Engineers at the US Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) are employing a novel, cost-effective strategy to prepare for the assembly of a critical component in their cutting-edge fusion energy device.
By creating detailed 3D-printed replicas of complex magnet systems, the National Spherical Torus Experiment-Upgrade (NSTX-U) team is ensuring a smoother, faster, and less risky construction phase for a machine pivotal to the future of fusion energy.
The “star of the show,” a massive magnet bundle crucial for the NSTX-U’s mission, is currently under construction in Spain. This bundle, comprising a 19-foot toroidal field (TF) magnet and a surrounding ohmic heating (OH) coil, will produce the highest magnetic field of any large spherical torus.
Its successful operation is key to determining if compact spherical tokamaks could offer a more efficient path to a fusion pilot plant.
Cost-effective understudy
Anticipating the arrival of this complex behemoth in fall 2025, the PPPL team has turned to an ingenious understudy: a 40-inch tall, 2-foot wide, red plastic 3D-printed model accurately replicating the top of the magnet bundle.
“If it were a Hollywood set and you painted the TF-OH 3D print a different color, it would look just like the machine,” said Tom Jernigan, a senior project manager on the NSTX-U project. “It’s the best money we ever spent.”
This ‘dress rehearsal’ approach is central to the project’s strategy.
“The use of 3D-printed prototypes has been instrumental toward reducing risk and accelerating the schedule,” explained Dave Micheletti, the NSTX-U project director.
“It allows us to positively confirm that components will fit together and eliminates the risk of rework once final assembly starts. It’s saving both time and money.”
Specifically, the current TF-OH model allows engineers to meticulously pre-fit 36 cooling water lines that will prevent the powerful magnets from overheating when plasma temperatures soar hotter than the sun during experiments. A similar 3D model will be printed for the bundle’s bottom section.
Accelerating schedule for construction
The meticulous pre-fitting even extends to the 2,000 plasma-facing tiles that protect the machine’s interior, with the team ensuring placements within tolerances of a few thousandths of an inch.
“After a huge effort by the team, everything is coming together very well,” Micheletti added.
Meanwhile, at Elytt Energy in Spain, the actual TF magnet is taking shape. Technicians there also utilized prototypes to test each construction step before building the real magnet, which involves assembling four quadrants “like pieces of a pie.”
These are currently being compacted and will then be wrapped in fiberglass and injected with hot resin to form a single solid magnet – a process Danny Cai, a senior PPPL engineer, described as a “major hurdle” now successfully cleared. The OH coil will subsequently be wound around the TF magnet and undergo a similar solidification.
Once completed and shipped to PPPL, the TF-OH bundle will be carefully integrated into the NSTX-U.