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Ernest Lawrence and M. Stanley Livingston developed repeated acceleration of ions in a cyclotron. An oscillating electric field accelerates a particle each time it crosses the gap between two hollow electrodes; a perpendicular magnetic field bends it back toward the gap. In the nonrelativistic approximation, the orbit period $2\pi m/(|q|B)$ is independent of radius, allowing successive crossings to stay synchronized. Their 1932 report obtained proton energies of $1.22\mathrm{MeV}$ with a maximum applied voltage of $4,000\mathrm{V}$.^[ref]

A physicist.^[ref]

Ernest Orlando Lawrence and Milton Stanley Livingston reported repeated ion acceleration in 1932. Their evacuated brass chamber used one driven hollow cyclotron dee; the grounded box and slotted divider supplied the other electrode. Filament electrons ionized hydrogen near the gap. A perpendicular magnetic field bent the ions; a high-frequency oscillator drove the gap. Deflecting plates and slits selected particles for a Faraday cup, read by an electrometer.^[ref]

Scanning the magnetic field produced narrow resonance peaks. The optimum deflecting voltage tracked the kinetic energy predicted from field and orbit radius, supporting the reported $1.22\mathrm{MeV}$ protons. Source width and slit geometry limited this check; it was not a direct energy measurement of every particle.^[ref]

This combination distinguishes producing a circulating electric current from establishing its kinetic energy. The electrometer measures collected electric charge per unit time; it cannot by itself tell whether the collected particles are fast. The separate deflection selection supplies a speed-dependent test. Agreement of two consequences of the model, the cyclotron resonance condition and the cyclotron energy and orbit radius relation, makes the inference stronger than either a current signal or a predicted orbit alone.

Milton Stanley Livingston built the early cyclotrons with Ernest Orlando Lawrence; the 1939 Nobel Prize in Physics went to Ernest Orlando Lawrence. His lecture, The evolution of the cyclotron, was delivered on 11 December 1951.^[ref][ref]

M. Stanley Livingston and Ernest Lawrence developed the cyclotron as a practical source of energetic ions. Their 1932 paper explains how an alternating electric field gives a new acceleration on every gap crossing while the magnetic field supplies the return path. Keeping the half-orbit time synchronized with the field oscillation lets many small energy increments accumulate. The paper also emphasizes beam focusing and magnetic field correction, showing why successful acceleration required control of the trajectories as well as the resonance condition.^[ref]

A physicist.^[ref]