The harsh environment inside future fusion power plants demands wall materials that do not crack or melt under the intense conditions. To tackle this challenge, researchers are exploring liquid metals like lithium and ask themselves: “Can we have lithium in a plasma facing component?” On 9 July 2025 Maria Morbey Affonso Demitrion Cunha successfully defended her thesis on this topic.
Imagine a world powered by the same force that fuels the Sun: clean, safe, and virtually limitless energy. That’s the promise of nuclear fusion, a process where light atoms like deuterium and tritium fuse to form helium, releasing vast amounts of energy. This process takes place under extreme conditions, with fuel heated up to over 150 million degrees Celsius, turning it into a super-hot, electrically charged plasma. This plasma must be kept stable and away from the fusion reactor walls long enough for fusion to occur.
Some particles escape and strike the reactor walls, especially in the divertor area that faces intense heat and particle bombardment, which can damage the materials over time. Currently, tungsten is the material of choice for the divertor because of its high melting point and durability. But even tungsten wears out after about 1.5 years of full operation. Sudden disruptions in the plasma can cause even more damage, leading to expensive and time-consuming repairs.
Liquid lithium: a smart alternative
To solve this, researchers are exploring liquid metals like lithium. Morbey: “Liquid lithium has several advantages: it can ‘self-heal’ from damage, spread heat more evenly through vapor shielding, and reduce impurities in the plasma. It also melts at relatively low temperatures, making it easier to handle.”
However, lithium has a downside. It tends to chemically bind with hydrogen isotopes, including tritium, the radioactive fuel used in fusion. When tritium gets trapped in the reactor walls, it becomes difficult to recover, which is a problem because tritium is both rare and valuable.
To better understand this issue, Morbey studied how lithium interacts with deuterium, a non-radioactive stand-in for tritium. Morbey: “I conducted experiments in several fusion research facilities, including the DIII-D tokamak at General Atomics in the U.S. and the Magnum-PSI facility at DIFFER in the Netherlands.”
The results showed that most deuterium gets trapped in thin layers formed when lithium and deuterium are deposited together. Morbey: “These layers hold onto deuterium tightly, even at high temperatures. Water vapor can release some of it by forming lithium oxide, but if the oxide layer becomes too thick, it blocks further release.”
One promising solution is hydrogen-deuterium isotope exchange, where regular hydrogen replaces the trapped deuterium. This method worked well, especially at higher temperatures, and was more effective than heating alone. By applying isotope exchange between plasma pulses, it may be possible to recover tritium efficiently. In systems where lithium circulates, this could allow continuous tritium recovery and better fuel management.
The research of Morbey helps us better understand how lithium behaves in a fusion environment. It contributes to the development of more sustainable reactors in which we can efficiently manage tritium. This brings us another step closer to a future where nuclear fusion is a reliable source of energy.
Journey in fusion
Morbey’s journey in physics started in 2015, when she decided to start a bachelor Physics in Lisbon. Despite some doubts between choosing Biology or Physics, she chose the latter. Morbey: “I like the puzzling aspect of physics. In my opinion, if you understand physics, you understand better the world around you.” In 2018 she decided to move to Eindhoven for a masters in Nuclear Fusion at the Eindhoven University of Technology.
In May 2021 Morbey started at DIFFER as a PhD student in the group of Thomas Morgan. In her research work, there is an overlap with DIFFER’s ion beam facility. Therefore, Morbey also worked closely with Beata Tyburska-Pueschel, who knows the trapping of the fuel issues. After her promotion Morbey will work at DIFFER as a postdoc researcher: “I’m moving my focus from liquid metals to solid (tungsten) materials, an area I’m going to explore with curiosity.”
On 9 July 2025 Maria Morbey Affonso Demitrion Cunha successfully defended her thesis called 'Deuterium Dynamics in Lithium Layers: Retention and Release Under Fusion Relevant Plasmas'. The thesis can be found on the TU/e website. It’s a thesis with a personal touch: Morbey’s love for the Dutch tulip can be seen in the watercolour paintings in it, a cheerful detail that should not go unnoticed.
Author: Rianne van Hoek
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