JP2919944B2 - Method and device for connecting oxide superconducting conductor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for connecting an oxide superconducting conductor, in which a connecting portion of the oxide superconducting conductor is connected via a thin oxide superconducting layer. Connect.

"Prior art" Oxide superconductors discovered in recent years are easy to flow current in a specific direction of the crystal, and have a large electrical anisotropy that current is difficult to flow in a specific direction. In order to obtain a current density, it is necessary to adopt a manufacturing method for controlling the crystal orientation. Conventionally, the manufacturing method of filling the baked powder into a metal sheath material, rolling it, processing it into a tape, mechanically adjusting the crystal orientation, and then sintering it afterwards is considered practical. Research and development are proceeding to obtain a superconducting wire having a current density close to the above.

However, oxide superconductors formed from powder compacts are polycrystalline even if the compaction density is sufficiently increased, and there are many grain boundaries and the degree of coupling of the superconducting state at the grain boundaries is low. Since it is known that the superconducting layer is extremely weak, a current density is improved by depositing a thin superconducting layer having few crystal grain boundaries on a tape material to produce an oxide superconducting conductor.

[Problems to be Solved by the Invention] By the way, when trying to use the oxide superconducting conductor for a field winding of a superconducting magnet or for a power transport line, of course, the oxide superconducting conductors are connected to each other. It becomes necessary. However, a method of connecting an oxide superconducting conductor formed by depositing a superconducting layer on a tape material as described above has not been proposed at present, and at present, the ends of the oxide superconducting conductor are overlapped or crossed. Spot welding tape materials together
A method of connecting the superconducting layers with each other has been considered.

However, in such a connection method, since the superconducting layers of the connection portion are merely in contact with each other, the crystal orientation of the oxide superconducting layer is disturbed at the contact portion, and the critical current density of the connection portion is greatly reduced. There was a problem to do.

The present invention has been made to solve the above problems,
It is an object of the present invention to provide a method and an apparatus capable of connecting oxide superconductors in a state in which a decrease in critical current density at a connection portion is reduced.

[Means for Solving the Problems] The invention described in claim 1 solves the above-mentioned problems by providing oxide superconducting conductors each having an oxide superconducting layer formed inside a hollow metal base material. In the connecting method, at the end of each oxide superconducting conductor, a part of the base material at the end and the oxide superconducting layer are removed, and the tongue-shaped projection made of the base material at the end of each oxide superconducting conductor. The exposed portion of the oxide superconducting layer is formed, and then the tongue-shaped protrusions of the base material of each oxide superconducting conductor are overlapped and welded, and then the oxide superconducting layer near each tongue-shaped protrusion is exposed with a mask material. Noble metal such as Au, Pt or SrTiO ₃ on the tongue between the exposed portions of both oxide superconducting layers covered with the mask material,
Forming a connection intermediate layer made of any of MgO,
Next, after removing the mask material, a connecting oxide superconducting layer for connecting the oxide superconducting layers of both oxide superconducting conductors is deposited on the connecting intermediate layer, on the exposed portion of the oxide superconducting layer, and on the tongue-shaped protrusion. Is what you do.

According to a second aspect of the present invention, there is provided a method for connecting oxide superconducting conductors each comprising an oxide superconducting layer formed on a metal base via an intermediate layer, in order to solve the above-mentioned problems. At the end of the superconductor, the intermediate layer protrudes forward from the oxide superconducting layer, and the end of each oxide superconducting conductor is processed so that the base material protrudes forward than the intermediate layer. The conductor base materials are overlapped and welded, and then the mask material covers the exposed portion of each oxide superconducting layer excluding the tip side and the intermediate layer tip portion. A noble metal such as Au, Pt, or a connection intermediate layer made of any of SrTiO ₃ and MgO is formed on the tip of the layer, and after removing the mask material, the connection intermediate layer and the intermediate layer are formed. Connection for connecting both oxide superconducting layers on oxide superconducting layer An oxide superconducting layer is deposited.

According to a third aspect of the present invention, there is provided an apparatus for connecting oxide superconducting conductors each including a substrate and an oxide superconducting layer, the internal vacuum vessel being connected to a vacuum pumping apparatus. A preliminary vacuum container connected to both sides of the internal vacuum container, and a target and a target holder provided inside the internal vacuum container, wherein the internal vacuum container and the preliminary vacuum container are each a container body. And a lid that opens and closes the upper opening of the container main body. At the boundary between each container main body and the lid, the internal vacuum container and the preliminary vacuum container penetrate, and the oxide superconducting conductor Is formed, and a vacuum seal member is provided on the periphery of the insertion hole.

"Action" A part of the base material is removed to form a tongue-shaped protrusion or the base end of the base material, and the oxide superconducting layer is bonded after welding the tongue-shaped protrusion or the base end of the base. Alternatively, even if a force acts on the oxide superconducting conductor after the joining, an unnecessary load is not applied to each oxide superconducting layer. In addition, an intermediate layer is formed on the tongue-shaped protrusion or the front end of the base material, and thereafter, an oxide superconducting layer for connection for connecting the oxide superconducting layers is formed. By the presence, the reaction between the oxide superconducting layer and the substrate is suppressed, and the phenomenon of lowering the critical current density of the connecting oxide superconducting layer is suppressed.

Furthermore, after covering the oxide superconducting layer exposed from the base material with a mask material, an intermediate layer for connection is formed, and after removing the mask material and exposing the oxide superconducting layer again, the oxide superconducting layer for connection is formed. Since the deposition is performed, the oxide superconducting layer exposed from the base material is not covered with the intermediate layer for connection, and the oxide superconducting layers of both oxide superconducting conductors are securely connected by the oxide superconducting layer for connection. The intermediate layer for connection does not hinder the superconducting connection. Also, at the time of deposition of the connecting oxide superconducting layer, most of the connecting oxide superconducting layer is deposited on the connecting intermediate layer and on the exposed oxide intermediate layer of each oxide superconducting conductor portion. The possibility that the oxide superconducting layer for connection will cause an interdiffusion reaction with the substrate at the time of vapor deposition is reduced, and the critical current density of the oxide superconducting layer for connection does not decrease.

On the other hand, an internal vacuum container having an insertion hole through which the oxide superconducting conductor is formed and a preliminary vacuum container are provided. The preliminary vacuum container surrounds the insertion hole of the internal vacuum container, and further has a vacuum seal material. Of the connecting oxide superconducting layer can be formed in the internal vacuum container with a sufficient degree of vacuum by ensuring the airtightness of the external vacuum container. Therefore, a connection oxide superconducting layer having a high critical current density can be formed, and the oxide superconducting layer is connected via this.

"Embodiment" FIGS. 1 to 5 show an example of the method of the present invention, and FIGS. 6 and 7 show an example of a film forming apparatus used in carrying out the method of the present invention. is there.

In this example, as shown in FIG. 1, a case where an oxide superconducting conductor 3 in which an oxide superconducting layer 2 is formed inside a base material 1 made of a metal flat pipe-shaped sheath material is connected. explain.

The oxide superconducting conductor 3 is manufactured by filling a pipe-shaped metal sheath material with a sintered powder of the oxide superconductor, subjecting the sheath material to mechanical processing such as rolling, and heat treatment. Things.

To connect the oxide superconductor 3, as shown in FIG. 2, the upper side of the base material 1 and the oxide superconductor layer 2 are fixed at a predetermined length at the end of the oxide superconductor 3. The length is removed, and a tongue-shaped protrusion 1a is formed on a portion of the base 1 at the front end side. Alternatively, in the case of the oxide superconducting conductor 3 in which a portion to be connected is known in advance, the tongue-shaped protrusion 1a can be formed on the base material 1 in advance when the oxide superconducting conductor 3 is manufactured.

Next, two oxide superconducting conductors 3 whose ends are machined as shown in FIG. 2 are opposed to each other with their ends facing each other as shown in FIG. Are overlapped, and the overlapped portions are connected by a connection method such as a spot welding method.

Next, a tape-shaped mask material 5 is applied at the connection portion so as to cover a portion where the oxide superconducting layer 2 is exposed, as shown in FIG. In this case, the mask material 5 is applied so as to cover the exposed portion of the oxide superconducting layer 2 and the substrate 1 around the exposed portion.

After the mask material 5 is applied as described above, the connection portion is inserted into a film forming device such as a sputtering device or a laser vapor deposition device, and a connection intermediate layer 6 is formed as shown in FIG. When the connection intermediate layer 6 is formed, means such as thermal spraying may be used.

The connection intermediate layer 6 is made of a crystalline oxide such as SrTiO ₃ or MgO, or a noble metal such as gold or platinum. The connection intermediate layer 6 reacts with the elements constituting the oxide superconducting layer 2. It is preferable to use an oxide superconductor having low crystallinity and a crystal structure close to the crystal structure of an oxide superconductor having perovskite as a basic structure. In addition, the connection intermediate layer 6
It is more preferable that the coefficient of thermal expansion has an intermediate value between the coefficient of thermal expansion of the oxide superconducting layer 2 and the coefficient of thermal expansion of the metal substrate 1. By using the connection intermediate layer 6 having a thermal expansion coefficient having an intermediate value in this way, the risk that the oxide superconducting layer 2 is peeled off from the base material 1 in a heat cycle accompanying a heat treatment described later can be reduced. it can.

After the connection intermediate layer 6 is formed, the mask material 5 of each oxide superconductor 3 is removed from the substrate 1 and the oxide superconductor layer 2 is removed.
After exposing the end surface of the substrate, the substrate is again inserted into the film forming apparatus, and the connecting oxide superconducting layer 7 is formed on the connecting portion as shown in FIG. By this processing, the oxide superconducting layer 7 for connection becomes
Since it is formed to cover the upper surface of the connection intermediate layer 6, the upper surface of the exposed end portion of each oxide superconducting layer 2, and the upper surface of the base material 1, the oxide superconducting layer 2 of one oxide superconductor 3 is formed. And the oxide superconducting layer 2 of the other oxide superconducting layer 3 are connected via the connecting oxide superconducting layer 7.

At the time of the connection, the base material 1 is previously connected by welding, and then the deposition of the connection intermediate layer 6 and the deposition of the connection oxide superconducting layer 7 are performed. No unnecessary load is applied to the intermediate layer 6 for connection and the oxide superconducting layer 7 for connection even if a force acts on the oxide superconducting layer 7 for connection.

When the connection oxide superconducting layer 7 is formed, the oxide superconducting layer 7 may be heated and heat-treated inside the film forming apparatus as necessary, or may be separately heat-treated after the film formation to form the connection oxide superconducting layer 7. The crystal structure of the material superconducting layer 7 can be adjusted and the critical current density can be improved. The heat treatment improves the crystal consistency at the boundary between the connecting oxide superconducting layer 7 and the oxide superconducting layers 2, 2, so that the critical current density at the connecting portion does not decrease. Most of the connection superconducting layer 7 is provided on the base material 1 via the connection intermediate layer 6.
Therefore, even when heat treatment is performed, the composition does not undergo thermal diffusion reaction with the metal elements constituting the base material 1, and the composition of the connecting oxide superconducting layer 7 is destroyed and the superconductivity of the connecting superconducting layer 7 is reduced. There is no deterioration in characteristics.

6 and 7 show an example of a film forming apparatus suitable for forming the connection oxide superconducting layer 7.

This film forming apparatus 10 has an internal vacuum vessel provided at the center.
11 and auxiliary vacuum vessels 12 and 13 provided on both sides of the internal vacuum vessel 11.
An exhaust hole 14 connected to a vacuum exhaust device is formed at the bottom of 1. Further, in the center of the internal vacuum vessel 11, a target 16 is mounted on the target holder 15 and the target 16 is installed facing upward.A heating device (not shown) is provided inside the internal vacuum vessel 11, The inside of the vacuum vessel 11 can be heated to a desired temperature.

The target holder 15 is connected to a high-frequency power supply 17 provided outside the internal vacuum vessel 11. The target holder 15 can strike out constituent particles of the target 16 upward by applying a high frequency to the target 16 by the action of the high-frequency power supply 17.

The target 16 is a sintered body of a composite oxide containing the same or a recent composition as the oxide superconducting layer 2 of the oxide superconducting conductor 3, or containing many components that easily escape during film formation, or , Formed from the bulk of an oxide superconductor. As the oxide superconductor having a high critical temperature known at present, specifically, Y-Ba-Cu-O-based, Bi-Pb-
Since there are an Sr-Ca-Cu-O system, a Tl-Ba-Ca-Cu-O system, etc., these targets can be used as the target 16. Note that among the constituent elements of the oxide superconductor, some elements have a high vapor pressure and are liable to be scattered at the time of vapor deposition.Therefore, when using the target 16 containing such an element, an element having a high vapor pressure is used. What is necessary is just to use the target which included more than the predetermined ratio. When the connection intermediate layer 6 shown in FIG. 4 is formed by the film forming apparatus 10, a crystal oxide such as SrTiO ₃ or MgO or a noble metal target is used as the target 16.

The internal vacuum vessel 11 and the preliminary vacuum vessels 12 and 13 are integrated with lids 11a, 12a and 13a, and an integrated container body 11
b, 12b, and 13b, and the lids 11a, 12a, and 13a are
11b, 12b, 13b
The upper opening surfaces of the container main bodies 11b, 12b, 13b can be closed by 1a, 12a, 13a. Also, the lids 11a, 12
In the lower side wall of a, 13a, a notch is formed respectively, and when the container body 11b, 12b, 13b is closed by the lids 11a, 12a, 13a,
The notch of each cover and the notch of each bottom are combined to form an insertion hole 19 through which the oxide superconductor 3 can be inserted. Further, a vacuum seal member 20 is mounted on an inner peripheral portion of each of the notches.

The film forming apparatus 10 having the structure shown in FIG. 6 and FIG. 7 is used for forming the connection intermediate layer 6 shown in FIG. 4 and forming the connection oxide superconducting layer 7 shown in FIG. Can be used.

To form the connection intermediate layer 6, a target such as a crystal oxide or a noble metal is mounted as the target 16, and the lids 11a, 12a, and 13a are released. Here, as shown in FIG. 3, the tongue-like projections 1a, 1a of the base material 1 are connected, and
The oxide superconducting conductors 3, 3 with the
As shown in FIG. 7, the b, 12b, and 13b are mounted in the upper insertion holes. In this case, as shown in FIG.
The substrate 3 is set so that the cut portions of the substrate 1 face the target 16.

In this state, as shown in FIG. 6, the lid portions 11a, 12a, and 13a are closed, the oxide superconducting conductors 3, 3 are sandwiched by the upper and lower vacuum seal members 20, and the internal vacuum vessel 11 and the preliminary vacuum vessels 12, 13 are separated. Completely seal.

Thereafter, the internal vacuum vessel 11 is evacuated and a high frequency is applied to the target 16, whereby the connection intermediate layer 6 can be formed as shown in FIG. When evacuating in this manner, the insertion holes 19, 19 of the internal vacuum vessel 11 are surrounded by the preliminary vacuum vessels 12, 13, and the oxide superconducting conductors 3, 3
Are sealed by the vacuum seal members 20, so that the insertion hole 19 of the internal vacuum vessel 11 is completely sealed.

After the connection intermediate layer 6 is formed, the vacuum state of the inner vacuum vessel 11 is released, and the lids 11a, 12a, 13a are released, the oxide superconductors 3, 3 are removed, and the mask materials 5, 5 are removed. At the same time, the target 16 was replaced with a target for forming an oxide superconducting layer, and vapor deposition was performed again in the same manner as described above.
As shown in the figure, the connecting oxide superconducting layer 7 is formed.

By performing the above operations, the connection work of the oxide superconductors 3, 3 can be completed as shown in FIG.

8 to 13 show another example of the method of the present invention. In this example, an intermediate layer is formed on a tape-shaped base material 20.
The case where the oxide superconducting conductor 23 formed by sequentially laminating the oxide superconducting layer 21 and the oxide superconducting layer 22 will be described.

In this example, first, each end of the oxide superconducting conductor 23 to be connected is machined stepwise in the order shown in FIG. 9 and FIG.

Next, the tip portions 20a of the base materials 20 of the oxide superconducting conductors 3 to be connected are overlapped and spot-welded as shown in FIG.

Subsequently, as shown in FIG. 11, mask materials 24, 24 are adhered so as to cover the exposed portion excluding the tip side of the oxide superconducting layer 22 and the tip portion of the intermediate layer 21.

From this state, the oxide superconductors 23, 23 are set in the film forming apparatus having the structure shown in FIGS. 6 and 7, and the connection intermediate layer 25 is formed as shown in FIG. Here, in the film forming apparatus shown in FIG. 6, the shape of the insertion hole 19 and the shape of the vacuum sealing members 20 are changed so that the oxide superconducting conductors 23 can be sandwiched without any gap. Has an internal vacuum vessel
The inside of 11 can be completely vacuum-sealed.

After the connection intermediate layer 25 is formed, the mask materials 24, 24 are removed, the target 16 of the film forming apparatus is replaced with a target for forming an oxide superconducting layer, and the film is formed again as described above. As shown in FIG. 13, a connecting oxide superconducting layer 26 for connecting the oxide superconducting layers 22, 22 can be formed.

After this connection, if necessary, heat treatment is performed to adjust the crystal consistency between the oxide superconducting layers 22 and 22 and the connecting oxide superconducting layer 26, thereby suppressing a decrease in the critical current density at the connection portion. be able to.

By connecting as described above, the oxide superconducting conductors 23, 23 can be connected as in the case described in the previous example.

The film forming apparatus 10 shown in FIG.
By appropriately changing the formation and size of the insertion holes 19 through which the holes 3 and 23 are inserted, and the shape of the vacuum seal member 20, they can be widely used for connecting oxide superconductors of various shapes.

[Effects of the Invention] As described above, the method of the present invention is characterized in that when connecting a substrate and an oxide superconducting conductor having an oxide superconducting layer to each other, a part of the substrate on the end side is tongue-shaped. The remaining portions are removed and the tongue-shaped protrusions of the base material are connected first, and then the oxide superconducting layer is formed to make the connection. This is a safe and reliable connection method in which an unnecessary load is not applied to the oxide superconducting layer even when 作用 acts. In addition, since the oxide superconducting layers are connected to each other by the connecting oxide superconducting layer, they can be connected by the dense oxide superconducting layer that is easy to maintain crystal consistency, and the critical current density of the connecting portion is reduced. A good connection can be made without any problem.

Next, after covering the oxide superconducting layer exposed from the base material with a mask material, an intermediate layer for connection is formed, the mask material is removed, the oxide superconducting layer is exposed again, and then the oxide superconducting layer for connection is formed. Is deposited, so that the oxide superconducting layer exposed from the base material is not covered with the intermediate layer for connection, and the oxide superconducting layers of both oxide superconductors are reliably connected by the oxide superconducting layer for connection. Therefore, the connection intermediate layer does not hinder the superconducting connection. Also, during the deposition of the connecting oxide superconducting layer, most of the connecting oxide superconducting layer is deposited on the connecting intermediate layer and on the exposed oxide intermediate layer at the end of each oxide superconducting conductor, The risk that the connecting oxide superconducting layer will undergo an interdiffusion reaction with the substrate during deposition is reduced, and the critical current density of the connecting oxide superconducting layer is not reduced.

Furthermore, when connecting an oxide superconducting conductor having a configuration in which an intermediate layer is provided between the base material and the oxide superconducting layer, the oxide superconducting layer for connection is formed after the formation of the intermediate layer. Even in this case, no mutual diffusion reaction occurs between the elements of the connecting oxide superconducting layer and the elements of the base material, and the critical current density of the connecting oxide superconducting layer does not decrease.

On the other hand, according to the apparatus of the present invention, since each oxide superconducting layer of the oxide superconducting conductor to be connected can be connected by the connecting oxide superconducting layer, the oxide superconducting layer can be connected with good crystal alignment at the connecting portion. Superconducting conductors can be joined. Therefore, the oxide superconducting conductor can be joined without lowering the critical current density at the connection portion. In addition, a vacuum sealing member is provided in the insertion hole of the internal vacuum container into which the oxide superconducting conductor is drawn, and the preliminary vacuum container is surrounded by a vacuum sealing member. It is possible to form a film while maintaining the connection portion of the material superconductor in a sufficient vacuum state in the internal vacuum vessel, so that an oxide superconducting layer for connection having a high critical current density is formed to improve the oxide superconductor. Can be connected in state.

[Brief description of the drawings]

1 to 5 are views for explaining an example of the method of the present invention. FIG. 1 is a perspective view showing an end of an oxide superconducting conductor, and FIG. FIG. 3 is a side view showing a state in which a pair of base materials of a pair of oxide superconducting conductors whose ends are processed are connected, and FIG. 4 is a side view showing a state in which a connection intermediate layer is formed. FIG. 5 is a side view showing a state in which an oxide superconducting layer for connection is formed. FIGS. 6 and 7 show an example of a film forming apparatus used for carrying out the method of the present invention. FIG. 7 is a sectional view showing a state in which the lid is closed, FIG. 7 is a sectional view showing a state in which the lid is released, and FIGS. 8 to 13 show a second example of the method of the present invention. Is a cross-sectional view of the oxide superconducting conductor, FIG. 9 is a cross-sectional view showing a state in which an end of the oxide superconducting layer is processed, and FIG. 10 is a state in which an end of the intermediate layer is processed. FIG. 11 is a cross-sectional view showing a state in which base materials are connected to each other, FIG. 12 is a cross-sectional view showing a state in which a connection intermediate layer is formed, and FIG. 13 is a cross-sectional view showing a connection oxide superconducting layer. It is sectional drawing which shows the state which formed. 1,20 base material, 2,22 oxide superconducting layer, 3,23 oxide superconducting conductor, 5,24 mask material, 6,25 intermediate layer for connection, 7,26 ... Oxide superconducting conductor, 10 ... Film forming device, 11 ...
… Internal vacuum vessel, 12,13 …… Preliminary vacuum vessel, 11a, 12a, 13a
... lid, 11b, 12b, 13b ... container body, 20 ... vacuum sealing member.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01B 12/00-12/16 H01B 13/00 561-565 H01F 6/06 H01R 4/68 H01R 43/00

Claims (3)

(57) [Claims] 1. A method for connecting oxide superconducting conductors each comprising an oxide superconducting layer formed inside a hollow metal substrate, wherein the base material is formed at the end of each oxide superconducting conductor. A part of the oxide superconducting layer and an oxide superconducting layer to form a tongue-shaped protrusion at the end of each oxide superconducting conductor and an exposed portion of the oxide superconducting layer. The tongue-shaped protrusions are overlapped and welded, and then the exposed portion of the oxide superconducting layer near each tongue-shaped protrusion is covered with a mask material, and the exposed portion of the oxide superconducting layer covered with the mask material is covered. Noble metal such as Au, Pt or Sr on the tongue between
After forming a connection intermediate layer made of either TiO ₃ or MgO, and then removing the mask material, both oxidations are formed on the connection intermediate layer, on the exposed portion of the oxide superconducting layer, and on the tongue-shaped protrusion. A method for connecting an oxide superconducting conductor, comprising depositing an oxide superconducting layer for connection for connecting the oxide superconducting layer of an object superconducting conductor. 2. A method of connecting oxide superconducting conductors each comprising an oxide superconducting layer formed on a metal substrate via an intermediate layer, wherein the oxide superconducting layer is formed at an end of each oxide superconducting conductor. The intermediate layer protrudes forward, the end of each oxide superconducting conductor is processed so that the base material protrudes forward than the intermediate layer, and then the base materials of each oxide superconducting conductor are overlapped and welded. Then, while covering the exposed portion except the tip side of each oxide superconducting layer and the tip portion of the intermediate layer with a mask material,
On the base material not covered with the mask material and on the tip of the intermediate layer
After forming a connection intermediate layer made of any of noble metals such as Au and Pt or SrTiO ₃ or MgO, and then removing the mask material, on the connection intermediate layer, on the intermediate layer, and on the oxide superconducting layer A method for connecting an oxide superconducting conductor, comprising depositing a connecting oxide superconducting layer for connecting both oxide superconducting layers. 3. An apparatus for connecting oxide superconducting conductors each comprising a base material and an oxide superconducting layer, comprising: an inner vacuum vessel connected to a vacuum pumping device; and an inner vacuum vessel connected to both sides of the inner vacuum vessel. A preliminary vacuum container, and a target and a target holder provided inside the internal vacuum container, wherein the internal vacuum container and the preliminary vacuum container respectively open and close a container body and an upper opening of the container body. A lid, and at the boundary between each container body and the lid, an insertion hole is formed, which penetrates the internal vacuum container and the preliminary vacuum container, and through which the oxide superconducting conductor can be inserted. A connection device for an oxide superconducting conductor, characterized in that a vacuum seal member is provided at a periphery of the insertion hole.