Timeline of nuclear fusion

This timeline of nuclear fusion is an incomplete chronological summary of significant events in the study and use of nuclear fusion.

1920s 1920 Based on F.W. Aston's measurements of the masses of low-mass elements and Einstein's discovery that , Arthur Eddington proposes that large amounts of energy released by fusing small nuclei together provides the energy source that powers the stars. Henry Norris Russell notes that the relationship in the Hertzsprung–Russell diagram suggests a hot core rather than burning throughout the star. Eddington uses this to calculate that the core would have to be about 40 million Kelvin. This was a matter of some debate at the time, because the value is much higher than what observations suggest, which is about one-third to one-half that value. 1928 George Gamow introduces the mathematical basis for quantum tunnelling. 1929 Atkinson and Houtermans provide the first calculations of the rate of nuclear fusion in stars. Based on Gamow's tunnelling, they show fusion can occur at lower energies than previously believed. When used with Eddington's calculations of the required fusion rates in stars, their calculations demonstrate this would occur at the lower temperatures that Eddington had calculated.

1930s 1932 Ernest Rutherford's Cavendish Laboratory at Cambridge University begins nuclear experiments with a particle accelerator built by John Cockcroft and Ernest Walton. In April, Walton produces the first man-made nuclear disintegration by using protons from the accelerator to split lithium into alpha particles. They discover the intermediary creation of the extremely short-lived beryllium-8 isotope. This could be considered the first artificial fusion. 1934 Using an updated version of the equipment firing deuterium rather than hydrogen, Mark Oliphant discovered helium-3 and tritium, and that heavy hydrogen nuclei could be made to react with each other. This is considered the first artificial fusion. 1937 George Gamow and Carl Friedrich von Weizsäcker suggest proton combination into deuterium may be the source of stellar energy.C.F. von Weizsäcker (1937) "Über Elementumwandlungen im Innern der Sterne. I" (On transformations of elements in the interiors of stars. I), Physikalische Zeitschrift (Physics Journal), vol. 38, pages 176–191. 1938 In March, Hans Bethe attends the Carnegie Institute and George Washington University's fourth annual Washington Conference on Theoretical Physics on Edward Teller's insistence. He works with Charles Critchfield to derive stellar nuclear reactions beyond the proton combination into deuterium. They publish two reactions based on the incorrect assumption tritium is more stable, and four reactions based on the correct assumption helium-3 is more stable, thereby discovering the proton–proton chain. Kantrowitz and Jacobs of the NACA Langley Research Center built a toroidal magnetic bottle and heat the plasma with a 150 W radio source. Hoping to heat the plasma to millions of degrees, the system fails and they are forced to abandon their Diffusion Inhibitor. This is the first attempt to make a working fusion reactor. 1939 Peter Thonemann develops a detailed plan for a pinch device, but is told to do other work for his thesis. Hans Bethe publishes the discovery of the carbon-nitrogen-oxygen cycle in higher mass stars. Along with the proton-proton chain, this work results in the 1967 Nobel Prize for Physics.

1940s 1945 The Smyth Report, detailing the history of fission research and the Manhattan Project, briefly refers to Bethe's discovery of the CNO cycle and the eventual possibility of laboratory fusion, without using the word "fusion". 1946 George Paget Thomson of Imperial College, London designs the toroidal solenoid, a simple fusion device. With Moses Blackman, he further develops the concept and files for a patent. This becomes the first fusion device to receive a patent. Repeated attempts to get development funding fail. 1947 A meeting at Harwell on the topic of fusion raises new concerns with the concept. On his return to London, Thomson gets graduate students James L. Tuck and Alan Alfred Ware to build a prototype device out of old radar parts. Peter Thonemann comes up with a similar idea, but uses a different method of heating the fuel. This seems much more practical and finally gains the mild interest of the UK nuclear establishment. Not aware of who he is talking to, Thonemann describes the concept to Thomson, who adopts the same concept. Herbert Skinner begins to write a lengthy report on the entire fusion concept, pointing out several areas of little or no knowledge. 1948 The Ministry of Supply (MoS) asks Thomson about the status of his patent filing, and he describes the problems he has getting funding. The MoS forces Harwell to provide some money, and Thomson releases his rights to the patent. It is granted late that year. Skinner publishes his report, calling for some experimental effort to explore the areas of concern. Along with the MoS's calls for funding of Thomson, this event marks the beginning of formal fusion research in the UK.

1950s 1950 In January, Klaus Fuchs admits to passing nuclear secrets to the Soviet Union. Almost all nuclear research in the UK, including the fledgling fusion program, is immediately classified. Thomson, until this time working at Imperial University, is moved to the Atomic Weapons Research Establishment. The tokamak, a type of magnetic confinement fusion device, was proposed by Soviet scientists Andrei Sakharov and Igor Tamm. 1951 Edward Teller and Stanislaw Ulam at Los Alamos National Laboratory (LANL) develop the Teller-Ulam design for the thermonuclear weapon, allowing for the development of multi-megaton weapons. A press release from Argentina claims that their Huemul Project had produced controlled nuclear fusion. This prompted a wave of responses in other countries, especially the U.S. Lyman Spitzer dismisses the Argentinian claims, but while thinking about it comes up with the stellarator concept. Funding is arranged under Project Matterhorn and develops into the Princeton Plasma Physics Laboratory. Tuck introduces the British pinch work to LANL. He develops the Perhapsatron under the codename Project Sherwood. The project name is a play on his name via Friar Tuck....the first money to be allocated [to controlled nuclear research] happened to be for Tuck, and was diverted from Project Lincoln, in the Hood Laboratory. The coincidence of names prompted the well-known cover name "Project Sherwood". James L. Tuck, "Curriculum Vita and Autobiography", declassified document from Los Alamos National Laboratory (1974), reproduced with permission. Archived 9 February 2012. Richard F. Post presents his magnetic mirror concept and also receives initial funding, eventually moving to Lawrence Livermore National Laboratory (LLNL). In the UK, repeated requests for more funding that had previously been turned down are suddenly approved. Within a short time, three separate efforts are started, one at Harwell and two at Atomic Weapons Establishment (Aldermaston). Early planning for a much larger machine at Harwell begins. Using the Huemul release as leverage, Soviet researchers find their funding proposals rapidly approved. Work on linear pinch machines begins that year. On May 9, the American nuclear test Greenhouse George, the first of a boosted fission weapon, yields 255 kilotons from an enriched uranium core and deuterium-tritium gas. This is the artificial thermonuclear fusion, and the first weaponization of fusion energy. Experimental research of toroidal magnetic confinement systems starts at the Kurchatov Institute, Moscow, led by a group of Soviet scientists led by Lev Artsimovich. Device chambers are constructed from glass, porcelain, or metal. Their largest device, TMP, uses a porcelain chamber with metal spirals.

1952 On November 1, the United States conducts the Ivy Mike shot of Operation Ivy, the first detonation of a hydrogen bomb, yields 10.4 megatons of TNT out of a fusion fuel of liquid deuterium. Cousins and Ware build a larger toroidal pinch device in England and demonstrated that the plasma in pinch devices is inherently unstable. 1953 The first Soviet fusion bomb test, RDS-6s, American codename "Joe 4", demonstrated the first fission/fusion/fission "layercake" design, limited below the megaton range, with less than 20% of the yield coming directly from fusion. It was quickly superseded by the Teller-Ulam design. This was the first aerial drop of a fusion weapon. Linear pinch devices in the US and USSR report detections of neutrons, an indication of fusion reactions. Both are later explained as coming from instabilities in the fuel, and are non-fusion in nature. Scientists at the Princeton Plasma Physics Laboratory construct Model A, the first operational stellarator. 1954 Early planning for the large ZETA device at Harwell begins. The name is a take-off on small experimental fission reactors which often had "zero energy" in their name, ZEEP being an example. Edward Teller gives a now-famous speech on plasma stability in magnetic bottles at the Princeton Gun Club. His work suggests that most magnetic bottles are inherently unstable, outlining what is today known as the interchange instability. 1955 At the first Atoms for Peace meeting in Geneva, Homi J. Bhabha predicts that fusion will be in commercial use within two decades. This prompts a number of countries to begin fusion research; Japan, France, and Sweden all start programs this year or the next. Scientists in the Soviet Union achieve the first fusion via a purely chemical explosive-driven implosion, using spherical shock waves to compress a UD2T target. 1956 Construction of ZETA begins at Harwell. Igor Kurchatov gives a talk at Harwell on pinch devices,"Lecture of I.V. Kurchatov at Harwell", from the address of I.V. Kurchatov: "On the possibility of producing thermonuclear reactions in a gas discharge" at Harwell on 25 April 1956. Archived 20 July 2015. revealing for the first time that the USSR is also working on fusion. He details the problems they are seeing, mirroring those in the US and UK. In August, a number of articles on plasma physics appear in various Soviet journals. In the wake of the Kurchatov's speech, the US and UK begin to consider releasing their own data. Eventually, they settle on a release prior to the 2nd Atoms for Peace conference in Geneva in 1958. On May 27, the United States conducts the Zuni test of Operation Redwing with a Mk-41 bomb, the first test of a three-stage hydrogen bomb. 1957 In the US, at LANL, Scylla IIn 1957, Los Alamos achieved the first controlled thermonuclear plasma., Now and Then at Los Alamos. begins operation using the θ-pinch design. ZETA is completed in the summer, it will be the largest fusion machine for a decade. In August, initial results on ZETA appear to suggest the machine has successfully reached basic fusion temperatures. UK researchers start pressing for public release, while the US demurs. Scientists at the AEI Research laboratory in Harwell reported that the Sceptre III plasma column remained stable for 300 to 400 microseconds, a dramatic improvement on previous efforts. Working backward, the team calculated that the plasma had an electrical resistivity around 100 times that of copper, and was able to carry 200 kA of current for 500 microseconds in total. 1958 In January, the US and UK release large amounts of data, with the ZETA team claiming fusion. Other researchers, notably Artsimovich and Spitzer, are sceptical. In May, a series of new tests demonstrate the measurements on ZETA were erroneous, and the claims of fusion have to be retracted.