Discovery provides a path to safe, clean, plentiful energy

By John Greenwald

Fusion — the energy-producing reaction that powers our sun and most stars — can be a safe, clean and virtually limitless source for generating electricity on Earth, ending reliance on fossil fuels and curbing greenhouse-gas emissions. In the sun, gravity traps particles inside an ultra-hot charged cloud of gas known as plasma, forcing them to fuse and release their energy. On Earth, we use powerful magnets to force plasma particles to fuse and release their power at temperatures many times hotter than the center of the sun.

At the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL), which is managed by Princeton University, scientists have been making great strides in determining how to trap those particles in doughnut-shaped facilities called “tokamaks” — fusion devices that confine the plasma in magnetic fields in place of gravity.

Now, PPPL scientists have for the first time reproduced the key elements that double the tokamak’s ability to prevent heat and energy loss that could slow or halt fusion reactions. Finding the factors that enable a doubling of the confinement of particles inside a plasma marks a major advance on the path to fusion energy and to creating an artificial sun on Earth to help power the world.

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“This discovery provides understanding of a path to improved plasma performance,” said Michael Zarnstorff, deputy director for research at PPPL. “It will enable physicists to predict with confidence the heating power required to keep plasma well-confined and to provide energy for the world.”

This doubling of confinement, which has been poorly understood, is vital to current and future fusion devices, sometimes called “star jars,” on the planet. The new understanding stems from a computer simulation that shows how a barrier can form to prevent the escape of heat and energy in plasmas.

ITER fusion facility

The construction of a major new experimental fusion facility called ITER in Cada-rache, France, will enable researchers to test the feasibility of fusion power. A Princeton Plasma Physics Laboratory discovery could help the giant reactor achieve success.

PPPL scientists used a sophisticated computer code to show how the formation of the barrier occurs and reduces the turbulence at the edge of the plasma that produces such losses. The simulation took three days and 90 percent of the capacity of Titan, the fastest U.S. supercomputer, which can perform 27,000 trillion calculations per second.

“After 35 years, the fundamental physics has been simulated, thanks to the rapid development of the computational hardware, software and detailed physics understanding,” said Choong-Seock Chang, managing principal research physicist at PPPL and leader of the nationwide team that developed the sophisticated code and produced the model.

Full understanding of the spontaneous transition to this mode, called high confinement, or H-mode, is essential for the demonstration of the feasibility of fusion power planned for a new international fusion facility known as ITER under construction in France. Operators of the seven-story, 23,000-ton machine must achieve H-mode to reach the goal of producing 10 times more energy than ITER will consume.

Understanding the transition will allow operators to predict the heating power needed to reach H-mode. The goal: to have predictions that are more accurate than projections based on today’s tokamaks, since conditions inside ITER, the largest and most powerful fusion facility so far conceived, will be significantly different.

Coming enhancements of the code will be part of the Exascale Computing Project, a nationwide program to develop computers that will run up to 50 times faster than Titan, improving U.S. security, economic competitiveness and scientific capability. PPPL leads an initiative that will develop the first complete model of an entire fusion plasma that could fuel a promising new era of energy production.

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

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