January 2, 1931

Cyclotron

M. Stanley Livingston obtains the first successful cyclotron beam

A machine about four inches across turned roughly 1,800 electrode volts into an 80,000-electron-volt ion beam.

Four inches, eighty thousand volts

On 2 January 1931 at the University of California, Berkeley, the graduate student M. Stanley Livingston obtained a beam of 80,000-electron-volt molecular hydrogen ions from a roughly four-inch cyclotron built under Ernest Lawrence's direction.

About 1,800 volts on the electrodes accelerated the ions to that energy by making them cross the accelerating gap repeatedly. The magnetic field bends the particles round; the alternating electric field gives them a push at each crossing.

The particles were molecular hydrogen ions, as the Berkeley historical account and the Nobel presentation describe them, rather than simply 80-keV protons.

The invention was not made that day

The listing says Lawrence invented the cyclotron on 2 January 1931. He had conceived the principle in 1929, after Rolf Widerøe's paper on a linear resonance accelerator, and an earlier crude model was built with Niels Edlefsen in 1930.

What 2 January marks is Livingston's successful working-beam test. Berkeley's historical record says Livingston made the first cyclotron that worked and obtained the beam that day.

The recycled Federal Telegraph arc-transmitter magnet often attached to this story belonged to a later, much larger machine, and was being modified late in 1931.

What the small beam bought

The result was not a dramatic nuclear reaction but a tiny detectable beam — practical proof that Lawrence's magnetic-resonance scheme could multiply a modest electrode voltage into a much larger particle energy in a compact apparatus.

Lawrence immediately began planning a larger cyclotron; later in 1931 a Berkeley machine exceeded one million electron volts.

The cyclotron patent was filed on 26 January 1932 and granted on 20 February 1934 — a distinction the shorthand "patented in 1932" loses.

Sources

Researched 24 Aug 2026 7 sources not yet audited

How this was checked

Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →

What the sources leave uncertain

2 January is well supported as the date of Livingston’s successful 80-keV beam, but it is not a unique “invention date.” Lawrence conceived the principle in 1929, an earlier crude model existed in 1930, and the mature method was published later.