Accelerator System

Abstract

To provide an accelerator system that can increase the diameter of a beam passage and reduce the power consumption.SOLUTION: There is provided an accelerator system according to an embodiment in which a plurality of acceleration cavities are connected with each other in the axial direction of a charged particle beam, the plurality of acceleration cavities including: a vacuum vessel that is held in the vacuum state and has a beam passage through which the charged particle beam passes and an acceleration gap at a position facing the beam passage; an antenna that is installed in the vacuum vessel to direct high-frequency energy into the vacuum vessel and forms an acceleration electric field in the acceleration gap to accelerate the charged particle beam; and a convergent magnet that is arranged outside the vacuum vessel and converges the charged particle beam flowing in the beam passage. The average aperture of the beam passage of a first acceleration cavity located on the upstream side in the axial direction in the acceleration cavities is larger than the average aperture of the beam passage of a second acceleration cavity located on the downstream side in the axial direction with respect to the first acceleration cavity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to accelerator systems. [Background technology]

[0002] Radio frequency quadrupole linear accelerators (RFQs), which are widely used as primary accelerators, have difficulty accelerating high-current ion beams of 1 A or more because the electrode bore diameter of an RFQ is small, on the order of millimeters, and the beam cannot be focused and transported due to divergence caused by the space charge effect. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 142389 Summary of the Invention [Problem to be solved by the invention]

[0004] By increasing the diameter of the beam passage, the beam size passing through it can be enlarged, suppressing the space charge effect and increasing the beam current that can be accelerated. However, increasing the diameter of the beam passage increases the power consumption required to accelerate the beam, which places restrictions on increasing the diameter of the beam passage and accelerating the beam.

[0005] The problem to be solved by the present invention is to provide an accelerator system that allows for a large diameter beam passage and reduced power consumption. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, an embodiment of the accelerator system is an accelerator system in which a plurality of acceleration cavities are connected in the axial direction of the charged particle beam, each of the acceleration cavities comprising: a vacuum vessel maintained in a vacuum state and having a beam passage through which a charged particle beam passes and an acceleration gap located at a position facing the beam passage; an antenna installed within the vacuum vessel for introducing radio frequency energy into the vacuum vessel and forming an acceleration electric field in the acceleration gap to accelerate the charged particle beam; and a focusing magnet located outside the vacuum vessel for focusing the charged particle beam flowing in the beam passage, wherein the average diameter of the beam passage of a first acceleration cavity located upstream in the axial direction is larger than the average diameter of the beam passage of a second acceleration cavity located downstream in the axial direction of the first acceleration cavity. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing an example of the configuration of an accelerator system according to a first embodiment. [Figure 2] FIG. 10 is a cross-sectional view showing a configuration example of an accelerator system according to a modified example of the first embodiment. [Figure 3] FIG. 10 is a cross-sectional view showing a configuration example of an accelerator system according to a modified example of the first embodiment. [Figure 4] FIG. 10 is a cross-sectional view showing a configuration example of an accelerator system according to a modified example of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments for carrying out the invention will be described.

[0009] (First embodiment) FIG. 1 is a cross-sectional view showing an example of the configuration of an accelerator system 1 according to the first embodiment. The accelerator system 1 includes a first acceleration cavity 10A and a second acceleration cavity 10B. In the following description, when it is not necessary to distinguish between the first acceleration cavity 10A and the second acceleration cavity 10B, they will be simply referred to as acceleration cavities 10. The acceleration cavities 10 include a vacuum vessel 12, an antenna 18, and a focusing magnet 24. Note that although an example in which the accelerator system 1 includes two acceleration cavities 10 is described here, the accelerator system 1 may include three or more acceleration cavities 10.

[0010] The vacuum vessel 12 is constructed by joining a vessel body 14 and a pair of conductive gap forming plates 16, and the interior is maintained in a vacuum state. A beam passage 40 is provided inside the vacuum vessel 12, through which a charged particle beam passes, penetrating the vessel body 14 and the gap forming plates 16. An acceleration gap 42, which is a space for forming an acceleration electric field, is provided between the pair of gap forming plates 16 at a position facing the beam passage 40.

[0011] The container body 14 and the gap forming plate 16 may be fastened together using bolts or the like, or may be formed integrally by cutting a single conductive ingot. Because a high voltage is generated at the joint between the container body 14 and the gap forming plate 16 when high-frequency energy is introduced from the antenna 18 (described later), it is preferable to perform curved processing (R processing) to smooth the surface.

[0012] The vacuum vessel 12, which is composed of the vessel body 14 and the gap-forming plate 16, can be manufactured by machining a metal material such as iron and then plating it with copper or other materials with high electrical conductivity. Alternatively, the entire vessel can be machined from an ingot of oxygen-free copper or tough-pitch copper, or by connecting components formed in this way. When connecting independent components, vacuum sealing is preferably performed using metal packing such as a metal gasket, rubber O-ring, or indium ring to prevent vacuum leakage. Furthermore, it is preferable to provide RF (radio frequency) contacts such as finger contacts between the components to reduce loss of surface current of high-frequency energy.

[0013] The vacuum vessel 12, particularly the vessel body 14, may be provided with multiple ports (not shown). These ports may be connected to vacuum pumps such as turbo vacuum pumps, ion pumps, cryopumps, scroll pumps, and rotary pumps, and may also be connected to vacuum gauges such as nude ion gauges, cold cathode gauges, Pirani gauges, and ionization vacuum gauges. Furthermore, analyzers such as quadrupole mass spectrometers may be connected to analyze the components of the gas inside the accelerating cavity 10. These ports may also be provided with slit structures to prevent leakage of high-frequency energy introduced from the antenna 18.

[0014] The beam passage 40 is made of a conductive metal and has a cylindrical shape, a rectangular parallelepiped shape, or a tapered shape thereof. To allow a high-current beam, e.g., 1 A or more, to pass through as a charged particle beam, its inner diameter is set to, e.g., 100 mm or more. The axis of the beam passage 40 is aligned with the beam axis P of the charged particle beam. The charged particle beam is accelerated in the direction of the beam axis P indicated by the arrow in FIG. 1 and passes through the beam passage 40. In the following description, the diameter of the cross section of the beam passage 40 perpendicular to the beam axis P direction will be referred to as the aperture of the beam passage 40. Furthermore, when the size of this aperture is mentioned, it is also intended to mean the size of the cross-sectional area.

[0015] The antenna 18 is provided inside the container body 14 and is formed into a loop from a metal material such as copper, with one end connected to a grounding portion such as a waveguide 22 (described later) or a flange 20 of a coaxial cable (not shown), and the other end connected to the waveguide 22 or the core wire of the coaxial cable. The grounding portion and core wire of the flange 20 are insulated by an insulating material such as ceramic. The ceramic surface is preferably protected by a coating such as TiN.

[0016] The flange 20 also serves as a vacuum bulkhead for the vacuum vessel 12, and on the atmospheric side, a circular or rectangular waveguide 22 and a coaxial cable such as an N terminal, a BNC (Bayonet Neill-Concelman) terminal, or an SHV (Safe High Voltage Connector) terminal are connected, and further on, a so-called RF amplifier (not shown) such as a high-frequency power supply and amplifier is connected. In other words, the antenna 18 is connected to an RF lamp such as a high-frequency power supply and amplifier via the waveguide 22 or the coaxial cable, and introduces high-frequency energy into the vacuum vessel 12. Introducing the high-frequency energy into the vacuum vessel 12 forms an acceleration electric field in the acceleration gap 42, accelerating the charged particle beam flowing through the beam path 40 in the direction of the beam axis P.

[0017] The high frequency power source may be a vacuum tube, klystron, semiconductor amplifier, etc. A signal generator that generates a reference signal to control the high frequency power source, or a low level control device may be provided. Furthermore, a dummy load, circulator, etc. may be connected.

[0018] Note that one RF power supply may be provided for multiple accelerating cavities 10, or one RF power supply may be provided for each accelerating cavity 10. For example, in FIG. 1, a first RF power supply may be connected to the antenna 18 (first antenna) of the first accelerating cavity 10A, and a second RF power supply may be connected to the antenna 18 (second antenna) of the second accelerating cavity 10B. By providing independent RF power supplies for each of the multiple accelerating cavities 10, the strength and phase of the accelerating electric field generated in the accelerating gap 42 can be adjusted for each accelerating cavity 10. In addition to manual adjustment, automatic frequency adjustment, automatic phase adjustment, and the like can be applied via low-level control.

[0019] The focusing magnet 24 is a solenoid magnet or quadrupole magnet made up of a permanent magnet or an electromagnet, and is arranged outside the vacuum vessel 12. One or more focusing magnets 24 are arranged in the direction of the beam axis P, and may focus the charged particle beam as a whole by repeatedly converging and diverging the beam. The focusing magnet 24 may be made of a normal conducting material or a superconducting material.

[0020] When the focusing magnet 24 is made of a superconducting material, it is preferable to provide a focusing cavity 26 containing the focusing magnet 24 adjacent to the vessel body 14. The interior of the focusing cavity 26 is a vacuum, and a vacuum gauge and a vacuum pump may be provided in a configuration similar to that of the vessel body 14. The superconducting magnet is also provided with a refrigerator, a radiation shield, a heat insulator, etc. for maintaining the superconducting state, and is connected to lead wires, etc. for passing a current (all not shown).

[0021] A plurality of the above-described accelerating cavities 10 are provided and connected in the direction of the beam axis P. The accelerating cavities 10 may be directly connected to each other, or a portion of the vacuum vessel 12 may be formed as a common element for each of the accelerating cavities 10, and the plurality of accelerating cavities 10 may be assembled to form each of the accelerating cavities 10.

[0022] In any of the adjacent accelerating cavities 10, the average diameter of the beam passage 40 of the upstream accelerating cavity 10 is larger than the average diameter of the beam passage 40 of the downstream accelerating cavity 10. The average diameter of the beam passage 40 is the average diameter (average or average cross-sectional area) of a cross section perpendicular to the beam axis P. That is, in FIG. 1 , the average diameter of the beam passage 40 of the first accelerating cavity 10A is larger than the average diameter of the beam passage 40 of the second accelerating cavity 10B.

[0023] In the present embodiment configured as described above, the average diameter on the upstream side of the beam passage 40, where the divergence force of the charged particle beam due to the space charge effect is strong, is configured to be larger than the average diameter on the downstream side. That is, by increasing the average diameter on the upstream side of the beam passage 40, collisions between the charged particle beam and the beam passage 40 due to divergence of the charged particle beam are suppressed. Furthermore, on the downstream side of the beam passage 40, where the charged particle beam is accelerated and a higher acceleration voltage is required, the divergence force decreases as the charged particle beam accelerates, so that the average diameter can be reduced while suppressing collisions between the charged particle beam and the beam passage 40. This allows the charged particle beam to be accelerated while reducing the power consumption when introducing radio frequency energy.

[0024] As a modification of this embodiment, as shown in FIG. 2 , a duct 28 may be provided between the first accelerating cavity 10A and the second accelerating cavity 10B, and the first accelerating cavity 10A and the second accelerating cavity 10B may be connected via this duct 28. The accelerating cavity 10A and the duct 28 are connected via a vacuum-sealable structure. The diameter of the duct 28 may be equal to or larger than the diameter of the upstream connection of the beam path 40, and may be tapered from the upstream side toward the downstream side. The duct 28 may be a cylindrical or rectangular container, or a container with individual ports (not shown) in a direction different from the beam axis P, such as a tee or cross. The ports allow connection of various monitors (not shown) for monitoring the status of the beam, such as a current detector (e.g., a Faraday cup or a current transformer), a profile monitor / position detector (e.g., a combination of an insulated metal plate, a wire monitor, a fluorescent screen, and a camera), or an emittance monitor (e.g., a pepper pot type). The ports may also be provided with slits (not shown) for blocking part or all of the charged particle beam. These monitors and slits are configured so that they can be inserted into and removed from the area through which the charged particle beam passes by a linear introducer, etc. Various vacuum gauges, vacuum pumps, gate valves for vacuum sealing, etc. (not shown) may also be connected.

[0025] This modification not only provides the same effects as the first embodiment, but also makes it possible to monitor the charged particle beam, vacuum state, etc., and adjust the operation of the accelerator system 1 based on the results.

[0026] As another modification of this embodiment, a movable inner wall 30 may be provided in the beam passage 40 of the vacuum vessel 12, as shown in FIG. 3 . The movable inner wall 30 is the inner wall of the beam passage 40 and is composed of, for example, a metallic inner wall 32 and a position adjustment mechanism 34 that supports it. The inner wall 32 comes into contact with the vacuum vessel 12 via an RF contact or the like, and is configured so that high-frequency energy can be conducted across its surface. The position adjustment mechanism 34 is composed of, for example, a manipulator, screws, etc., and can be controlled from the outside. The movable inner wall 30 can change the diameter of the beam passage 40 by adjusting the position of the inner wall 32 with the position adjustment mechanism 34.

[0027] This modification not only provides the same effects as the first embodiment, but also makes it possible to arbitrarily adjust the diameter of the beam passage 40 while monitoring the power consumption and the transmittance, size, and other conditions of the charged particle beam. Furthermore, since the diameter of the beam passage 40 can be arbitrarily adjusted, even if accelerating cavities 10 each having a beam passage 40 with the same diameter are configured, the same effects as the first embodiment can be obtained by adjusting the diameter of the beam passage 40 using the movable inner wall 30 after assembly.

[0028] As a further modification of this embodiment, as shown in FIG. 4 , the diameter of the beam passage 40 of each accelerating cavity 10 may be larger at its upstream end 44 in the direction of the beam axis P than at its downstream end 46. While the diameter changes continuously from the upstream end 44 to the downstream end 46 in FIG. 4 , it may also change intermittently. This can be achieved, for example, by changing the diameter of the beam passage 40 during the cutting process of forming the beam passage 40. The diameter of the beam passage 40 can be changed from upstream to downstream by reducing the radius of the circular cross section if the cross section of the beam passage 40 is circular; by changing the reduction rates of the major and minor axes in the direction of the beam axis P if the cross section is elliptical; or by changing the reduction rates in each direction in the cross section if the cross section is rectangular or trapezoidal.

[0029] According to this modification, in addition to the same effects as those of the first embodiment, the diameter can be made smaller toward the downstream side of the beam passage 40, so that the power consumption in the acceleration cavity 10 can be further reduced.

[0030] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0031] 1...accelerator system, 10...acceleration cavity, 10A...first acceleration cavity, 10B...second acceleration cavity, 12...vacuum vessel, 14...vessel body, 16...gap forming plate, 18...antenna, 20...flange, 22...waveguide, 24...focusing magnet, 26...focusing cavity, 28...duct, 30...movable inner wall, 32...inner wall, 34...position adjustment mechanism, 40...beam passage, 42...acceleration gap, 44...upstream end, 46...downstream end.

Claims

1. a vacuum vessel that is maintained in a vacuum state and has a beam passage through which a charged particle beam passes and an acceleration gap at a position facing the beam passage; an antenna installed in the vacuum vessel to introduce high frequency energy into the vacuum vessel and form an accelerating electric field in the acceleration gap to accelerate the charged particle beam; a focusing magnet disposed outside the vacuum vessel and configured to focus the charged particle beam flowing through the beam passage; An accelerator system in which a plurality of accelerating cavities comprising the above are connected in the axial direction of the charged particle beam, an average diameter of a beam passage of a first accelerating cavity located upstream in the axial direction among the accelerating cavities is larger than an average diameter of a beam passage of a second accelerating cavity located downstream in the axial direction than the first accelerating cavity.

2. 2. The accelerator system according to claim 1, wherein the acceleration cavity includes a movable inner wall in the beam passage of the vacuum vessel, the movable inner wall being capable of changing the diameter of the beam passage by adjusting its position.

3. 2. The accelerator system according to claim 1, wherein the diameter of the upstream end of the beam passage in the axial direction is larger than the diameter of the downstream end.

4. 4. The accelerator system according to claim 3, wherein a diameter of the beam passage continuously decreases from the upstream end toward the downstream end.

5. 5. The accelerator system according to claim 1, further comprising a duct maintained in a vacuum state between the first acceleration cavity and the second acceleration cavity.

6. a first radio frequency power supply connected to a first antenna included in the first accelerating cavity; a second radio frequency power supply connected to a second antenna included in the second accelerating cavity; 5. The accelerator system according to claim 1, further comprising:

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