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REKINDLINGTHE FLAME

After decades of decline,
the U.S. government’s fusion lab seeks a rebirth

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Energy’s (DOE’s) fusion budget and shut
down TFTR. In 2003, the United States
joined the effort to build ITER, the giant
international reactor under construction
near Cadarache in France—a commitmentthat squeezed fusion research at home evenharder. In 2008, DOE canceled another unfinished fusion reactor at PPPL, leading toa reshuffling of lab leadership. Now, PPPL
employs 560 people. Its one large machine,
NSTX, sits idle 3 years after breaking down.

PPPL director Steven Cowley wants to grow the lab.
His first task is to repair its main fusion reactor.

Yet things may be looking up for the lab.
After years of DOE reviews, PPPL researchers
expect to start to rebuild NSTX in April. Anda year ago, a report from the National Academies of Sciences, Engineering, and Medicine(NASEM) urged the United States not only tostick with ITER—which is hugely overbudget
and behind schedule—but also to prepare tobuild the machine after it (Science, 21 December 2018, p. 1343). This would be a prototype

power plant, smaller and cheaper than ITER,
and PPPL would likely play a leading role inbuilding it.
Perhaps most important, in 2018 Princeton
University, which runs the lab for DOE, hired
a new lab director. Steven Cowley, a strapping 60-year-old Englishman with a shock ofsilver hair and a knighthood, makes no bones
about his role as an agent of change. “My job
as a director is not to be an administrator,” hesays in his velvety baritone. “It’s about scientific vision. What should we be doing? What
are the interesting questions? How do we get
to fusion?” He already has a plan to diversify the lab’s work, grow its staff, and start tobuild things again.
Physicists are watching PPPL as a bellwether for the fortunes of the U.S. fusion
program, whose share of the world’s public fusion research has slipped to just onesixth. And some observers who have been
critical of the lab’s previous leadership andculture think PPPL is finally on the righttrack. “Steve is the best person on the planet
for the job,” says William Madia, former director of two other DOE national labs, who
urged Princeton to hire Cowley. “I’m optimistic.” Yet the lab still faces obstacles on
the path to redemption.
NSTX RESEMBLES an extraterrestrial space-ship. The two-story orb nestles in a cocoonof pipes and cables, the red coils of its main
magnet arching up out of the chaos like flying buttresses. Within the orb—the reactor’s
partially disassembled vacuum chamber—copper plates and graphite tiles line thesilvery walls. One could imagine that some
reptilian alien slumbered away the eons here
while traveling to the Solar System. During
sciencemag.org SCIENCE

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oseph Winston, a technician here at
the Princeton Plasma Physics Laboratory (PPPL), knew something
was wrong with the fusion reactor just by listening. In 2016, PPPL
physicists had restarted their National Spherical Torus Experiment(NSTX), after a 5-year, $94 million
upgrade. During one of the machine’s runs, which last just seconds, millionsof amps course through NSTX’s magnet coils,
creating fields that squeeze an ionized gas sotightly that atomic nuclei can fuse. The currents also stress the coils, which emit a groan
loud enough to be heard through more thana meter of concrete. But the sound was petering out prematurely, Winston recalls.
When Winston and his team traced the
problem to a short in one coil, the 50-year
PPPL veteran knew the reactor, or tokamak,
would be down for a long time. The machine is “like a one-way street,” he says. “Ifanything happens to these coils, the wholething has to come apart just to get to it.”After running for just 10 weeks, NSTX wasshut down again.
It was a body blow to a lab that was already staggering. In the 1980s, PPPL ran
multiple machines, employed nearly 1300
people, and led the worldwide quest to harness fusion, the energy source of the Sun.
“The action was almost frantic,” says Dale
Meade, a PPPL physicist emeritus. “We weretaking risks, building one thing before theother was finished.” In 1994, PPPL’s largest
machine ever, the Tokamak Fusion Test Reactor (TFTR), briefly generated 10.7 megawattsof power, still the record for U.S. efforts.
The good times didn’t last. Within years,
Congress had slashed the Department of

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By Adrian Cho, in Princeton, New Jersey

Achilles’ heel

Sun in a bottle

In 2016, soon after an
upgrade, an upper
coil failed. The machine
was disassembled
and has sat idle,
forcing a reckoning
over PPPL’s future.

When it restarts in 2021, therepaired National Spherical Torus
Experiment (NSTX) at Princeton
Plasma Physics Laboratory (PPPL)
will use magnetic fields to trap
and squeeze a hot ionized gas,or plasma, coaxing atomic nuclei
to fuse and generate energy thesame way as in the Sun. NSTX
will test how efficiently a sphericalshape can squeeze the plasma.
It will also test using liquid lithium
to protect NSTX’s chamber walland help shunt out heat.

Poloidalfeld line

Toroidalfeld line

MovingplasmaPoloidal magnetic coil

Field line

Toroidal magnetic coil

A crucial twist

Rev it up!
During a secondslong
run, a current of
24,000 amps quickly
reverses in the tubelike
central solenoid coilto propel the plasmaaround the torus
40,000 times per
second. That motion
helps generate
the poloidal field.

Divertor

Tokamaks on parade
PPPL’s star has fallen, along with the size of its
fusion reactors. But a refurbished NSTX could
revive the lab, and set the stage for a leading rolein building a fusion power plant after ITER.

GRAPHIC: C. BICKEL/SCIENCE*reactors drawn
to scale?

Tokamak Fusion
Test Reactor

National Compact
Stellarator Experiment

National Spherical
Torus ExperimentInternational Thermonuclear
Experimental Reactor

PPPL’s biggest machineran from 1982 to 1997.
In 1994, it set a U.S. record
for power produced.

Canceled in 2008, NCSX would
have generated a twisting
field with asymmetric coils,
enabling it to run continuouslywith a stationary plasma.

Built in 1999, NSTX tests
how a spherical shapeboosts plasma pressures.
Tests will resume in 2021.

The $25 billion reactor, aninternational effort under construction
in France, aims to produce moreenergy than it consumes. It should
begin operations in 2025.

a run, something nearly as otherworldly fills
the chamber: a wispy ionized gas, or plasma,heated to 100 million degrees Celsius—
hotter than the core of the Sun. Injected
microwaves and churning magnetic fields
heat and squeeze the plasma and whirl it
around the chamber 40,000 times per second.
The plasma is made of deuterium, aheavier isotope of hydrogen, and the goal
is to bring it to temperatures and pressuresat which colliding nuclei can fuse to form
helium. The reactions release energy, carried away by free-flying neutrons. Replacing some of the deuterium with tritium,
an even heavier isotope of hydrogen, could
make the reactions self-sustaining. Such
fusion promises abundant, carbon-free energy with little of the radioactive waste generated by fission-powered nuclear reactors.
That prospect has fired PPPL for the past

SCIENCE sciencemag.org

Compact Pilot Plant
To be built in the 2030s,
the prototype power
plant would leverage
emerging technologies
and be smaller andcheaper than ITER.

half-century. Yet, on a rainy Monday morning in October 2019, the lab is eerily quiet.
Nestled among pines in a technology park
east of tony Princeton, PPPL grew out of theuniversity’s classified work on the hydrogenbomb and astrophysicist Lyman Spitzer’s
parallel effort to tame fusion as a powersource. Founded in 1961, PPPL built a seriesof ever bigger devices that in 1982 culminated in TFTR, a reactor three times as wide
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To trap a plasma andkeep it away from thewalls of the vacuum
chamber, the totalmagnetic field—thesum of the toroidal
and poloidal fields—
must twist like a candy
cane. That winding
is produced by
the current in theplasma itself.

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The plasma chamber of
NSTX seen in 2014,
before a short forced it
to be disassembled.

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of its magnetic field. An investigation revealed numerous problems in addition to theshorted coil, Hawryluk says. “We felt strongly
that we really needed to understand what
was going on,” he says, “and not just fix one
thing and then come back and say, ‘Well, now
something else is wrong.’” Additionally, DOE
put PPPL’s $199 million repair plan throughthe same yearslong approval process it requires for a whole new project.
That was an overreaction, says Martin
Greenwald, a physicist at the Massachusetts
Institute of Technology. “Instead [of fixing
the problem] it’s like, ‘Oh, we’re going have amillion reviews,’” he says. But Madia says thelab brought the scrutiny on itself by failingto catch the problem and reacting slowly toit. “The problem was really leadership at thelab,” he says.
If NSTX’s failure strained the lab’s relations with DOE, it nearly broke those withthe university, Meade says. The lab’s director
at the time, Stewart Prager, was forced out
and a few months later Princeton President
Christopher Eisgruber took the staff to task
in an all-hands meeting, Meade says. “Hegave about a 20-minute talk admonishing
the laboratory, telling them how deeply dissciencemag.org SCIENCE

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suffer from a limitation, however. To trap a
plasma, the magnetic field going around thetorus must twist like the stripes on a candy
cane. To generate that twist, the plasma itself
has to race around the doughnut to produce
a current. And the laws of electrodynamics
state that to push the plasma around, physicists need another rapidly changing magnetic field, which is generated by a coil inthe doughnut hole. A run lasts as long as it
takes to reverse the current in the coil—justa couple of seconds. Moreover, in a spherical torus, several different magnet coils arecrammed precariously into the narrow hole.
A machine called a stellarator avoids thefirst limitation by generating the twist notwith a moving plasma, but with twisted magnetic coils. In principle it can run steadily
and more efficiently (Science, 23 October
2015, p. 369). In 2001, PPPL started work on
one called the National Compact Stellarator
Experiment (NCSX). However, by 2008—a year after it was supposed to be finished—
its cost had nearly tripled to $170 million.
DOE canceled the project, leaving PPPL with
one machine and a black eye.
Then came the failure of NSTX after its
upgrade, which aimed to double the strength

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as NSTX that set its power record while running on deuterium and tritium. “We made atremendous splash in the newspapers,” recalls Michael Zarnstorff, PPPL’s chief scientist. “People would ask, ‘When are you goingto have electricity from fusion?’”That prospect has eluded physicists. ITER
aims to be the first tokamak to produce
more energy than it consumes. But TFTR
was also supposed to do that and it cameup short. Controlling a plasma turned out
to be harder than anticipated, the electromagnetic equivalent of grasping an eel. After DOE shut down TFTR, PPPL researchers developed two smaller, more radical
machines with different advantages.
NSTX was the more conventional design.
A traditional tokamak has the shape of adoughnut. But a spherical torus like NSTX
resembles a cored apple. For the same magnetic field, the rounder shape should put
more pressure on the plasma, says Richard
Hawryluk, a physicist at PPPL. “Basically you
want to optimize the bang for the buck,” hesays. From 1999 to 2009, NSTX confirmedthat prediction, which could make reaching
the elusive break-even power point easier.
All tokamaks, including spherical ones,

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appointed and embarrassed he was about
this incident,” he says. Eisgruber says he simply told researchers the situation was urgent.
“It’s our obligation to deliver on the contracts
we form with DOE,” he says. “There has to be
a commitment to excellence.”
IN SOME WAYS, Cowley seems an odd choiceadvanced microchips. “The U.S. dominates
the industry that makes the machines thatmake the chips,” he says. “If we’re not careful we’ll lose that to China.”
Cowley plans to double the lab’s staff,
with the cold plasma work accounting for
30% to 50% of the total. Craig Arnold, director of the Princeton Institute for the Science and Technology of Materials, envisions
close ties to PPPL. “You have these two entities that are literally next door to each otherand part of the same overall organization.

to guide the beleaguered lab—a Brit who
doesn’t drive leading an American lab
in car-clogged New Jersey. (He takes thebus to work.) For a person in the hot seat,
Cowley also exudes a curious ebullience. “I’m a very lucky person because
my serotonin level is pretty much always right,” he says. “So I pretty much
like anywhere I am.”
Steven Cowley, Princeton Plasma Physics Laboratory
Cowley is no stranger to PPPL. He
earned his doctorate here in 1985, before going on to positions at the University ofIt’s silly for us not to be working together,”
California, Los Angeles, and University Colhe says. The university and the lab are negolege London. He also has ample leadership
tiating to construct a $100 million building
experience. From 2009 to 2016, he served as
at PPPL for the cold plasma and material
CEO of the UK Atomic Energy Authority andscience work.
director of the Culham Centre for Fusion EnIn the longer term, Cowley says he wants
ergy. There he oversaw work on a competitor
to get PPPL back to building big machines.
to NSTX, the Mega Ampere Spherical Toka“What’s the facility after NSTX?” he asks.
mak, which was upgraded last year.
“My mission is to define that and get it to
At PPPL, job No. 1 is to get NSTX running
happen.” In particular, he would like toagain. To do that, Cowley brought in John
revisit the idea of building a stellarator.
Galayda, an accelerator physicist who led
But instead of fashioning bizarrely shaped
construction of the world’s first hard x-ray lacoils for the machine, Cowley envisions
ser, the Linac Coherent Light Source at SLAC
using conventional ones and adding highNational Accelerator Laboratory, which instrength permanent magnets on electroni2009 worked on the first attempt. PPPL recally adjustable mounts to shape the field.
searchers have begun to fabricate new parts“It’s just an idea and maybe it’ll go noand aim to have NSTX running in summer
where,” says Cowley, who sketches out the2021. For Jessica Guttenfelder, a mechanicalidea with colleagues in a paper in press atengineer who started at PPPL weeks before
Physical Review Letters.
the machine conked out, it feels like a rebirth.
Other U.S. fusion physicists welcome his“Everything you’re exposed to is so unique,”ambitions, noting that aside from parts forsays Guttenfelder, who is in charge of a deITER, DOE hasn’t built a major fusion mavice that shoots hydrogen atoms into NSTX’schine since NSTX. “At some point we needplasma to help it spin.
to be building,” says Erik Trask, a physicist
The 20-year-old reactor still has work toat the fusion startup TAE Technologies. “I
do, Hawryluk says. With its stronger magwould love to see many midscale machines
netic field, NSTX will test whether a spheriget built.” Eisgruber says he is “greatly encal tokamak’s favorable scaling of pressure
thusiastic” about the plans for the lab. “Stevewith magnetic field persists at temperaCowley has a vision that I fully support.”tures where fusion can occur. Physicists
will also have to figure out how to handle
THE PLAN ALSO SEEMS to dovetail with the viunprecedented loads on the divertors, ansion outlined in the December 2018 NASEM
exhaust system for the reactor’s heat. They
report, which urged the United States towill explore whether lining the reactor withbuild a prototype power plant in the 2030s
molten lithium helps stabilize the plasma
as a successor to ITER. Taking advantage ofand tame the exhaust.
innovations such as powerful magnet coils
At the same time, Cowley aims to transmade from high temperature superconducform PPPL into a multipurpose lab withtors, that Compact Pilot Plant (CPP) would bemuch stronger ties to the university andsmaller and cheaper than ITER, a $25 billion
industry. PPPL’s nonfusion work has typibehemoth. Such miniaturization will be vital
cally focused on the plasmas in stars andin the U.S. energy market, Cowley predicts,
interstellar space. Cowley plans to expand
as no utility will buy a plant that expensive.
into the use of cold plasmas to process maThe call to build the CPP might help
terials, in particular to make ever-morefill PPPL’s sails. PPPL wouldn’t build themachine on its campus, researchers say,because it would produce too much radioactive material for a densely populated
place like Princeton. But the lab would undoubtedly play a leading role in designingand building the machine. “We’re enthusiastic about the report,” Zarnstorff says. The
first step for the CPP would be to make itinto DOE’s next long-range plan for fusion,
which researchers and the agency aim tohash out by year’s end.
But that rosy scenario faces several uncertainties. For example, even if DOE
embraces the CPP, it would likely
build a power plant only as part of apublic-private partnership, Zarnstorffsays. So the fate of the project may
depend on whether companies suchas TAE Technologies and Commonwealth Fusion Systems can help bear thecosts and risks of the project.
The push toward a working fusion power
plant also highlights a tension within DOE.
Since 1998, the department’s fusion energy
science program has resided in its basic research wing, the Office of Science. Many U.S.
fusion researchers say the basic research
tag handcuffs them. “There’s a lot of cuttingedge research in fusion technology that we
can’t support that because it’s not science,”
Greenwald says. Zarnstorff says that to pursue the CPP, DOE ultimately may have to
move fusion into applied research.
Cowley says such talk is premature. “I don’t
think we can get to commercial fusion power
without solving some really quite profoundscientific problems,” he says. For instance, hesays, researchers still need to figure out how
to deal with exhaust heat.
And then there’s the question of money.
The NASEM report calls for a $200-millionper-year increase in U.S. fusion research, andCongress boosted DOE’s budget for fusion energy sciences from $564 million in fiscal year
2019 to $671 million this year. But all of that
increase will go to ITER, and it remains to be
seen whether Congress will continue to ramp
up the fusion budget.
For now, Cowley is focused on rejuvenating a fallen lab and boosting its morale. Overa group lunch in a conference room, Laura
Xin Zhang, a fourth-year graduate student
at Princeton, says she chose fusion because
she was seeking a mission in her work. “We’rethe generation of climate change, so everyone
wants to do something with climate change,”says Zhang, a native of Dalian, China. Fusion
could offer an answer. “Someone has to workon this, or it will never happen,” Zhang says.
“It will happen in your lifetime,” Cowleyinterjects.
“You think?” Zhang says.
“Mine, it’s touch and go,” Cowley says witha smile. “I need to keep fit.” j“What’s the facility after NSTX? My mission
is to define that and get it to happen.”

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SCIENCE sciencemag.org

Rekindling the flame
Adrian Cho

Science 367 (6478), 618-621.
DOI: 10.1126/science.367.6478.618

http://science.sciencemag.org/content/367/6478/618

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