Fusion energy is possible: the breakthroughs explained

01How nuclear fusion works

Nuclear fusion is a reaction in which two or more atomic nuclei combine to form a larger nucleus. The difference in mass between the reactants and products is manifested as either the release or the absorption of energy. This difference in mass arises as a result of the difference in nuclear binding energy between the atomic nuclei before and after the fusion reaction. Active stellar cores are powered by fusion. Nucleosynthesis via fusion, in the Big Bang and in stars, creates all elements lighter than nickel.

In the most commonly pursued fusion reaction for energy production, two isotopes of hydrogen, deuterium and tritium, combine to form helium and release a neutron along with enormous energy. This reaction requires temperatures exceeding 100 million degrees Celsius, several times hotter than the core of the sun. At such temperatures, matter exists as plasma, a state where electrons are stripped from their nuclei.

Containing this superheated plasma is the central engineering challenge of fusion energy. Two main approaches dominate: magnetic confinement, which uses powerful magnetic fields to contain plasma in a donut-shaped device called a tokamak, and inertial confinement, which uses high-energy lasers to compress and heat a fuel target to fusion conditions. Both approaches have made significant progress but neither has yet achieved sustained, economically viable fusion.

02The ITER project and its timeline

ITER is an international nuclear fusion research and engineering project designed to demonstrate the feasibility of fusion power. The facility is under construction near the Cadarache research center in southern France. ITER has been under construction since 2013. It is expected to achieve first plasma in 2033–2034, at which point it will be the world's largest fusion reactor, with a plasma volume about six times that of Japan's JT-60SA, previously the largest tokamak.

ITER is the most ambitious fusion experiment ever attempted. When operational, it aims to produce 500 megawatts of fusion power from 50 megawatts of input heating power, a ratio of 10 known as Q equals 10. This would demonstrate that fusion can produce more energy than it consumes at scale, a critical milestone on the path to commercial power.

The project has faced repeated delays and cost overruns. Originally planned to begin operations in 2016 with a budget of approximately 5 billion euros, ITER is now expected to achieve first plasma in 2033-2034 with total costs exceeding 20 billion euros. The complexity of manufacturing components to unprecedented precision standards, the coordination challenges of a seven-member international collaboration, and the novelty of the technology itself have all contributed to the delays.

Despite the setbacks, ITER remains the flagship project for demonstrating fusion feasibility at scale. Its success or failure will significantly influence the trajectory of fusion energy development and public confidence in the technology. Full deuterium-tritium operation is not expected until the late 2030s at the earliest.

03Private fusion startup progress

While ITER represents the public-sector approach, a growing ecosystem of private companies is pursuing alternative paths to fusion. Commonwealth Fusion Systems, spun out of MIT, is building the SPARC tokamak using high-temperature superconducting magnets that can achieve stronger magnetic fields in a smaller device. The company has raised over 2 billion dollars and aims to demonstrate net energy gain by the late 2020s.

Helion Energy is pursuing a pulsed magnetic fusion approach using deuterium and helium-3 as fuel, avoiding the need for tritium breeding. The company has secured a major power purchase agreement with Microsoft, committing to deliver fusion electricity by 2028. TAE Technologies is developing a field-reversed configuration approach that aims for cleaner fusion reactions using boron and proton fuel.

Other notable players include Tokamak Energy, Zap Energy, and Xcimer Energy, each pursuing different confinement strategies. The diversity of approaches is healthy for the field, as it hedges against the risk that any single path may encounter insurmountable obstacles. However, most of these companies are years away from demonstrating commercial viability.

04Net energy gain milestones

The milestone that captured public attention was achieved at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. In December 2022, NIF achieved scientific breakeven, producing more energy from fusion than the energy delivered to the fuel target. This was repeated and improved upon in subsequent shots, with the July 2023 experiment producing approximately 1.5 times the input energy.

Fusion power is a potential method of electric power generation from heat released by nuclear fusion reactions. In fusion, two light atomic nuclei combine to form a heavier nucleus and release energy. Devices that use this process are known as fusion reactors. The NIF results demonstrated that net energy gain is physically possible, answering a question that had hung over fusion research for decades. However, the achievement must be understood in context: the energy gain was relative to the laser energy delivered to the target, not the total energy consumed by the facility, which was vastly larger.

The Joint European Torus (JET) in the UK set records for sustained fusion power, producing 69 megajoules over five seconds in its final deuterium-tritium campaign in 2023. While not achieving net energy gain, JET demonstrated the feasibility of sustained fusion reactions using the same fuel mixture planned for ITER, providing valuable data for future operations.

05The engineering challenges remaining

Achieving scientific breakeven is necessary but far from sufficient for commercial fusion power. The engineering challenges between laboratory demonstrations and a power plant that reliably produces electricity are immense. First among these is sustaining the fusion reaction for extended periods. Most experiments to date have achieved fusion for seconds or less. A commercial reactor must operate continuously or in long pulses for months at a time.

Materials science is another critical gap. The inner walls of a fusion reactor must withstand extreme heat, intense neutron bombardment, and plasma erosion for years of operation. No existing material has been demonstrated to survive these conditions for the lifetime of a commercial reactor. Developing radiation-resistant materials is an active research area but remains a potential showstopper.

Tritium breeding is essential for deuterium-tritium fusion, as tritium is rare and radioactive with a short half-life. Reactors must breed tritium from lithium using neutrons from the fusion reaction itself, creating a closed fuel cycle. This breeding blanket technology has never been demonstrated at scale and represents a significant engineering risk.

06Cost and scalability questions

The economics of fusion power are highly uncertain, as no commercial reactor has ever been built. Current estimates suggest that a first-generation fusion power plant would cost several billion dollars to construct, comparable to or exceeding the cost of nuclear fission plants. The levelized cost of electricity from fusion would depend on reactor utilization, fuel costs, maintenance requirements, and the cost of capital, none of which can be precisely estimated at this stage.

Proponents argue that the advantages of fusion, including no long-lived radioactive waste, no risk of meltdown, and effectively unlimited fuel supply, could justify a higher upfront cost. The fuel for fusion, deuterium from seawater and lithium for tritium breeding, is abundant and relatively inexpensive. If reactor designs can be standardized and mass-produced, costs could fall significantly.

However, fusion must compete not only with existing energy sources but with rapidly improving alternatives. Solar and wind power with battery storage are already cost-competitive in many markets, and their costs continue to decline. For fusion to be economically viable, it must offer capabilities that these alternatives cannot, such as baseload power without fuel supply constraints or geographic limitations.

07When fusion could power the grid

The timeline for commercial fusion power depends on which projection one believes. The most optimistic scenario, primarily from private companies seeking investment, suggests demonstration power plants in the early 2030s and commercial deployment by the late 2030s. This timeline assumes that engineering challenges are resolved quickly and that regulatory frameworks can be established in parallel.

A more conservative assessment, shared by many in the scientific community, places the first demonstration power plant in the 2040s, with commercial deployment in the 2050s or later. This timeline accounts for the complexity of the remaining engineering challenges, the time needed for materials development, and the iterative nature of learning from operational experience.

Fusion is unlikely to contribute meaningfully to global electricity supply before 2050 in even the most optimistic scenarios. This does not diminish its long-term importance as a potential source of clean, abundant energy, but it means that fusion cannot be relied upon to address the urgent climate challenges of the next two decades. Near-term decarbonization must come from technologies that are already available.