Plasma inside Tokamak Energy’s spherical ST40 reactor could reach 100 million degrees Celsius.

In the 1980s, however, theorists predicted that changing the shape of the tokamak from a doughnut to a cored apple would improve plasma stability (Science, 22 May 2015, p. 854). Tokamak Energy is betting on that shape, called a spherical tokamak. It also aims to crank up the strength of the confining magnetic fields with super- conducting magnets. Conventional super- conductors must be cooled to liquid helium temperatures—a great expense. Tokamak En- ergy is experimenting with layered tapes that contain high-temperature superconductors (HTS) sandwiched between other materials and only need cooling with far cheaper liquid nitrogen. “I’m very convinced that this ma- terial will make the difference in fusion over ENERGY the next few ,” Kingham says. In 2015, Tokamak Energy built a spherical tokamak just over a meter across and showed Private fusion machines aim it could confine plasma at a million degrees. Now, it says its 2-meter device, called ST40, on April 27, 2017 will be able to heat a plasma to 100 million to beat massive global effort degrees within a magnetic field of 3 tesla—as strong as the field in a medical MRI machine. Startups avoid ITER’s path with new prototype reactors Science was given an exclusive look at the new machine before it begins operation in a few By Daniel Clery and welcome the competition. “Fusion is too months’ time. It will use conventional copper- important for one approach or one device,” wire magnets while researchers develop hen finally complete in 2025, the says Dennis Whyte, director of the Plasma HTS magnets for a successor machine. Even $20 billion fusion reactor called Science and Fusion Center at the Massachu- without HTS magnets, ST40 could reach ITER, rising near Cadarache in setts Institute of in Cambridge. 100 million degrees by 2019, enough “to vali- France, will be seven stories tall. Since the 1960s, one shape has dominated date this concept of spherical tokamaks for

Even then, nothing guarantees that fusion: the tokamak, a ring-shaped vessel for fusion power,” Kingham says. http://science.sciencemag.org/ it can hold nuclei together at tem- containing plasma, the ionized gas that must Tokamak Energy, with £20 million in Wperatures of 150 million degrees Celsius, in- be heated to more than 100 million degrees funding, “has achieved a huge amount with ducing them to fuse and release energy. Now, Celsius to achieve fusion. Powerful magnets a relatively small amount of money,” says a small U.K. company has unveiled a 2-meter- around the tokamak create fields that not Mark White of the Rainbow Seed Fund, a tall chamber that looks like an oversized beer only keep the plasma from damaging the in- U.K.-backed venture capital fund for com- keg and cost about £10 million to develop. terior surfaces, but also compress and heat mercializing science from government

Using a different reactor shape than ITER it. Yet scientists have struggled to keep the labs that has invested in Tokamak Energy. Downloaded from and, eventually, superconducting magnets, plasma stable and hot enough for a fusion re- In contrast, its competitor Tri Alpha has the company says it has a cheaper and faster action that produces excess energy. Because amassed more than $500 million from a path to an energy-producing fusion reaction. theory and experiment suggest that large to- mix of investors including the Wellcome “Fusion hasn’t been exciting enough in kamaks retain heat better, they have tended Trust and Kuwait’s sovereign wealth fund. recent years,” says David Kingham, CEO of to get ever bigger—and more expensive. Tri Alpha exploits a phenomenon called a Tokamak Energy near Oxford, U.K. “Some- one has to inject some excitement and can- do attitude.” Great balls of fire Tokamak Energy is not alone. A few other Three startup fusion companies are challenging ITER, an over-budget and overdue public project. privately financed startups are challeng-

ing the publicly funded, slow-moving NAME LOCATION TECHNOLOGY STAFF FUNDING STATUS TARGET TEMPERATURE ITER behemoth (Science, 25 July 2014, p. 370). Two of the startups, Tri Alpha Energy Tokamak Milton, U.K. Spherical 35 $25 million New ST40 device 100 million degrees Energy tokamak in 2017 Celsius of Foothill Ranch, California, and General Fusion of Burnaby, Canada, are also building Tri Alpha Foothill Ranch, Beam-driven 160 >$500 New C-2W device 30 million degrees new machines in the next few years that aim Energy California plasma rings million in 2017 Celsius to get close to the break-even point, where the General Burnaby, Target 65 >$75 million Prototype in 100 million degrees energy generated equals the energy put into Fusion Canada implosion 3–5 years Celsius the system. Mainstream fusion researchers ITER Cadarache, Tokamak 2300 $20 billion Under construction. 150 million degrees

say the approaches are technically plausible France First plasma in 2025 Celsius 2017 LTD ENERGY TOKAMAK PHOTO:

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field-reversed configuration (FRC), a spinning ARCHAEOLOGY smoke ring of plasma that produces its own confining magnetic field because of the cur- rents of electrons and ions within it. Known Claim of very early in since the 1960s, FRCs could be coaxed to last only for a fraction of a millisecond before fizz- ling out. In 2015, Tri Alpha revealed it could Americas shocks researchers make an FRC last 5 milliseconds and confine plasma at 10 million degrees Celsius (Sci- Skepticism greets report of smashed mastodon bones ence, 28 August 2015, p. 912). In its 25-meter- long device, plasma guns at both ends fired By Lizzie Wade breaking the bones to reach the marrow, FRCs at high speed toward the center, where or to turn the bone itself into a sharper they merged and converted kinetic energy hat broke the 130,000--old tool. The nearby stones, hefty and round, into heat, boosting the temperature. The mastodon bones in California? show wear patterns consistent with be- machine further heated and stabilized the Most archaeologists would tell ing smashed against bone, the authors say. merged FRC by bombarding it with particles. you it couldn’t have been hu- In experiments, they used that method to Over the past year, Tri Alpha has dis- mans, who didn’t leave conclu- break elephant bones and produced identi- mantled its machine and built a new one, sive evidence of their presence in cal fracture patterns. 30 meters long, with more particle beams Wthe Americas until about 14,000 years ago. The bones’ collagen, a protein that can be and better control of the heat loss from the But a small group of experts now says that used for radiocarbon dating, was long gone. plasma. When the researchers fire it up in a the fracture patterns on the bones, found Instead, the team relied on a dating tech- few months, they hope to achieve 30-million- during highway construction near San nique based on the radioactive decay of ura- degree plasmas lasting up to 40 milliseconds. Diego, California, must have been left by nium in minerals within the bone. Several Chief Technology Officer Michl Binderbauer humans pounding them with stones found dating experts said the methods were sound says they should learn enough physics from nearby. If correct, the paper, published and found the 130,000-year date trust- on April 27, 2017 this machine to move on to much higher this week in , would push back worthy. “At face value, these results are about temperatures. That path may be long: Tri Al- the presence of people in the Americas by as good as you can get,” says Alistair Pike, pha wants to use a different fuel that does not more than 100,000 years—to a time when a uranium dating expert at the University create hazardous high-energy neutrons, but modern humans sup- of Southampton in the requires billion-degree plasmas to fuse. posedly had not even United Kingdom. Across the border in Canada, General expanded out of But that still leaves Fusion is taking another radical approach. to Europe or Asia. “The claims made are the question of what The company also relies on self-confining “The claims made extraordinary and the splintered the bones. plasma rings but will inject them into a are extraordinary and “It is one thing to show spherical reaction chamber whose walls the potential implica- potential implications that broken bones and are coated with liquid lithium metal. Doz- tions staggering,” says staggering.” modified rocks could ens of pneumatic pistons, sticking out from Jon Erlandson, an have been produced http://science.sciencemag.org/ the chamber like porcupine quills, will then archaeologist at the Jon Erlandson, University of Oregon by people, which [this hammer down on the lithium in unison, University of Oregon paper does],” says Don generating a shock wave that converges on in Eugene who studies the peopling of the Grayson, an archaeologist at the Univer- the plasma and crushes it, creating high Americas. “But broken bones and stones sity of Washington in Seattle. “It is quite temperature and pressure. alone do not make a credible archaeological another to show that people alone could With more than CA$100 million from site in my view.” He and many other archaeo- have produced those modifications.” And

government and private sources, Gen- logists say it will take much stronger evi- Gary Haynes, an archaeologist at the Uni- Downloaded from eral Fusion since 2002 has been working dence to convince them that the bones were versity of Nevada in Reno, notes that “the separately on the three components of the fractured by ancient people. features of the broken bones … are also pro- system—plasma injector, lithium vortex, Archaeologists first excavated the Cerutti duced when heavy construction equipment and pneumatic pistons. “Now we have to Mastodon site in 1992, after the construc- crushes buried bones.” put it all together,” says CEO Chris Mowry. tion exposed bones. Over time they found Author and site excavator Thomas The final device may have as many as 400 more splintered bones and a smattering Deméré, a paleontologist at the San Diego pistons, and will take between 3 and 5 years of large round rocks embedded in other- Natural History Museum, says the team to build, he says. The aim is to heat plasma wise fine-grained sediment. More recently, carefully excavated 50 square meters begin- to 100 million degrees, close to energy- Daniel Fisher, a respected paleontologist ning in 1992, and the bones described in the producing conditions. Mowry says the at the University of Michigan in Ann Ar- paper were “deeply buried. … There was no device will rely on -understood me- bor, took a close look at the fractures and equipment damage to the heart of the site.” chanical systems, which will produce “an found patterns he says are consistent with The lack of actual shaped stone tools, affordable and practical power plant.” blows from a rounded stone, which leave a a “universal” at Old World sites, troubles Despite such bold claims, plasma physicist characteristic notch at the point of impact. archaeologist John Shea of the State Uni- Glen Wurden of the Los Alamos National Other chips of bone show what he calls un- versity of New York in Stony Brook. Even Laboratory in New Mexico says he and others mistakable signs of being popped off by the the archaic humans that might have been are impressed with the results that the fusion impact. “Nobody has ever explained those present then, like erectus or the mys- startups are now reporting. But, he adds, that [characteristic bone flakes] satisfactorily terious , left such flakes. “This respect is “tempered by what are perceived as in any way not involving activity,” evidence is well documented, but it’s not overly optimistic schedules.” j Fisher says. He says humans were probably sufficient to close the case,” Shea says. j

SCIENCE sciencemag.org 28 APRIL 2017 • VOL 356 ISSUE 6336 361

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DA_0428NewsInDepth.indd 361 4/26/17 10:18 AM Private fusion machines aim to beat massive global effort Daniel Clery (April 27, 2017) Science 356 (6336), 360-361. [doi: 10.1126/science.356.6336.360]

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