JP2018025413A - Magnetic measuring device and geological exploration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a highly sensitive magnetic measurement in which foreign noises can be reduced by a magnetic measuring device using a superconductive magnetic sensor.SOLUTION: The magnetic measuring device includes: a low temperature holding container; a cylindrical magnetic shield in the low temperature holding container having an open end and a closed end; a superconductive magnetic sensor in the magnetic shield; and a coolant filled in at least between the low temperature holding container and the magnetic shield.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a magnetometer and a geological exploration system using the same.

  As a technique for exploring underground structures such as geology, there is an electromagnetic exploration method called a TEM (Transient ElectroMagnetic) method. A DC current is passed through a looped cable installed on the ground surface to generate an electromagnetic field, and the eddy current generated in the ground due to sudden interruption of the cable current is measured by a magnetic field sensor installed on the ground surface. The underground structure is extracted as a resistivity distribution. A mineral layer containing a metal or an aquifer layer containing water has a specific resistance different from that of its surroundings, so that its distribution position can be specified. As a magnetic field sensor used in this method, a small and highly sensitive SQUID (Superconducting Quantum Interference Device) sensor is advantageous.

  SQUID measures a weak external magnetic field by detecting a superconducting current flowing through a Josephson junction of a superconductor. Therefore, for example, as shown in FIG. 1, the SQUID is held at a very low temperature by filling a cryogenic holding container such as a cryostat with a coolant such as liquid helium or liquid nitrogen. Generally, the SQUID is disposed on the bottom surface of the cryogenic holding container, and the magnetic field sensor is installed on the ground or embedded near the ground surface.

  As a SQUID containment vessel that accurately measures magnetic fields without generating magnetic flux traps, a cylindrical magnetic shield with open ends is cooled with liquid nitrogen to transition to a superconducting state, and a magnetically shielded space is generated inside the magnetic shield Is known (see, for example, Patent Document 1). Further, a portable cooler that uses a liquid nitrogen and has a fiber assembly that absorbs and holds liquid nitrogen therein has been proposed (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 7-321381 JP 2009-47335 A

  A general magnetic sensor used in the TEM method is scheduled to be used in a situation where there are few artificial noise sources in the surrounding area, such as a wilderness or a forest. When conventional magnetic sensors are applied to excavation sites and tunnel excavation sites for metal resources and hydrothermal deposits, measurement cannot be performed due to scattering of magnetic noise from metal or magnetic construction equipment or excavation equipment.

  The present invention realizes highly sensitive magnetic measurement with reduced external noise by a magnetic measurement device using a superconducting magnetic sensor.

In one aspect, the magnetic measurement device comprises:
A cryogenic container;
A magnetic shield disposed in the low temperature holding container, a cylindrical magnetic shield having one end opened and the other end closed,
A superconducting magnetic sensor disposed inside the magnetic shield;
A coolant filled at least between the cryostat container and the magnetic shield;
Have

  High-sensitivity magnetic measurement with reduced external noise is realized with a magnetic measurement device using a superconducting magnetic sensor.

It is the schematic of the general magnetic sensor used by geological search. It is a schematic block diagram of the magnetic measuring apparatus of embodiment. It is a figure which shows the structural example of the superconducting magnetic sensor using SQUID. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the structural example of a magnetic shield. It is a figure which shows the geological exploration system which applied the magnetic measurement apparatus of embodiment to tunnel excavation. It is a figure which shows the geological exploration system which applied the magnetic measurement apparatus of embodiment to underground structure estimation. It is a figure explaining the magnetic flux density which a transmission current produces. It is a figure which shows the magnetic flux density in each depth point when a transmission loop diameter and transmission current are changed variously. It is a figure which shows the suitable search distance of the aquifer layer in tunnel excavation.

  In the embodiment, in order to prevent extraneous noise in a magnetic measurement device using SQUID, a SQUID sensor is arranged in a magnetic shield of a superconductor having an opening only in the direction of a useful magnetic signal source. The magnetic shield is closed except for the opening that faces the direction of arrival of the target signal, and prevents the intrusion of external noise. Moreover, it is set as the structure which can be used by arbitrary attitude | positions, such as horizontal (horizontal direction) and vertical installation (vertical direction) irrespective of the direction of an incoming signal.

  FIG. 2 is a schematic configuration diagram of the magnetic measurement apparatus 1 according to the embodiment. The magnetic measurement apparatus 1 includes a low temperature holding container 2, a magnetic shield 20 disposed in the low temperature holding container 2, a superconducting magnetic sensor 10 disposed in the magnetic shield 20, a low temperature holding container 2 and a magnetic shield 20. It has the coolant 8 filled in between. The low temperature holding container 2 is a heat insulating vacuum container, and can hold the inside in a cryogenic environment. For example, it has a double structure of a resin container and a glass (quartz) dewar, and a vacuum is maintained between the outer resin container and the inner glass dewar. In the embodiment, an SQUID of an oxide-based high-temperature superconductor that operates at a liquid nitrogen temperature (77 K) is used, and the inside of the low-temperature holding container 2 is maintained at least at the temperature of liquid nitrogen.

  The magnetic shield 20 has a cylindrical main body 21 having an opening 22 in a single direction, and the superconducting magnetic sensor 10 is disposed in the vicinity of the opening 22 inside the main body 21. The cross-sectional shape of the cylindrical main body 21 is an arbitrary shape that can accommodate the superconducting magnetic sensor 10 inside, and is a cross-sectional shape such as a circle, an ellipse, or a polygon. The main body 21 of the magnetic shield 20 is formed of a bismuth (Bi) -based or yttrium (Y) -based oxide superconducting material. As an example, BiSrCaCuO, YBaCuO, or the like can be used. The opening 22 is preferably formed only in a single direction in order to block magnetic signals other than the target signal.

  The coolant 8 is formed of, for example, a liquid nitrogen absorber, and has a configuration in which the coolant does not leak no matter what angle the magnetic measurement device 1 is used. The liquid nitrogen absorber is a foam that does not freeze or contract at the liquid nitrogen temperature, such as foam metal, glass fiber, and melamine foam having open cells, and retains liquid nitrogen in the bubbles. The coolant 8 may be filled in at least a part of the internal space of the magnetic shield 20. The use of the liquid nitrogen absorber is not essential, and the inside of the low temperature holding container 2 may be filled.

  The superconducting magnetic sensor 10 has a superconducting loop for detecting magnetism and a SQUID having one or two Josephson junctions. A lead wire 9 extending from the superconducting magnetic sensor 10 passes through the lid 3 with a pressure release valve, is drawn to the outside of the magnetic measurement device 1, and is connected to an FLL (Flux Locked Loop) 4. The output voltage of the FLL 4 is filtered by an ASP (Analog Signal Processor) 5 and recorded in the data recorder 6. In the configuration example of FIG. 2, the magnetic measurement device 1 is arranged in a direction in which the opening 22 of the magnetic shield 20 is desired to be measured.

  FIG. 3 shows a configuration example of the superconducting magnetic sensor 10 used in the embodiment. In this example, the superconducting magnetic sensor 10 is a SQUID magnetometer using a single coil (pickup coil) 11. The superconducting magnetic sensor 10 includes a pickup coil 11, an input coil 14, a SQUID ring 13, and a feedback coil 15. Although illustrated as a planar circuit for convenience of illustration, the pickup coil 11, the input coil 14, and the feedback coil 15 may be formed in a different layer from the SQUID ring 13 through an insulating film.

  The input coil 14 transmits the magnetic flux captured by the pickup coil 11 to the SQUID ring 13. The SQUID ring 13 has two Josephson junctions 131 in the configuration example of FIG. A Josephson junction refers to a configuration in which two superconductors are weakly coupled, for example, through a thin insulator or normal conductor barrier layer of several nanometers. A bias current in the vicinity of the critical current value of the Josephson junction is passed through the SQUID ring 13, and a superconducting electron pair tunnels the barrier layer so that a superconducting current flows between the two superconductors. When an external magnetic field is applied to the SQUID, a superconducting current flows in a direction to cancel the magnetic field, and a voltage proportional to the magnetic field is generated at both ends of the Josephson junction 131. Since the relationship between the magnetic flux change and the output voltage is not linear, negative feedback is performed by the external FLL 4. The FLL 4 integrates the output voltage of the SQUID ring 13 and outputs the integrated voltage to the ASP 5, and returns the integrated voltage to the SQUID ring 13 through the feedback coil 15 as a feedback magnetic flux. Thereby, the interlinkage magnetic flux of the SQUID ring 13 is locked to zero, and the output voltage of the FLL 4 becomes proportional to the detected signal magnetic flux.

  The superconducting magnetic sensor 10 may be formed as one SQUID chip and disposed in the magnetic shield 20. The SQUID chip can be manufactured in an arbitrary configuration by an arbitrary method. For example, a superconductor loop (washer) pattern and a Josephson junction 131 are formed on the surface of a 10 mm to 15 mm square 0.5 mm thick magnesium oxide (MgO) substrate. The Josephson junction 131 is made of a metal-based superconductor or an oxide-based superconductor. Metal-based superconductors are highly sensitive, but oxide-based superconductor Josephson junctions can be used at liquid nitrogen temperatures, providing excellent operability and cost.

In the embodiment, an oxide high-temperature superconductor such as a YBCO-based material (for example, YBa ₂ Cu ₃ O ₇ ) or a BSCCO-based material (for example, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ ) is used, but is not limited to this example. . The SQUID ring 13 having the Josephson junction 131 may be formed of a metallic superconductor such as Nb, Pb, or NbTi, and liquid helium may be used as the coolant 8.

  The Josephson junction 131 may be formed in a slope or step formed on the substrate (step edge junction). Alternatively, the lower superconductor layer deposited on the MgO substrate may be processed into a step shape, and the upper superconductor layer may be deposited thereon (lamp edge bonding). When an oxide-based superconducting material is used, a crystal grain boundary formed at the interface of the superconducting material can be used as a barrier layer of the Josephson junction. An insulating film is formed on the SQUID ring 13, and a pickup coil 11, an input coil 14, a feedback coil 15, and other necessary wiring are formed on the insulating film.

  In the example of FIG. 3, a single-coil magnetometer is formed, but instead of the pickup coil 11, a SQUID gradiometer is formed using a pair of coils wound in opposite phases (differentially configured). It may be produced. Also in the case of the SQUID gradiometer, it is disposed near the opening 22 inside the main body 21 of the magnetic shield 20. By arranging the opening 22 of the magnetic shield 20 close to the ground or tunnel wall surface to be measured, it is possible to block a large amount of noise magnetic signals from construction equipment (a lump of metal or magnetic material).

  4 to 8 show configuration examples of the magnetic shield 20. The magnetic shield 20A shown in FIG. 4 has a plastic (resin) or nonmagnetic metal base 23 that is not damaged at the liquid nitrogen temperature inside a cylindrical main body 21 that is open at only one end. The superconducting magnetic sensor 10 is fixed to the exposed surface 23s of the base 23 with a resin adhesive or the like. The inside of the pedestal 23 may be hollow, or may be filled with foam metal or glass fiber containing liquid nitrogen. Alternatively, the pedestal 23 may be filled with liquid nitrogen itself.

  The fixed position of the superconducting magnetic sensor 10 can be appropriately determined from the solid angle of the target signal incident on the superconducting magnetic sensor 10. A lead wire 19 extending from the superconducting magnetic sensor 10 is drawn out of the magnetic shield 20.

  The main body 21 of the magnetic shield 20A may be formed by processing a BiCaCuO or YBaCuO bulk into a cylindrical shape, or may be molded and fired from a Bi-based or Y-based material. Bi-based or Y-based materials are superconducting at liquid nitrogen temperature and have a high magnetic shielding effect due to complete diamagnetism. By disposing the superconducting magnetic sensor 10 in the magnetic shield 20A having an opening on one side as shown in FIG. 4, a magnetic signal from a target direction can be selectively captured.

  FIG. 5 shows a magnetic shield 20B as a modification. The magnetic shield 20B has a high-permeability shield 27 disposed outside the magnetic shield 20A of the high-temperature superconductor of FIG. The high-permeability shield 27 has a high-permeability shield material arranged in a single to triple manner as the magnetic shield 20A. The high magnetic permeability material is, for example, mu metal. By arranging the shield 27 having a high magnetic permeability, an external magnetic field is captured by the outer shield 27 and the magnetic field is prevented from entering inside.

  FIG. 6 shows a magnetic shield 20C as another modification. The magnetic shield 20 </ b> C has a sintered body 25 of a superconducting material disposed inside a cylindrical high-temperature superconductor main body 21. The sintered body 25 is formed of a Bi-based oxide superconductor (BiCaCuO) or a Y-based oxide superconductor. The sintered body 25 has a cavity 26, and the superconducting magnetic sensor 10 is fixed to the bottom surface of the cavity 26. The opening of the cavity 26 becomes the opening 22 of the magnetic shield 20 </ b> C, and the lead wire 19 extending from the superconducting magnetic sensor 10 is drawn out of the cavity 26.

  FIG. 7 shows a magnetic shield 20D as still another modified example. The main body 21 of the magnetic shield 20D has a cavity 28 formed in the bulk of BiCaCuO or YBaCuO, and the superconducting magnetic sensor 10 is fixed to the bottom surface of the cavity 28.

  FIG. 8 shows a magnetic shield 20E as still another modified example. The magnetic shield 20E has a liquid nitrogen absorber 24 inside a cylindrical main body 21 made of a superconducting material. The liquid nitrogen absorber 24 is a foam metal, glass fiber, melamine foam or the like having open cells, and holds liquid nitrogen in the bubbles. The superconducting magnetic sensor 10 is fixed to the exposed surface 24s of the liquid nitrogen absorber 24, and the lead wire 19 extending from the superconducting magnetic sensor 10 is drawn out of the magnetic shield 20E through the opening 22.

  4 to 8, the superconducting magnetic sensor 10 is disposed in the magnetic shield having one side opening, so that external noise can be blocked and a magnetic signal from a target direction can be selectively captured. it can. A high-permeability shield 27 as shown in FIG. 5 may be disposed outside the magnetic shields 20C to 20E shown in FIGS. In this case, the external noise blocking effect is further improved.

  FIG. 9 shows a geological exploration system 101 to which the magnetic measurement device 1 of the embodiment is applied. FIG. 9A is a side view, and FIG. 9B is a front view of the installation position of the magnetic measurement apparatus 1. The geological exploration system 101 is used to detect springs or aquifers at tunnel excavation sites. At a tunnel excavation site, it is meaningful to determine whether or not there is an aquifer in front of the excavation position.

  At the time of measurement, a loop-shaped conductive wire or cable 40 is installed on the surface of the excavation surface 30 or in the vicinity thereof, and the magnetic measurement device 1 is arranged at the center of the cable 40. The magnetic measurement apparatus 1 includes a superconducting magnetic sensor 10 disposed inside a magnetic shield 20, and an opening 22 (see FIGS. 4 to 8) of the magnetic shield 20 faces the excavation surface 30.

  The cable 40 forms a loop with a radius a. The loop is not necessarily a circular loop, and may be a rectangular loop. A direct current is passed from the current supply source 41 to the looped cable 40 to generate an artificial electromagnetic field F. By suddenly interrupting the cable current, the magnetic flux (magnetic signal) from the eddy current generated in the bedrock is measured. The cable current is periodically interrupted, and the attenuation of the magnetic field at the time of interruption is observed. From the magnetic field observation results, the specific resistance value at each time after the current is cut at each point in the bedrock is obtained, and the presence or absence of the aquifer is judged from the specific resistance distribution.

  Various excavating machines exist in the tunnel, and unnecessary magnetic field signals reach the magnetic measurement device 1. However, the superconducting magnetic sensor 10 having the SQUID is disposed inside the magnetic shield 20 closed except for the opening 22. Has been. In order to capture the magnetic flux from the excavation surface in the loop, the superconducting magnetic sensor 10 is preferably disposed relatively close to the opening 22 of the magnetic shield 20. The superconducting magnetic sensor 10 detects only a magnetic signal included in the solid angle of the opening 22 viewed from the SQUID. By arranging the opening 22 of the magnetic shield 20 close to the excavation surface 30, the incidence of reflected electromagnetic waves from the ceiling or floor of the tunnel can be reduced. When a liquid nitrogen absorber is used as the coolant 8, liquid leakage can be prevented even when the magnetic measurement device 1 is used in the horizontal direction (horizontal direction).

  FIG. 10 shows another application example of the magnetic measurement apparatus 1 of the embodiment. In FIG. 10, the magnetometer 1 is used for geological exploration in the plain. In FIG. 10A, the cables 40 are arranged in a loop on the ground surface. One side of the loop is, for example, 100 m to 200 m. The cable 40 is connected to the transmitter 50. The magnetic measurement device 1 connected to the receiver 60 is arranged in the center of the loop.

  As shown in FIG.10 (b), the electric current sent through the cable 40 with a transmitter is intermittently interrupted. As an example, the sweep current by the transmitter 50 has a pulse waveform with three amplitude levels. The cable 40 becomes an artificial signal source, electromagnetic waves generated near the ground surface penetrate into the underground, and an induced current (eddy current) is generated in the ground. Magnetic flux generated by the eddy current is detected by the magnetometer 1 and a detection signal is received by the receiver 60. The magnetometer 1 captures magnetic signals from each depth. As shown in the lower part of FIG. 10B, the received waveform has a transient response (dotted line circle). Non-resistance in each layer is obtained from this response characteristic, and the underground structure is estimated. Presence of a layer containing metal resources and groundwater is estimated by the value of specific resistance.

FIG. 11 is a diagram illustrating the magnetic flux density generated by the transmission current. The magnetic flux density B _p of the magnetic field generated at the point P at the depth Z [m] in the ground when the transmission current I [A] is passed through the transmission loop with the radius a [m] is expressed by the equation (1). Is done.

^{_{B p = μ 0 Ia 2/}} 2 (a 2 + Z 2) 3/2 (1)
Here, μ ₀ is the magnetic permeability in a vacuum.

When Z = 0 is substituted into equation (1), that is, the magnetic flux density at the origin O is
B _O = μ ₀ I / 2a (2)
It is.

  The transmission loop diameter (radius) a and the transmission current I are variously changed, and the magnetic flux density at each depth is calculated with the SQUID arranged at the origin O. The transmission loop diameter a for metal resource exploration is 100 meters, the transmission loop radius at the tunnel excavation site is 3 meters, and the reference loop radius is 25 meters. The transmission current I of the 100 m radius loop is changed to 10A, 20A, and 40A. The transmission current I of the 3 m radius loop is changed to 10A, 1A, and 0.5A. The transmission current I in the reference loop is 15A.

  FIG. 12 is a diagram illustrating the calculation result of FIG. The dashed curves A to C are the calculation results in the loop of 100 m radius, the solid curves D to F are the calculation results in the loop of 3 m radius, and the thick dashed curve R is the calculation result in the reference loop. From FIG. 12, it is not appropriate to flow 10A through a loop of 3 m radius because it exceeds the reference value on the ground surface (Z = 0), but it is possible to flow a current of 1 A through the loop of 3 m radius.

  When a current of 1 A is passed through a 3 m radius loop (curve E), the accuracy is about the same as the detection result of the magnetic flux from the depth of 800 m by the reference loop (R) within the depth range of about 100 m from the ground surface. can get.

  FIG. 13 is a diagram showing an appropriate search distance of the aquifer layer when a 3 m radius loop is used in tunnel excavation. As in FIG. 12, the magnetic flux density detected by the reference loop R at a depth of 800 meters underground is used as a reference. The magnetic flux density detected at a depth of 1000 meters when a current of 20 A is passed through a 100 m radius loop is used as the second reference.

  In order to obtain the same accuracy as the magnetic flux density observed in the reference loop R at a depth of 800 m in the ground by passing a current of 1 A through a 3 m radius loop, a depth of 80 m from the ground surface is appropriate. . In addition, when comparing a case where a current of 1 A is passed through a loop with a radius of 3 m and a case where a current of 20 A is passed through a loop with a radius of 100 m, it is the same as the magnetic flux density observed at a depth of 1000 meters from the ground surface. A degree value is obtained at a depth of 30 m from the ground surface with a loop of 3 m radius.

  From this result, when the presence or absence of the aquifer is confirmed at the tunnel excavation site using the loop of 3 m radius and the magnetic measurement device 1 of the embodiment, a good measurement result is obtained in the range of 30 m to 80 m from the excavation surface. I understand that. If the presence of an aquifer is detected, measures such as changing the tunnel excavation direction can be taken.

  The magnetic measurement apparatus 1 of the embodiment uses a magnetic shield 20 having a single opening 22 and arranges the opening in the direction of arrival of a desired signal, thereby blocking external noise and detecting a fine magnetic signal. can do.

  The magnetic measurement device of the embodiment is suitably used for magnetic field measurement under a noisy environment, and is applied to exploration of metal resources, petroleum resources, water resources hydrothermal deposits, and the like. It is also applied to exploration of water veins and aquifers at tunnel excavation sites. It can also be applied to exploration of underground structures in urban areas.

The following notes are presented for the above explanation.
(Appendix 1)
A cryogenic container;
A magnetic shield disposed in the low temperature holding container, a cylindrical magnetic shield having one end opened and the other end closed,
A superconducting magnetic sensor disposed inside the magnetic shield;
A coolant filled at least between the cryostat container and the magnetic shield;
A magnetic measuring device.
(Appendix 2)
The magnetic shield has a cylindrical main body formed of a superconducting material and a pedestal disposed inside the main body, and the superconducting magnetic sensor is fixed to the surface of the pedestal. The magnetic measurement apparatus according to appendix 1.
(Appendix 3)
The magnetic measurement apparatus according to appendix 2, wherein the pedestal is formed of a nonmagnetic metal or a resin material that does not freeze or break at the operating temperature of the superconducting magnetic sensor.
(Appendix 4)
The magnetic measurement apparatus according to appendix 2 or 3, wherein the inside of the pedestal is filled with a cavity or a liquid nitrogen absorber.
(Appendix 5)
The magnetic shield has a cylindrical main body formed of a superconducting material, and a sintered body of a superconducting material disposed inside the main body,
The magnetic measurement apparatus according to appendix 1, wherein the superconducting magnetic sensor is fixed to a bottom surface of a cavity formed in the sintered body.
(Appendix 6)
The magnetic shield has a body having a cavity formed on one end side of a columnar bulk of superconducting material;
The magnetic measurement apparatus according to appendix 1, wherein the superconducting magnetic sensor is fixed to a bottom surface of the cavity.
(Appendix 7)
The magnetic shield has a cylindrical main body formed of a superconductive material, and a liquid nitrogen absorber disposed inside the main body,
The magnetic measurement apparatus according to appendix 1, wherein the superconducting magnetic sensor is fixed to the liquid nitrogen absorber.
(Appendix 8)
The magnetic measurement apparatus according to any one of appendices 2 to 7, wherein the magnetic shield further includes a shield made of a high magnetic permeability material arranged outside the main body.
(Appendix 9)
The cryogenic holding container has a lid for drawing a lead wire extending from the superconducting magnetic sensor to the outside,
The magnetic measurement apparatus according to any one of appendices 1 to 8, wherein the opening of the magnetic shield is disposed at an end portion on the opposite side to the lid.
(Appendix 10)
The superconducting magnetic sensor has a superconducting quantum interference device formed of a high-temperature superconducting material,
10. The magnetic measurement apparatus according to any one of appendices 1 to 9, wherein the coolant is a liquid nitrogen absorber that absorbs and holds liquid nitrogen.
(Appendix 11)
A conductive wire forming a loop;
A current supply source for supplying a current to the conductive wire;
The magnetic measurement device according to any one of supplementary notes 1 to 10 disposed at a center of the loop;
A geological exploration system characterized by comprising:
(Appendix 12)
The geological exploration system according to appendix 11, wherein the loop is formed perpendicular to the ground surface.

DESCRIPTION OF SYMBOLS 1 Magnetic measuring apparatus 2 Low temperature holding container 3 Lid 4 FLL
5 ASP
6 Data recorder 8 Coolant 9, 19 Lead wire 10 Superconducting magnetic sensor 20, 20A-20E Magnetic shield 21 Main body 22 Opening 23 Base 24 Liquid nitrogen absorber 25 Sintered body 26, 28 Cavity 27 Shield 40 Cable (conductive wire) )
41 Current supply source 50 Transmitter 60 Receiver 101, 102 Geological exploration system

Claims (7)

A cryogenic container;
A magnetic shield disposed in the low temperature holding container, a cylindrical magnetic shield having one end opened and the other end closed,
A superconducting magnetic sensor disposed inside the magnetic shield;
A coolant filled at least between the cryostat container and the magnetic shield;
A magnetic measuring device.   The magnetic shield has a cylindrical main body formed of a superconducting material and a pedestal disposed inside the main body, and the superconducting magnetic sensor is fixed to the surface of the pedestal. The magnetic measurement apparatus according to claim 1. The magnetic shield has a cylindrical main body formed of a superconducting material, and a sintered body of a superconducting material disposed inside the main body,
The magnetic measurement apparatus according to claim 1, wherein the superconducting magnetic sensor is fixed to a bottom surface of a cavity formed in the sintered body. The magnetic shield has a body having a cavity formed on one end side of a columnar bulk of superconducting material;
The magnetic measurement apparatus according to claim 1, wherein the superconducting magnetic sensor is fixed to a bottom surface of the cavity. The magnetic shield has a cylindrical main body formed of a superconductive material, and a liquid nitrogen absorber disposed inside the main body,
The magnetic measurement apparatus according to claim 1, wherein the superconducting magnetic sensor is fixed to the liquid nitrogen absorber.   The magnetic measurement apparatus according to claim 2, wherein the magnetic shield further includes a shield made of a high magnetic permeability material disposed outside the main body. A conductive wire forming a loop;
A current supply source for supplying a current to the conductive wire;
The magnetic measurement apparatus according to any one of claims 1 to 6, which is disposed at the center of the loop;
A geological exploration system characterized by comprising:

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