Cyclotron

The cyclotron emerged because nuclear physics in the late 1920s faced an energy ceiling—particles needed to be accelerated to millions of electron volts to probe atomic nuclei, but existing linear accelerators grew impossibly long. The solution came to Ernest Lawrence one evening in 1929 while browsing a journal in the Berkeley library, sketched on a napkin.

The key insight came from a diagram in Rolf Wideroe's paper on linear acceleration. Lawrence realized that if charged particles were bent into a spiral path by a magnetic field, they could be accelerated repeatedly by the same electric field. Each time they crossed the gap between two hollow D-shaped electrodes, they gained energy, curving outward in an ever-larger spiral until reaching the target at the edge.

Lawrence had arrived at UC Berkeley in 1928, lured from Yale at age 27. He published the cyclotron concept in Science in 1930, after his graduate student M. Stanley Livingston built a crude model that April. Their first working cyclotron became operational on January 2, 1931—a palm-sized device just 4.5 inches in diameter that accelerated protons to 80,000 electron volts.

The cyclotron scaled magnificently. Lawrence founded the Radiation Laboratory at Berkeley in 1931 to house ever-larger machines. The 11-inch cyclotron gave way to the 27-inch, then the 37-inch, the 60-inch, and finally the 184-inch behemoth with its 4,000-ton magnet. Each increase in diameter exponentially increased particle energy.

In April 1932, John Cockcroft and Ernest Walton at Cambridge announced they had transmuted lithium into helium using proton bombardment. Their energy requirement—well within the 11-inch cyclotron's capability—validated Lawrence's approach. The cyclotron became the essential tool for nuclear physics research.

In November 1939, as Germany invaded Poland, Lawrence received the Nobel Prize in Physics at age 38—the youngest physics laureate at that time and the first from UC Berkeley. But the cyclotron's greatest impact came from what it produced: isotopes for medical diagnosis and treatment, new elements like neptunium and plutonium, and the calutron (an electromagnetic separator derived from cyclotron principles) that enriched uranium for the atomic bomb.

The cyclotron established 'Big Science'—the model of large, expensive, team-operated machines requiring institutional resources far beyond individual laboratories. The laboratory Lawrence built was renamed Lawrence Berkeley National Laboratory after his death in 1958, anchoring the Department of Energy's network of national laboratories. Every modern particle accelerator descends from that napkin sketch in the Berkeley library.