NSTX-U is poised to close the gaps between today’s research tokamaks and tomorrow’s commercial utilities

Written by
John Greenwald
Jan. 3, 2024

As the Princeton Plasma Physics Laboratory (PPPL) readies its primary fusion experiment for a relaunch, the team itself is undergoing a bit of a relaunch, too. The National Spherical Torus Experiment-Upgrade (NSTX-U) has a newly appointed deputy director of research: Jack Berkery.

Berkery said his background in engineering — he holds a bachelor’s degree in mechanical engineering from Cornell University and a doctorate in mechanical and aerospace engineering from Princeton University — should serve him well in this new role.

He also worked on a small plasma physics experiment at Columbia University, which he joined as a postdoctoral fellow after receiving his doctorate in 2005. Two years later, Columbia sent him on long-term assignment to collaborate on the NSTX spherical tokamak at the U.S. Department of Energy’s (DOE) PPPL. In 2022, Berkery switched his affiliation from Columbia to Princeton.

“There’s a lot of engineering involved in experimental fusion, and having that background has been a help,” said Berkery, now a widely recognized expert on spherical tokamak fusion reactors. “More specifically, it helps me relate to aspects of NSTX-U that are more engineering-related, such as controls and diagnostics.”

Berkery will work closely with NSTX-U research director Stanley Kaye to coordinate the directions, activities and scope of work of NSTX-U researchers plus hundreds of collaborators worldwide. “It gives me great pleasure that Jack has taken on this job,” Kaye said. “Jack will be helping with programmatic planning, and he will take on primary responsibility for coordinating meetings, invited talks and papers submitted for journal publication.”

Research on the NSTX-U, which is currently under repair, focuses largely on investigating data the machine produced during its 13 years as NSTX prior to its upgrade. It is also developing tools to analyze the tokamak’s condition once it resumes operation. “Researchers are checking their theories and calculations to see whether they match the experimental results that exist already,” said Berkery, “and are seeing how well theories that match the old data will fit the NSTX-U and future spherical tokamaks.”

One critical challenge is preventing the loss of power that researchers will inject into the NSTX-U to heat it to the 100-million-degree temperatures needed to create fusion energy. Computer simulations are underway to identify and reduce the source of heat loss in the repaired machine. 

Also in progress are artificial intelligence (AI) techniques to improve the prediction of disruptions that can halt fusion reactions and damage the machine. This research accelerates computer simulations to prepare the tokamak for faster and more accurate disruption control.

The NSTX-U is currently 80% rebuilt and is scheduled to relaunch in 2025. A major remaining task is the replacement of the central magnet that runs down the middle of the tokamak as the backbone of the machine. This key component is being built by Elytt Energy, a leading manufacturing company in Spain, with parts coming from around the world. Once installed, the component will perform a dual role: It will start and maintain the current that generates the plasma that fuels fusion reactions and complete the magnetic field that keeps the plasma bottled up. Delivery to PPPL is scheduled for fall 2024.

The NSTX-U is shaped more like a cored apple than the doughnut-like shape of more widely used conventional tokamaks. The compact design of the spherical tokamak allows it to produce the essential plasma conditions for fusion energy — the same energy that drives the sun and stars — with relatively low and cost-effective magnetic fields. This economical design makes the NSTX-U a strong candidate to serve as the model for a fusion pilot plant.

For Berkery, such research builds upon his previous role as coordinator of collaborations between PPPL and spherical tokamaks worldwide. These devices include the Mega Ampere Spherical Tokamak-Upgrade (MAST-U) at the UK Atomic Energy Agency — a similar machine to NSTX-U — along with the ST40 at Tokamak Energy, a private U.K. company, and spherical tokamaks in Japan and Spain.

He is also principal investigator on a public-private DOE Innovation Network for Fusion Energy (INFUSE) project and a co-principal investigator on a DOE Milestone program. Both roles will collaborate with Tokamak Energy on the development of next-step spherical tokamaks, and these many partnerships span the breadth of research on plasma confinement in spherical tokamaks.

Berkery joined the staff of PPPL in 2022 when he took on the previous collaboration job after 17 years as a Columbia University researcher. He has authored more than 20 peer-reviewed scientific papers, including two in the prestigious Physical Review Letters and one among the most cited pieces in Physics of Plasmas in 2014. His honors include the 2016 Landau-Spitzer Award presented by the American Physical Society and the European Physical Society for outstanding contributions to plasma physics and advancing joint research between the U.S. and the European Union.

PPPL is mastering the art of using plasma — the fourth state of matter — to solve some of the world's toughest science and technology challenges. Nestled on Princeton University’s Forrestal Campus in Plainsboro, New Jersey, our research ignites innovation in a range of applications including fusion energy, nanoscale fabrication, quantum materials and devices, and sustainability science. The University manages the Laboratory for the U.S. Department of Energy’s Office of Science, which is the nation’s single largest supporter of basic research in the physical sciences. Feel the heat at https://energy.gov/science and https://www.pppl.gov.