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A charged-particle beam accelerator includes an RF-KO unit for increasing the amplitude of betatron oscillation of a charged-particle beam within a stable region of resonance and an extraction quadrupole electromagnet unit for varying the stable region of resonance. The RF-KO unit is operated withi

A charged-particle beam accelerator includes an RF-KO unit for increasing the amplitude of betatron oscillation of a charged-particle beam within a stable region of resonance and an extraction quadrupole electromagnet unit for varying the stable region of resonance. The RF-KO unit is operated within a frequency range in which the circulating beam does not go beyond a boundary of the stable region of resonance, and the extraction quadrupole electromagnet unit is operated with appropriate timing as required for beam extraction so that the charged-particle beam is extracted with desired timing.

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What is claimed is: 1. A charged-particle beam accelerator comprising: means for accelerating a charged-particle beam and circulating the charged-particle beam along an orbiting path; means for causing betatron oscillation of charged particles in a resonating state outside a stable region of resona

What is claimed is: 1. A charged-particle beam accelerator comprising: means for accelerating a charged-particle beam and circulating the charged-particle beam along an orbiting path; means for causing betatron oscillation of charged particles in a resonating state outside a stable region of resonance; means for increasing the amplitude of the betatron oscillation of the charged-particle beam within the stable region of resonance; and means for varying the stable region of resonance; wherein said means for increasing the amplitude of the betatron oscillation is controllably operated within a frequency range in which the circulating beam does not go beyond a boundary of the stable region of resonance, and said means for varying the stable region of resonance is controllably operated with appropriate timing as required for beam extraction so that the charged-particle beam is extracted with desired timing. 2. The charged-particle beam accelerator according to claim 1, wherein the charged-particle beam is extracted by alternately operating said means for increasing the amplitude of the betatron oscillation of the charged-particle particle beam within the stable region of resonance and said means for varying the stable region of resonance, or by repetitively operating one of said means for increasing the amplitude of the betatron oscillation of the charged-particle beam within the stable region of resonance and said means for varying the stable region of resonance at first and then alternately operating both means. 3. The charged-particle beam accelerator according to claim 1, wherein said means for accelerating and circulating the charged-particle beam along the orbiting path includes a high-frequency acceleration device, a bending electromagnet and a quadrupole electromagnet, said means for causing the betatron oscillation to go into the resonating state outside the stable region of resonance includes a sextupole electromagnet, said means for increasing the amplitude of the betatron oscillation of the charged-particle beam within the stable region of resonance includes a radio frequency knockout device, and said means for varying the stable region of resonance includes a quadrupole magnetic field generating device, and wherein the stable region of resonance is created at the time of extraction of the charged-particle beam and said means for increasing the amplitude of the betatron oscillation of the charged-particle beam within the stable region of resonance and said means for varying the stable region of resonance are controllably operated by controlling the quadrupole electromagnet and the sextupole electromagnet. 4. The charged-particle beam accelerator according to claim 3, wherein the charged-particle beam accelerator begins beam extraction when said means for varying the stable region of resonance reduces the stable region of resonance and the charged-particle beam accelerator terminates beam extraction when said means for varying the stable region of resonance stops reducing the stable region of resonance after the stable region of resonance has reduced by a specified amount, and wherein said means for increasing the amplitude of the betatron oscillation of the charged-particle beam within the stable region of resonance increases the amplitude of the betatron oscillation up to the proximity of the boundary of the stable region of resonance. 5. The charged-particle beam accelerator according to claim 3, wherein the charged-particle beam accelerator begins beam extraction when the stable region of resonance is reduced and the charged-particle beam accelerator terminates beam extraction when the reduction of the stable region of resonance stops. 6. The charged-particle beam accelerator according to claim 4, wherein the stable region of resonance in a standby state of the charged-particle beam accelerator for commencing beam extraction is set to a region in which the charged-particle beam is not extracted even when the stable region of resonance is reduced due to a ripple component contained in an output of a power supply for any of the electromagnets of the charged-particle beam accelerator. 7. The charged-particle beam accelerator according to claim 3, wherein said means for varying the stable region of resonance includes one of a quadrupole air-core coil and a quadrupole electromagnet including a magnetic core having a high-frequency response characteristic. 8. The charged-particle beam accelerator according to claim 1, wherein said means for varying the stable region of resonance accelerates and decelerates the charged-particle beam by use of a high-frequency acceleration device. 9. The charged-particle beam accelerator according to claim 1, wherein said means for varying the stable region of resonance accelerates and decelerates the charged-particle beam by use of a high-frequency acceleration device which is included in said means for accelerating and circulating the charged-particle beam along the orbiting path. 10. A particle beam radiation therapy system comprising: the charged-particle beam accelerator as defined in claim 1; and a beam transport line for transporting a charged-particle beam extracted from said charged-particle beam accelerator to a treatment room. 11. The particle beam radiation therapy system according to claim 10 further comprising a beam delivery device disposed in the treatment room, wherein the charged-particle beam is extracted from said charged-particle beam accelerator in synchronism with irradiation timing of said beam delivery device. 12. The particle beam radiation therapy system according to claim 11 further comprising a target displacement sensor disposed in the treatment room for detecting a displacement of an irradiation target, wherein said beam delivery device irradiates the irradiation target with the charged-particle beam when a sensing signal output from said target displacement sensor is at a level within a preset range. 13. The particle beam radiation therapy system according to claim 11, wherein said beam transport line includes a beam bending device for bending the charged-particle beam, wherein said beam bending device prevents the charged-particle beam from being transported to said beam delivery device except during a desired period of time. 14. The particle beam radiation therapy system according to claim 11, wherein said beam transport line includes a beam bending device for quickly interrupting the charged-particle beam when the amount of irradiation from said beam delivery device has reached a prescribed dose, and wherein said beam bending device includes one of an air-core coil and an electromagnet including a magnetic core having a high-frequency response characteristic. 15. A method of operating the particle beam radiation therapy system as defined in claim 11, said method comprising the step of transferring said charged-particle beam accelerator to an operating pattern including deceleration, reinjection and acceleration of the circulating beam when the intensity of the circulating beam in said charged-particle beam accelerator is not high enough upon completion of irradiation for a specific period of time from said beam delivery device to irradiate a specified target in succession for more than an intended irradiation time.