JPS61225800A - Accelerator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a device for accelerating charged particles using high frequency electromagnetic waves (C microwaves).

[Background of the invention]

When accelerating charged particles at high speed with a linac (linear accelerator; also called linear accelerator), the amount of acceleration per unit length and acceleration efficiency are important points. These quantities are highly dependent on the structure of the accelerating tube as well as the materials that make up the accelerating tube.

Related structures of conventional accelerator tubes include, for example, the literature [I.
E Transactions on Nucl.
earScience, VoL, N5-28.43 (
1981) 34401. Taking as an example the case where the particles to be accelerated are electrons, the structure of a conventional acceleration tube is shown schematically in FIGS. 2 and 3. In each figure, the right-hand view represents an axial cross-sectional view of the accelerator tube, and the left-hand view represents a radial cross-sectional view.

When microwaves are passed through a simple cylindrical structure,
The phase velocity of microwaves exceeds the speed of light (of course, the energy propagation speed does not exceed the speed of light). Therefore, in order to accelerate charged particles that are slower than the speed of light, the structure of the accelerator tube makes the phase speed of the microwave propagating inside the tube slower than the speed of light, so that the phase speed and the speed of the charged particles become equal. It has a structure like this. Specifically, Figures 2 and 3
As shown in the figure, it has a periodic fishing force structure along the acceleration tube axis, and each cell (cavity) is separated by two disks 22 in FIG. 2, and one disk in FIG. washer 32
It is separated by In addition, in the structure shown in Figure 2, an arc-shaped hole 23 is provided around the central axis of the disk in order to strengthen the coupling of electromagnetic wave modes between each cell and smooth the energy flow of electromagnetic waves (microwaves). It is being

Figure 4 shows the performance of the accelerating tube in these structures. %EI1m represents the maximum electric field %E on the central axis of the accelerating tube, that is, the beam axis, and represents the large amount of field in the entire structure of the accelerating tube. Further, v5 represents the microwave energy propagation speed, and C represents the speed of light.

R is the effective shunt impedance and is defined as:

In particular, L: Period length of the accelerator tube Eo (2): Electric field distribution on the beam axis P: Energy loss due to wall current per cycle = 2 = , β = - βλ C λ: Microwave tube wavelength V Velocity of Two Particles This effective shunt impedance is a measure of acceleration efficiency in standing wave type acceleration. The values in FIG. 4 are for the case where the microwave frequency is 3GH2.

Now, as the first indicator of linac performance, E=/
There is E. Here, the upper limit of %Et is determined by the internal discharge of the accelerating tube. Therefore, in order to obtain a high particle accelerating electric field E1, it is desirable to have a structure in which k has a large E, . . . /E, and is as close to 1 as possible.

From this point of view, the structure in Figure 2 is E, /E.

〉0.9, which is excellent, but the structure in Figure 3 is E@
/g, ~0.4, making it unsuitable for high electric fields.

In the structure shown in FIG. 3, since the washer 32 has a nose cone 34 for increasing the effective shunt impedance R, the electric field is concentrated and stationary at this portion. This is the reason why E, /E p is low.

A second indicator of linac performance is v1/C. When accelerating particles, the microwave energy supplied to the acceleration tube is eaten up by the particles being accelerated.

Therefore, in order to continue accelerating particles, it is necessary to supply microwave energy smoothly. For this purpose, a high energy propagation speed is required. From this point of view, in the structure shown in FIG. 2, the value of v, /C can be reduced to about 0.1 at most. On the other hand, in the structure shown in FIG. 3, v1/C can be reduced to about 0.5, and it can be argued that the structure shown in FIG. 3 is superior from the viewpoint of energy flow.

The third indicator of linac performance is the effective shunt impedance.This is a measure of acceleration efficiency, which indicates how effectively the injected microwave energy can contribute to the acceleration of particles. It can be interpreted that the larger R is, the better the acceleration efficiency is. As can be seen from FIG. 4, the structure shown in FIG. 3 is superior to the structure shown in FIG. 2 in this respect.

As mentioned above, the conventional structure shown in FIG. 2 and FIG.
/ b p rvt / 0% and ordinary, all of which have their advantages and disadvantages, and there is no structure that is superior to both.

[Purpose of the invention]

An object of the present invention is to provide a high acceleration electric field type accelerator in which both E, /g and Vt/C are large without significantly sacrificing the effective shunt impedance R.

[Summary of the invention]

The basic structure of the present invention is shown in FIG. In the present invention, two washers 12 are installed coaxially in a cylinder 11 at a distance d and periodically with a period length, and each washer 12 has an opening in the center through which charged particles pass. 15 are provided.

However, the portion connecting the bushing 12 and the cylinder 11 is omitted here. This structure is the second conventional example.
Although it is similar to the periodic structure of the two disks 22 shown in the figure, it is essentially different in the following points. That is, in the structure of FIG. 2, the coupling cavity 28 is coaxial with the accelerator @29 and the former is never on the circumference of the latter.

In contrast, in the structure of FIG. 1 according to the present invention, the coupling cavity 18 also extends over the circumference of the acceleration cavity 9. With this point in mind, the background to the present invention will be described.

First, in order to increase g wa / E p and ensure a high acceleration electric field, the presence of a protrusion such as the nose cone 34 on the washer 32 shown in FIG. 31 is not desirable. This is because, as mentioned above, the four fields are concentrated on this protrusion. Therefore, regarding the structure of the washer, as seen in the disk 22 shown in FIG.
A disk-shaped one that is smooth in the direction perpendicular to the beam axis 100 is preferable.

In addition, in order to increase Vg/C and smooth the microwave energy propagation, as shown in Figure 3,
It is preferable to have a structure in which a coupling cavity 38 is provided around the acceleration cavity 39 to strengthen the coupling of microwave modes between each cell.

In this case, a certain gap (which forms the coupling cavity 38) will exist between the washer and the cylinder, and this will cause the electric field to concentrate in this gap of the washer.

Furthermore, the electric field is concentrated near the opening in the center of the washer through which the particles pass. These electric field concentrations are much lower in degree than the electric field concentration at the nose cone 340 portion on the washer 34 in FIG. 3, but they should still be noted. The washer spacing at both ends of one cell is g
Let the length of one cell be L. The ratio of g to L
When /L is changed from 0.5 to 1, the ratio between the electric field strength in the gap between the washer and the cylinder around the washer and the electric field strength near the opening through which particles pass through the center of the washer also changes greatly. Here, when gZL is reduced, if the washer is constructed using only one washer, the thickness of the washer itself becomes large, and such a situation cannot be said to be a desirable structure when considering the effective shunt impedance FLt. Therefore, when gZL is made smaller, the structure of the accelerator tube is such that each cell is separated by two relatively thin washers.

The ratio of the electric field strength around the washer to the electric field strength at the center of the washer is one of the characteristics of the accelerator tube, E, /
It has a big impact on E. In Figure 5, gZL is 065
The change in H-/E p when changing from to 11 is shown. Here, the reason why we did not look at g/L below 0.5 is because, structurally speaking, g/L=0.5 and gZL>o, s are equivalent just by completing half a cycle. As can be seen from FIG. 5, at g/La O, 65, 3. /Ep is maximum.

In the structure described above, although the effective shunt impedance R, which is a measure of acceleration efficiency, is inferior to that of the structure shown in FIG.
, /C can both be increased. That is, in the structure according to the present invention, the acceleration electric field strength on the beam axis can be brought close to the maximum electric field strength determined by the discharge limit, and microwave energy can be smoothly supplied.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG. 6. In a cylinder 11 made of a good i1!4 body with low high frequency loss, a set of two discs separated by a distance d are arranged in the axial direction. A set of disks is formed periodically with the period length. The disc is stem 1
It is connected to the cylinder by 3. The number and size of the stems 13 must be determined in consideration of the axisymmetric and non-axisymmetric TE, TM modes, etc. of the microwaves generated in the cylinder 11 so as not to impede particle acceleration.

The particle beam was inserted into the center of the washer 12.
15 and runs on the central axis of the cylinder 11. As for the material of the washer 12, like the cylinder 11, a good conductor with little high frequency loss is used. As shown in Figure 1, in this ditch h, there are two bodies separated by a distance g.
An acceleration cavity 19 is formed between the two washers, and the microwave acceleration modes in each acceleration cavity are combined by the space around the cavity 19 and the space formed by the two washers separated by a distance d. forming a bonding cavity.

To help understand the acceleration cavity and the coupling cavity, Figure 7(a) shows the distribution of electric lines of force inside the acceleration tube, and the seventh factor (b)
The electric field strength distribution on the central axis of the K-acceleration tube is shown.

In addition, figure (a) is obtained as (linear density of electric lines of force) oc (g field strength) x (radius 1. In addition, figure (b)
) correspond to position r11 shown in IC in FIG. [Modifications of the present invention and their effects] Since the essence of the present invention is the structure of the washer 12 itself and the arrangement relationship with the cylinder 11, the following are modifications of the present invention:
Stem 13 that fixes the wax sear 12 to the cylinder 11
Various variations of the structure of can be considered.

First, an example of this is shown in Figure gJc7. A stem 13 is provided for each washer 12 to support it in the radial direction.

The unique advantage of this structure is its ease of manufacture. One way to manufacture this type of accelerator tube is to first make the stem 1.
3 and the washer 12, and then the cylinder 11
A possible method is to combine them by electroforming or the like. in this case,
In this structure, the structure in which the stem 13 and the washer 12 are combined is exactly the same, which has the effect of increasing mass productivity. Furthermore, since the structure itself is simpler than that shown in FIG. 6, it also has the effect of increasing processing accuracy.

A second modification is shown in FIG. Although the structure in which the stem 13 and the washer 12 are connected is the same as that shown in FIG. 7, the position in which the stem 13 and the cylinder 11 are connected is different. When the number of stems is three, as shown in FIG. 8, the positions of the stems are shifted in phase by 60 degrees in the circumferential direction. This structure has the following effects in addition to the unique effects shown in FIG. In other words, in the structure shown in Fig. 6, there is a risk that higher-order modes of TMss may occur, but in the structure shown in Fig. 8, such higher-order modes can be prevented from occurring, and the microwave energy is concentrated in the acceleration mode. This makes it possible to increase acceleration efficiency by supplying the fuel to the TMos mode.

A third modification is shown in FIG. This changes the structure of the stem from a radial support system to an axial support system. This structure has the advantage that there is no radial support and the stem 90 supporting the washer 12 only needs to be supported at both ends of the acceleration tube in the axial direction, making it much easier to manufacture the 5-acceleration tube. Further, generally, a cooling pipe for cooling the washer and the stem runs through the stem, but in this structure, the pipe is in a straight line, so even if this point is taken into account, manufacturing is easier.

A fourth modification is shown in FIG. This supports several washers as a set in the radial direction. When the length of the accelerating tube becomes very long, in the structure shown in FIG. 9, the thickness of the stem 90 becomes thick in order to ensure the rigidity of the stem 90, and the loss of microwave energy increases. Therefore, as shown in FIG. 10, a stem structure can be considered in which the whole is divided into several groups and each group is supported together. This corresponds to an intermediate structure between the structure shown in FIG. 6 and the structure shown in FIG. 9.

Various structures of the stem supporting the 17 shears 12 have been described above as modified examples of the present invention, but the essence of the present invention is the structure of the washer 12 itself and the mutual positional relationship between the washer 12 and the cylinder 11. It goes without saying that other embodiments of the same nature also apply to the present invention.

Although the present invention has been described above with reference to an example in which it is applied to a linac, the present invention can also be applied to an acceleration cavity 11G in a ring-shaped accelerator as shown in FIG.

Furthermore, regarding the effective shunt impedance, which is a measure of acceleration efficiency, the present invention is inferior to the conventional example shown in FIG. Weaknesses can be completely eliminated.

[Effects of Examples]

For example, according to the embodiment shown in FIG. 6, the effective shunt impedance, which is a measure of acceleration efficiency, is not significantly sacrificed compared to the structure shown in FIG. E-/EP, which is the ratio to the maximum electric field strength, can be made close to 1. This means that the maximum electric field strength on the beam axis can be increased to a level approximately equal to the electric field strength determined by the discharge limit. In addition, since the energy propagation speed v5 of the microwave can be increased to about 50 tones of the speed of light C, it also has the effect of smoothing the energy supply of the microwave to the accelerator tube.

〔Effect of the invention〕

According to the present invention, a high acceleration electric field type linac can be provided without significantly sacrificing particle acceleration efficiency. As a result, for example, in the case of an IGeV-class high-energy acceleration linac, the length of conventional linacs was approximately 30 m, but
It can be completed with a length of about 10 m, making a great contribution to making linacs more compact.

[Brief explanation of drawings]

FIG. 1 is a typical structural diagram showing the contents of the present invention, FIGS. 2 and 3 are diagrams showing a conventional example, and FIG. 4 is a diagram showing a comparison between the present invention and the conventional one. Fig. 5 is a diagram showing the relationship between the structure of the present invention and performance characteristics, Fig. 6 is a diagram showing one embodiment of the present invention, and Fig. 7 (a) is a diagram showing the lines of electric force in the structure of the present invention. FIG. 7 is a diagram showing the electric field strength distribution in the structure. Figures 8 to 8 are diagrams showing modified examples of the present invention, and Figure 8 is a diagram showing an applied example of the present invention. 11.21,31...Cylinder, 12...Washer, 13.33,90.91...Stem, 15,25
゜35...Charged particle beam passage opening, 18,28゜38...Coupling cavity, 19,29.39...Acceleration cavity, 22.36...Disk, 23...Coupling acceleration mode Aperture for passing microwaves, 100...
Charged particle beam. ￥11 口′fJt 口次＋ 口 横浜express ￥JS Kuchishishima et al■ L (11th generation) Arithmetic 8 figure 10 II

Claims (1)

[Claims] 1. The accelerator tube is composed of a cylinder made of a good conductor, and a plurality of washers arranged inside the cylinder so that the center axis is the same as that of the cylinder. In an accelerator that accelerates charged particles by forming a coupling cavity with a periodic acceleration cavity, the washer that partitions each of the acceleration cavities is composed of two disks having an opening in the center through which the charged particles to be accelerated pass. an accelerator, characterized in that there is a gap for forming a coupling cavity between the outer periphery of the disks and the inner periphery of the cylinder. 2. In the accelerator described in claim 1, the ratio g/L of the distance g between the disks on both sides of the acceleration cavity that partitions the acceleration cavity to the periodic length L of the acceleration tube is 0. 6
An accelerator characterized by being located near 5. 3. The accelerator as set forth in claim 1 or 2, wherein the two discs that partition the coupling cavity are supported as a set by the cylinder. 4. The accelerator according to claim 1 or 2, wherein each of the disks is independently supported by the cylinder. 5. In the accelerator described in claim 1 or 2, all the disks are coupled in the axial direction,
An accelerator characterized in that the accelerator is supported at an end of the accelerator tube. 6. The accelerator according to claim 3, wherein a plurality of pairs of the disks are supported by the cylinder.