Abstract: There is provided a circular accelerator that accelerates a beam of charged particles circulating in a magnetic field such that a closed orbit for each energy of the beam is eccentric. The circular accelerator includes a beam extraction port for extracting beams of different energies from the closed orbit, a first bending magnet and a second bending magnet that bend the beam extracted from the beam extraction port, and a control unit that controls magnetic field strengths of the first bending magnet and the second bending magnet in accordance with the energy of the extracted beam. When the energy of the extracted beam is a designed maximum energy of the circular accelerator, the control unit excites both the first bending magnet and the second bending magnet to bend the beam.

Abstract: A particle therapy system in which the efficiency of extracting a beam from a synchrotron can be improved and time required for therapy can be shortened is provided. The synchrotron 10 of the particle therapy system 100 extracts a charged particle beam, which circulates in the synchrotron 10, out of the synchrotron 10 by means of a slow extraction method using the resonance of a betatron oscillation, and magnetic poles 73 included in a bending magnet 12 of the synchrotron 10 have a SIM structure that generates a magnetic field distribution that makes the horizontal tune of the charged particle more closely approach a resonant line used in the slow extraction method as the amplitude of the horizontal betatron oscillation of a charged particle included in the charged particle beam becomes larger.

Abstract: A particle therapy system in which the efficiency of extracting a beam from a synchrotron can be improved and time required for therapy can be shortened is provided. The synchrotron 10 of the particle therapy system 100 extracts a charged particle beam, which circulates in the synchrotron 10, out of the synchrotron 10 by means of a slow extraction method using the resonance of a betatron oscillation, and magnetic poles 73 included in a bending magnet 12 of the synchrotron 10 have a SIM structure that generates a magnetic field distribution that makes the horizontal tune of the charged particle more closely approach a resonant line used in the slow extraction method as the amplitude of the horizontal betatron oscillation of a charged particle included in the charged particle beam becomes larger.

Abstract: The accelerator includes a circular vacuum container which contains a circular return yoke. With respect to the central axis of the vacuum container, an incidence electrode is arranged towards the entrance of a beam emission path inside of the return yoke. Inside of the return yoke, electrodes are arranged radially from the incidence electrode in the periphery of the incidence electrode. Recesses are arranged alternately with the electrodes in the circumferential direction of the return yoke. In the vacuum container, an orbit-concentric region is formed in which multiple beam orbits centered on the incidence electrode are present, and, in the periphery of said region, an orbit-eccentric area is formed in which multiple beam orbits eccentric to the incidence electrode are present. In the orbit-eccentric region, the beam orbits between the incidence electrode and the entrance to the beam emission path are denser.

Abstract: The accelerator includes a circular vacuum container which contains a circular return yoke. With respect to the central axis of the vacuum container, an incidence electrode is arranged towards the entrance of a beam emission path inside of the return yoke. Inside of the return yoke, electrodes are arranged radially from the incidence electrode in the periphery of the incidence electrode. Recesses are arranged alternately with the electrodes in the circumferential direction of the return yoke. In the vacuum container, an orbit-concentric region is formed in which multiple beam orbits centered on the incidence electrode are present, and, in the periphery of said region, an orbit-eccentric area is formed in which multiple beam orbits eccentric to the incidence electrode are present. In the orbit-eccentric region, the beam orbits between the incidence electrode and the entrance to the beam emission path are denser.

Abstract: When controlling the ejection of a charged particle beam from a synchrotron, a radiofrequency voltage is applied, which serves as the radio-frequency voltage to be applied to an ejection radio-frequency electrode equipping the synchrotron, and which is constituted by a first radio-frequency voltage for increasing an oscillation amplitude in such a way as to exceed a stable limit in order to eject to the exterior of the synchrotron a beam that circles inside the synchrotron, and a second radio-frequency voltage for preferentially ejecting a charged particle beam that circles in the vicinity of the stable limit, with the amplitude value of the second radiofrequency voltage being controlled in such a way that the amplitude value is 0 prior to the beam ejection start, the amplitude value increases gradually from the beam ejection start, and, once a predetermined amplitude value has been reached, this value is maintained.

Abstract: When controlling the ejection of a charged particle beam from a synchrotron, a radiofrequency voltage is applied, which serves as the radio-frequency voltage to be applied to an ejection radio-frequency electrode equipping the synchrotron, and which is constituted by a first radio-frequency voltage for increasing an oscillation amplitude in such a way as to exceed a stable limit in order to eject to the exterior of the synchrotron a beam that circles inside the synchrotron, and a second radio-frequency voltage for preferentially ejecting a charged particle beam that circles in the vicinity of the stable limit, with the amplitude value of the second radio-frequency voltage being controlled in such a way that the amplitude value is 0 prior to the beam ejection start, the amplitude value increases gradually from the beam ejection start, and, once a predetermined amplitude value has been reached, this value is maintained.

Abstract: When a beam acceleration high frequency control section turns on an accelerating cavity in synchronization with a beam irradiation on state, the beam acceleration high frequency control section rapidly increases an amplitude value of an applied voltage of the accelerating cavity. The control section rapidly decreases the amplitude value of the applied voltage of the accelerating cavity before beam irradiation off timing. When the control section turns off the accelerating cavity, the control section gradually decreases the amplitude value of the applied voltage of the accelerating cavity before the irradiation off timing. When the control section turns on the accelerating cavity and starts the beam irradiation, the control section gradually increases the applied voltage of the accelerating cavity.