JPH01130889A - Method for joining superconducting thin film wave guides - Google Patents

Abstract

PURPOSE:To obtain a wave guide and an accelerating tube with satisfactory energy efficiency by pressing the joining faces mutually in a vacuum and heating these at the temperature lower than melting points of both base materials and superconductive materials and enabling joining the superconducting wave guides. CONSTITUTION:Two superconducting thin film hollow simple substances 5 which are finished by gas-spattering niobium 4 on the insides and cylindrical flange part end faces 3 of the hollow simple substances of hollow resonators having small through holes 2 on the centers of cross sections of the centers of the axial directions of the pure copper cylindrical base materials 1, for instance, are manufactured. The flange part end faces 3 are made to diffusion joining faces and the joining faces are abutted on each other and fixed by a bolt and a nut 7. A connector 8 of the hollow simple substances 5 joined respectively is heated at the temperature lower than the melting points of both the base materials and the superconductive materials in a vacuum furnace and the niobium 4 on the joining faces is subjected to diffusion joining mutually. As a result, the joining faces are extremely smooth and uniform without the difference with other parts and maintained completely airtight.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides superconductivity on the inner surface of waveguides for microwave transmission, particularly disk-loaded traveling wave accelerator tubes, microwave cavities, etc. The present invention relates to a method for joining superconducting thin film waveguides in which a thin film is formed to reduce microwave power loss.

[Conventional technology]

The above-mentioned waveguide cavity resonator is used as a microwave amplifier such as the Talistron, or as a particle accelerator for electrons, protons, etc.; An accelerator tube with a plurality of connected body resonators is used.

Among these applications, microwave energy loss in waveguides used for transmitting microwaves from several hundred MHz to several tens of GHz can be significantly reduced by using materials with high electrical conductivity such as copper as the waveguide material. can be made smaller. However, when microwave energy is stored in a cavity resonator used in a particle accelerator, a large amount of energy is released to the outside through the wall of the acceleration tube, so the energy input to the microwave is There was a problem that the size had to be increased accordingly, resulting in low efficiency.

In order to cope with this problem, a cavity resonator in which a cavity is formed of a superconducting material, which can obtain a large accelerating electric field with extremely low microwave power, has recently been attracting attention. However, even in a superconducting state, there is some resistance to microwaves, which generates heat, and this heat is usually removed by liquid helium immersed in the cavity to maintain it in a superconducting state. are doing. However, since materials in a superconducting state generally have poor thermal conductivity, as the accelerating electric field increases and heat generation increases, the heat generation increases, especially at surface defects on the inner wall of the material, and the heat cannot be removed completely. The material temperature rises above the critical temperature for superconductivity and the superconducting state is destroyed.

For this reason, superconducting cavity resonators usually have a structure in which a superconducting thin film is plated on the inside of a tube made of a base material with good thermal conductivity. By doing this, the heat generated in the superconducting thin film is quickly conducted to the outside through the base material, and the thin film is always maintained in a superconducting state, so the accelerating electric field can be increased.
Furthermore, in order to maintain superconductivity, superconductivity can be achieved by providing a pipe outside the base material without immersing the entire tube in liquid helium, and by passing liquid helium through the pipe for indirect cooling. It can be simplified to

[Problem that the invention seeks to solve]

Although superconducting thin film cavity resonators have these characteristics, they have not yet been put into practical use.

One of the causes is a bonding problem. This is because - generally, electron beam welding is used to join superconducting materials, for example, for plates such as niobium, but the thickness is from several μm to several tens of μm.
U') When joining thin films, if electron beam welding is used, not only the superconducting material such as niobium but also the base material will melt, making it impossible to obtain sufficient superconducting properties. A thin film of material must be formed. However, such post-treatment is generally difficult to implement, and problems arise such as the surface finish of the post-treated portion and the adhesion of the thin film.

(Means for Solving the Problems) In view of this, the present invention has been made various studies, and it has been found that a technique for bonding materials by vacuum heating in a state in which they are pressed together without any gaps, that is, a diffusion bonding technique, can be applied, and a rough study has been carried out. As a result, we have developed a method for bonding superconducting thin film waveguides that allows stable bonding without any post-processing. In the method of bonding waveguides to each other, a superconducting thin film identical to that inside the base material is formed on each bonding surface, and then the bonding surfaces are pressed together in a vacuum to increase the melting point of both the base material and the superconducting material. It is characterized by diffusion bonding by heating at a temperature lower than .

(Function) The bonding surfaces of the waveguides are brought into pressure contact and the atoms of both superconducting materials at the bonding surfaces are interdiffused at a temperature below the melting point.
This is because, according to this diffusion bonding, the superconducting material is smoothly continuous at the bonded portion, so that there is no material change in the material or any adverse effect on the base material, and good superconducting properties are maintained.

In addition, there are cavity resonators and disk-loaded traveling wave types that have a structure in which disks with a hole in the center are periodically provided in the longitudinal direction of a waveguide with a circular cross section, which is a type of waveguide. In the case of joining accelerator tubes, the joining part is most effective at the part where the electric field is the smallest, that is, between the two discs. This is because as more energy is stored in the cavity formed by the disks, the electric field increases, becoming largest at the center of the cross-section of the cavity and smallest at the outermost part of the cross-section. The larger this electric field is, the more electrons jump out from the surface of the cavity, taking away some of the energy, which is one of the causes of lowering the electric field reached by the cavity. Furthermore, the rougher the surface of the cavity, the greater the amount of electrons that fly out in this way, so it is undesirable to form a portion, such as a bonding portion, that may impede surface uniformity in a location where the electric field is strong.

〔Example〕

The present invention will be explained using an example.

As shown in Fig. 1, the inner surface of the single cavity of the cavity resonator and the end surface of the flange portion of the cylinder have a small hole (2) penetrating through the cross-section center of the pure copper cylindrical base material (1) in the axial direction. (3)
Two superconducting thin film cavities (5) finished by gas sputtering niobium (4) were prepared, and the flange end face (3)
) were used as diffusion bonding surfaces, and the bonding surfaces were butted against each other and fixed with bolts (6) and nuts (7). A structure in which a large number of single cavities are connected together is a multi-connected cavity with a π mode standing wave type, in which the TM010 mode electromagnetic field is excited, and the abutting portion between the bonding surfaces is the area with the lowest electric field. It is.

The above-mentioned connected body (8) of single cavities (5H5) was heated in a vacuum furnace at 900'C in a vacuum of 10-s torr for 1 hour to mutually diffuse the niobium on the joint surfaces and separate the single cavities. They were diffusion bonded to each other. As a result, the joint surface was extremely smooth and uniform with no difference from other parts, and was completely airtight.

[Effects of the Invention] As described above, according to the present invention, it is possible to join superconducting wave tubes, and a wave guide and an accelerating tube with good energy efficiency can be obtained.
In addition, since there is almost no change in the dimensions of the material, when joining cavity resonators or disk-loaded traveling wave accelerator tubes, the change in resonance frequency before and after joining is very small, and there is no rough change in material quality. It has remarkable industrial effects.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a side cross section of an embodiment of the present invention. 1...Pure copper cylindrical base material 2...Small hole 3...Flange end face 4...Niobium 5... ...Single superconducting thin film cavity 6...
...Bolt 7...Nut 8...Connection body Fig. 1-

Claims (2)

[Claims] (1) In a method of bonding superconducting thin film waveguides in which a superconducting thin film is formed on the inside of a base material with good thermal conductivity, the same superconducting thin film as on the inside of the base material is formed on each bonding surface. A method for bonding superconducting thin film waveguides, which is characterized in that the bonding surfaces are then pressed together in a vacuum and diffusion bonding is performed by heating at a temperature lower than the melting points of both the base material and the superconducting material. (2) A method for joining a superconducting thin film waveguide according to claim (1), using a superconducting thin film waveguide having a copper base material and a niobium thin film formed inside.