The Princeton Plasma Physics Laboratory: The quest for clean energy continues


After a three-year, $94 million overhaul, the Princeton Plasma Physics Laboratory’s primary fusion reactor has resumed the quest for clean energy. The fusion of parts of the atom inside the reactor could release a near limitless amount of energy and reduce our dependence on fossil fuels, while generating minimal hazardous waste. The upgrade included replacing the center of the apple-shaped reactor with a new 29,000-pound magnetic core. PHOTO BY JAMES CHRZANOWSKI

FUSION — the energy-making process that powers the sun — could provide us with a near limitless source of energy, ending our dependence on fossil fuels for making electricity.

This summer, after a nearly three-year overhaul, the world-leading fusion research facility at the Princeton Plasma Physics Laboratory (PPPL) switched on its newly outfitted flagship reactor, the National Spherical Torus Experiment-Upgrade (NSTX-U). The reactor uses electrical current and heat to create a hot, charged state called a plasma, which is encased by powerful magnets so that parts of the atoms can collide and fuse, releasing massive quantities of energy in the process.

The $94 million upgrade has made the NSTX-U the world’s most powerful spherical tokamak — the name given to donut-shaped fusion reactors — while doubling its heating power and magnetic fields, and making it the first major addition to the U.S. fusion program in the 21st century.

“The upgrade boosts NSTX-U operating conditions closer to those to be found in a commercial fusion power plant,” said Stewart Prager, director of PPPL, which is managed by Princeton University for the U.S. Department of Energy and is located some three miles from the campus. “Experiments will push into new physics regimes and assess how well the spherical design can advance research along the path to magnetic fusion energy.”

Fusion reactor

The upgrade included bringing in a 70-ton machine (above) that produces beams that heat the plasma. PHOTO BY MICHAEL VIOLA

The key feature of the design is its compact, cored apple-like shape, as compared with the bulkier, donut-like form of conventional tokamaks. The compact shape enables spherical tokamaks to confine highly pressurized plasma gas — the hot, charged fuel for fusion reactions — within comparatively low magnetic fields. This capability makes spherical tokamaks a cost-effective alternative to conventional tokamaks, which require stronger and thus more expensive magnetic fields.

Building the NSTX-U posed novel challenges for engineers and technicians throughout PPPL. Tasks ranged from flying a 70-ton neutral beam machine over a 22-foot wall to building a 29,000-pound center stack. These huge components fit alongside and inside an existing facility — the original NSTX — with hair-thin precision, requiring an effort that one engineer likened to rebuilding a ship in a bottle.

Researchers now plan to test whether the NSTX-U can continue to produce high-pressure plasmas under the hotter and more powerful conditions that the upgrade allows. Also on the research agenda are tests of how effectively the NSTX-U can keep temperatures approaching 100 million degrees centigrade from dissipating, and whether its spherical design can be a strong candidate for a major next step in the U.S. fusion program.

–By John Greenwald

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Elusive particles found

IN THE PAST YEAR, PRINCETON PHYSICISTS have detected two particles that were predicted decades ago to exist but had not been found until now. Both particles were detected using a scanning-tunneling microscope to image the particles inside a crystal. The particles may someday enable powerful computers based on quantum mechanics.

A team led by Ali Yazdani, the Class of 1909 Professor of Physics, detected the “Majorana fermion,” which behaves simultaneously like matter and antimatter and was first proposed in 1937 by Italian physicist Ettore Majorana. The team, which received funding from the National Science Foundation and the Office of Naval Research, included B. Andrei Bernevig, an associate professor of physics, and other colleagues at Princeton and at the University of Texas-Austin. They published their results in the Oct. 2, 2014, issue of the journal Science.

A few months later, an international team led by M. Zahid Hasan, professor of physics, detected another elusive particle, the “Weyl fermion,” first theorized by the mathematician and physicist Hermann Weyl in 1929. The particle is massless and can also behave like matter and antimatter. The research team, which received support from the Gordon and Betty Moore Foundation and the U.S. Department of Energy, published their work in Science on July 16, 2015.

–By Steven Schultz and Morgan Kelly

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A farewell to arms? New technique could aid nuclear disarmament

A Farewell to Arms?

A new method that borrows from strategies used in computer cryptography could verify the presence of nuclear warheads without collecting classified information. The technique fires high-energy neutrons at a non-nuclear target (pictured above), called a British Test Object, that will serve as a proxy for warheads. (Photo by Elle Starkman)

SCIENTISTS at Princeton University and the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) are developing a system to verify the presence of nuclear warheads without collecting classified information, as a step toward the further reduction of nuclear arms.

While efforts have been made to develop systems for verifying the content of warheads covered by disarmament treaties, no such methods are currently in use. The new method borrows from strategies used in computer cryptography to identify nuclear warheads while learning nothing about the materials and design of the warheads themselves.

The research was published in the June 26, 2014, issue of Nature and was conducted by Alexander Glaser, an assistant professor in Princeton’s Woodrow Wilson School of Public and International Affairs and the Department of Mechanical and Aerospace Engineering; Robert Goldston, former director of PPPL, a fusion researcher and a professor of astrophysical sciences at Princeton; and Boaz Barak, a senior researcher at Microsoft New England who has taught computer science at Princeton.

–By John Greenwald

Captured on video: Virus-sized particle trying to enter cell

Virus video

Researchers captured video of a virus-like particle trying to enter a cell (Image courtesy of Kevin Welsher)

RESEARCHERS AT PRINCETON UNIVERSITY achieved an unprecedented look at a virus-like particle as it tries to break into and infect a cell. The video reveals the particle zipping around in a rapid, erratic manner until it encounters a cell, bounces and skids along the surface, and either lifts off again or, in much less time than it takes to blink an eye, slips into the cell’s interior. The work, conducted by Professor of Chemistry Haw Yang and postdoctoral researcher Kevin Welsher, was supported by the U.S. Department of Energy and published in the Feb. 23, 2014, issue of Nature Nanotechnology.

–By Catherine Zandonella