Tag: Fusion Energy

Massimo Garribba, Deputy Director-General responsible for the co-ordination of EURATOM policies in the Directorate-General for Energy at the European Commission, details Europe’s journey towards the realisation of fusion energy.

As Europe works towards achieving net zero targets and sustainability goals, could fusion – powering the sun and stars – be the energy of the future?

With a long history in fusion science and technology, Europe is well positioned as a leader in the journey to fusion commercialisation. Most notably, Europe is home to one of the most ambitious energy projects in the world – ITER, located in southern France. ITER is a major international collaboration working to build the world’s largest tokamak – an experimental machine designed to validate the scientific and engineering viability of fusion energy. ITER Members will then be able to be design their prototype or demonstration power plants on the basis of ITER construction experience, technological and scientific results. This will further drive the transition from a scientific experiment to fusion commercialisation.

The EU also co-funds EUROfusion consortium through the Horizon Europe Euratom Research and Training Programme. Via this consortium, European fusion laboratories collaborate to further advance the fusion research, design and manufacture systems that are necessary for the future fusion reactors.

To find out more about Europe’s fusion activities, The Innovation Platform spoke to Massimo Garribba, Deputy Director-General responsible for the co-ordination of EURATOM policies, Directorate-General for Energy, European Commission.

Can you elaborate on the current state of fusion in the EU?

The European Union (EU) considers fusion has the potential to provide a safe, cost-efficient and sustainable solution to European and global energy needs in the future. For this reason, the EU has supported for decades cutting-edge research and innovation, with the goal of developing fusion power plants for electricity production for a greener and more sustainable energy mix.

The EU is part of one of the most ambitious energy projects in the world – ITER. Located in the south of France, ITER is a unique project to build the world’s largest and most advanced fusion machine – a tokamak. Once completed, ITER will be approximately 30m high and 30m wide, weighing 23,000 tonnes. It aims to prove the technical and scientific feasibility of using the fusion process for electricity production. Tokamaks are vacuum-chambered devices designed to replicate on Earth the process of fusion – the energy source of the sun and stars – using a powerful magnetic field generated by superconducting magnets.

Beyond ITER, the EU collaborates with Japan on fusion activities under the Broader Approach Agreement. This privileged partnership oversees the development of key infrastructures, such as a test facility for fusion materials (The International Fusion Materials Irradiation Facility / Engineering Design and Engineering Validation Activities – IFMIF-EVEDA). The materials to be used in fusion reactors will need to withstand immense temperature and neutron fluence generated during the fusion process. Under the same agreement, the EU and Japan have jointly built a tokamak device known as JT-60SA. This device, located in Naka, Japan, is currently the largest operational superconducting tokamak in the world, after its inauguration in December 2023. JT-60SA was designed to support the operation of ITER by providing a complementary research and development programme.

Recently, Spain and Croatia have teamed up to lead the development of the International Fusion Materials Irradiation Facility – Demo Oriented Neutron Source (IFMIF-DONES), which is being constructed in Spain. IFMIF-DONES builds on the results of IFMIF-EVEDA and will provide a neutron source essential for further testing and validating materials that will be used in future fusion power plants.

The EU has also been supporting research in national fusion laboratories and universities, such as the Joint European Torus (JET) in the UK and the Wendelstein 7-X stellarator in Germany. Now, we are looking into opportunities to support joint initiatives between the private and public sectors. For instance, the European Innovation Council has recently awarded a €2.5m grant to a fusion start-up to support progress on the design of its stellarator and the integration of key stellarator components. We are encouraging EU fusion start-ups to work and co-operate with EU fusion laboratories, but also with industrial partners who are part of the current ITER supply chain.

How can findings from major European fusion activities and organisations such as JET, EUROfusion and ITER inform the future direction of European fusion development?

Fusion development is a long-term endeavour that requires sustained efforts across various initiatives, including the ones you mentioned.

ITER is one of the most complex machines ever to be constructed. It is meant to establish a demonstration fusion power plant and there are no shortcuts on this path. ITER will help demonstrate the feasibility of technologies needed for a fusion power plant, bridging the gap between today’s smaller-scale experimental fusion devices and the future demonstration of fusion power plants. Through ITER, scientists will be able to study plasmas under conditions similar to those expected in a future power plant and test essential technologies such as heating, control, diagnostics, cryogenics, and remote maintenance. Moreover, ITER will provide a unique opportunity to test, under real fusion conditions, the production of one of the fusion fuels for future fusion reactors: tritium.

In other words, ITER operations and the results of its research and experiments in the production of tritium and construction materials for fusion machines are necessary steps for the EU to transition fusion energy from research to demonstration reactors.

The findings from major European fusion activities, such as JET and EUROfusion, play a crucial role in informing the future of European fusion development. The JET machine concluded its operational journey on 18 December 2023, over four decades after its inception. It has been fundamental in laying the groundwork for ITER and future fusion power plants through its innovative deuterium-tritium experiments. JET also played a key role in training several generations of fusion scientists and engineers across Europe.

EUROfusion – a consortium of around 30 national fusion research laboratories across the EU – conducts fusion research under the Euratom Research and Training Programme. This focuses on the development of key fusion-related technologies, advancing training and education, and the development of the conceptual design of a future demonstration fusion power reactor (DEMO). EUROfusion’s co-ordinated efforts continue to drive progress in critical technologies while fostering new generations of fusion experts.

The collective knowledge obtained from all these different initiatives (e.g. on plasma behaviour, fusion materials, operational challenges, etc.), will shape the future course of European fusion development. Co-ordinated research efforts will help the EU transition from research to industrialisation, paving the way for the development and operation of commercial fusion power plants.

What are the main bottlenecks preventing fusion energy from being fully realised? How can these be removed?

There are a series of key technological bottlenecks related to the demonstration of critical technologies of future fusion reactors. For example, the qualification of materials that can withstand the extreme conditions within fusion reactors, or the demonstration of key components’ performance under reactor conditions. The development of plasma scenarios and the remote maintenance design and qualification remain significant challenges as well.

Another important bottleneck is the demonstration of tritium production within the reactor for fuel self-sufficiency. Fusion reactors rely on tritium, which is scarce in nature. Therefore, future commercial power plants will need to ‘breed’ their own tritium for economic viability. Breeding blanket concepts are being developed, and will need to be tested, to produce tritium fuel directly during the fusion reaction.

Addressing these challenges is crucial for fusion to transition from experimental reactors to a reliable and sustainable energy source. This can be achieved by the fusion industry and research institutions complementing their knowledge and helping to close the technological gaps affecting the path to fusion energy generation.

What is needed to enable fusion research and technology to flourish in Europe?

Several key actions are required to support the growth and development of fusion research and technology.

Firstly, we need to secure continued and sufficient commitment of financial, technical, and human resources to complete the ITER project. Despite the challenges the project is facing and the rise of private investment in multiple fusion machine designs, ITER remains not only highly relevant, but in fact the centrepiece of global efforts towards the commercialisation of fusion energy.

Secondly, an appropriate fusion-specific regulatory framework will also facilitate the deployment of fusion technologies. In this regard, the European Commission has launched a dialogue with the European nuclear safety authorities in the European Nuclear Safety Regulators Group on possible regulatory approaches to fusion facilities.

Thirdly, as indicated in Draghi’s latest report on the future of European competitiveness, we need to create ‘a stable and predictable fusion ecosystem for industrial innovation, leveraging the ITER project, while ensuring a clear technology development roadmap.’ A coherent EU-level approach should be adopted to facilitate research and technology innovation, incentivise private sector engagement, de-risk investments when necessary, and create the environment where private companies and publicly funded research organisations work hand in hand towards a common goal – bringing fusion energy to the grids.

Finally, once the first commercial power plants are built, there will be a massive industrial effort required to scale up production. Therefore, we will need to support the EU utilities and supply chain industry to be well positioned – either as fusion energy deployers or as key suppliers to leading commercial fusion projects.

How close do you think Europe is to fusion commercialisation?

We are seeing several private initiatives working to achieve electricity production with ambitious timelines. Some of them have announced that they will demonstrate significant progress within the next five years, aiming for a technology readiness level (TRL) of 4 or 5 and potential net energy gain or high-power multiplication. These companies plan to complete a pilot plant between 2030 and the mid-2030s. The success of these plants depends on the performance of the upcoming devices, securing further funding, and resolving design, engineering, procurement, and construction issues. We also need to recognise important differences between public and private approaches to fusion technology development: Public initiatives, like ITER, aim to develop the entire fusion system, including fusion-enabling technologies such as blanket breeding and tritium technologies. While it may require more time, this comprehensive approach addresses long-term issues critical to the future commercial deployment of fusion power plants.

It’s hard to predict an exact timing, but we can realistically expect to still have some decades of work ahead of us before achieving fusion commercialisation. Although, there’s always hope for a breakthrough or major discovery in the meantime.

What is important to keep in mind is that the benefits of having fusion energy as a part of the future energy mix are worth pursuing and we remain committed to making fusion energy a reality as fast as possible.

Please note, this article will also appear in the 20th edition of our quarterly publication.

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.

As sustainable fusion energy inches closer to reality, Dr Simon Bott-Suzuki of the University of California San Diego explores progress and persistent challenges.

Fusion energy has the potential to help address global energy needs as the demand for power continues to rise. Renewable sources such as solar and wind are a vital piece of the puzzle. However, renewables only produce energy when, for example, the sun shines or the wind blows. Modern society, and what is aspired to by the enormous population of the developing world, demands power be available at a moment’s notice, any time of day.

Storage methods can help optimise these for our usage demands throughout the day, but this doesn’t increase the overall energy available, it just makes what is generated more flexible. This is one reason the move from fossil fuel power plants continues to be so difficult: they provide a baseload – the ‘always on’ power we demand to run our lives 24/7.

Magnetic Drive Inertial Fusion Energy (MD-IFE)

Fusion plants will produce this baseload power and accelerate the retirement of fossil fuel power plants. The U.S. Department of Energy has recently set out several programmes to accelerate the realisation and commercialisation of fusion power based on the White House’s Bold Decadal Vision for Fusion Energy.

This investment is driving innovation in the field and pushing researchers to develop the practical implementation of their research schemes. Alongside this, the rapid emergence of the private fusion industry means fusion power can be achieved by more than one solution – an unlikely scenario under solely federal support. The co-operation of federal and private funding seems to be the most practicable way forward and is already allowing productive partnerships to develop.

Within the two main approaches, magnetic and inertial confinement, MD-IFE sits within inertial fusion energy. The inertial fusion approach has been supported for several decades by the National Nuclear Security Administration (NNSA), which includes both the achievement of ignition at the laser-fusion National Ignition Facility (NIF), and the underpinnings for development of MD-IFE discussed here. This support has enabled the investigation and understanding of many of the basic physics principles governing how we can achieve fusion in single experiments. The Department of Energy funding focuses on the engineering challenges of repeating those experiments sufficiently quickly and accurately to achieve net energy gain.

The MD-IFE approach

The magnetic drive approach to inertial fusion has been led by Sandia National Laboratories, and takes advantage of the high efficiency of energy delivery possible with large pulsed power drivers. But what is pulsed power, and how can it be used to make energy? Conceptually, pulsed power is quite simple; it is the compression of electrical energy in time to provide a large electrical pulse to a target. It’s the same method we use to make lights blink or generate a camera flash; a capacitor is charged slowly, then discharged quickly by closing a switch when we want it to fire.

For fusion, it’s only the scale that is different. Instead of charging one small capacitor with, say, 9V from a battery or 110V from a wall outlet, we charge hundreds of capacitors to 100 kilo-volts (kV), and fire them all at the same time, giving short mega-volt output voltages. This electrical pulse drives a very high current in the target, typically millions of amperes. The world’s largest pulsed power driver, called ‘Z’, is housed at Sandia National Laboratories, and can apply 26,000,000 amps (26 MA) to a centimeter-sized target in just 100 billionths of a seconds (100ns).

In accordance with the laws of electromagnetism, a current makes a magnetic field, and it is this magnetic field that is used to compress a metal target filled with fuel very quickly and uniformly to drive fusion. Very large currents make very large magnetic fields, and compressional forces of billions of atmospheres (Gbar) are regularly achieved. Presently, experiments on Magnetised Liner Inertial Fusion (MagLIF) ^1-4 are carried out one at a time on Sandia’s Z Machine to optimise performance. This fusion target is central to the MD-IFE method, and again is relatively simple.

We start with a 6mm diameter metal cylinder, 10mm tall, and fill it with deuterium and tritium gas. This is placed inside the Z machine and attached to the electrodes so we can drive the large current through it. The whole experiment takes place in a vacuum and is shielded to prevent radiation and neutrons from escaping.

This ‘liner’ is then seeded with a magnetic field (MagLIF 1), heated with a laser beam (MagLIF 2), and then rapidly compressed onto its central axis (MagLIF 3) using the current drive. The compression is very similar to the ‘can crusher’ experiments hobbyists build, but on a much larger and far more accurate scale. The liner contains and rapidly heats the fusion fuel (deuterium and tritium) to high temperatures, releasing energy primarily as neutrons. These neutrons are captured in a power plant, and their energy is used to heat water to turn a steam turbine and produce electricity. We then take out the electrodes, which are damaged from the fusion event, replace them along with a new liner target and electrode set, and repeat the process. This method is well suited to generate large yields (500 MJ to several GJ) with each fusion shot, and to repeat shots every ten seconds in a large-scale power station.

Recent performance breakthroughs

Since the introduction of the MagLIF approach for MD-IFE in 2011, fusion performance has progressed at a remarkable rate. Performance of a fusion system can be measured in a number of different ways, but one primary method is the ‘triple product’ derived from the Lawson Criterion. This allows a fair comparison between the wide range of methods presently being pursued both in federal and private endeavors.

The three important quantities are the plasma density (ion density n_i), the plasma temperature (more specifically the ion temperature T_i) and the time the plasma is held together (the confinement time, t). The higher the product of these quantities are, the closer a system is to achieving fusion, and we need n_iT_it > 3 x 10²¹ (m^-3 keV s) to make energy.

Fig. 1 reproduces Fig. 2 from Wurzel and Hsu 2022.⁵ This plots the triple product (nTτ) against the measured ion temperature for a wide range of experimental platforms. The premier laser-driven IFE platforms, OMEGA and NIF, show high nTτ at moderate ion temperatures (few keV), with a notable exception being the NIF ignition shot N210808, with an nTτ of 5.2×10²¹ keV m^-3 s and an ion temperature of 10 keV. This is the only point on the plot above a Lawson criterion of unity. Magnetic confinement facilities like D-IIID at General Atomics, JET in the UK and TFTR previously at Princeton Plasma Physics Laboratory, typically show significantly higher ion temperatures, triple products in the range of ~10²⁰ keV m^-3 s, and a Lawson criteria between 0.1 and 1. The MagLIF data for MD-IFE on the original plot (black x points labeled “MagLIF”) showed data from Z shots in 2015 which demonstrated nTτ ~3×10²⁰ keV m^-3 s and ion temperatures approaching 3 keV. Data from Knapp 2022⁶ (yellow circles points labelled ‘MagLIF 2022’) improves on these values, where the best shot gives nTτ exceeding 10²¹ keV m^-3 s.

This makes MagLIF the only platform other than NIF to achieve such a high triple product value to date. Peak ion temperatures were 3.3 keV and the Lawson criterion was close to 0.1. This breakthrough result places MagLIF and MD-IFE in an ideal position to make rapid progress on the technological challenges that remain for energy production.

Translating physics progress to energy production

This excellent single shot performance needs translation to a repetition-rated environment suitable for fusion energy. The large-scale machines we are presently using to achieve fusion in one-time experiments will not work to produce energy; they were simply never designed to do so. There remain significant challenges to build a power station from these highly promising foundations, and much of the fusion field is working hard to understand and address how we will achieve this.

There are a number of areas we can work on together as a community, such as making sure materials are developed that give a power station a long lifetime, or how we handle and recover fusion fuels. Both of these will determine the costs of a fusion power plant, and how it will operate safely close to populated areas where the power is needed. There are also needs for each specialised fusion approach that must be addressed by those developing it. Here, MD-IFE may have significant advantages over several other approaches which are enabled by two key technologies; advanced targets and scalable pulsed power drivers.

Advanced targets: The Liner targets on the Z machine use large external field coils to produce the initial seed magnetic field required. These are difficult to build and expensive, and so not compatible with repetition-rated operation for energy. Advanced targets are under development in which the magnetic field is generated through the target itself by introducing a helical element to the current flow.^7,8 These targets also reduce load inductance, allowing higher energy deposition, and are more amenable to mass manufacture for a power plant. Testing so far looks very promising, and experiments and simulation works continue to optimise designs.

Scalable pulsed power driver technology: The Z machine is sub-scale, in that there is insufficient electrical current to achieve fusion ignition. Z is also based on 1970s Marx bank technology, which has proven very effective for the job it was designed for, but is not tailored to fusion energy needs. A power plant will use a 70MA driver, about a 3x scale-up of Z, and capable of one shot every ten seconds. Sandia and its collaborators have already developed several pulsed power architectures which could be used to construct this driver, including Linear Transformer Driver (LTD)⁹ and the Impedance Match Marx Generator (IMG).¹⁰ These can be designed specifically for achieving energy output, can operate rapidly, and deliver electrical pulses far more efficiently to the liner target than can be achieved at present.

Building any new power plant is a complicated and expensive endeavor, and a fusion energy power plant is no exception. As we engineer solutions to critical issues, the costings and efficiencies will become more apparent and each individual fusion scheme will make advances. Of those approaches with triple products close to the required threshold, MD-IFE is likely to be one of the most economical and practical on the timescales required to be part of the solution to the energy crisis.

The fusion driver and target technology exist, and performs impressively at sub-ignition scale. The required repetition rate is consistent with our ability to reload the system to produce energy. The technology challenges to automatically reload targets, safely recycle damaged electrodes and fuel, and to recover heat are under rapid development. The next five to ten years will be very exciting as we piece together the complicated puzzle of fusion energy.

The university ecosystem supporting progress

To reach this point in the long development of fusion energy has taken several decades of continued research into how to control the physics of plasmas. Recent achievements not only in fusion plasmas, but in broader plasma physics, high energy physics, semiconductors, quantum computing, nano- and meta-materials, amongst many others, show the importance of sustained efforts to unlocking the potential of new areas of physics. University programmes supported by federal funding are the keystone to progress in research. Researchers and faculty develop enthusiastic undergraduates into high quality, well-trained graduate students, and help place them in national laboratory programmes, private industry R&D efforts, federal programmes, and more.

The Pulsed Plasma Physics Group at UC San Diego is working with a number of collaborators to drive MD-IFE forward. These include Sandia National Laboratories, Pacific Fusion Inc, the University of Michigan, Lawrence Livermore National Laboratory, Imperial College London, Los Alamos National Laboratory, and General Atomics.

A key collaboration that has allowed a highly productive research environment to develop has been an NNSA-sponsored Center of Excellence. This was led by Professor David Hammer and Professor Bruce Kusse at Cornell University since 2003, and is now being led by Professor Ryan McBride at the University of Michigan since 2023. This foundational support has allowed students and researchers to thrive, develop innovative solutions, and push the boundaries of plasma physics research. The students we train actively participate in many areas of plasma science, including remarkable achievements in fusion science. Each achievement moves us one step closer to the realisation of fusion power in our modern lives.

References

1. S. A. Slutz et al, Phys. Plasmas 17, 056303 (2010)
2. S. A. Slutz and R. A. Vesey, Phys. Rev. Lett., 108, 025003 (2012)
3. Gomez, M. R. et al, Phys. Rev. Lett. 113, 155003 (2014)
4. Gomez, M. R et al, Phys. Rev. Lett. 125, 155002 (2020)
5. S.E. Wurzel and S. C. Hsu, Phys. Plasmas, 29, 062103 (2022)
6. P. F. Knapp et al, Phys. Plasmas 29, 052711 (2022)
7. S. A. Slutz et al, Phys. Plasmas 24, 012704 (2017)
8. P. F. Schmit et al, Phys. Rev. Lett. 117, 205001 (2016)
9. Stygar, W. A. et al, Phys. Rev. Accel. Beams (2015)
10. Stygar, W. A. et al, Phys. Rev. Accel. Beams 20, 040402 (2017)

Please note, this article will also appear in the 20th edition of our quarterly publication.