US ITER has completed delivery of all components for the support structure of the central solenoid, the 60-foot-tall superconducting magnet that is the heart of the ITER fusion machine. Comprised of more than 9,000 individual parts, the support structure was manufactured by eight U.S. suppliers across six states.
ITER, now under assembly in France, is an international project that will demonstrate the production and control of a sustained fusion power source for hundreds of seconds at power-plant relevant scale.
With the final delivery crossing the Atlantic in January, this milestone was the culmination of more than a decade of work by US ITER staff and U.S. suppliers. Contributors included Kamatics in Connecticut; Major Tool & Machine in Indiana; Keller Technology in New York; Hamill Manufacturing, Precision Custom Components, and Superbolt in Pennsylvania; Petersen in Utah; and Robatel Technologies in Virginia.
"Designing and manufacturing the first-of-a kind superconducting central solenoid is a major engineering challenge," said ORNL's David Vandergriff, a senior project engineer who has been part of the central solenoid team since joining US ITER in 2016. "But this magnet can't deliver for ITER without the support structure."
The support structure can be described as an exoskeleton, or a cage, that surrounds the central solenoid at the center of the ITER machine. Composed of a stack of six individual magnet modules, each weighing 121 tons, the central solenoid induces the majority of the magnetic flux change needed to initiate the plasma, generate the plasma current and maintain this current during the burn time.
"The first role of the structure is to hold the six central solenoid modules in position within strict tolerances measured in millimeters," said Kevin Freudenberg, US ITER's engineering technical director. "Then the real challenge occurs during operation. At key times, the resultant vertical force on the module stack is up to 60 meganewtons - more than twice the force of a space rocket at blast off."
To achieve a structure that can withstand the levels of extreme force that the central solenoid will generate, the team had to overcome numerous challenges. One example was the development of the 27 connectors, called tie plates, that form the vertical bars of the support structure. The tie plates connect the lower key blocks on the solenoid's foundation platform to the upper key blocks at the top of the structure, forming a cage around the central solenoid.
"When we began the initial design work, there was significant concern over whether we could make each tie plate as a single piece," Freudenberg said. "These pieces are 50 feet long and must be incredibly straight, meeting strict tolerances. We worked with forging shops and specialized engineering companies to achieve this, changing our initial design from a two-piece concept to a single piece."
Another challenge was fastening the structure components together sufficiently to withstand the extreme force that the central solenoid will generate. This led the team to turn to a U.S. company that had developed what is known as Superbolt® technology.
With four of the central solenoid modules now in place, and the final two expected to be stacked this year, the team is looking forward to the next phase of construction of the support cage at the ITER site in southern France.
"The real reward for the team will be watching the structure be assembled around the central solenoid, seeing their more than a decade of work coming to fruition and knowing we are one step closer to ITER operations," said Freudenberg.
U.S. contributions to ITER are sponsored by the US Department of Energy Office of Science and managed by UT-Battelle at Oak Ridge National Laboratory in Tennessee, with contributions by partner labs Princeton Plasma Physics Laboratory and Savannah River National Laboratory. For more information, see https://usiter.org . The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit https://science.energy.gov .
UT-Battelle manages ORNL for DOE's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, visit energy.gov/science .
