Are there any experimental fusion reactors that have achieved sustained fusion reactions?
Yes, there have been several experimental fusion reactors that have achieved sustained fusion reactions. The most notable one is the tokamak design called Joint European Torus (JET), which has successfully sustained fusion reactions for limited periods of time. However, none of these experiments have achieved the sustained and controlled fusion required for practical energy production.
Long answer
Sustained fusion reactions involve maintaining a state where the power produced by the fusion process is continuously greater than the input power needed to initiate and sustain the reaction. While achieving this goal has proven to be challenging, there have been significant advancements made in experimental fusion reactors. The most prominent experiment to achieve sustained fusion reactions is known as JET (Joint European Torus), based in the United Kingdom.
Using a tokamak design, JET was able to demonstrate self-sustained plasma heating through superheated hydrogen isotopes, deuterium and tritium. In 1997, it set a record by producing 16 megawatts of fusion power with an input power of 24 megawatts – surpassing the break-even point for the first time, albeit for a short duration. JET has since continued experimenting with different fuel mixtures and reactor configurations to improve performance.
Other experimental reactors such as TFTR (Tokamak Fusion Test Reactor) in the United States and JT-60U (Japan Tokamak-60 Upgrade) in Japan also achieved some milestones in sustaining fusion reactions. TFTR attained approximately ten times more thermal output power than consumed, validating key aspects of plasma physics needed for future fusion development. Similarly, JT-60U demonstrated several modes of high-performance plasmas useful for extending knowledge on achieving conditions suitable for sustained nuclear fusion.
Despite these accomplishments, none of these experiments have realized sustained and controlled fusion conditions required for reliable energy production. The main obstacle lies in finding an economically viable way to contain and control the extremely high-temperature plasma, as well as dealing with various technical challenges like managing heat loads, maintaining stable plasma conditions, and mitigating neutron flux on surrounding structures.
Nevertheless, these experimental reactors have provided invaluable scientific insight and paved the way for future fusion research efforts. Modern projects such as ITER (International Thermonuclear Experimental Reactor) aim to achieve sustained fusion reactions through international collaboration. ITER’s construction is underway in France and aims to demonstrate a net energy gain from fusion by the mid-2030s. By building upon the knowledge garnered from previous experiments, scientists are optimistic about eventually achieving practical fusion power production.