A cyclotron is a type of particle accelerator in which charged particles accelerate outwards from the center along a spiral path. The particles are held to a spiral trajectory by a static magnetic field and accelerated by a rapidly varying (radio frequency) electric field.
The cyclotron was invented and patented by Ernest Lawrence of the University of California, Berkeley, where it was first operated in 1932. A graduate student, M. Stanley Livingston, did much of the work of translating the idea into working hardware. Lawrence read an article about the concept of a drift tube linac by Rolf Widerøe, who had also been working along similar lines with the betatron concept. The first European cyclotron was constructed in Leningrad in the physics department of the Radium Institute, headed by Vitaly Khlopin (ru). This instrument was first proposed in 1932 by George Gamow and Lev Mysovskii (ru) and was installed and became operative by 1937.
Cyclotrons accelerate charged particle beams using a high frequency alternating voltage which is applied between two "D"-shaped electrodes (also called "dees"). An additional static magnetic field is applied in perpendicular direction to the electrode plane, enabling particles to re-encounter the accelerating voltage many times at the same phase. To achieve this, the voltage frequency must match the particle's cyclotron resonance frequency