Ernest Lawrence (1901-1958) was an American physicist who worked from 1929 to produce particles sufficiently energetic for nuclear reactions. Linear accelerators used high voltages and were awkwardly long. Lawrence decided to accelerate his particles in a spiral path within a pair of semi-cylinders mounted in a vacuum between the poles of an electromagnet. The first small cyclotron, using a magnet of only 10 cms, operated in 1931.
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