DIII-D Research ‘Fuses’ Data, Networking
Jeremy Mateja, a PhD student in the Department of Nuclear Engineering, began his doctoral program at Rocky Top with a trip to San Diego, California.
Professor David Donovan, Mateja’s doctoral advisor, had invited him out West to gain in-person experience conducting experiments at a tokamak—a donut-shaped tungsten chamber used to create and study fusion plasma. San Diego is the site of DIII-D, the largest and most productive research tokamak in the United States.
“I was mostly just observing the experiment that Seth Messer, another PhD student in the lab, had designed,” said Mateja. “Even so, we generated so much data that I was able to take one piece of it and turn it into a paper, which I presented in France at the 26th International Conference on Plasma Surface Interaction in Controlled Fusion Devices in May of 2024.”
The impacts of Mateja’s first tokamak experience go far beyond that early-career publication; working with Messer also gave him the tools and connections to tackle his own research question.
When a highly energetic plasma is contained within a tokamak, the energetic ions erode material off the tokamak’s walls, creating debris. Sufficient debris can disrupt the plasma, ending reactions early.
“Trying to remove debris while the tokamak is running is not well explored,” Mateja explained, “but that question has a clear effect on how we will operate tokamaks for energy generation in the future.”
Just two years after presenting his first findings, Mateja has had two experiments accepted and successfully run on DIII-D. That is a tremendous feat, not just because PhD student experiment slots are extremely competitive but because one of the experiments was delayed due to mechanical issues outside of DIII-D’s control.
Mateja’s incredible progress in research is due not just to his head start on tokamak research but to the deep connections he has made with experts in the field.
“Jeremy was able to persevere and innovate with the support of many collaborators,” Donovan said. “He has shown he can adapt to changing situations and take advantage of new opportunities as they arise, which is one of the most essential traits of a successful researcher.”
Sweeping Up After Fusion
Tokamak operators can alter the current running through certain components to clean the chamber somewhat, using some of the energetic ions expelled from the plasma to “sweep” debris out of plasma contact.
“We know that sweeps are effective at eroding the debris, but we don’t know where the material is deposited after sweeping, or even how the material is eroded—is it vaporized into atoms or eroded as chunks of dust?” Mateja said.
Mateja collaborated with several researchers at DIII-D and other institutions to develop an experiment that would investigate the fate of swept debris.
Mateja planned to drop boron into the tokamak as it ran. He would then perform sweeps and evaluate how effectively they removed the boron debris, as well as how the debris itself changed as it was swept away.
While a mechanical problem required Mateja’s first time slot to be canceled, the generosity of his collaborators in San Diego meant he was still able to move the experiment forward while waiting to be rescheduled.
“Some DIII-D staff members were nice enough to conduct the dust collection for me,” Mateja said. “While their samples were not doped with boron the way they would have been in my experiment, they gave me a control value I could compare my experimental results with later and a good chance to test my analysis methods.”
With help from Donovan, other UT scientists, and researchers at DIII-D, ORNL, the Princeton Plasma Physics Laboratory, and the University of California San Diego, Mateja also developed a secondary experiment investigating how sweeps may be used to recover plasma fuel trapped in debris.
The secondary experiment ran successfully in June 2025; two months later, Mateja was able to complete a modified version of his primary experiment.
Flexibility and Connections
While he and his collaborators are still evaluating the physical samples from both experiments, Mateja already knows one of the biggest results: developing his communication skills.
“When I started as a PhD student, I was very shy–I got nervous reaching out to experts,” he said. “This whole process has forced me to become a better collaborator as well as a more confident researcher. Those are soft skills, but they’re still very important to being a successful scientist.”
Actively collaborating with other researchers also allowed Mateja to build much deeper connections than his previous participation in conferences.
“When planning an experiment—especially in fusion—there are so many considerations and things that can be easily overlooked if you don’t have the right expertise involved,” Mateja said. “Getting to work with so many experts across multiple institutions was a great networking opportunity and a tremendous learning experience.”
Contact
Izzie Gall (egall4@utk.edu)