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November 5, 2018, American Physical Society
https://phys.org/news/2018-11-faster-cheaper-path-fusion-energy.html
Scientists are working to dramatically speed up the development of fusion energy in an effort to deliver power to the electric grid soon enough to help mitigate impacts of climate change. The arrival of a breakthrough technology—high-temperature superconductors, which can be used to build magnets that produce stronger magnetic fields than previously possible—could help them achieve this goal. Researchers plan to use this technology to build magnets at the scale required for fusion, followed by construction of what would be the world’s first fusion experiment to yield a net energy gain.
The effort is a collaboration between Massachusetts Institute of Technology’s Plasma Science & Fusion Center and Commonwealth Fusion Systems, and they will present their work at the American Physical Society Division of Plasma Physics meeting in Portland, Ore.
Fusion power is generated when nuclei of small atoms combine into larger ones in a process that releases enormous amounts of energy. These nuclei, typically heavier cousins of hydrogen called deuterium and tritium, are positively charged and so feel strong repulsion that can only be overcome at temperatures of hundreds of millions of degrees. While these temperatures, and thus fusion reactions, can be produced in modern fusion experiments, the conditions required for a net energy gain have not yet been achieved.
One potential solution to this could be increasing the strength of the magnets. Magnetic fields in fusion devices serve to keep these hot ionized gases, called plasmas, isolated and insulated from ordinary matter. The quality of this insulation gets more effective as the field gets stronger, meaning that one needs less space to keep the plasma hot. Doubling the magnetic field in a fusion device allows one to reduce its volume—a good indicator of how much the device costs—by a factor of eight, while achieving the same performance. Thus, stronger magnetic fields make fusion smaller, faster and cheaper.
A breakthrough in superconductor technology could allow fusion power plants to come to fruition. Superconductors are materials that allow currents to pass through them without losing energy, but to do so they must be very cold. New superconducting compounds, however, can operate at much higher temperatures than conventional superconductors. Critical for fusion, these superconductors function even when placed in very strong magnetic fields.
While originally in a form not useful for building magnets, researchers have now found ways to manufacture high-temperature superconductors in the form of “tapes” or “ribbons” that make magnets with unprecedented performance. The design of these magnets is not suited for fusion machines because they are much too small. Before the new fusion device, called SPARC, can be built, the new superconductors must be incorporated into the kind of large, strong magnets needed for fusion.
Once the magnet development is successful, the next step will be to construct and operate the SPARC fusion experiment. SPARC will be a tokamak fusion device, a type of magnetic confinement configuration similar to many machines already in operation (Figure 1).
As an accomplishment analogous to the Wright brothers’ first flight at Kitty Hawk, demonstrating a net energy gain, the aim of fusion research for more than 60 years, could be enough to put fusion firmly into national energy plans and launch commercial development. The goal is to have SPARC operational by 2025.
Provided by: American Physical Society
-https://en.wikipedia.org/wiki/Tokamak-
A tokamak (Russian: Токамáк) is a device which uses a powerful magnetic field to confine a hot plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being developed to produce controlled thermonuclear fusion power. As of 2016, it is the leading candidate for a practical fusion reactor.
Discovered: Optimal magnetic fields for suppressing instabilities in tokamaks
September 10, 2018, Princeton Plasma Physics Laboratoryhttps://phys.org/news/2018-09-optimal-magnetic-fields-suppressing-instabilities.html
Fusion, the power that drives the sun and stars, produces massive amounts of energy. Scientists here on Earth seek to replicate this process, which merges light elements in the form of hot, charged plasma composed of free electrons and atomic nuclei, to create a virtually inexhaustible supply of power to generate electricity in what may be called a “star in a jar.”
A long-time puzzle in the effort to capture the power of fusion on Earth is how to lessen or eliminate a common instability that occurs in the plasma called edge localized modes (ELMs). Just as the sun releases enormous bursts of energy in the form of solar flares, so flare-like bursts of ELMs can slam into the walls of doughnut-shaped tokamaks that house fusion reactions, potentially damaging the walls of the reactor.
To control these bursts, scientists disturb the plasma with small magnetic ripples called resonant magnetic perturbations (RMPs) that distort the smooth, doughnut shape of the plasma—releasing excess pressure that lessens or prevents ELMs from occurring. The hard part is producing just the right amount of this 3-D distortion to eliminate the ELMs without triggering other instabilities and releasing too much energy that, in the worst case, can lead to a major disruption that terminates the plasma.
Making the task exceptionally difficult is the fact that a virtually limitless number of magnetic distortions can be applied to the plasma, causing finding precisely the right kind of distortion to be an extraordinary challenge. But no longer.
Physicist Jong-Kyu Park of the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), working with a team of collaborators from the United States and the National Fusion Research Institute (NFRI) in Korea, have successfully predicted the entire set of beneficial 3-D distortions for controlling ELMs without creating more problems. Researchers validated these predictions on the Korean Superconducting Tokamak Advanced Research (KSTAR) facility, one of the world’s most advanced superconducting tokamaks, located in Daejeon, South Korea.
KSTAR was ideal for testing the predictions because of its advanced magnet controls for generating precise distortions in the near-perfect, doughnut-shaped symmetry of the plasma. Identifying the most beneficial distortions, which amount to less than one percent of all the possible distortions that could be produced inside KSTAR, would have been virtually impossible without the predictive model developed by the research team.
The result was a precedent-setting achievement. “We show for the first time the full 3-D field operating window in a tokamak to suppress ELMs without stirring up core instabilities or excessively degrading confinement,” said Park, whose paper—written with 14 coauthors from the United States and South Korea—is published in Nature Physics. “For a long time we thought it would be too computationally difficult to identify all beneficial symmetry-breaking fields, but our work now demonstrates a simple procedure to identify the set of all such configurations.”
Researchers reduced the complexity of the calculations when they realized that the number of ways the plasma can distort is actually far fewer than the range of possible 3-D fields that can be applied to the plasma. By working backwards, from distortions to 3-D fields, the authors calculated the most effective fields for eliminating ELMs. The KSTAR experiments confirmed the predictions with remarkable accuracy.
The findings on KSTAR provide new confidence in the ability to predict optimal 3-D fields for ITER, the international tokamak under construction in France, which plans to employ special magnets to produce 3-D distortions to control ELMs. Such control will be vital for ITER, whose goal is to produce 10 times more energy than it will take to heat the plasma. Said authors of the paper, “the method and principle adopted in this study can substantially improve the efficiency and fidelity of the complicated 3-D optimizing process in tokamaks.”
More information: Jong-Kyu Park et al, 3D field phase-space control in tokamak plasmas, Nature Physics (2018). DOI: 10.1038/s41567-018-0268-8
Journal reference: Nature Physics
Provided by: Princeton Plasma Physics Laboratory
-https://en.wikipedia.org/wiki/KSTAR-
The KSTAR (or Korea Superconducting Tokamak Advanced Research) is a magnetic fusion device at the National Fusion Research Institute in Daejeon, South Korea. It is intended to study aspects of magnetic fusion energy which will be pertinent to the ITER fusion project as part of that country’s contribution to the ITER effort.
New testing of model improves confidence in the performance of ITER
April 21, 2018 by John Greenwald, Princeton Plasma Physics Laboratory
https://phys.org/news/2018-04-confidence-iter.html
Scientists seeking to bring fusion—the power that drives the sun and stars—down to Earth must first make the state of matter called plasma superhot enough to sustain fusion reactions. That calls for heating the plasma to many times the temperature of the core of the sun. In ITER, the international fusion facility being built in France to demonstrate the feasibility of fusion power, the device will heat both the free electrons and the atomic nuclei—or ions—that make up the plasma. The question is, what will this heating mix do to the temperature and density of the plasma that are crucial to fusion production?
New research indicates that understanding the combined heating shows how we could improve the production of fusion in ITER and other next-generation fusion facilities—a key finding of physicists at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), the DIII-D National Fusion Facility that General Atomics operates for the DOE, and other collaborators. “This shows what happens when electron heating is added to ion heating,” said PPPL physicist Brian Grierson, who led testing of a computer model that projected the DIII-D results to ITER.
The model, created by Gary Staebler of General Atomics and reported in a paper in Physics of Plasmas with Grierson as first author, investigated the DIII-D experimental results in conditions mimicking those expected in ITER. Diagnostics supplied by the University of Wisconsin-Madison and the University of California, Los Angeles measured the resulting turbulence, or random fluctuations and eddies, that took place in the plasma.
The measurements revealed turbulence with short-to-long wavelengths caused by electron and ion heating, respectively. The combination produced “multiscale” turbulence that modified the way particles and heat leak from the plasma. Turbulence can reduce the rate of fusion reactions.
The combined electron and ion heating altered the gradient, or spatial rate of change in the plasma density. This finding was significant because the fusion power that ITER and other next-generation tokamaks produce will increase as the density grows greater. Moreover, the increase took place without causing impurities to accumulate in the core of the plasma and cool it down, which could halt fusion reactions.
The scientists used a “reduced physics” model called TGLF that simplified the massively parallel and costly simulations of multiscale turbulence that require millions of hours of computing time on supercomputers. The researchers ran this simplified version hundreds of times on PPPL computers to test the impact on the model of uncertainties stemming from the DIII-D experiments.
“The TGLF model exploits the weak turbulence properties of tokamaks like ITER,” said Staebler. “It approximately computes the plasma transport billions of times faster than a gyrokinetic multiscale turbulence simulation run on high-performance supercomputers.”
The model looked specifically at the impact of electron heating on the overall heating mix. Researchers produce such heating by aiming microwaves at the electrons gyrating around magnetic field lines—a process that increases the thermal energy of the electrons, transfers it to the ions through collisions, and supplements the heating of the ions by neutral beam injection.
Results indicated that studying multiscale turbulence will be essential to understanding how to deal with the multiscale effect on the transport of heat, particles and momentum in next-generation tokamaks, or fusion devices, Grierson noted. “We need to understand transport under ion and electron heating to confidently project to future reactors,” he said, “because fusion power plants will have both types of heating.”
ore information: B. A. Grierson et al, Multi-scale transport in the DIII-D ITER baseline scenario with direct electron heating and projection to ITER, Physics of Plasmas (2018). DOI: 10.1063/1.5011387
Journal reference: Physics of Plasmas
Provided by: Princeton Plasma Physics Laboratory
-https://en.wikipedia.org/wiki/High-temperature_superconductivity-
High-temperature superconductors (abbreviated high-Tc or HTS) are materials that behave as superconductors at unusually high temperatures. The first high-Tc superconductor was discovered in 1986 by IBM researchers Georg Bednorz and K. Alex Müller, who were awarded the 1987 Nobel Prize in Physics “for their important break-through in the discovery of superconductivity in ceramic materials”.
-https://en.wikipedia.org/wiki/Net_energy_gain-
Net Energy Gain (NEG) is a concept used in energy economics that refers to the difference between the energy expended to harvest an energy source and the amount of energy gained from that harvest. The net energy gain, which can be expressed in joules, differs from the net financial gain that may result from the energy harvesting process, in that various sources of energy (e.g. natural gas, coal, etc.) can be priced differently for the same amount of energy.
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