JP4911477B2 - IH type drift tube linear accelerator - Google Patents

Description

  The present invention relates to an IH type drift tube linear accelerator using an electrode called a drift tube for accelerating a particle beam by a high frequency acceleration electric field.

In the IH type drift tube linear accelerator, a plurality of drift tubes are arranged in a cylindrical acceleration cavity by arranging stems that protrude alternately in the radial direction from the top and bottom of the inner wall surface of the acceleration cavity, and attaching the drift tubes to the stems. Are arranged in the cylindrical axis direction. A high frequency electric field is generated between the drift tubes. The particle beam passes through a plurality of drift tubes and is accelerated by a high-frequency electric field between the drift tubes. This high frequency electric field is usually called an acceleration electric field. In the IH type accelerator, a magnetic field rotating in the horizontal direction in the acceleration cavity is generated, and an electric field is induced thereby, so that the acceleration electric field at the center of the acceleration cavity is large. As a result, the accelerating electric field becomes smaller at both ends, so in order to increase the accelerating electric field on the incident side, increase the outer diameter of several drift tubes on the incident side, decrease the inner diameter, or decrease the radius of curvature outside the drift tube. Thus, the acceleration electric field has been improved (for example, see Patent Document 1).
In order to accelerate most efficiently, the average value of the electric field strength between the drift tubes needs to be equal. However, when the adjustment is made such that the average electric field strength between the drift tubes is equal, the electric field strength on the surface increases on the emission side where the distance between the drift tubes is long, and the risk of discharge increases. The present invention is intended to reduce such a discharge risk, and this point is different from the conventional example.

JP 2006-351233 (page 6-7, FIG. 5, FIG. 8)

In the IH type drift tube linear accelerator, when the electric field strength on the surface of the drift tube increases, discharge occurs and the particle beam cannot be accelerated stably.
When the particle beam is accelerated and the energy of the particle beam increases, the particle becomes faster and the distance between the drift tubes needs to be longer, so the distance between the drift tubes on the particle beam exit side is between the drift tubes on the particle beam incident side. Longer than the distance. When the design is performed under the condition that the average value of the electric field strength distribution between the drift tubes is constant, the surface electric field strength at the drift tubes increases as the distance between the drift tubes increases.

  To adjust the resonant frequency of the accelerating cavity and the average value of the electric field strength distribution between the drift tubes, a hole is made in the cylindrical wall of the accelerating cavity and a tuner made of a copper rod or a copper-plated metal rod is inserted into the hole. And do it. When the tuner is inserted through the cylindrical wall, the electric field strength near the center of the tuner insertion portion is small, and the electric field strength near both sides of the tuner is large. Therefore, when the tuner is inserted in this way, the surface electric field strength in the drift tube is further increased. Further, the surface electric field strength of the drift tube located on the emission side further than the tuner becomes larger than the surface electric field strength of the drift tube located on the incident side of the tuner as the distance between the drift tubes becomes larger. Also, the electric field strength distribution between the drift tubes on the incident side than the tuner located on the most exit side can be adjusted by adjusting the tuners, and the surface electric field strength can be lowered, but it is lower than the tuner located on the most exit side. The electric field intensity distribution between the drift tubes on the exit side cannot be adjusted by the tuner. This is because both the electric field strength between the drift tubes and the resonant frequency of the cavity need to be adjusted by the tuner.

  The distance between the drift tubes on the particle beam exit side becomes longer, the surface electric field strength of the drift tube located on the exit side becomes larger than the inserted tuner, and the tuner located on the most exit side is closer to the exit side. Since the electric field strength distribution between certain drift tubes cannot be adjusted by the tuner, the surface electric field strength is larger at the outer peripheral edge of the cylindrical axial end of the drift tube located on the exit side than the tuner located on the most exit side. Therefore, there is a problem in that discharge may occur and stable acceleration of the particle beam may not be performed.

  The present invention has been made to solve the above-described problems, and there is a possibility that the surface electric field strength of the drift tube on the exit side becomes larger than the tuner located on the most exit side and discharge may occur. The purpose is to provide an IH type drift tube linear accelerator that reduces the surface electric field strength of this drift tube in some cases, thereby mainly preventing discharge between drift tubes and enabling stable acceleration of particle beams. And

An IH drift tube linear accelerator according to the present invention includes a cylindrical acceleration cavity, a plurality of drift tubes arranged in the axial direction of the cylinder inside the acceleration cavity and generating a high-frequency accelerating electric field, and each of the drift tubes. A plurality of stems fixed to the distal end and having the other distal end held on the inner peripheral wall surface of the accelerating cavity, and a tuner inserted in a hole penetrating the cylindrical wall of the accelerating cavity and arranged in the cylindrical axis direction The tuner is configured such that the lengths of the insertion portions inserted into the through-holes of the tuners can be adjusted to each other, and one end of the acceleration cavity in the cylindrical axis direction is an incident end and the other end is An IH type drift tube linear accelerator for accelerating a particle beam incident from the incident end as an exit end with a high frequency acceleration electric field applied between the drift tubes and exiting from the exit end,
The drift tube has a predetermined radius of curvature at the outer peripheral edge portion of the cylindrical axial end portion,
The curvature radius of the drift tube located on the side of the exit end of the center position of the tuner arranged in the exit end closest position, the center position of the upper Symbol tuner located on the side of the incident end It is larger than the curvature radius of each drift tube.

According to the IH drift tube linear accelerator according to the present invention, a cylindrical acceleration cavity, a plurality of drift tubes arranged in the axial direction of the cylinder inside the acceleration cavity and generating a high-frequency accelerating electric field, and the drift tubes are provided. A plurality of stems fixed to one tip and the other tip held on the inner peripheral wall surface of the accelerating cavity, and inserted into a hole penetrating the cylindrical wall of the accelerating cavity and arranged in the cylindrical axis direction The tuner is configured such that the lengths of the insertion portions inserted into the through-holes of the tuners can be adjusted with respect to each other. An IH type drift tube linear accelerator that accelerates a particle beam incident from the incident end with a high-frequency accelerating electric field applied between the drift tubes with an end as an exit end and exits from the exit end. Te,
The drift tube has a predetermined radius of curvature at the outer peripheral edge portion of the cylindrical axial end portion,
The radius of curvature of the drift tube, which is located closer to the exit end than the center position of the tuner disposed at the position closest to the exit end and the surface electric field strength is likely to exceed the allowable value, is set to the exit end. Since the radius of curvature of each of the drift tubes located closer to the incident end than the center position of the tuner located at the closest position is larger than the curvature radius of each of the drift tubes, discharge between the drift tubes is prevented and the particle beam is stably accelerated. can do.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing a first embodiment of a drift tube linear accelerator according to the present invention, and shows a cross-sectional view of an IH (Interdigital H-mode) type drift tube linear accelerator. As shown in FIG. 1, the IH type drift tube linear accelerator includes a cylindrical acceleration cavity 1, a plurality of drift tubes 3 arranged in the cylinder axis direction of the acceleration cavity 1 to generate a high-frequency acceleration electric field, The drift tube 3 is fixed to one tip portion, and the other tip portion is held on the inner peripheral wall surface of the accelerating cavity 1 and the cylindrical wall is passed through a hole penetrating the cylindrical wall of the accelerating cavity 1. And a plurality of tuners arranged in the cylindrical axis direction. The resonance frequency of the accelerating cavity 1 and the average value of the electric field intensity distribution between the drift tubes 3 are the same between the drift tubes 3 by adjusting the length of the insertion portion inserted into the hole of the cylindrical wall between the plurality of tuners. And the electric field strength distribution between the drift tubes 3 is adjusted so that the surface electric field strength in the drift tube 3 is less than the allowable value, and one of the cylindrical axes of the accelerating cavity 1 is incident as the incident end and the other as the incident end. The particle beam incident from the end is accelerated and emitted from the emission end. The tuner is made of a copper rod or copper-plated metal or the like, and is inserted into, for example, through holes provided at tuner installation positions 4, 5, 6, and 7 in the cylindrical portion of the acceleration cavity 1.

  In the IH type drift tube linear accelerator, a high frequency accelerating electric field is generated in the space between the drift tubes 3 and the particle beam is accelerated. Therefore, since the energy of the particle beam gradually increases from the incident side toward the emission side, it is necessary to gradually increase the distance between the drift tubes 3 from the incident end side toward the emission end side. The electric field intensity distribution in the direction of the particle beam acceleration axis (cylindrical axis) a between the drift tubes 3 is high on the surface of the drift tube 3 and is low between the drift tubes 3. That is, the electric field intensity distribution between the drift tubes 3 has peaks at both ends between the drift tubes 3. Therefore, when the design is performed under the condition that the average value of the electric field intensity distribution between the drift tubes 3 is equal, the maximum value of the surface electric field intensity of the drift tube 3 on the emission side with the longer distance between the drift tubes 3 is The distance between the drift tubes 3 located on the incident side is larger than the maximum value of the surface electric field strength of the drift tube 3.

  When the tuner is inserted through the cylindrical wall, the electric field strength near the tuner insertion position 16 (tuner center position) decreases as shown in FIG. 2, and the electric field distribution between the drift tubes 3 after the tuner is inserted. 18, the electric field strength becomes larger than the electric field strength in the electric field distribution 17 before the tuner is inserted as the distance from the insertion position of the tuner increases toward the incident end side and the outgoing end side. For such a situation, with respect to the electric field intensity distribution between the drift tubes 3 located closer to the incident end than the center position of the tuner located closest to the emission end, the insertion lengths of the plurality of tuners are adjusted to each other. The strength of the drift tube 3 can be adjusted below the allowable value by adjusting the strength. However, since it is necessary to adjust both the surface electric field strength and the resonance frequency using a tuner, the electric field strength distribution between the drift tubes 3 positioned further on the exit end side than the center position of the tuner located closest to the exit end side is adjusted. Since the range is limited, in the conventional method of adjusting the tuner, the surface electric field strength of the drift tube 3 located on the exit end side from the center position of the tuner located closest to the exit end side exceeds the allowable value for discharge. There is.

  As described above, the distance between the drift tubes 3 is increased, the tuner is inserted, and the electric field intensity distribution between the drift tubes 3 positioned on the output end side from the center position of the tuner positioned closest to the output end side cannot be adjusted. For this reason, the surface electric field strength of the drift tube 3 located on the emission end side further increases from the center position of the tuner located closest to the emission end side, which may cause a discharge.

  In this invention, the outer periphery of the end of the drift tube 3 that is located further on the emission end side than the center position of the tuner installation position 7 that is located closest to the emission end side and in which discharge may occur (in the direction of the particle beam acceleration axis a) The radius of curvature of the edge portion of the edge portion of the edge portion is made larger than the radius of curvature of the edge portion of the outer periphery of the end portion of each drift tube 3 located on the incident end side of the center position of the tuner installation position 7. By avoiding electric field concentration and reducing electric field intensity, discharge is prevented, and disturbance of acceleration electric field due to discharge is prevented, thereby enabling stable particle beam acceleration. Moreover, the life of the drift tube linear accelerator and the safety of the product are achieved by preventing discharge.

  FIG. 3 is a cross-sectional view showing two types of drift tubes in which the radius of curvature of the outer peripheral edge portion of the end portion of the drift tube 3 is changed. 3A shows the curvature radii of the outer peripheral edge portions 8 and 9 of the drift tube 3 located on the incident end side with respect to the center position of the tuner installation position 7, and FIG. 3B shows the tuner installation position. 7 shows the radii of curvature of the outer peripheral edge portions 10 and 11 of the end portion of the drift tube 3 located closer to the emission end side than the center position of FIG.

  As described above, according to the first embodiment, in the end outer peripheral edge portions 10 and 11 of the drift tube 3 positioned further on the emission end side than the center position of the tuner installation position 7 located on the most emission end side. Discharge is prevented by increasing the radius of curvature compared to the radius of curvature of the outer peripheral edge portions 8 and 9 of each drift tube 3 located on the incident end side from the center position of the tuner installation position 7, and stable particle beam acceleration Can be able to.

  In addition, when there are a plurality of drift tubes 3 that are targets for increasing the radius of curvature of the outer peripheral edge portion, the surface electric field strength is different at both ends of one drift tube 3, and the possibility of discharge occurring at both ends is different. In this case, as shown in FIG. 4, the curvature radius of the end outer peripheral edge portion 12 of the drift tube 3 is different from the curvature radius of the end outer peripheral edge portion 13, and the drift tube 3 The radius of curvature of the end outer peripheral edge portion 14 and the radius of curvature of the end outer peripheral edge portion 15 are different, and the radius of curvature of the end outer peripheral edge portions 13 and 14 of the opposing surfaces where discharge easily occurs is increased.

  Further, when there are a plurality of drift tubes 3 that increase the radius of curvature of the end outer peripheral edge portion, the surface electric field strength of each drift tube 3 is different, so that the end outer peripheral edge portion 12 of the drift tube 3 is shown in FIG. And the curvature radius of the end edge edge portions 14 and 15 are different from each other. In this case, since the surface electric field strength may be different at both ends of one drift tube 3, in this case, the curvature radii of the outer peripheral edge portions at the both ends are different.

  The drift tube linear accelerator of the present invention can be effectively used for medical equipment.

It is sectional drawing which shows the structure of Embodiment 1 of the IH drift tube linear accelerator which concerns on this invention. 5 is a graph showing a change in electric field strength distribution when a tuner is inserted according to the first embodiment. FIG. 3 is a cross-sectional view showing an IH drift tube in the first embodiment. FIG. 3 is a cross-sectional view showing an IH drift tube in the first embodiment. FIG. 3 is a cross-sectional view showing an IH drift tube in the first embodiment.

Explanation of symbols

1 Acceleration cavity, 2 stem, 3 drift tube, 4-7 tuner installation position,
a beam acceleration axis, 8 to 15 end outer peripheral edge, 16 tuner insertion position,
17 Electric field distribution before inserting the tuner, 18 Electric field distribution after inserting the tuner.

Claims (3)

A cylindrical acceleration cavity, a plurality of drift tubes arranged in the axial direction of the cylinder inside the acceleration cavity and generating a high-frequency accelerating electric field, and each drift tube is fixed to one tip and the other tip is A plurality of stems held on the inner peripheral wall surface of the accelerating cavity; and tuners that are inserted into holes that penetrate the cylindrical wall of the accelerating cavity and that are arranged in the cylindrical axis direction. The length of the insertion portion inserted into the through-hole of each of the accelerating cavities is configured to be mutually adjustable. Is an IH type drift tube linear accelerator that accelerates with a high frequency acceleration electric field applied between the drift tubes and exits from the exit end,
The drift tube has a predetermined radius of curvature at the outer peripheral edge portion of the cylindrical axial end portion,
The curvature radius of the drift tube located on the side of the exit end of the center position of the tuner arranged in the exit end nearest position, the center position of the upper Symbol tuner located on the side of the incident end An IH type drift tube linear accelerator characterized by being larger than the curvature radius of each of the drift tubes. 2. The IH type drift tube linear accelerator according to claim 1, wherein when there are a plurality of drift tubes having a larger curvature radius, the curvature radii of the plurality of drift tubes are different from each other. 3. The IH drift tube linear shape according to claim 1, wherein the curvature radius of the drift tube having a larger curvature radius is different between the incident end side and the emission end side of the drift tube. Accelerator.

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