Acceleration cavity

Abstract

This acceleration cavity is a cylindrical shape having conductivity, and includes: a housing in which division members divided into a plurality of parts in a plane along a central axis are provided in a state of facing each other with a gap between the division surfaces; a plurality of cell parts which are arranged inside the housing in a state of being aligned in an axial direction of the central axis of the housing, and which are in communication with each other by a communication part capable of passing charged particles; and a switch member which is arranged in a gap of the housing, is movable in the gap along the plane, and switches the magnitude of an electric field for accelerating the charged particles by movement.

Description

acceleration cavity

[0001] The present disclosure relates to acceleration cavities.

[0002] When a high frequency wave is input into an accelerating cavity, the accelerating cavity generates an accelerating electric field therein, thereby accelerating charged particles such as electrons. For example, a known configuration of such an accelerating cavity includes a plurality of cells arranged in the axial direction of a central axis, and the cells are connected to each other by communication portions (see, for example, Patent Document 1).

[0003] Japanese Unexamined Patent Publication No. 1-107499

[0004] For the above-mentioned accelerating cavities, a configuration has been proposed that allows the energy of charged particles to be switched by changing the magnitude of the accelerating electric field. For such accelerating cavities, a configuration that allows the energy of charged particles to be switched without using a complex mechanism is required.

[0005] The present disclosure has been made in view of the above, and aims to provide an acceleration cavity that can switch the energy of charged particles without using a complicated mechanism.

[0006] The acceleration cavity according to the present disclosure comprises a cylindrical, electrically conductive housing in which a plurality of divided members are arranged along a plane along a central axis, with the divided surfaces along the plane facing each other with a gap therebetween; a plurality of cell sections arranged inside the housing in a line along the axial direction of the central axis of the housing and connected to each other by communication sections that allow charged particles to pass through; and a switch member arranged in the gap in the housing, movable through the gap along the plane, and that switches the magnitude of the electric field that accelerates the charged particles as it moves.

[0007] According to the present disclosure, it is possible to provide an acceleration cavity capable of switching the energy of charged particles without using a complicated mechanism.

[0008] FIG. 1 is a plan view showing an example of an acceleration cavity according to an embodiment. FIG. 2 is a diagram showing a configuration along the A-A cross section in FIG. 1 . FIG. 3 is a diagram showing a configuration along the B-B cross section in FIG. 2 . FIG. 4 is a diagram showing an example of a configuration for moving a switch member. FIG. 5 is a diagram showing an example of a configuration for moving a switch member. FIG. 6 is a diagram showing an example of a configuration for moving a switch member. FIG. 7 is a diagram showing an example of a configuration for moving a switch member. FIG. 8 is a diagram showing an example of a configuration for moving a switch member. FIG. 9 is a diagram showing an example of a configuration for moving a switch member. FIG. 10 is a diagram showing another example of an acceleration cavity. FIG. 11 is a diagram showing an example of a usage mode of the acceleration cavity. FIG. 12 is a diagram showing an example of a usage mode of the acceleration cavity.

[0009] Hereinafter, embodiments of an acceleration cavity according to the present disclosure will be described with reference to the accompanying drawings. However, the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially identical.

[0010] Fig. 1 is a plan view showing an example of an acceleration cavity 100 according to this embodiment. Fig. 2 is a diagram showing the configuration along the cross section A-A in Fig. 1. Note that Fig. 2 shows the dividing surface 12 with hatching, although it is not a cross section. Fig. 3 is a diagram showing the configuration along the cross section B-B in Fig. 2.

[0011] The accelerating cavity 100 shown in FIGS. 1 to 3 generates an accelerating electric field therein when a radio frequency is input from a radio frequency input unit WI, and accelerates charged particles M, such as electrons, emitted from a radiation source BS. The accelerating cavity 100 and the radiation source BS constitute an accelerator AC. Accelerators AC are used in various fields, such as academic fields such as high-energy physics experiments and synchrotron radiation facilities, medical fields such as radiation therapy and testing, and industrial fields such as non-destructive testing. In the following description, when describing the axial direction of the central axis AX of the accelerating cavity 100, the radiation source BS side (the side where charged particles M are incident) is referred to as the entrance side or rear, and the side opposite the entrance side (the side where charged particles are exited) is referred to as the exit side or front. Furthermore, when the accelerating cavity 100 is installed in a facility, the vertical direction is referred to as the up-down direction, and the direction perpendicular to the up-down direction when viewed from the rear of the central axis AX to the front is referred to as the left-right direction.

[0012] As shown in FIGS. 1 to 3 , the acceleration cavity 100 according to this embodiment includes a housing 10 , a cell unit 20 , a coupling cavity 30 , a vacuum manifold 40 , and a switch member 50 .

[0013] The housing 10 has a conductive cylindrical shape. The housing 10 is formed by joining multiple divided members 11. The divided members 11 have planar dividing surfaces 12 along the central axis AX. The divided members 11 are joined with the dividing surfaces 12 facing each other. The divided members 11 are arranged with a gap 13 between the opposing dividing surfaces 12. In this embodiment, an example will be described in which the housing 10 is divided in the left-right direction of the central axis AX along a plane that is perpendicular to the horizontal plane and passes through the central axis AX. The number of divided parts of the housing 10 is not limited to two, and may be three or more. The divided members 11 have a generally rounded shape at the portions that face each other. This suppresses localized application of voltage.

[0014] The cell units 20 are formed inside the housing 10. The cell units 20 are arranged side by side in the axial direction of the central axis AX of the housing 10. The cell units 20 are connected to each other by communication units 22 that allow charged particles to pass through. The communication units 22 are formed along the central axis AX. The cell units 20 accelerate the charged particles by high frequency waves.

[0015] The coupling cavities 30 connect adjacent cell units 20. The coupling cavities 30 propagate high frequency waves between adjacent cell units 20. The coupling cavities 30 are arranged in locations that do not contribute to the acceleration of charged particles. The coupling cavities 30 are arranged outside the cell units 20 in the same direction perpendicular to the central axis AX. In this embodiment, all of the coupling cavities 30 are arranged above the cell units 20 with respect to the central axis AX. The coupling cavities 30 include a first space 31 connected to the cell units 20, a second space 32 arranged at a position radially outwardly of the first space 31 with respect to the central axis AX, and a connecting portion 33 connecting the first space 31 and the second space 32 in the radial direction. The first space 31, the second space 32, and the connecting portion 33 are, for example, cylindrical in shape with an axis extending in the up-down direction as their center. The first space 31, the second space 32, and the connecting portion 33 may be in the shape of a rectangular prism, etc. The connecting portion 33 has a smaller diameter centered in the vertical direction than the first space 31 and the second space 32.

[0016] The vacuum manifold 40 is a part that creates negative pressure when evacuating the multiple cell units 20. The vacuum manifold 40 is connected to a vacuum creating unit 42, such as a vacuum pump, via piping 43. In this embodiment, the vacuum manifold 40 is provided, for example, inside the housing 10. The vacuum manifold 40 is formed as a single space and is disposed above each of the coupling cavities 30. The vacuum manifold 40 is connected to the multiple cell units 20 via the gaps 13 between the dividing members 11. Each cell unit 20 is connected to one vacuum manifold 40. In this embodiment, the vacuum manifold 40 is also connected to the coupling cavities 30 via a communication unit 45. Therefore, the vacuum manifold 40 is connected to the second space 32 of each coupling cavity 30, and the second space 32 is connected to the multiple cell units 20 via the coupling cavities 30. This configuration ensures a reliable connection between the vacuum manifold 40 and the multiple cell units 20.

[0017] As shown in Figure 2, in the housing 10, the dividing surface 12 of each dividing member 11 is formed with a unit cell portion 21 and a unit communicating portion 23 that form part of the cell portion 20 and the communicating portion 22, a unit connecting cavity 35 that forms part of the connecting cavity 30, and a unit manifold 41 that forms part of the vacuum manifold 40.

[0018] The cell section 20 is formed by combining unit cell sections 21 provided in each divided member 11. The communication section 22 is formed by combining unit communication sections 24 provided in each divided member 11. The coupling cavity 30 is formed by combining unit coupling cavities 35 provided in each divided member 11. The vacuum manifold 40 is formed by combining unit manifolds 41 formed in each divided member 11.

[0019] The switch member 50 is disposed in the gap 13 of the housing 10. The switch member 50 is movable in the gap 13 along a plane passing through the central axis AX. In this embodiment, the switch member 50 is movable in the gap 13 along a plane passing through the central axis AX and perpendicular to the left-right direction. The switch member 50 switches the magnitude of the electric field that accelerates the charged particles as it moves. By switching the magnitude of the electric field with the switch member 50, the magnitude of the energy of the charged particles can be switched.

[0020] The switch member 50 is formed using a conductor such as metal. The switch member 50 is, for example, plate-shaped and thinner than the dimension of the gap 13. The switch member 50 is arranged so as to appear and disappear from the coupling cavity 30. When the switch member 50 is arranged in a state where it is inserted inside the coupling cavity 30, it is able to block the electromagnetic field of the coupling cavity 30. The switch member 50 is movable between a retracted position P1 where it is retracted from the coupling cavity 30 and a blocking position P2 where it is inserted inside the coupling cavity 30. In this embodiment, the blocking position P2 can be set to a position where it is inserted into the connection portion 33 of the coupling cavity 30.

[0021] The switch member 50 is coupled to a transmission mechanism 51. The transmission mechanism 51 is connected to the outside of the housing 10. The transmission mechanism 51 transmits a driving force generated outside the housing 10 to the switch member 50. The driving force to be transmitted to the switch member 50 may be generated manually by an operator, for example, or may be generated by a driving source such as a motor.

[0022] 4 to 9 are diagrams showing examples of a configuration for moving the switch member 50. Figures 4, 6 and 8 are plan views. Figures 5, 7 and 9 are diagrams showing a configuration along the AA cross section of Figure 1.

[0023] In the example shown in FIGS. 4 and 5 , the switch member 50 is configured to rotate around a rotation axis BX perpendicular to the central axis AX. The rotation axis BX is set along the left-right direction. In this example, the transmission mechanism 51A is formed in a rod shape and extends from the switch member 50 along the rotation axis BX, penetrating the housing 10 and to the outside of the housing 10. In this manner, the transmission mechanism 51A extends in a direction perpendicular to a plane along the central axis AX. Note that a bearing with a sealing mechanism may be provided at the portion where the transmission mechanism 51A penetrates the housing 10 to maintain a vacuum state inside the housing 10. Alternatively, the switch member 50 may be configured to be rotated from outside the housing 10 in a contactless manner using a magnetic coupling or the like. A rotating unit 52A that rotates the transmission mechanism 51A is provided outside the housing 10. The rotating unit 52A is, for example, a motor device. Note that the rotating unit 52A may be configured so that an operator manually rotates the transmission mechanism 51A.

[0024] By rotating the transmission mechanism 51A using the rotating part 52A, the switch member 50 rotates about the rotation axis BX. The switch member 50 rotates along a plane including the central axis AX between a retracted position P1A where the switch member 50 is retracted from the coupling cavity 30 and a blocking position P2B where the switch member 50 is inserted into the coupling cavity 30. The rotation range of the switch member 50 may be adjusted by providing an encoder or the like to adjust the amount of rotation by the rotating part 52A, or may be adjusted by a physical mechanism such as a stopper.

[0025] In the example shown in FIGS. 6 and 7 , the switch member 50 is configured to slide along the central axis AX. In this example, the transmission mechanism 51B includes a rotating member 53B, a rod-shaped member 54B, and a support member 55B. The rotating member 53B is L-shaped and extends in two directions (e.g., left-right and front-rear directions) from its base end. The rotating member 53B rotates about a rotation axis CX that passes through the base end and extends in the up-down direction. The tip of the portion of the rotating member 53B that extends in the left-right direction is connected to the switch member 50. The tip of the portion of the rotating member 53B that extends in the front-rear direction is connected to the rod-shaped member 54B. The rod-shaped member 54B extends outside the housing 10 in the left-right direction. In this way, the transmission mechanism 51B extends in a direction perpendicular to a plane along the central axis AX.

[0026] A drive unit 52B is provided outside the housing 10 to move the rod-shaped member 54B in the left-right direction. The drive unit 52B is, for example, a bellows mechanism. The rod-shaped member 54B can be moved in the left-right direction by expanding and contracting the bellows. Note that instead of a bellows mechanism, other drive mechanisms such as a ball screw mechanism or an air cylinder mechanism may be used as the drive unit 52B.

[0027] By expanding the bellows in the drive unit 52B, the rod-shaped member 54B moves to the right. When the rod-shaped member 54B moves to the right, the rotating member 53B rotates clockwise around the rotation axis CX when viewed from above. In this case, the tip of the portion extending in the left-right direction from the base end moves forward. As a result, the switch member 50 moves forward.

[0028] By compressing the bellows in the drive unit 52B, the rod-shaped member 54B moves to the left. When the rod-shaped member 54B moves to the left, the rotating member 53B rotates counterclockwise around the rotation axis CX when viewed from above. In this case, the tip of the portion extending in the left-right direction from the base end moves rearward. As a result, the switch member 50 moves rearward.

[0029] In this way, the switch member 50 can be slid in the front-rear direction by the transmission mechanism 51B and the drive unit 52B. In the example shown in Figures 6 and 7, the position where the switch member 50 moves forward is the retracted position P1B, and the position where the switch member 50 moves rearward is the disconnecting position P2B. Note that the position where the switch member 50 moves forward may be the disconnecting position P2B, and the position where the switch member 50 moves rearward may be the retracted position P1B.

[0030] In the example shown in FIGS. 8 and 9 , the switch member 50 is configured to slide along the central axis AX. In this example, the transmission mechanism 51C includes a linear member 53C and a guide member 54C. One end (the switch-side end) of the linear member 53C is connected to the switch member 50. The linear member 53C may be a member, such as a wire, that is rigid in the longitudinal direction and deformable in a direction perpendicular to the longitudinal direction. The linear member 53C is, for example, pulled forward from the switch member 50, bent to the left by the guide member 54C, and disposed with its tip extending outside the housing 10. The guide member 54C may be a tubular member, such as a tube. The linear member 53C is disposed in a state where it is passed through the guide member 54C. In this manner, the transmission mechanism 51C extends in a direction perpendicular to a plane along the central axis AX.

[0031] A drive unit 52C is provided outside the housing 10, and moves the linear member 53C in the left-right direction. The drive unit 52C is connected to the other end (drive side end) of the linear member 53C. Like the drive unit 52B described above, the drive unit 52C is, for example, a bellows mechanism. The linear member 53C can be moved in the left-right direction by expanding and contracting the bellows. Note that instead of a bellows mechanism, other drive mechanisms such as a ball screw mechanism or an air cylinder mechanism may be used as the drive unit 52C.

[0032] By stretching the bellows in the drive unit 52C, the drive-side end of the linear member 53C is pulled to the right. The linear member 53C is bent by the guide member 54C, and the switch-side end is arranged along the front-to-rear direction. Therefore, when the drive-side end of the linear member 53C is pulled to the right, the switch-side end moves forward. This causes the switch member 50 to move forward.

[0033] By compressing the bellows in the drive unit 52C, the drive-side end of the linear member 53C is pushed leftward. The linear member 53C is bent by the guide member 54C so that the switch-side end is arranged along the front-to-rear direction. Therefore, when the drive-side end of the linear member 53C is pushed leftward, the switch-side end moves rearward. This causes the switch member 50 to move rearward.

[0034] In this way, the transmission mechanism 51C and the drive unit 52C can slide the switch member 50 in the front-rear direction. In the example shown in Figures 8 and 9, as in the example shown in Figures 6 and 7, the position to which the switch member 50 has moved forward is the retracted position P1C, and the position to which the switch member 50 has moved rearward is the blocking position P2C. Note that the position to which the switch member 50 has moved forward may be the blocking position P2C, and the position to which the switch member 50 has moved rearward may be the retracted position P1C.

[0035] 10 is a diagram showing another example of acceleration cavity 100. As shown in FIG. 10 , a movement gap 14 may be provided in at least a part of the movable range of switch member 50 in gap 13, where switch member 50 is disposed. Movement gap 14 is a portion where the distance between dividing surfaces 12 is greater than gap 13. Providing movement gap 14 can prevent switch member 50 from interfering with dividing surfaces 12 of housing 10.

[0036] 11 and 12 are diagrams showing an example of how the acceleration cavity 100 is used. As shown in Fig. 11 , when the switch member 50 is placed in the retracted position P1, the radio frequency input from the radio frequency input unit WI is propagated to all of the cell units 20. Therefore, the charged particles M that are extracted from the radiation source BS and enter the acceleration cavity 100 are accelerated by and extracted from all of the cell units 20 that they pass through.

[0037] In contrast, as shown in FIG. 12 , when the switch member 50 is positioned at the cutoff position P2, the radio frequency waves input from the radio frequency input unit WI are cut off at the cutoff position P2. In the accelerating cavity 100, radio frequency waves are not propagated to the cells 20 beyond the cutoff position P2. Therefore, charged particles M emitted from the radiation source BS and entering the accelerating cavity 100 are accelerated in the cells 20 through which the radio frequency waves are propagated, and are emitted without acceleration from the cells 20 through which the radio frequency waves are not propagated. In this case, the energy of the charged particles M is smaller than when the switch member 50 is positioned at the retracted position P1. By switching the energy of the charged particles M in this way, the accelerating cavity 100 can be used for a wide range of applications, such as examination devices and treatment devices.

[0038] As described above, according to the first aspect of the present disclosure, there is provided an acceleration cavity including: a cylindrical, electrically conductive housing 10 in which a dividing member 11 is divided into a plurality of parts along a plane along the central axis AX, with dividing surfaces 12 along the plane facing each other with gaps 13 therebetween; a plurality of cell sections 20 arranged inside the housing 10 in a line along the axial direction of the central axis AX of the housing 10 and connected to each other by communicating sections 22 that allow charged particles to pass through; and a switch member 50 arranged in the gaps 13 in the housing 10 and movable through the gaps 13 along a plane passing through the central axis AX, the switch member switching the magnitude of the electric field that accelerates the charged particles as it moves.

[0039] According to this configuration, in a configuration in which the housing 10 is arranged with the divided surfaces 12 of the divided members 11 divided into multiple parts facing each other with a gap 13 between them, by moving the switch member 50 using the gap 13, it is possible to easily switch the energy of the charged particles M without using a complex mechanism.

[0040] In the acceleration cavity according to the second aspect of the present disclosure, in the first aspect, a coupling cavity 30 is provided inside the housing 10 and connects adjacent cell sections 20, and the switch member 50 is arranged so as to appear and disappear in the coupling cavity 30.

[0041] According to this configuration, the switch member 50 is arranged so as to appear and disappear from the coupling cavity, so that it is possible to efficiently switch between transmitting and blocking high frequency waves.

[0042] In the acceleration cavity according to the third aspect of the present disclosure, in the second aspect, all of the coupling cavities 30 are arranged on the same side of the cell unit 20 in the direction perpendicular to the central axis AX.

[0043] According to this configuration, by positioning the coupling cavities 30 on the same side of the cell unit 20 in the direction perpendicular to the central axis AX, the center of the electric field distribution in the direction perpendicular to the central axis AX can be aligned with the central axis AX, thereby suppressing the deflection of the charged particle beam.

[0044] In the acceleration cavity according to the fourth aspect of the present disclosure, in the second aspect, the coupling cavity 30 has a first space portion 31 connected to the cell portion 20, a second space portion 32 arranged at a position radially outwardly spaced apart from the first space portion 31 with respect to the central axis AX, and a connection portion 33 radially connecting the first space portion 31 and the second space portion 32, and the switch member 50 is arranged to appear and disappear from the connection portion 33.

[0045] According to this configuration, the switch member 50 is disposed so as to appear and disappear from the connection portion 33 of the coupling cavity 30, so that it is possible to efficiently switch between transmitting and blocking high frequency waves.

[0046] In the acceleration cavity according to the fifth aspect of the present disclosure, in the first aspect, the second space portion 32 of the coupling cavity 30 is connected to the vacuum manifold 40 .

[0047] According to this configuration, the vacuum manifold 40 is connected to the cell section 20 via the coupling cavity 30, so that the cell section 20 can be evacuated more reliably by the vacuum manifold 40.

[0048] In the acceleration cavity according to the sixth aspect of the present disclosure, in any of the first to fifth aspects, the housing 10 has a movement gap 14 in at least a portion of the movable range of the switch member 50, in which the distance between the dividing surfaces 12 is greater than the gap 13.

[0049] According to this configuration, the provision of the movement gap 14 can prevent the switch member 50 from interfering with the dividing surface 12 of the housing 10 .

[0050] The acceleration cavity according to the seventh aspect of the present disclosure is in any one of the first to sixth aspects, and further includes a transmission mechanism 51 that transmits a driving force generated outside the housing 10 to the switch member 50 .

[0051] According to this configuration, the transmission mechanism 51 is provided, so that the switch member 50 can be moved from outside the housing 10 .

[0052] In an acceleration cavity according to an eighth aspect of the present disclosure, in the seventh aspect, the transmission mechanism 51 extends in a direction perpendicular to the plane.

[0053] According to this configuration, the transmission mechanism 51 extends in a direction perpendicular to the plane, so that the driving force can be appropriately transmitted whether the switch member 50 is rotated or slid.

[0054] In the acceleration cavity according to the ninth aspect of the present disclosure, in any of the first to seventh aspects, the transmission mechanism 51 transmits a driving force so that the switch member 50 rotates around a rotation axis BX along a direction perpendicular to the central axis AX.

[0055] According to this configuration, the transmission mechanism 51 can move the switch member 50 so as to rotate about the rotation axis BX along a direction perpendicular to the central axis AX.

[0056] In the acceleration cavity according to the tenth aspect of the present disclosure, in any of the first to seventh aspects, the transmission mechanism 51 transmits the driving force so that the switch member 50 slides in a direction along the central axis AX.

[0057] According to this configuration, the transmission mechanism 51 can move the switch member 50 so as to slide in a direction perpendicular to the central axis AX.

[0058] In the above embodiment, a configuration in which one switch member 50 is provided has been described as an example, but the present invention is not limited to this configuration. A plurality of switch members 50 may be provided. In this case, the plurality of switch members 50 can be independently movable and can be provided so as to appear and disappear into different coupling cavities 30.

[0059] DESCRIPTION OF SYMBOLS 10 Housing 11 Dividing member 12 Dividing surface 13 Gap 14 Movement gap 20 Cell portion 21 Unit cell portion 22, 45 Communication portion 23, 24 Unit communication portion 30 Coupled cavity 31 First space portion 32 Second space portion 33 Connection portion 35 Unit coupled cavity 40 Vacuum manifold 41 Unit manifold 42 Vacuum forming portion 43 Piping 50 Switch member 51, 51A, 51B, 51C Transmission mechanism 52A Rotating portion 52B, 52C Driving portion 53B Rotating member 53C Linear member 54B Rod-shaped member 54C Guide member 55B Support member 100 Accelerating cavity AC Accelerator AX Central axis BS Radiation source BX, CX Rotation axis M Charged particle P1, P1A, P1B, P1C Retreat position P2, P2A, P2B, P2C Cutoff position WI High frequency input section

Claims

1. An acceleration cavity comprising: a cylindrical, conductive housing in which a divided member is divided into a number of parts along a plane along a central axis, with the divided surfaces along the plane facing each other with a gap therebetween; a number of cell sections arranged inside the housing in a line along the central axis of the housing and connected to each other by communication sections that allow charged particles to pass through; and a switch member arranged in the gap in the housing and movable through the gap along the plane, the switch member switching the magnitude of the electric field that accelerates the charged particles as it moves.

2. The acceleration cavity according to claim 1, further comprising a coupling cavity provided inside the housing and connecting adjacent cell sections at a position offset from the central axis, the switch member being positioned so as to appear and disappear from the coupling cavity.

3. The acceleration cavity according to claim 2, wherein all of the coupling cavities are arranged on the same side of the cell portion in a direction perpendicular to the central axis.

4. The acceleration cavity described in claim 2, wherein the coupled cavity has a first space portion connected to the cell portion, a second space portion arranged at a position radially outwardly spaced from the first space portion with respect to the central axis, and a connection portion connecting the first space portion and the second space portion in the radial direction, and the switch member is arranged so as to appear and disappear from the connection portion.

5. The acceleration cavity according to claim 4, further comprising a vacuum manifold connected to a plurality of said cell portions via said gap, wherein said second space portion of said coupled cavity is connected to said vacuum manifold.

6. The acceleration cavity according to claim 1, wherein the housing has a movement gap in which the distance between the divided surfaces is greater than the gap in at least a part of the movable range of the switch member.

7. The accelerating cavity according to claim 1, further comprising a transmission mechanism for transmitting a driving force generated outside the housing to the switch member.

8. The acceleration cavity according to claim 7, wherein the transmission mechanism extends in a direction perpendicular to the plane.

9. The acceleration cavity according to claim 7, wherein the transmission mechanism transmits the driving force so that the switch member rotates about a rotation axis aligned in a direction perpendicular to the central axis.

10. The acceleration cavity according to claim 7, wherein the transmission mechanism transmits the driving force so that the switch member slides in a direction along the central axis.

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