It was a moment three years in the making, based on intensive research and
design work: On Sept. 5, for the first time, a large high-temperature
superconducting electromagnet was ramped up to a field strength of 20 tesla,
the most powerful magnetic field of its kind ever created on Earth. That
successful demonstration helps resolve the greatest uncertainty in the quest
to build the world's first fusion power plant that can produce more power
than it consumes, according to the project's leaders at MIT and startup
company Commonwealth Fusion Systems (CFS).
That advance paves the way, they say, for the long-sought creation of
practical, inexpensive, carbon-free power plants that could make a major
contribution to limiting the effects of global climate change.
"Fusion in a lot of ways is the ultimate clean energy source," says Maria
Zuber, MIT's vice president for research and E. A. Griswold Professor of
Geophysics. "The amount of power that is available is really game-changing."
The fuel used to create fusion energy comes from water, and "the Earth is
full of water—it's a nearly unlimited resource. We just have to figure out
how to utilize it."
Developing the new magnet is seen as the greatest technological hurdle to
making that happen; its successful operation now opens the door to
demonstrating fusion in a lab on Earth, which has been pursued for decades
with limited progress. With the magnet technology now successfully
demonstrated, the MIT-CFS collaboration is on track to build the world's
first fusion device that can create and confine a plasma that produces more
energy than it consumes. That demonstration device, called SPARC, is
targeted for completion in 2025.
"The challenges of making fusion happen are both technical and scientific,"
says Dennis Whyte, director of MIT's Plasma Science and Fusion Center, which
is working with CFS to develop SPARC. But once the technology is proven, he
says, "it's an inexhaustible, carbon-free source of energy that you can
deploy anywhere and at any time. It's really a fundamentally new energy
source."
Whyte, who is the Hitachi America Professor of Engineering, says this week's
demonstration represents a major milestone, addressing the biggest questions
remaining about the feasibility of the SPARC design. "It's really a
watershed moment, I believe, in fusion science and technology," he says.
The sun in a bottle
Fusion is the process that powers the sun: the merger of two small atoms to
make a larger one, releasing prodigious amounts of energy. But the process
requires temperatures far beyond what any solid material could withstand. To
capture the sun's power source here on Earth, what's needed is a way of
capturing and containing something that hot—100,000,000 degrees or more—by
suspending it in a way that prevents it from coming into contact with
anything solid.
That's done through intense magnetic fields, which form a kind of invisible
bottle to contain the hot swirling soup of protons and electrons, called a
plasma. Because the particles have an electric charge, they are strongly
controlled by the magnetic fields, and the most widely used configuration
for containing them is a donut-shaped device called a tokamak. Most of these
devices have produced their magnetic fields using conventional
electromagnets made of copper, but the latest and largest version under
construction in France, called ITER, uses what are known as low-temperature
superconductors.
The major innovation in the MIT-CFS fusion design is the use of
high-temperature superconductors, which enable a much stronger magnetic
field in a smaller space. This design was made possible by a new kind of
superconducting material that became commercially available a few years ago.
The idea initially arose as a class project in a nuclear engineering class
taught by Whyte. The idea seemed so promising that it continued to be
developed over the next few iterations of that class, leading to the ARC
power plant design concept in early 2015. SPARC, designed to be about half
the size of ARC, is a testbed to prove the concept before construction of
the full-size, power-producing plant.
Until now, the only way to achieve the colossally powerful magnetic fields
needed to create a magnetic "bottle" capable of containing plasma heated up
to hundreds of millions of degrees was to make them larger and larger. But
the new high-temperature superconductor material, made in the form of a
flat, ribbon-like tape, makes it possible to achieve a higher magnetic field
in a smaller device, equaling the performance that would be achieved in an
apparatus 40 times larger in volume using conventional low-temperature
superconducting magnets. That leap in power versus size is the key element
in ARC's revolutionary design.
The use of the new high-temperature superconducting magnets makes it
possible to apply decades of experimental knowledge gained from the
operation of tokamak experiments, including MIT's own Alcator series. The
new approach uses a well-known design but scales everything down to about
half the linear size and still achieves the same operational conditions
because of the higher magnetic field.
A series of scientific papers published last year outlined the physical
basis and, by simulation, confirmed the viability of the new fusion device.
The papers showed that, if the magnets worked as expected, the whole fusion
system should indeed produce net power output, for the first time in decades
of fusion research.
Martin Greenwald, deputy director and senior research scientist at the PSFC,
says unlike some other designs for fusion experiments, "the niche that we
were filling was to use conventional plasma physics, and conventional
tokamak designs and engineering, but bring to it this new magnet technology.
So, we weren't requiring innovation in a half-dozen different areas. We
would just innovate on the magnet, and then apply the knowledge base of
what's been learned over the last decades."
That combination of scientifically established design principles and
game-changing magnetic field strength is what makes it possible to achieve a
plant that could be economically viable and developed on a fast track. "It's
a big moment," says Bob Mumgaard, CEO of CFS. "We now have a platform that
is both scientifically very well-advanced, because of the decades of
research on these machines, and also commercially very interesting. What it
does is allow us to build devices faster, smaller, and at less cost," he
says of the successful magnet demonstration.
Proof of the concept
Bringing that new magnet concept to reality required three years of
intensive work on design, establishing supply chains, and working out
manufacturing methods for magnets that may eventually need to be produced by
the thousands.
"We built a first-of-a-kind, superconducting magnet. It required a lot of
work to create unique manufacturing processes and equipment. As a result, we
are now well-prepared to ramp-up for SPARC production," says Joy Dunn, head
of operations at CFS. "We started with a physics model and a CAD design, and
worked through lots of development and prototypes to turn a design on paper
into this actual physical magnet." That entailed building manufacturing
capabilities and testing facilities, including an iterative process with
multiple suppliers of the superconducting tape, to help them reach the
ability to produce material that met the needed specifications—and for which
CFS is now overwhelmingly the world's biggest user.
They worked with two possible magnet designs in parallel, both of which
ended up meeting the design requirements, she says. "It really came down to
which one would revolutionize the way that we make superconducting magnets,
and which one was easier to build." The design they adopted clearly stood
out in that regard, she says.
In this test, the new magnet was gradually powered up in a series of steps
until reaching the goal of a 20 tesla magnetic field—the highest field
strength ever for a high-temperature superconducting fusion magnet. The
magnet is composed of 16 plates stacked together, each one of which by
itself would be the most powerful high-temperature superconducting magnet in
the world.
"Three years ago we announced a plan," says Mumgaard, "to build a 20-tesla
magnet, which is what we will need for future fusion machines." That goal
has now been achieved, right on schedule, even with the pandemic, he says.
Citing the series of physics papers published last year, Brandon Sorbom, the
chief science officer at CFS, says "basically the papers conclude that if we
build the magnet, all of the physics will work in SPARC. So, this
demonstration answers the question: Can they build the magnet? It's a very
exciting time! It's a huge milestone."
The next step will be building SPARC, a smaller-scale version of the planned
ARC power plant. The successful operation of SPARC will demonstrate that a
full-scale commercial fusion power plant is practical, clearing the way for
rapid design and construction of that pioneering device can then proceed
full speed.
Zuber says that "I now am genuinely optimistic that SPARC can achieve net
positive energy, based on the demonstrated performance of the magnets. The
next step is to scale up, to build an actual power plant. There are still
many challenges ahead, not the least of which is developing a design that
allows for reliable, sustained operation. And realizing that the goal here
is commercialization, another major challenge will be economic. How do you
design these power plants so it will be cost effective to build and deploy
them?"
Someday in a hoped-for future, when there may be thousands of fusion plants
powering clean electric grids around the world, Zuber says, "I think we're
going to look back and think about how we got there, and I think the
demonstration of the magnet technology, for me, is the time when I believed
that, wow, we can really do this."
The successful creation of a power-producing fusion device would be a
tremendous scientific achievement, Zuber notes. But that's not the main
point. "None of us are trying to win trophies at this point. We're trying to
keep the planet livable."
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