Vacuum duct and accelerator

Abstract

The present invention provides a vacuum duct and an accelerator which make it possible for charged particles to pass through in intersecting directions without causing a plurality of ducts having differing degrees of vacuum to cross three-dimensionally.　A vacuum duct (10) comprises: a first duct (21) that forms a first beam trajectory (11) of a charged particle; a vacuum container (15) that is provided so as to divide a linear portion of the first duct (21) partway therealong; and a second duct (22) that forms a second beam trajectory (12) which intersects the first beam trajectory (11) inside the vacuum container (15).

Description

Vacuum duct and accelerator

[0001] SUMMARY OF THE INVENTION Embodiments of the present invention relate to vacuum ducts and accelerators for passing charged particles.

[0002] Research is underway into the application of charged particle beams, which are created by supplying charged particles (ions) to an accelerator and accelerating them to a high-energy state, in a wide range of fields, including engineering and medicine. Accelerator systems currently in widespread use are roughly composed of an ion source, a linear accelerator, and a circular accelerator, which accelerate the charged particles in this order. When the charged particles circulating in the circular accelerator reach a predetermined energy, an extraction control device is activated, and the charged particle beam is redirected from its orbit and extracted into a beam transport system.

[0003] If gas molecules exist in the area through which charged particles pass in a circular accelerator, the accelerated charged particles will be scattered and dissipated due to interactions with them. For this reason, the area through which charged particles pass in a circular accelerator is formed inside a vacuum duct set to an ultra-high vacuum.

[0004] On the other hand, the beam transport system connecting the ion source to the circular accelerator does not require a high degree of vacuum compared to the circular accelerator. This is because, while charged particles pass through the circular accelerator repeatedly, they pass through the beam transport system only once and at a slower speed.

[0005] Japanese Patent Application Laid-Open No. 2021-012776

[0006] In recent years, the miniaturization of circular accelerators has progressed, and it has become necessary to place the ion source and linear accelerator, which were previously located inside the circular accelerator, outside it. As a result, it is sometimes necessary to create an overpass between the circular accelerator and the beam transport system for equipment layout reasons. In this case, it is necessary to install additional bending magnets in the vacuum duct to bend the beam trajectory of the charged particle beam passing through the beam transport system.

[0007] The embodiments of the present invention have been made taking these circumstances into consideration, and aim to provide a vacuum duct and accelerator that allows charged particles to pass in directions that intersect with each other without having multiple ducts with different vacuum levels intersect each other.

[0008] FIG. 1 is a top view of an accelerator system equipped with a vacuum duct according to an embodiment of the present invention. (A) A horizontal cross-sectional view of a vacuum duct according to a first embodiment, and (B) its vertical cross-sectional view. In each embodiment, a horizontal cross-sectional view of a vacuum duct provided with a focusing lens element for a charged particle beam. In each embodiment, a horizontal cross-sectional view of a vacuum duct provided with an opening / closing valve for a charged particle beam. In each embodiment, a horizontal cross-sectional view of a vacuum duct according to a second embodiment. In each embodiment, a horizontal cross-sectional view of a vacuum duct according to a third embodiment.

[0009] First Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a system top view of an accelerator 30 equipped with a vacuum duct 10 according to an embodiment of the present invention. As described above, the accelerator 30 is a system comprising an ion source 35, a linac 36 (a linear accelerator), and a synchrotron 20 (a circular accelerator), which accelerate a charged particle beam 24 (24a, 24b) in stages in this order. When the charged particles circulating in the synchrotron 20 reach a predetermined energy level, the extraction device 29 is operated while maintaining that energy, and a charged particle beam 24c, whose traveling direction has been changed from the orbit, is extracted into a beam transport system 28.

[0010] The ion source 35 may be a high frequency (including microwave) irradiation type ion source such as an ECR (Electron Cyclotron Resonance) ion source or a PIG (Penning Ionization Gauge) ion source, or a laser irradiation type ion source, but is not limited to these.

[0011] The linac 36 has a plurality of accelerating electric fields arranged in a line, each having an electric field component in an opposite direction to the adjacent electric field, and repeatedly reverses the electric field direction at a high frequency to always accelerate the charged particle beam 24 a passing through the accelerating electric fields in only one direction. The linac 36 accelerates the ions incident from the ion source 35 to a predetermined energy and then extracts them into the synchrotron 20.

[0012] The synchrotron 20 is composed of a radio-frequency acceleration cavity 25 that accelerates charged particles injected from the linac 36 using radio-frequency power, a plurality of bending electromagnets 26 that generate a magnetic field that imparts a centripetal force to the circulating charged particles, a plurality of quadrupole electromagnets 27 that generate a magnetic field that diverges and converges the circulating charged particles and keeps them within the circulating orbit, and an extraction device 29 that extracts the charged particle beam 24 b circulating in the synchrotron 20 to a transport system 28.

[0013] The synchrotron 20 configured in this manner accelerates charged particles injected at low energy from the linac 36 while circulating them, ultimately accelerating them to an upper limit energy of 70 to 80% of the speed of light, and causes the charged particle beam 24c to pass through the beam transport system 28.

[0014] The beam transport system 28 is also provided with a quadrupole electromagnet 27 for confining the linearly traveling charged particle beam 24c within its orbit, and a bending electromagnet 26 for applying a centripetal force to the charged particle beam 24c to bend its orbit. A facility (not shown) for irradiating the charged particle beam 24c is connected to the end of the beam transport system 28.

[0015] Figure 2(A) is a horizontal cross-sectional view of the vacuum duct 10A (10) according to the first embodiment. Figure 2(B) is a vertical cross-sectional view of the vacuum duct 10A (10). As described above, the vacuum duct 10A includes a first duct 21 that forms a first beam orbit 11 of charged particles, a vacuum vessel 15 that is provided by dividing the straight portion of the first duct 21, and a second duct 22 that forms a second beam orbit 12 that intersects with the first beam orbit 11 inside the vacuum vessel 15.

[0016] Here, the first duct 21 constitutes a part of the beam transport system extending from the linear accelerator side (the ion source 35 and the linac 36), and the second duct 22 constitutes a part of the circular accelerator (the synchrotron 20).

[0017] In the vacuum duct 10A, the second duct 22 penetrates the vacuum vessel 15 and is provided with openings 16 (16a, 16b) through which the first beam orbit 11 passes. The vacuum vessel 15 is configured to have a sufficiently large vertical cross section compared to the first duct 21 and the second duct 22. The openings 16 (16a, 16b) are configured to be sufficiently smaller than the vertical cross section of the second duct 22. This provides a differential pumping effect, making it possible to suppress the inflow of gas molecules from the vacuum vessel 15 connected to the first duct 21 into the second duct 22.

[0018] Here, differential pumping refers to connecting a first duct 21 with a relatively low degree of vacuum to a second duct 22 with a higher degree of vacuum by providing a vacuum vessel 15 with a volume sufficiently larger than these ducts and connecting the vacuum pump 17 with a large diameter and a short distance. This allows the conductance of the first duct 21 and the second duct 22 to be smaller than the conductance of the vacuum pump 17, suppressing the amount of gas molecules flowing into the second duct 22 with a higher degree of vacuum and stably maintaining the difference in degree of vacuum with the first duct 21 with a lower degree of vacuum. Furthermore, when crossing the first duct 21 and the second duct 22, there is no need to use an electromagnet or the like to create a three-dimensional structure.

[0019] 2B, the vacuum pump 17 is provided in the vacuum duct 10A on the bottom surface of the vacuum vessel 15. However, this is not limiting, and the vacuum pump 17 may be provided on the top surface or side surface of the vacuum vessel 15, or a combination of these may be installed. Because the first duct 21 and the second duct 22 are connected to the side surface of the vacuum vessel 15 when viewed from the outside, the position and number of vacuum pumps 17 to be installed can be freely determined. This makes it possible to avoid interference with peripheral equipment while expecting an improvement in the degree of vacuum.

[0020] Note that the vacuum pump 17 may not be installed in the vacuum vessel 15. Alternatively, the inner surface of the vacuum vessel 15 may be coated with or installed with a substance (getter pump) that has a gettering effect that adsorbs gas molecules. Such a getter pump adsorbs gas molecules without affecting the charged particle beam 24, achieving high conductance evacuation and enabling a high degree of vacuum to be maintained inside the vacuum vessel 15.

[0021] In the vacuum duct 10 incorporated in the accelerator 30 (FIG. 1) of this embodiment, the vacuum vessel 15 is provided in the first duct 21, which has a lower vacuum than the second duct 22. This prevents leakage from the vacuum vessel 15 or gas released from its inner surface from entering the duct on the higher vacuum side (second duct 22), thereby minimizing loss of the beam accelerated through this duct.

[0022] However, there is no particular need to be limited to this configuration, and the first duct 21 provided with the vacuum container 15 may be set to a higher vacuum than the second duct 22. Also, although the first duct 21 and the second duct 22 have different degrees of vacuum in the above example, they may have the same degree of vacuum.

[0023] 3 is a horizontal cross-sectional view of the vacuum duct 10 provided with focusing lens elements for the charged particle beam 24. As described above, the first duct 21 is provided with a pair of quadrupole electromagnets 27 (27a, 27b) as lens elements for focusing the charged particle beam 24, on both sides of the vacuum vessel 15.

[0024] In this way, by providing the quadrupole electromagnets 27 (27a, 27b) and focusing the charged particle beam 24, it is possible to reduce the diameter size of the openings 16 (16a, 16b) provided in the second duct 22. This makes it possible to suppress a decrease in the degree of vacuum in the duct on the high vacuum side (the second duct 22), and further reduce the loss of the beam accelerated while passing through this duct.

[0025] 4 is a horizontal cross-sectional view of the vacuum duct 10 provided with an on-off valve 37 for the charged particle beam. In this manner, the on-off valves 37 (37a, 37b) are provided in the first duct 21 on both sides of the vacuum vessel 15. By providing the on-off valves 37 (37a, 37b) in the first duct 21, which has a relatively low degree of vacuum, the on-off valves 37 can be set to open only when the beam is passing through and closed otherwise. This makes it possible to suppress a decrease in the degree of vacuum in the duct on the high-vacuum side (the second duct 22), further reducing the loss of the beam accelerated while passing through this duct.

[0026] Second Embodiment Next, a second embodiment of the present invention will be described with reference to Figure 5. Figure 5 is a horizontal cross-sectional view of a vacuum duct 10B (10) according to the second embodiment. In contrast to the configuration of the first embodiment described above, the vacuum duct 10B of the second embodiment has a configuration in which the second duct 22 is joined to the outer peripheral surface of the vacuum vessel 15 after being cut off midway through a straight section. In Figure 5, parts having the same configuration or function as those in Figure 1 are designated by the same reference numerals, and duplicated explanations will be omitted.

[0027] The second embodiment is a suitable configuration when there is no significant difference in the degree of vacuum between the first duct 21 and the second duct 22, when the inflow of gas molecules from one duct to the other is not a problem, etc. Furthermore, by employing the opening and closing valve 37 for the charged particle beam shown in Fig. 4, it is possible to suppress a decrease in the degree of vacuum in the duct on the high vacuum side (second duct 22), and reduce the loss of the beam accelerated while passing through this duct.

[0028] (Third Embodiment) Next, a third embodiment of the present invention will be described with reference to Figure 6. Figure 6 is a horizontal cross-sectional view of a vacuum duct 10C (10) according to the third embodiment. The vacuum duct 10C of the third embodiment has a configuration in which the number N of ducts provided is three or more (N = 3 in the illustration). In Figure 6, parts having the same configuration or function as Figure 1 are indicated by the same reference numerals, and duplicated explanations will be omitted.

[0029] The vacuum duct 10C comprises a first duct 21 that forms a first beam orbit 11 of charged particles, a first vacuum vessel 151 that is provided by dividing the straight portion of the first duct 21 midway, and a second duct 22 that forms a second beam orbit 12 that intersects with the first beam orbit 11 inside the first vacuum vessel 151, and further comprises a second vacuum vessel 152 that is provided by dividing the straight portion of the second duct 22 midway, and a third duct 23 that forms a third beam orbit 13 that intersects with the second beam orbit 12 inside the second vacuum vessel 152.

[0030] Furthermore, the vacuum duct 10C of the third embodiment can be expanded to include N ducts (N≧3). In this case, for all natural numbers n in the range of 3 to N, the vacuum duct 10C includes an (n-1)th vacuum vessel provided by dividing the straight portion of the (n-1)th duct midway, and an nth duct that forms an nth beam orbit that intersects with the (n-1)th beam orbit inside the (n-1)th vacuum vessel.

[0031] This allows a number N of ducts with different vacuum degrees (N=3 or more) to intersect while suppressing changes in the vacuum degree. In this case, the vacuum duct 10C can be configured as a first duct 21 with the lowest vacuum degree, a second duct 22 with the next lowest vacuum degree, and an Nth duct with the highest vacuum degree.

[0032] According to at least one of the vacuum duct embodiments described above, the first duct and the second duct are connected to the vacuum vessel so that the first beam trajectory of the first duct and the second beam trajectory of the second duct intersect inside the vacuum vessel, making it possible to provide a vacuum duct and accelerator that allows charged particles to pass in directions that intersect with each other without having multiple ducts with different degrees of vacuum intersect with each other in three-dimensional space.

[0033] 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 embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations 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, as well as the inventions described in the claims and their equivalents.

Claims

1. A vacuum duct comprising: a first duct that forms a first beam trajectory of charged particles; a vacuum vessel that is provided by dividing the straight portion of the first duct midway; and a second duct that forms a second beam trajectory that intersects with the first beam trajectory inside the vacuum vessel.

2. A vacuum duct according to claim 1, wherein the second duct is a vacuum duct having an opening that penetrates the vacuum vessel and allows the first beam orbit to pass through.

3. A vacuum duct according to claim 2, wherein the first duct is provided with lens elements for focusing the beam of charged particles at positions on both sides of the vacuum vessel.

4. A vacuum duct according to claim 1, wherein the second duct is joined to the outer circumferential surface of the vacuum vessel by cutting off the middle of the straight section.

5. A vacuum duct according to any one of claims 1 to 4, wherein a vacuum pump is provided in the vacuum vessel.

6. A vacuum duct according to any one of claims 1 to 4, wherein the first duct and the second duct have different degrees of vacuum.

7. A vacuum duct according to any one of claims 1 to 4, wherein the first duct is provided with opening and closing valves at positions on both sides of the vacuum vessel.

8. A vacuum duct as claimed in any one of claims 1 to 4, wherein the number of ducts is set to N (N≧3), and for all natural numbers n in the range of 3 to N, the vacuum duct comprises: an (n-1)th vacuum vessel provided by dividing the straight section of the (n-1)th duct midway; and an (n-1)th duct that forms an (n-1)th beam orbit that intersects with the (n-1)th beam orbit inside the (n-1)th vacuum vessel.

9. An accelerator comprising a vacuum duct according to any one of claims 1 to 4.

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