The cyclotron was the first "cyclical" accelerator. The advantage of the cyclotron design over the existing electrostatic accelerators of the time such as the Cockcroft-Walton accelerator and Van de Graaff generator, was that in these machines the particles were only accelerated once by the voltage, so the particles' energy was equal to the accelerating voltage on the machine, which was limited by air breakdown to a few million volts. In the cyclotron, in contrast, the particles encounter the accelerating voltage many times during their spiral path, and so are accelerated many times, so the output energy can be many times the accelerating voltage.