JPH0283475A - Cryostat for squid - Google Patents

Abstract

PURPOSE:To enhance measuring accuracy and to reduce the consumption quantity of a liquid He by providing the firs cooling layer (liquid He) for cooling an element and the second cooling layer (liquid He) for cooling a pickup coil while providing the first vacuum tank for thermally insulating the second cooling layer from the open air and providing the second vacuum tank for thermally insulating the first and second cooling layers. CONSTITUTION:The first cooling medium (liquid He) is received in an inner tank 2 for cooling an element 16 and the second cooling medium (liquid N2) is received in an outer tank 1 for cooling a pickup coil 12 and the first vacuum tank 7 is formed between the outer case 3 and inner case 4 of the outer tank 1 and the second vacuum tank 14 is provided between the outer case 5 and inner case 6 of the inner tank 2. By reducing the thickness of the vacuum tank 7, the distance between the coil 12 and an object to be measured can be shortened and measuring accuracy can be enhanced. Further, the consumption quantity of liquid He can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cryostand for a SQUID that cools an element and a pickup coil of the SQUID with a refrigerant.

SQUID (superconducting quantum interferometer) is attracting attention as an application of the Josephson junction. This SQUID is capable of measuring minute magnetic fields, and is being applied to research in medical fields such as magnetocardiography and magnetoencephalography, as well as exploration of minerals and geothermal sources. The above-mentioned SQUID is composed of an element made of a superconductor (SC) and a pickup coil, and conventionally both the element and the pickup coil were cooled with liquid helium. Here, when measuring with SQUID, SQUID
Even if there is a metal piece near the ID, magnetic field fluctuations (noise) occur, so a magnetic shield is required. Therefore, a non-magnetic FRP container is used as a taliostat that cools the SQUID.

Incidentally, oxide superconductors have been discovered in recent years, and attempts have been made to manufacture SQUIDs using them.

This oxide superconductor becomes superconducting when cooled with liquid nitrogen, which has a higher temperature and lower cost than liquid helium, so if it is used in a SQUID, running costs can be reduced.

In this case, the pickup coil will work if it is in a superconducting state, so it can be cooled with liquid nitrogen.

However, since the noise generated in the element increases as the temperature rises (noise increases in proportion to the 473rd power of the temperature), it was necessary to cool the element using low-temperature liquid helium. For this reason, in the conventional two-component structure (consisting of a cooling layer and a vacuum layer), it is necessary to use high-cost liquid helium as a refrigerant, and SQU
ID running costs cannot be reduced. Furthermore, since liquid helium has a lower temperature than liquid nitrogen, it is required to have high heat insulation properties, and accordingly, it is necessary to increase the thickness of the vacuum layer that insulates liquid helium from the outside air. Therefore, there is a problem in that the distance between the pickup coil and the object to be measured becomes wide, making it impossible to improve the measurement accuracy of the SQUID.

Therefore, the present invention improves the measurement accuracy of SQUID by shortening the distance between the pickup coil and the object to be measured, and reduces the amount of liquid helium consumed.
The purpose is to provide a cryostand for SQUID that can reduce the running cost of UID.

In order to achieve the above object, the present invention provides a SQUID Taliostuft that cools an SQUID element and a pink-up coil with a refrigerant. a cooling layer; a second cooling layer in which a second refrigerant that is higher in temperature than the first refrigerant and cools the pickup coil is stored; a first vacuum layer that insulates the second cooling layer from outside air; It is characterized by having a second vacuum layer that insulates the first cooling layer and the second cooling layer.

■ If the four-layer structure is used as described above, the noise-sensitive elements will be placed in the first layer.
It becomes possible to cool the big amplifier coil, which can be cooled with a refrigerant and operates accurately in a superconducting state, with a second refrigerant having a higher temperature than the first refrigerant. Therefore, the element and the pickup coil can be made of an oxide superconductor.

In addition, since the thickness of the first vacuum layer that insulates the second cooling layer from the outside air can be reduced, it is possible to shorten the distance between the pickup coil and the object to be measured.

Further, the first coolant cools only the element and does not cool the pickup coil, and a first vacuum layer, a second cooling layer, and a second vacuum layer are provided between the first cooling layer and the outside air. So,
Vaporization of the first refrigerant is suppressed, and the amount of consumption of the first refrigerant can be reduced.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

As shown in FIG. 1, the SQUID cryostand of the present invention has an outer tank 1 and an inner tank 2 both made of FRP. The outer tank 1 is composed of an outer case 3 for an outer tank and an inner case 4 for an outer tank, while the inner tank 2 is composed of an outer case 5 for an inner tank and an inner case 6 for an inner tank. At the lower portions of the outer case 3 for the outer tank and the inner case 4 for the outer tank, convex portions 3a and 4a are formed that project toward the object to be measured (not shown).

Here, a first vacuum layer 7 for heat insulation is formed in the space between the outer case 3 for the outer tank and the inner case 4 for the outer tank,
In order to form this first vacuum layer 7, a vacuum valve 8 is provided on the side wall of the outer case 3 for the outer tank. The inner space of the convex portion 4a of the inner case 4 for the outer tank is filled with YBaCu○ (Tc94K).
A pick amplifier coil 12 is provided, and this pickup coil 12 is supported by a support 13 fixed to the bottom wall of the outer case 5 for the inner tank. In addition, the above-mentioned pickup coil 1 is inside the inner case 4 for the outer tank.
Liquid nitrogen 9 is stored in the upper wall 4b of the inner case 4 for the outer tank.
A liquid nitrogen supply port 10 for supplying liquid nitrogen and a gaseous nitrogen discharge port 11 for discharging vaporized liquid nitrogen 9 are provided. On the other hand, in the space between the outer case 5 for the inner tank and the inner case 6 for the inner tank, a second vacuum layer 14 (10-b to 10-"
Torr) is formed, and this second vacuum layer 14
A vacuum valve 1 is installed on the side wall of the outer case 5 for the inner tank to form a
5 is provided. An element 16 made of YBaCuO and connected to a control circuit (not shown) is provided inside the inner case 6 for the inner tank. It is connected by a lead wire 37 and an induction coil 21. In addition, an element 1 is placed inside the inner case 6 for the inner tank.
Liquid helium F, which cools the 6, is stored. The upper wall 6a of the inner case 6 for the inner tank is provided with a liquid helium supply port 18 for supplying liquid helium into the inner case 4 for the outer tank, and a gas helium discharge port 19 for discharging vaporized liquid helium. A pressure valve 20 is installed on the side wall of the inner case 6 for the inner tank.
is provided.

By the way, the element side lead wire 35 and the pickup coil side lead wire 37 pass through the bottom wall 5c of the outer case 5 for the inner tank and the bottom wall 6c of the inner case 6 for the inner tank, and are connected to the pickup coil 12 and the element 16. The detailed structure is shown in FIG. 2.

A through hole 25 and a through hole 26 are formed in both the bottom walls 5c and 6c, respectively. An inner cylinder 27 and an inner cylinder 28 are fixed to these through holes 25 and 26, respectively, and this fixing method involves threading the through holes 25 and 26 and the inner cylinders 27 and 28, and then sealing them with adhesive. did. These inner cylinders 2
Epoxy resin 29 and epoxy resin 30 are filled in 7 and 28, respectively. Above epoxy resin 2
An element side lead wire 35 connected to the element 16 is inserted into the element 9, and an input coil 21a of the induction coil 21 is formed at the end of the element side lead wire 35.

On the other hand, a pickup coil side lead wire 37 connected to the pickup coil 12 is inserted into the epoxy resin 30, and the end of the pickup coil side lead wire 37 is connected to the output coil 2 facing the input coil 21a.
1b is formed. In addition, the input coil 21a and the output coil 21b have a diameter of 5 to 2011 mm, and the input coil 21a
The distance between the output coil 21b and the output coil 21b is 500 μm or less, and there is no contact between the output coil 21b and the output coil 21b. In addition, the induction coil 21 and the element side lead wire 35
The pick-up coil side lead wire 37 is made of an oxide superconductor.

In the above configuration, when the SQUID of the present invention is operated, the signal obtained by the pickup coil 12 is given to the element 16 via the element side lead wire 35, the induction coil 21, and the pickup coil side lead wire 37. A signal is output from the rear element 16 to the control circuit.

By the way, with the four-layer structure as described above, the element 16, which is sensitive to noise, can be cooled with liquid helium, and the pickup coil 12, which operates accurately in a superconducting state, can be cooled with liquid nitrogen. . Further, a first vacuum layer 7, liquid nitrogen 9, and a second vacuum 114 are provided between the liquid helium 17 and the outside air. Therefore, the amount of vaporized high-cost liquid helium 17 is reduced, and the amount of liquid helium 17 consumed is reduced, making it possible to reduce the running cost of the SQUID.

In addition, the distance l between the top surface of the bottom wall 4C of the inner case 4 for the outer tank below the pickup coil 12 and the bottom surface of the bottom wall 3C of the outer case 3 for the outer tank is 51 m [bottom wall 3C・4c (2 mm x 2
) 10 vacuum layers 7 (1 m)], the distance between the pickup coil 12 and the object to be measured can be shortened.

In addition, in the conventional taliostat, the distance l is 10 to 30 f.
l (bottom wall 3C, 4C (3~l□nX2) + vacuum layer 7 (3
~1011)).

Furthermore, since the element side lead wire 35 and the pickup coil side lead wire 37 pass through the epoxy resin 29 and the epoxy resin 30 having elastic force, the second vacuum layer 14 can be completely sealed. Can be done.

As explained above, according to the present invention, elements that are susceptible to noise can be cooled with the first refrigerant, and the pickup coil, which operates accurately in the superconducting 4° conductive state, can be cooled with the first refrigerant. It also becomes possible to cool the air with the high-temperature second refrigerant. Therefore, the element and the pick amplifier coil can be made of an oxide superconductor. In addition, since the thickness of the first vacuum layer that insulates the second cooling layer from the outside air can be reduced, it is possible to shorten the distance between the pickup coil and the object to be measured. Furthermore, the first coolant cools only the element and does not cool the pick amplifier coil;
Between the cooling layer and the outside air, there are a first vacuum layer, a second cooling layer, and a second vacuum layer.
Since the vacuum layer is provided, vaporization of the first refrigerant is suppressed and the consumption amount of the first refrigerant can be reduced.

For these reasons, it is possible to dramatically improve the measurement accuracy of the SQUID using the Taliostuft of the present invention, and it is also possible to reduce the running cost of the SQUID.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a cryostat for SQUID according to the present invention, and FIG. 2 is a sectional view showing a connection structure between a pink-up coil and an element. 7... First vacuum layer, 9... Liquid nitrogen, 12... Pickup coil, 14... Second vacuum layer, 16...
Element 17...Liquid helium. Patent applicant: Sanyo Electric Co., Ltd.

Claims (1)

[Claims] (1) In a SQUID cryostat that cools an SQUID element and a pickup coil with a refrigerant, a first cooling layer in which a first refrigerant for cooling the element is stored, and a first cooling layer having a higher temperature than the first refrigerant and cooling the pickup coil. a second cooling layer in which a second refrigerant to be cooled is stored; a first vacuum layer insulating the second cooling layer from the outside air; and a second vacuum layer insulating the first cooling layer and the second cooling layer. A cryostat for SQUID, characterized by having the following.