Magnet tests kick off bid for net fusion energy

doi:10.1126/science.371.6534.1091

GSTDTAP > 气候变化

DOI	10.1126/science.371.6534.1091
	Magnet tests kick off bid for net fusion energy
	Daniel Clery
	2021-03-12
发表期刊	Science
出版年	2021
英文摘要	A startup chasing the dream of plentiful, safe, carbon-free electricity from fusion, the energy source of the Sun, has settled on a site for its compact reactor. Flush with more than $200 million from investors, including Bill Gates's Breakthrough Energy, 3-year-old Commonwealth Fusion Systems announced last week that later this year it will start to build its first test reactor, dubbed SPARC, in Devens, Massachusetts. The company says the reactor, which would be the first in the world to produce more energy than is needed to run the reaction, could fire up as soon as 2025. Commonwealth and a rival U.K. company have also chosen the technology they think will let them leap ahead of the giant, publicly funded ITER reactor under construction in France and a U.S. pilot plant being considered by the Department of Energy: small but powerful magnets, made from high-temperature superconductors. Commonwealth is assembling its first nearly full-scale magnet and hopes to test it in June. “It's a big deal,” CEO Bob Mumgaard says. “It's beyond what everyone else aspires to.” Fusion reactors burn an ionized gas of hydrogen isotopes at more than 100 million degrees Celsius—so hot that the plasma must be contained by a mesh of magnetic fields to keep it from melting the reactor walls. At ITER, sufficiently powerful fields are achieved with magnetic coils made of niobium alloy superconducting wires that can carry huge currents without resistance. But such superconductors must be chilled to 4° above absolute zero, which requires bulky and expensive liquid helium cooling. And there's a limit to the amount of current niobium wires can carry, forcing ITER to adopt large magnets with many wire turns. ITER's largest magnets are 24 meters across, adding to its $20 billion price tag. Newer high-temperature superconductors—so called because some can superconduct at relatively balmy liquid nitrogen temperatures above 77 K—were not around when ITER was designed. They can carry much more current, tantalizing fusion designers with the prospect of smaller, cheaper reactors. Yet they are brittle, persnickety materials, so “a lot of people had given up on them,” says Rod Bateman of Tokamak Energy, the U.K. startup that is also betting on the technology. “They were just too unreliable.” In the past decade, researchers have developed ways to deposit thin layers of superconducting rare-earth barium copper oxide (ReBCO) on metal tape. The tapes can be manufactured reliably in long lengths, and perform best at about 10 K. But in terms of low-temperature engineering, “10 K is a lot easier than 4 K,” says magnet engineer John Smith of General Atomics in San Diego. The ReBCO tapes can be bent but, being flat, are challenging to wind into coils, Mumgaard says. “You have to stop treating it like a wire and asking it to do the things that wire does.” Commonwealth has developed a cable with stacked layers of tape twisting like candy cane stripes. Tokamak Energy takes a simpler, more compact approach: winding coils with the tape flat, one layer on top of another like a roll of Scotch tape. “It makes winding so much simpler,” Bateman says. Another challenge for both companies is supply. Together, manufacturers of ReBCO tape were only producing a few hundred kilometers per year, and Commonwealth needs 500 kilometers just to build its first test magnet. “Manufacturers are scaling up like crazy now,” Bateman says. “Fusion is the market high-temperature superconductors have been waiting for.” The next few months are critical for the two companies. Following years of modeling and experiments, they are both constructing test magnets to demonstrate 20-tesla fields—1.5 times stronger than ITER's—in coils just a few meters across. Commonwealth is winding a single 2.5-meter-tall, D-shaped magnet, slightly smaller than what's planned for SPARC. Still, Mumgaard says, when completed in June it will be the largest high-temperature superconducting magnet ever built. Tokamak Energy is planning to test a full set of 16 coils, sized for a test reactor about 1 meter across. Bateman says the company will start to wind its magnets in the next few weeks and hopes to test them by the end of the year. If successful, the company plans to embark on building a demo reactor, ST-F1, in 2027. Smith says successful demonstrations of the coils will be “a phenomenal statement on the technology.” But Hartmut Zohm, of the Max Planck Institute for Plasma Physics, says Commonwealth's goal of operating in 2025 is overly ambitious. Simultaneously developing a technology, building a reactor, and satisfying regulators about using radioactive fusion fuel will take more than 4 years, he says. “This will take more time,” he says. “But I'm happy to be proven wrong.”
领域	气候变化 ; 资源环境
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文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/318668
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Daniel Clery. Magnet tests kick off bid for net fusion energy[J]. Science,2021.
APA	Daniel Clery.(2021).Magnet tests kick off bid for net fusion energy.Science.
MLA	Daniel Clery."Magnet tests kick off bid for net fusion energy".Science (2021).