Doctoral thesis on nuclear fusion at over one hundred million degrees Celsius awarded European physics prize
Current nuclear energy production is based on fission, which also produces dangerous and long-lasting nuclear waste. Its flipside is nuclear fusion, which generates the same amount of energy with considerably less waste. That is why researchers have for decades now been attempting to build a fusion reactor—a device that turns hydrogen into plasma to create energy. One example is the international megaproject ITER in France, set to produce nuclear fusion energy sometime in the late 2030s.
The biggest technical problem is the plasma itself: its temperature is well over 100 000 000 degrees Celsius and nothing survives contact with it. The donut-shaped reactor uses magnets to keep the plasma intact in a vacuum. Then the problem becomes how to extract the energy generated by the plasma without destroying the vacuum chamber.
‘One solution is to build the chamber out of tungsten. It can withstand high temperatures and the erosion caused by the plasma. But even a tiny number of tungsten impurities can weaken the relationship between the energy used to heat up the plasma and the overall energy created by the reactor. Right now, researchers are focusing on predicting tungsten’s behaviour in the plasma,’ says Doctoral Researcher Henri Kumpulainen.
Kumpulainen’s thesis recently won the European Physical Society’s 2025 Plasma Physics Division PhD Research Award. The thesis was completed at Aalto University in 2023 and directed by Department of Applied Physics Professor Mathias Groth.
’My PhD research showed that new simulations can predict the behaviour and qualities of tungsten much more accurately than previous ones. That helps reduce impurities in the plasma, which, in turn, in a step towards a functional fusion reactor.’
Kumpulainen headed to Germany after graduating with his PhD.
‘I received a two-year grant from the Finnish Cultural Foundation for carrying out research in Germany at Forschungszentrum Jülich, where I had already visited multiple times. So I moved to Jülich and started as a postdoc in February 2024. Now I work on simulating deuterium-based plasma—wall interactions in fusion devices.’
For Kumpulainen, the main thing is to help develop technology that could some day revolutionise global energy production.
‘After February next year, my plan is to keep working on fusion and plasma physics either in Finland, Germany or elsewhere, depending on how jobs and grants are available,’ Kumpulainen says.
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