Accelerator and particle beam irradiation system

A particle beam irradiation system comprising:

• an accelerator;
• a transport configured to transport ion beams extracted from the accelerator;
• an irradiation apparatus configured to irradiate, on an irradiation target, the ion beams transported by the transport;
• wherein the accelerator, configured to extract the ion beams of different energies according to a request of the irradiation apparatus, includes
• a pair of iron cores which are installed to face each other and between which magnetic fields are formed;
• an acceleration electrode configured to accelerate ion beams;
• a beam extraction path configured to extract the ion beams to an outside, wherein multiple annular beam turning trajectories, which are formed by the pair of iron cores and along which the ion beams of different energies respectively turn, are densely formed in an inlet of the beam extraction path;
• and
• an ion injection portion to receive ions from an ion inlet port formed at a tip end of an ion injection tube, the ion injection portion being formed inside an innermost beam turning trajectory at a periphery of an injection electrode which is attached to the tip end of the ion injection tube, the ion injection portion being disposed offset away from a center of the iron cores and toward the inlet of the beam extraction path.

An accelerator comprising:

• a pair of iron cores which are installed to face each other and between which magnetic fields are formed;
• an acceleration electrode configured to accelerate ion beams;
• and
• a beam extraction path configured to extract the ion beams to an outside, wherein multiple annular beam turning trajectories, which are formed by the pair of iron cores and along which the ion beams of different energies respectively turn, are densely formed in an inlet of the beam extraction path;
• wherein the magnetic field includes multiple first magnetic field regions formed on the trajectory plane and multiple second magnetic field regions having magnetic field strength lower than magnetic field strength of the first magnetic field regions,
• wherein the multiple first magnetic field regions and the multiple second magnetic field regions radially extend from a position of an ion injection portion on the trajectory plane,
• wherein the first magnetic field region and the second magnetic field region are alternately formed at a periphery of the ion injection portion,
• wherein a region having the highest magnetic field strength on the trajectory plane is formed closer to the ion injection portion side than the outermost beam turning trajectory in the first magnetic field region,
• wherein a sextet of the first magnetic field regions and a sextet of the second magnetic field regions are present, and
• wherein, in the beam turning trajectory having maximum energy among the beam turning trajectories, among six maximum peaks of the strength of the magnetic field through which the ion beam passes during one turn, maximum peaks positioned second and fifth from a position corresponding to the inlet of the beam extraction path from which ions are extracted are lower than others, and values of minimum peaks on both sides of the maximum peaks are higher than others.