Plasma Science Enabling Technology, Sustainability, Security, and Exploration (2021) / Chapter Skim
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6 Magnetic Confinement Fusion Energy: Bringing Stars to Earth
6 Magnetic Confinement Fusion Energy: Bringing Stars to Earth
Pages 264-321
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From page 264... ...
Only a small fraction of the colliding beam particles will undergo fusion reactions. As a result, it is nearly impossible to produce net energy by this approach (although similar schemes can be useful in using fusion to produce neutrons for other applications, including the generation of medically relevant isotopes)
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From page 265... ...
To produce net energy through fusion, the D-T particles must be confined in a region of space long enough to undergo many, many scattering interactions before finally fusing and releasing energy. The goal is then to efficiently confine a hot soup of charged particles, a plasma, with a temperature around 100 million K to enable the D-T particles to have enough energy to overcome their mutual electrostatic repulsion and produce fusion reactions.
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From page 266... ...
In MFE, magnetic fields are used to confine a sufficiently hot and dense plasma so that fusion reactions can occur. Magnetic forces can limit the motion of and confine charged particles in directions perpendicular to the magnetic field.
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From page 267... ...
In a tokamak, the additional magnetic field (called the poloidal field) necessary to produce the helical field structure is generated by running a current through the plasma itself.
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From page 268... ...
Following the path of compact fusion reactors would uniquely position the United States in the international pursuit of fusion power, leveraging recent advances in our understanding of fusion plasmas and new developments in technology. The Burning Plasma report recommenda tions set the stage for a focused plasma science and engineering research program needed to enable a compact fusion pilot plant.
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From page 269... ...
to achieve a burning plasma. Global plasma instabilities can ultimately limit the pressure and fusion power that can be generated while microinstabilities can lead to turbulence and transport of heat, limiting the efficiency of magnetic confinement.
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From page 270... ...
(See Figure 6.3.) Besides providing energy and process heat, fusion reactions can be used to provide a source of neutrons for the generation of radioisotopes (e.g., for medical applications)
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From page 271... ...
Magnetic reconnection (where magnetic field lines are broken and, reconnect, producing large releases of energy -- see Chapter 2) is ubiquitous in space and astrophysical plasmas, leading to stellar flares and perhaps gamma ray bursts (see Chapter 7)
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From page 272... ...
The pedestal's formation, height, and stability are therefore key drivers of overall fusion performance, since fusion power scales with the square of the plasma pressure. Numerous mechanisms, including collisional "neoclassical" transport and electron scale turbulence, can drive heat and particle transport across the pedestal.
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From page 273... ...
EPED predicted pedestal pressure compared to observations on 6 devices across a wide range of size, shape, magnetic field and plasma current find good agreement. The highest pressure cases shown (green circles)
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From page 274... ...
A significant breakthrough over the last 10 years is the use of small, nonaxi symmetric, three-dimensional (3D) magnetic fields called Resonant Magnetic Perturbations (RMP)
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From page 275... ...
SOURCE: S.A. Lazerson, 2014, The ITER 3D magnetic diagnostic response to applied n=3 and n=4 resonant magnetic perturbations, Plasma Physics and Controlled Fusion 56:095006, https://doi.org/10.1088/0741-3335/56/9/095006, © IOP Publishing, reproduced with permission, all rights reserved relative to L-mode, (4)
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From page 276... ...
Although results from linear stability analysis have provided a significant under standing of the mode, we need a complete theory of the saturated, nonlinear state and how the EHO drives cross magnetic field transport. Some promising initial modeling of the EHO has been performed but much remains to be done.
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From page 277... ...
Greenwald and J Candy, 2015, Multi-scale gyrokinetic simulation of tokamak plasmas: Enhanced heat loss due to cross-scale coupling of plasma turbulence, Nuclear Fusion 56:014004.
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From page 278... ...
(See Figure 6.8.) This is caused by rapid transport (parallel to the magnetic field)
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From page 279... ...
The role played by zonal flows makes this phenomenon potentially relevant to the most important types of instabilities in magnetic confinement fusion. Recent experimental measurements and
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From page 280... ...
. Right: Without the external magnetic field perturbation there are strong zonal flows (a)
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From page 281... ...
license, https://creativecommons.org/licenses/by/4.0. of plasma physics from the interstellar medium to tokamaks.
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From page 282... ...
In a stellarator, the helical magnetic field is produced entirely by specially designed external coils, and no plasma current is required. (See Figure 6.11.)
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From page 283... ...
Wolf, H.-S. Bosch, and the Wendelstein 7-X Team, 2016, Confirmation of the topology of the Wendelstein 7-X magnetic field to better than 1:100,000, Nature Communications 7:13493.
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From page 284... ...
A 7 MW neutral beam system and 1 MW ion cyclotron resonance heating system will enable investigations of energetic particles in three dimensional magnetic fields. Fluctuation diagnostics will be used to investigate how both magnetic fields and plasma gradients influence turbulence.
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From page 285... ...
. compact fusion reactor, such as an order unity plasma beta and no magnetic field coils.
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From page 286... ...
Progress Toward a Burning Plasma: ITER Successful fusion concepts require a core plasma that is "burning" -- that is, the absorption of energy released by fusion reactions is the dominant source of heat ing within the plasma. In particular, this heating is dominated by energetic alpha particles born in fusion reactions.
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From page 287... ...
The first recommendation from that report, that the United States remain a partner in the ITER project, represents the lowest risk route to studying the physics of a burning plasma. The Burning Plasma Committee released an interim report which states: "burning plasma research is essential to the development of magnetic fusion energy and contributes to advancements in plasma science, materials science, and the nation's
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From page 288... ...
SOURCE: © ITER Organization, http://www.iter.org. industrial capacity to deliver high-technology components." Further, the report states that "any strategy to develop magnetic fusion energy requires study of a burn ing plasma." Active participation in the ITER project is necessary for the United States to derive full benefit from the ITER project in its quest for a domestic fusion power plant.
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From page 289... ...
The second recommendation of the Burning Plasma Report is that the U.S. program pursue science and engineering activities leading to the development of a compact fusion pilot plant, representing a more economical approach to fusion power.
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From page 290... ...
(See Figure 6.15.) For tokamak concepts that rely on increasing the magnetic field, this scaling implies extremely large fluxes that could exceed material limits.
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From page 291... ...
There is a key capability gap that the United States could fill through a new facility focused on testing power exhaust solutions together with a high performance core plasma. In the plasma core, well-defined dimensionless parameters are expected to govern the plasma physics.
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From page 292... ...
of these issues was presented in the National Academies report on a Strategic Plan for U.S. Burning Plasma Research.7 Some of the key findings are noted here.
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From page 293... ...
This turbulence can be substantially stabilized by plasma flow and through the radial variation in the magnetic field line pitch that is established by the plasma current profile. Variation in flow and magnetic field line pitch can "tear apart" the turbulent eddies and twist them magnetically.
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From page 294... ...
In addition, there is significant magnetic stored energy associated with the plasma current in a tokamak. Sudden disruption of this current causes very large induc tive electric fields that can induce currents in conducting structures around the tokamak and accelerate plasma electrons to very high energies.
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From page 295... ...
Herfindal, et al., 2018, The role of kinetic instabilities in formation of the runaway electron current after argon injection in DIII-D, Plasma Physics and Controlled Fusion 60:124003, permission conveyed through Copyright Clearance Center, Inc. Right: © ITER Organization, http://www.iter.org.
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From page 296... ...
To achieve a steady state burning plasma, auxiliary means to drive current are needed to operate for longer times in order to maintain the desired, self-stained configuration of current and magnetic fields. Radiofrequency waves can be injected into the plasma to directly drive currents, either by injecting momentum and "pushing" particles in a particular direction or by introducing collisional asym metries, making it easier to push particles in one particular direction.
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From page 297... ...
However, challenges remain to fully realize the potential of 3D shaping of magnetic fields to optimize plasma confinement. Creating the "perfect magnetic bottle" using 3D magnetic fields is one of the outstanding challenges in plasma physics.
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From page 298... ...
• How do 3D perturbations in otherwise symmetric magnetic fields affect particle and energy transport? • How can theory and computations be improved and leveraged to optimize and understand 3D shaping, and investigate configurations that are now beyond current experimental capabilities?
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From page 299... ...
First, high-temperature superconductors enable new options for electromagnetic coils. While it may be difficult to increase the magnetic field strength in stellarators due to the need to support complicated distributions of electromagnetic forces, reducing conductor thickness and cooling demands would still provide additional flexibility in the design.
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From page 300... ...
Developing Predictive Capability to Enable Design and Control of Fusion Reactors Experiments have been absolutely essential to progress in MFE research, lead ing to key discoveries such as the H-mode and edge-localized mode (ELM) sup pression using 3D magnetic fields.
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From page 301... ...
Validation should focus on regimes that are relevant to burning plasmas where possible. Innovations in data analysis and machine learning should be used to complement more conventional model development where appropriate.
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From page 302... ...
. It can operate with a 2.2 T toroidal magnetic field and 3 MA plasma current, although it generally operates at lower currents, ≤ 2 MA.
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From page 303... ...
, École Polytechnique Fédérale de Lausanne, Switzerland HIDRA Hybrid Illinois Device for Research and TFTR* Tokamak Fusion Test Reactor, Princeton Application, University of Illinois Plasma Physics Laboratory HL-2A Tokamak, Chengdu, China VEST Versatile Experiment Spherical Torus, Seoul National University, S
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From page 304... ...
304 Plasma Science FIGURE 6.20 Interior of the DIII-D Tokamak vacuum vessel. SOURCE: Rswilcox, https://commons.
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From page 305... ...
Many of ST physics challenges were investigated in NSTX, the predecessor to NSTX-U. NSTX had an aspect ratio of R/a = 0.85/0.68~1.25, operated with plasma currents up to 1.5 MA and with toroidal magnetic fields of up to 0.55 T
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From page 306... ...
The toroidal magnetic field will be increased from 0.55-1 T, the plasma current from 1.5-2 MA, and the pulse length from 1-5 s. A second, more tangentially injecting neutral beam was added, doubling the total available power up to 12 MW under normal operating conditions.
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From page 307... ...
The plasma is heated to very high power densities using radio-frequency heating from novel antennae and sustained with microwave current drive. The third in a series of high-magnetic field tokamaks at MIT, C-Mod leveraged PSFC expertise in high-field magnets, high power radio-waves, plasma physics, fusion materials,
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From page 308... ...
Studies on C-Mod have clarified the roles of rotation and shear on transport and stability across the plasma and have demonstrated stable operating regimes at high magnetic field that may eliminate explosive instabilities. Until 2016, C-Mod was one of three domestic tokamaks and a DOE user facility.
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From page 309... ...
Lithium Tokamak Experiment upgrade (LTX-b) is also a low aspect ratio tokamak at Princeton Plasma Physics Laboratory having R = 40 cm, R/a ~1.55, a toroidal magnetic field of 0.17 T and plasma currents up to 100 kA.
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From page 310... ...
With magnetic field lines having a low pitch, its configuration approximates that of an infinite cylinder. Flow shear is externally applied and can be controlled.
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From page 311... ...
Non-U.S. proposals for new facilities include the superconducting Divertor Tokamak Test facility that would be built by the Italian National Agency for New Technologies, Energy, and Sustainable Economic Development's fusion laboratory in Frascati, Italy, and the China Fusion Engineering Test Reactor (CFETR)
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From page 312... ...
universities (Auburn University, University of Wisconsin, Madison, and Massachusetts Institute of Tech nology) , supporting W7-X with equipment that has been funded, designed, and produced in the United States and with related magnetic field and plasma diagnosis and modeling.
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From page 313... ...
Prominent examples include: • TAE Technologies (Foothill Ranch, CA) has raised the largest amount of venture capital of any privately funded fusion company to date.
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From page 314... ...
Tokamak Energy is planning to utilize high temperature superconductors to enable high-field, compact spherical tokamak fusion reactors. The company is currently operating the ST40 device which uses a 3T magnetic field and has a major radius of 0.4 m.
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From page 315... ...
program, was discontinued. At the time of these transitions, there were limited funding opportunities, and more importantly, access to intellectual leadership opportunities, for affected university researchers to reengage with FES-funded MFE research.
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From page 316... ...
These programs are very welcome and have provided new opportunities to engage university researchers in the program. However, they do represent a shift to a new paradigm of off-campus research and a potentially more difficult path to intellectual leadership in the field.
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From page 317... ...
Opportunities to site these kinds of facilities at universities would offer a clear path to scientific leadership and enhanced visibility of MFE research. These demographic changes and shifts in the types of funding opportunities for universities come at the same time as strong growth in privately funded fusion ventures and also a recent growth in federal funding for fusion research from DOEFES and DOE ARPA-E.
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From page 318... ...
magnetic confinement fusion energy community, as recom mended in A Strategic Plan for U.S. Burning Plasma Research (National Academies of Sciences, Engineering, and Medicine, 2019)
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From page 319... ...
Recommendation: DOE-FES should structure funding opportunities in magnetic confinement fusion energy to provide leadership opportunities to university researchers and to directly stimulate the hiring of university faculty. Examples of the above include major new facilities or missions that could be organized with leadership teams that involve university researchers; major activities in the field could be organized around centers that are led by teams including university researchers; and specific programs could be implemented to provide funds or other incentives for the creation of faculty positions (example: NSF Faculty Development Program in Space Sciences)
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From page 320... ...
It should further be noted that the removal of student support for university based MFE research further disincentives universities from hiring or retaining faculty engaged in MFE science. Recommendation: The DOE Office of Science should restore discipline specific graduate fellowships and undergraduate research programs that support magnetic confinement fusion energy (MFE)
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From page 321... ...
Many of the privately funded efforts and those being proposed by ARPA-E are closely related to projects that were formerly supported at universities. There are also private entities whose business models are focused on supporting capabilities like computation or technology and not the development of a fusion power source per se.
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