Located on Princeton University's Forrestal Campus, the Princeton Plasma Physics Laboratory (PPPL) is a United States Department of Energy national laboratory for plasma physics and nuclear fusion science. Established in 1961, PPPL's primary mission is research into and development of fusion as an energy source. The lab aims to improve fusion through innovations in shaping and plasma composition, and in the creative use of powerful magnets to confine hot plasmas.

PPPL's founder Professor Lyman Spitzer conceived of a plasma being confined in a figure-eight-shaped tube by an externally generated magnetic field. He called this concept the “stellarator,” and took this design before the Atomic Energy Commission in Washington. As a result of this meeting and a review of the invention by designated scientists throughout the nation, the stellarator proposal was funded and Princeton University's controlled fusion effort was born.

In addition to studying the astrophysical properties of plasma, researchers are exploring how to confine it within doughnut-shaped devices known as tokamaks to harness fusion reactions that produce the vast energy of the sun and stars. Replicating fusion on Earth could provide a virtually inexhaustible supply of power to generate electricity. For the past three decades, PPPL has been conducting magnetic confinement experiments utilizing the tokamak approach. This work culminated in the Tokamak Fusion Test Reactor, which operated at PPPL from 1982 to 1997.

PPPL researchers are now leading work on an advanced fusion device — the National Spherical Torus Experiment-Upgrade (NSTX-U) — and are developing other novel concepts.

Plasma Research Advances

PPPL Physicist Fatima Ebrahimi in front of an artist's conception of a fusion rocket. (Photo: Elle Starkman, PPPL Office of Communications, and ITER)

PPPL is developing advanced low-temperature plasma applications ranging from nanofabrication for microelectronics to plasma thrusters for space travel.

The team developing the spherical NSTX-U, PPPL's flagship fusion device, is advancing the physics and engineering basis for a next-step fusion reactor based on the spherical design. Operating in parallel is the Lithium Tokamak Experiment -Beta, which studies the beneficial effects of lithium on energy confinement in fusion reactors.

PPPL plays a role in the operation and research direction of other tokamaks around the country and the world, including the leading international tokamak collaboration, ITER, under construction in France.

The second most studied magnetic confinement fusion concept, the stellarator, was invented at PPPL by its founder Professor Spitzer. Concepts now being developed at the laboratory include the Permanent Magnet Stellarator under study in the Advanced Projects department and scientists collaborate closely with stellarator projects throughout the world.

PPPL Physicist Yuhu Zhai in front of a series of images related to his magnet research. Clockwise from top left: A computer image of a tokamak fusion facility, two images showing magnetic forces in new superconducting magnets, a photo of a magnet prototype. (Photo: Headshot courtesy of Elle Starkman; collage courtesy of Kiran Sudarsanan)

The Laboratory for Plasma Nanosynthesis is a collaboration with Princeton University that enables scientists to use plasma to manipulate materials at the nanoscale level, the size of bil-lionths of a meter. This can help create microscopic structures like carbon nanotubes, far stronger than steel, to replace silicon in computer chips and improve performance.

The Princeton Collaborative Low Temperature Plasma Research Facility is a joint venture involving PPPL and Princeton University providing researchers with access to world-class diagnostics and computational tools for measuring and experimenting with low-temperature plasmas.

Technology Breakthroughs

A new type of rocket thruster that could take humankind to Mars and beyond was proposed by PPPL's Fatima Ebrahimi. The device would apply magnetic fields to cause particles of plasma, electrically charged gas also known as the fourth state of matter, to shoot out the back of a rocket and, because of the conservation of momentum, propel the craft forward. Current space-proven plasma thrusters use electric fields to propel the particles.

The new concept would accelerate the particles using magnetic reconnection, a process found throughout the universe, including the surface of the sun, in which magnetic field lines converge, suddenly separate, and then join again, producing lots of energy.

PPPL scientists have designed a new type of magnet that could aid devices ranging from doughnut-shaped fusion facilities known as tokamaks to medical machines that create detailed pictures of the human body.

Tokamaks rely on a central electromagnet known as a solenoid to create electrical currents and magnetic fields that confine the plasma, so fusion reactions can occur. But after being exposed over time to energetic subatomic particles known as neutrons emanating from the plasma, insulation surrounding the electromagnet's wires can degrade. If they do, the magnet could fail and reduce a tokamak's ability to harness fusion power.

PPPL Physicist Federico Nespoli at the Large Helical Device in Japan. (Photo: Japanese National Institute of Fusion Science. Collage by Kiran Sudarsanan)

In this new type of magnet, metal acts as insulation, and therefore, would not be damaged by particles. In addition, it would operate at higher temperatures than current superconducting electromagnets do, making it easier to maintain.

PPPL scientists have achieved a break-through in the conceptual design of twisty stellarators, experimental magnetic facilities that could reproduce on Earth the fusion energy that powers the sun and stars. The breakthrough shows how to more precisely shape the enclosing magnetic fields in stellarators to create an unprecedented ability to hold the fusion fuel together.

The new research uses new open-source software called SIMSOPT (Simons Optimization Suite) that is designed to optimize stellarators by slowly refining the simulated shape of the boundary of the plasma that marks out the magnetic fields.

When ITER, the international fusion experiment fires up in 2025, a top priority will be avoiding or mitigating violent disruptions that can seriously damage the giant machine. PPPL researchers have built and successfully simulated the prototype of a novel device to mitigate the consequences of a damaging disruption before one can proceed.

The simulated railgun-like device, called an electromagnetic particle injector is designed to mitigate the problem by firing a high-speed projectile of material that will radiate away the energy in the core of the plasma at the first sign of a disruption. The payload will cool and shut down the reaction in a controlled manner to avoid damage to the walls of the reactor chamber.

Scientists have found that adding a common household cleaning agent — the mineral boron contained in such cleaners as Borax — can vastly improve the ability of some fusion energy devices to contain the heat required to produce fusion reactions on Earth the way the sun and stars do.

A PPPL team working with Japanese researchers, made the observation on the Large Helical Device in Japan, a twisty magnetic facility that the Japanese call a “heliotron.” The results demonstrated for the first time a novel regime for confining heat in facilities known as stellarators, similar to the heliotron. The findings could advance the twisty design as a blueprint for future fusion power plants.

Technology Transfer

PPL's Technology Transfer Office guides inventors to commercialize technologies in partnership with the Princeton University Office of Technology Licensing. For more information contact Laurie Bagley, Head, Technology Transfer at This email address is being protected from spambots. You need JavaScript enabled to view it. or 609243-2425.