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

Private fusion machines aim
to beat massive global effort
Startups avoid ITER’s path with new prototype reactorsW

hen finally complete in 2025, the$20 billion fusion reactor called
ITER, rising near Cadarache inFrance, will be seven stories tall.
Even then, nothing guarantees thatit can hold nuclei together at temperatures of 150 million degrees Celsius, inducing them to fuse and release energy. Now,a small U.K. company has unveiled a 2-metertall chamber that looks like an oversized beer
keg and cost about £10 million to develop.
Using a different reactor shape than ITER
and, eventually, superconducting magnets,
the company says it has a cheaper and faster
path to an energy-producing fusion reaction.
“Fusion hasn’t been exciting enough inrecent years,” says David Kingham, CEO of
Tokamak Energy near Oxford, U.K. “Someone has to inject some excitement and cando attitude.”
Tokamak Energy is not alone. A few otherprivately financed startups are challenging the publicly funded, slow-moving
ITER behemoth (Science, 25 July 2014,p. 370). Two of the startups, Tri Alpha Energyof Foothill Ranch, California, and General
Fusion of Burnaby, Canada, are also building
new machines in the next few years that aim
to get close to the break-even point, where theenergy generated equals the energy put intothe system. Mainstream fusion researchers
say the approaches are technically plausible
360

and welcome the competition. “Fusion is too
important for one approach or one device,”says Dennis Whyte, director of the Plasma
Science and Fusion Center at the Massachusetts Institute of Technology in Cambridge.
Since the 1960s, one shape has dominatedfusion: the tokamak, a ring-shaped vessel forcontaining plasma, the ionized gas that mustbe heated to more than 100 million degrees
Celsius to achieve fusion. Powerful magnets
around the tokamak create fields that not
only keep the plasma from damaging the interior surfaces, but also compress and heatit. Yet scientists have struggled to keep theplasma stable and hot enough for a fusion reaction that produces excess energy. Because
theory and experiment suggest that large tokamaks retain heat better, they have tended
to get ever bigger—and more expensive.

Great balls of fireThree startup fusion companies are challenging ITER, an over-budget and overdue public project.
NAME

LOCATIONTECHNOLOGYSTAFF

FUNDINGSTATUSTARGET TEMPERATURE

Tokamak
EnergyMilton, U.K.

Spherical
tokamak35$25 million

New ST40 device
in 2017100 million degrees
Celsius

Tri Alpha
EnergyFoothill Ranch,
California

Beam-driven
plasma rings

160

>$500
million

New C-2W device
in 201730 million degrees
CelsiusGeneralFusion

Burnaby,
CanadaTarget
implosion

65>$75 million

Prototype in3–5 years

100 million degrees
Celsius

ITER

Cadarache,FranceTokamak

2300$20 billion

Under construction.
First plasma in 2025

150 million degrees
Celsiussciencemag.org SCIENCE

28 APRIL 2017 • VOL 356 ISSUE 6336

Published by AAASPHOTO: TOKAMAK ENERGY LTD 2017

By Daniel Clery

Downloaded from http://science.sciencemag.org/ on May 7, 2017

ENERGYIn the 1980s, however, theorists predictedthat 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 ofthe confining magnetic fields with superconducting magnets. Conventional superconductors must be cooled to liquid heliumtemperatures—a great expense. Tokamak Energy 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 material will make the difference in fusion overthe next few years,” Kingham says.
In 2015, Tokamak Energy built a sphericaltokamak just over a meter across and showed
it could confine plasma at a million degrees.
Now, it says its 2-meter device, called ST40,
will be able to heat a plasma to 100 million
degrees within a magnetic field of 3 tesla—asstrong as the field in a medical MRI machine.
Science was given an exclusive look at the newmachine before it begins operation in a few
months’ time. It will use conventional copperwire magnets while researchers develop
HTS magnets for a successor machine. Evenwithout HTS magnets, ST40 could reach
100 million degrees by 2019, enough “to validate this concept of spherical tokamaks forfusion power,” Kingham says.
Tokamak Energy, with £20 million infunding, “has achieved a huge amount witha relatively small amount of money,” says
Mark White of the Rainbow Seed Fund, aU.K.-backed venture capital fund for commercializing science from government
labs that has invested in Tokamak Energy.
In contrast, its competitor Tri Alpha has
amassed more than $500 million from a
mix of investors including the Wellcome
Trust and Kuwait’s sovereign wealth fund.
Tri Alpha exploits a phenomenon called aNEWS | I N D E P T H

ARCHAEOLOGY

Claim of very early humans inAmericas shocks researchers
Skepticism greets report of smashed mastodon bones
breaking the bones to reach the marrow,or to turn the bone itself into a sharper
hat broke the 130,000-year-oldtool. The nearby stones, hefty and round,mastodon bones in California?
show wear patterns consistent with beMost archaeologists would telling smashed against bone, the authors say.
you it couldn’t have been huIn experiments, they used that method tomans, who didn’t leave conclubreak elephant bones and produced identisive evidence of their presence in
cal fracture patterns.
the Americas until about 14,000 years ago.
The bones’ collagen, a protein that can be
But a small group of experts now says thatused for radiocarbon dating, was long gone.
the fracture patterns on the bones, foundInstead, the team relied on a dating techduring highway construction near San
nique based on the radioactive decay of uraDiego, California, must have been left bynium in minerals within the bone. Several
humans pounding them with stones founddating experts said the methods were soundnearby. If correct, the paper, publishedand found the 130,000-year date trustthis week in Nature, would push backworthy. “At face value, these results are about
the presence of people in the Americas by
as good as you can get,” says Alistair Pike,
more than 100,000 years—to a time whena uranium dating expert at the University
modern humans supof Southampton in theposedly had not even
United Kingdom.
expanded out of Africa
But that still leaves
to Europe or Asia.
the question of what
“The claims madesplintered the bones.
are extraordinary and“It is one thing to show
the potential implicathat broken bones andtions staggering,” says
modified rocks could
JonErlandson,
anhave been produced
Jon Erlandson, University of Oregonarchaeologist at theby people, which [thisUniversity of Oregon
paper does],” says Don
in Eugene who studies the peopling of theGrayson, an archaeologist at the UniverAmericas. “But broken bones and stonessity of Washington in Seattle. “It is quite
alone do not make a credible archaeologicalanother to show that people alone couldsite in my view.” He and many other archaeohave produced those modifications.” Andlogists say it will take much stronger eviGary Haynes, an archaeologist at the Unidence to convince them that the bones wereversity of Nevada in Reno, notes that “thefractured by ancient people.
features of the broken bones … are also proArchaeologists first excavated the Cerutti
duced when heavy construction equipment
Mastodon site in 1992, after the construccrushes buried bones.”tion exposed bones. Over time they foundAuthor and site excavator Thomas
more splintered bones and a smattering
Deméré, a paleontologist at the San Diegoof large round rocks embedded in otherNatural History Museum, says the teamwise fine-grained sediment. More recently,
carefully excavated 50 square meters beginDaniel Fisher, a respected paleontologist
ning in 1992, and the bones described in theat the University of Michigan in Ann Arpaper were “deeply buried. … There was nobor, took a close look at the fractures andequipment damage to the heart of the site.”found patterns he says are consistent withThe lack of actual shaped stone tools,
blows from a rounded stone, which leave aa “universal” at Old World sites, troubles
characteristic notch at the point of impact.
archaeologist John Shea of the State UniOther chips of bone show what he calls unversity of New York in Stony Brook. Even
mistakable signs of being popped off by thethe archaic humans that might have been
impact. “Nobody has ever explained thosepresent then, like Homo erectus or the mys[characteristic bone flakes] satisfactorily
terious Denisovans, left such flakes. “Thisin any way not involving human activity,”
evidence is well documented, but it’s not
Fisher says. He says humans were probably
sufficient to close the case,” Shea says. j

By Lizzie WadeW“The claims made are
extraordinary and thepotential implications
staggering.”

SCIENCE sciencemag.org

28 APRIL 2017 • VOL 356 ISSUE 6336

Published by AAAS361

Downloaded from http://science.sciencemag.org/ on May 7, 2017

field-reversed configuration (FRC), a spinningsmoke ring of plasma that produces its own
confining magnetic field because of the currents of electrons and ions within it. Known
since the 1960s, FRCs could be coaxed to last
only for a fraction of a millisecond before fizzling out. In 2015, Tri Alpha revealed it could
make an FRC last 5 milliseconds and confine
plasma at 10 million degrees Celsius (Science, 28 August 2015, p. 912). In its 25-meterlong device, plasma guns at both ends fired
FRCs at high speed toward the center, where
they merged and converted kinetic energy
into heat, boosting the temperature. The
machine further heated and stabilized themerged FRC by bombarding it with particles.
Over the past year, Tri Alpha has dismantled its machine and built a new one,30 meters long, with more particle beams
and better control of the heat loss from theplasma. When the researchers fire it up in afew months, they hope to achieve 30-milliondegree plasmas lasting up to 40 milliseconds.
Chief Technology Officer Michl Binderbauer
says they should learn enough physics fromthis machine to move on to much higher
temperatures. That path may be long: Tri Alpha wants to use a different fuel that does notcreate hazardous high-energy neutrons, butrequires billion-degree plasmas to fuse.
Across the border in Canada, GeneralFusion is taking another radical approach.
The company also relies on self-confining
plasma rings but will inject them into aspherical reaction chamber whose walls
are coated with liquid lithium metal. Dozens of pneumatic pistons, sticking out fromthe chamber like porcupine quills, will thenhammer down on the lithium in unison,
generating a shock wave that converges on
the plasma and crushes it, creating hightemperature and pressure.
With more than CA$100 million fromgovernment and private sources, General Fusion since 2002 has been workingseparately on the three components of thesystem—plasma injector, lithium vortex,
and pneumatic pistons. “Now we have toput it all together,” says CEO Chris Mowry.
The final device may have as many as 400pistons, and will take between 3 and 5 years
to build, he says. The aim is to heat plasma
to 100 million degrees, close to energyproducing conditions. Mowry says thedevice will rely on well-understood mechanical systems, which will produce “anaffordable and practical power plant.”
Despite such bold claims, plasma physicist
Glen Wurden of the Los Alamos National
Laboratory in New Mexico says he and others
are impressed with the results that the fusion
startups are now reporting. But, he adds, that
respect is “tempered by what are perceived as
overly optimistic schedules.” j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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