Professor Christian Linsmeier, Director of the Institute for Fusion Energy and Nuclear Waste Management, outlines Germany’s recent increase in funding for fusion research and the Institute’s role in advancing fusion technology.
Germany has been investing in fusion research for several decades, creating a programme that encompasses a variety of projects and topics. About a year and a half ago, the German government announced an increase in funding to further advance these efforts towards the construction of the first fusion reactor.
The German fusion programme is carried out by three research organisations: the Max-Planck-Institute for Plasma Physics (IPP), with two locations: the main site in Garching and another in Greifswald, along the Baltic coast. At the Garching site, researchers operate the ASDEX Upgrade tokamak. The Greifswald facility is home to the globally renowned Wendelstein 7-X stellarator, celebrated for being the most advanced and closest to a reactor among current technologies.
The Max-Planck-Institute for Plasma Physics is Germany’s leading fusion research institution, representing approximately three-quarters of the nation’s research efforts in this area. The IPP operates these devices and conducts essential plasma physics research to advance fusion technology. The Karlsruhe Institute of Technology plays a significant role in this field. Finally, the Jülich Research Centre (FZJ) houses the Institute of Fusion Research and Nuclear Waste Management, which consists of two primary institutes: one focused on fusion research (IFN-1) and the other on nuclear waste management (IFN-2).
FZJ, with its IFN-1, specialises in the research areas of plasma-wall interactions and plasma-facing materials and components. This includes the diagnostics and modelling of the edge plasmas of tokamaks and stellarators, the physics of plasma-wall interactions, as well as development, characterisation and testing of materials and components for the plasma-facing units. As one of the few international research sites, FZJ includes nuclear aspects by operating a lab with hot cells in a radiation-controlled area.
Investment in Germany’s fusion landscape
Germany has launched a programme called Fusion 2040, stimulating collaborative efforts among fusion researchers and industry. The programme has been allocated a budget of €370m for the next four years. This funding is in addition to Germany’s standard fusion budget and contributions to the European Union’s ITER programme. Notably, this €370m constitutes supplementary funding for cooperative activities between research centers and the fusion industry. This strategy aims to realise a fusion reactor by transferring knowledge from research to industry.
The Fusion 2040 programme was established by interactions between the federal government and fusion research representatives and finally commenced its first project between FZJ and industry partners on November 1, 2024.
Our strategy is to utilise this funding to strengthen traditional research institutions such as Jülich, Karlsruhe, Garching and Greifswald and promote collaborative efforts between fusion researchers and industry partners. This funding concept by federal ministries, known in German as ‘Verbundprojekte, i.e. Collaborative Projects,’ requires us to establish partnerships with industry stakeholders for any topics submitted within this programme.
The situation is quite flexible, allowing for a small part of the industry to link with a larger public sector or vice versa. There are various options available. The primary aim is to leverage the knowledge we have developed over decades in fusion, plasma-wall interactions, technology, and plasma physics, transferring that knowledge to industry to foster its growth. This concept of collaborative projects is not new; it typically requires funding from federal government sources in other technological areas as well, and it must be accomplished in collaboration with industry.
The Institute of Fusion Research and Nuclear Waste Management
The Jülich contribution to the German fusion programme via the Plasma Physics institute within the Institute of Fusion Energy and Nuclear Waste Management (IFN-1), is the smallest organisational partner within the German fusion programme. Our primary focus is on plasma interactions with and materials for the first wall and divertor. This topic is closely linked to understanding plasma physics at the edge of the fusion plasma, the physics of the plasma-material interactions, as well as surface and materials physics and chemistry. Therefore, this field is, by definition, genuinely multi-disciplinary. Our strength lies in our ability to study the behaviour of particles at the plasma edge, bridging the plasma-material interface, and extending a few centimetres into the materials.
There are many institutes worldwide specialising in materials and plasma physics; however, none combine these fields in the same way we do. Our team consists of engineers, material scientists, chemists, and physicists who collaborate to address the challenges related to optimising plasma-facing components and their interactions with fusion plasma. Ultimately, this interface determines the components’ lifetime and, therefore, the economic viability of fusion as a new primary energy source.
Researching edge plasma
The fusion process occurs primarily in the hot plasma core, while the edge plasma limiting that volume presents additional unique challenges. Transitioning from the hot core to the wall requires a high-density barrier to confine the plasma and maintain temperature; without it, surrounding structures risk damage. The principles governing edge plasma physics are distinct from those of the core.
The core plasma behaves mostly like a fluid, but at the edge, individual atomic collisions and neutral atom behaviour become significant. Our research is focused on the edge plasma in order to control the plasma-material interface. In fusion reactors, perfect confinement is unrealisable, as it would suffocate the plasma and halt fusion reactions that generate alpha particles and impurities from wall erosion. Therefore, it is vital to remove fusion byproducts, mainly helium, and impurities, through the edge plasma to sustain fusion reactions.
We are investigating edge plasma and developing models and codes, including EIRENE and ERO 2, which are widely used in the fusion community for edge plasma processes. Our work also explores interactions with the reactor wall, studying particles that escape the plasma toward the first wall or the divertor, where most power and particles are expelled.
These areas experience high power and particle loads.
In fusion systems, we focus on a range of up to 20 megawatts per square meter, managing heat and particle load effectively.
Developing effective materials
The German Helmholtz Fusion programme, focuses on four key areas: Stellarator, Tokamak (both led by IPP), Materials and Fusion Technology (led by KIT), and Plasma-Wall Interactions, which we lead at Forschungszentrum Jülich (FZJ). Plasma-wall interactions are relevant to both stellarators and tokamaks, enabling us to apply our findings across different fusion confinement concepts.
Our research examines the interactions between plasma and wall materials, particularly those exposed to plasma. Effective materials must demonstrate low erosion rates, minimal retention of fuel (specifically deuterium and tritium), and efficient heat transfer to prevent overheating in the divertor.
Tungsten is a strong candidate due to its properties, including a high melting point of over 3,400 degrees Celsius. However, it is very brittle, especially after exposure to high temperatures and neutrons, which can further increase brittleness.
Tungsten’s high surface binding energy leads to quite a high sputtering threshold, meaning that if the energy of impinging plasma particles is maintained below that threshold, erosion is minimised. This characteristic significantly extends the lifespan of the divertor and first wall, making tungsten a preferable choice despite its brittleness. Clearly, the lifetime of plasma-facing components before a necessary replacement greatly impacts the economy of fusion as an electricity source.
The brittleness issue of tungsten is tackled and solved by one of our main material development strategies: By integrating tungsten fibers into a tungsten matrix – and providing a stable and well-defined interface between fibers and matrix – the brittleness problem can be solved. Such fiber-matrix composites behave like a ductile material, although the constituents are still brittle. The trick is the clever interface: cracks, which would immediately destroy a brittle component, are stopped at these internal interfaces and can therefore control the macroscopic behaviour of such a composite material.
Besides its intrinsic brittleness, pure tungsten poses an additional problem in case of an off-normal reactor condition. In a loss-of-coolant accident with air ingress, the plasma-facing components quickly reach high temperatures due to the decay of neutron-activated elements. Above around 700°C, air and humidity react with pure tungsten, producing tungsten oxide, which sublimates at these temperatures. This volatilisation of activated elements raises safety concerns in such an accident scenario.
Our approach to solving this issue is inspired by stainless steel, where pure iron, which tends to rust, is alloyed with elements like chromium to create a rust-resistant material. We applied this principle to tungsten by selecting specific alloying elements, including also chromium, to develop what we call a self-passivating tungsten alloy. This innovation enhances tungsten’s stability in the presence of moisture and air without sacrificing its premier qualities as a plasma-facing material.
Our research in these two exemplary material fields, conducted over approximately 15 years, led to the development of these material solutions to a degree where a transfer into the industry – and, therefore, an upscaling from lab scale to production – has started.
Dedicated and specialised technology
In addition to our focus on material development, edge plasma physics and modelling, we design diagnostic systems, including spectrometers, for fusion facilities like the Wendelstein 7-X and over decades for the European tokamak JET in Culham. Our instruments investigate interactions between edge plasma and the first wall and are essential tools for studying the physics of plasma-wall interactions at large-scale fusion devices.
As a further research field, we specialise in Jülich in analysing hydrogen isotopes in materials, particularly also the hydrogen isotopes deuterium and tritium. Hydrogen isotopes can weaken tungsten, steel, and other metals by penetrating into atomic spaces in the lattice of metal atoms. To analyse these changes, we use e.g. thermal desorption analysis, ion-beam based accelerator techniques, as well as laser-based techniques. For the latter, we also develop technological concepts in order to apply them not only in a laboratory environment but also as analysis techniques compatible with large-scale fusion devices like ITER.
Finally, we operate a specific laboratory with a controlled area and hot cells to handle and analyse radioactive materials and components, e.g. after exposure to neutrons and the respective activation reactions.
Research at neutron-exposed components
In a fusion reaction, deuterium combines with tritium to produce an alpha particle (a Helium-4 nucleus) and a neutron. The neutron, as indicated by its name, is electrically neutral. However, the plasma itself is contained within a magnetic cage in a stellarator or tokamak; the neutrons from the fusion reaction escape because they carry no charge and are, therefore, not affected by the magnetic field.
As the neutron travels through materials – specifically the first wall and the blanket behind it – it plays a beneficial role in breeding tritium. However, neutron impact also has drawbacks, as it can alter the properties of the materials it passes through. The neutron can displace some atoms, which leads to disorder and affects material properties, including hydrogen or tritium trapping, as well as mechanical properties.
Another important aspect to consider is the divertor, which experiences very high power loads. It is crucial to test both the materials and components under these high power loads and in exposure to plasmas, including after exposure to neutrons. Typically, when a material has been exposed to neutrons, it becomes radioactive due to various transmutation reactions.
Therefore, it is essential to have a controlled-area laboratory where the radioactivity of all incoming and outgoing samples is monitored and measured. If the radioactivity of the samples is too high, additionally, a hot cell may be required within that controlled laboratory space in order to protect operators and the environment during the experiments with those components and materials.
State-of-the-art facilities
Our “High-Temperature Materials Laboratory – HML” is unique, providing the ability to handle radioactive materials and components. In particular, they can be exposed to electron beam devices for high-power loading tests, as well as to plasmas from a linear plasma device for plasma-wall interaction studies. These devices are located in hot cells and provide a unique environment for these studies.
Unlike tokamaks or stellarators, the new linear plasma device “JULE-PSI” generates plasma in a horizontal column, allowing us to simulate reactor first wall conditions with greater operational control than in large fusion devices. This allows well-defined plasma-material interaction studies. Currently, we are constructing two new hot cells to house JULE-PSI and the electron beam device “JUDITH 3”. These cells will enable us to safely work with radioactive materials irradiated in nuclear reactors.
Globally, our linear plasma device JULE-PSI is one of a kind; while other labs can also handle nuclear materials, none have a linear plasma setup like JULE-PSI within a hot cell. This allows for a comprehensive exploration of plasma-wall interactions under conditions that are unique to a fusion reactor.
Cooperation is key
We work together with various large-scale fusion devices, including Wendelstein 7-X, JET, and other international facilities. This is particularly significant for us when combining our extensive laboratory and theory research on plasma-wall interactions with research at large fusion experiments.
Although we operate as a separate institute and are not part of the Max-Planck-Institute for Plasma Physics (IPP), the Greifswald branch of the Max-Planck Institute for Plasma Physics frequently seeks our expertise in plasma-wall interactions. They do not have a dedicated Department of Plasma-Wall Interactions, so this responsibility falls to us in Jülich. Our work includes operating research devices, conducting physics research, and engaging in modelling.
To the UK, we have strong connections, particularly with Culham as the JET site, and this network is expanding as the UK STEP programme progresses. In Europe, we also collaborate with the WEST tokamak located in Cadarache, France, to expose materials and components in the course of our cooperative research. Outside Europe, we have particularly strong collaborations with colleagues in Hefei, China, who operate EAST (Experimental Advanced Superconducting Tokamak), a modern superconducting tokamak, leading in many aspects of tokamak research. In the US, the Oak Ridge National Laboratory is one of our strong partners, along with the University of Wisconsin at Madison.
The outlook for fusion
Germany’s fusion research landscape has significantly evolved with the emergence of four notable companies, two of which focus on magnetic fusion: Proxima Fusion and Gauss Fusion. Both companies focus on a stellarator fusion reactor (like Wendelstein 7-X). In particular Gauss Fusion’s efforts are centred on constructing the stellarator as core of a fusion reactor facility, including the necessary infrastructure.
While the concept of nuclear fusion differs from traditional energy methods, concerns about its long-term viability persists. However, successful demonstrations have generated global interest, particularly in the US and Europe.
Facilities like the Joint European Torus (JET) are crucial for fusion research but primarily serve experimental purposes. Unlike experimental setups, developing a reactor that generates electricity requires specialised design and careful consideration of operational parameters. The focus must shift towards energy production, necessitating significant investment and large-scale construction, as exemplified by ITER in southern France, which relies on extensive infrastructure to function effectively.
Achieving fusion power in a first-of-a-kind reactor still depends on government funding and support, as no large-scale industrial project of this magnitude can succeed without it. Typically, such developments take about 20 years, similar to past advancements in photovoltaics and wind energy, which have also relied and still rely on government initiatives.
Overall, the current landscape for realising fusion in Germany is quite positive. We are witnessing an influx of additional funding, and our objective is to construct a fusion reactor rather than merely establish a new experimental setup. The Fusion 2040 programme, designed to attract industry involvement, is a pivotal component in the development of a fusion reactor. This collaboration is only feasible if we set a clear goal and allocate funding to support it, something the government is currently facilitating. I am convinced that we can be optimistic that this initiative will continue with the aim of developing the first prototype reactor.
Please note, this article will also appear in the 20th edition of our quarterly publication.
