Final Report of the Committee on a Strategic Plan for U.S. Burning Plasma Research (2019) / Chapter Skim
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2 Progress in Burning Plasma Science and Technology
2 Progress in Burning Plasma Science and Technology
Pages 20-59
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From page 20... ...
New ideas to control and sustain a burning plasma have been discovered, and theoretical and computational models developed in the United States have substantially improved the ability to control plasma stability, predict plasma confinement, and enhance fusion energy performance. Methods to control and mitigate transients and scenarios that will guide operation of ITER have been successfully tested.
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Scientific readiness was determined from empirical confinement predictions, knowledge of operational limits set by plasma stability, methods to mitigate abnormal events like plasma current disruptions, the ability to maintain plasma purity, methods to measure and characterize a burning plasma, and techniques to control a burning plasma. Technical readiness was determined by successful prototyping of ITER components, evidence of adequate component lifetime in a nuclear environment, tests of plasma-facing components and materials, initial analysis of the safe control of tritium, demonstrations of remote maintenance systems, and demonstration of the required fueling, heating, and current drive control.
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Theoretical and computational models developed in the United States have substantially improved the ability to control plasma stabil ity, predict plasma confinement, and enhance fusion energy performance. The ITER Organization and a team of international scientists developed the ITER Research Plan (IRP)
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Waltz, and R.V. Budny, 2011, ITER predictions using the GYRO verified and experimentally validated trapped gyro-Landau fluid transport model, Nuclear Fusion 51:083001; (b)
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Granetz, 2018, Access to pedestal pressure relevant to burning plasmas on the high magnetic field tokamak Alcator C-Mod, Nuclear Fusion, in press, https://doi.org/10.1088/1741-4326/aabc8a. Q = 10 can be achieved with the expected performance in conventional operation, applying these optimization techniques to ITER plasmas can potentially enhance performance beyond the Q = 10 range.
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However, the ITER baseline scenario is susceptible to NTM that are driven by plasma current density.32,33 Significant progress toward meeting the challenge posed by tearing instabilities has occurred for the ITER baseline stability by way of better understanding of the roles of plasma rotation, plasma collisionality, and the use of various control actuators, including cancelation of unwanted magnetic field errors34 and localized plasma current drive35 and optimized with advanced feedback and search algorithms.36 Active techniques include tailoring the plasma profiles with various heating and current drive schemes, as well as applying 3D magnetic field perturbations at the plasma edge.37 Achieving high plasma βN can also be aided by a judicious choice of plasma shaping and configuration. For instance, in the more "spherically shaped" NSTX plasmas, stable high-βN discharges were produced routinely with the aid of stabilization techniques.38 Stabilization studies in the mid-sized U.S.
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SOURCE: T.C. Luce, 2011, Realizing steady-state tokamak operation for fusion energy, Physics of Plasmas 18:030501.
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The past decade has seen significant progress in both understanding and mitigating the EP-driven instabilities in both stellarators and tokamaks.43,44 Theory and numerical simulation advances have led to the development of models, validated FIGURE 2.5 Energetic particle (EP) "phase space" for National Spherical Torus Experiment-Upgrade (NSTX-U)
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These same actuators are planned for ITER. While the tools and understanding that have developed over the past decade are sufficient for developing scenarios in which ITER can achieve its Q = 10 goal, only the study of the α-particle population generated by these burning plasmas will help ensure extrapolation from relative short-pulse fusion power production to one where α-particle modes can remain stable in long-pulse, steady-state operation.
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A variety of mitigation methods have been developed and tested successfully on present-day devices. Three-dimensional edge magnetic fields have been applied FIGURE 2.6 Examples of visible images from different rapid shutdown methods from DIII-D showing (a)
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, the ITER cryostat, and vacuum components is in progress. ITER has been licensed as a first-of-a-kind basic nuclear fusion facility.
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the development of vacuum and gas species management,88,89 tritium fusion fuel cycle systems,90 pellet injection for fueling and disruption mitigation,91 and the manufacture of the ITER central solenoid.92 RESEARCH PROGRESS BEYOND ITER TOWARD FUSION ELECTRICITY International research progress preparing for burning plasma study on ITER has also increased the state of readiness to undertake research beyond ITER leading toward the construction of follow-on devices that demonstrate fusion power production and the potential for economical fusion electricity. In Europe, Japan, South Korea, and China, research beyond ITER is directed to develop the interconnected science and technology needed to design and construct a device to demonstrate fusion power.
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While detachment in a conventional divertor alone is estimated to reduce heat loading in ITER to an acceptable level by radiating 60-70 percent of the escaping heat flux, a next-step burning plasma may have heating and fusion powers greater than those expected in ITER. With a conventional divertor, up to 90 percent of the heat exhaust would have to be radiated away to avoid material surface damage; at these levels, core plasma performance could be severely affected.99 Studies of the compatibility of innovative divertor designs with divertor plasma detachment, which can significantly relax the radiated power requirement, are needed.
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Guo and General tomics A and reprinted from G.H. Neilson, ed., 2016, Magnetic Fusion Energy: From Experiments to Power Plants, W oodhead Series in Energy, No.
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LMs can handle heat fluxes up to factors of several over the upper limits for solid walls.108 One of the leading candidates for LM walls is lithium, which, when coated on solid walls through evaporation, led to improved confinement109,110 and suppressed or miti gated ELMs.111,112 Liquid lithium surface research and development on tokamaks is in the early stage,113,114 and the challenges involve their design, stability in the presence of magnetic fields, retention of tritium (an issue for both liquid and solid walls) ,115 and impact on plasma performance.116,117 Driving Plasma Current Among the key challenges for obtaining a steady-state burning plasma beyond ITER is the capability to drive the plasma current noninductively.
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Progress toward this integration has been slow since plasma science and device performance are each a necessary first step. As devices approach the burning plasma regime it is appropriate to embrace design choices that are compatible with
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Because tokamaks and stellarators have strong magnetic fields and toroidal geometries, the fusion science and technologies of tokamaks and stellarators are similar. The fundamental dynamics of plasma confinement are described with the same methods; scientists produce and diagnose confined plasma using the same technologies; and tokamaks and stellarators are challenged to achieve and sustain the same fusion equivalent conditions.
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fully designed stellarators with reduced neoclassical transport.132 A major new facility with such optimization, W7-X in Germany,133 recently began operating, and experi ents have confirmed the three-dimensional magnetic field optimiza m tion.134 A prime goal of W7-X is to test fusion magnetic confinement for one such optimization scheme and the balance between neoclassical and turbulence-driven transport. The experiments will serve to validate results of several gyrokinetic codes, including the first fully global and physically comprehensive turbulence codes, which have recently been developed.135 Some MHD and energetic particles instabilities are predicted to behave differently in stellarators than in tokamaks.
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Both analytic theory and reduced models and high-fidelity physics simulations development comprise this impressive set of accomplishments. Theory and simulation offer important new opportunities for accelerating progress toward the objective of economical fusion energy development by incor porating recent advances in theoretical understanding, validated physics models, computing infrastructure, and diagnosis of experiments.145,146 As described in the Report of the 2015 Workshop on Integrated Simulations for Magnetic Fusion Energy Sciences,147 what is needed is to comprehensively and self-consistently ad vance the many complex, nonlinear, and multi-scale plasma descriptions into an integrated suite of whole device modeling (WDM)
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for the U.S. to pursue that could promote efficient advance toward fusion energy," The 2018 FESAC report149 identified four areas of transformative enabling capabilities where, building from significant progress in certain areas of research, the United States has a strategic opportunity to develop transformative technologies to enable fusion energy.
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Strong magnetic fields are critical to the success of magnetic fusion as a source of energy. Achieving higher magnetic field strength extends the allowable plasma properties to higher plasma density, higher plasma current, and higher plasma pressure while retaining the same di mensionless scaling parameters found at lower magnetic field strength.
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coils made of niobium-tin superconductors and consistent with the strength of steel.152 New developments of rare-earth barium-copper-oxide high-temperature super onductors (Figure 2.12) may lead to larger magnetic field strength153 and c improved maintenance that potentially improve the prospects for economical magnetic fusion energy.154 Advanced Materials and Manufacturing The behavior and integrity of materials in a fusion system are of great importance to the long-term viability of fusion energy.155 The flux of energetic neutrons to the vessel and structural materials poses a serious materials problem that will require substantial testing, some of which may be done on a burning plasma experiment. The high energy neutrons from the D-T fusion reaction generate between 50 to 100 times higher helium to dpa ratio in materials such as ferritic steels than does fission reactor irradiation.
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From page 42... ...
Linear plasma simu lators allow for long-duration study of material evolution under fusion-relevant plasma flux, but they are not useful to test integrated plasma-material effects ex pected in fusion divertors. In the United States, linear plasma simulators include the PISCES facility at University of California, San Diego,163 the Tritium Plasma Experiment at Idaho National Laboratory (INL)
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As reported by the 2018 U.S. DOE FESAC Committee on Transformative Enabling Capabilities, "Advances in novel synthesis, manufacturing and materials design are providing for some of the most promising transformation enabling technologies in PMI and nuclear fusion materials to enable fusion energy for the future."165 The novel features enabled by advanced manufacturing and additive manufacturing include complex geometries and transitional structures, often with materials or constituents including hard-to-machine refractory metals; the potential for local control of material microstructure; rapid design-build-test iteration cycles; and exploration of materials and structures for containing and delivering liquid metals.
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Enhanced Surfaces by Selective Laser Melting (SLM) FIGURE 2.13 Advanced manufacturing used for enhanced heat exchanger structures.
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The 2018 FESAC report recognizes this challenge, and identifies several opportu ities to develop technologies with potential to address existing gaps, such n as novel blanket technologies for tritium breeding that allow for higher hermal t to electrical efficiencies and improved tritium breeding ratios,174,175 advanced ritium extraction technologies,176 and new fuel recycling technologies that allow t for minimization of tritium inventories.177 Fusion Safety A burning plasma experiment offers the opportunity to begin development of the technologies needed for a fusion reactor, including important safety-related technologies. Many components and systems needed for fusion's safety objectives are unique, such as source diagnostics and cleaning technologies, state-of-the-art safety analyses tools, technologies for the remote handling of large activated components, technologies for the control of routine tritium releases, and innovative approaches for the control of tritiated and mixed waste streams.178 A burning plasma experiment will be an integrated demonstration of the safety, reliability, and effectiveness of these technologies.179 In the United States, recent progress has been remarkable in the areas of safety code development and understanding of tritium behavior in fusion systems.
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Integrated Systems Engineering for Fusion Integrated systems studies guide research and identify programs that can reduce cost and lower risk to the development of fusion power. Integrated systems studies combine burning plasma science, materials science, fusion nuclear science, and systems engineering to evaluate safety, environmental and maintainability ssues, i and technical requirements to progress toward fusion energy.
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Colling, R Raman, et al., 2016, Fusion nuclear science facilities and pilot plants based on the spherical tokamak, Nuclear Fusion 56:106023, (b)
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fusion energy science program as part of the international research effort has made leading advances in burning plasma science and tech nology that have substantially improved our confidence that a burning plasma experiment such as ITER will succeed in achieving its scientific mission. Although the primary focus of the world's fusion research program is the preparation for ITER experiments, progress has also resulted in the research aimed beyond ITER to address remaining science and technology challenges and demon strate innovative solutions that lead to a reduced size, lower cost, full-scale power source.
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From page 49... ...
Liu, 2017, Pedestal . transport in H-mode plasmas for fusion gain, Nuclear Fusion 57:064001.
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From page 50... ...
al., 2018, Access to pedestal pressure relevant to burning plasmas on the high magnetic field tokamak Alcator C-Mod, Nuclear Fusion 58:112003.
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R Wenninger, 2017, A stepladder approach to a tokamak fusion power plant, Nuclear Fusion 57:086002, for discussion of this formula.
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Brezinsek, M Brix, et al., 2011, Disruption mitigation by massive gas injection in JET, Nuclear Fusion 51:123010.
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Combs, and S.J. Meitner, 2018, Dissipation of post-disruption runaway elec tron plateaus by shattered pellet injection in DIII-D, Nuclear Fusion 58:056006.
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McLean, W.H. Meyer, et al., 2018, Developing physics basis for the snowflake divertor in the DIII-D tokamak, Nuclear Fusion 58:036018.
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Whyte, et al., 2015, ADX: A high field, high power density, advanced divertor and RF tokamak, Nuclear Fusion 55:053020.
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B u r n i n g P l as m a R e s e a r c h 119 . ITER Physics Expert Group on Energetic Particles, 1999, ITER Physics Basis, Chapter 6: Plasma Auxiliary Heating and Current Drive, Nuclear Fusion 39:2495.
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, 2018, Report on Transformative Enabling Capabilities . for fficient Advance Toward Fusion Energy, Fusion Energy Sciences Advisory Committee, E Washington, DC.
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and H Tanigawa, 2017, Development of next generation tempered and ODS reduced activation ferritic/martensitic steels for fusion energy applications, Nuclear Fusion 57:092005.
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Humrickhouse, S Malang, et al., 2015, The Fusion Nuclear Science Facility, the critical step in the pathway to fusion energy, Fusion Science and Technology 68(2)
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