around the world began constructing tokamaks in earnest, more
than 200 working machines have been built. A key sign of progress
in the fusion field is the chart of the so-called triple product, a
measure of reactor performance. Plot this number—how hot, how
dense, and how well-insulated the systems are —against a timeline,
and it looks a lot like Moore’s law, the famous doubling of computing
power every two years. But fusion’s improvement is even faster.
“Tokamaks have beat Moore’s law,” says Bob Mumgaard, chief
executive officer of Commonwealth Fusion Systems, which was
spun out of MIT.
So why does it matter how hot a fusion system gets? Consider
the sun. Our local star has a lot of plus-size gravity to apply to the
fusion process. Its interior brings the pressure of a mass equivalent
to about 333,000 Earths and a temperature of about 15 million C
(27 million F). That’s the kind of forge in which fusion happens.
On Earth, with so much less gravity, you need higher tem-
peratures: 100 million C, for example. So the first step to get there
is to heat a gas and turn it into a plasma, says Michl Binderbauer,
CEO of TAE Technologies Inc., based in Foothill Ranch, Calif.
“That happens through adding more energy, so at some point the
ions and electrons that make up the atoms fall apart into a soup of
charges,” he says. “That’s the state that actually most of the universe
is in—what we call a plasma.”
Almost all of the visible stuff in the universe is plasma. “We’re
living probably in one of the few specks of the universe where there’s
no plasma in our immediate surroundings other than lightning or
something,” Binderbauer explains. What’s more, in the 1950s,
when instabilities and other “funky behavior” in plasma turned out
to make fusion much harder than expected, Mumgaard says, it led
to the development of an entire discipline, plasma physics. The
field has in turn contributed advances in medicine and in manu-
facturing semiconductors.
Now, heating plasma to 100 million C sounds daunting and
terrifying. Wouldn’t it vaporize whatever it touches? Short answer:
no. The plasma is a handful of particles in a vacuum chamber, Bin-
derbauer says. It’s millions of times less dense than air, its state is
extremely fragile, and if it touches anything it instantly cools down.
TAE’s Norman machine heats plasma to 35 million degrees, says
Binderbauer. If, hypothetically, he could stick his hand into the
vacuum shell, he says the plasma wouldn’t burn him. “My arm will
absorb all of the energy,” he says. “I won’t even turn very warm.”
Fusion, unlike fission, has no risk of meltdown. “You have to protect
the plasma from the surrounding environment, not the other way
around,” he says.
Fusion would have one other important benefit over solar,
wind, and other intermittent sources of renewable energy, says
Christofer Mowry, CEO of General Fusion Inc., based in Burnaby,
B.C., near Vancouver: It’s “dispatchable” power. In most of the
applications anticipated for fusion, the energy created in a reaction
would heat water and run a conventional steam turbine generator.
Plants could be safely and conveniently situated in cities and other
places power is needed, Mowry says.
One obvious downside to fusion, reflected in the field’s
70 years of history and dashed hopes for imminent breakthroughs:
It’s extraordinarily difficult to bring off.
In 1983 the late Lawrence Lidsky, an associate director of
what was then called MIT’s Plasma Fusion Center, wrote an article
titled “The Trouble With Fusion.” Fusion, he wrote, “is a textbook
example of a good problem for both scientists and engineers. Many
regard it as the hardest scientific and technical problem ever tackled,
yet it is nonetheless yielding to our efforts.” Still, Lidsky laid out a
laundry list of problems that, he contended, made it unlikely that
fusion would ever be an economically viable source of power.
More than three decades later, the problems Lidsky identi-
fied remain. Chief among them is radioactivity. To be sure, the fuel
used in fusion doesn’t pose quite the same dangers as fission’s
uranium and nuclear waste. To understand fusion’s radioactivity
challenge requires a slightly deeper dive into the science.
To begin, a variety of different light elements can be combined
in a fusion reaction. However, the fuel that’s easiest to fuse is a
50-50 combination of two isotopes of hydrogen: deuterium and
tritium. D-T, as it’s called, has been the main focus of the field.
Deuterium is heavy hydrogen, the stuff found in seawater. Its
nucleus consists of a proton plus a neutron (in contrast to plain old
hydrogen’s lonely proton). Tritium is heavy, heavy hydrogen: a
proton with two neutrons. It’s radioactive, with a half-life of about1920
British astronomer
Arthur Eddington’s
“The Internal
Constitution of the
Stars” posits that stars
including the sun are
powered by the fusion
of hydrogen.1938
Nuclear physicist Hans
Bethe describes the
fusion reactions that
create the energy
emitted by stars, for
which he later wins
the Nobel Prize.1951
Juan Perón (far right)
and scientist Ronald
Richter (second
from right) announce
that Argentina
has developed
fusion energy.1952
The first test of a
hydrogen bomb,
code-named Ivy Mike,
uses a fission explosion
to ignite a fusion
reaction in deuterium
fuel. The 10-megaton
blast leaves a big crater
on Enewetak atoll.1958
ZETA excitement
and disappointment
as U.K. researchers
announce they’ve likely
created a controlled
fusion reaction, but
later retract.1964
A fusion demonstration
at Progressland at
the World’s Fair in
New York.Long Road
Fusion’s history is studded with disappointments as well as advances72 BLOOMBERG MARKETS