Accelerator and particle therapy system

An accelerator that accelerates an ion beam while circulating the ion beam by a main magnetic field and an accelerating radiofrequency electric field, the accelerator comprising:

• a main magnetic field magnet that has a plurality of magnetic poles arranged to face each other and excites the main magnetic field in a space interposed between the magnetic poles;
• a magnetic channel that extracts the ion beam from an inside of the main magnetic field magnet toward an outside of the main magnetic field magnet;
• and
• a displacement unit that displaces the ion beam circulating in a main magnetic field region where the main magnetic field is excited to an outer side of the main magnetic field region,
• wherein a disturbance magnetic field region is provided in an outer peripheral portion of the main magnetic field region,
• wherein a magnetic field which disturbs the ion beam displaced to the outer side and guides the ion beam to the magnetic channel is excited in the disturbance magnetic field region,
• wherein the magnetic channel includes a predetermined mechanism that suppresses a magnetic field gradient generated radially inward in a circulating ion beam region,
• wherein the magnetic channel includes a septum located on a radially inner side of the main magnetic field magnet and an anti-septum located on a radially outer side with a beam extraction passage interposed between the anti-septum and the septum, and
• wherein the predetermined mechanism is achieved by forming a recessed part in a predetermined region where a median plane, orthogonal to an axial middle of the main magnetic field magnet, intersects with the septum.

An accelerator that accelerates an ion beam while circulating the ion beam by a main magnetic field and an accelerating radiofrequency electric field, the accelerator comprising:

• a main magnetic field magnet that has a plurality of magnetic poles arranged to face each other and excites the main magnetic field in a space interposed between the magnetic poles;
• a magnetic channel that extracts the ion beam from an inside of the main magnetic field magnet toward an outside of the main magnetic field magnet;
• and
• a displacement unit that displaces the ion beam circulating in a main magnetic field region where the main magnetic field is excited to an outer side of the main magnetic field region,
• wherein a disturbance magnetic field region is provided in an outer peripheral portion of the main magnetic field region,
• wherein a magnetic field which disturbs the ion beam displaced to the outer side and guides the ion beam to the magnetic channel is excited in the disturbance magnetic field region,
• wherein the magnetic channel includes a predetermined mechanism that suppresses a magnetic field gradient generated radially inward in a circulating ion beam region,
• wherein the magnetic channel includes a septum located on a radially inner side of the main magnetic field magnet and an anti-septum located on a radially outer side with a beam extraction passage interposed between the anti-septum and the septum, and
• wherein the predetermined mechanism is achieved by setting a radial width dimension of the septum to be smaller than a radial width dimension of the anti-septum, and forming a recessed part in a predetermined region where a median plane, orthogonal to an axial middle of the main magnetic field magnet, intersects with the septum to set a radial width dimension of the septum to minimum.