JP3943568B2 - Circular particle accelerator - Google Patents

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 an 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 configuration of FIG. 4, the rf knockout electrode 12 and the emission septum 14 are arranged on the particle beam orbit 11, and the particle beam is emitted through the deflector 15.

  In the circular particle accelerator, the particle beam that circulates in the ring-shaped particle beam orbit 11 is oscillated with a slight vibration in the horizontal and vertical directions of the particle beam orbit 11. This minute vibration is referred to as betatron vibration, and the vibration frequency 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 taking out the particle beam. For example, when a tune is selected to be an integer of 1/3 and a particle beam is vibrated by a hexapole magnet to form a separatrix on the phase space, the particle beam that has emerged outside the separatrix, that is, in an unstable region, moves around the particle beam orbit 11. The amplitude increases each time it circulates, eventually 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 guides the light 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 a circular particle accelerator, when there are a plurality of particle beam transport systems to be extracted, it is necessary to sort the destination of the particle beam. There is a high-frequency cavity that forms an electric field in the direction of the particle beam orbit around which the particle beam circulates. When a high-frequency electric field is applied to this, the particle beam that circulates around the orbit forms a pulse synchronized with the frequency of the high-frequency power source. The particle lump that generates this pulse is called a bunch, and a kicker electromagnet as shown in FIG. 5 is arranged downstream of the bunched particle beam, and the kicker is started up or rises during the blank time between the bunch. By lowering, it becomes possible to distribute the beam for each bunch. 5 includes a vacuum duct 21 held in a vacuum around which a particle beam circulates in the center, a coil 22 that applies a magnetic field in a direction perpendicular to the central axis of the internal particle beam to the vacuum duct 21, and a return yoke for magnetic flux. 23.

  When a high-frequency magnetic field is generated in the cavity formed in this way, and the bunch is raised or lowered during the blank time of the bunch, the bunch is kicked by the magnetic field and taken out to the particle beam transport system. The on / off operation for starting and lowering the kicker by such an electromagnetic field is limited to about 100 ns, and the distribution ability cannot be sufficiently obtained.

Japanese Patent Publication No. 5-198397

  In the circular particle accelerator, when there are a plurality of particle beam transport systems to be taken out, the on / off operation of the configuration in which the kicker electromagnet for starting or stopping the kicker is arranged in the blank time between the bunches is 100 ns. There was a problem that the degree was the limit and the distribution ability was not enough.

  The present invention has been made to solve the above problems, and when there are a plurality of particle beam transport systems to be taken out, a high-frequency cavity that forms an electric field in the direction of the particle beam orbit is disposed. As a beam kicker that gives a kick angle in a predetermined direction to a particle beam that has become a bunch when a beam is given, a circular particle accelerator equipped with a kicker in which the on / off operation operates reliably in a blank time between the bunches is configured For the purpose.

  A circular particle accelerator according to the present invention includes a particle beam orbit around which the particle beam circulates, a quadrupole electromagnet that circulates the particle beam along the particle beam orbit, a deflection electromagnet, an acceleration cavity that accelerates the particle beam, and the particle beam In a circular particle accelerator equipped with an exit septum for extracting from a beam orbit and having a plurality of beam ducts from which particle beams are extracted, a cavity is arranged in series with the particle beam orbit, and electromagnetic waves are introduced into the arranged cavity, thereby A high-frequency cavity excited by the TM110 mode having a magnetic field component perpendicular to the beam is provided with a beam kicker that gives the particle beam a kick angle in a predetermined direction.

  According to the present invention, the beam kicker provided in the beam orbit is arranged in series with the particle beam orbit, the electromagnetic wave is introduced into the cavity, and the TM110 mode having a magnetic field component perpendicular to the particle beam is excited. By configuring the high-frequency cavity with a high-frequency cavity that gives the particle beam a kick angle in a predetermined direction, it is possible to perform an on / off operation at a high speed of several tens to several hundreds ns, and to accurately distribute the destination of the particle beam. .

Embodiment 1 FIG.
The circular accelerator of the first embodiment has the same configuration as that shown in FIG. 3 shown in the prior art, and a plurality of beam channels of the particle beam transport system taken out from the circular particle accelerator are provided. In addition, the configuration of the beam kicker that distributes the destination for each bunch is a configuration of a circular particle accelerator in which a high-frequency cavity (HOM = Higher Order Mode, hereinafter referred to as HOM) is inserted immediately before the exit septum 8 of the circular particle accelerator. FIG. 1 shows a cross section of a beam kicker in which electromagnetic waves are introduced into a HOM cavity and a TM110 mode is excited, and a magnetic field distribution. In the figure, 71 is a HOM cavity, 73 is a high frequency power source, 75 is a waveguide, and 76 is a loop coupler.

  When electromagnetic waves are introduced into the HOM cavity 71 from the high-frequency power source 73 through the waveguide 75 and the TM110 mode is excited by the loop coupler 76, the magnetic field distribution becomes perpendicular to the beam traveling direction as shown in the figure. Is kicked in the direction perpendicular to the magnetic field. The direction of kicking is determined by synchronizing the bunch interval and the phase of the high-frequency magnetic field, and can be separated into the downstream beam transport system.

FIG. 2 shows a configuration in which a plurality of HOM cavities 71 are connected when one HOM cavity 71 cannot provide a sufficient kick. A plurality of cavities 71 a, 71 b,... 71 n are connected in multiples so that the particle beam is emitted to the emission septum 74. In this configuration, an electromagnetic wave is introduced into each of the cavities, the TM110 mode having a magnetic field component perpendicular to the particle beam is excited, and the cavities are operated in a π mode in which the magnetic field directions of the cavities are staggered, A kick in a predetermined direction is given to the particle beam to obtain an appropriate kick angle, which is distributed to the beam transport system.

  Thus, when the kicker is configured to excite the TM110 mode with the HOM cavity, the on / off operation can be performed at high speed. The speed of the on / off operation is determined by the excited frequency, and can be operated in several tens to several hundreds ns, so that the particle beam can be accurately separated.

FIG. 6 is an operation explanatory diagram of a beam kicker using the HOM cavity of the first embodiment. It is a block diagram of the beam kicker comprised in multiple. It is a block diagram of the conventional particle accelerator. It is the block diagram which showed typically the state in which the rf knockout electrode was inserted in the linear part of the particle beam circuit orbit of a particle beam. It is operation | movement explanatory drawing of the conventional beam kicker.

Explanation of symbols

71 HOM cavity, 71a, 72b ... 72n HOM cavity, 73 high frequency power supply,
74 Outgoing septum, 75 waveguide, 76 loop coupler.

Claims (2)

A particle beam orbit around which the particle beam circulates, a quadrupole electromagnet that circulates the particle beam along the particle beam orbit, an accelerating cavity that accelerates the particle beam, and the particle beam is taken out from the particle beam orbit. In a circular particle accelerator having an exit septum and a plurality of beam ducts from which particle beams are extracted, a cavity is arranged in series with the particle beam orbit, and electromagnetic waves are introduced into the arranged cavity to A circular particle accelerator comprising a beam kicker that gives a kick angle in a predetermined direction to a particle beam in a high-frequency cavity that excites a TM110 mode having a perpendicular magnetic field component. In the beam kicker, a plurality of cavities are connected and arranged in series in the particle beam orbit, and an electromagnetic wave is introduced into each of the plurality of cavities to excite a TM110 mode having a magnetic field component perpendicular to the particle beam. The circular particle accelerator according to claim 1, wherein the circular particle accelerator is configured by a high-frequency cavity operated in a π mode in which the magnetic field directions of the cavities are staggered.

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