Accelerator system

Abstract

To provide an accelerator system capable of implementing a beam converging manner for accelerating a high current beam and transporting the high current beam with a relatively weak converging strength.SOLUTION: An accelerator system 1 is provided with a plurality of sections S that are arranged along a traveling direction of a charged particle beam and accelerate the charged particle beam, and the plurality of sections S include a strong convergence section S1 in which the strength of the magnetic field for converging the charged particle beam is a first convergence strength, and a weak convergence section S2 in which the strength of the magnetic field is a second convergence strength smaller than the first convergence strength. At least one weak convergence section S2 is provided between two strong convergence sections S1 before and after in the traveling direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Radio frequency quadrupole linear accelerators (RFQs), which are widely used as first-stage accelerators, have difficulty accelerating high-current beams of 1A or more. This is because the electrode bore diameter of RFQs is small, on the order of mm, and it is not possible to converge and transport high-current beams that have strong divergence due to the space charge effect of the beam. Therefore, in order to accelerate high-current beams of 1A or more, it is expected that high-current beams can be accelerated by accelerators consisting of multiple single-cell cavities (accelerating cavities) connected together, each of which has a large-diameter beam passage and a beam-converging element. Unlike conventional linear accelerators, such accelerators accelerate the beam in a single large-diameter accelerating gap, and furthermore, in order to suppress the divergence force of the high-current beam and converge the beam, focusing elements such as permanent magnets or electromagnets are placed near or inside the accelerating cavity. [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] In single-cell cavities, each cavity has its own acceleration gap and focusing element. Therefore, a simple method of beam adjustment is to give each cavity periodicity and repeat the period of convergence and divergence for each cavity. This method has the advantage that the connection parts of the cavities can be used as periodic boundaries to transfer the beam to the subsequent stage under the same beam conditions, and the beam adjustment is simple and easy. This method is a general-purpose method that is used not only in single-cell cavities but also in general accelerators and beam transport systems.

[0005] On the other hand, when a similar adjustment method is used for a high-current beam with a beam current value of 1A or more, the periodicity that was established immediately after the accelerator injection cannot be maintained due to the divergence force of the beam. In addition, even if the periodicity of the beam can be maintained in calculations, the required convergence strength of the magnetic field may be excessive. This is because the beam repeats convergence and divergence over a short distance to maintain the periodicity of the beam, and the focal length of the beam optics becomes too short. Under such conditions, in the case of permanent magnets, the magnetic force is insufficient, or the retention force is generally weak because materials with a large residual magnetic flux density are used, and they are sensitive to changes in the external environment and are easily demagnetized by external influences such as heat. In the case of normal conductive magnets, the yoke made of metal materials such as iron becomes saturated, resulting in insufficient magnetic force or insufficient cooling performance. In the case of superconducting magnets, the critical current is reached. Therefore, there is a limit to the beam current value that can be accelerated and transported. In addition, the magnetic field required for the magnet becomes stronger, which leads to increased costs. In the case of electromagnets, even if the magnet specifications are the same, the stronger the required magnetic field, the larger the power supply required, which leads to increased costs.

[0006] An embodiment of the present invention has been made in consideration of the above circumstances, and has an object to provide an accelerator system that realizes a beam focusing form for accelerating a high current beam and is capable of transporting the high current beam with a relatively weak focusing strength. [Means for solving the problem]

[0007] An accelerator system according to an embodiment of the present invention includes a plurality of sections arranged along a direction of propagation of a charged particle beam and accelerating the charged particle beam, the plurality of sections including a strong convergence section having a first convergence strength and a weak convergence section having a second convergence strength smaller than the first convergence strength, and at least one of the weak convergence sections is provided between two adjacent strong convergence sections in the direction of propagation. Effect of the Invention

[0008] According to an embodiment of the present invention, an accelerator system is provided that realizes a beam focusing form for accelerating a high current beam and is capable of transporting the high current beam with a relatively weak focusing strength. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a configuration diagram showing an accelerator system according to a first embodiment. [Diagram 2] FIG. 11 is a configuration diagram showing an accelerator system according to a second embodiment. [Diagram 3] FIG. 13 is a configuration diagram showing an accelerator system according to a third embodiment. [Figure 4] FIG. 13 is a configuration diagram showing an accelerator system according to a fourth embodiment. [Diagram 5] FIG. 13 is a configuration diagram showing an accelerator system according to a fifth embodiment. [Figure 6] FIG. 13 is a configuration diagram showing an accelerator system according to a sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (First embodiment) Hereinafter, embodiments of the accelerator system will be described in detail with reference to the drawings. First, a first embodiment will be described with reference to FIG.

[0011] Reference numeral 1 in Fig. 1 denotes an accelerator system of a first embodiment. This accelerator system 1 is used to accelerate a charged particle beam such as ions or electrons. In particular, this accelerator system 1 can accelerate a high current beam of 1 A or more. In the following description, the upstream side (left side of the paper in Fig. 1) in the traveling direction of the charged particle beam is defined as the front side of the accelerator system 1, and the downstream side (right side of the paper in Fig. 1) is defined as the rear side of the accelerator system 1.

[0012] The accelerator system 1 includes a plurality of sections S arranged along the traveling direction of the charged particle beam and accelerating the charged particle beam. The plurality of sections S include a strong convergence section S1, which is a first convergence strength in which the strength of the magnetic field for converging the charged particle beam is set to an arbitrary value in advance, and a weak convergence section S2, which is a second convergence strength smaller than the first convergence strength. In addition, one weak convergence section S2 is provided between two strong convergence sections S1 in the traveling direction of the charged particle beam. That is, the strong convergence section S1 and the weak convergence section S2 are alternately arranged. The arrangement of the strong convergence section S1 and the weak convergence section S2 is appropriately set according to the period of convergence and divergence of the charged particle beam. The second convergence strength smaller than the first convergence strength includes the second convergence strength being zero.

[0013] One section S is composed of one accelerator 10. In the example of Fig. 1, for ease of understanding, only three accelerators 10 are illustrated, but in reality, for example, one accelerator system 1 is composed of an array of ten or more accelerators 10.

[0014] The accelerator 10 constituting each section S includes an accelerating cavity 11 , an antenna 12 , and a focusing magnet 13 .

[0015] The inside of the acceleration cavity 11 is maintained in a vacuum state. The acceleration cavity 11 has a beam passage 14 through which a charged particle beam passes, an acceleration gap 15 provided at a position facing the beam passage 14, and a resonance region 16 for resonating high frequency waves.

[0016] The center of the acceleration cavity 11 has openings on both ends, and the charged particle beam is transported and accelerated between these openings. Here, the traveling direction of the charged particle beam is defined as the beam axis P. In other words, the traveling direction of the charged particle beam coincides with the extending direction of the beam axis P. A beam passage 14 is provided along this beam axis P.

[0017] The beam passage 14 passes through the center of the acceleration cavity 11. For example, the beam passage 14 is made of a conductive metal and has a cylindrical shape, a rectangular parallelepiped shape, or a tapered shape thereof, and a charged particle beam passes through the inside of the beam passage 14. The beam passage 14 is a space with an inner diameter set to 100 mm or more in order to pass a high current beam of 1 A or more as a charged particle beam. The wall surface forming the beam passage 14, which is the inner peripheral surface of the acceleration cavity 11, is formed into a continuous flat surface up to the acceleration gap 15. However, a tapered surface may be formed on the wall surface of the beam passage 14.

[0018] A beam duct 2 through which the charged particle beam passes is connected to an accelerating cavity 11 of the accelerator 10 at the most upstream side in the traveling direction of the charged particle beam. The charged particle beam is introduced from the beam duct 2 into the accelerator 10 at the most upstream side, and travels toward the accelerator 10 at the rear side (downstream side).

[0019] The acceleration gap 15 is a gap formed inside the acceleration cavity 11. For example, the acceleration cavity 11 has a beam passage 14 penetrating therethrough and two opposing metal walls 17. These metal walls 17 are arranged side by side in the traveling direction of the charged particle beam. The acceleration gap 15 is a space sandwiched between the opposing metal walls 17. These metal walls 17 form part of the high frequency structure of the accelerator 10.

[0020] The metal wall portion 17 constituting the acceleration gap 15 may be formed as a separate part from the main body portion 18 of the acceleration cavity 11 and connected by members such as bolts. Also, the metal wall portion 17 and the main body portion 18 may be manufactured by cutting from a single ingot.

[0021] In the accelerating cavity 11, the connection portion between the accelerating gap 15 and the main body portion 18 is preferably subjected to curved surface processing (R processing) and the surface is also preferably smoothed, since a high voltage is generated at the connection portion by application of a high frequency wave.

[0022] There are various methods for manufacturing the accelerating cavity 11. For example, there is a manufacturing method in which a metal material such as iron is processed and then plated with a metal material such as copper having high electrical conductivity. There is also a manufacturing method in which the accelerating cavity 11 is formed by cutting an ingot of oxygen-free copper, tough pitch copper, or the like, entirely. Furthermore, the accelerating cavity 11 may be formed by connecting a number of parts formed by cutting.

[0023] When the accelerating cavity 11 is fabricated by connecting a number of independent parts, it is preferable to seal the parts with a sealing member such as a metal gasket, a rubber O-ring, an indium ring, or other metal packing to prevent vacuum leakage. It is also preferable to install RF (Radio Frequency) contacts such as finger contacts between the parts to reduce the loss of high-frequency surface current.

[0024] Furthermore, a water passage for circulating cooling water for removing generated heat may be provided inside the metal wall portion 17 constituting the acceleration gap 15 and the acceleration cavity 11 .

[0025] The resonance region 16 is a space provided inside the acceleration cavity 11. This resonance region 16 is provided continuous with the acceleration gap 15. For example, inside the acceleration cavity 11, the resonance region 16 is provided, which is a space of a certain volume or more that resonates high frequency waves in a region other than the acceleration gap 15.

[0026] The antenna 12 is provided inside the acceleration cavity 11, and inputs high frequency waves into a resonance region 16 to generate an acceleration electric field in the acceleration gap 15, accelerating the charged particle beam. The antenna 12 is connected to a high frequency generator 20 that generates high frequency energy. The antenna 12 is for inputting high frequency waves into the acceleration cavity 11. The antenna 12 is, for example, a metal material such as copper formed into a loop, one end of which is connected to a ground part such as a flange, and the other end is connected to a core wire. Here, the ground part and the core wire are insulated by an insulating material such as ceramic. It is desirable to coat the surface of the ceramic insulating material with a material such as TiN for protection. The high frequency waves input by the antenna 12 are resonated at a predetermined resonance frequency (for example, about 20 MHz), thereby generating an acceleration electric field in the acceleration gap 15. The charged particle beam passing through the beam passage 14 is accelerated by the acceleration electric field generated in the acceleration gap 15.

[0027] The flange also functions as a vacuum bulkhead. Although not shown in the drawings, for example, a circular or rectangular waveguide, a coaxial cable such as an N terminal, a BNC terminal, or an SHV terminal may be connected to the atmosphere side of the flange, and a high frequency generator 20 including a high frequency power source, an amplifier (RF amplifier), etc. may be connected to the end of the coaxial cable.

[0028] A plurality of ports 19 are provided at arbitrary positions in the main body 18 of the accelerating cavity 11. Vacuum pumps such as turbo vacuum pumps, ion pumps, cryopumps, scroll pumps, and rotary pumps are connected to these ports 19. Furthermore, vacuum gauges such as nude ion gauges, cold cathode gauges, Pirani gauges, and ionization vacuum gauges may be connected to these ports 19. Furthermore, analyzers such as Q-MASS (quadrupole mass spectrometer) may be connected to these ports 19 for component analysis of the gas inside the accelerating cavity 11. Furthermore, these ports 19 may have a slit structure formed of an opening for preventing high frequency leakage according to the frequency of the input high frequency.

[0029] A focusing magnet 13 is provided outside the beam passage 14 (beam axis P) of the acceleration cavity 11. The focusing magnet 13 provided in one acceleration cavity 11 is arranged so as to surround in the circumferential direction the outer periphery of the beam passage 14 that passes through the center of this acceleration cavity 11.

[0030] The focusing magnet 13 generates a magnetic field for focusing the high current charged particle beam. The focusing magnet 13 is composed of a permanent magnet or an electromagnet. The focusing magnet 13 is composed of one to a plurality of solenoids or quadrupole magnets. For example, one to three solenoids or quadrupole magnets may be arranged in the direction of the beam axis P to repeatedly converge and diverge the charged particle beam, thereby converging it as a whole.

[0031] The focusing magnet 13 in the first embodiment is a superconducting electromagnet, and is provided outside the acceleration cavity 11 to focus the charged particle beam traveling through the beam passage 14. The focusing magnet 13 is connected to a predetermined excitation power supply 21. The focusing magnet 13 receives a predetermined amount of power from the excitation power supply 21. The focusing magnet 13 is housed in a thermally insulated vacuum vessel 22, the inside of which is kept in a vacuum state and has thermal insulation properties.

[0032] The wire of the superconducting electromagnet may be made of a niobium-based low-temperature superconducting material, or an yttrium-based or rare earth-based high-temperature superconducting material. In order to maintain the superconducting state, the superconducting electromagnet is fixed to a heat-insulating vacuum vessel 22 independent of the acceleration cavity 11 via a support having low thermal conductivity. If necessary, a heat shield is arranged around the superconducting electromagnet. The superconducting electromagnet is cooled to a temperature at which the superconducting state can be maintained by a refrigerator (not shown) connected to the heat-insulating vacuum vessel 22. Alternatively, the superconducting electromagnet may be cooled using a specified refrigerant.

[0033] A plurality of accelerators 10 configured as described above are connected along the direction of the beam passage 14 (beam axis P).

[0034] The multiple accelerators 10 may be connected in such a manner that adjacent accelerating cavities 11 are directly connected to each other, or adjacent accelerating cavities 11 may be connected to each other with another vacuum vessel (not shown) inserted between them. Also, by providing a beam duct 2 between adjacent accelerating cavities 11, adjacent accelerating cavities 11 may be connected to each other via the beam duct 2.

[0035] In the accelerator system 1 configured in this manner, the focusing strength of a given focusing magnet 13 is smaller than the focusing strengths of the two focusing magnets 13 disposed before and after it along the traveling direction of the charged particle beam.

[0036] In the first embodiment, one weak convergence section S2 is provided between two strong convergence sections S1 in the traveling direction of the charged particle beam. The intensity of the magnetic field generated by the convergence magnet 13 provided in the weak convergence section S2 is smaller than the intensity of the magnetic field generated by the convergence magnet 13 provided in the strong convergence section S1. For example, the convergence magnet 13 provided in the strong convergence section S1 generates a magnetic field of a first convergence strength. The convergence magnet 13 provided in the weak convergence section S2 generates a magnetic field of a second convergence strength smaller than the first convergence strength.

[0037] Here, the magnitude of the focusing strength refers not only to the simple magnitude of the strength of the magnetic field generated by the focusing magnet 13, but also to the strength of the magnetic field relative to the charged particle beam. For example, it is an index expressed as the so-called GL product obtained by multiplying the magnetic field strength by the length of the focusing magnet 13 in the direction of the beam axis P, and the sum of the strengths of the magnetic fields applied to the charged particle beam within a certain section can be used as an index of the magnetic field strength.

[0038] When the convergence magnet 13 is a permanent magnet, the convergence strength can be adjusted by the magnetic force of the permanent magnet itself and the distance between the permanent magnet and the beam axis P. When the convergence magnet 13 is an electromagnet, the convergence strength can be adjusted by the value of the current flowing through the electromagnet.

[0039] When the accelerator system 1 is composed of four or more accelerators 10, the specific range in which the focusing magnets 13 with a relatively large focusing strength (strong focusing section S1) and the focusing magnets 13 with a relatively small focusing strength (weak focusing section S2) are alternately arranged may be only a part of the accelerator system 1. Also, multiple specific ranges may exist consecutively, or multiple specific ranges may exist with an interval between them. Furthermore, the entire range of the accelerator system 1 may be a specific range.

[0040] A strong divergence force may act due to the space charge effect of a high current charged particle beam. Even in this case, in comparison with a configuration in which the focusing strength is monotonically increased and the accelerator 10 is focused and diverged one by one, in the first embodiment, the period of focusing and divergence of the charged particle beam is lengthened, and the focusing strength required for each focusing magnet 13 can be reduced.

[0041] In the conventional beam adjustment method, the beam repeats convergence and divergence for each accelerator 10, so the period of the amplitude of the charged particle beam is short, and stronger convergence and divergence are required as the charged particle beam progresses. As a result, the beam size increases due to over-convergence, and the charged particle beam may collide with the wall surface (inner peripheral surface) of the beam passage 14, which limits the transport of a large current charged particle beam. In the accelerator system 1 of the first embodiment, such an increase in beam size can be reduced.

[0042] According to the first embodiment, the focusing strength required for each of the focusing magnets 13 can be reduced, and therefore the focusing magnets 13 can be manufactured inexpensively. Also, since there is a limit to the magnetic force that can be realized in each of the focusing magnets 13, the beam current value that can be transported and accelerated can be improved compared to the conventional case in which simple focusing and divergence are repeated for each magnet.

[0043] The focusing magnet 13 is disposed at a position overlapping at least a part of the resonance region 16 of the acceleration cavity 11 in the (beam axis P) direction of the beam passage 14. In other words, the focusing magnet 13 overlaps at least a part of the resonance region 16 in the direction of the beam axis P. The size (width) of the region where the focusing magnet 13 overlaps at least a part of the resonance region 16 depends on the high frequency design of the acceleration cavity 11. Furthermore, the focusing magnet 13 may completely overlap the resonance region 16.

[0044] Furthermore, the conductor of the permanent magnet or electromagnet that generates the magnetic field of the focusing magnet 13 does not have to overlap with the resonance region 16. For example, only the support parts such as the yoke, support part, and winding around the magnet body, or the magnet's auxiliary components such as the shield, need to be positioned so as to overlap at least a part of the resonance region 16. Note that, although at least a part of the focusing magnet 13 and the resonance region 16 needs to overlap in the direction of the beam axis P, there is no need for them to physically contact each other.

[0045] In this way, a magnetic field can be generated by the converging magnet 13 in most of the region close to the acceleration gap 15 of the acceleration cavity 11 in the direction of the beam axis P. In most of the region close to the acceleration gap 15, the converging force of the magnetic field can be sufficiently applied to the charged particle beam passing through the beam passage 14. As a result, even if the charged particle beam has a large current, the divergence of the charged particle beam can be suppressed and the charged particle beam can be accelerated.

[0046] In addition, the resonance region 16 of the acceleration cavity 11 can be extended in the direction of the beam axis P. This makes it possible to reduce the radial dimension of the acceleration cavity 11. Therefore, the radial dimension of the acceleration cavity 11 can be reduced.

[0047] In the first embodiment, the convergent magnet 13 is a superconducting electromagnet, but other configurations are also possible. For example, the convergent magnet 13 may be a resistive electromagnet. Also, the convergent magnet 13 may be a permanent magnet.

[0048] Second embodiment Next, a second embodiment will be described with reference to Fig. 2. Note that the same components as those shown in the above-described embodiment are denoted by the same reference numerals and will not be described again.

[0049] The accelerator system 1A of the second embodiment includes accelerators 10A and 10B having different configurations in the strong convergence interval S1 and the weak convergence interval S2. Specifically, the configuration of a convergence magnet 13A of the accelerator 10A in the strong convergence interval S1 is different from that of a convergence magnet 13B of the accelerator 10B in the weak convergence interval S2.

[0050] These focusing magnets 13A and 13B are made up of superconducting electromagnets as electromagnets. Note that these focusing magnets 13A and 13B may also be made up of normal conducting magnets.

[0051] In the second embodiment, the number of turns of the coil of the convergent magnet 13B provided in the weak convergence section S2 is smaller than the number of turns of the coil of the convergent magnet 13A provided in the strong convergence section S1. In other words, the number of turns of the coil of the convergent magnet 13B in the weak convergence section S2 is smaller than the number of turns of the coil of the two convergent magnets 13A disposed before and after the weak convergence section S2 along the traveling direction of the charged particle beam.

[0052] In this way, in the multiple sections S, a strong convergence section S1 with a first convergence strength is formed by the convergence magnet 13A having a large number of turns in the coil. Furthermore, a weak convergence section S2 with a second convergence strength smaller than the first convergence strength is formed by the convergence magnet 13B having a small number of turns in the coil. Then, one weak convergence section S2 is provided between the two strong convergence sections S1 in the traveling direction of the charged particle beam.

[0053] The electric wires of the coils constituting the respective focusing magnets 13A and 13B may be made of simple copper wires, or may be made of hollow conductors through which cooling water can circulate.

[0054] In the accelerator system 1A configured in this way, the strength of the focusing magnetic field applied to the charged particle beam along the traveling direction does not increase monotonically, but its strength is repeatedly increased and decreased. As a result, even when a strong divergence force due to the space charge effect of a high current beam acts, the period of convergence and divergence of the charged particle beam can be made longer than in the conventional configuration in which the focusing strength is increased monotonically and the beam converges and diverges for each of the accelerators 10A and 10B. Therefore, the focusing strength required for the focusing magnets 13A and 13B can be reduced.

[0055] According to the second embodiment, it is possible to reduce the convergence strength required for each of the convergence magnets 13A and 13B. Therefore, in particular, the convergence magnet 13B, which has a relatively weak convergence strength, can be manufactured at low cost by reducing the number of windings.

[0056] Third embodiment Next, a third embodiment will be described with reference to Fig. 3. Note that the same components as those shown in the above-described embodiment are denoted by the same reference numerals, and duplicated description will be omitted.

[0057] The accelerator system 1B of the third embodiment includes accelerators 10C and 10D having different configurations in the strong convergence interval S1 and the weak convergence interval S2. Specifically, the configuration of a convergence magnet 13C of the accelerator 10C in the strong convergence interval S1 is different from that of a convergence magnet 13D of the accelerator 10D in the weak convergence interval S2.

[0058] The convergent magnet 13C provided in the strong convergence section S1 is a superconducting electromagnet, and the convergent magnet 13D provided in the weak convergence section S2 is a resistive electromagnet. Since the convergent magnet 13D in the weak convergence section S2 is a resistive electromagnet, the thermally insulated vacuum vessel 22 of this convergent magnet 13D is omitted.

[0059] In this way, in the multiple sections S, a strong convergence section S1 with a first convergence strength is formed by the convergence magnet 13C, which is a superconducting electromagnet. Furthermore, a weak convergence section S2 with a second convergence strength smaller than the first convergence strength is formed by the convergence magnet 13D, which is a resistive electromagnet. Then, one weak convergence section S2 is provided between the two strong convergence sections S1 in the traveling direction of the charged particle beam.

[0060] In the accelerator system 1B configured in this way, the strength of the focusing magnetic field applied to the charged particle beam along the traveling direction does not increase monotonically, but its strength is repeatedly increased and decreased. As a result, even when a strong divergence force due to the space charge effect of a high current beam acts, the period of convergence and divergence of the charged particle beam can be made longer than in the conventional configuration in which the focusing strength is increased monotonically and the beam converges and diverges for each of the accelerators 10C and 10D. Therefore, the focusing strength required for the focusing magnets 13C and 13D can be reduced.

[0061] According to the third embodiment, it is possible to reduce the focusing strength required for each of the focusing magnets 13C and 13D. Therefore, the focusing magnet 13D, which has a relatively weak focusing strength, can be constructed of a normal electroconductive magnet instead of a superconductive electromagnet, and therefore can be manufactured inexpensively by simplifying not only the electromagnet body but also the surrounding incidental elements.

[0062] (Fourth embodiment) Next, a fourth embodiment will be described with reference to Fig. 4. Note that the same components as those shown in the above-described embodiments are given the same reference numerals and the duplicated description will be omitted.

[0063] The accelerator system 1C of the fourth embodiment includes accelerators 10E and 10F having different configurations in the strong convergence interval S1 and the weak convergence interval S2. Specifically, the configuration of an excitation power supply 21A connected to the accelerator 10E in the strong convergence interval S1 is different from that of an excitation power supply 21B connected to the accelerator 10F in the weak convergence interval S2.

[0064] The converging magnet 13 is made of a superconducting electromagnet as an electromagnet. The converging magnet 13 may be made of a resistive magnet.

[0065] In the fourth embodiment, the capacity of the excitation power supply 21B connected to the convergence magnet 13 provided in the weak convergence interval S2 is smaller than the capacity of the excitation power supply 21A connected to the convergence magnet 13 provided in the strong convergence interval S1. Here, the capacities of the excitation power supplies 21A and 21B are generally expressed in a predetermined formula such as the maximum current value or voltage value that each of them can output.

[0066] In this way, in the multiple sections S, a strong convergence section S1 with a first convergence strength is formed by supplying power from the excitation power supply 21A with a large capacity to the convergence magnet 13 in the strong convergence section S1. Furthermore, a weak convergence section S2 with a second convergence strength smaller than the first convergence strength is formed by supplying power from the excitation power supply 21B with a small capacity to the convergence magnet 13 in the weak convergence section S2. Then, one weak convergence section S2 is provided between the two strong convergence sections S1 in the forward and backward directions in the traveling direction of the charged particle beam.

[0067] In the accelerator system 1C configured in this way, the strength of the focusing magnetic field applied to the charged particle beam along the traveling direction does not increase monotonically, but its strength repeatedly fluctuates. As a result, even when a strong divergence force due to the space charge effect of a high current beam acts, the period of convergence and divergence of the charged particle beam can be made longer than in the conventional configuration in which the focusing strength increases monotonically and the beam converges and diverges for each of the accelerators 10E and 10F. Therefore, the focusing strength required for each focusing magnet 13 can be reduced.

[0068] According to the fourth embodiment, it is possible to reduce the convergence strength required for each of the convergence magnets 13. Therefore, the convergence magnets 13 in the weak convergence section S2, in particular, where the convergence strength is relatively weak, can be configured with a small-capacity excitation power supply 21B, and the entire accelerator system 1C can be manufactured at low cost.

[0069] Fifth embodiment Next, a fifth embodiment will be described with reference to Fig. 5. Note that the same components as those shown in the above-mentioned embodiments are denoted by the same reference numerals and the duplicated description will be omitted.

[0070] The accelerator system 1D of the fifth embodiment includes accelerators 10G and 10H having different configurations in the strong convergence interval S1 and the weak convergence interval S2. Specifically, the configuration of a convergence magnet 13E of the accelerator 10G in the strong convergence interval S1 is different from that of a convergence magnet 13F of the accelerator 10H in the weak convergence interval S2.

[0071] The convergent magnet 13E provided in the strong convergence section S1 is a resistive magnet serving as an electromagnet, and the convergent magnet 13F provided in the weak convergence section S2 is a permanent magnet. The convergent magnet 13E in the strong convergence section S1 may be a superconducting magnet.

[0072] In this way, in the multiple sections S, a strong convergence section S1 with a first convergence strength is formed by the focusing magnet 13E, which is a normal conductive magnet. Furthermore, a weak convergence section S2 with a second convergence strength smaller than the first convergence strength is formed by the focusing magnet 13F, which is a permanent magnet. Then, one weak convergence section S2 is provided between the two strong convergence sections S1, one before and one after, in the traveling direction of the charged particle beam.

[0073] In the accelerator system 1D configured in this way, the strength of the focusing magnetic field applied to the charged particle beam along the traveling direction does not increase monotonically, but its strength repeatedly fluctuates. As a result, even when a strong divergence force due to the space charge effect of a high current beam acts, the period of convergence and divergence of the charged particle beam can be made longer than in the conventional configuration in which the focusing strength increases monotonically and the beam converges and diverges for each of the accelerators 10G and 10H. Therefore, the focusing strength required for each of the focusing magnets 13E and 13F can be reduced.

[0074] According to the fifth embodiment, the convergence strength required for each of the convergence magnets 13E and 13F can be reduced. Therefore, the convergence magnet 13F in the weak convergence section S2, in which the convergence strength is relatively weak, can be configured with a permanent magnet, and the convergence magnet 13E in the strong convergence section S1, in which the convergence strength is relatively strong, can be configured with an electromagnet. Therefore, the entire accelerator system 1D can be manufactured at low cost.

[0075] Sixth embodiment Next, a sixth embodiment will be described with reference to Fig. 6. Note that the same components as those shown in the above-mentioned embodiments are given the same reference numerals and the duplicated description will be omitted.

[0076] The accelerator system 1E of the sixth embodiment includes accelerators 10J and 10K having different configurations in the strong convergence interval S1 and the weak convergence interval S2.

[0077] The accelerator 10J constituting the strong convergence interval S1 includes at least an accelerating cavity 11, an antenna 12, and a convergence magnet 13. The accelerator 10K constituting the weak convergence interval S2 includes at least an accelerating cavity 11 and an antenna 12. Here, the accelerator 10K in the weak convergence interval S2 is configured not to include a convergence magnet 13. That is, the convergence strength is zero in the accelerator 10K in the weak convergence interval S2.

[0078] In this way, among the multiple sections S, a strong convergence section S1 with a first convergence strength is formed by the section S in which the convergence magnet 13 is provided. Furthermore, a weak convergence section S2 with a second convergence strength (convergence strength is zero) smaller than the first convergence strength is formed by the section S in which the convergence magnet 13 is not provided. Then, one weak convergence section S2 is provided between two strong convergence sections S1 in the traveling direction of the charged particle beam.

[0079] In the accelerator system 1E configured in this way, the strength of the focusing magnetic field applied to the charged particle beam along the traveling direction does not increase monotonically, but its strength is repeatedly increased and decreased. As a result, even when a strong divergence force due to the space charge effect of a high current beam acts, the period of convergence and divergence of the charged particle beam can be made longer than in the conventional configuration in which the focusing strength is increased monotonically and the beam converges and diverges for each of the accelerators 10J and 10K. Therefore, the focusing strength required for each focusing magnet 13 can be reduced.

[0080] According to the sixth embodiment, it is possible to reduce the convergence strength required for each of the convergence magnets 13. Therefore, in the weak convergence section S2 where the convergence strength is relatively weak, the convergence magnets 13 are not arranged in the first place, and the acceleration cavities 11 are arranged continuously, so that the entire accelerator system 1E can be manufactured at low cost.

[0081] In addition, since the spatial region used for the focusing magnet 13 is no longer necessary, the number of acceleration gaps 15 per unit length can be increased, and the effective acceleration efficiency can be improved. As a result, the charged particle beam can be made highly energetic at an early stage, the divergence force due to the space charge effect can be reduced, and the beam current value that can be transported and accelerated can be improved.

[0082] The present invention has been described above based on the first to sixth embodiments, but the configuration applied in any of the embodiments may be applied to other embodiments, and the configurations applied in each embodiment may be combined.

[0083] For example, in a modified example, in one accelerator system 1, the accelerators 10J, 10K (FIG. 6) of the sixth embodiment are arranged in the front stage on the most upstream side. The accelerators 10C, 10D (FIG. 3) of the third embodiment are arranged in the next middle stage. Then, the accelerator 10 (FIG. 1) of the first embodiment is arranged in the rear stage on the most downstream side. In this way, it is possible to reduce manufacturing costs while optimizing the convergence intensity according to the traveling direction of the charged particle beam.

[0084] In the above embodiment, the strong convergence section S1 having the first convergence strength and the weak convergence section S2 having the second convergence strength are alternately arranged in the traveling direction of the charged particle beam. The arrangement of the strong convergence section S1 and the weak convergence section S2 may be appropriately changed according to the manner of convergence and divergence of the charged particle beam.

[0085] In the above embodiment, one weak convergence interval S2 is provided between two strong convergence intervals S1, but other embodiments are also possible. For example, two or more weak convergence intervals S2 may be provided between two strong convergence intervals S1.

[0086] In the above embodiment, all of the multiple sections S are either the strong convergence section S1 or the weak convergence section S2, but other configurations are also possible. For example, some of the multiple sections S may be either the strong convergence section S1 or the weak convergence section S2.

[0087] According to at least one of the embodiments described above, at least one weak focusing section S2 is provided between two strong focusing sections S1 in the traveling direction of the charged particle beam, thereby realizing a beam focusing form for accelerating a high current beam and transporting the high current beam with a relatively weak focusing strength.

[0088] Although some 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 or modifications thereof are within the scope of the invention and its equivalents as described in the claims, as well as within the scope and spirit of the invention. [Explanation of symbols]

[0089] 1, 1A, 1B, 1C, 1D, 1E...accelerator system, 2...beam duct, 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10J, 10K...accelerator, 11...accelerating cavity, 12...antenna, 13, 13A, 13B, 13C, 13D, 13E, 13F...focusing magnet, 14...beam passage, 15...accelerating gap, 16...resonance region, 17...metal wall portion, 18...main body portion, 19...port, 20...high frequency generator, 21, 21A, 21B...excitation power supply, 22...insulated vacuum vessel, P...beam axis, S...section, S1...strong focusing section, S2...weak focusing section.

Claims

1. A charged particle beam accelerating device includes a plurality of sections arranged along a traveling direction of the charged particle beam, the plurality of sections accelerating the charged particle beam, the plurality of sections include a strong focusing section in which a strength of a magnetic field for focusing the charged particle beam is a first focusing strength, and a weak focusing section in which a strength of a magnetic field for focusing the charged particle beam is a second focusing strength smaller than the first focusing strength, At least one of the weak convergence sections is provided between two of the strong convergence sections, one before and one after in the traveling direction. Accelerator system.

2. Each of the sections is an acceleration cavity having a beam passage through which the charged particle beam passes, an acceleration gap provided at a position facing the beam passage, and a resonance region for resonating high frequency waves, the interior of which is maintained in a vacuum state; an antenna provided inside the acceleration cavity, for injecting the high frequency wave into the resonance region, forming an acceleration electric field in the acceleration gap, and accelerating the charged particle beam; a focusing magnet provided outside the acceleration cavity for focusing the charged particle beam traveling through the beam passage; It is composed of The intensity of the magnetic field generated by the focusing magnet provided in the weak focusing section is smaller than the intensity of the magnetic field generated by the focusing magnet provided in the strong focusing section. The accelerator system of claim 1 .

3. the focusing magnet is an electromagnet, The number of turns of the coil of the convergence magnet provided in the weak convergence section is smaller than the number of turns of the coil of the convergence magnet provided in the strong convergence section. The accelerator system of claim 2 .

4. the focusing magnet provided in the strong focusing section is a superconducting electromagnet, The focusing magnet provided in the weak focusing section is a resistive magnet. The accelerator system according to claim 2 or 3.

5. the focusing magnet is an electromagnet, a capacity of an excitation power supply connected to the convergence magnet provided in the weak convergence section is smaller than a capacity of an excitation power supply connected to the convergence magnet provided in the strong convergence section; The accelerator system according to claim 2 or 3.

6. the focusing magnet provided in the strong focusing section is an electromagnet, The focusing magnet provided in the weak focusing section is a permanent magnet. The accelerator system according to claim 2 or 3.

7. The strong convergence section is an acceleration cavity having a beam passage through which the charged particle beam passes, an acceleration gap provided at a position facing the beam passage, and a resonance region for resonating high frequency waves, the interior of which is maintained in a vacuum state; an antenna provided inside the acceleration cavity, for injecting the high frequency wave into the resonance region, forming an acceleration electric field in the acceleration gap, and accelerating the charged particle beam; a focusing magnet provided outside the acceleration cavity for focusing the charged particle beam traveling through the beam passage; It is composed of the weak convergence section is composed of the acceleration cavity and the antenna, The accelerator system of claim 1 .

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