Accelerating Cavities and Accelerating Cavity Systems

Abstract

To suppress the leakage of high-frequency energy within a vacuum vessel, form an intended accelerating electric field in an acceleration gap within the vacuum vessel, and accelerate the charged particle beam as designed.SOLUTION: An acceleration cavity includes a vacuum vessel 11 that is maintained in a vacuum state and includes a beam path 17 through which a charged particle beam passes, and an acceleration gap 18 at a position facing the beam path, an antenna 12 that is installed in the vacuum vessel to guide high frequency energy into the vacuum vessel and accelerate the charged particle beam by forming an accelerating electric field in an acceleration gap, a focusing magnet 13 that is installed outside the vacuum vessel and focuses the charged particle beam flowing within the beam path, and a high frequency blocking structure 14 that is installed in the beam path of the vacuum vessel to block leakage of high frequency energy within the vacuum vessel.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] SUMMARY OF THE INVENTION Embodiments of the present invention relate to acceleration cavities and acceleration cavity systems for accelerating charged particle beams. [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. This is because the electrode bore diameter of an RFQ is small, about 1 cm, and it is therefore not possible to focus and transport high-current ion beams that diverge strongly due to the space charge effect of the beam. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 142389 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-12620 [Patent Document 3] Japanese Patent Application Publication No. 7-37698 [Patent Document 4] Japanese Patent Application Publication No. 8-190997 Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, in order to accelerate a high-current ion beam of 1 A or more, it is expected that the high-current beam can be accelerated by an accelerator composed of multiple single-cell cavities connected together, each having a large-diameter beam duct and a beam focusing element (for example, Patent Document 1).

[0005] In the accelerator described in Patent Document 1, unlike conventional coupled cavity accelerators, radio frequency energy is applied independently to each accelerating cavity, and the output, phase, etc. of the radio frequency energy are adjusted for each accelerating cavity. Furthermore, in the accelerator described in Patent Document 1, unlike RFQ and drift tube linear accelerators (DTL) that are widely used for ion beam acceleration, it is assumed that the accelerating cavities will be connected and arranged at a short distance in order to accelerate the ion beam at a short distance, reduce the space charge effect, and suppress the divergence of the high-current ion beam.

[0006] For this reason, in the accelerator described in Patent Document 1, the high-frequency energy input into an accelerating cavity, which should originally be excited only within a single accelerating cavity, leaks into adjacent accelerating cavities, which causes interference between the high-frequency energies, making it impossible to obtain the expected accelerating electric field, and resulting in a decrease in beam acceleration performance. In particular, the influence of leakage becomes significant for high-frequency energy higher than the reference frequency, as it easily passes through narrow openings.

[0007] Furthermore, unlike the acceleration of low-current beams in conventional accelerators, with high-current ion beams, even slight beam divergence or halo components can have significant effects of activation and heat generation when they collide with the accelerator or surrounding vacuum vessel, posing a problem that can hinder normal operation.

[0008] The embodiments of the present invention have been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide an accelerating cavity and an accelerating cavity system that can suppress leakage of radio frequency energy within a vacuum vessel, form an intended accelerating electric field in an accelerating gap within the vacuum vessel, and accelerate a charged particle beam as designed.

[0009] Another object of the present invention is to provide an acceleration cavity and an acceleration cavity system that can prevent unnecessary heat generation and activation due to collision of a charged particle beam. [Means for solving the problem]

[0010] An acceleration cavity in an embodiment of the present invention is characterized by comprising: a vacuum vessel that is maintained in a vacuum state and that has a beam passage through which a charged particle beam passes and an acceleration gap located at a position facing the beam passage; an antenna that is installed within the vacuum vessel and that introduces radio-frequency energy into the vacuum vessel and forms an acceleration electric field in the acceleration gap to accelerate the charged particle beam; a focusing magnet that is located outside the vacuum vessel and that focuses the charged particle beam flowing within the beam passage; and a radio-frequency blocking structure that is installed in the beam passage of the vacuum vessel and that blocks leakage of radio-frequency energy within the vacuum vessel.

[0011] An accelerating cavity system according to an embodiment of the present invention is characterized in that it is configured by connecting a plurality of accelerating cavities having a high-frequency blocking structure, as described in the above embodiment, in the axial direction of a beam path. [Effects of the Invention]

[0012] According to an embodiment of the present invention, leakage of high frequency energy within a vacuum vessel is suppressed, and an intended acceleration electric field is formed in an acceleration gap within the vacuum vessel, thereby accelerating a charged particle beam as designed. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a longitudinal cross-sectional view showing an acceleration cavity according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional view of an acceleration cavity according to a second embodiment, corresponding to FIG. 2. [Figure 4] FIG. 11 is an enlarged cross-sectional view showing a part of an acceleration cavity according to a third embodiment. [Figure 5] 5 is a cross-sectional view taken along line VV in FIG. 4. [Figure 6] FIG. 10 is an enlarged cross-sectional view showing a part of an acceleration cavity according to a fourth embodiment. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. [Figure 8]FIG. 11 is an enlarged cross-sectional view showing a part of an acceleration cavity according to a fifth embodiment. [Figure 9] 9 is a cross-sectional view taken along line IX-IX in FIG. 8. [Figure 10] FIG. 10 is a longitudinal cross-sectional view showing an acceleration cavity system according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [A] First embodiment (Figs. 1 and 2) Fig. 1 is a longitudinal cross-sectional view of an accelerating cavity according to the first embodiment. The accelerating cavity 10 shown in Fig. 1 accelerates a charged particle beam (not shown), for example, a high-current ion beam of 1 A or more, and includes a vacuum vessel 11, an antenna 12, a focusing magnet 13, and a high-frequency blocking structure 14.

[0015] The vacuum vessel 11 is constructed by joining a pair of conductive gap forming plates 16A and 16B to a vessel body 15, and the interior is maintained in a vacuum state. A beam passage 17 through which a charged particle beam passes is provided inside the vacuum vessel 11, penetrating the vessel body 15 and the gap forming plates 16A and 16B. Furthermore, an acceleration gap 18 for forming an acceleration electric field is provided between the pair of opposing gap forming plates 16A and 16B at a position inside the vacuum vessel 11 facing the beam passage 17.

[0016] The beam passage 17 has an inner diameter D of, for example, 10 cm or more to allow a charged particle beam, such as a high-current ion beam of 1 A or more, to pass through. The axis O of the beam passage 17 is set to coincide with the beam axis P of the charged particle beam. The open end of the beam passage 17 is indicated by the reference symbol 17A.

[0017] Here, gap forming plates 16A and 16B and container body 15 may be fastened together using bolts or the like, or may be integrally formed by, for example, cutting a single conductive ingot. Furthermore, since a high voltage is generated at joints 24 between gap forming plates 16A and 16B and container body 15 when high-frequency energy is introduced by antenna 12, which will be described later, it is preferable to subject joints 24 to curved surface processing (R processing) and further smooth the surface.

[0018] The vacuum vessel 11, which is composed of the gap-forming plates 16A and 16B and the vessel body 15, 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 vessel 11 can be formed by cutting an ingot of oxygen-free copper, tough-pitch copper, or the like, or by joining components formed in this manner. When joining separate 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, to reduce high-frequency surface current loss, it is desirable to install RF (radio frequency) contacts such as finger contacts, particularly between the gap-forming plates 16A and 16B and the vessel body 15.

[0019] Furthermore, a plurality of ports (not shown) are provided in the vacuum vessel 11, particularly in the vessel body 15. These ports may be connected to vacuum pumps such as turbo vacuum pumps, ion pumps, cryopumps, scroll pumps, rotary pumps, etc., and may also be connected to vacuum gauges such as nude ion gauges, cold cathode gauges, Pirani gauges, ionization vacuum gauges, etc. These ports may have slit structures to prevent leakage of high-frequency energy in accordance with the frequency of the high-frequency energy introduced from the antenna 12, as will be described later.

[0020] Antenna 12 is installed within vessel body 15 of vacuum vessel 11, introduces high-frequency energy into vacuum vessel 11, and forms an acceleration electric field in acceleration gap 18. This acceleration electric field accelerates the charged particle beam flowing through beam path 17. That is, antenna 12 is formed into a loop from a metal material such as copper, one end of which is connected to a ground part such as waveguide 19 or flange part 20 of a coaxial cable, and the other end to the core of waveguide 19 or the coaxial cable. This antenna 12 is then connected to a so-called RF amplifier, such as a high-frequency power source and amplifier, via waveguide 19 or the coaxial cable, and introduces high-frequency energy into vacuum vessel 11.

[0021] The waveguide 19 is formed in a circular or rectangular shape, and the coaxial cable has an N-type terminal, a BNC (Bayonet Neill Concelman) terminal, an SHV (Safe High Voltage Connector) terminal, or the like. The earth parts, such as the flange part 20, of these waveguides 19 and coaxial cables are insulated from the core wire by an insulating material such as ceramics, and it is preferable that the surface of this ceramic is coated with TiN or the like for protection. The waveguide 19 and the flange part 20 of the coaxial cable also serve as a vacuum bulkhead, which is a partition wall for the vacuum state inside the vacuum vessel 11.

[0022] The focusing magnet 13 is installed outside the vacuum vessel 11 and focuses the charged particle beam, for example, a high-current ion beam of 1 A or more, flowing through the beam passage 17 inside the vacuum vessel 11. Specifically, this focusing magnet 13 can be configured by arranging one to three solenoid or quadrupole magnets made of permanent magnets or electromagnets in the direction of the beam axis P of the charged particle beam (axis center O of the beam passage 17), repeatedly converging and diverging the beam, thereby focusing the beam as a whole. The electromagnet can be made of a normal conducting material or a superconducting material.

[0023] When a superconducting electromagnet made of a superconducting material is used, it is preferable to provide a magnet vessel 21 containing the focusing magnet 13 adjacent to the vacuum vessel 11. The interior of this magnet vessel 21 is also maintained at a vacuum, maintaining the focusing magnet 13 in a vacuum state. The configuration of the vacuum gauge, vacuum pump, etc. can be similar to that of the vacuum vessel 11. In addition, the superconducting electromagnet is provided with a refrigerator, radiation shield, heat insulating material, etc. to maintain the superconducting state, and current leads, etc. to pass current are connected to it.

[0024] The radio frequency blocking structure 14 is installed in the beam path 17 of the vacuum vessel 11 and is configured as a blocking protrusion 22 that blocks leakage of radio frequency energy within the vacuum vessel 11. That is, the blocking protrusion 22 as the radio frequency blocking structure 14 is formed from a metal material such as iron as is, or by plating the metal material with copper or the like which has high electrical conductivity, or by cutting oxygen-free copper, tough pitch copper, or the like. As shown in Figures 1 and 2, a plurality of blocking protrusions 22 are provided on the inner surface 23 of the beam path 17, for example, at predetermined intervals in the circumferential direction of the beam path 17, protruding toward the axis O of the beam path 17. These blocking protrusions 22 block (suppress) leakage of radio frequency energy within the vacuum vessel 11 to the outside of the vacuum vessel 11.

[0025] As configured as above, the first embodiment provides the following effect (1). (1) Since the blocking protrusion 22 is installed in the beam passage 17 of the vacuum vessel 11 as the high frequency blocking structure 14 that blocks leakage of high frequency energy inside the vacuum vessel 11, even if the inner diameter of the beam passage 17 is large, the blocking protrusion 22 can suppress leakage of high frequency energy inside the vacuum vessel 11. As a result, an intended acceleration electric field is formed by the high frequency energy in the acceleration gap 18 inside the vacuum vessel 11, and this acceleration electric field can accelerate the charged particle beam flowing through the beam passage 17 as designed.

[0026] (B) Second embodiment (Fig. 3) Fig. 3 is a cross-sectional view of an accelerating cavity according to a second embodiment, corresponding to Fig. 2. In this second embodiment, parts similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and descriptions thereof will be simplified or omitted.

[0027] The acceleration cavity 25 of the second embodiment differs from the first embodiment in that the radio-frequency blocking structure 26 is configured as a ring-shaped blocking ring 27 having an opening 28 with an inner diameter d smaller than the inner diameter D of the beam passage 17 of the vacuum vessel 11, and the blocking ring 27 is fixed to the inner surface 23 of the beam passage 17. The inner diameter d of the blocking ring 27 is set to be larger than the diameter of the circular cross section of the charged particle beam passing through the beam passage 17.

[0028] As configured as above, the second embodiment provides the following effect (2) in addition to the effect (1) of the first embodiment.

[0029] (2) The radio frequency blocking structure 26 is configured as a ring-shaped blocking ring 27 fixed to the inner surface 23 of the beam path 17, and the inner diameter d of this blocking ring 27 is set to be larger than the diameter of the circular cross section of the charged particle beam passing through the beam path 17. This prevents the charged particle beam passing through the beam path 17 from colliding with the blocking ring 27. As a result, it is possible to avoid a decrease in the charged particle beam passing through the beam path 17, and also to prevent unnecessary heat generation and radioactivity of the blocking ring 27 and, ultimately, the vacuum vessel 11 due to collision of the charged particle beam with the blocking ring 27.

[0030] [C] Third embodiment (Figs. 4 and 5) 4 is an enlarged cross-sectional view of a portion of an acceleration cavity according to the third embodiment. In the third embodiment, parts similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and descriptions thereof will be simplified or omitted.

[0031] The acceleration cavity 30 of the third embodiment differs from the first and second embodiments in that the high-frequency blocking structure 31 is configured as a ring-shaped blocking ring 32 fixed to the inner surface 23 of the beam passage 17, as in the second embodiment, and the inner diameter t of the opening 33 of this blocking ring 32 is formed to vary along the axis O of the beam passage 17.

[0032] Specifically, when the charged particle beam passing through the beam path 17 diverges in the traveling direction, the opening 33 of the blocking ring 32 is formed into a tapered shape by setting the inner diameter t to be smaller on the entrance side of the beam and larger on the exit side. As a result, the blocking ring 32 is set to a dimension that protrudes maximally toward the axis O of the beam path 17 in order to block leakage of high frequency energy inside the vacuum vessel 11 while avoiding collision with the charged particle beam passing through the beam path 17.

[0033] As configured as described above, the third embodiment achieves the same effects as the effects (1) and (2) of the first and second embodiments, as well as the following effects (3) and (4).

[0034] (3) The opening 33 of the blocking ring 32 fixed to the inner surface 23 of the beam path 17 is formed in a tapered shape with its inner diameter t decreasing on the inlet side of the charged particle beam. Therefore, the blocking ring 32 is set to protrude to the maximum extent toward the axial center O of the beam path 17 while avoiding collision with the charged particle beam flowing through the beam path 17. As a result, the blocking ring 32 can suppress leakage of high-frequency energy within the vacuum vessel 11 even if the high-frequency energy has a higher frequency.

[0035] (4) The opening 33 of the shield ring 32 fixed to the inner surface 23 of the beam path 17 is tapered so that its inner diameter t decreases on the inlet side of the charged particle beam. Therefore, the shield ring 32 is set to protrude as far as possible toward the axial center O of the beam path 17 while avoiding collision with the charged particle beam flowing through the beam path 17, and is configured to have a large heat capacity. Therefore, even if the charged particle beam passing through the beam path 17 slightly collides with the shield ring 32, the heat generated in the shield ring 32 can be diffused. As a result, the shield ring 32 can have excellent resistance to temperature rise.

[0036] [D] Fourth embodiment (Figs. 6 and 7) 6 is an enlarged cross-sectional view of a portion of an acceleration cavity according to the fourth embodiment. In this second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0037] The acceleration cavity 40 of the fourth embodiment differs from the first embodiment in that, as shown in Figures 6 and 7, the high-frequency blocking structure 41 is composed of multiple rectangular blocking sections 42 that are divided circumferentially around the beam path 17, and these blocking sections 42 are configured to be movable in the radial direction of the beam path 17 by a driving mechanism 43.

[0038] That is, the blocking portions 42 are made of conductive plates such as metal, and a plurality of them are arranged in the non-passage region of the beam passage 17, excluding the passage region of the charged particle beam having a circular cross section. The plurality of blocking portions 42 do not need to be arranged densely without gaps in the non-passage region, as long as they can block a large region that is prone to leak high-frequency energy. Furthermore, the plurality of blocking portions 42 are preferably arranged offset in the direction of the axis O of the beam passage 17, but may also be arranged so as to overlap each other.

[0039] The drive mechanism 43 has, for example, drive rods 44 or drive bellows attached to each of the cutoff portions 42 via Wilson seals (not shown), and a drive motor 45 (e.g., an induction motor or a stepping motor) connected to the drive rods 44 or drive bellows and installed outside the vacuum vessel 11, and drives the cutoff portions 42 from outside the vacuum vessel 11 while maintaining the vacuum vessel 11 in a vacuum state. Alternatively, the drive mechanism 43 may use an introducer (not shown) to manually drive the cutoff portions 42 from outside the vacuum vessel 11 while maintaining the vacuum vessel 11 in a vacuum state.

[0040] The drive motor in the drive mechanism 43 may be installed inside the vacuum vessel 11. The drive motor 45 in the drive mechanism 43 is not limited to a case where each of the drive motors drives a plurality of the cutoff portions 42, but one drive motor may drive a plurality of the cutoff portions 42.

[0041] As configured as above, the fourth embodiment provides the following effect (5) in addition to the effect (1) of the first embodiment.

[0042] (5) The radio frequency blocking structure 41 is configured so that the multiple blocking portions 42, which are divided in the circumferential direction of the beam path 17, can be moved in the radial direction of the beam path 17 by a drive mechanism 43. Therefore, even if the charged particle beam flowing through the beam path 17 has a beam size different from that at the time of design, the multiple blocking portions 42 can be moved in the radial direction of the beam path 17 to match the beam size of the charged particle beam, thereby preventing collisions between the charged particle beam and the blocking portions 42. As a result, it is possible to avoid a decrease in the charged particle beam passing through the beam path 17, and to prevent unnecessary heating and activation of the blocking portions 42 and, ultimately, the vacuum vessel 11 due to collisions of the charged particle beam with the blocking portions 42.

[0043] [E] Fifth embodiment (Figs. 8 and 9) 8 is an enlarged cross-sectional view of a portion of an acceleration cavity according to the fifth embodiment. In the fifth embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0044] The acceleration cavity 50 of the fifth embodiment differs from the first embodiment in that, as shown in Figures 8 and 9, the high-frequency blocking structure 51 is composed of multiple rectangular blocking sections 52 divided circumferentially around the beam path 17, and an insulator 53 is interposed between the blocking sections 52 and the beam path 17 of the vacuum vessel 11, so that the blocking sections 52 and the beam path 17 are at different potentials.In addition, an electrical signal generated at the blocking section 52 when a charged particle beam collides with the blocking section 52 can be extracted to the outside of the vacuum vessel 11 by a measuring device 54.

[0045] The blocking portion 52 is configured and installed in the same manner as the blocking portion 42 of the fourth embodiment. The insulator 53 is made of alumina ceramics, Teflon (registered trademark), Delrin (registered trademark), glass epoxy resin, Reny, or the like. A conductive anti-electrostatic member 55 is installed on the inner surface 23 of the beam passage 17, upstream of the insulator 53 with respect to the charged particle beam. The anti-electrostatic member 55 prevents the insulator 53 from being directly irradiated with the charged particle beam and from being charged up.

[0046] The measuring device 54 is configured to include a lead wire 56 connected to the interrupting portion 52, a feedthrough 57 installed in the beam path 17 of the vacuum vessel 11 and connected to the lead wire 56, a coaxial cable 58 connected to the feedthrough 57 and equipped with an N-type terminal, a BNC terminal, an SHV terminal, etc., and a signal processing unit 59 to which the coaxial cable 58 is connected. The signal processing unit 59 includes an oscilloscope, an ADC (Analog to Digital Converter), a TDC (Timing to Digital Converter), etc.

[0047] Here, as in the fourth embodiment, the blocking portion 52 may be configured to be movable in the radial direction of the beam passage 17 by a drive motor 45 via a drive rod 44, in which case the drive rod 44 is made of an insulator (insulating material).

[0048] As configured as above, the fifth embodiment provides the same effect as effect (1) of the first embodiment, as well as the following effect (6).

[0049] (6) An insulator 53 is interposed between the blocking portion 52 and the beam path 17 of the vacuum vessel 11, and the blocking portion 52 and the beam path 17 are configured to have different potentials, and an electrical signal generated in the blocking portion 52 by the collision of the charged particle beam can be measured by the measuring device 54. Therefore, even if the charged particle beam flowing through the beam path 17 has a beam size different from that at the time of design, the measuring device 54 can measure the beam intensity of the charged particle beam that has collided with the blocking portion 52.

[0050] Therefore, if the blocking part 52 can be moved in the radial direction of the beam path 17 by the drive motor 45 or the like, the blocking part 52 can be adapted to the beam size of the charged particle beam by adjusting the movement amount of the blocking part 52 based on the measurement value of the measurement device 54. Alternatively, by adjusting the output and phase of the high frequency energy introduced into the vacuum vessel 11 by the antenna 12 based on the measurement value of the measurement device 54, operations such as focusing and acceleration of the charged particle beam can be optimized.

[0051] [F] Sixth embodiment (Fig. 10) 10 is a longitudinal cross-sectional view showing an acceleration cavity system according to the sixth embodiment. In the sixth embodiment, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0052] The acceleration cavity system 60 of the sixth embodiment is configured by connecting multiple acceleration cavities 10, 25, 30, 40, and 50 (for example, acceleration cavity 10 in Figure 10) of the first to fifth embodiments directly or indirectly using a vacuum duct 61 in the direction of the axis O of the beam passage 17 (i.e., the beam axis P of the charged particle beam).

[0053] As configured as above, the sixth embodiment provides the following effect (7). (7) Each of the accelerating cavities 10, 25, 30, 40, and 50 (e.g., accelerating cavity 10) is provided with a radio-frequency blocking structure 14, 26, 31, 41, and 51 (e.g., radio-frequency blocking structure 14). Therefore, leakage of radio-frequency energy within, for example, one accelerating cavity 10 can be suppressed not only by the radio-frequency blocking structure 14 of that accelerating cavity 10, but also by the radio-frequency blocking structure 14 of an adjacent accelerating cavity 10. As a result, leakage of radio-frequency energy from each of the accelerating cavities 10, 25, 30, 40, and 50 constituting the accelerating cavity system 60 can be reliably prevented.

[0054] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the spirit of the invention. Furthermore, such substitutions, changes, and combinations are included in the scope and spirit of the invention, and are also included in the inventions and their equivalents as set forth in the claims. [Explanation of symbols]

[0055] 10...acceleration cavity, 11...vacuum vessel, 12...antenna, 13...focusing magnet, 14...high frequency blocking structure, 17...beam passage, 18...acceleration gap, 22...blocking protrusion, 25...acceleration cavity, 26...high frequency blocking structure, 27...blocking ring, 28...opening, 30...acceleration cavity, 31...high frequency blocking structure, 32...blocking ring, 33...opening, 40...acceleration cavity, 41...high frequency blocking structure, 42...blocking portion, 43...driving mechanism, 50...acceleration cavity, 51...high frequency blocking structure, 52...blocking portion, 53...insulator, 54...measuring device, D, d, t...inner diameter

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 that is located 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; a high frequency blocking structure that is installed in the beam path of the vacuum vessel and blocks leakage of high frequency energy within the vacuum vessel.

2. 2. The accelerating cavity according to claim 1, wherein the high frequency blocking structure is configured as a ring-shaped blocking ring having an opening with an inner diameter smaller than the inner diameter of the beam passage of the vacuum vessel.

3. 3. An accelerating cavity according to claim 2, wherein an inner diameter of the opening in said blocking ring is formed to vary along the axial direction of the beam passage.

4. 2. The accelerating cavity according to claim 1, wherein the high-frequency blocking structure is composed of a plurality of blocking sections divided in the circumferential direction of the beam path, and these blocking sections are configured to be movable in the radial direction of the beam path by a driving mechanism.

5. 5. The accelerating cavity according to claim 1, wherein an insulator is interposed between the high-frequency blocking structure and the beam path of the vacuum vessel, the high-frequency blocking structure and the vacuum vessel are configured to have different potentials, and an electrical signal generated in the high-frequency blocking structure can be extracted outside the vacuum vessel.

6. 3. An accelerating cavity system comprising a plurality of accelerating cavities having the high frequency blocking structure according to claim 1 or 2 connected in the axial direction of a beam path.

7. 5. An accelerating cavity system comprising a plurality of accelerating cavities having the high frequency blocking structure according to claim 3 or 4 connected in the axial direction of a beam path.

8. An accelerating cavity system, comprising a plurality of accelerating cavities having the high frequency blocking structure according to claim 5 connected in the axial direction of a beam path.

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