JP2005353610A - Circular particle accelerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compose a medical circular particle accelerator equipped with a tune shifter capable of extracting and stopping a high-speed particle beam in three-dimensional radiation and rapidly turning on and of the particle beam, and used for cancer treatment. <P>SOLUTION: This circular particle accelerator is equipped with: a particle beam orbit; a quadrupole magnet for circulating a particle beam along the particle beam orbit; a bending magnet; an acceleration cavity for accelerating the particle beam; a betatron oscillation amplitude amplification means for amplifying the betatron oscillation amplitude of the particle beam; and an emission septum for extracting the particle beam from the particle beam orbit. This circular particle accelerator is composed by having a tune shifter used for rapidly turning on and off the particle beam and formed with a high-frequency cavity that is so structured that the cavity is arranged on the upstream of the emission septum of the particle beam orbit, and electromagnetic waves are introduced into the cavity to excite a TM210 mode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a circular particle accelerator.

  A general circular particle accelerator is configured as shown in FIG. In FIG. 3, 1 is an incident duct into which a particle beam is incident, 2 is an incident septum that bends the incident particle beam in a circumferential direction, 3 is a particle beam orbit around the particle beam, 4 is a quadrupole electromagnet, and 5 is a particle A deflecting electromagnet arranged at a curved portion of the beam trajectory and bending the particle beam in a circumferential direction; 6 an acceleration cavity for accelerating the particle beam; 7 a higher-order mode cavity; 8 an exit septum for guiding the accelerated particle beam to the exit duct; Reference numeral 9 denotes a hexapole electromagnet, and 10 denotes an exit duct that emits accelerated particles.

  There are two main methods for extracting a particle beam from a circular particle accelerator as shown in FIG. 3, called “fast extraction” for extracting a low energy particle beam and “slow extraction” for extracting a high energy particle beam. Yes, this invention relates to "slow retrieval".

  When the boundary between the stable region and the unstable region called the separatrix of the particle beam orbiting the particle beam orbit is formed, as a method of moving outside the separatrix, that is, the unstable region, a method of gradually reducing the separatrix, There is a method of increasing the emittance to the separatrix by applying vibrations to the particle beam in a stable region without moving the separatrix with a high-frequency electric field, and the latter method is called slow extraction using rf knockout.

  Extraction using a rf knockout for extracting a particle beam from a conventional circular particle accelerator is, for example, a method disclosed in Patent Document 1. FIG. 4 is a schematic view showing a state in which the rf knockout electrode is inserted in the linear portion of the particle beam orbit of the particle beam.

In the circular particle accelerator, the particle beam that circulates in the ring-shaped particle beam orbit 11 is oscillated with slight vibration in the horizontal and vertical directions of the particle beam orbit 11. This minute vibration is called betatron vibration, and the number of vibrations per round of the ring-shaped particle beam orbit 11 is called betatron tune or simply tune. This tune is selected so that the particle beam circulates stably, but it is selected by selecting a tune that becomes unstable for extraction of the particle beam. For example to select the tune 1/3 to the integer, the case of forming the separatrix in phase space given the dynamic vibration particle beam by sextupole electromagnets, outer or particle beam enters the unstable region is particles separatrix beam orbit 11 Each time it circulates, the amplitude increases and finally reaches the exit septum 14 installed for extraction, and is kicked outward by a static electric or magnetic field formed on the exit septum 14 and installed downstream. The deflector 15 is guided to the exit duct.

  The rf knockout electrode 12 is composed of a pair of parallel plates, and a high frequency voltage having a frequency Frf is applied therebetween. This frequency Frf is expressed by (Equation 1), where n is the decimal part of the betatron tune, Frev is the circulation frequency, and m is an arbitrary integer.

  The angle θ kicked by the electric field between the rf knockout electrodes 12 has the relationship of (Equation 2).

  Here, the electric field is obtained for each parameter value shown in Table 1 below.

  Under this condition, when the gap between the electrodes is 100 mm, it is necessary to apply 10 kV as the high frequency voltage. Thus, in the region where the momentum p due to the electric field exceeds 10 GeV / c, the necessary high-frequency voltage is higher than 10 kV, and a very high value is required. In order to apply this voltage, the generated high-frequency power source and the rf knockout electrode have an insulating configuration that can withstand high voltages.

  In medical circular particle accelerators used for cancer treatment and the like, it is necessary to take out and stop a high-speed particle beam during three-dimensional irradiation. In such a case, it is necessary to change the tune of the frequency per revolution of the betatron oscillation of the particle beam that is orbiting along the orbit of the particle beam in the lateral direction from 100 μs to several ms. Usually, due to the power supply ripple of the deflection electromagnet and the quadrupole electromagnet, the tune changes and the separatrix pulsates, and the intensity of the extracted particle beam may fluctuate in synchronization with the ripple. In this case, the ripple component is fast and is 1200 Hz (1440 Hz when the power source is 60 Hz). In such particle beam extraction, when the tune is shifted, a quadrupole electromagnet having a magnetic field distribution as shown in FIG. 5 is usually used, and its operation speed is about several tens of ms, and sufficient high-speed response can be obtained. Absent.

Japanese Patent Publication No. 5-198397

  A medical circular particle accelerator used for cancer treatment or the like requires a tune shifter that takes out and stops a high-speed particle beam during three-dimensional irradiation. Normally, a quadrupole electromagnet is used as the tune shifter, the operation speed is about several tens of ms, and the high-speed response necessary for the slow extraction that takes out the high-energy particle beam that turns the particle beam on / off at high speed cannot be obtained. There was a problem.

  The present invention also constitutes a circular particle accelerator for medical use for cancer treatment, equipped with a tune shifter that can turn on / off the particle beam at high speed that can take out and stop the particle beam at high speed during three-dimensional irradiation. Objective.

  According to a first aspect of the present invention, a circular particle accelerator includes a high-frequency cavity in which a cavity is disposed upstream of an exit septum of a particle beam orbit, an electromagnetic wave is introduced into the cavity, and a TM210 mode is excited. Is configured to include a tune shifter for turning on / off at high speed.

  Since the electromagnetic wave is introduced into the cavity disposed upstream of the exit septum of the particle beam orbit, the tune shifter that turns the particle beam composed of the high-frequency cavity excited by the TM210 mode at high speed is provided. The magnetic field is a high-frequency magnetic field, and an on / off operation is possible on the order of several tens to several hundreds of μs, and a circular particle accelerator used for cancer treatment without misirradiation can be configured.

Embodiment 1 FIG.
In the first embodiment, a HOM cavity for turning on / off a particle beam at high speed is arranged as a tune shifter arranged upstream of an exit septum arranged in a beam orbit of a circular particle accelerator used for cancer treatment or the like. The electromagnetic wave is introduced to excite the TM210 mode to form a magnetic field similar to that of a quadrupole electromagnet.

FIG. 1 shows a configuration in which a HOM cavity in which a TM210 mode is excited is arranged on a beam orbit. FIG. 2 shows the distribution of the particle beam and magnetic field in the HOM cavity.
The particle beam trajectory 11, the exit septum 14 and the deflector 15 having this configuration are the same as the conventional configuration in which the rf knockout electrode is disposed on the particle beam orbit.
In this configuration, a HOM cavity 41 and a high-frequency power source 43 are provided in a circular orbit, and a waveguide 45 for introducing electromagnetic waves and a loop coupler 46 for exciting the TM210 mode are provided in the HOM cavity 41.

  When the electromagnetic wave is introduced into the HOM cavity 41 of FIG. 3 to excite the TM210 mode, the magnetic field distribution of the central part through which the particle beam passes as shown in FIG. 2 is the center of the magnetic field distribution of the quadrupole electromagnet of FIG. And a tune shifter that operates on / off at a high speed of several tens to several hundreds of μs.

  By using the HOM cavity 41 excited with the TM210 mode as a tune shifter of the circular particle accelerator, the magnetic field is a high-frequency magnetic field, and can be turned on / off in the order of several tens to several hundreds μs, and there is no erroneous irradiation. A circular particle accelerator for cancer treatment can be constructed.

FIG. 3 is a configuration diagram schematically showing a configuration of a tune shifter according to the first embodiment. It is a cross-sectional view which shows the condition of the beam and magnetic field of the HOM cavity of FIG. It is a block diagram of the conventional particle accelerator. It is the block diagram which showed typically the structure of the amplification means which amplifies the betatron oscillation amplitude of the conventional particle beam. It is a magnetic field distribution map of the quadrupole electromagnet used for the conventional particle accelerator.

Explanation of symbols

11 particle beam orbit, 14 exit septum, 15 deflector,
41 HOM cavity, 43 high frequency power supply, 45 waveguide, 46 loop coupler.

Claims (1)

Particle beam orbit, quadrupole electromagnet that makes the particle beam circulate along the particle beam orbit, deflecting electromagnet, acceleration cavity that accelerates the particle beam, betatron oscillation amplitude amplification means that amplifies the betatron oscillation amplitude of the particle beam, particle beam In a circular particle accelerator equipped with an exit septum for extracting the particle beam from the particle beam orbit, a particle composed of a high-frequency cavity excited by the TM210 mode by introducing electromagnetic waves into the cavity disposed upstream of the exit septum of the particle beam orbit A circular particle accelerator comprising a tune shifter for turning on and off a beam at high speed.

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