Patent ID: 7977656

Claim:
A charged particle beam irradiation system comprising: a synchrotron for accelerating a charged particle beam, the synchrotron including a radio frequency applying device for beam extraction; a beam irradiation apparatus having a beam energy modulator and arranged for irradiating an object with the charged particle beam extracted from said synchrotron and having passed said beam energy modulator, the beam energy modulator being rotated and a thickness thereof in an axial direction differing in a rotational direction; and a controller for controlling the extraction intensity of the charged particle beam extracted from the synchrotron by controlling an amplitude of a radio frequency signal supplied to the radio frequency applying device on the basis of a rotational angle of the beam energy modulator in the rotational direction, the extraction intensity being controlled to vary among different levels on the basis of the rotational angle of the beam energy modulator during a period after a start of the extraction of the charged particle beam and before a stop of the extraction of the charged particle beam while the charged particle beam is being extracted.