JPH02220400A - Manufacture of superconducting cavity - Google Patents

Abstract

PURPOSE:To improve heat radiation effect to make it possible to increase a generating electric field and a magnetic field by making plasma spraying to the outside of the cavity of a thin wall-thickness superconductor in an anoxia atmosphere to laminate good heat conductive metal. CONSTITUTION:A cavity 1 is put in a vacuum chamber 7 and the inside of the chamber 7 and the inside of the cavity 8 are vacuum-formed at the same time. Next, the cavity 1 is translated and rotated so that flame coating can be uniformed, and while inert gas is flowed into a plasma spraying gun 5, a steady state current is made to cause ionization by electric arc for converting into plasma so that it is jetted out as a flame 6. A powder-like substrate material made up of good heat conductive metal is sent into that flame 6 through a capillary 12 to be molten and sprayed on the cavity 1. Thereby, it is possible to improve heat radiation effect and increase a generating electric field and a magnetic field. Moreover, a light element can be absorbed and the purity of Nb metal, improved by arranging a titanium bar 3 in the cavity inside 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a superconducting cavity constituting a superconducting cavity resonator used in a charged particle accelerator.

[Conventional technology]

A superconducting cavity resonator utilizes the superconductivity of the surface layer made of a superconductor, and can generate a higher electric or magnetic field internally than a normal cavity resonator.
This has the advantage that power consumption can be reduced. Nb is often used as a superconducting material.

When a superconducting cavity resonator is operated, high frequency loss occurs in the superconducting surface layer due to normal conduction resistance due to the presence of impurities and high frequency resistance of the superconductor surface, and the temperature of the superconducting surface layer increases. An increase in the temperature of a superconductor lowers its critical magnetic field and increases its high-frequency resistance, resulting in a destruction of superconducting performance called quenching. Therefore, in a superconducting cavity resonator, it is necessary to select a material with good thermal conductivity in order to immediately eliminate heat generation in the surface layer. For example, Nb is used as the surface layer and Cu is used as the base structure material. Composite materials using this material are suitable as materials for electrically stabilizing superconducting cavity resonators.

By the way, metal Nb has strong oxidizing properties, and Nb in the air
A strong oxide film is formed on the surface.

Therefore, even if Cu is electroplated or vacuum-deposited directly on Nb, the adhesion is weak and it is easy to peel off.Therefore, the conventional method for producing a composite material by bonding Nb and Cu as a base is as follows. Methods such as this are used. That is, (a) the outer surface of the Nb cavity is electrolytically polished or chemically polished to remove the oxide film, immediately immersed in a plating tank, and plated with Cu several inches thick by electroplating.

After this, if the temperature is maintained at 400'C or higher in a non-oxidizing atmosphere, the adhesion can be improved due to the diffusion effect of Cu and Nb.

(1) Place the Nb cavity in a vacuum chamber, perform ion bombardment in low-pressure Ar gas to remove the oxide layer on Nb, and then form about 10 layers of Cu film by Cu sputtering or ion blating.

Next, Cu thick plating is applied to the Cu film to form a several-inch thick Cu film.
A layer is formed to form a base.

(Problems to be Solved by the Invention) However, the conventional method for manufacturing a cavity made of a composite of Nb and Cu has the following problems.

That is, a) In the first method above, the oxide film cannot be completely removed even if electrolytic polishing or chemical polishing is performed;
In addition, during the transition from the polishing tank to the plating tank, oxidation progresses due to exposure to outside air. As a result, when electroplating is performed, poor adhesion occurs such as blistering on the surface. Furthermore, this method has a problem in that the steps of Nb polishing, Cu plating, and heat treatment are complicated. Furthermore, both electrolytic polishing and chemical polishing use a large amount of hydrofluoric acid, and No.

and HF gas is generated, resulting in deterioration of the working environment and pollution problems.

In the second method described above, the deposition rate of Cu by sputtering and ion blasting is 1 to 2μ.
/Hr to form a 10-thick Cu layer,
It is necessary to operate the equipment for more than 5 hours. In addition, with sputtering and ion blating, since there is little wraparound of deposits, it is difficult to form a 00 layer on parts with complex shapes such as around pipes, and it is also difficult to form a 00 layer on parts with complex shapes such as around pipes. Several weeks of equipment operation are required to obtain this.

As described above, this manufacturing method has poor manufacturing efficiency, and also has problems in terms of economic efficiency because sputtering equipment and ion blating equipment equipped with ion bombardment equipment are very expensive.

The present invention has been made in view of the above points.
The objective is to provide a method for laminating a material with good thermal conductivity on the outer surface of a cavity formed from a thin superconductor with good adhesion, in a short time, and at low cost.

[Means and actions to solve the problem]

In order to achieve the above object, the present invention provides a method for manufacturing a superconducting cavity in which a metal with good thermal conductivity is laminated on the outside of a cavity formed from a thin-walled superconductor. The first invention is to laminate the above, and the second invention is to perform plasma spraying in a state where the inside of the cavity is made into an ultra-high vacuum and hermetically sealed, and titanium metal is disposed inside the cavity which is made into an ultra-high vacuum. A third aspect of the invention is to perform plasma spraying, and a fourth aspect of the invention is to wrap a metal tube around the outside of the cavity in contact with the surface and perform plasma spraying thereon.

Plasma spraying uses a high-temperature, high-velocity flame (
This is a technique in which a coating layer is formed on the surface of a target material by ejecting a plasma jet, supplying powder metal into the plasma jet, melting it, and applying the molten powder metal to a target material.

According to the present invention, when molten powder metal collides with the surface of a cavity made of a superconductor, the surface oxide layer of the superconductor is destroyed and removed, and the molten powder metal solidifies there, forming a superconductor. Tightly bond. Sequential spraying of molten powder metal allows it to agglomerate and deposit to form a thick, tightly bonded coating. When this plasma spraying treatment is performed in a low pressure, oxygen-free atmosphere, oxygen is not trapped within the coating layer, and a uniform coating layer with high purity can be obtained at high speed. In addition, if plasma spraying is performed with the inside of the cavity made into an ultra-high-speed vacuum or filled with inert gas and sealed, the inside of the cavity will not react with the gas remaining in the plasma spraying equipment or the plasma gas. Moreover, since the molten powder metal does not adhere to the inner surface of the cavity, thermal spraying can be performed on the outer surface of the cavity without impairing the superconducting high frequency characteristics as a superconducting cavity resonator.

Furthermore, titanium metal has the property of easily absorbing light elements in ultra-high vacuum, and it is known that the purity of niobium metal can be improved by placing titanium metal, especially when annealing niobium metal. There is. Therefore, by placing titanium metal inside the sealed cavity, titanium absorbs the gas released due to the temperature rise of the Nb cavity during plasma spraying, increasing the purity of the cavity surface layer and obtaining better superconducting high frequency characteristics. .

[Example] The present invention will be described below based on the example shown in the drawings.

FIG. 1 is a cross-sectional view of an embodiment of an apparatus used in the method of manufacturing a superconducting cavity according to the present invention. (1) is a cavity made of a thin superconductor, and this cavity (1) is installed on a pedestal (2) that moves linearly by a linear drive mechanism OJ using air pressure, oil pressure, a motor, etc. Rotation mechanism (
4) allows rotation around the central axis. (
5) is a plasma injection gun in which an inert gas is ionized by an electric arc, converted into plasma, and ejected as a flame (6) (plasma jet stream). Powdered base material is fed through a thin tube into this flame (6), melted, and sprayed onto the cavity (1). As the inert gas, argon gas, argon gas mixed with hydrogen, nitrogen gas, helium gas, etc. are used. For the purpose of the present invention, as the powdered base material, copper, copper alloy, aluminum, and aluminum alloy, which are materials with good thermal conductivity, are preferable. The above-mentioned thermal spray gun (5) and cavity (1) are surrounded by a vacuum chamber (7) and maintained in a low pressure, oxygen-free atmosphere. In addition, in this example,
Although the cavity (1) has been translated and rotated, the spray gun (5) may be moved to allow spraying over the entire surface of the cavity (1).

The inside of the cavity (8) has an airtight structure in addition to the vacuum provided by the vacuum chamber (7) so that the superconductor surface layer (9) on the inner surface is not contaminated by oxidation, reaction with atmospheric gas, or adhesion of evaporated metal. It is maintained in an inert gas atmosphere or ultra-high vacuum. In order to create an ultra-high vacuum, the cavity (
11 is connected to a vacuum pipe Oω and is evacuated by an ion pump 00. Incidentally, the inside of the cavity may be sufficiently evacuated using an ultra-high vacuum pump, and the ultra-high vacuum state may be maintained by sealing off using a valve or the like.

An example will be described in which a copper substrate with a thickness of about 3 rm is formed in a cavity made of Nb with a thickness of 0.5 m and has a large diameter of 100 mm, a small diameter of 20 m+φ, and a length of 1.5 m using the above-mentioned apparatus. The cavity (1) is placed in a vacuum chamber (7), and the interior of the vacuum chamber (7) and the interior of the cavity (8) are simultaneously evacuated so as not to create a large pressure difference.
) was evacuated to 10-7 Torr, and the outside was evacuated to 10-' Torr. A titanium plate (3) was placed inside the cavity (8) so as not to touch the Nb surface. Next, the cavity (1) is translated and rotated so that the sprayed coating becomes uniform, and the plasma? 8
While flowing argon gas into the No. 14 gun (5), a steady current is applied to create a flame (6), and particles with an average diameter of 50
- When a copper substrate was formed on the cavity (1) by feeding copper powder, it was possible to form a copper substrate with good adhesion at a pressure of about 3 m after thermal spraying for 20 minutes. The superconducting cavity formed in this way has improved heat dissipation, which is 3 times higher than that of conventional cavities. An electric field of IV/m was obtained.

As another example using the above device, as shown in FIG. When a copper tube Oa with a diameter of 5Iiffl, which is in contact with l1iI00 and serves as a flow path for the coolant, is wound, and copper powder is plasma sprayed in the same manner as in the previous example, the molten copper powder flows into the gap between the cavity 0ω and the copper tube θ4. , copper tube 04) with cavity 0
0, it was possible to obtain a cavity having a desired thickness of the copper substrate θ. Note that an aluminum tube or a thin-walled stainless steel tube may be used instead of a copper tube as the coolant flow path.

〔Effect of the invention〕

As explained above, according to the present invention, since a metal with good thermal conductivity is laminated on the outer surface of the cavity by plasma spraying in an oxygen-free atmosphere, the heat dissipation effect is good, and the generated electric and magnetic fields can be controlled only by superconductors. It has the excellent effect of being able to increase the amount of energy by several times. Furthermore, a cooling channel can be easily provided outside the cavity, and the taliostat that maintains the cavity at a low temperature can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of a device used in the method of manufacturing a superconducting cavity according to the present invention, and FIG. 2 is a sectional view of a main part of an embodiment of a cavity manufactured by the method of manufacturing the present invention. be. 1.16... Cavity, 2... Frame, 3... Titanium rod, 4... Rotating mechanism, 5... Plasma spray gun, 6... Flame (plasma jet stream), 7...・
- Vacuum chamber 8...Cavity interior, 9...Surface layer, 1O...Vacuum piping, 11...Ion pump, 12...Thin tube, 13...Linear drive mechanism,
14...Steel pipe, 15...Copper base.

Claims (4)

[Claims] (1) A method for manufacturing a superconducting cavity in which a metal with good thermal conductivity is laminated on the outside of a cavity formed from a thin-walled superconductor, characterized in that the metal is laminated by plasma spraying in an oxygen-free atmosphere. Method for manufacturing superconducting cavities. (2) The method for manufacturing a superconducting cavity according to claim 1, characterized in that plasma spraying is performed in a state where the inside of the cavity is made into an ultra-high vacuum and hermetically sealed. (3) The method for manufacturing a superconducting cavity according to claim 2, characterized in that titanium metal is disposed inside the cavity. (4) The method for manufacturing a superconducting cavity according to claim 1, 2 or 3, characterized in that a metal tube is wound around the outside of the cavity in contact with the surface thereof, and the metal is laminated thereon.