Patent ID: 8525448

Claim:
A circular accelerator that accelerates charged particles injected into the center thereof by a radio-frequency electric field while making the particles orbit along a spiral orbit by a bending magnetic field, the circular accelerator comprising: a bending electromagnet that is excited by an exciting coil and thereby generates the bending magnetic field, the bending electromagnet including an electromagnet hill for forming a narrow magnetic pole gap and an electromagnet valley for forming a wide magnetic pole gap alternately disposed in an orbiting direction of the charged particles; a radio-frequency power source that generates the radio-frequency electric field in accordance with an orbital frequency of the charged particles; a radio-frequency electromagnetic field coupling part connected to the radio-frequency power source; an acceleration electrode connected to the radio-frequency electromagnetic field coupling part; and an acceleration-electrode-opposing ground plate provided to form an acceleration gap between the plate itself and the acceleration electrode, for generating the radio-frequency electromagnetic field in the orbing direction of the charged particles; wherein the bending electromagnet generates the bending magnetic field varying in such a way that the orbital frequency of the charged particles varies in a variation range of 0.7% to 24.7% with respect to an orbital frequency at the charged-particles' extraction portion, during a time of injection to extraction of the particles.