From Fermi to the Z Machine
posted: 6/11/2018
listed in Hertz Foundation
Two Fellows Trace the Tangled History of Magnetized Target Fusion
The year was
1991. The Soviet Union was in turmoil, yet still very much firmly planted
behind the Iron Curtain. Even so, Hertz Scholar/Fellow and Los Alamos National
Laboratory physicist Irvin Lindemuth just had to know what the Soviet fusion
scientists had been up to all these years.
Just weeks
after an August coup attempt nearly toppled Soviet President Mikhail Gorbachev, Lindemuth
found himself aboard a small Aeroflot plane en route from Moscow to Sochi, on the
Black Sea. He and his wife, Hedy were heading for a young student plasma
physics school, where he had been invited to lecture. He looked out to the
aircraft’s wing, emblazoned with four red letters CCCP, the Cyrillic acronym
for the Union of Soviet Socialist Republics.
“Getting up
in the clouds you could see nothing but that wing out there,” Lindemuth
recalled. “We just wondered if anything were to happen in Russia, another coup
attempt or something, would anybody even know where we were at? It was an eerie
feeling to say the least.”
Eight years
prior, Lindemuth, a Hertz Scholar and Hertz Fellow, published a landmark
scientific paper on what would later become known as Magnetized Target Fusion
(MTF). It was an approach to fusion intended to blend the best components of
inertial confinement and magnetic confinement, the two vanguard approaches
scientists had been working on for decades. While some of the basic principles
of MTF had been discussed since the 1940s by scientific luminaries such as
Enrico Fermi, it had never really taken root.
In his 1983
paper, published by Nuclear Fusion, Lindemuth theorized that by generating a
magnetic field in the fuel of a fusion target (a shell containing tritium or
deuterium) it would be easier to heat. Putting a magnetic field in the fuel
inhibits thermal conduction, trapping the heat inside, keeping the fuel warm
and requiring less power to implode it. Theoretically with this method, fusion
could be produced at a fraction of the power and cost as laser-based
approaches. At the time, the work went largely ignored.
However, in
1988, the US intelligence community became interested in a 1979 paper on an
unconventional approach to fusion. Although the main author of the paper was
unknown, the paper had been submitted for publication by academician Yulii
Borisovich Khariton, known through classified circles as the “Soviet
Oppenheimer,” who had overseen the development of the Soviet Union’s first
nuclear weapons.
Although the
fusion concept was discounted by many in the U.S., Lindemuth made the
then-provocative conclusion that the concept made sense if it were based on MTF
principles. A year later, while attending an international Megagauss conference
in central Russia, Lindemuth had a brief conversation with a co-author of the
paper, who was obviously not at liberty to discuss specifics.
“At that
time they couldn’t even tell us they were from the Russian Los Alamos but we
knew they were because of classified information that we had,” Lindemuth said.
“We just started talking about things of mutual interest and they said maybe
one day maybe we could work together.”
Then in
1990, a team of American scientists who had participated in the “joint
verification experiments,” became the first Western visitors to the highly
secretive All-Russian Scientific Research Institute of Experimental Physics (RFNC-VNIIEF).
The lab, located in the gated town of Sarov (known then as Arzamas-16) was
affectionately nicknamed the “Russian Los Alamos.” The visitors brought home a
prospectus that gave the U.S. its best look ever at the institution previously
known only through classified information.The prospectus confirmed that the Soviet scientists had been working on
a fusion method called MAGO, essentially the same magnetic compression idea Lindemuth
had written about years before.
Lindemuth’s
prior acquaintance with Russian scientists put him on the plane from Moscow to
Sochi in Sept. 1991, where he had worried about his fate in the event of
another coup. On his return trip, Lindemuth was met at his Moscow hotel by the
Soviet fusion scientists who had written the 1979 paper. They had a proposal;
Lindemuth and Los Alamos scientists would be allowed to work together with the
Soviet scientists on the magnetic compression projects.
But because
of the rapid change enveloping the Soviet Union, Los Alamos never made a formal
response to the proposal. By late 1991, the Berlin Wall had fallen, the Soviet
Union was collapsing, and Russia had begun a remarkable transformation. The
U.S. government was concerned about where the Russian scientists would go after
the collapse. Would they go off to work for Saddam Hussein or take their
nuclear secrets to America’s other adversaries?
In December,
Siegfried “Sig” Hecker, director at Los Alamos, attended a Russian-focused
meeting in Washington. When it was clear the Soviet Union might collapse,
then-Energy Secretary James Watkins expressed concern about the fate of the
Soviet laboratories.Hecker responded:
“Why don’t we just go and ask them?”
“Fortuitously,
there I was in a position to go to Russia, not just for technical talks but to
seek out the leaders of the Russian laboratories and tell them ‘our directors
want you to come to Los Alamos and Livermore and we’ll come back over there,’”
Lindemuth said. “From our scientific perspective, they had gadgets that we
didn’t have, and we were interested in them and wanted to learn more about the
stuff they’d been doing. It was just scientific curiosity and the belief that
the tools they had could help us reach our own goals.”
And from a
global security perspective, Lindemuth said, the United States simply had to
know the fate of the Soviet nuclear weapons design labs and their scientists.
“It’s hard
to describe what it was like to go over there,” Lindemuth said. “Instead of
just being a technical visit, our visit turned out to be a political visit,
where we were tasked to go over there and find out as much as we could about
what was happening over there.”
The ensuing
exchanges of directors and scientists began a collaboration between Los Alamos
and its Russian counterpart that would last the next 20-plus years. A series of
experiments began in 1993 in high magnetic fields the American scientists
hadn’t been able to generate before. For the Russian scientists, it was their
first chance to become part of the global scientific community.
“They wanted
to tell people what they did and never had the opportunity before, so this was
a big thing for them,” Lindemuth said. “In a bigger picture it was the
scientific collaboration that convinced the Russians that the Americans from
Los Alamos were for real and would work with them on more sensitive issues.”
Lindemuth
discovered that about the same time he’d published his landmark paper on
magnetized fuel targets, the fusion scientists in Sarov had come up with
essentially the same idea. The work led Lindemuth to conclude he was on the
right path.
“I don’t
think there would be a lot of activities in MTF right now if the Russian
collaboration hadn’t stirred it up,” Lindemuth said. ‘I think everybody that’s
involved learned about it, at least in part, from people that were involved in
the Russian activities.”
From MTF to MagLIF
Stimulated by the
fledgling US-Russian MAGO collaboration, Lindemuth and Dick Siemon, head of Los
Alamos’ fusion energy program, had given talks, workshops and published papers
on MTF, and by the late 1990s, word had gotten around, even if many fusion
scientists were skeptical. Their work, along with the ongoing Russian
collaboration, stirred up interest in MTF at a time when some in the scientific
community were looking for alternatives to the conventional approaches that
required large lasers.
“There’s
always been optimism about fusion, both inertial confinement and magnetic
confinement,” Lindemuth said. “People were starting to realize it was going to
be a lot harder problem than they thought it was, so at least some people were
starting to look at other options, and MTF reared its head.”
Meanwhile,
at Sandia National Laboratory in New Mexico, Hertz Fellow Stephen Slutz was becoming
frustrated by his research in pulse power fusion. He had pursued many different
approaches involving electron and ion beams. Enter Irv Lindemuth, who by then
had become an advocate of magnetized target fusion.
“I started
thinking about alternatives,” Slutz said. “I honestly think Irv was very
important to me in considering this. He came several times to Sandia to talk
about MTF. I knew about it. I worked on the radiation driven approach, and
people would ask me why don’t you put a magnetic field in the target? The idea
isn’t new, but a magnetic field in a spherical target is a problem. It’s not a
natural geometry.”
Sandia had a
unique capability not found anywhere else, at the Z Pulsed Power Facility,
touted as the world’s most powerful facility of its kind. The “Z machine” could
implode objects with something called a zeta pinch, or simply “z pinch,” which
uses an electric current outside the plasma fuel to generate a magnetic field
that compresses the fuel.
Looking for a way to use the Z machine, Slutz
started thinking seriously about MTF in 2008, a slightly different version he
called magnetized liner inertial fusion, or MagLIF. The approach was initially
classified, so Slutz couldn’t discuss it openly for about a year. He eventually
published a paper on MagLIF in 2010. It described different geometries and
magnetic field configurations than Lindemuth had proposed for MTF, but was
essentially the same idea, putting a magnetic field in the fusion target to reduce
thermal losses and using a second magnetic field, instead of a laser, to crush
a fuel-filled metal tube (called a liner) to produce fusion energy.
Imagine,
Slutz said, a vertical pipe, where the electrical current from the Z machine is
driven vertically, producing a magnetic field around the pipe. This field
produces a pressure that drives the pipe inward. The current, and thus the
field around the outside of the pipe, is fired for about 100 nanoseconds, which
is an extremely long time in conventional fusion science timeframe. On an even
longer time-scale a set of Helmholtz-like coils is fired about 3 milliseconds
before the Z machine so the magnetic field can diffuse into the conductive
metal tube. Then, as the tube starts to implode, a laser heats the fuel and z
compresses the tube, a bit like rubber bands crushing a soda can.
“When I
first started talking about it, everybody said what about these ends (of the
tube) because they’re open,” Slutz said. “It took a while for people to accept
that if the tube is long enough, it’s a tolerable loss. We lose both fuel and
energy out the ends, but when you start imploding this thing, the area at the
two ends is very small compared to the area of the tube, so it’s not a dominant
loss”
Slutz’s
published papers on MagLIF caught Lindemuth’s attention, and although he had
retired from Los Alamos, Lindemuth started doing his own computer experiments,
dusting off the old computer code he’d written in 1983. With Slutz’s help,
Lindemuth reviewed his old research and began writing again about how MTF might
work.
“When I read
their papers I felt almost like a zealot who just converted someone to their
religion; it was really exciting to see their results,” LIndemuth said. “I’d
probably put in my mind that other magnetic field approaches would work better
than what Steve claimed would work, but when I saw it worked I thought I’ve got
to convince myself that it would work.”
To test the
idea at Sandia, the laboratory needed a new device to create the uniform, high
magnetic fields within the fuel, which was commissioned in 2013.The first
MagLIF experiments on the Z machine began the following year. So far, Slutz
said, the results have been promising. The reaction does in fact produce
fusion, but needs to produce more, he said.
“We’ve fired
quite a number of shots now, and we demonstrated that if you don’t use magnetic
fields or the laser, you get almost no yields, and when you fire them both you
change the yield by approximately 1,000 times,” Slutz said. “We’ve demonstrated
that it works, now we’re trying to demonstrate that we know how it works.”
While Slutz
is confident the experiments in the Z machine have demonstrated that
magnetizing fuel will be a successful method to fusion, he’s busy working out
the flaws, namely why the system doesn’t produce more yields. He cautioned
there’s still a long way to go to reach the Holy Grail of fusion energy, the
“breakeven” point where the energy yield is greater than the energy put in.
“My feeling
is that this is just the beginning,” Slutz said. “We just know it won’t work if
you don’t put a magnetic field in, and it does when you do, so we know it has a
positive effect. But it’s going to take a lot of time before we have a really
solid quantitative understanding exactly how it all works.”
Plainly,
Slutz said, he needs a bigger machine. Reaching breakeven would require at
least four times the pulse power energy the Z machine is capable of. Meanwhile,
he’s looking at ways to increase the fuel density and preheat energy, and
considering adding a layer separating the fuel from the liner to help deflect
the blast wave caused by the laser.
“If we did
these things within range of what we’re capable of we should be able to
increase the yield by a factor of 10 or even 100,” Slutz said. “If we could do
that before I retire I would be happy. I think that would demonstrate enough
understanding that it would be sensible to talk about a new machine.”
The Hertz connection
Now approaching 40
years working at Sandia, Slutz didn’t start out wanting to be on the forefront
of fusion energy. As a Hertz Fellow, he attended the California Institute of
Technology (Caltech), where he earned his PhD in astrophysics. His interest in
fusion came “indirectly” through the Hertz Foundation, and Lawrence Livermore
astrophysicist and Hertz Director Emeritus Lowell Wood, who interviewed him for
the Fellowship and offered him a summer job at Livermore to work on x-ray
lasers. During that summer, he was introduced to laser-driven inertial fusion
primarily through discussions at lunch where LLNL physicist John Nuckolls and
Steven Bodner, head of laser fusion at the Naval Research Laboratory.
“It had a
profound effect, that introduction to inertial fusion at Livermore. It was
because of Lowell that I got that job,” Slutz said.
At Sandia,
Slutz would work with Mark Herrmann, another Hertz Fellow who is currently the
head of Livermore’s National Ignition Facility. Herrmann, Slutz said, pushed
him to think about MTF from different angles. He also credits Lindemuth with
providing a basis for his research.
Lindemuth, who retired from Los Alamos in 2003, continued to
make trips to Russia, meeting with high-ranking Russian scientists and DOE
officials to discuss possible collaborations. In 2013, the U.S. and Russian
governments signed an historic agreement to have scientists from Los Alamos,
Livermore and Sandia work with Russian scientists on fusion and other projects.
The collaborations ended abruptly in 2016, when Russia invaded the Ukraine. The
Americans, in response, barred their scientists from working with the Russians.
The work is currently in limbo.
Today,
Lindemuth resides in Tucson, Ariz., is an avid golfer, and occasionally
lectures on fusion at UC San Diego’s Center for Energy Research. He looks back
fondly on his Hertz Scholarship, which allowed him, a minister’s son raised in
Pennsylvania, to attend Lehigh University, where he got his BS in electrical
engineering. As a Hertz Fellow, he studied applied physics and computer coding,
earning his PhD in Engineering-Applied Science from the University of
California Davis/Livermore.
He was
interviewed for the Fellowship by one of his graduate school advisors, former
Lawrence Livermore Lab director and legendary physicist Edward Teller, which
opened the door to a job at LLNL, where he worked on thermonuclear fusion. He
remained at Livermore for several years, moving to Los Alamos in 1978, where he
grew his interest into pulse power and MTF for the next 25 years.
“The Hertz
made my career possible. Period,” Lindemuth said. “I don’t know what kind of
college education I would’ve gotten without it. Hertz’s scholarship was
generous enough that it wasn’t hard for my parents to get me through college.
Then, somehow I heard about Hertz Fellowship and started thinking maybe it would
be good to get more education. I’m sure if I hadn’t gotten the Fellowship I
might still be working in the aircraft industry as an electrical engineer.”
Regarding
the promise of MTF, Lindemuth and Slutz are true believers in the approach and
the impact it could have on the world. MTF-related projects based on
Lindemuth’s work are ongoing at ARPA-E, as well as efforts at several private
startup companies, Los Alamos and the University of Washington. Above all else
however, Lindemuth said Slutz’s research at Sandia is the “most exciting thing
going on.”
“Certainly
in the U.S. what Steve’s kicked off at Sandia is pretty fantastic stuff,”
Lindemuth said. “It’s in its relative infancy, but when you look at the results
Steve has gotten and how quickly he’s got them, there’s every reason to be
excited. If I had money to invest in fusion, I’d invest in MTF.”
Interestingly,
Slutz’s interest lies not in fusion energy, but in fusion-propelled rockets,
which could fly many times faster than conventional chemical rockets. As he
nears retirement, Slutz said he’d like to continue working on MagLIF at Sandia
part-time, with a focus on solving the laser heating and blast wave challenges.
“Fusion
energy would be great, but a fusion rocket is more motivating to me, and the
reason is economic,” Slutz said. “By nature of how difficult it is, fusion will
be difficult to make cheaply. I’d like to see energy, but the niche of making a
fusion rocket that goes faster than a chemical rocket can go has no
competitors.”
“It’s been
quite a long period of development and things move slowly,” Slutz added. “You
have to have a lot of patience. When you think nothing’s happening, then
something interesting happens.”