Keywords

1 Bridges in the Times of Walls

“No sensational reports were made at the conference, and to an outside observer it may have possibly appeared not outstanding”. Even considering the typical understatement of scientific communication—at least that of those times—from this description it sounds like the Third International Conference on Plasma Physics and Controlled Nuclear Fusion Research, held in Novosibirsk from August 1st to August 7th, 1968, was not such a big excitement for the delegates who attended it. The sentence comes from a summary report about the meeting written by the famous soviet physicists B. B. Kadomstsev and published in the journal Soviet Physics Uspekhi [1].

But, reading the next lines in the paper, some hints that something interesting happened appear: “However, to the participants of the conference—some 700 delegates and guests from 20 countries—it was not only a propitious opportunity to form a general picture of the development of thermonuclear studies, but also a rather impressive demonstration of progress in all directions, and of the ever-growing advancement in the parameters of thermonuclear plasmas”. And indeed, the progress that the soviet T-3 tokamak reported was such to impress the whole western fusion community. We should not forget that we were in the middle of Cold War, tension was very high between the two blocs and nuclear fusion was a very strategic area of research. The news that soviet scientists achieved in their tokamak plasma temperatures as high as 10 million degrees—with energy confinement times an order of magnitude larger than any other fusion device—shocked the rest of the world, suggesting that Soviet Union was taking the leadership in such an important research field. Numbers were hard to believe, and the international community asked for independent assessment.

Despite the political divisions, the scientific channels in fusion science had remained open.

So, when Lev Artsimovitch, head of fusion research in Moscow, suggested to his British colleague Bas Pease, Director of the Culham Fusion Research Center, to have an independent evaluation conducted by UK physicist, the proposal was accepted. British physicists were not only from the western bloc, but also had recently developed a very high precision plasma temperature measurement based on laser and Thomson scattering. If the collaboration was successful, this would have meant for the Soviets a confirmation of their measurements and for the British a spectacular testing ground and an international visibility for their applied physics team. After weeks of preparation, the measurements were successful and confirmed what their Soviet colleagues had reported the previous year, opening the way to the international success of the tokamak configuration. Just a few months later, the United States transformed their main experiment in the Princeton laboratory into a tokamak and quickly obtained similar results. In short, the tokamak configuration became the leading player in worldwide research on controlled thermonuclear fusion.

In a period when walls were erected, fusion demonstrated that scientific collaboration has no borders.

I find this anecdote particularly relevant to introduce my contribution, dedicated to fusion, to the XXII Edoardo Amaldi Conference, which has the title “Nuclear Risks and Arms Control. Problems and Progress in the Time of Pandemics and War”. Despite being a process first used by humans for military applications—the hydrogen bomb—pacific research on controlled thermonuclear fusion has always been characterized by very open worldwide collaborations. For example, our present flagship experiment, ITER, will demonstrate the scientific feasibility of magnetic fusion and is under construction in France as the result of a partnership which involves European Union, People Republic of China, India, Japan, Republic of Korea, Russian Federation, and the United States. And the origin of the project dates to 1985, when at the November Summit in Geneva dedicated to arm control, Mikhail Gorbachev and Ronald Reagan spoke also about the peaceful use of nuclear energy. The official press release at the close of the summit noted that the “two leaders emphasized the potential importance of the work aimed at utilizing controlled thermonuclear fusion for peaceful purposes and, in this connection, advocated the widest practicable development of international cooperation in obtaining this source of energy, which is essentially inexhaustible, for the benefit of all mankind.” This commitment was soon translated into the start of ITER [2]. One year later, an agreement was reached among the European Union, Japan, the Soviet Union, and the United States for the joint design of the program. The People’s Republic of China and the Korean Republic signed on to the project in 2003, followed by India in 2005.

On the medium-term fusion must be a big player of the energy transition, which is an issue for all the world. International collaboration is therefore crucial to win such a big challenge and fusion is a neat example on how such cooperation may work despite political difficulties.

2 Fusion and Energy Transition

The transition to non-fossil energy sources has a rapidly increasing importance in the international agenda. The global disruptions caused by the pandemic and more recently by the Ukrainian crisis add to the growing concern about the consequences of climate change, now more and more evident. All situations that have highlighted how crucial energy is for sustainable development and for international relations, and the extreme vulnerability of a world still largely depending on fossil sources. We should also not forget the issue of energy poverty—undoubtedly less felt in rich economies—which reminds us of the responsibility of dealing with a world strongly divided between north and south also in terms of energy, with 770 million people who do not have access to electricity. A problem, the latter, with ethical implications, but also strategic and international relations (just think of the consequences on migratory flows).

It is therefore not surprising that research on energy issues is attracting increasing interest. One source that a large community has been working on for decades is fusion. For some a utopia, for others a short-term panacea for all energy problems, in reality fusion is neither. It is an extremely attractive potential source of electricity, and I would say necessary, for a future CO2-free energy basket. It uses widely available fuel, does not produce high-level radioactive waste and its plants are inherently safe. For its practical applicability still high-level scientific and technological research is required and its penetration in the electricity market is foreseen in the second half of this century. This is not a short time scale, but it is comparable to that necessary for the penetration of other energy sources. And, in any case, time scale will not diminish the need for a source such as fusion. In fact, if in the short term the energy transition cannot make use of fusion, in the medium to long term its role as a source of “baseload” will be unavoidable and necessary in a fully electric and hydrogen-based economy [3].

For fusion to become one of the key actors of the electricity market, research is needed. This research will increasingly benefit from interactions with other sectors of physics, given that plasma—the fully ionized gas that is the fuel for fusion—is widely present in the universe. It is this ubiquity that inevitably makes fusion physics interdisciplinary.

3 The International Fusion Research

The fusion reaction most studied for energy purposes is that between two isotopes of hydrogen, deuterium (D) and tritium (T), which gives rise to an alpha particle and a neutron:

$$ {\text{D}} + {\text{T}} \to {}^{4}{\text{He}} + {\text{n}}\left( { + {17.6}\,{\text{MeV}}} \right) $$

17.6 meV of energy are released for each reaction, 3.5 meV are associated with the alpha particle and 14.1 meV with the neutron. To obtain enough fusion reactions in a reactor, and therefore in a space necessarily limited by practical reasons, two approaches are mainly used for fuel confinement: inertial and magnetic. In inertial confinement, the mixture of deuterium and tritium—in the form of small capsules—is compressed by electromagnetic radiation produced by very high-density lasers, up to a thousand times greater than that of matter in the liquid state [4]. With magnetic confinement, the reactants, initially in the form of gas, are heated in a discharge vessel up to temperatures of 108 K in a reactor. This vessel for the larger experiments has linear dimensions of the order of a few meters and a toroidal shape. Under these conditions the gas ionizes and becomes a plasma composed of positive ions and electrons. The plasma can be confined within the reaction chamber by a suitable magnetic field. At sufficiently high temperatures the reaction rate for D-T is maximum and therefore the optimal conditions for controlled thermonuclear fusion are achieved. This paper deals only with magnetic confinement fusion.

The fusion of light nuclei has been the subject of international research since the 1950s. If realized, controlled thermonuclear fusion would have the potential to provide nearly unlimited and widely available energy, free from CO2 emissions. Raw fuels will be water—from which deuterium is extracted—and lithium, that will turn into tritium by neutron bombardment directly inside the reactor. Unlike nuclear fission (what is today often referred to as ‘nuclear energy’), it would not produce long-lasting radioactive waste, and it minimizes the risks of serious industrial accidents.

The most used magnetic configuration is tokamak [5]. It was invented in the 1950s in the Soviet Union [6, 7]. Numerous experiments currently in operation around the world belong to the tokamak configuration. The largest currently in operation is JET, located in Culham, UK and managed by the European Union. JET has recently reported ground-breaking results [8] with the production of a total of 59 Megajoules of heat energy from fusion over a five second period, corresponding to the duration of the fusion experiment. During this experiment, JET averaged a thermal fusion power of around 11 megawatts.

The ITER experiment is also a tokamak. It will be the largest tokamak ever made [9] and will aim to demonstrate the scientific feasibility of fusion as a source of energy. Alternative configurations to the tokamak and different from it for the spatial distribution of the confinement magnetic field are the stellarator [10] and the Reversed Field Pinch (RFP). The largest RFP device in the world is in operation in Padua [11].

At the scientific, political, strategic, and industrial level, in recent months a broad international attention has been concentrated on fusion research. The European Union is proceeding, through the EUROfusion consortium, in the implementation of the “Roadmap to the realization of fusion energy” [12], which identifies the main research priorities to be addressed to achieve the objective of producing electricity from fusion around the middle of this century. The European program has as its future pivotal elements ITER and the Italian DTT tokamak, now under construction at the ENEA laboratory in Frascati, which will be described later in this document. Both will be crucial for the design and construction of DEMO, the reactor prototype dedicated to the conversion of fusion energy into electricity. The W7-X stellarator at the Max-Planck Institut für Plasmaphysik in Greifswald [13], Germany will also provide information for the stellarator line, while the renewed RFX-mod2 device will advance the RFP concept. Interestingly, the RFP is also studied as a configuration suitable for a novel fusion-fission hybrid reactor (FFHR) [14], which could accelerate the penetration of fusion in the energy mix and contribute to the sustainability of fission. A FFHR has a fusion core, which supplies a steady flux of fast neutrons to a surrounding blanket of fissile materials. FFHR is a tool to transmute the long-lived minor actinides which constitute high level nuclear waste into shorter-lived waste more safely disposable, and to generate electricity and produce tritium fuel for fusion reactors.

All major world fusion communities are developing strategies for fusion exploitation. Just to give two notable examples, in March 2022, the White House launched a program to build “A Bold Decadal Vision for Commercial Fusion Energy” [15]. This is a notable bipartisan initiative promoted by the Biden administration to accelerate the exploitation of fusion for energy purposes. The People’s Republic of China has instead developed a strategy that, in addition to ITER, provides for the realization of an intermediate national experiment between ITER and DEMO, called “Chinese Fusion Engineering Testing Reactor” (CFETR, with a production of thermal energy from fusion of the order of 1 GW), again with the aim of finding solutions that speed up the construction of a series of fusion reactors [16].

An element that has recently aroused strong interest in the panorama of fusion research has been the growing synergy between public and private research. In fact, in recent years there has been a drastic growth in the commitment of private companies for the development of fusion, as well summarized in a recent article in the journal Nature [17]. This resulted in a significant injection of capital into research: according to the 2022 survey of the Fusion Industry Association [18] declared private funding surpasses $4.7 bn, plus an additional $117+ million in grants and other funding from governments. This is a 139% increase in funding since the 2021 version of their survey. The case of the Commonwealth Fusion System (CFS), a spin-off of MIT [19] (in which the Italian energy company ENI, also a partner of the Italian DTT experiment, participates) is striking: according to the Wall Street Journal in 2021 it raised 1.8 billion dollars from investors [20]. CFS and MIT are working together to develop SPARC, a compact, high-field, net fusion energy device. SPARC would be the size of existing mid-sized fusion devices, but with a much stronger magnetic field [21].

4 The Italian Program

Italy has always had a leading role in the scientific and technological program on fusion and in plasma physics in Europe and worldwide. Today the Italian fusion program has about six hundred researchers—physicists and engineers—and is the second largest in Europe, together with the French one and immediately after Germany. The main laboratories are those of ENEA of Frascati, of the RFX Consortium in Padua (of which ENEA, CNR, INFN, University of Padua and Acciaierie Venete s.p.a. are members), of the CREATE Consortium in Naples and of the Institute of Physics and Technology of Plasmas of the CNR. To these add research groups mainly in the Universities of Bologna, Cassino, Catania, Cosenza, Milan, Naples, Padua, Palermo, Pisa, Rome, Viterbo and in the Polytechnics of Milan and Turin. Recently the ENI company has started a growing research program in fusion, with the involvement in the SPARC project and, in Italy, in the construction of the DTT tokamak. The Italian plasma and fusion community is engaged on many fronts, both experimental and theoretical. In the following I list only the main ones, but there are many others of great scientific importance.

First, there is the DTT project, currently under construction in Frascati [17], home to one of the main ENEA research centers and formerly of the FTU tokamak [22], which was in operation until about a couple of years ago.

DTT is a large size, high magnetic field experiment, which answers to a crucial research need expressed by the EUROfusion roadmap [12]. DTT has major radius of the torus 2.20 m, minor radius 0.7 m and is capable of a maximum plasma current of 5.5 MA [23,24,25]. It will be equipped with plasma heating systems that will be able to deliver a power to the plasma of up to 45 MW. The experiment is designed in such a way as to be able to tackle the problem of dissipating the intense energy loads due to heat, radiation, impact of particles and neutrons that the plasma releases and that will pour onto the components facing the plasma itself in a future reactor. These loads are currently beyond the capabilities of known materials. The fundamental processes that regulate them must therefore be understood and solutions studied both to control them and to develop suitable materials and components. This will be one of the main scientific missions of DTT which will be addressed with a broad scientific cooperation.

DTT was conceived by physicists and engineers of the Italian fusion community under the guidance of the ENEA laboratories in Frascati and is now under construction. A complete description of the project can be found in the Interim Design Report [17]. The scientific and financial approval process for the experiment was completed in 2019. Over 80% of the 500 million euros that will be used for its construction are financed by the Italian government, thanks also to a loan from the European Investment Bank under the Juncker Plan. 60 million have been allocated by the European consortium EUROfusion and the Chinese government is expected to collaborate through the Hefei laboratory of the Chinese Academy of Sciences. In 2019, the Consortium DTT s.c.a r.l. was established, which currently sees ENEA as the majority shareholder. ENI participates in the DTT s.c.a r.l. with a share of 25%. The other shareholders of DTT s.c.a r.l. they are the CNR National Research Council, the CREATE Consortium of Naples, the RFX Consortium of Padua, the INFN, the Polytechnic of Turin, the University of Milan Bicocca, the University of Rome Tor Vergata and that of Tuscia. Construction of the device is currently underway, and it is expected to be completed by 2028.

The other main Italian research center is Padua, by the RFX Consortium for Research, Innovation and Training. About 150 people work in its laboratories, which host the Reversed Field Pinch experiment called RFX-mod [11, 26]. It is now in the operational recovery phase after a significant improvement [27]. Also in Padua, in close collaboration with INFN, the Neutral Beam Test Facility (NBTF) [28] is being carried out, an experiment that consists in the 1: 1 scale prototype of a powerful linear accelerator of negative ions (acceleration voltage 1 MV and beam current 40 A). It will be used to heat the ITER plasma. Italian physicists and engineers are also involved in the operation of the JT-60SA tokamak [29], as part of a Euro-Japanese collaboration agreement that sees our country in a leading position. Italy also participates in numerous scientific activities aimed at the realization of ITER measuring instruments, the study of the physical processes that will characterize it and the design of the DEMO demonstration reactor. Italian physicists also occupy positions of undisputed international importance also in the theoretical and modeling sectors.

5 The Scientific and Technical Route to Fusion

The present and planned magnetic fusion experiments—and the associated theoretical work—aim at demonstrating the scientific feasibility of magnetic fusion by sustaining in nearly steady state conditions fusion thermal energy production. ITER, for example, will produce 500 MW of thermal fusion power for about an hour, with an amplification factor x10 with respect to the power needed to heat the plasma. This calls for addressing the main physics and technology open problems, which need to be solved to move towards practical exploitation of fusion energy. They can be summarized as followsFootnote 1:

  1. (a)

    Identification of the most efficient operational plasma regimes, where:

    • plasma confinement is optimized in high density conditions, with minimal energy and particle losses, i.e. with reduced transport driving turbulence);

    • magnetohydrodynamic plasma stability is under control—both with passive and active means—and strategies for the avoidance/mitigation of transient events due to instabilities are implemented;

    • additional heating to reach thermonuclear burning conditions is used in efficient manner.

  2. (b)

    Understanding dynamics of thermonuclear burning plasmas, which will be characterized by significant population of super-thermal particles, like alpha’s.

  3. (c)

    Managing intense heat and particle loads at the plasma edge.

  4. (d)

    Developing neutron tolerant materials.

  5. (e)

    Designing efficient strategies for tritium self-sufficiency.

In parallel with the solution of these challenges the community works to design the next step device, which will need to demonstrate practical conversion of thermal energy into electric energy. These will be the DEMO-class experiments previously mentioned. Their detailed goals may vary from approach to approach, but the overarching mission is well summarized in [30]: “DEMO in Europe is considered to be the nearest-term reactor design to follow ITER and capable of producing electricity, operating with a closed fuel-cycle and to be a facilitating machine between ITER and a commercial reactor…. It is a device which lies between ITER and First-of-a-Kind (FoaK) Fusion Power Plant”. Its main targets will be:

  • Conversion of fusion heat into electricity (∼500 MWe).

  • Achievement of tritium self-sufficiency (Tritium Breeding Ratio >1).

  • Reasonable availability with several full power years.

  • Minimize activation waste without long-term storage.

  • To be component test facility and pathfinder to a First-of-a-Kind Fusion Power Plant.

While detailed roadmaps to fusion may vary in different countries and considering that sudden accelerations may occur—for example due to private efforts or grand political decisions driven by energy and environmental crisis—there is a consensus that at the present pace fusion will become a key component of the global energy mix in the second half of this century. This confidence is mirrored in growing investments in this form of energy from private capital markets, as we have seen before.

This is only apparently a long timescale. As the science progresses and the realization of fusion comes closer, it necessitates a debate about non-technical issues associated with this energy source, including diverse social and ethical implications. Now the—by far—largest fraction of efforts is devoted to scientific and technical problems. A few decades horizon for fusion commercialization calls instead for coping also with issues related to public acceptance, development of scenarios for fusion penetration as an energy source and, more generally, with energy ethics considerations.

How to balance energy demands with concerns for anthropogenic climate change and with strategic and geopolitical issues is one of the most profound and urgent challenges facing humanity today. As the global economies move towards a lower carbon energy future, great emphasis is placed on developing new energy technologies. But the challenge of transitioning to a more sustainable energy mix for the whole mankind is not just a technical one. It also requires us to collectively address questions about how to create a better energy future for us all.

Given the importance that fusion will have in a sustainable energy mix, questions like the following need to be addressed: what are the ethical implications of sourcing electricity from fusion? What kinds of evaluations (financial, environmental, ethical) are at play here? How would the costs and benefits associated with fusion technology be distributed? What factors may affect availability of fusion energy? How to deal with public acceptance of an energy source that, despite being very different from fission, has a nuclear nature? And, ultimately, considered in a broader environmental, social and geopolitical context—would this form of energy deliver a better energy future for all?

6 Social, Environmental, and Ethical Aspects of Fusion

The questions I closed the previous section with, need to be tackled starting now. This requires a multi-disciplinary approach, which includes conversation outside the traditional technical borders of fusion research. Fusion scientists will be required to talk more and more both with experts outside their communities—sociology, environmental science, psychology, economics, political sciences, communication science, journalism are just some examples of fields that need to be involved—and with the public. For many of us this requires a significant change of attitude that needs to be nurtured with appropriate education and supported by additional new resources. In the following I will mention some areas where work needs to be done, obviously without the ambition of being complete. I will briefly talk about energy scenarios, safety and environmental risks, non-proliferation, which are all central to public acceptance of fusion.

6.1 Energy Scenarios

The energy system is characterized by a strong inertia and therefore policies need to be implemented and penetration scenarios must be analyzed well before the technology is expected to enter the energy market. Work on this topic has already started and will certainly grow soon. To give a significant example of this kind of activity, Bustreo, Zollino et al. are addressing the question on how fusion power can contribute to a fully decarbonized European power mix after 2050 [31]. The European energy mix will be likely decarbonized in the second half of this century, and this may happen thanks to two main driving forces: relying on renewable energy sources only or integrating renewables with fusion power plants (and with a new generation of fission nuclear power plants). If only renewables are used, a large storage capacity and/or dispatchable generation are required to compensate for the variable electricity generation. Since a carbon-free economy will heavily rely on electricity, there will be a higher electricity demand during cold seasons—for heating—and in the nighttime, to recharge electric vehicles. This request might be difficult to be matched with offer in countries with prevailing solar electricity, and therefore needs significant investments in long term storage. The size of the necessary storage systems and dispatchable power plants can be strongly reduced if a base-load carbon free power technology like fusion is available.

Bustreo et al. have performed cost analyses [31] to assess whether and to what extent fully decarbonized power mixes could take benefits from nuclear fusion power concluding that “fusion would reduce the cost of electricity, in comparison with 100%-RES scenarios. This is true as long as the overnight cost of a fusion power plant will be lower than 8500 Euro/kW in the North-Europe case and lower than 12,500 Euro/kW in the South-Europe case. …the convenience of a power mix with fusion would result even higher if a detailed electric grid model were considered. In addition to cost, warnings on soil consumption, linked with hundreds GW size deployment of PV and Wind power plants, is a further issue in favor of power generation scenarios with fusion”.

A strong program on the simulation of the role—and the cost—of fusion in CO2 free energy scenarios will be extremely important both for attracting public and private investments and for gaining political and popular support towards fusion.

6.2 Safety and Environmental Risks

Unlike nuclear fission (what is today often referred to as ‘nuclear energy’), fusion would minimize the risks of serious industrial accidents and not produce long-lasting radioactive waste.

The fusion process is inherently safe since the physics requirements to start and maintain the nuclear fusion process make impossible—by nature and not by human technics—an accident like those which happened in Chernobyl and Fukushima, leading to nuclear meltdown due to chain reaction. In a fusion reactor, there will only be a limited amount of fuel (a few grams) at any given moment. Operation of fusion reactor relies on a continuous input of fuel and on maintaining the plasma parameters within a very narrow range. If there is any perturbation and plasma parameters deviate from the optimal conditions the reaction ceases immediately, making a runaway chain reaction impossible. In other words, fusion is a self-limiting process: either you keep the plasma in good shape, or physics itself switches the reactions off.

As for radioactive waste, exploitation of nuclear energy by fusion has the enormous advantage with respect to fission that no long-lasting radiotoxic elements like actinides and other fission products are generated, thus avoiding the need of geological storages. Nevertheless, nuclear fusion is not totally free from radioactive waste, albeit of a very different nature. As a result of the operation of a fusion reactor there will be an inventory of low level and intermediate level waste, for example from the activated bio-shield, activated reactor components and from tritiated material. Available predictions are that this will be a easily manageable issue without long term environmental or health consequences. As we are still in an early stage of fusion technology development, work is needed to fully characterize the radioactive products of fusion electricity generation and to design an efficient waste management strategy. Communicating in a transparent way the outcome of this work will be crucial for the social acceptance of fusion. While it is probably little known that coal-fired power plants also produce radioactive waste since coal combustion creates small amounts of naturally occurring radioactive material [32], due to the nuclear nature of fusion we should expect a very high level of public sensibility that needs to be considered and openly addressed. In this respect it is interesting to note that in the UK, where the government is investing in the ambitious STEP program [33], the Committee on Radioactive Waste Management has recently released a preliminary position paper on radioactive waste from fusion energy [34], that illustrates the state of the art and recommends several initiatives.

6.3 Nonproliferation

While in practical terms the vertical and horizontal proliferation risks for nuclear fusion reactors will be negligible because of economic reasons, difficulty to conceal clandestine production given the size of the plants and standard operation with zero fissile material—in other words it is cheaper and simpler to produce weapon relevant materials with other means than fusion—it will be nonetheless important to openly address and communicate even the more remote ones to the public and the stakeholders.

Given the low priority of the subject very little literature is available (see for example [35] and [36]). Potential proliferation issues derive from the availability of neutrons and tritium. Pure fusion systems do not contain source or special fissionable material, but in principle neutrons could be misused for production of 239Pu and 233U. The nuclear cycle of interest which is planned to be used to breed tritium in a reactor is:

$$ \begin{aligned} & {\text{D}} + {\text{T}} \to {}^{4}{\text{He}}\left( {{3}.{\text{5 MeV}}} \right) \, + {\text{n}}\left( {{14.1}\,{\text{MeV}}} \right) \\ & {\text{n}} +{}^{6}{\text{Li}} \to {\text{T}}\left( {{2}.{\text{7 MeV}}} \right) \, +{}^{4}{\text{He}}\left( {{2.1}\,{\text{MeV}}} \right) \\ \end{aligned} $$

While the first fusion reaction happens in the plasma, the second takes place in a special blanket around the plasma chamber. Since the blanket modules in a fusion reactor will be maintained and/or replaced on a regular basis, it is in principle possible to replace a fraction of the lead–lithium alloy stored in the blanket to breed tritium with fertile nuclear material like natural uranium or thorium. During plasma operation neutron irradiation of the fertile material will produce fissile materials like plutonium or uranium 233, which can be retrieved in the next maintenance cycle [36].

Moreover a 2.5 GW(th) fusion power plant will contain an onsite tritium inventory of several kilograms of tritium and will need to produce about 400 g/day of this isotope, which in principle may be used for nuclear weapons (a limited amount of tritium boost a nuclear weapon). Now tritium is not controlled by the Non-Proliferation Treaty but, as stated in [36], “there is no credible risk that a gigawatt-scale fusion power system… could be built or operated in a clandestine fashion”. The same paper concludes that “if designed to accommodate appropriate safeguards, fusion power plants would present low proliferation risks compared with fission. Our analysis suggests that clandestine production of weapons materials using fusion research facilities can be considered a highly implausible scenario”.

7 Conclusions

The energy transition necessitated by anthropogenic climate change, and the implications of the war in Ukraine on the world’s energy supply markets have stimulated in recent months a lot of talks in the media and on a range of public fora about nuclear energy and fusion. This happens in a period when existing magnetic fusion experiments are achieving important results, new important facilities are under construction (like ITER, DTT and SPARC) or close to start operation (JT-60SA) and significant private capitals are being invested in fusion research. Whilst in the past excessive optimism has at times pervaded the scientific community, now there is solid confidence that fusion will become a player in a future CO2-free energy mix provided that enough resources will be invested in the field.

This positive moment for fusion research calls for new challenges for the scientific community. In addition to technical efforts, it is now time to start conversations about wider ethical implications of this form of energy that consider its social, environmental, and geopolitical impacts. The potential acceleration towards fusion exploitation calls for anticipating an alliance with the public to facilitate social acceptance, build public trust, make a strong case for a change of paradigm in fusion funding (a drastic increase, in particular on the public side, it is necessary in the short term to bring fusion to the plug and in general to support energy R&D) and to keep the internationally open attitude of fusion research.

Ethical thoughts on fusion should also address the dramatic problem of energy poverty. According to the International Energy Agency (IEA) [37] today 770 million people live without access to electricity, mostly in Africa and Asia. This has tragic implications on health, quality of life, education and is a drive for conflicts and migrations. In principle fusion promises “infinite” energy—and therefore a tool to contribute to solve the energy poverty problem—but for an energy source dependent on high-tech devices and infrastructure, how could it be made available widely and equitably among countries and areas of various economic and technical capacities? Will future fusion energy be available for all, or only for the richest part of the world? Answers to questions like these obviously go beyond the realm of science and involve a multiplicity of factors and actors. Nevertheless, scientists must ask themselves those questions and work on them, be prepared to go outside their laboratories and to exercise their active citizenship to communicate with the public, the governments, and the stakeholders.

In 1969 fusion science—with its laser thermometer—built a bridge between two very separate world. Half a century later we need to make our voices heard for a more peaceful and equitable world.