JPH0711564B2 - Superconducting device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting device, and more particularly to a superconducting device suitable for measuring a weak magnetic field using a superconducting quantum interference device SQUID.

[0002]

2. Description of the Related Art A conventional SQUID system equipped with a refrigerator is described in the document "DS Buchanan et al., Advances In Cryogenic Engineering, Vol. 33, pp. 97-106, Plenum Press, 1988 ( D.S. Buchanan et
al. , Advances in Cryogeni
cEngineering, Vol. 33, PP97-
106, Plenum 1988) ". Here, the Gihoed McMahon Cycle and Jules
The superconducting element is thermally coupled to the 4K stage of the refrigerator combined with the Thomson expansion circuit to cool it.

[0003]

In this system, the mechanical vibration generated by the refrigerator causes a considerable amount of magnetic noise. The frequency of this noise is in the low frequency region of 1 to several tens Hz, which is particularly inconvenient for biomagnetic measurement. Further, since the combined refrigeration cycle is adopted, the device becomes large and complicated, and the number of pressure pipes from the compressor is as large as three. The present invention has been made to overcome such problems, and an object of the present invention is to obtain a superconducting device that uses a small and compact refrigerator and suppresses the generation of magnetic noise caused thereby.

[0004]

In order to achieve the above-mentioned object, the present invention has a built-in regenerator having at least first and second cooling stages, a part of which is filled with a high specific heat magnetic material. A small refrigerator having a two-stage cylinder, and a compressor connected to this cylinder by a pressure pipe, an inner tank into which the cylinder is inserted and which stores a liquid coolant, and an inside or outside of the inner tank. A superconducting element mounted away from the second cooling stage of the cylinder,
A radiation shield that is connected to a part of the inner tank that is thermally coupled to the first cooling stage of the cylinder and that surrounds the inner tank; and a radiation shield that is installed at a distance from the radiation shield and that includes the radiation shield. An enclosing outer tank, a vibration isolation mechanism for connecting the cylinder and the inner tank, and an inlet for gas liquefied in the second cooling stage of the cylinder were included.

Further, a heat insulating support disposed between the inner tank near the element mounting portion for mounting the superconducting element and the outer tank in such a manner that an intermediate portion contacts the radiation shield. The effect is enhanced by including.

Further, the above object is to provide a two-stage cylinder which has at least first and second cooling stages and which has a built-in regenerator partially filled with a high specific heat magnetic material, and a cylinder and pressure piping. A small refrigerator having a connected compressor, a magnetic shield member covering a part or all of the outer surface of the cylinder, an inner tank in which the magnetic shield member and the cylinder are inserted, and which stores a liquid coolant. A superconducting element mounted inside or outside the inner tank, and a radiation shield connected to a part of the inner tank thermally coupled to the first cooling stage of the cylinder and surrounding the inner tank; An outer tank that is installed at a distance from the radiation shield and surrounds the radiation shield, a vibration isolation mechanism that connects the cylinder and the inner tank, and is liquefied by the second cooling stage of the cylinder. An inlet of the gas that, also include a is achieved.

[0007]

With this structure, helium can be liquefied in the second cooling stage only by the Gihod-McMahon cycle without the Joule-Thomson expansion circuit. The number of pressure pipes connected to the compressor is at most two. A gas layer is interposed between the cylinder with moving parts and the inner tank in which the superconducting element is mounted, and the mechanical connection is cut off, and the mounting part of the cylinder is connected to the inner tank via a vibration isolation mechanism. . Therefore, the mechanical vibration accompanying the reciprocating motion of the regenerator propagates to the inner tank while being attenuated. Further, the magnetic noise due to the magnetic substance contained in the regenerator is reduced by separating the distance between the regenerator and the superconducting element. Furthermore, if the element mounting area of the inner tank is directly supported from the outer tank, vibration will be reduced,
And its natural frequency also becomes high. Further, by placing a magnetic shielding member around the regenerator containing a magnetic material, the magnetic influence due to the reciprocating motion of the regenerator is blocked.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. Reference numeral 1 is a regenerator of a small refrigerator using a Gifode McMahon cycle, which has a two-stage piston shape.
The steps are filled with a copper net 2a and lead balls 2b, and the second step is filled with balls of a magnetic material 3 represented by an erbium-nickel compound. The regenerator 1 is housed in a cylinder 4 and is driven by high-pressure helium gas supplied from a separately installed compressor 5 via a pressure pipe 6. The timing of gas compression, expansion, and reciprocation is controlled by the valve 7, and the first cooling stage 8
And cold is generated in the second cooling stage 9. In the conventional small refrigerator in which lead balls were used for the second-stage regenerator, the temperature reached by the second cooling stage was about 7K in absolute temperature, but by using a magnetic substance with a large specific heat at extremely low temperature, It has recently become clear that a liquefaction temperature of 5.2K or less can be realized. The cylinder 4 is inserted into an inner tank 10 made of glass fiber reinforced resin or ceramics, but both are connected by a vibration absorbing portion 11 composed of rubber, bellows, springs or the like in a room temperature atmosphere. Helium gas 13 is introduced into the space formed by the cylinder 4 and the inner tank 10 from the gas inlet 12 and is partially liquefied in the second cooling stage 9 and stored as liquid helium 14 at the bottom. A thermally conductive element mounting portion 15 is provided at the bottom of the inner tank 8, and an element 16 such as a superconducting quantum interference device SQUID or a magnetic flux detection coil is attached to the thermally conductive device mounting portion 15 while keeping thermal contact therewith. The lead wire 17 from the element 16 is pulled out from the seal terminal 18 after once contacting with the liquid helium temperature level. The lead wire 17 is inserted as a twisted wire into a tube of stainless steel or copper-nickel alloy to reduce noise. The low temperature side of the inner tank 10 is surrounded by a radiation shield 19, and one end thereof is fixed to the wall of the inner tank 10 corresponding to the first cooling stage 8 while keeping thermal contact. The radiation shield 19 must have good thermal conductivity, but in order to reduce noise, a strip of copper foil is used, and the bottom part is made of a copper net with insulated wires. Further, it is surrounded by a multilayer heat insulating material 20 in which a polyester foil having slits and aluminum vapor-deposited thereon and a polyester fiber net are stacked, and is enclosed in an outer tank 21 formed of glass fiber reinforced resin or the like, and the inside is evacuated. Reference numeral 22 is a support member for the outer tank 21.

The element 16 is composed of one or a plurality of elements and is separated from the bottom of the cylinder 4 by 30 cm or more. By doing so, the magnetic field fluctuation width exerted on the element 16 when the magnetic body 3 having a diameter of 2 cm and a length of 5 cm moves with a stroke of 1 cm becomes approximately the same as the magnitude of the external magnetic field.

The radiation shield 19 is preferably an insulator having good thermal conductivity, but may be a ceramic such as high-purity alumina or silicon carbide. The heat transfer between the first cooling stage and the inner tank 10 is by heat conduction or convection of the helium gas 13. A porous filler 23 may be inserted between the cylinder 4 and the inner tank 10 except for the cooling stage to suppress unnecessary heat convection. Further, it is possible to provide a constriction 24 in which the diameter of the lower portion of the inner tank 10 is partially reduced so that the entire apparatus can be used by inclining it so that the liquid helium 14 does not overflow.

FIG. 2 shows another embodiment of the present invention. The same parts as those in FIG. 1 are represented by the same reference numerals. A bellows 30 is inserted below the inner tank 10, and a support 31 is arranged between the inner tank 10 and the radiation shield 19 near the element mounting portion 15 and between the radiation shield 19 and the outer tank 21. The support 31 is preferably a fiber-reinforced resin having low thermal conductivity and high strength. In this way, the element mounting portion 15 is directly supported from the outer tank 21, and the bellows 30
As a result, the vibration from the upper part of the inner tank 10 can be blocked, so that the noise accompanying the mechanical vibration can be reduced. Further, since the support is not a cantilever structure as in the embodiment of FIG. 1, the natural frequency is high, which is convenient for measuring biomagnetism.

Another embodiment of the present invention is shown in FIG. Portions having the same names as those in FIG. 1 are represented by the same symbols. The difference from FIG. 1 is that a magnetic shielding member 33 made of a high-permeability metal or a high temperature superconductor of yttrium / barium / strontium / copper oxide is arranged outside the cylinder 4. The magnetic shielding member 33 may be attached to the cylinder 4, but it is better to fix the magnetic shielding member 33 to the inner tank 10 in order to reduce the influence of vibration. This structure has an advantage that the influence of the reciprocating motion of the magnetic body 3 can be greatly reduced and the distance between the element 16 and the cylinder 4 can be shortened.

FIG. 4 shows still another embodiment of the present invention. This differs from FIG. 3 in that the element mounting portion 15 is attached so that its axial direction is 45 degrees with respect to the axis of the inner tank 10. By doing so, even if the axis of the element mounting portion 15 is changed from a state almost vertical to the gravity state to a horizontal state, the state of the liquid helium 14 in the inner tank is not adversely affected.

[0014]

As described above, since the superconducting device according to the present invention is equipped with the small refrigerator without the Joule-Thomson expansion circuit, it is compact and highly reliable. Further, since the vibration is hard to be transmitted between the movable part of the small refrigerator and the superconducting element, magnetic noise due to mechanical vibration is small. Further, the magnetic noise generated by the movement of the magnetic material in the regenerator can be suppressed as small as possible by the use of the magnetic shielding member, so that a highly sensitive refrigerator-integrated superconducting device can be obtained, which has a great industrial effect.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

FIG. 2 is a vertical sectional view showing another embodiment of the present invention.

FIG. 3 is a vertical sectional view showing still another embodiment of the present invention.

FIG. 4 is a vertical sectional view showing still another embodiment of the present invention.

[Explanation of symbols]

 1 Regenerator 3 Magnetic Material 4 Cylinder 8 First Cooling Stage 9 Second Cooling Stage 10 Inner Tank 14 Liquid Helium 16 Element 19 Radiation Shield 21 Outer Tank 31 Support 33 Magnetic Shielding Member

Continuation of front page (56) Reference JP-A-2-298765 (JP, A) JP-A-4-37031 (JP, A) JP-A-1-170880 (JP, A) JP-A-2-81486 (JP , A) JP-A-2-302680 (JP, A) JP-A-62-185383 (JP, A)

Claims (3)

[Claims] 1. A two-stage cylinder having at least a first and a second cooling stage and containing a regenerator partially filled with a high specific heat magnetic material, and a compression connected to the cylinder by a pressure pipe. A small refrigerator having a machine, an inner tank into which the cylinder is inserted and which stores a liquid coolant, and an ultra-cooler mounted inside or outside the inner tank, apart from the second cooling stage of the cylinder. A conductive element, a radiation shield connected to a part of the inner tank thermally coupled to the first cooling stage of the cylinder, and surrounding the inner tank; and a radiation shield provided at a distance from the radiation shield, and An outer tank surrounding the radiation shield, an anti-vibration mechanism connecting the cylinder and the inner tank, and an inlet for gas liquefied in the second cooling stage of the cylinder. Electrical apparatus. 2. The superconducting device according to claim 1, wherein the intermediate portion is arranged between the inner tank and the outer tank near the element mounting portion for mounting the superconducting element so that the intermediate portion contacts the radiation shield. And a heat insulating support. 3. A two-stage cylinder having at least first and second cooling stages, a regenerator having a high specific heat magnetic material partially filled therein, and a compression connected to the cylinder by a pressure pipe. A small refrigerator having a machine, a magnetic shield member covering a part or all of the outer surface of the cylinder, an inner tank into which the magnetic shield member and the cylinder are inserted, and which stores a liquid coolant, the inner tank And a radiation shield connected to a part of the inner tank thermally coupled to the first cooling stage of the cylinder and surrounding the inner tank, and the radiation shield. An outer tank surrounding the radiation shield, spaced apart from the outer tank, a vibration isolation mechanism for connecting the cylinder and the inner tank, and introduction of gas liquefied in the second cooling stage of the cylinder. A superconducting device comprising: a mouth.