JPH0782927B2 - Insulation anchor for low temperature equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to an insulating anchor for a current lead for energization in a low temperature device such as a superconducting magnet.

(Prior Art) As an example of a cryogenic device, an overall view of a cryostat for a superconducting magnet including a current lead is shown in FIG. 3, and an example of a conventional Teflon insulation anchor method used therein is shown in FIG. .

In FIG. 3, the superconducting magnet 7 is mounted in a liquid helium tank 6 through which a pipe 8 communicates, and the liquid helium tank 6 is placed in a vacuum tank 5 which is vacuum-insulated. Radiation between the vacuum tank 5 and the liquid helium tank 6,
A liquid nitrogen shield plate 4 is provided in order to cut off heat invasion by conduction on the way. On the other hand, since a copper pipe or the like is used for the current lead 3 of the superconducting magnet 7 connected to the power source 2, heat intrusion due to heat conduction is large. Therefore, it is thermally joined to the liquid nitrogen shield plate cooled by liquid nitrogen to prevent this heat intrusion. However, the current leads 3 need to be electrically insulated from each other, and cannot be directly anchored to a conductive liquid nitrogen shield plate or the like. Therefore, an insulating material 9 is installed between the vacuum tank 5 and the liquid helium tank 6 and the current lead 3, and a metal provided as an insulating anchor 1 in contact with the liquid nitrogen shield plate 4 as shown in FIG. A thermal anchor is formed by interposing an electrical insulator such as Teflon 31 between the member 30 and the current lead 3. However, this Teflon itself has poor heat conduction, and the thermal contact resistance at the end surface of the Teflon and the electrode lead is also large. There was a problem of being extremely bad.

(Problems to be Solved by the Invention) The present invention solves the problem of cooling in the conventional anchor portion, has excellent heat conduction and good electric insulation, and easily anchors the anchor portion of the current lead to the liquid nitrogen temperature. An object is to provide an insulating anchor for a low temperature device that can be cooled.

[Structure of Invention]

(Means and Actions for Solving Problems) As a result of intensive studies to achieve the above object, the present inventors have found that ceramics rich in electrical insulation and having high thermal conductivity, and high thermal conductive metal By using an anchor that is composed of, and the interface between the two is in a good heat conduction state, good heat conduction between the current lead and the liquid nitrogen shield plate, and
The present invention has been completed by finding that it can be an insulating anchor for a low temperature device which is also excellent in electrical insulation.

That is, the insulating anchor for a low temperature device of the present invention is characterized by comprising a heat conductive ceramics and a metal member arranged in contact with the heat conductive ceramics.

A configuration example of the present invention is shown in FIG. In the figure, the current lead 3
The liquid nitrogen shield plate 4 is joined to the metal member 12 joined to the substrate via the ceramics 11. The ceramics used here may be those having high electrical insulation and high thermal conductivity, such as AlN, SiC / BeO, BeO.
Etc. Also, the number to be used is variously selected according to the shape of the part. And heat conduction is ceramics 11
Since it is conducted through the interface between the metal member 12 made of a metal having high thermal conductivity and the metal member 12 made of a highly heat conductive metal, it is important that the portions are in close contact with each other so as to reduce the thermal resistance of the portion as much as possible. And as a joining method therefor, (1) the ceramic and the metal member are directly connected to each other, for example, the active metal brazing material (Ti-Cu, Ti-Ag-Cu, Z) containing the active metal Ti, Zr or the like.
A method of brazing using a brazing material containing a metal such as r-Cu alloy) or Au, Pt, Al or the like as a main component.

(2) A method in which a ceramic surface is previously coated with a mixed powder of a powder containing Mo and W as a main component and an organic binder, heated in a humidified atmosphere to be metallized, and then brazed to a metal member.

(3) Active metals and metals that form eutectic alloys with the active metals on the ceramic surface (eg Ti and Cu, Zr and Cu)
A method in which a mixed powder such as the above or these foils or alloy foils are placed, and then heated in an inert atmosphere such as a vacuum for metallization and then bonded to a metal member.

Etc. Furthermore, after applying an active metal powder such as Ti or Zr to the adhesion surface of the ceramics in advance, a transition metal, Cu or Ni, and a metal such as Ag that forms a low melting point alloy are placed in an inert atmosphere. You may heat and it may be metallized.

Although many irregularities exist on the surface of ceramics, it is necessary to deform the irregularities so that the irregularities do not remain as voids on the contact surface. However, in general, ceramics are very difficult to deform, so
Difficult to adhere to metal. However, by preliminarily metallizing the close contact surface of the ceramic, the close contact surface is easily deformed, and the close contact with the metal member is improved.

When the metal member is a soft metal, the metal is easily deformed by an external force to fill the irregularities on the contact surface of the ceramic, and the ceramic and the metal member can be closely adhered to each other. Specifically, by arranging the high thermal conductive ceramics and the metal member in contact with each other via a thin plate of soft metal such as In, Al, Ag, Cu, Au, it is possible to bring them into close contact with each other. Also in this case, good adhesion can be obtained more effectively by metallizing the contact surface with the ceramic.

By using ceramics in this way, an anchor having high thermal conductivity and high insulation can be obtained.

(Example) As a ceramic constituting the anchor of the present invention, AlN
A plate with a thickness of 3 mm was prepared.

0.5 mg / cm ² of Ti powder with a diameter of 10 μm or less was applied to the AlN contact surface.
The amount was applied. Then, 10 mg / cm ² of Ag—Cu alloy (72% Ag—Cu) powder was placed on the coated surface. These were placed in a vacuum of 2 × 10 ⁻⁵ Torr and heated at 830 ° C. for 10 minutes. After cooling, the AlN contact surface was well metallized.

Thickness of ceramics (φ13 × 3) that has been treated in this way
A copper plate (φ15 × 3) was pressure-bonded through an In foil of 0.1 mm, and a sample piece in the order of copper plate-In foil-ceramics-In foil-copper plate was produced.

As a comparative example, a copper plate (φ15 × 3) -Teflon (φ15 × 3)
A test piece was also prepared by crimping in the order of 1) -copper plate (φ15 × 3).

The test piece thus obtained was placed between a copper flange cooled by liquid nitrogen and a copper flange heated by a heater so that the copper plate of the test piece and these copper flanges were in contact with each other, and between the two copper plates. The temperature difference was measured. The results are shown in a and b of FIG. 2, respectively. As can be seen from FIG. 2, it was confirmed that the test pieces of the example according to the present invention had a heat transfer rate of about 50 times that of the comparative example.

〔The invention's effect〕

As described above, the insulating anchor for a low temperature device of the present invention has high thermal conductivity and rich in insulating property, and the heat transfer loss at the interface with the high thermal conductive metal is very small. Therefore, it is suitable as an insulating anchor for cryostats for superconducting magnets.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of an insulating anchor according to the present invention, FIG. 2 is a characteristic diagram showing the heat transmission rate of the embodiment of the present invention and a comparative example, and FIG. 3 is a conventional superconductivity. FIG. 4 is a simulated cross-sectional view showing the entire magnet cryostat, and FIG. 4 is a schematic cross-sectional view showing the structure of a conventional insulating anchor. 1 ... Insulation anchor, 2 ... Power supply 3 ... Current lead, 4 ... Liquid nitrogen shield plate 5 ... Vacuum tank, 6 ... Liquid helium tank 7 ... Superconducting magnet, 8 ... Piping 9 ... Insulation material, 11 ... Ceramics 12,30 ... Metal Material, 31 ... Teflon

Claims (5)

[Claims] 1. An insulating anchor for a low temperature device, comprising a heat conductive ceramics and a metal member arranged in contact with the heat conductive ceramics. 2. The invention according to claim 1, wherein the interface between the heat conductive ceramics and the metal member is joined.
An insulating anchor for a low temperature device according to the item. 3. An insulating anchor for a low temperature device according to claim 1, wherein a surface of the heat conductive ceramics which is joined to or in contact with the metal member is metallized. 4. The thermally conductive ceramic is In, Cu, Al, Au, Ag
The insulating anchor for a low temperature device according to claim 1, wherein the insulating anchor is arranged in contact with a metal member via a thin plate made of any of these alloys. 5. The insulating anchor for a low temperature device according to claim 1, wherein the thermally conductive ceramic is selected from AlN, BeO and SiC.