JP7778673B2 - Accelerator System - Google Patents

Description

Embodiments of the present invention relate to accelerator systems.

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

International Publication No. 2019/142389

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

The problem that this invention aims to solve is to provide an accelerator system that enables a larger diameter beam passage and reduced power consumption.

In order to solve the above problem, the accelerator system of one embodiment is an accelerator system in which multiple acceleration cavities are connected in the axial direction of the charged particle beam, each of which includes a vacuum vessel maintained in a vacuum state and having a beam passage through which a charged particle beam passes and an acceleration gap located facing the beam passage; an antenna installed within the vacuum vessel that introduces radio frequency energy into the vacuum vessel and forms an acceleration electric field in the acceleration gap to accelerate the charged particle beam; and a focusing magnet located outside the vacuum vessel that focuses the charged particle beam flowing within the beam passage; and is characterized in that the average diameter of the beam passage of a first acceleration cavity located upstream in the axial direction is larger than the average diameter of the beam passage of a second acceleration cavity located downstream in the axial direction from the first acceleration cavity.

FIG. 1 is a cross-sectional view showing an example of the configuration of an accelerator system according to a first embodiment. FIG. 10 is a cross-sectional view showing a configuration example of an accelerator system according to a modified example of the first embodiment. FIG. 10 is a cross-sectional view showing a configuration example of an accelerator system according to a modified example of the first embodiment. FIG. 10 is a cross-sectional view showing a configuration example of an accelerator system according to a modified example of the first embodiment.

The following describes an embodiment of the invention.

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

The vacuum vessel 12 is constructed by joining a vessel body 14 and a pair of conductive gap-forming plates 16, and its interior is maintained in a vacuum state. Inside the vacuum vessel 12, a beam passage 40 is provided, through which a charged particle beam passes, penetrating the vessel body 14 and the gap-forming plates 16. Opposite the beam passage 40, an acceleration gap 42, which is a space for forming an acceleration electric field, is provided between the pair of gap-forming plates 16.

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

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

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

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

The antenna 18 is provided inside the container body 14 and is formed into a loop from a metal material such as copper. One end of the antenna is connected to a grounding portion such as a waveguide 22 (described below) or a flange 20 of a coaxial cable (not shown), and the other end is connected to the core wire of the waveguide 22 or coaxial cable. The grounding portion and core wire of the flange 20 are insulated by an insulating material such as ceramic. It is also preferable to protect the ceramic surface by coating it with TiN or the like.

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

The high-frequency power source may be a vacuum tube, klystron, semiconductor amplifier, etc. A signal generator that emits a reference signal or a low-level control device may also be provided to control these high-frequency power sources. Furthermore, a dummy load, circulator, etc. may also be connected.

It is possible to provide one high-frequency power supply for multiple accelerating cavities 10, or one high-frequency power supply for each accelerating cavity 10. That is, in FIG. 1, a first high-frequency power supply connected to the antenna 18 (first antenna) provided in the first accelerating cavity 10A and a second high-frequency power supply connected to the antenna 18 (second antenna) provided in the second accelerating cavity 10B may be provided. By providing independent high-frequency power supplies for each of the multiple accelerating cavities 10, the strength and phase of the accelerating electric field generated in the accelerating gap 42 can be adjusted for each accelerating cavity 10. In addition to manual adjustment, automatic frequency adjustment, automatic phase adjustment, etc. can be applied via low-level control.

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

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

Multiple accelerating cavities 10 such as those described above are connected in the direction of the beam axis P. The multiple accelerating cavities 10 may be directly connected, or multiple accelerating cavities 10 may be constructed by assembling a portion of the vacuum vessel 12 as a common element for each accelerating cavities 10.

Of the adjacent accelerating cavities 10, the average diameter of the beam passage 40 of the upstream accelerating cavity 10 is larger than the average diameter of the beam passage 40 of the downstream accelerating cavity 10. Note that the average diameter of the beam passage 40 is the average diameter (average or average cross-sectional area) of a cross section perpendicular to the beam axis P. In other words, in Figure 1, the average diameter of the beam passage 40 of the first accelerating cavity 10A is larger than the average diameter of the beam passage 40 of the second accelerating cavity 10B.

In this embodiment configured as described above, the average aperture on the upstream side of the beam passage 40, where the divergence force due to the space charge effect of the charged particle beam is strong, is configured to be larger than the average aperture on the downstream side. In other words, by increasing the average aperture on the upstream side of the beam passage 40, collisions between the charged particle beam and the beam passage 40 due to divergence of the charged particle beam are suppressed. Furthermore, on the downstream side of the beam passage 40, where the charged particle beam is accelerated and requires a higher acceleration voltage, the divergence force decreases as the charged particle beam accelerates, so the average aperture can be reduced while suppressing collisions between the charged particle beam and the beam passage 40. This reduces the power consumption when introducing high-frequency energy and allows the charged particle beam to be accelerated.

As a modification of this embodiment, as shown in FIG. 2, a duct 28 may be provided between the first and second acceleration cavities 10A and 10B, and the first and second acceleration cavities 10A and 10B may be connected via this duct 28. The acceleration cavity 10 and the duct 28 are connected using a vacuum-sealable structure. The diameter of the duct 28 may be equal to or greater than the diameter of the upstream connection of the beam path 40, and may decrease from the upstream side toward the downstream side. The duct 28 may be a cylindrical or rectangular container, or a container with individual ports (not shown) in a direction different from the beam axis P, such as a tee or cross. The ports allow the connection of various monitors (not shown) for monitoring the status of the beam, such as current detectors such as Faraday cups and current transformers; profile and position detectors combining an insulated metal plate, wire monitor, fluorescent screen, and camera; and emittance monitors using a pepper-pot method. The ports may also be provided with slits (not shown) that block part or all of the charged particle beam. These monitors and slits are configured so that they can be inserted into and removed from the area through which the charged particle beam passes using a linear introduction device or the like. Various vacuum gauges, vacuum pumps, gate valves for vacuum sealing, etc. (not shown) may also be connected.

In addition to providing the same effects as the first embodiment, this modification allows the charged particle beam and vacuum conditions to be monitored, and the operation of the accelerator system 1 to be adjusted based on the results.

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

In addition to providing the same effects as the first embodiment, this modification makes it possible to arbitrarily adjust the diameter of the beam passage 40 while monitoring the power consumption and the transmittance and size of the charged particle beam. Furthermore, because the diameter of the beam passage 40 can be arbitrarily adjusted, even if an accelerating cavity 10 with a beam passage 40 having the same diameter is constructed, the same effects as the first embodiment can be achieved by adjusting the diameter of the beam passage 40 using the movable inner wall 30 after assembly.

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

In addition to achieving the same effects as the first embodiment, this modification allows the diameter of the beam passage 40 to be smaller downstream, thereby further reducing power consumption in the acceleration cavity 10.

While several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

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

Claims (6)

a vacuum vessel that is maintained in a vacuum state and has a beam passage through which a charged particle beam passes and an acceleration gap at a position facing the beam passage;
an antenna installed in the vacuum vessel to introduce high frequency energy into the vacuum vessel and form an accelerating electric field in the acceleration gap to accelerate the charged particle beam;
a focusing magnet disposed outside the vacuum vessel and configured to focus the charged particle beam flowing through the beam passage;
An accelerator system in which a plurality of accelerating cavities comprising the above are connected in the axial direction of the charged particle beam,
an average diameter of a beam passage of a first accelerating cavity located upstream in the axial direction among the accelerating cavities is larger than an average diameter of a beam passage of a second accelerating cavity located downstream in the axial direction than the first accelerating cavity. The accelerator system of claim 1, wherein the acceleration cavity has a movable inner wall in the beam passage of the vacuum vessel, the position of which can be adjusted to change the diameter of the beam passage. The accelerator system of claim 1, wherein the diameter of the beam passage at the upstream end in the axial direction is larger than the diameter of the downstream end. The accelerator system of claim 3, wherein the diameter of the beam passage continuously decreases from the upstream end to the downstream end. The accelerator system described in any one of claims 1 to 4, further comprising a duct maintained in a vacuum state between the first acceleration cavity and the second acceleration cavity. a first radio frequency power supply connected to a first antenna included in the first accelerating cavity;
5. The accelerator system according to claim 1, further comprising a second high frequency power supply connected to a second antenna provided in the second accelerating cavity.