Control method for accelerator, control device for accelerator, and particle-beam radiation treatment system

A control method for an accelerator including an injector configured to accelerate charged particles to an injection energy and inject the charged particles into a main accelerator, a high-frequency acceleration cavity configured to give an acceleration energy to the charged particles injected into the main accelerator, a plurality of deflection electromagnets configured to generate a magnetic field that causes the charged particles to revolve in the main accelerator in accordance with the acceleration energy of the charged particles, a power supply configured to supply a current that generates the magnetic field to the deflection electromagnets based on a current-value instruction signal, and an emission device for causing the charged particles to be emitted from the main accelerator to a beam transport system, the method comprising:

• generating a flat bottom section corresponding to a lowest energy of the charged particles, a top point or a flat top section corresponding to a highest energy, an acceleration section for acceleration from the flat bottom section, and a deceleration section for deceleration from the top point or the flat top section to the flat bottom in time change of a current value of the deflection electromagnet in an acceleration cycle not involving emission of the charged particles to the beam transport system, and not generating a flat region that makes the current value of the deflection electromagnet constant to correspond to a predetermined extraction energy;
• generating, in time change of the current value of the deflection electromagnet in an acceleration cycle involving emission of the charged particles to the beam transport system, the flat region in which the current value is constant to correspond to a predetermined extraction energy in a middle of a section corresponding to at least either the deceleration section or the acceleration section;
• and
• smoothing the time change of the current value in a transition from the corresponding section to the flat region or a transition from the flat region to the corresponding section, and determining a time required for the smoothing based on a predetermined energy for extracting the charged particles or a difference between energies before and after change to the predetermined extraction energy.

A control device for an accelerator including a plurality of deflection electromagnets configured to generate a magnetic field that causes charged particles to revolve in a main accelerator in accordance with an acceleration energy of the charged particles and a power supply configured to supply a current that generates the magnetic field to the deflection electromagnets based on a current-value instruction signal, comprising a current signal generator configured to

• generate the current-value instruction signal provided with a flat region that makes a current value of the deflection electromagnet constant to correspond to a predetermined energy for extracting the charged particles in a case of an acceleration cycle involving emission of the charged particles to a beam transport system, and
• generate the current-value instruction signal not provided with the flat region in a case of an acceleration cycle not involving emission of the charged particles to the beam transport system, wherein
• the current-value instruction signal includes a smoothing section in which current change is made smooth in a transition of the current value of the deflection electromagnet to the flat region or a transition from the flat region, and
• a length of time of the smoothing section is determined based on a predetermined energy for extracting the charged particles or a difference between energies before and after change to the predetermined extraction energy.

A particle-beam radiation treatment system comprising:

• an injector configured to accelerate charged particles to an injection energy and inject the charged particles to a main accelerator;
• a high-frequency acceleration cavity configured to give an acceleration energy to the charged particles injected into the main accelerator;
• a plurality of deflection electromagnets configured to generate a magnetic field that causes the charged particles to revolve in the main accelerator in accordance with the acceleration energy of the charged particles;
• a power supply configured to supply a current that generates the magnetic field to the deflection electromagnets based on a current-value instruction signal;
• an emission device for causing the charged particles to be emitted from the main accelerator to a beam transport system;
• and
• a control device configured to control at least the power supply among the injector, the high-frequency acceleration cavity, the power supply, and the emission device, wherein
• the control device includes a current signal generator configured to
• generate the current-value instruction signal provided with a flat region that makes a current value of the deflection electromagnet constant to correspond to a predetermined energy for extracting the charged particles in a case of an acceleration cycle involving emission of the charged particles to the beam transport system,
• generate the current-value instruction signal not provided with the flat region in a case of an acceleration cycle not involving emission of the charged particles to the beam transport system,
• generate a smoothing section that smoothes current change in a transition to the flat region or a transition from the flat region, and
• determine a length of time of the smoothing section based on a predetermined energy for extracting the charged particles or a difference between energies before and after change to the predetermined extraction energy.