JP7453029B2 - Cryogenic refrigerator and biomagnetic measuring device - Google Patents

Description

The present invention relates to a cryogenic refrigerator and a biomagnetic measuring device.

Conventionally, for example, Patent Document 1 describes a configuration including a transfer tube that introduces a refrigerant cooled by a refrigerator into a cryostat.

Biomagnetic measurement devices such as magnetoencephalography and magnetospinography use high-sensitivity magnetic sensors such as superconducting quantum interference devices, and liquid helium is used as a coolant to maintain a superconducting state. Alternatively, liquid helium is used as a refrigerant when measuring physical properties at extremely low temperatures. Since liquid helium easily vaporizes, economical and continuous use of measurements in such devices requires helium circulation using a cryogenic refrigerator.

Here, some cryogenic refrigerators include a heat insulating part (cryostat) that maintains a low temperature and a transfer tube that sends liquid helium from the heat insulating part. In a cryogenic refrigerator with this configuration, during long-term operation, minute amounts of impurities (nitrogen, oxygen, water, etc.) contained in the circulating gas whose main component is helium are adsorbed to the low-temperature part of the cooling section and solidified. This impurity inhibits heat conversion in the cooling section, thereby reducing recondensation ability. Furthermore, if there is a small amount of leakage in the circulation system, impurities may be continuously supplied from the atmosphere, reducing the recondensation ability over time. On the other hand, when the operation of the cryogenic refrigerator is stopped, the impurity components fixed in the low-temperature part of the cooling section liquefy or vaporize as the temperature of the cooling section rises and flow into the transfer pipe, and the end of the transfer pipe is connected. There is a risk that the transfer pipe may be blocked by being re-cooled in a dewar such as a biomagnetic measuring device and becoming solid. For this reason, in a cryogenic refrigerator where helium circulation is repeatedly started and stopped, operational reliability may be impaired.

The present invention has been made in view of the above, and an object of the present invention is to suppress the influence of impurities contained in a refrigerant.

In order to solve the above-mentioned problems and achieve the objects, the cryogenic refrigerator of the present invention includes a cooling part for cooling a refrigerant, a receiving part for receiving the refrigerant cooled by the cooling part, and a receiving part for the receiving part. A communicating transfer pipe; and a storage part provided between the receiving part and the transfer pipe to store the refrigerant , the storage part having an upper end of the transfer pipe extending to the bottom of the receiving part. The receiving portion is formed such that the bottom of the receiving portion narrows downward toward the connecting portion with the transfer pipe .

According to the present invention, the influence of impurities contained in the refrigerant can be suppressed.

FIG. 1 is a schematic configuration diagram showing an example of a biomagnetic measurement device. FIG. 2 is a schematic configuration diagram showing an example of a helium circulation system. FIG. 3 is a flowchart when the cryogenic refrigerator of the helium circulation system is operated. FIG. 4 is an operational diagram when the cryogenic refrigerator of the helium circulation system is driven. FIG. 5 is a flowchart when the cryogenic refrigerator of the helium circulation system is stopped. FIG. 6 is an operational diagram when the cryogenic refrigerator of the helium circulation system is stopped. FIG. 7 is an enlarged view of the main parts of the cryogenic refrigerator. FIG. 8 is a flowchart showing the operation of the helium circulation system.

Embodiments of a cryogenic refrigerator and a biomagnetic measuring device will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing an example of a biomagnetic measurement device.

The biomagnetic measuring device 100 is a biological information measuring device, and includes a brain function measuring device (also referred to as a measuring device) 101 and an information processing device 102 .

The brain function measuring device 101 is a magnetoencephalograph that measures magnetoencephalography (MEG) signals of the brain, which is an organ of the subject 110 who is the measurement target. The brain function measuring device 101 has a dewar 1 into which the head of the subject 110 is inserted. The dewar 1 is a helmet-shaped sensor-accommodating dewar that surrounds almost the entire head of the subject 110. Dewar 1 is a vacuum insulation device in a cryogenic environment using liquid helium. The dewar 1 has a large number of magnetic sensors 2 arranged therein for measuring brain magnetism. The magnetic sensor 2 uses a superconducting quantum interference device (SQUID). The brain function measuring device 101 collects brain magnetic signals from the magnetic sensor 2 . The brain function measuring device 101 outputs the collected biological signals to the information processing device 102.

The information processing device 102 displays the waveforms of the electroencephalogram signals from the plurality of magnetic sensors 2 on a time axis. Magnetic brain signals are induced by the electrical activity of neurons (the flow of ionic charges that occurs in the dendrites of neurons during synaptic transmission) and represent minute magnetic field fluctuations caused by the electrical activity of the brain.

FIG. 2 is a schematic configuration diagram showing an example of a helium circulation system.

The brain function measuring device 101 described above includes a helium circulation system 10 for making the dewar 1, which is a vacuum insulation device, a cryogenic environment. The helium circulation system 10 includes a cryogenic refrigerator 11, a dewar 1, an evaporative gas recovery section (buffer tank) 13, an evaporative gas recovery pipe 14, a storage gas supply pipe 15, a circulation pipe 16, and a control section 19. and.

The cryogenic refrigerator 11 constitutes a pulse tube refrigerator, and includes a cooling section 21, a receiving section 22, a heat retaining section 23, a transfer pipe 24, a drive system circulation section 25, and a thermometer 26. have

The cooling unit 21 includes a main body 21A, a cylindrical first cylinder part 21B, a cylindrical second cylinder part 21C, a disc-shaped first cold stage 21D, and a disc-shaped second cold stage 21E. and. The main body 21A is the base of the cooling unit 21 and is arranged at the top. The first cylinder portion 21B is provided to extend downward from the main body portion 21A. The second cylinder portion 21C is provided to extend downward from the first cylinder portion 21B. The first cold stage 21D is provided between the first cylinder part 21B and the second cylinder part 21C. The second cold stage 21E is provided at the lower end of the second cylinder portion 21C.

The receiving portion 22 is formed into a dish shape with an open upper end and a bottom 22A at the lower end. The receiving part 22 is arranged directly below the cooling part 21.

The heat retaining section 23 is a vacuum-insulated cryostat, and is formed into a cylindrical shape of, for example, stainless steel or glass fiber reinforced resin, with an open upper end and a bottom 23A at the lower end. The heat retaining section 23 houses the cooling section 21 therein and is provided so as to surround the outer periphery of the cooling section 21 at intervals. The upper end of the heat retaining section 23 is sealed by the main body section 21A of the cooling section 21. Moreover, the receiving part 22 is arranged inside the heat retaining part 23. The heat retaining section 23 functions to maintain the internal temperature.

The transfer pipe 24 has an upper end 24a connected to the bottom 22A of the receiving portion 22, and is provided in communication with the receiving portion 22. The transfer pipe 24 extends downward from the bottom 22A of the receiving part 22, passes through the inside of the heat retaining part 23, and is provided with a lower end 24b facing downward. The heat retaining portion 23 is formed so that the bottom 23A extends downward together with the transfer tube 24 so as to surround the outer periphery of the transfer tube 24 at intervals. The lower end 24b of the transfer tube 24 is connected to the dewar 1 of the brain function measuring device 101. The transfer pipe 24 is also referred to as a first path for sending the liquid refrigerant from the cooling unit 21 to the dewar 1.

The drive system circulation section 25 includes a compressor 25A, which is a compressor, and a valve motor 25B, which is an operating section. Compressor 25A compresses compressed gas. The compressed gas is, for example, helium gas. Compressed gas compressed by the compressor 25A is supplied to the valve motor 25B. The valve motor 25B switches opening and closing to intermittently supply compressed gas to the main body 21A of the cooling unit 21. In the drive system circulation section 25, compressed gas is circulated between the compressor 25A and the cooling section 21 by switching the valve motor 25B. The cooling unit 21 is activated by this intermittent supply of compressed gas, and generates cold heat in the first cold stage 21D and the second cold stage 21E. Note that the compressor 25A exhausts heat by water cooling or air cooling.

The thermometer 26 measures the temperature inside the heat retaining section 23, and measures the temperature near the receiving section 22, the second cold stage 21E, etc. in the cooling section 21, for example. That is, the thermometer 26 measures the temperature of the receiving section 22 (storage section 27 described later) and the cooling section 21 inside the heat retaining section 23 .

When the cryogenic refrigerator 11 is driven, gas refrigerant is supplied to the cooling section 21 inside the heat retaining section 23 . The gas refrigerant is, for example, helium gas, and is liquefied by being cooled by the cold heat generated in the first cold stage 21D and the second cold stage 21E to become liquid helium, which is a liquid refrigerant, and reaches the bottom 22A of the receiving part 22. It can be dripped and collected. The liquid helium collected on the bottom 22A of the receiving section 22 is sent to the outside of the heat-retaining section 23 via the transfer pipe 24, and is supplied to the helium tank inside the dewar 1 of the brain function measuring device 101. As a result, the liquid helium in the Dewar 1 of the brain function measuring device 101 is retained. The liquid helium inside the dewar 1 gradually evaporates due to heat intrusion from the outside and becomes helium gas (also referred to as evaporative gas).

The evaporated gas recovery section 13 is a pressure vessel for collecting and storing the evaporated gas evaporated by the dewar 1.

The evaporative gas recovery pipe 14 is a pipe that connects the dewar 1 and the evaporative gas recovery section 13. The evaporative gas recovery pipe 14 includes a first evaporative gas recovery pipe 14A and a second evaporative gas recovery pipe 14B.

The first evaporative gas recovery pipe 14A has one end 14Aa connected to the dewar 1 and the other end 14Ab connected to the evaporative gas recovery section 13. The first evaporative gas recovery pipe 14 is provided with a pump 14Ac, which is a compressor, in the middle to send the evaporative gas from the dewar 1 to the evaporative gas recovery section 13. Further, the first evaporated gas recovery pipe 14A is provided with a first on-off valve 14Ad closer to the end 14Aa than the pump 14Ac in order to open and close the feeding of the evaporated gas. The first on-off valve 14Ad is controlled by the control section 19. The first evaporative gas recovery pipe 14A is also referred to as a second path for directly sending the evaporative gas from the dewar 1 to the evaporative gas recovery section 13.

The second evaporative gas recovery pipe 14B is a pipe that connects the middle of the first evaporative gas recovery pipe 14A and the inside of the heat retention section 23 of the cooling section 21. One end 14Ba of the second evaporative gas recovery pipe 14B is connected between one end 14Aa of the second evaporative gas recovery pipe 14B and the on-off valve 14Ad, and the other end 14Bb is connected to the heat retaining section 23. In this embodiment, the other end 14Bb of the second evaporative gas recovery pipe 14B is connected to the heat retaining section 23 via a part of the storage gas supply pipe 15. The second evaporative gas recovery pipe 14B is provided with a second on-off valve 14Bc in the middle to open and close the feeding of evaporative gas. The second on-off valve 14Bc is controlled by the control section 19. Further, the second evaporative gas recovery pipe 14B is provided with an exhaust valve (exhaust part) 14Bd closer to the other end 14Bb than the second on-off valve 14Bc. The exhaust valve 14Bd is controlled by the control section 19. The exhaust valve 14Bd is connected to the heat retaining section 23 via a part of the second evaporative gas recovery pipe 14B and the storage gas supply pipe 15.

The storage gas supply pipe 15 is a pipe that connects the evaporated gas recovery section 13 and the cooling section 21. The storage gas supply pipe 15 has one end 15a connected to the evaporated gas recovery section 13, and the other end 15b connected to the cooling section 21 of the cryogenic refrigerator 11. A pump 15c is provided in the storage gas supply pipe 15 in order to send the evaporative gas (storage gas) stored in the evaporative gas recovery section 13 from the evaporative gas recovery section 13 to the cooling section 21. Further, the storage gas supply pipe 15 is provided with an on-off valve 15d closer to the other end 15b than the pump 15c in order to open and close the feeding of evaporated gas. The on-off valve 15d is controlled by the control section 19. Further, the storage gas supply pipe 15 is provided with an on-off valve 15e closer to one end 15a than the pump 15c in order to open and close the feeding of evaporated gas. The on-off valve 15e is controlled by a control section 19. The storage gas supply pipe 15 is also referred to as a third path for sending the evaporative gas from the evaporative gas recovery section 13 to the cooling section 21 .

The circulation pipe 16 is a pipe that connects the middle of the evaporated gas recovery pipe 14 and the middle of the storage gas supply pipe 15. The circulation pipe 16 has one end 16a connected between the on-off valve 14Ad and the on-off valve 14Bc of the evaporated gas recovery pipe 14, and the other end 16b connected between the on-off valve 15e of the storage gas supply pipe 15 and the pump 15c. has been done. The circulation pipe 16 is also referred to as a bypass path that directly sends the evaporated gas from the dewar 1 to the cooling section 21 .

The control unit 19 controls the helium circulation system 10, and is an arithmetic device including a CPU (Central Processing Unit), a storage device, and the like. The control unit 19 includes a compressor 25A of the cryogenic refrigerator 11, a pump 14Ac and each on-off valve 14Ad, 14Bc, and an exhaust valve 14Bd of the evaporative gas recovery pipe 14, a pump 15c, an on-off valve 15d, and an on-off valve 15d of the storage gas supply pipe 15. The operation of the on-off valve 15e is controlled. Further, the control unit 19 acquires the temperature measured by the thermometer 26 of the cryogenic refrigerator 11.

Here, the operation of the helium circulation system 10 will be explained. FIG. 3 is a flowchart when the cryogenic refrigerator of the helium circulation system is operated. FIG. 4 is an operational diagram when the cryogenic refrigerator of the helium circulation system is driven. FIG. 5 is a flowchart when the cryogenic refrigerator of the helium circulation system is stopped. FIG. 6 is an operational diagram when the cryogenic refrigerator of the helium circulation system is stopped.

As shown in FIG. 3, when the cryogenic refrigerator 11 is driven, the control unit 19 stops the pump 14c of the evaporative gas recovery pipe 14, and also closes the first on-off valve 14Ad, the second on-off valve 14Bc, and the exhaust valve 14Bd. Close (step S1). Further, the control unit 19 drives the pump 15c of the storage gas supply pipe 15 and opens the on-off valve 15d and the on-off valve 15e (step S2). Then, the control unit 19 drives the cooling unit 21 of the cryogenic refrigerator 11 (step S3). As a result, as shown in FIG. The gas refrigerant is sent from the dewar 1 to the cooling section 21 via a part of the recovery pipe 14A and the circulation piping 16, and the gas refrigerant is cooled in the cooling section 21 to become a liquid refrigerant, which is then sent to the dewar 1. Note that the operations from steps S1 to S3 may be performed simultaneously.

Further, as shown in FIG. 5, when the cryogenic refrigerator 11 is stopped, the control section 19 stops the cooling section 21 of the cryogenic refrigerator 11 (step S11). Further, the control unit 19 stops the pump 15c of the storage gas supply pipe 15 and closes the on-off valve 15d and the on-off valve 15e (step S12). Further, the control unit 19 opens the first on-off valve 14Ad of the evaporative gas recovery pipe 14, closes the second on-off valve 14Bc and the exhaust valve 14Bd, and drives the pump 14c (step S13). As a result, as shown in FIG. 6, the helium circulation system 10 sends the gas refrigerant from the dewar 1 to the evaporative gas recovery unit 13 via the first evaporative gas recovery pipe 14A of the evaporative gas recovery pipe 14, and Collect at 13. Note that the operations from steps S11 to S13 may be performed simultaneously.

In the helium circulation system 10 of this embodiment, for example, when the brain function measuring device 101 is not used from 5:00 pm to 9:00 am the next day, the operation shown in FIGS. The refrigerant is cooled to become a liquid refrigerant and sent to the dewar 1. Furthermore, in the helium circulation system 10 of the present embodiment, when the brain function measuring device 101 is used from 9:00 a.m. to 5:00 p.m., the operations shown in FIGS. 5 and 6 are performed, and the evaporated gas is The gas refrigerant is sent to the recovery section 13 and recovered by the evaporated gas recovery section 13. Therefore, the helium circulation system 10 of the present embodiment stops the cryogenic refrigerator 11 during measurement using the brain function measuring device 101 to prevent the influence of vibrations of the cryogenic refrigerator 11 on the brain function measuring device 101. , When the brain function measuring device 101 is not used to perform measurements, the cryogenic refrigerator 11 can be driven to bring the dewar 1 into a cryogenic environment.

FIG. 7 is an enlarged view of the main parts of the cryogenic refrigerator.

As described above, the cryogenic refrigerator 11 includes a cooling section 21 that cools the gas refrigerant, a receiving section 22 that collects the liquid refrigerant R cooled by the cooling section 21, and a transfer pipe 24 that communicates with the receiving section 22. Equipped with. The cryogenic refrigerator 11 also includes a storage section 27 that is provided between the receiving section 22 and the transfer pipe 24 and stores the liquid refrigerant R cooled by the cooling section 21 .

As shown in FIG. 7, the storage portion 27 is formed such that the bottom 22A of the receiving portion 22 narrows downward toward the connecting portion with the transfer tube 24, and the upper end 24a of the transfer tube 24 is connected to the receiving portion 22. By penetrating upward through the bottom 22A of the receiving portion 22 and extending above the bottom 22A of the receiving portion 22, the liquid refrigerant R collected in the receiving portion 22 is configured to accumulate up to the upper end 24a of the transfer pipe 24. has been done.

In this way, the storage section 27 can store the liquid refrigerant R between the receiving section 22 and the transfer pipe 24.

As described above, in the cryogenic refrigerator 11, there is a possibility that impurities S such as nitrogen, oxygen, and water that have been adsorbed and solidified in the cooling part 21 etc. will liquefy or vaporize as the temperature rises and flow into the transfer pipe 24. . In the cryogenic refrigerator 11 of this embodiment, by providing the storage section 27, as shown in FIG. It is stored at the bottom of the storage section 27 (bottom 22A of the receiving section 22) and is separated from the upper end 24a of the transfer pipe 24. Therefore, the cryogenic refrigerator 11 of this embodiment prevents the impurities S from flowing into the transfer pipe 24 by retaining them in a solidified state. The cryogenic refrigerator 11 of this embodiment can prevent the liquefied or vaporized impurities S from solidifying by recooling in or at the end of the transfer pipe 24, thereby preventing the transfer pipe 24 from being clogged. Further, in the cryogenic refrigerator 11 of the present embodiment, since the impurities S do not remain stuck to the cooling section 21, the recondensation ability is prevented from decreasing without impeding the heat conversion of the cooling section 21. As a result, the cryogenic refrigerator 11 of this embodiment can suppress the influence of impurities contained in the refrigerant.

In the cryogenic refrigerator 11 of this embodiment, the storage section 27 is formed by extending the upper end 24a of the transfer pipe 24 to the bottom 22A of the receiving section 22, so that it can be easily configured. In addition, in the cryogenic refrigerator 11 of this embodiment, since the storage part 27 is formed so that the bottom 22A of the receiving part 22 is narrowed downward toward the connection part with the transfer pipe 24, the contaminant S The distance from the deepest part of the storage section 27 where S is accumulated to the upper end 24a of the transfer pipe 24 can be increased, and the contaminants S can be further prevented from flowing into the transfer pipe 24.

Furthermore, in the cryogenic refrigerator 11 of this embodiment, the storage section 27 is arranged directly below the cooling section 21 . Therefore, the cryogenic refrigerator 11 of this embodiment can reliably receive the impurities S that have been adsorbed and solidified by the cooling unit 21.

By the way, FIG. 8 is a flowchart showing the operation of the cryogenic refrigerator. In the cryogenic refrigerator 11 of this embodiment, the control unit 19 acquires the temperature of the cooling unit 21 or the storage unit 27 measured by the thermometer 26. The control unit 19 opens the exhaust valve 14Bd of the exhaust unit when the acquired temperature is equal to or higher than a predetermined temperature. Specifically, as shown in FIG. 8, in the cryogenic refrigerator 11, the control unit 19 closes the exhaust valve 14Bd except for the main control (step S21: see FIGS. 4 and 6). Then, when the control unit 19 stops the cooling unit 21 as shown in FIG. 6 (step S22: Yes), and when the temperature measured by the thermometer 26 is equal to or higher than a predetermined temperature (step S23: Yes) , the exhaust valve 14Bd is opened (step S24). The predetermined temperature is a temperature at which the impurity S component can be vaporized. Note that in step S22, stopping the cooling unit 21 means that compressed gas is not being supplied, and driving the cooling unit 21 means that compressed gas is being supplied. When the control unit 19 is driving the cooling unit 21 in step S22 (step S22: No), the process returns to step S21. Further, in step S23, if the temperature measured by the thermometer 26 is not equal to or higher than the predetermined temperature (step S23: No), the control unit 19 continues to acquire the temperature measured by the thermometer 26.

As described above, the cryogenic refrigerator 11 of the present embodiment includes the heat retaining part 23 that accommodates the cooling part 21 and the storage part 27, the thermometer 26 that measures the temperature of the cooling part 21 or the storage part 27, and the heat retaining part 23. The exhaust valve 14Bd is an exhaust section connected to the exhaust valve 14Bd, and a control section 19 that opens the exhaust section 26 when the temperature measured by the thermometer 26 reaches a predetermined temperature or higher. According to this cryogenic refrigerator 11, when the impurity S component is vaporized, the impurity S component can be discharged to the outside of the heat retaining section 23. As a result, the cryogenic refrigerator 11 of this embodiment can prevent the impurity S from solidifying by recooling in the transfer pipe 24 and clogging the transfer pipe 24. In this embodiment, the control unit 19 uses the control unit 19 of the helium circulation system 10 described above, but may include another control unit that performs the above control of the cryogenic refrigerator 11.

Furthermore, the biomagnetic measuring device 100 of this embodiment includes the above-described cryogenic refrigerator 11 and can suppress the influence of impurities contained in the refrigerant, so that the measurement by the brain function measuring device 101 can be carried out economically and continuously. .

Although not clearly shown in the figure, the storage section 27 is connected to the outer periphery of the receiving section 22 and below the second cold stage 21E of the cooling section 21, and is connected to the transfer pipe 24 below the bottom 22A of the receiving section 22. The upper end 24a may be located upward, so that the liquid refrigerant R collected in the receiving portion 22 may be stored up to the upper end 24a of the transfer pipe 24.

Further, although not explicitly shown in the figure, the exhaust valve 14Bd, which is an exhaust section, may be directly connected to the heat retaining section 23. In this case, the second evaporative gas recovery pipe 14B, the on-off valve 14Bc, and the exhaust valve 14Bd may not be provided.

11 Cryogenic refrigerator 14Bd Exhaust section 19 Control section 21 Cooling section 22 Receiving section 22A Bottom 23 Heat retention section 24 Transfer pipe 24a Upper end 27 Storage section 26 Thermometer 100 Biomagnetic measuring device 101 Brain function measuring device (measuring device)

Patent No. 5839734

Claims (4)

a cooling unit that cools the refrigerant;
a receiving part that collects the refrigerant cooled in the cooling part;
a transfer pipe communicating with the receiving part;
a storage part provided between the receiving part and the transfer pipe and storing the refrigerant;
Equipped with
The storage portion is formed by extending the upper end of the transfer pipe to the bottom of the receiving portion, and is formed such that the bottom of the receiving portion narrows downward toward a connecting portion with the transfer pipe. ,
Cryogenic refrigerator. The cryogenic refrigerator according to claim 1 , wherein the storage section is arranged directly below the cooling section. a heat retention section that accommodates the cooling section and the storage section;
a thermometer that measures the temperature of the cooling section or the storage section;
an exhaust section connected to the heat insulation section;
a control unit that opens the exhaust section when the temperature measured by the thermometer exceeds a predetermined temperature;
The cryogenic refrigerator according to claim 1 or 2 , comprising: A cryogenic refrigerator according to any one of claims 1 to 3 ,
a measuring device cooled by a refrigerant sent from the cryogenic refrigerator;
A biomagnetic measuring device comprising:

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