In 1946, George Thomson, an English Physicist, and Moses Blackman, an English Physicist, were working at the Imperial College in England. They proposed a device that would utilize an electric current in a plasma (a gas of ionized hydrogen) to generate a magnetic field that would compress the plasma and could potentially lead to a fusion reaction. This type of plasma confinement system was referred to as a zeta pinch. The name was taken from the mathematical diagram for the system along with pinch as a reference to the compression of the plasma.
In 1947, Thomson, Blackman, Cousins, Ware and other physicists meet in Harwell, U.K, to discuss development of the pinch effect. Cousins and Ware create the first plasma energized by kiloamperes of electricity in a glass vessel shaped like a doughnut otherwise known as a torus. The plasma was very unstable despite the pinch effect and only lasted for a few seconds.
In 1950, the Soviet scientists Andre Sakharov and Igor Tamm proposed a nuclear fusion reactor they called a “tokamak” based on an original idea by Oleg Lavrentiev. In order to achieve a more stable plasma, the design called for a toroidal electrical field that travels around the torus. A poloidal field that is generated by the circulating toroidal field circulates around the cross sections of the torus. Electromagnets are used to induce the current in the plasma. These two fields at right angles to each other result in a magnetic field that travels around the torus in a helical configuration. (See diagram at end of article.)
In 1951, Lymen Spitzer came up with the idea for a fusion reactor called a stellarator. Unlike the tokamak design, the stellarator called for a lower density plasma and a longer confinement time. The big challenge was to keep all the plasma particles confined. Winding a wire in a cylindrical shape causes a plasma to be pushed to the center of the cylinder by the magnetic field. However, the plasma can still escape out either end of the cylinder. However, the plasma can still escape out either end of the cylinder. Bending the cylinder around into a torus shape solves that problem but because the windings will be closer together on the inside of the torus than the windings will be on the outside. This results in an asymmetrical confinement field which allows plasma to escape. Lymen came up with a design where the torus shape was drawn out into more of a race track shape with two long sides joined by curved ends. This allowed the cancellation of the asymmetries for the plasmas and extended the confinement time.
In 1952, Cousins and Ware build a larger toroidal pinch device and conclusively demonstrate that plasma instabilities make such pinch devices fundamentally unstable. In 1953, the U.S. and the U.S.S.R. build pinch devices and try to generate a fusion reaction without concern for the instabilities in the plasmas or long term plasma confinement.
Diagram of electrical fields in a tokomak. The blue arrow is the toroidal field and the red arrow is the poloidal field:
