The heart of the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) is the National Spherical Torus Experiment (NSTX-U), a device that will help researchers develop magnetic fusion as a safe, abundant and inexpensive source of electric energy. Magnetic fusion harnesses the same process that fuels the sun. Researchers heat an ionized gas called a plasma to a temperature far hotter than the core of the sun in a device called a tokamak, which controls the gas with powerful magnets. The extreme heat and magnetic confinement force positively charged atomic nuclei — or ions — to fuse together and create a powerful burst of energy that could ultimately produce steam to generate electric energy.

The NSTX-U is undergoing a $94 million upgrade that will make the facility the most powerful tokamak of its type in the world when it is completed around the end of the year. The two main components of the upgrade are the central magnet, or center stack, and a second neutral beam injector to heat the plasma. These components will double the heat and electric current in the tokamak and quintuple the duration of the plasma.

Jeanne Jackson Devoe
PPPL, Office of Communications


“We’re building a scientific tool for the country and the Laboratory and there’s been great progress over the last year,” said PPPL Director Stewart Prager during the annual State of the Laboratory address. “To date, every technical challenge has been met.”

The second neutral beam is already in place in the NSTX-U and the center stack magnet is being constructed. Prager noted that the center stack is really two magnets in one: A cylinder composed of 36 copper bars that create a magnetic field, and a coil around the cylinder that drives a current through the plasma. Constructing the center stack “requires incredible engineering and craftsmanship and it’s gone extremely successfully,” Prager stated.

He noted that the U.S. Department of Energy has strongly supported the NSTX-U project despite the ups and downs of federal funding. “This is a fantastic result for this year. Next year we’ll be talking about the initial experiments on the NSTX-U,” Prager said.

The NSTX-U will allow researchers to produce “a sustained high pressure plasma” over the next decade, Prager explained.


PPPL has a 63-year history of discovery and leadership in the field of fusion, going back to Princeton astrophysicist Lyman Spitzer, the laboratory’s cofounder who began research under the code name “Project Matterhorn” in 1951. The Laboratory was declassified in 1958, allowing researchers to collaborate with scientists in other countries. The name was changed to the Princeton Plasma Physics Laboratory in 1961.

Spitzer’s achievements were many. He first came up with the idea of creating magnetic fusion in a figure-eight shaped device called a “stellarator,” and is credited with inspiring the development of the Hubble Space Telescope.

PPPL produced a then-world record 10.7 million watts of controlled fusion power in the Tokamak Fusion Test Reactor (TFTR) in 1994 — enough power to briefly meet the needs of more than 3,000 homes.


The next step in developing magnetic fusion as an energy source is the huge fusion experiment called ITER (Latin for “the way”) in Cadarache, France, that is supported by seven international partners that include the United States.

ITER is designed to create a sustained fusion reaction — or burning plasma — that produces more energy than it takes to create the reaction. Experiments are to begin in the 2020s.

PPPL is strongly contributing to ITER, Prager said. For example, PPPL is designing and engineering diagnostic port plugs and is responsible for procuring ITER’s steady-state electric power network. “When ITER is constructed, it will be a landmark scientific experiment for the 21st century,” Prager predicted.

ITER won’t solve all the problems of nuclear fusion, Prager said, and researchers are looking ahead to a device called a fusion nuclear science facility (FNSF) that could lead to a demonstration power plant. PPPL’ers are involved in preliminary research for an FNSF, Prager said.

Theory and computation are also essential to the Laboratory, Prager said. PPPL researchers last year were awarded 275 million core hours on supercomputers — the equivalent of some 20,000 years on a personal computer — to study the plasma edge and plasma confinement.


In addition to NSTX-U, PPPL’s main experiment, the Laboratory has moved ahead with a range of new experiments and collaborations. One such facility is a new version of a current PPPL device called the Magnetic Reconnection Experiment (MRX). The new experiment, called the Facility for Laboratory Reconnection Experiment (FLARE), will study a process that gives rise to auroras, solar flares, geomagnetic disturbances, and numerous astronomical phenomena. FLARE will be three times larger and much more powerful than the MRX. It will be constructed over three years and funded with $3 million from the National Science Foundation and $1.2 million from Princeton University.

PPPL began the Center for Heliospheric Physics last year, a joint project with the University’s Department of Astrophysical Sciences. The center will study the region surrounding the sun that produces space weather that can interrupt cell phone service, damage satellites and knock out power grids.

Researchers at the Laboratory have pursued numerous collaborations nationally and internationally, including the Max- Planck/Princeton Center for Plasma Physics, a collaboration between Princeton University and the Max Planck Society of Germany.

The Laboratory has also begun studies of plasma-based nanotechnology. Other technologies being investigated at PPPL include a plasma mass filter that could be used to clean up large amounts of radioactive waste. Researchers are working as well on X-ray imaging techniques that could have “enormous impact in a huge array of applications,” Prager noted.

Researchers at PPPL and the U.S. Department of Agriculture are developing a technique that uses radio frequency waves to pasteurize eggs. Princeton University and PPPL researchers are also working on a method to verify that presumed nuclear warheads that are to be decommissioned actually are nuclear warheads.

“All of this diversity of activities does not add up to a huge pile of money,” Prager commented. “However, it does lead to huge scientific creative activity at the Laboratory, so in that way it is incredible.”

Some of PPPL’s research is geared toward educating and informing students and the general public. One example is the Remote Glow Discharge Experiment (RGDX) devised by Arturo Dominguez, a postdoctoral fellow in the Science Education Department. The RGDX allows users anywhere in the world to log on to a program that enables them to create and manipulate a glowing plasma in a device at PPPL, and to watch the results via a live web stream video.

Prager said the past year “was a good year for the fusion program and a great year for PPPL.” He added that PPPL has “planted the seeds for an even greater harvest next year.”

PPPL is one of 17 national laboratories funded by the Department of Energy. (Photo by Elle Starkman/PPPL Office of Communications)