Final Report of the Committee on a Strategic Plan for U.S. Burning Plasma Research (2019) / Chapter Skim
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3 Extending the Frontier of Burning Plasma Research
3 Extending the Frontier of Burning Plasma Research
Pages 60-88
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From page 60... ...
compact pilot plant. This chapter begins with a brief summary of the committee's Interim Report assessment of the importance of burning plasma research to the development of fusion energy and of the ongoing activities of the United States that support burning plasma science and the ITER project is included.
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THE IMPORTANCE OF BURNING PLASMA RESEARCH The importance of a burning plasma experiment as a required step in the development of practical fusion energy has been endorsed by all previous strategic planning documents prepared for the U.S. fusion research program.1 As ITER partners, the fusion research programs of the United States and other nations have focused on preparations for the study of burning plasmas using the ITER experiment for more than a decade.
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From page 62... ...
These ITER research targets are ambitious, but the understanding of burning plasma science has advanced significantly and the international effort to prepare for ITER operation has further increased confidence in the burning plasma performance that can be achieved in ITER. As explained in Chapter 2, this is due to the discovery of new ideas to control and sustain a burning plasma, the substantial improvements in the ability to predict plasma confinement and fusion energy performance, and the demonstration of burning plasma scenarios that are expected to simultaneously satisfy the requirements for stability, confine ment, fuel purity, and compatibility with plasma-facing components.
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From page 63... ...
• A burning plasma experiment tests integrated scenarios that simultaneously test the requirements for stability, confinement, fuel purity, and compat ibility with plasma-facing components needed for a fusion energy source. Plasma operation and control scenarios have been developed and tested in preparation for ITER experiments, and integrated models using the latest advances in high-performance computing now routinely interpret experi mental measurements and make progress in predicting the results of burn ing plasma experiments.
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Construction and operation of the ITER facility addresses important research in fusion nuclear science and engineering science, including: • Fusion fuel processing, blanket design, and tritium breeding. The release of fusion energy results from the fusion reactions of tritium and deuterium ions heated to 100 million K
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As the world's first burning plasma experiment at the scale of power plant, ITER will provide scientists the first opportunity to access the frontier of burning plasma research. The complex processes within a burning plasma that couple plasma confinement, energetic particles created by fusion reactions, plasma stability, and fusion materials and technologies will be investigated.
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scientists to take leading roles in the international effort to develop fusion energy and to benefit significantly from nternational collaboration. Because the United States is a key contributor to i ITER construction, participation in ITER has resulted in significant advances in U.S.
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General Atomics has completed the first module of the 1,000-metric-ton central s olenoid, which will produce ITER's highest magnetic field of 13 T Besides initiating plasma current within ITER, the currents in the six modules of the central solenoid will be independently controlled to shape and position the plasma.
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From page 68... ...
operates under the auspices of ITER, and the ITPA provides an international framework for coordinated fusion research useful for all fusion programs and for broad progress toward fusion energy. The United States continues to make significant contributions to the ITPA, which coordinates the international tokamak physics research and development activities and provides the physics basis for the ITER project.
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From page 69... ...
Integrated understanding of the plasma core-edge integration with the mate rials science of the divertor and first-wall is an ongoing research area that will benefit burning plasma experiments in ITER and contribute to U.S. efforts toward an attractive compact fusion pilot plant.
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These include the following: • Disruption mitigation research, including development of prediction and avoidance algorithms using passive and active control as well as mitigation (i.e., shattered pellet injection, SPI) ; • ELM control through pellet injection, applied external magnetic perturba tions, natural ELM-free regimes; • Controlling heat exhaust through detached divertor and innovative divertor configurations; • Development of ITER-relevant steady-state, noninductive high-performance scenarios with acceptable divertor power loading; • Development of predictive computational tools within integrated sim ulations enabling extrapolation to ITER regimes, including models for noninductive current drive, core confinement, pedestal physics, core-edge c oupling, energetic particle-induced instabilities, plasma transient control, and plasma surface interactions; • Development of integrated frameworks for plasma control algorithm development; • Understanding material properties under the combined load condition and neutron loading present in ITER with verification of models against irradiated samples from test reactors; and • Understanding the redistribution and loss of energetic particles and how Alfvénic instabilities can be mitigated in burning plasmas.
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From page 71... ...
Examples include vacuum and gas species management,26,27 tritium fusion fuel cycle development,28 pellet injection for fueling and disruption mitigation,29 and the manufacture of the ITER central solenoid.30 The capabilities of the U.S. pellet injection technology will be used in future fusion experiments at the JET (Joint European Torus)
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Research results in support of ITER's scientific mission also support the scientific missions of fusion energy facilities that will follow ITER. Three active research areas are: controlling the high heat flux on the divertor, preventing or minimizing transient edge instabilities that could damage the divertor armor, and preventing or mitigat ing an uncontrolled loss of plasma confinement, called a plasma current disruption, that could damage the first wall or the vessel structure.
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Wilson, et al., 2018, "High Fusion Performance in Super H-Mode Experiments on Alcator C-Mod and DIII-D," Paper EX/2-4, 27th IAEA Fusion Energy Conference 2018, https://conferences.iaea.org/indico/event/151/contributions/5887/contribution.pdf.
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From page 74... ...
In this way, the fusion performance parameter, W/PhIaB, measures both high plasma pressure and high plasma confinement relative to the provided plasma current, field, and minor radius. High performance has also been demonstrated relative to empirical H-mode confinement scalings.41 Existing devices such as DIII-D and National Spherical Torus Experiment Upgrade (NSTX-U) |
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are both strongly coupled to confinement and energetic particle physics. Understanding Plasma Confinement at the Scale of a Power Plant The move from existing fusion experiments to experiments at the scale of a power plant, like ITER, brings important changes to the underlying plasma and atomic physics.
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, short neutral penetration depth λ* , and high plasma pressure and fusion power density is a scientific frontier of burning plasma research.
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Ongoing studies on existing devices such as DIII-D and NSTX-U can further explore the role of geometry, fueling and 3D fields on the L-H transition. The early operation phase of ITER, including operation at reduced field to reduce the L-H threshold power, will provide valuable data to further develop physics understanding, and burning plasma experiments on ITER will address L-H transition physics at high power density and reactor-like physics parameters.
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In addition, ITER will operate with a variety of hydrogen isotopes, including protium, deuterium, and tritium, and so will provide important data on the isotope effect on transport. Density Limit Tokamaks are observed empirically to encounter a density limit that scales roughly with the ratio of the plasma current to the square of the minor radius.55
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From page 79... ...
In present devices, energetic ions can be produced by injecting beams of high-energy neutrals into the plasma that, after ionization, subsequently heat it; alternatively, radio frequency waves accelerate an energetic ion population. In a fusion power device, fusion reactions between deuterium and tritium produce energetic alpha particles (also known as the nuclei of helium gas)
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Exploring and Controlling a Burning Plasma A burning plasma is a highly coupled, nonlinear system. The energy and m omentum that alpha particles provide to the plasma will affect the plasma cur rent, transport, and stability in a manner that will alter the density and temperature of the burning fuel, which, in turn, changes the rate of fusion reactions.
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DEVELOPING AN ALTERNATE APPROACH WITHOUT ITER PARTICIPATION Previous sections of this chapter describe the importance of burning plasma research, explain why continued participation as an ITER partner is important to U.S. fusion energy research, and describe how ITER participation will inform the design of a compact fusion pilot plant as a new element of the U.S.
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From page 82... ...
With access to a burning plasma experiment, scientists will have the means to answer fundamental questions pertaining to energetic alpha particles created by fusion reactions, plasma transport processes in fusion reactor conditions, methods to control of plasma transients, divertor science, and the integrated scenarios that simultaneously test the require ments for stability, confinement, fuel purity, and compatibility with plasma-facing components needed for a fusion energy source. If the United States wishes to maintain scientific and technical leadership in fusion energy development and undertake a program toward a compact pilot plant, national expertise in burning plasma science needs to be developed through hands-on operational participation and scientific study by U.S.
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A decision by the United States to withdraw from the ITER partnership would make international collaboration more difficult. Nevertheless, the United States would need to explore other avenues for collaboration and international costsharing, such as the engagement of the United States in the physics design for the China Fusion Energy Test Reactor.
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Because the ITER partnership is the central focus in the large international effort to develop fusion energy, the United States significantly benefits from participation in the ITER partnership. Recommendation: Because the scientific and technical benefits from ITER are compelling and because ITER is the only existing project to create a burn ing plasma at the scale of a power plant, the Committee recommends that the U.S.
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DOE Office of Fusion Energy Sciences research program should encourage the development and testing of burning plasma scenarios on ITER that contribute to reliable operation of a compact fusion pilot plant. Finding: If the United States withdraws from the ITER project, the national research effort would be significantly disrupted, U.S.
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to control neoclassical tearing modes in burning plasmas, Plasma Physics and Controlled Fusion 52:025002.
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2018, "High Fusion Performance in Super H-Mode Experiments on Alcator C-Mod and DIII-D," 27th IAEA Fusion Energy Conference.
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55 M Greenwald, 2002, Density limits in toroidal plasmas, Plasma Physics and Controlled Fusion .
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