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 E=mc2, 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 fission by using protons from the accelerator to split lithium into alpha particles. 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 the first direct demonstration of fusion in the lab. 1938 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 provides detailed calculations of the proton–proton chain reaction that powers stars. This work results in a Nobel Prize for Physics.
1940s
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. Repeated attempts to get development funding fails.
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.