A rotating capacitor is used in a circular accelerator that accelerates a charged particle beam by feeding a first radio frequency to a DC main magnetic field. The rotating capacitor modulates a frequency of the first radio frequency. The rotating capacitor includes a stator electrode and a rotor electrode used for modulating the frequency of the first radio frequency together with the stator electrode. A vacuum seal performs vacuum sealing around a shaft for rotating the rotor electrode. A bearing that supports the shaft is installed on an atmosphere side.

An object of the present invention is to speed up an operation of extracting an ion beam from an accelerator. An accelerator 100 includes an upper magnetic pole 8 and a lower magnetic pole 9 sandwiching an ion circulation space 10 in which ions circulate. At least one of the upper magnetic pole 8 and the lower magnetic pole 9 is formed such that a magnetic pole interval between the upper magnetic pole 8 and the lower magnetic pole 9 varies when the ion circulation space 10 is viewed along an ion beam trajectory. That is, a wide interval region 11 having a larger magnetic pole interval than a peripheral region is formed in a region closer to a center point of the ion circulation space 10 than a center point of the ion beam trajectory.

An object of the present invention is to speed up an operation of extracting an ion beam from an accelerator. An accelerator 100 includes an upper magnetic pole 8 and a lower magnetic pole 9 sandwiching an ion circulation space 10 in which ions circulate. At least one of the upper magnetic pole 8 and the lower magnetic pole 9 is formed such that a magnetic pole interval between the upper magnetic pole 8 and the lower magnetic pole 9 varies when the ion circulation space 10 is viewed along an ion beam trajectory. That is, a wide interval region 11 having a larger magnetic pole interval than a peripheral region is formed in a region closer to a center point of the ion circulation space 10 than a center point of the ion beam trajectory.

An example particle accelerator includes a particle source to provide particles to a magnetic cavity; circuitry to provide a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from the ionized plasma in orbits in the magnetic cavity, where the RF voltage has a slope that is less when the particles are injected into the magnetic cavity than when the particles are accelerated in the magnetic cavity; and an extraction channel to receive the particles from the magnetic cavity for output as a particle beam from the particle accelerator.

An example particle accelerator includes a particle source to provide particles to a magnetic cavity; circuitry to provide a radio frequency (RF) voltage to the magnetic cavity to accelerate particles from the ionized plasma in orbits in the magnetic cavity, where the RF voltage has a slope that is less when the particles are injected into the magnetic cavity than when the particles are accelerated in the magnetic cavity; and an extraction channel to receive the particles from the magnetic cavity for output as a particle beam from the particle accelerator.