costly “miniature suns” in development around
the world, it’s arguably the bellwether for self-
sustaining fusion, given the seven countries that
share its high cost and are invested in its success.
All this time, engineers have been designing
and fabricating the planned 1 million compo-
nents needed for the reactor. In May, they finally
installed the first permanent piece at the reac-
tor’s Provence, France, campus: a steel base for the
outer shell of the reactor, which has taken 10 years
to forge and weld. This piece is the foundation for
the “giant thermos,” or cryostat, that holds the
reactor and contains its heat. The cryostat will be
made from 54 parts combined into four main sec-
tions, and it will weigh over 3,800 tons.
It’s a big step on the path toward 2025, when
ITER says all the core parts of the reactor will
be installed, fully integrated, and ready to pro-
duce its first plasma. That November—to mark
the 40th anniversary of Reagan and Gorbachev’s
historic U.S.-Soviet Geneva summit—the reactor
will begin a monthlong process of heating up to
150 million degrees Celsius, with a trio of heat-
ing elements pulling a combined 50MW of power,
enough for about 10,000 homes. That will bring
the plasma to a temperature 10 times greater than
the sun’s in the doughnut-shaped reactor to gener-
ate as much as 500MW of energy for brief bursts.
The sun’s fusion is powered by colliding hydro-
gen nuclei (atomic number 1) that fuse and make
helium (atomic number 2) while releasing energy.
But at the heart of the ITER tokamak is a more
efficient duo of deuterium and tritium, two hydro-
gen isotopes that release even more energy when
smashed together.
In December 2025, once ITER is hot enough,
the first plasma reaction will last just a few milli-
seconds to indicate that the fully integrated plant
is ready for operation. From there, it will go off line
for the installation of final parts before the full-
scale fusion ITER plans for the mid-2030s. After
the lengthy incubation period and progressively
longer test plasmas, ITER seeks to hit a state
called ignited plasma. This means the deuterium-
tritium reaction becomes self-sustaining—no
energy is required for the reactions to continue.
While ITER is designed to be a working power
plant, it’s also proof of concept for its components.
The biggest concern scientists have will be how
well each piece of the reactor contains the plasma
and its associated heat. Not only is the plasma
constantly moving, but any disruption can cool
the reactor in a matter of seconds and lose the
plasma state.
Inside the reactor, plasma is kept flowing by
superconducting electromagnets made of encir-
cling coils of wire. A central solenoid—basically
a coil of wire in a corkscrew shape—is bolstered
by smaller numbers of external and correction
coils. These are made from the superconductors
niobium–tin (Nb3Sn) and niobium-titanium
(NbTi). All of the coil assembly is held in a high-
vacuum pressure chamber (the cryostat).
The magnets are held at cryogenically cold
temperatures of –269 degrees Celsius to help
create a temperature buffer. Actively cooled ther-
mal shields reduce the radiation heat load that
is transferred by thermal radiation and conduc-tion from warm components (vessel) to the cold
components (magnets), and the entire 23,000-ton
tokamak is cooled by circulating water.
The ITER component-by-component focus
ref lects a larger goal in the nuclear field to make
fusion not just feasible, but modular, too. Instead
of reactors tailored for specific sites, this gener-
ation of nuclear engineers seeks parts that are
easier to manufacture, test, and contain. ITER
embodies the modular approach by putting suc-
cessful individual pieces of technology together
into the largest-ever full assembly. With existing
information on small tokamaks, ITER scientists
feel confident in their goals. But the future isn’t a
sure thing—until it happens.THE REACTOR WILL BEGIN A
MONTHLONG PROCESS OF HEATING
UP TO 150 MILLION DEGREES CELSIUS,
W I T H A T R I O O F H E AT I N G E L E M E N T S
PULLING A COMBINED 50MW OF POWER,
ENOUGH FOR ABOUT 10,000 HOMES.
"
September/October 2020 27