak research -- involve modifications to the tokamak, leading to improved steady state. In addition, the current program includes re 4The ARIES program is a national, multi-institutional research activity for performing advanced integrated design studies of the long-term fusion energy embodiments to identify key research and development directions and to provide visions for the fusion science program.
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From page 95... ...
The discussion here focuses on the impor tance of these issues to the progress of the understanding of fusion science from the perspective of a non-burning-plasma program. How a burning plasma experi ment, such as ITER, might address some of these questions was discussed in Chap
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From page 96... ...
Further improvements in the under standing of plasma turbulence will enable better configuration designs. Stability Limits to Plasma Pressure Increasing the plasma pressure that can be confined stably is key to developing more attractive fusion energy.
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From page 97... ...
Stochastic Magnetic Fields and Self-Organized Systems In configurations in which plasma currents dominantly produce the magnetic field, or in which the plasma is unstable owing to tearing (or reconnection) insta bilities, the magnetic field can become stochastic or turbulent.
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From page 98... ...
Toroidally symmetric configurations -- including the tokamak, spherical torus, and reversed-field pinch -- create part or most of the magnetic field using plasma current. This current must be generated either by the plasma pressure (the bootstrap current for the tokamak and spherical torus)
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From page 99... ...
Theoretically, the pressure limit in stellarators can be relatively insensitive to the detailed profiles of pressure and the bootstrap current. This compatibility with steady state is a signifi cant motivation for investigating stellarator plasmas for fusion energy.
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From page 100... ...
The recent DOE Integrated Program Planning Activity5 and the Snowmass studies by the fusion community itself6 have described challenges and research opportunities for nonburning plasma fusion science. The DOE Integrated Program Planning Activity plan for the fusion program is organized around a detailed set of scientific issues and objectives.
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From page 101... ...
fusion program goals and international fusion activities. Nevertheless, the committee agrees that, generally, the aggregate level of activity implied below is needed both to support the move to a burning plasma program and to maintain a vibrant, productive domestic research program that is making progress toward the long-range goal of establishing the knowledge base for fusion energy.
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From page 102... ...
102 B U R N I N G P L A S M A Shot 110493 at 3500 ms 3500 3000 2500 2000 [eV]
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From page 103... ...
· Steady-state and advanced tokamak operating regimes. The tokamak would be much more attractive as a fusion energy source if it were able to operate in steady state.
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From page 104... ...
Associ ated with these phenomena is the need to understand the generation of electric fields in the plasma -- these can either be spontaneously generated or externally driven -- since they can profoundly affect the turbulence and thus the resulting plasma confinement. Theoretical models and experimen tal measurements for short-wavelength turbulence, which is predicted to play the most important role in electron transport, are just beginning to be developed.
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From page 105... ...
New measurement techniques must also be developed; for example, a method is needed to measure the confined and escaping alpha-particle dis tributions in the burning plasma. These techniques must be developed and tested on ongoing experiments to avoid costly delays in undertaking burn ing plasma experiments.
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From page 106... ...
In addition, these experiments will expand to investigate wider ranges of plasma shape and stability limits so as to test the fundamental understanding of possible AT regimes. In summary, the major goals of the advanced tokamak program are these: · To demonstrate integrated advanced tokamak scenarios with current sus tained dominantly by the bootstrap current and enhanced confinement at high pressure, and to develop predictive understanding of AT regime acces sibility and control; · To develop techniques to control plasma current, pressure, flow, and trans port profiles while maintaining plasma stability in this highly nonlinear, self-organizing regime; · To develop radiative divertor operation regimes that can minimize power deposition and maintain helium pumping in low-density AT operational regimes compatible with external current drive;
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From page 107... ...
The ST may provide a reduced-cost path to the development of fusion energy if the central induction solenoid can be eliminated through the development of start-up and sustainment techniques. In summary, the major goals of the spherical torus program are these: · To test MHD stability theory at conditions of extreme toroidicity in order to elucidate physics of very high normalized plasma pressure and high frac tion of self-generated (bootstrap)
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From page 108... ...
In summary, the major goals of the reversed-field pinch program are these: · To demonstrate the generation of RFP equilibria without a dynamo driven by large-scale MHD instabilities, using efficient current sustainment techniques; · To evaluate the confinement properties of the RFP in the absence of large scale MHD fluctuations; · To investigate the ability to improve the RFP via control of the plasma geometry and/or profiles and via control of the spectral properties of fluc tuations; · To investigate the stability limit of the plasma pressure and to develop methods to increase it using feedback stabilization; and · To improve the understanding of the physics that is common to the RFP and astrophysical plasmas. Explore the Potential for Passive Stability and Steady-State Operation in Three-Dimensional Stellarators with Underlying Magnetic Symmetry The stellarator is a toroidal configuration in which the magnetic fields needed for plasma confinement and stability are generated by twisting the shape of exter nal coil sets to produce closed magnetic-flux surfaces.
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From page 109... ...
In summary, the major goals of the stellarator program are these: · To test theory of MHD stability boundaries in three-dimensional plasmas, varying the contribution from plasma currents, and to explore the sensitiv ity of the plasma pressure stability limit to strong three-dimensional shaping; · To test the understanding of current-driven disruptive instabilities in stellarators; · To demonstrate the predicted ability to achieve tokamak-like confinement properties in stellarators with magnetic symmetry; · To test theories of turbulence-driven transport in three-dimensional mag netic configurations of varying symmetry; and · To explore the ability to access improved confinement regimes in stellarators -- the strong rotational damping, which is drastically reduced in stellarators with symmetry, provides a test of the mechanisms of turbulence suppression. Explore Novel and Emerging Fusion Science and Technology Concepts Small-scale experiments can address some unique fusion research issues that may be relevant to near-term applications of fusion science and technology, or allow the study of speculative emerging concepts for advanced fusion systems.
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From page 110... ...
In addition to developing those technologies related to the burning plasma program, the domestic fusion program, in collaboration with international part ners, must advance the knowledge base for fusion energy by addressing issues in three main areas: plasma technologies in support of advanced fusion science ex periments, plasma chamber technologies, and fusion materials. Regardless of the degree of commitment to developing a fusion reactor in any specific time frame, research activity in these areas supports the long-range goal of developing attrac tive fusion concepts.
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From page 111... ...
THEORY AND COMPUTATION One important goal of a burning plasma experiment is to use the knowledge gained to predict performance in other toroidal confinement devices (i.e., poten tial candidates for subsequent steps toward useful fusion energy)
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From page 112... ...
, allowing a piecemeal simplification of the complex physics. This approach has led to a new level of understanding and has served the fusion program well.
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From page 113... ...
The computation and simulation part of the fusion program will need attention and possible expansion for the ITER program. It may be that other areas of science, heavily dependent on computation, have developed tools that can be adopted for the progress of fusion science.
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From page 114... ...
The NRC FUSAC report noted that the fusion and plasma science workforce in the universities and at large fusion facilities is aging, with too few young people entering the field. The same report also noted that the nation's fusion and plasma science programs are concentrated in relatively few universities.11 Responding to the FUSAC report and to earlier studies, the Office of Fusion Energy Sciences took important actions that will help to increase the talent pool and ensure the vitality of the basic plasma research efforts in the universities.
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From page 115... ...
(b) Funding level of DOE Office of Fusion Energy Sciences program in constant FY00 dollars.
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From page 116... ...
[T] he hoped-for hiring in fusion science over the next five years indicates a hiring-to-retirement ratio of at most two hires for every three retirements."12 As shown in Figure 4.5, the age distribution of the scientific and engineering workforce at the nation's three largest fusion laboratories -- General Atomics, the Princeton Plasma Physics Laboratory, and the Massachusetts Institute of Technol ogy -- is similarly skewed toward older ages.
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From page 117... ...
12 Faculty 10 Total of 8 6 4 Percentage 2 0 25 37.5 47.5 57.5 67.5 77.5 Age FIGURE 4.4 (a) The age distribution of fusion science faculty at 23 institutions with active plasma and fusion science programs.
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From page 118... ...
This population comprises roughly one-half of the professional research staff supported by the fusion science program, excluding the university population, and is reasonably representative of the community as a whole. by the fusion community (for example, at the undergraduate level)
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From page 119... ...
Options might include highlighting a program of nationally competed, prestigious fellowships in fusion science and technology to attract outstanding Ph.D.'s to the field. To infuse new talent into the aging university plasma and fusion faculties, the fusion program could consider providing increased matching salary and start-up funds for new assistant professors in plasma and fusion science.
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From page 120... ...
Projects that have traditionally been the major source of trained personnel for the fusion program include smaller scale confinement experiments, diagnostics development, theory and modeling, and technology research. Recognizing that much of fusion science research is mov ing to team-oriented research on larger, shared facilities, it is also important that the university community have the opportunity to become integrally involved in these regional, national, and international fusion research activities.
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From page 121... ...
fusion program to creating intern ships in fusion technology for established scientists and engineers in order to jump-start the training of new fusion personnel. The program could also consider increasing its involvement in industries that provide fusion-relevant technology.
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From page 122... ...
PROGRAM STRUCTURE AND ITS EVOLUTION Considering the previous discussions in this chapter and in Chapter 3, the com mittee believes it to be clear that, in order to look at the broad range of fusion science issues, the U.S. fusion program needs to support both the study of burning
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From page 123... ...
fusion program that pursues burning plasma studies and addresses science issues beyond the burning plasma experiment itself has been affirmed by the fusion community's 2002 Snowmass study, by reviews from the DOE's Fusion Energy Sciences Advisory Committee (FESAC) , and by outside re views of the U.S.
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From page 124... ...
Develop fusion science, technology, and plasma confinement innovations as the central theme of the domestic program; and (3) Pursue fusion energy science and technology as a partner in the international effort."17 Pursuing all three of these goals supports the development of the knowledge base for an attractive energy source and has effectively defined a balanced fusion program.
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From page 125... ...
Sauthoff, 2002 Fusion Summer Study Report, 2003, available online at http://www.pppl.gov/snowmass_2002/snowmass02_report.pdf; Fusion Energy Sciences Advisory Committee, A Restructured Fusion Energy Sciences Program, Washington, D.C.: U.S. De partment of Energy, 1996, available online at http://wwwofe.er.doe.gov/more_html/PDFFiles/ FEACREPORT.pdf, accessed September 1, 2003.
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From page 126... ...
The issue, then, is how to strike the relative balance of activities across a tightly integrated program that addresses, as much as possible, all of the critical fusion science issues. As the balance is clearly influenced by available funding, conditions could lead to the suppression of activity in one area or another, which occurred when the pursuit of a burning plasma experiment was halted in the late 1990s.
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From page 127... ...
The second major component of the U.S. fusion program is the investigation of fusion science issues on innovative magnetic configurations (other than the standard tokamak)
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From page 128... ...
Finally, the program requires a fusion technology component, the scale of which is commensurate with the level of com mitment and timing required to achieve the fusion energy goal. However, the technology programs at the present time will be those focused on enabling a suc cessful burning plasma experiment -- that is, focused primarily on those technolo gies important for the development of ITER.
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From page 129... ...
fusion program as it moves forward. Organizing the research efforts on the larger domestic facilities -- the advanced tokamaks, spherical torus, stellarator, and reversed-field pinch -- in a similar manner will support the transformation of the community to more of a user-group model and will more effectively engage the research community in those efforts.
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From page 130... ...
The committee concludes that in order to develop a balanced program that will maximize the yield from participation in a burning plasma project, the prioritization process should be organized with three program objectives in mind: · Advance plasma science in pursuit of national science and technology goals; · Develop fusion science, technology, and plasma-confinement innovations as the central theme of the domestic program; and · Pursue fusion energy science and technology as a partner in the interna tional effort.
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From page 131... ...
fusion program be linked to current and planned international fusion research programs?
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From page 132... ...
It is thus important that consideration be given to coordinating all non-ITER-related ac tivities discussed here with the global fusion program, as appropriate.
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