Patent ID: 7741781

Claim:
An RF accelerating cavity for use in a circular accelerator which accelerates a charged particle beam and accumulates accelerated electrically charged particles where necessary, said RF accelerating cavity comprising: an accelerating cavity unit including an acceleration electrode gap for generating an RF electric field for accelerating the charged particle beam and an acceleration core forming a magnetic path surrounding an orbit of the charged particle beam; and an inductance varying device of which magnetic member is connected parallel to said acceleration electrode gap; wherein inductance produced by said inductance varying device is varied in accordance with a changing pattern of a charged particle beam acceleration frequency to tune said RF accelerating cavity such that the charged particle beam acceleration frequency matches a resonant frequency of said RF accelerating cavity; said inductance varying device including: a toroidal core in which a radially cut gap is formed; a rotatable flat toroidal magnetic member disposed in a plane perpendicular to said toroidal core, a central axis of rotation of said flat toroidal magnetic member being located at a position separated outward from an outer periphery of said toroidal core, and a turning mechanism for turning said flat toroidal magnetic member; wherein said turning mechanism turns said flat toroidal magnetic member in accordance with the changing pattern of the charged particle beam acceleration frequency to cause said flat toroidal magnetic member to turn through the gap formed in said toroidal core, thereby varying the inductance produced by said inductance varying device, such that the charged particle beam acceleration frequency matches the resonant frequency of said RF accelerating cavity.