JP2000294399A - Superconducting high-frequency acceleration cavity and particle accelerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, at a relatively low cost, a simplified cooling structure, in particular, a structure for helium freezing and magnetic shielding, around a cavity body made of a superconducting material. SOLUTION: This superconducting high-frequency acceleration cavity is equipped with a cavity body 1 for accelerating a charged particle beam BE by high-frequency power, a vacuum container 10 for housing beam pipes 2a, 2b for inputting/outputting the beam BE into/out of the cavity body along a beam axis AX and housing an input coupler 4 for supplying high-frequency power into the cavity body 1, a liquid helium storage tank 11 disposed around the cavity body 1 within the vacuum container 10 and storing cryogenic helium capable of maintaining a superconducting state of the cavity body 1, a radiant heat shield 13 disposed around the liquid helium storage tank 11 in the vacuum container 10 and suppressing heat invasion from the exterior, and a magnetic shield 12 disposed around the liquid helium storage tank 11 in the vacuum container 10 and reducing the strength of a magnetic field in the cavity body 1. The magnetic shield 12 is made up in a dual manner of mutually independent first and second magnetic shields 12a, 12b, and the first magnetic shield 12a is integrally formed with the vacuum container 10, which the second magnetic shield 12b is disposed in a cryogenic part positioned near the liquid helium storage tank 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a superconducting high-frequency accelerating cavity and a particle accelerator, and more particularly to an improvement in a cryostat structure of a superconducting high-frequency accelerating cavity suitable for a linear accelerator, a synchrotron, a storage ring, and the like.

[0002]

2. Description of the Related Art A particle accelerator such as a linear accelerator, a synchrotron, and a storage ring for accelerating charged particles such as electrons, protons, and ions has a high-frequency accelerating cavity mounted on a beam line of the charged particles. . This high-frequency accelerating cavity
The charged particles are accelerated by high-frequency electric power, but this generates a high-frequency circulating current on the inner surface and causes Joule loss, so that the electric resistance becomes substantially zero to avoid this high-frequency loss A device made of a superconducting material is known. For example, using a niobium material which is a superconducting material, a cavity body having a thickness of about 1.5 mm is manufactured, and a plurality of the pure niobium cavity bodies are mechanically connected in the beam axis direction to form a multiple structure. Resonant frequency 500MH configured
An example of a z-band high-frequency accelerating cavity can be given.

In such a high-frequency accelerating cavity, a superconducting material cavity body is housed in a horizontal cryostat,
By immersing and cooling in a large amount of 4K liquid helium inside, the inside surface of the cavity body is brought into a superconducting state under an extremely low temperature environment. An example of this is shown in FIG.

A superconducting high-frequency accelerating cavity shown in FIG. 8 is mounted at a predetermined position on a beam line of a particle accelerator (not shown), and is formed by using a superconducting niobium material for forming and electron beam welding. , And beam pipes 101a (input side) and 101b connected to both ends of the body 100, respectively.
(Output side), an input coupler 103 for inputting high frequency power for beam acceleration into the cavity main body 100 through an input port (high frequency power supply port) 102 provided in the input side beam pipe 101a, and HO for taking out harmonics (HOM) excited by beam passage
A stainless steel vacuum container (constituting a cryostat main body) 110 accommodating each of the M couplers 104, a helium liquid storage tank 111 disposed in the vacuum container 110,
A radiation heat shield 112 and a magnetic shield 113 are provided. A piezoelectric element tuner is provided at an end of the vacuum vessel 110 in the beam axis direction AX in order to correct a change in the resonance frequency of the cavity body 1 due to a pressure change in the cryostat, mechanical vibration, or the like. 105 is attached so that the length of the cavity body 100 can be finely adjusted.

The helium reservoir 111 is a container surrounding the cavity body 100, the two beam pipes 101a and 101b, the input port 102, etc., as shown in FIG. Helium HE is received into the 4K liquid via the provided helium supply port 111a, and the cavity body 100 is introduced into the helium HE.
So as to cool it to an extremely low temperature and maintain its superconducting state.

The radiant heat shield 112 is disposed around the helium liquid storage tank 111 so as to form an adiabatic vacuum tank.
Liquid nitrogen or gas helium is received via a cooling pipe (not shown), thereby suppressing heat intrusion from the atmosphere.

The magnetic shield 113 is made of, for example, an iron-nickel soft magnetic alloy (permalloy), and is placed, for example, on the radiant heat shield 112 so as to reduce the magnetic field inside the cavity body 100 by 10 to 10. 20
The purpose of the present invention is to reduce to about milligauss, and to prevent deterioration of superconductivity on the inner surface of the cavity due to the influence of the magnetic field. As another example of the arrangement of the magnetic shield 113, there is also known an arrangement along the inner surface of the vacuum vessel 5.

[0008]

In the conventional superconducting high-frequency accelerating cavity described above, the cavity main body is put into a liquid helium liquid storage tank together with an input port and the like, immersed in 4K liquid helium, and cooled. Maintaining the superconducting state of the cavity body and preventing the deterioration of superconducting characteristics due to the magnetic field inside the cavity body by tying the magnetic shield to the 80K radiation heat shield or placing it between the 80K radiation heat shield and the vacuum vessel Therefore, there are the following problems.

First, in the case of the above-mentioned 4K cooling system using 4K liquid helium, the amount of heat infiltration per cavity body is about 30 W. That is all. The amount of heat generated by the latter high frequency is determined by the surface resistance of the niobium material forming the cavity body. The surface resistance of this niobium material depends on temperature and is 4
In the case of K, for example, it is 10 times or more larger than the case of 2K. This means that in the case of 4K, the consumption of liquid helium for cooling the heat generated by the cavity heat is considerably larger than in the case of 2K. Therefore, there has been a problem that the configuration of the entire helium refrigeration system is complicated and relatively expensive. Also, if the surface resistance is large, the RF characteristics in the cavity deteriorate, and the electric field characteristics also deteriorate.

On the other hand, since the magnetic shield is arranged near the vacuum vessel remote from the cavity body to be magnetized, the magnetic shield requires a thickness and a large shield shape, so that the amount of material used increases. There was a problem. In addition, the assembly structure of the magnetic shield material is considerably complicated because there are a considerable number of openings such as coupler ports and the like, helium supply, discharge pipes, supports and the like.

The present invention has been made in consideration of such a conventional problem, and simplifies a cooling structure around a cavity body made of a superconducting material, in particular, a structure of a helium refrigeration and a magnetic shield. The purpose is to provide a reasonable price.

Another object of the present invention is to improve the RF characteristics of the cavity body.

[0013]

Means for Solving the Problems To achieve the above object, the present inventor first focused on reducing the surface resistance of niobium material by lowering the cooling temperature of a cavity body by a cooling system from 4K to 2K. did. When the surface resistance of the niobium material is low, the amount of heat generated by the high frequency of the cavity body is reduced, and as a result, the total helium consumption is reduced to less than half, so that the overall configuration of the helium refrigeration system is simplified. And can be provided at low cost. In addition, when the surface resistance of the niobium material is small, the RF characteristics in the cavity are improved, so that the acceleration performance can be greatly improved.

At the same time, if the vacuum vessel is made of a conventional stainless steel material such as an iron-based steel material having a magnetic shielding effect and is also used as a magnetic shield, a dedicated magnetic shield inside the vacuum vessel can be arranged in the above-described conventional arrangement. It was found that it could be placed closer to the cavity body side than the location, and that further miniaturization was possible.

The present invention has been completed based on the above findings.

That is, a superconducting high-frequency accelerating cavity according to the first aspect of the present invention is a cavity main body for accelerating a charged particle beam by high-frequency electric power, and the charged particle beam is inserted into the cavity main body in the beam axis direction. Beam pipe to output,
And a vacuum container containing a coupler for supplying the high-frequency power in the cavity main body through the beam pipe, and disposed around the cavity main body in the vacuum container and capable of maintaining the superconducting state of the cavity main body. A helium reservoir for storing extremely low-temperature helium, a radiant heat shield disposed around the helium reservoir in the vacuum vessel and suppressing heat intrusion from outside the vacuum vessel, and a helium reservoir in the vacuum vessel. And a magnetic shield arranged to reduce the magnetic field intensity in the cavity body, wherein the magnetic shield is constituted by a first and a second magnetic shield which are independent of each other, and wherein the first magnetic shield is The second magnetic shield is formed integrally with the vacuum vessel, and is disposed near the periphery of the helium liquid storage tank.

According to this configuration, the cavity main body, the helium reservoir for keeping the cavity main body at a very low temperature, the magnetic shield, the radiant heat shield, and the vacuum vessel disposed outside the helium reservoir. A beam pipe connected to both ends of the cavity body, and an input coupler attached to the beam pipe, a vacuum vessel is used as a first magnetic shield to reduce a magnetic field inside the cavity body, and the cavity body is A second magnetic shield may be provided in the cryogenic portion just outside the helium reservoir for cryogenic conditions.

According to a second aspect of the present invention, in the first aspect of the present invention, the helium liquid storage tank has a shape surrounding the cavity body concentrically with its beam axis as a center axis. It is characterized by.

According to a third aspect of the present invention, in the first aspect, the helium stored in the helium liquid storage tank is superfluid helium capable of cooling the cavity body to a temperature of 2 K or less. And

According to this configuration, the helium liquid storage tank has a capacity of 2K.
By storing the superfluid helium, cooling the cavity body to 2K or less, and providing a magnetic shield at the cryogenic portion just outside the 2K helium liquid storage tank, the high-frequency characteristics can be further improved.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the radiant heat shield includes a low-temperature side and a high-temperature side radiant heat shield, and the low-temperature side radiant heat shield is disposed around the helium liquid storage tank. The high-temperature-side radiant heat shield is disposed around an outer periphery of the low-temperature-side radiant heat shield.

According to this configuration, the helium liquid storage tank has a capacity of 2K.
The superfluid helium is stored and the cavity body is cooled to 2K or less, and a 4K radiant heat shield is provided outside the helium reservoir tank as a low-temperature radiant heat shield, and the 4K cooling system is independent of the 2K superfluid helium cooling system. And high-frequency characteristics can be further improved.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, a low-temperature side reservoir for storing a refrigerant for cooling the low-temperature side radiant heat shield and a high-temperature side for storing a refrigerant for cooling the high-temperature side radiant heat shield are provided. A side liquid reservoir is provided in the vacuum container.

According to this configuration, the helium liquid storage tank has a capacity of 2K.
Liquids of a low-temperature side refrigerant such as 4K liquid helium and a high-temperature side refrigerant such as liquid nitrogen for cooling the cavity main body to 2K or less by storing the superfluid helium and cooling each radiant heat shield on the low temperature side and the high temperature side. The reservoirs are separately provided, so that the high-frequency characteristics can be further improved. In this configuration, for example, thermal anchors corresponding to respective temperatures can be provided at predetermined positions of the beam pipe and the input coupler. In this case, the thermal anchor can be cooled by the refrigerant from each liquid reservoir.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, an indirect cooling unit is provided between each of the liquid reservoirs on the low temperature side and the high temperature side and each radiant heat shield.

According to this configuration, for example, the radiant heat shield (and the thermal anchor) can be cooled by indirect cooling from the reservoir of the low-temperature side refrigerant and the high-temperature side refrigerant.

The invention according to claim 7 is characterized in that, in the invention according to claim 6, each of the liquid reservoirs is constituted by a pipe.

According to an eighth aspect of the present invention, in the invention of the seventh aspect, each of the pipes is arranged so as to be inclined so that the outlet side of the refrigerant is higher than the inlet side. It is characterized by.

According to a ninth aspect of the present invention, in the first aspect of the present invention, a guide mechanism for centering the cavity body in a beam axis direction is further provided in the vacuum vessel. Features. This guide mechanism can be configured to be shared by, for example, a 4K radiation heat shield. In this case, the 2K superfluid helium is stored in the helium liquid storage tank to cool the cavity main body to 2K or less, and the beam axis accuracy of the cavity main body can be enhanced by the guide mechanism for centering which is also used by the 4K radiation heat shield, Thereby, high frequency characteristics can be improved.

According to a tenth aspect of the present invention, in the first aspect of the present invention, the cavity body has a niobium material on an inner portion in a thickness direction thereof and a metal material having excellent thermal conductivity on an outer portion thereof. It is characterized by comprising a clad material. Examples of the metal material having excellent heat conductivity include copper or an aluminum alloy.

According to an eleventh aspect of the present invention, there is provided a particle accelerator including the superconducting high-frequency accelerating cavity according to any one of the first to tenth aspects.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a superconducting high-frequency accelerating cavity and a particle accelerator according to the present invention will be described below with reference to the drawings.

(First Embodiment) The superconducting high-frequency accelerating cavity shown in FIG. 1 is applied to a particle accelerator such as a linear accelerator, a synchrotron, and a storage ring, and the charged particle beam BE in the particle accelerator is used. A cavity body 1 and beam pipes 2a (input side) and 2b (output side) connected to both ends thereof are provided at a predetermined position in the axial direction AX, and the input side pipe 2a is provided with an input port 3 for beam acceleration. An input coupler 4 for supplying high-frequency power is connected, and these cavity bodies 1 and the like are housed in a vacuum vessel 10, and a helium liquid storage tank 11, a magnetic shield 12, and the like are provided around the cavity body 1 in the vacuum vessel 10. The radiation heat shield 13 is arranged.

The cavity body 1 is formed into a predetermined cylindrical member by a method such as molding and electron beam welding using a niobium material which is a superconducting material, and a beam axis A in the vacuum vessel 10 is formed.
It is arranged coaxially with X. In the cavity body 1, the charged particle beam BE input from the outside (beam line) of the vacuum vessel 10 to the beam axis AX via the input side beam pipe 2 a is resonated and accelerated by the high frequency power from the input coupler 4. Are output through the output side beam pipe 2b.

The helium reservoir 11 surrounds the cavity body 1 in the vacuum vessel 10 concentrically around its beam axis AX, and its length in the beam axis direction is the cavity body 1 and both beam pipes 2a, The dimensional conditions are set so as to substantially cover the area between the connection portion 2b and the connection portion, and the amount of liquid helium used for this purpose is greatly reduced. In addition, this allows only the cavity main body 1 to be immersed in the liquid helium HE so that the superconducting state of the niobium material can be maintained and cooled. This helium reservoir 1
The liquid helium HE in 1 is supplied through a helium supply port 10a provided in the vacuum vessel 10.

The magnetic shield 12 is composed of two independent first and second magnetic shields 12a and 12b.

The first magnetic shield 12a is formed integrally with the vacuum vessel 10 by using, for example, a steel material having iron-based magnetism, thereby reducing the magnetic field level such as geomagnetism around the vacuum vessel 10 to a predetermined level. Has become.

The second magnetic shield 12b is made of, for example, iron-
It is composed of a nickel-based soft magnetic alloy (Permalloy)
The first magnetic shield 12 is installed concentrically with the beam axis AX near the cryogenic portion just outside the helium reservoir 2.
The level of the magnetic field reduced by the vacuum vessel 10 constituting a can be further reduced to a level of about 10 to 20 milligauss inside the cavity body 1.

The radiant heat shield 13 is disposed outside the second magnetic shield 12b as an adiabatic tank, whereby heat intrusion from the atmosphere can be suppressed. In the vicinity of the radiation heat shield 13, for example, a pipe 13a for a shield cooling system through which liquid nitrogen (or gas helium) flows is installed, and the radiation heat shield 13 can be cooled by the liquid nitrogen in the pipe 13a.

According to this embodiment, double magnetic shields independent of each other are employed, the first magnetic shield is formed integrally with the vacuum vessel using an iron-based material, and the second magnetic shield is formed as the cavity body. Since it is provided exclusively in the vicinity, it can be reduced to about 10 to 20 milligauss which does not affect the reduction of the high frequency characteristics without impairing the shielding effect of the external magnetic field with respect to the inside of the cavity body. The shape of the magnetic shield can be reduced and the assembly structure can be simplified. As a result, the amount of use of a dedicated magnetic shield using expensive permalloy or the like can be significantly reduced, so that a superconducting high-frequency accelerating cavity and a particle accelerator can be provided more simply and at lower cost than in the conventional example.

It is known that ordinary permalloy used in a dedicated magnetic shield has a drawback that its magnetic field characteristics are high at room temperature and its characteristic value is 1/5 or less at extremely low temperatures. Taking into account the above, it is possible to reduce the magnitude of the magnetic field in the cavity body by installing the magnetic shield at a position close to the cavity body side as compared with the conventional example. As the type of permalloy, besides permalloy at room temperature, it is also possible to use permalloy for low temperature, which is a little more expensive but commercially available. In the case of this permalloy for low temperature, it has almost the same magnetic field characteristics as at room temperature even at extremely low temperatures, and the magnitude of the magnetic field in the cavity body can be greatly reduced.
It is possible to further reduce the amount of use compared to the increase in material unit price, and in terms of overall material costs, it is possible to provide a magnetic shield at a lower cost than if room temperature permalloy was provided near the inner wall of the vacuum vessel There are advantages too.

In this embodiment, the cavity body is formed in a single-cell shape. However, the present invention is not limited to this shape and structure. For example, a plurality of single-cell-shaped cavity bodies are continuously connected. The present invention can be applied to a multiple cavity (for example, five or nine cavities).

Also, the input port may be installed at a location where the coupling is weak because most of the high-frequency power from the input coupler to the cavity body is used for the beam, and the input port is provided on the input beam pipe. However, the present invention is not limited to this, and the present invention can also be applied to a configuration in which it is provided directly on the cavity body or provided at another position. It is also possible to provide a sealing material (wire or ribbon) made of indium at the connection between the input port and the coupler.

The input coupler can be formed of a coaxial tube or a waveguide (for example, a coaxial tube in the case of a frequency of 1.5 GHz or more) depending on the frequency used. Since it is necessary to prevent high frequency loss and heat intrusion from the room temperature especially for a superconducting acceleration cavity, it is desirable to manufacture the stainless steel with a copper plated material.

(Second Embodiment) In the first embodiment described above, a helium liquid reservoir having a shape surrounding only the cavity body is provided, but this embodiment utilizes the advantages of this helium liquid reservoir and the like. In addition, a structure is devised for preventing high-frequency loss and suppressing heat generation in the cryogenic portion due to heat intrusion from the room temperature side. This structure is shown in FIG.

The superconducting high-frequency accelerating cavity shown in FIG. 2 has the same structure as the above-described double magnetic shields 13a and 13b, etc. A structure using 2K superfluid helium, which cools the cavity body 1 to 2K or less and brings it into a superfluid state, is adopted. That is, this structure is the same as the vacuum vessel 1 described above.
0 (first magnetic shield 12a), helium reservoir (2
K helium reservoir) 11, the second magnetic shield 12b,
In addition to the radiation heat shield (high-temperature side radiation heat shield) 13,
2K helium cooling system (pipe) 1 for supplying 2K liquid helium to helium liquid storage tank 11 via cooling port 10a
4 and a 4K radiant heat shield (low-temperature radiant heat shield) which is disposed around the second magnetic shield 12b and prevents heat from entering by radiation separately from the high-temperature radiant heat shield 13 described above.
15 is included.

According to the second embodiment, in addition to the same effect as the double magnetic shield described above, by cooling the cavity body to 2K or less, the surface resistance of the cavity body can be reduced as much as possible. As a result, the amount of heat generated by the cavity body can be reduced to reduce the overall helium consumption, and a high electric field can be achieved due to the low surface resistance of the cavity, and accordingly, the high-frequency characteristics of the cavity body, in other words, This has the advantage that acceleration performance can be enhanced. As a result, the high-frequency characteristics of the cavity main body can be enhanced, and the number of high-frequency acceleration cavities can be reduced even from the viewpoint of the entire particle accelerator. Further, the total helium consumption can be reduced, and an economically excellent particle accelerator can be provided.

In this embodiment, a 4K radiant heat shield is provided as a low-temperature radiant heat shield. However, the present invention is not limited to this. For example, a configuration in which several tens of aluminum vapor-deposited thin films are provided is also applicable. .

(Third Embodiment) In the above-described second embodiment, the space between the 2K helium liquid storage tank and the high-temperature side heat radiation shield is 4 mm.
Although a K radiation heat shield is provided, in this embodiment, the structure is further devised while utilizing the advantages such as the 4K radiation heat shield. This structure is shown in FIG.

The superconducting high-frequency accelerating cavity shown in FIG. 3 includes a vacuum vessel 10 (first magnetic shield 12a) similar to that described above,
A 2K helium liquid storage tank 11, a second magnetic shield 12b,
In addition to the high-temperature radiant heat shield 13, the 2K cooling system 14, the 4K radiant heat shield 15, the 4K cooling system 16 for the 4K radiant heat shield cooling independent of the 2K helium cooling system 14, the beam pipe 2a and the input port 3 A 4K thermal anchor 17 thermally connected to the 4K cooling system 16 at a predetermined position is provided. An ordinary system for circulating liquid helium can be applied to the 4K cooling system 16.

In this embodiment, a 4K radiant heat shield is provided between the 2K helium liquid storage tank and the high-temperature side heat radiation shield, so that heat invasion due to radiation into the cavity body can be reduced and independent 4K helium cooling can be performed. There is an advantage that a 4K thermal anchor can be installed in the system and the beam pipe and the input port, thereby greatly reducing heat invasion due to heat transfer to the 2K side.

Further, by providing a separate 4K helium cooling system independent of the 2K helium cooling system for cooling the cavity body, a 4K radiant heat shield or 4K thermal anchor can be provided by using, for example, a 2K return line. Compared to a system that cools down to 4K, 4K cooling can be performed stably without being affected by a change in the thermal load in the cavity body, and 2K cooling of the cavity body can be stably maintained accordingly. Furthermore, in order to cut off heat intrusion from the high temperature side at the 4K part,
The heat load of the 2K helium cooling system can be reduced, and the scale of the 2K helium cooling system can be reduced.

Therefore, according to this embodiment, in addition to the same effects as the above-described second embodiment, since a 2K helium cooling system and a 4K helium cooling system are provided independently, radiation and transmission from the high temperature side are performed. Most of the heat intrusion due to heat can be cooled by the 4K helium cooling system, and the 2K helium cooling system only cools the heat generated from the inside of the cavity body.
The size of the K superfluid helium system can be made as small as possible, and as a whole, a cooling system that is less expensive than before can be provided.

In this embodiment, the 2K helium cooling system and the 4K helium cooling system are provided independently of each other inside the vacuum vessel. However, the present invention is not limited to this.
For example, it is possible to simultaneously generate 2K superfluid helium and 4K normal liquid helium outside the vacuum vessel with one cooling system and supply them through another piping system.

(Fourth Embodiment) In this embodiment, in addition to the structure similar to that of the above-described third embodiment, a mechanism for adjusting the centering of the cavity main body using a part of the components in the vacuum vessel is devised. It was done. This configuration is shown in FIG.

The superconducting high-frequency accelerating cavity shown in FIG. 4 serves as a guide mechanism for adjusting the centering of the cavity main body 1 in addition to the 4K radiant heat shield 15 and from the vacuum vessel 10 via the 4K radiant heat shield 15. And a support structure 18 whose position in the axial and radial directions is adjustable. 4
The K radiation heat shield 15 is formed in a cylindrical structure, and its end plate portions are fixed to flange portions of both beam pipes 2a and 2b, respectively. The support structure 18 is provided in the vacuum vessel 10.
It is made of a material having a low thermal conductivity, such as FRP, in order to suppress heat intrusion from the outside.

Here, the centering method by the above-mentioned guide mechanism will be described.

Usually, the positioning of the cavity body 1 with respect to the beam axis AX is required to have an accuracy within 1 mm in consideration of the acceleration characteristics of the charged particle beam BE passing therethrough. It is difficult to align the cavity body 1 with the beam axis AX of the beam line BL. this is,
This is because the cavity body 1 is accommodated in the vacuum vessel 10 and is restricted.

Therefore, when assembling the vacuum vessel 10,
The end plates of the 4K radiation heat shield 15 and the flanges of the beam pipes 2a and 2b coaxially connected to the cavity body 1 are fixed to each other so that the center axes of the cavity body 1 and the 4K radiation heat shield 15 coincide with each other. In this state, the 4K radiation heat shield 1 is supported by the support structure 18 supported by the vacuum vessel 10.
Support 5 Then, by adjusting the length and angle of the support structure 18 after assembling the vacuum vessel 10, 4K
The central axes of the beam pipes (beam pipes for vacuum vessel connection) 2a and 2b, that is, the central axis of the cavity main body 1, and the beam axis direction AX of the beam lines BL and BL are made to coincide with accuracy of 1 mm or less via the radiation heat shield 15. Can be adjusted as follows.

Therefore, according to this embodiment, in addition to the same effects as those of the third embodiment, one cavity body which is usually housed in a vacuum vessel and is difficult to align with the beam axis is provided.
The centering can be performed with the required accuracy of not more than mm, thereby providing an accelerating cavity having excellent installation accuracy and accompanying acceleration characteristics.

(Fifth Embodiment) In this embodiment, the structure is further devised in addition to the same structure as the above-described fourth embodiment. This structure is shown in FIG.

In the superconducting high-frequency accelerating cavity shown in FIG. 5, the high-temperature-side radiant heat shield 13 similar to that described above is constituted by an 80K-wide radiant heat shield using liquid nitrogen of 80K, and the 80K-wide radiant heat shield 13 is cooled. On the bottom side along the beam axis AX of the high-temperature side radiant heat shield cooling system 13b, an 80K liquid nitrogen reservoir 19 and a beam pipe 2a,
An 80K thermal anchor 20 is installed at the end of the vacuum vessel 2b.

The beam axis A of the 4K helium cooling system 16 is provided on the 4K radiant heat shield 15 side in the vacuum vessel 10.
A 4K liquid helium reservoir 21 is provided on the bottom side along X, and a 4K thermal anchor 17 is provided on the cavity body side of the beam pipes 2a and 2b.

Further, between the 80K thermal anchor 20 and the 80K liquid nitrogen reservoir 19, between the 80K radiant heat shield 13 and the 80K liquid nitrogen reservoir 19, and between the 4K thermal anchor 17 and the 4K liquid helium reservoir 21. Between the 4K radiant heat shield 15 and the 4K liquid helium reservoir 21, there is a copper plate, an aluminum plate, and an indirect cooling unit 22 such as a high-purity aluminum sheet, copper foil, or copper wire.
... 22 are installed. By adopting a cooling structure for indirectly cooling the above-mentioned elements by the indirect cooling unit 22, the piping system is provided with a cooling system using liquid nitrogen, nitrogen gas vaporized by the liquid nitrogen, liquid helium and helium gas vaporized by the liquid nitrogen. , The cooling structure can be made simpler, and the structure of the whole vacuum vessel can be simplified.

Both the 80K and 4K reservoirs 19, 2
Each of the pipes 1 has a configuration in which, for example, pipes having a diameter larger than pipes (supply pipes and discharge pipes) forming the cooling systems 6 and 13 are used, each refrigerant is stored in the pipes, and both ends are covered with lids. ,
Beam pipes 2a and 2b in an installed state in a vacuum vessel
It is arranged substantially parallel to the beam axis direction AX at a predetermined position below. The configuration using this piping has an advantage that the heat transfer distance can be made as uniform as possible in a narrow space so that each part can be cooled evenly without having to separately provide and arrange a liquid storage container. In addition, the two reservoirs 1
9 and 21 are not limited to piping, but can be applied to other liquid storage containers.

As described above, the 4K liquid reservoir 21 is provided inside the vacuum vessel.
By storing 4K liquid helium therein, the 4K portion can be reliably cooled, and stable ripening at the 4K portion is ensured, which is useful for always keeping the liquid level constant. In the case of the 80K liquid reservoir 19, the same effect as in the case of 4K can be expected. Especially in the case of 80K, the vacuum vessel 1
Since it is necessary to maintain the temperature at 80K over a wide range along the inner surface of zero and the calorific value at 80K is quite large at several tens of W to 100W, the liquid reservoir 19 for storing 80K liquid nitrogen is required.
By cooling each part from the above, the 80K radiation heat shield 13 and the 80K thermal anchor 20 can be uniformly cooled.

Therefore, according to this embodiment, the fourth
In addition to the same effects as those of the embodiment, there is an advantage that the radiant heat shields of 4K and 80K and the portions of each thermal anchor can be reliably cooled with a simple structure, and a more compact vacuum vessel structure can be provided.

(Sixth Embodiment) In this embodiment, in addition to the structure of the above-described fifth embodiment, while utilizing the advantages of the 4K liquid reservoir 21 and the 80K liquid reservoir 19 constituted by piping, the vacuum container structure is further improved. It is something devised. This structure is shown in FIG.

In the superconducting high-frequency accelerating cavity shown in FIG. 6, each of the pipes forming the 4K liquid reservoir 21 and the 80K liquid reservoir 19 as described above is connected from the inlet (upstream) side of each refrigerant (liquid helium, liquid nitrogen) to the outlet. The beam axis AX has an upward slope toward the (downstream) side (the lower side is the entrance, the upper side is the exit).
Are arranged at a predetermined angle with respect to. Similar to the inclined arrangement of the pipes, other pipes for routing the inside of the vacuum vessel are also arranged so as to be always parallel to the beam axis AX on the downstream side from the liquid reservoirs 19 and 21 or have an upward inclination toward the downstream side. I do.

As described above, the 4K liquid reservoir 21, the 80K liquid reservoir 19, and the pipe downstream of each of the liquid reservoirs have an inclination, so that the 4K liquid helium and the 80K liquid nitrogen can be shielded by the shields 13, 15 and each thermal liquid. Even when the gas is vaporized by the heat load on the anchors 17 and 20, the gas is reliably discharged and does not remain in the pipe. Further, since the pipes downstream of the liquid reservoirs 19 and 21 are arranged from the lower side to the upper side, there is an advantage that the pipe structure inside the vacuum vessel can be simplified.

Therefore, according to this embodiment, the supply of 4K liquid helium and 80K liquid nitrogen to the vacuum vessel, and the discharge of helium gas and nitrogen gas vaporized by the heat load can be reliably performed, and the superconducting high-frequency acceleration air The cooling system for the body can be efficiently provided, and the structure of the vacuum vessel can be simplified.

(Seventh Embodiment) In this embodiment, in addition to the structure of the above-described sixth embodiment, the material of the cavity body is particularly improved. FIG. 7 shows the structure of the cavity body.

In the superconducting high-frequency accelerating cavity shown in FIG. 7, the cavity main body 1 to be put into the helium liquid reservoir 11 is made of a conventional niobium alone material, and only the inner surface of the cavity main body 1 requiring a superconducting state is made of niobium material. A clad material formed by joining a copper or aluminum alloy which is excellent in heat conduction and electric conductivity in a normal conductive material to the outside of the niobium material is used.

If the cladding material of niobium-copper or niobium-aluminum alloy is employed, the cavity body 1
Has a low value as before due to the superconducting state of niobium, while the heat conduction at cryogenic temperature and the mechanical strength of the cavity body 1 are maintained by the copper or aluminum alloy bonded to the outside of niobium. .

Therefore, according to this embodiment, the amount of niobium material, which is an expensive superconducting material, can be significantly reduced, the cavity body can be manufactured at low cost, and the strength of the cavity body can be reduced to copper or aluminum alloy. Since it can be made dependent on various shapes, it can be easily manufactured in a thin shape compared to the case of using only niobium. As a result, the range of design options for the superconducting high-frequency accelerating cavity can be greatly expanded, and the entire cavity system can be produced economically.

[0076]

As described above, according to the present invention,
Since the magnetic shield of the superconducting high-frequency accelerating cavity is constituted by a vacuum vessel and a dedicated shield for a low-temperature portion, the high-frequency characteristics of the cavity in the superconducting state can be improved. In addition, if a configuration in which the cavity body is cooled to 2K or less is adopted, the surface resistance of the cavity can be suppressed, and the acceleration electric field can be increased, thereby improving the performance of the cavity. Furthermore, if the structure inside the vacuum vessel is simplified by using a liquid reservoir or indirect cooling, the structure of the vacuum vessel of the superconducting high-frequency acceleration cavity can be simplified. As a result, a high-performance accelerating cavity can be obtained with a simplified structure and at a low cost, and the number of high-frequency accelerating cavities can be reduced in the entire particle accelerator, or the high-frequency An accelerator can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the entire configuration of a superconducting high-frequency acceleration cavity according to a first embodiment.

FIG. 2 is a schematic cross-sectional view illustrating the entire configuration of a superconducting high-frequency acceleration cavity according to a second embodiment.

FIG. 3 is a schematic cross-sectional view illustrating the entire configuration of a superconducting high-frequency acceleration cavity according to a third embodiment.

FIG. 4 is a schematic cross-sectional view illustrating the entire configuration of a superconducting high-frequency acceleration cavity according to a fourth embodiment.

FIG. 5 is a schematic cross-sectional view showing the entire configuration of a superconducting high-frequency acceleration cavity according to a fifth embodiment.

FIG. 6 is a schematic cross-sectional view showing the entire configuration of a superconducting high-frequency acceleration cavity according to a sixth embodiment.

FIG. 7 is a schematic cross-sectional view showing the entire configuration of a superconducting high-frequency acceleration cavity according to a seventh embodiment.

FIG. 8 is a schematic sectional view showing the entire configuration of a conventional superconducting high-frequency accelerating cavity.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cavity main body 2a, 2b Beam pipe 3 Input port 4 Input coupler 10 Vacuum container 10a Helium supply boat 11 Helium liquid storage tank 12 Magnetic shield 12a First magnetic shield 12b Second magnetic shield 13 Radiant heat shield (high-temperature side radiant heat shield) , 80K
Radiation heat shield) 13a High temperature side radiant heat shield cooling system (liquid nitrogen cooling system) 14 2K helium cooling system (piping) 15 Low temperature side radiant heat shield (4K radiant heat shield) 16 4K helium cooling system 17 4K thermal anchor 18 Support structure 19 80K liquid Nitrogen reservoir 20 80K thermal anchor 21 4K liquid helium reservoir 22 Indirect cooling unit AX Beam axis BE Charged particle beam BL Beam line HE Helium

Claims (11)

[Claims] 1. A cavity body for accelerating a charged particle beam by high frequency power, a beam pipe for inputting / outputting the charged particle beam in a beam axis direction in the cavity body, and the cavity via the beam pipe. A vacuum vessel containing a coupler for supplying the high-frequency power inside the main body, and a helium liquid that is disposed around the cavity body in the vacuum vessel and stores cryogenic liquid helium so that the superconducting state of the cavity body can be maintained. A storage tank, a radiant heat shield disposed around the helium liquid storage tank in the vacuum vessel to suppress heat intrusion from outside the vacuum vessel, and a radiant heat shield disposed around the helium liquid storage tank in the vacuum vessel and inside the cavity body. A magnetic shield for reducing a magnetic field strength, wherein the magnetic shield is double-configured with first and second magnetic shields independent of each other, Shield is formed integrally with the vacuum chamber, said second magnetic shield superconducting RF cavity for being disposed in the vicinity around the liquid helium reservoir tank. 2. The superconducting high-frequency accelerating cavity according to claim 1, wherein the helium liquid reservoir has a shape surrounding the cavity body concentrically with its beam axis as a center axis. . 3. The superconducting high-frequency accelerating cavity according to claim 1, wherein the helium stored in the helium liquid storage tank is a superfluid helium capable of cooling the cavity main body to a temperature of 2 K or less. 4. The radiant heat shield includes a radiant heat shield on a low temperature side and a high temperature side, the radiant heat shield on the low temperature side is disposed around the helium reservoir, and the radiant heat shield on the high temperature side is a radiant heat shield on the low temperature side. 4. The superconducting high-frequency accelerating cavity according to claim 3, wherein the cavity is arranged on an outer periphery. 5. The vacuum vessel includes a low-temperature side liquid reservoir for storing a refrigerant for cooling the low-temperature side radiant heat shield and a high-temperature side liquid reservoir for storing a refrigerant for cooling the high-temperature side radiant heat shield. The superconducting high-frequency accelerating cavity according to claim 4, characterized in that: 6. The superconducting high-frequency accelerating cavity according to claim 5, further comprising an indirect cooling portion between each of the liquid reservoirs on the low temperature side and the high temperature side and each radiant heat shield. 7. The superconducting high-frequency accelerating cavity according to claim 6, wherein each of the liquid reservoirs is constituted by a pipe. 8. The superconducting high-frequency accelerating cavity according to claim 7, wherein each of the pipes is arranged so as to be inclined such that the outlet side of the refrigerant is higher than the inlet side. . 9. The superconducting high-frequency accelerating cavity according to claim 1, further comprising a guide mechanism for centering which adjusts a positional accuracy of the cavity main body in a beam axis direction in the vacuum vessel. 10. The hollow body is made of a cladding material having a niobium material on an inner portion in a thickness direction and a metal material having excellent heat conductivity on an outer portion thereof. The superconducting high-frequency accelerating cavity described. 11. A particle accelerator comprising the superconducting high-frequency accelerating cavity according to any one of claims 1 to 10.