Circular accelerator and particle therapy system

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 comprising:

• 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,
• wherein the control unit excites the first bending magnet and the second bending magnet so that a difference in the orbit of the beam, which varies depending on the energy, is smaller at the position of the second bending magnet than at the position of the first bending magnet, and
• wherein 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.