History

 

Ernest Lawrence

In 1929 Ernest O. Lawrence came up with a new technique to accelerate a particle, with the help of a article by a Norwegian engineer, Rolf Wideröe. The idea was that particles with a positive electric charge are drawn into the first cylindrical electrode by a negative potential; by the time they emerge from the tube the potential has switched to positive, which propels them away from the electrode with a second boost. Adding gaps and electrodes can extend the scheme to higher energies. This is the very technique used to date to accelerate particles to high speeds.

The the first circular accelerator was only about 4 inches in diameter, and was invented by Lawrence in 1929.

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The cyclotron used two D-shaped magnets separated by a small gap. The magnets produced a circular magnetic field. By having an oscillating voltage that created an electric field across the small gap you were able to accelerate the particles each time around. As the particles moved faster, the radius of the their circular path became bigger until they hit the target on the outermost circle. Lawrence's cyclotron was effective, but could never reach the energies that our modern day circular accelerators do.

In 1930 a David Sloan built the first linear accelerator, using Wideröe's ideas. Sloan’s device eventually had a series of thirty electrodes and by May 1931 it accelerated mercury ions to energies of a million volts.

The first experiments involving atom smashing occurred in the 1930's. Cosmic rays are made up of highly energetic (meaning very fast) protons, and come from outer space. What the scientists observed was that when these cosmic rays hit the nuclei of atoms of lead, many smaller particles sprayed out. These particles were not just protons and neutrons, which was what was expected, but were much much smaller. This discovery of more "elementary" particles began the great search to find out all about these new particles.

In the early 1930’s, Brasch and Lange worked to use the huge potential differences available in lightning storms for accelerating particles. An insulated wire was hung across a valley in the Swiss Alps, with a conducting terminal suspended from it. Sparks several hundred feet long were seen between this terminal and an earthed one on the valley floor but the project was abandoned when Lange was fatally electrocuted.

Cockcroft and Walton

In 1932 Cockcroft and Walton produced the first nuclear reaction using artificially accelerated particles, bombarding and disintegrating lithium nuclei with protons accelerated to several hundred keV. By opening and closing switches in proper sequence they could build up a potential of 800 kilovolts. They used the potential to accelerate protons down an evacuated tube eight feet long. They then put a lithium target at the end of the tube and found that protons disintegrated a lithium nucleus into two alpha particles. A Soviet team in Kharkov found the same result several months later.

Cockcroft-Walton accelerator.

 

These early accelerators began the long race to probe the nucleus, searching for the answers to our questions about
"Life, the Universe, and Everything."

 

 

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