“Europe is such a nice place to be right now,” says Julijan Peric. He has just received the Fusion Engineering and Design Student Award at the International Symposium on Fusion Nuclear Technology (ISFNT) for his work on KATANA, an experimental facility in Ljubljana, Slovenia. Named after the Japanese sword, the facility uses activated water from a fission reactor to generate a stable neutron and gamma source for diagnostic research — the kind of measurements that will help ITER.
Sometimes, you really do have to cut things to fuse them.
Focusing and Being Celebrated
“It’s amazing to be recognized across the community for our work as a team. As a researcher, you can never work alone,” he says. Since 2021, he and his colleague Domen Kotnik, along with their advisors, have been writing proposals, applying for funding, and documenting their results to forge a “sword” sharp enough to cut through the edge of fusion research – and they succeeded.
“Our research is dry and precise but being part of the fusion community is incredibly encouraging and fun,” Julijan adds, thinking back to the conference where he received the prestigious award.
It’s the Neutrons
KATANA is hosted at the TRIGA reactor at the Jožef Stefan Institute and is designed to provide a stable, ITER-relevant source of neutrons and gammas. Its scope is testing and calibrating computational tools for ITER’s safety assessment.
When ITER begins operating, it will produce huge numbers of neutrons. Those neutrons will activate the cooling water which will then flow around different parts of ITER machine, even outside of the biological shield.
Another Tokamak’s Trash Was a Treasure
“We travelled to JET many times to work with neutron-activated water. It was extremely difficult to work in such a big project. Whenever there was cooling water from the fusion reaction, our detectors were overexposed,” Julijan recalls from the early days of his PhD.
Since the Joint European Torus (JET) remains one of a few fusion experiments ever to operate with deuterium-tritium (DT), it is still the only tokamak where neutron-activated water from actual fusion reactions was measured. But JET is now being decommissioned, and its data must be verified, re-evaluated, and combined with new computational methods to help set up ITER correctly.
Your At-Home Fusion Experiment
So Julijan and Domen decided to create a machine that could generate neutron-activated water on demand – allowing them to continue their measurements independently. That idea became KATANA.
What Julijan loves most about the facility is its flexibility – and the simplicity it brings to his work.
“It’s so cool. I can be creative, develop ideas, and test them immediately because I work right next to the machine,” he says.
Simulating ITER’s Waters
In KATANA’s safe, controlled environment, Julijan and his team measure, simulate, and validate everything long before ITER is even switched on. The results are impressive: their method achieves an uncertainty of less than 3.1 percent, a level of precision that stands out in reactor diagnostics. This gives ITER a reliable foundation for designing its future cooling circuit shielding. A major step forward.
Julijan – now finishing his PhD – has already received postdoc offers from several European institutions, thanks in part to the ISFNT award. “I like that we are visible in the community now, especially because Slovenia isn’t one of the big fusion players,” he says.
Putting Theory Into Practice at ITER?
Laying the theoretical foundations for ITER is one thing – but contributing directly on site in France is another goal Julijan hopes to achieve.
“It’s amazing to see so many brilliant minds from so many nations working together to solve this puzzle. I would love to help install the water activation experiment there,” he says.