National Spherical Torus Experiment-Upgrade (NSTX‑U)

The National Spherical Torus Experiment-Upgrade (NSTX-U) is the primary fusion experiment at PPPL. The spherical device is shaped more like a cored apple than the doughnut-like shape of conventional tokamaks and can produce high-pressure plasmas — essential ingredients for fusion reactions — with relatively low and cost-effective magnetic fields.

Using both neutral beams and high-power radio waves, the NSTX-U will heat the plasma to 100 million degrees: seven times hotter than the sun. Its compact design makes it an ideal candidate to serve as the model for a fusion pilot plant followed by a commercial fusion reactor.





NSTX-U Exterior view

Overview of the National Spherical Torus Experiment-Upgrade (NSTX-U).



A Sum of Its Intricate Parts

The components and diagnostics on the device were designed and custom-built at PPPL and custom-built and sourced from around the world. 

  • PPPL built and tested prototype coils before constructing the poloidal field coils. These small magnets, nestled against the center stack, are used to shape the plasma.
  • PPPL replaced the device’s central magnetic bundle and its casing. The casing, which is made of Inconel, was forged in Italy and shipped to Holtec Manufacturing Inc. in Turtle Creek, Pennsylvania, near Pittsburgh, and from there to Camden, New Jersey.
  • PPPL designed and custom-built 1,600 graphite tiles that will line the inside of the tokamak to protect the walls and have a special castellated design meant to withstand heat. Each one was designed in-house and created using exotic materials. If the part couldn't be produced in-house, it was outsourced.
  • PPPL researchers traveled internationally to find the world's most powerful magnets. Two sets of three magnets that are used to shape the plasma were built in France under PPPL supervision. 

This experimental fusion device is stronger, better, and more uniquely designed than before. 

The Recovery Project

A failed coil led to a full-scale investigation of the NSTX-U's hundreds of intricate parts. Along the way, PPPL engineers determined other upgrades, improvements, and replacements that could make the machine more powerful, efficient, and precise.

PPPL has rebuilt many of the components of NSTX-U through a rigorous process in which each component is designed, analyzed, and built to exact specifications under the guidance of PPPL engineers and technicians, and tested before being installed in the device.

Today, the NSTX-U Recovery Project is 84% complete.


NSTXU Recovery Still


NSTXU render



Global Collaboration

Hundreds of scientists from around the world are working on NSTX-U. It’s a unique user facility that allows fusion researchers to test, experiment, and determine how best to control the hot and unpredictable plasma to produce clean energy. 

The device is a model of the Laboratory’s core belief that partnerships are required for the development of commercial fusion. PPPL alone won’t construct a fusion pilot power plant — but, through industry partnerships, will help the world figure out how to do so.

United States

College of William and Mary
Columbia University
Florida International University
General Atomics
Idaho National Laboratory
Johns Hopkins University
Lawrence Livermore National Laboratory
Lehigh University
Lodestar Research Corporation
Los Alamos National Laboratory
Massachusetts Institute of Technology
Nova Photonics Inc.
Oak Ridge National Laboratory
Old Dominion University
Princeton Plasma Physics Laboratory

Princeton University
Purdue University
Sandia National Laboratory
University of California-Davis
University of California-Irvine
University of California-Los Angeles
University of California-San Diego
University of California, Space Sciences Laboratory
University of Colorado
University of Illinois
University of Maryland
University of Rochester
University of Tennessee
University of Texas
University of Washington
University of Wisconsin


Culham Centre for Fusion Energy
FOM Institute DIFFER
Hiroshima University
Institute for Nuclear Research-National Academy of Science
Institute of Plasma Physics-Czech Republic
Ioffe Physical-Technical Institute
Japan Atomic Energy Agency
International Thermonuclear Experimental Reactor
KAIST-Korea Advanced Institute of Science and Technology
Kyoto University Kyushu University
NFRI-National Fusion Research Institute
Niigata University

Seoul National University
Tech-X Corporation
Tokamak Energy
TRINITI-Troitskii Institute of Innovative and Thermonuclear Research
Ulsan Science Institute of Science and Technology
University of Costa Rica
University of Hyogo
University of Tokyo
University of York