JPH0611554A - SQUID magnetometer - Google Patents

Abstract

PURPOSE:To correctly regulate a relative position of a pickup coil with respect to a vacuum container by interposing a thermal anchor which has high thermal conductivity and is not superconductive even at an extremely low temperature level. CONSTITUTION:A pickup coil 2b is held at a tip 1f of a vacuum container via a heat insulation layer 1g. By airtightly coupling the tip to a vacuum container part 1b in this state, good thermal coupling between a final cooling stage 1e and the coil 2b via a thermal anchor 2c can be attained. In addition since the coil 2b is pressed against an upper bottom of the tip if by means of spring property of the anchor 2c, correct positioning with respect to the tip 1f can be attained. Therefore without subsequently performing task of estimating the position of the coil 2b using an external coil or the like, (eliminating need for operating a freezer to obtain a superconductive transition temperature which is needed to perform the above task), correct measurement of a living body magnetic field or the like can be performed based on position information of the coil 2b which has been obtained at the time of assembly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SQUID magnetometer, and more specifically, to a superconducting quantum interference device that is in a superconducting state at a cryogenic level.
The present invention relates to an SQUID magnetometer suitable for operating an SQUID magnetometer including a terference device (hereinafter abbreviated as SQUID) and a magnetic flux input circuit with a cryogenic refrigerator.

[0002]

2. Description of the Related Art Conventionally, SQUIDs utilizing the Josephson effect have been known as one of superconducting devices. By connecting a magnetic flux input circuit having a superconducting pickup coil to this SQUID, it is possible to measure an extremely weak magnetic flux such as a magnetic field associated with a minute current flowing in the living body or a magnetic field from a minute magnetic body in the living body. SQUID
A magnetometer can be obtained.

As a method for cooling the SQUID magnetometer to a cryogenic level, that is, a temperature level at which the SQUID and the superconducting coil are transformed into a superconducting state, liquid helium is stored in a cryostat and converted into liquid helium. There is a method of immersing the SQUID magnetometer.
Incidentally, when adopting this method using a refrigerator, insert the cooler of the refrigerator for cold generation in the cryogenic container,
Helium gas evaporated in the cryogenic container is condensed and liquefied by a refrigerator.

When this method is adopted, the SQUID
Since the magnetometer is immersed in liquid helium, the SQUID magnetometer can be cooled stably and quickly in its entirety. However, on the other hand, since helium is interposed in the cryostat for cooling the SQUID magnetometer,
The cooling system becomes large and the operability deteriorates. In consideration of this point, a method of directly contacting an SQUID magnetometer with a cooler of a refrigerator so as to be capable of heat transfer and cooling to a cryogenic level has been attracting attention (see, for example, JP-A-2-302680).

[0005]

When the method of directly contacting the SQUID magnetometer with the cooler of the refrigerator so as to be able to transfer heat to cool it to the cryogenic level is adopted, the heat from the external atmosphere is absorbed by the SQUID magnetometer. In order to prevent the heat from being transmitted to the vacuum container, a structure in which a cooler, a SQUID magnetometer and the like are housed in a vacuum container, and a radiation shield is further arranged in the vacuum container is generally adopted. Therefore, in the actual assembling work, after the magnetic flux input circuit including the pickup coil and the SQUID are assembled to the cooler, the vacuum container is assembled so as to surround them.

As a result, the relative position of the pickup coil with respect to the SQUID, that is, the relative position of the pickup coil with respect to the cooler is accurately determined.
The relative position with respect to the vacuum container cannot be accurately determined due to dimensional error of the vacuum container itself, dimensional error of the vacuum container mounting portion, and the like. By the way, in the SQUID magnetometer, if the relative position of the pickup coil with respect to the vacuum container is not accurately determined, for example, the accurate relative position of the pickup coil with respect to the living body or the like to be measured cannot be obtained, and thus the relative position error. Due to, the analysis result obtained based on the biomagnetic flux measurement signal contains a large error.

Therefore, conventionally, after the assembly is completed as described above, a magnetic field is applied from the outside of the vacuum container by using an external coil, and this magnetic field is detected by the SQUID magnetometer to pick up the inside of the vacuum container. The relative position of the coil is estimated. As a result, in order to estimate the relative position of the pickup coil after completion of assembly, work to operate the refrigerator to obtain a cryogenic level and work to detect the magnetic field applied by the external coil after the cryogenic level is obtained. There is an inconvenience that the above becomes necessary.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide an SQUID magnetometer capable of accurately defining the relative position of the pickup coil with respect to the vacuum container.

[0009]

In order to achieve the above-mentioned object, the SQUID magnetometer according to claim 1 is arranged such that the SQUID is thermally connected to a cryogenic stage of a cryogenic refrigerator. With cryogenic stage and SQU
A vacuum container surrounding the ID is arranged, an external magnetic flux detecting coil of the magnetic flux input circuit is arranged at a predetermined position inside the vacuum container through a heat insulating layer, and between the cryogenic stage and the external magnetic flux detecting coil. In addition, a thermal anchor having a predetermined spring constant, a high thermal conductivity, and a superconducting state even at an extremely low temperature level is interposed.

[0010]

According to the SQUID magnetometer of claim 1, since the external magnetic flux detecting coil is arranged at a predetermined position inside the vacuum container via the heat insulating layer, the relative position of the external magnetic flux detecting coil to the vacuum container can be accurately measured. It can be set, and it is possible to eliminate the work of estimating the relative position of the external magnetic flux detection coil by generating a magnetic field using the external coil after the assembly is completed and measuring the generated magnetic field. Also, the relative position between the external magnetic flux detection coil and the cryogenic stage changes, but because the thermal anchor interposed between the two has a predetermined spring constant, there are variations in relative position. Can be absorbed by a thermal anchor to achieve good thermal coupling between the external magnetic flux detection coil and the cryogenic stage. That is, the position of the external magnetic flux detecting coil can be grasped at the completion of the assembly without any special work, and good thermal coupling between the external magnetic flux detecting coil and the cryogenic stage can be achieved.

[0011]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is an exploded vertical sectional view schematically showing an embodiment of the SQUID magnetometer of the present invention.
A vacuum container base 1b is provided on the first cooling stage 1a. A radiation shield 1d is provided on the second cooling stage 1c supported by the first cooling stage 1a. Further, the SQUID 2a is arranged in direct contact with the final cooling stage 1e supported by the second cooling stage 1c, and the thermal anchor 2c is supported by the final cooling stage 1e. Further, 1f is a vacuum container tip portion, which holds the pickup coil 2b at a predetermined position via a heat insulating layer 1g. The vacuum container base portion 1b and the vacuum container tip portion 1f are integrally connected to form a vacuum container that houses each cooling stage, the SQUID 2a and the pickup coil 2b.

The thermal anchor 2c is shown in FIG.
As shown in Fig. 7, an ultrafine wire such as copper is knitted in a mesh shape to form a band having a predetermined width, and engaging portions are integrally provided at both ends, and a predetermined position is bent in a folded shape. By interposing between the final cooling stage 1e and the pickup coil 2b in this state, good thermal coupling between them can be achieved by the spring property and bolting of the thermal anchor itself.

The heat insulating layer 1g is formed by winding a vinyl mesh, for example, and the pickup coil 2b can be stably held by interposing it in a gap of an arbitrary size. That is, as shown in FIG.
Support frame 1 made of a material having a remarkably low thermal conductivity inside f
Since h is integrally provided, the pickup coil 2b can be stably held in the internal space formed by the support frame 1h via the heat insulating layer 1g. Further, since the pickup coil 2b is held via the heat insulating layer 1g, the radiation shield surrounding the pickup coil 2b becomes unnecessary. Of course, you may provide a radiation shield in the state which surrounds the heat insulation layer 1g.

With the SQUID magnetometer having the above structure,
By holding the pickup coil 2b in the vacuum container tip 1f via the heat insulating layer 1g and secretly connecting the vacuum container tip 1f to the vacuum container base 1b in this state, the final cooling stage is performed via the thermal anchor 2c. 1e and the pickup coil 2b can be satisfactorily thermally coupled, and the spring property of the thermal anchor 2c enables the pickup coil 2
Since c is pressed against the upper bottom of the vacuum container tip 1f, accurate positioning with respect to the vacuum container tip 1f can be achieved.

Therefore, thereafter, the work of estimating the position of the pickup coil 2b using an external coil or the like is not performed (in order to perform this work, it is necessary to operate the refrigerator to obtain the superconducting transition temperature). It is possible to accurately measure the biomagnetic field based on the position information of the pickup coil 2b obtained at the time of assembly.

FIG. 4 is a cross-sectional view showing the holding state of the pickup coil 2b in the case where the SQUID magnetometer has a multi-channel structure. The holding frame 1j is used to divide the interior of the vacuum container tip portion 1f into a plurality of small regions. The pickup coil 2b is held in each small area defined by the holding frame 1j via the heat insulating layer 1g. Of course, the SQUID 2a corresponding to each pickup coil 2b is arranged in a state of being in direct contact with the final cooling stage 1e. A thermal anchor 2c is provided corresponding to each pickup coil 2b.

Therefore, also in this case, it is not necessary to estimate the position of each pickup coil 2b, and the magnetic field to be measured can be measured immediately by cooling to the superconducting transition temperature. The present invention is not limited to the above-described embodiment, and for example, the thermal anchor 2c may be made of a material other than copper, a configuration other than the mesh configuration, etc. As the layer 1g, a mesh structure made of other materials, a foam material, or the like can be adopted, and various design changes can be made within a range not changing the gist of the present invention.

[0018]

As described above, the invention of claim 1 is SQU
It is possible to accurately set the relative position of the pickup coil arranged at a position away from the ID with respect to the vacuum container, and to achieve good thermal coupling between the pickup coil and the final cooling stage, thus eliminating the work of estimating the position of the pickup coil. It has the unique effect of being able to do it.

[Brief description of drawings]

FIG. 1 is an exploded vertical sectional view schematically showing an embodiment of a SQUID magnetometer of the present invention.

FIG. 2 is a front view showing a specific configuration of an example of a thermal anchor.

FIG. 3 is a cross-sectional view showing a state in which a pickup coil for one channel is held at the tip of the vacuum container.

FIG. 4 is a transverse cross-sectional view showing a state in which pickup coils for multiple channels are held at the tip of the vacuum container.

[Explanation of symbols]

 1 Cryogenic refrigerator 1b Vacuum container base 1f Vacuum container tip 1g Thermal insulation layer 1e Final cooling stage 2a SQUID 2b Pickup coil 2c Thermal anchor

Claims (1)

[Claims] 1. A superconducting quantum interference device (2a) and a magnetic flux input circuit (2b) which are in a superconducting state at a cryogenic level, wherein the superconducting quantum interference device (2a) and the magnetic flux input circuit (2b) are cryogenic. SQU cooled by refrigerator (1)
An ID magnetometer, in which a superconducting quantum interference device (2a) is arranged while being thermally connected to a cryogenic stage (1e) of a cryogenic refrigerator (1), and a cryogenic stage (1e). ) And a vacuum container (1b) (1f) surrounding the superconducting quantum interference device (2a) are arranged, and a magnetic flux input circuit (2b) is provided at a predetermined position inside the vacuum container (1f) via a heat insulating layer (1g). ), The external magnetic flux detecting coil (2b) is arranged, and the external magnetic flux detecting coil (2b) has a predetermined spring constant and a high thermal conductivity between the cryogenic stage (1e) and the external magnetic flux detecting coil (2b). The SQUID magnetometer is characterized in that a thermal anchor (2c) which does not become a superconducting state even at a cryogenic level is interposed.