JP3858269B2 - Cooling tube and cryogenic cryostat using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cryogenic cryostat for biomagnetic measurement using a cold material such as liquid helium, and provides a cold supply means for extending the low temperature holding time and reducing the amount of helium evaporation.
[0002]
The present invention is applicable not only to cryogenic cryostats for biomagnetic measurements, but also to cryostats that require refrigerants to maintain low temperatures, such as MRI (nuclear magnetic resonance imaging apparatus) using superconducting magnets and helium cryostats for physical property research. Is also applicable.
[0003]
[Prior art]
[0004]
[Non-Patent Document 1]
Kawakatsu et al. “Development of helium reliquefaction and circulation system for biomagnetic measurement system” Vol.14 No.1 2001,
p274-275, The 16th Annual Meeting of the Biomagnetic Society of Japan.
[Non-Patent Document 2]
S. Fujimoto et.al. "Cooling of SQUIDs using a
Gifford-McMahorn cryocooler containing magnetic regenerative
material to measure biomagnetism ", Cryogenics,
35 (1995) pp.138-143.]
[0005]
Cited from the prior art described in Non-Patent Document 1, FIG. 13 shows a configuration diagram of a liquid helium circulation system. This is a method in which helium gas evaporated from the cryogenic cryostat 2 is temporarily stored in the gas bag 4, returned to the liquid helium by the reliquefier 8, and recirculated to the cryogenic cryostat. Is.
[0006]
In the figure, reference numeral 1 denotes a magnetic shield room for obtaining a quiet magnetic environment for measuring biomagnetism. Reference numeral 2 denotes a cryogenic cryostat, which cools a highly sensitive superconducting magnetic sensor (SQUID) by holding liquid helium as a refrigerant. The liquid helium stored in the cryogenic cryostat 2 evaporates little by little due to heat penetration from the outside. Usually, it is thrown away into the atmosphere, but this is stored in the gas bag 4 through the exhaust pipe 3.
[0007]
The stored helium gas is pressurized by the circulation pump 5, and moisture and impurity gas mixed in the middle are removed through the moisture remover 6 and the impurity gas remover 7, and purified to high purity helium gas, and then the cryogenic refrigerator. After being cooled and condensed to the liquid helium temperature in the recondenser 8 that is cooled by the above, it is once stored in the helium container 9. After a certain amount of liquid helium has accumulated, it is transferred to the cryogenic cryostat 2 through the liquid helium transfer tube 10.
[0008]
In this method, the evaporated gas is re-liquefied with a small liquefaction facility. However, in a facility that consumes a large amount, a recovery line is provided in the facility, and the large-scale liquefaction facility reconstitutes it in a helium container. The means of delivering to the equipment is taken.
[0009]
On the other hand, in Non-Patent Document 2, a cryogenic refrigerator is directly connected to a cryostat to keep the internal gas in a cold state and reliquefy it for measurement. FIG. 14 is a simplified transcription of FIG. 5 described in Non-Patent Document 2.
[0010]
A refrigerator 106 is connected to an upper portion of a cryostat 105 installed in the magnetic shield room 104. A rotary valve 107 for supplying and exhausting compressed gas is connected to the refrigerator 106, and high-pressure and low-pressure gas pipes are connected to the compressor 108.
[0011]
The cold generation unit 109 of the refrigerator 106 is exposed to a helium gas tank 110 that is a separate chamber inside the cryostat 105, and the cryogenic temperature cools the entire helium gas tank 110 by cooling the helium gas. A SQUID sensor 112 is connected to a sensor mount 111 connected to the lower part of the helium gas tank 110, and the SQUID is cooled by heat conduction.
[0012]
A space vacuum layer 113 surrounding the helium gas tank 110 is provided for heat insulation. In addition, a heat radiation shield foil (not shown in the figure) is housed in the vacuum layer to reduce radiation heat transfer.
[0013]
[Problems to be solved by the invention]
A common problem with cryogenic cryostats for biomagnetic measurements is that the vacuum insulation layer is narrow due to its structure and cannot provide sufficient heat shielding. This is derived from the measurement purpose that a sufficient SN (signal-to-noise ratio) cannot be obtained unless a sensor placed at a very low temperature is brought as close as possible to a weak magnetic signal source.
[0014]
Therefore, liquid helium used as a cryogen evaporates rapidly, and the replenishment cycle is about one week at the longest. If the capacity of the cryogenic cryostat is increased, the structural distortion increases and the narrow vacuum heat insulating layer may be crushed, resulting in a thermal short circuit. Therefore, the size cannot be increased unnecessarily. In order to cover such problems, techniques such as Non-Patent Documents 1 and 2 have been proposed.
[0015]
A general problem of recirculation similar to Non-Patent Document 1 is the mixing of impurity gas. The gas bag 4 is usually made of rubber, but is easily permeable to impurity gases such as water, air, and carbon dioxide. Since the cryogenic cryostat itself uses a lot of resin, it has the property of allowing gas to permeate, and if a resin pipe is used for the piping, it also enters from there.
[0016]
When the impurity gas is mixed, it solidifies in the cold part of the recondenser 8 and clogs the piping. Therefore, the impurity gas having a high boiling point / freezing point temperature other than liquid helium to be liquefied is removed by the impurity gas remover 7 by using molecular sieve, activated carbon, cryotrap or the like.
[0017]
However, the impurity gas remover 7 does not completely remove the impurity gas, but clogs the recondenser 8 or the impurity gas remover 7 itself, so that a large amount of impurity gas is trapped and heated and discharged. Must play back. Therefore, even a small helium circulation system requires maintenance as well as a large facility.
[0018]
In addition, the scale of equipment for circulating helium includes gas bags and the like, and even if the cryogenic cryostat is small, the equipment related to circulation becomes large, which is disadvantageous in terms of cost and space.
[0019]
Furthermore, the loss at the time of liquid helium transfer is large, and the normal gas bag cannot be recovered and must be exhausted and the recovery efficiency is reduced accordingly. In order to increase the recovery efficiency, a gas bag of an unrealistic size must be prepared.
[0020]
On the other hand, there is a method similar to Non-Patent Document 2, which is direct cooling by a refrigerator, regardless of helium circulation, but it has not been put into practical use due to the following magnetic noise problem.
(1) Magnetic noise generation by magnetic regenerator material:
In order to generate cold, the antiferromagnetic material and the superconducting material are held inside the expander. However, the vibration accompanying the pulsation of the internal circulation gas pressure causes weak magnetic and magnetic gradient fluctuations in the surroundings. This is several tens to several hundreds pT (picotesla), and becomes a very large interference signal when measuring weakness such as biomagnetism of several tens of fT (femtotesla) to several tens of pT.
[0021]
(2) The expander of the cryogenic refrigerator is made of stainless steel (SUS) having a small thermal conductivity, but is weak but has magnetism. Since vibration is generated by fluctuations in the expansion gas pressure, magnetic noise is generated as described above.
[0022]
(3) Since the cold part and the normal temperature part form a loop with dissimilar metals, a thermoelectromotive force is generated, and a current flows in the loop. This is close to a steady current if the temperature is constant, but when a vibration is applied, the magnetic field fluctuates according to the amplitude and disturbs the external magnetic field.
[0023]
From the above, in the field of biomagnetism measurement, it is difficult to directly attach a cryogenic refrigerator to a cryogenic cryostat, and a helium circulation system has been proposed as the next best means. However, as described above, facilities are becoming larger and cost problems are newly generated.
[0024]
As a representative example of the above-mentioned two non-patent documents, problems of conventional techniques are shown. To summarize, the cryogenic cryostat for biomagnetic measurement has a large amount of evaporation, and there are only two countermeasures: gas recovery / reliquefaction cycle, or a means for generating cold, directly connected to the cryogenic cryostat. Although the former is a problem of equipment, the latter is a problem of noise generated from the refrigerator.
[0025]
However, the root cause is large heat penetration into the cryogenic cryostat. The cryogenic cryostat uses the sensible heat of evaporating helium gas to cool the thermal shield.
[0026]
However, the temperature of the thermal shield of the cryogenic cryostat for biomagnetism measurement is high because of the large amount of intrusion heat, which eventually contributes to the high evaporation amount. Therefore, the first solution to the problem is to lower the temperature of the thermal shield by providing the cryostat with low-noise supply means in the cryostat.
[0027]
However, even if the thermal shield temperature is lowered, once helium gas has evaporated, it will be exhausted, so if the cold is supplied in a cryogenic cryostat and not liquefied again, the cold gas will be exhausted and the amount of evaporation will be greatly increased. Such a reduction cannot be expected. Therefore, the second solution is to reliquefy the liquid without taking it out to an external system such as recirculation.
[0028]
The first object of the present invention is to provide a cooling pipe that does not cause the blockage problem seen in helium circulation and a cryogenic cryostat using the same.
[0029]
A second object of the present invention is to provide a cooling pipe which is not affected by magnetic noise by a small cooling means and a cryogenic cryostat using the same.
[0030]
A third object of the present invention is to provide a cooling pipe capable of reducing helium consumption with a small facility and a cryogenic cryostat using the same.
[0031]
[Means for Solving the Problems]
  The configuration of the present invention for achieving such an object is as follows.
(1) Attached to the upper end of the cylindrical vacuum vesselFreezerAnd placed in the vacuum vesselThe refrigeratorAnd a heat transfer tube having a predetermined length that has one end connected to the cold generator and the other end exposed to the outside from the lower end of the vacuum vessel to form a cold exposed portion.And the cold generator includes a first stage cold generator (high temperature side) and a second stage cold generator (low temperature side) coupled to the refrigerator, and is connected to the first stage cold generator. 1 heat transfer tube is provided, and a heat radiation shield member that is thermally connected to the first heat transfer tube and surrounds the first-stage and second-stage cold-generation portions is provided, and one end of the heat-radiation shield member is disposed on the inside of the heat-radiation shield member. A cooling pipe comprising a second heat transfer tube of a predetermined length connected to a two-stage cold-generating part and having the other end exposed to the outside from the lower end of the vacuum vessel to form a cold-exposed part.
[0033]
(2)Nitrogen is sealed in the first heat transfer tube, and helium is sealed in the second heat transfer tube.Claim 1The described cooling pipe.
[0034]
(3)One end is connected to the first stage cold generation part, and the other end is provided with a third heat transfer pipe extending concentrically around the second heat transfer pipe and extending below the vacuum vessel.Claims 1 to 2The cooling pipe in any one of.
[0035]
(4)The other end of the third heat transfer tube is exposed to the outside in the middle of the vacuum vessel to form a cold exposure portion.Claim 3The described cooling pipe.
[0036]
(5)A strain absorbing member is provided on both sides or one end of the heat transfer tube.Claims 1 to 4The cooling pipe in any one of.
[0037]
(6)The heat transfer tube is configured such that both ends or one end of the heat transfer tube are made of a highly heat conductive material, and the other tube portions are made of a material having low heat conductivity.Claims 1 to 5The cooling pipe in any one of.
[0038]
(7)In the heat transfer tube, a vacuum heat insulating portion is formed around a tube portion made of a material having low thermal conductivity.Claim 6The described cooling pipe.
[0039]
    (Claim 8)
(8)At the upper end of the vacuum vesselThe refrigeratorOne or more units arranged in addition toExpansion refrigeratorAnd thisExpansion refrigeratorAnd an additional cold generating part coupled in the vacuum vessel, and the additional cold generating part is connected to the thermal radiation shield member or the first cold generating part.Claims 1 to 7The cooling pipe in any one of.
[0040]
(9)SaidClaims 1 to 8A cooling pipe according to any one of the above, a vacuum part of a cryogenic cryostat, and the cold discharge part of the cooling pipe is brought into contact with a high temperature part of a thermal radiation shield plate inside the cryogenic cryostat, or a plurality of A cryogenic cryostat characterized in that a cooling pipe having a cold exposure portion is brought into contact with a plurality of temperature shield plates corresponding to the cryogenic cryostat.
[0041]
(10)SaidClaims 1 to 8The cooling pipe according to any one of the above is inserted into the opening of the cryogenic cryostat and is in contact with the isothermal surface generated near the root of the heat radiation shield plate connected in the vacuum layer near the opening of the cryogenic cryostat. A cryogenic cryostat characterized in that the cold exposure portion of the cooling pipe is arranged as described above.
[0042]
(11)SaidClaims 1 to 8Among the plurality of cold exposure portions of the cooling pipe according to any one of the above, the coldest cold exposure portion is positioned so as to be in contact with the cryogenic gas phase portion above the liquid reservoir of the cryogenic cryostat. Cryogenic cryostat.
[0043]
(12)The heat radiation shield plate of the vacuum layer and separate cooling pipes inserted into the upper gas phase of the liquid reservoir are provided.Claims 9 to 11A cryogenic cryostat as described in any of the above.
[0044]
(13)In the cooling pipe or cryogenic cryostat,The refrigeratorA magnetically shielded plate with a high permeability material so as to surround the vibration absorbing material is inserted into the weight holding portion of the cooling pipe.Claims 1 to 12Or a cryogenic cryostat using the same.
[0045]
(14)In the cooling pipe or cryogenic cryostat, from the magnetic shield device with a through holeThe refrigeratorAnd the cooling tube weight holding part is installed with a vibration absorbing material provided outside.Claims 1 to 12Or a cryogenic cryostat using the same.
[0046]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing a basic structure of a cooling pipe to which the present invention is applied.
[0047]
The constitutional feature of the present invention is that a cryogenic refrigerator as a cold generation part and a cold exposure part requiring cold are separated by a vacuum heat insulating container, and a predetermined length of heat radiation shield is provided between them. It is to be connected with a heat transfer tube.
[0048]
For convenience of explanation, the term “cold” means to absorb heat, and is used in the opposite sense to heat divergence and heat flow. Also, the high-pressure gas supply pipe and gas compressor attached to the refrigerator are omitted.
[0049]
In FIG. 1, reference numeral 11 denotes an expander portion of a refrigerator, which is made of a nonmagnetic metal having a low thermal conductivity such as SUS, and is airtightly attached to an upper end portion of a SUS cylindrical vacuum vessel. The vacuum vessel is composed of an upper vacuum vessel 12 to which the refrigerator is coupled and a lower vacuum vessel 17 made of SUS pipe connected and extended to the lower portion thereof.
[0050]
Reference numeral 13 denotes a copper cold generating portion, which is disposed in a hollow portion in the upper vacuum vessel 12. The cold generator 13 is combined with the expander 12 of the refrigerator to form a part of the structure of the refrigerator, and generates an extremely low temperature at this portion.
[0051]
Reference numeral 14 denotes a multilayer heat radiation shield foil that forms a heat radiation shield member. The structure is made of heat radiation shield foil obtained by evaporating a metal with high heat reflection efficiency such as aluminum on a plastic film such as Mylar, etc., and made of multilayers with thin plastic spacers with low thermal conductivity so as not to contact each other. It functions as a high-performance cold insulator that prevents radiant heat transfer from the outside of the foil.
[0052]
Reference numeral 15 denotes a heat transfer tube formed of a heat pipe or the like whose one end is connected to the cold generating part 13. This heat transfer tube is housed in the lower vacuum vessel 17, and the other end is exposed to the outside from the lower end of the lower vacuum vessel 17 to form a cold exposed portion 18 that transmits cold to the outside.
[0053]
The function of the heat transfer tube 15 is to transmit cold to the outside, and may be a copper or aluminum block when the distance is short or the heat transport amount is small. In the case of a heat pipe, the internal sealed gas type is changed according to the temperature of the cold generating part 13, but for example, nitrogen gas is sealed at an appropriate pressure to transmit a nitrogen temperature of 50K to 80K, or the temperature region and the internal A gas that can be in a liquid-gas phase with gas pressure is enclosed.
[0054]
  The thermal radiation shield foil 14The topIt is disposed so as to surround the cold generating part 13 in the vacuum vessel 12 and the heat transfer tube 15 in the lower vacuum vessel 17 and prevents radiant heat transfer from the outside of the foil. Reference numeral 16 denotes a spacer made of resin or the like having a low thermal conductivity, and is inserted for the purpose of preventing the lower vacuum vessel 17 and the heat transfer tube 15 from being short-circuited thermally.
[0055]
Reference numeral 19 denotes a vacuum sealing valve attached to the outer peripheral portion of the upper vacuum vessel 12. This function is used only when the valve is opened by connecting to a vacuuming device when discharging the gas inside, and is normally closed and kept airtight. Reference numeral 20 denotes a sealing plate, which is located at the lower end of the lower vacuum vessel 17 through the heat transfer tube 15 and ensures airtight joining between them.
[0056]
The lower vacuum vessel 17 of the SUS tube is made thinner as it goes to the tip, and the conduction heat transfer from the cold exposure portion 18 toward the upper portion of the lower vacuum vessel 17 is reduced. The sealing plate 20 is thin and has a spring property, and has a spring property that absorbs strain due to a difference in linear expansion due to a temperature difference between the lower vacuum vessel 17 and the heat transfer tube 15 and a temperature difference between the upper and lower portions of the lower vacuum vessel 17. Shall have.
[0057]
When a 1-stage refrigerator such as a GM refrigerator, a Stirling refrigerator, or a pulse tube refrigerator is used as the refrigerator, the copper cold generator 13 of the refrigerator expander 11 generates a cold of about 40 to 80K. Heat exchange with the outside takes place through this part. Since helium gas fluctuates in pressure as the working fluid and the piston moves in the GM refrigerator, the expander 11 of the refrigerator made of SUS generates magnetic noise accompanying vibration.
[0058]
This is because SUS has a weak residual magnetism and forms a magnetic noise field in the surrounding space at the vibration frequency. Also, the inside is filled with SUS mesh and antiferromagnetic material and functions as a cold storage material, but the residual magnetism of this part also contributes.
[0059]
On the other hand, heat is exchanged when high-pressure gas flows to the low-pressure side during cooling, but because there is a temperature difference between the copper and SUS pipes of the cold-generating part that constitutes the refrigerator, a thermocouple is formed and the internal current is Reflux. The internal gas flow pulsates in a pulsed manner, and the temperature also pulsates, so that electromagnetic noise is generated due to the temporal variation of the gas flow.
[0060]
The above magnetic noise is generated centering on the upper vacuum vessel 12 that houses the expander 11 and the cold generator 13 of the refrigerator, but the magnetic noise has a large distance attenuation and is attenuated by the second to the third power of the distance. Therefore, if the cold generating part 13 is extended by another means, it can be used for weak magnetic measurement such as biomagnetic measurement.
[0061]
The heat transfer tube 15 may be formed of a bar having a high thermal conductivity such as copper or aluminum when the amount of heat transport to be transferred is small, but the heat transfer distance d (conveyance distance d) having a predetermined length sufficient for magnetic noise attenuation. If the length of the heat pipe 15 and the interval of 13 to 18) are secured, and if the amount of heat transported is several watts or more, the temperature of the cold exposure part 18 will rise, so a heat pipe enclosing a working fluid inside Use.
[0062]
Heat pipes transport heat when the upper part is cold and the lower part is hot, and the fluid moves up and down while undergoing phase conversion in the gas-liquid phase. The mobility that moves from the lower part to the upper part in the gas phase is particularly high. Therefore, efficient heat transport can be realized.
[0063]
Since the gas phase-liquid phase must be mixed inside in the temperature range to be used, for example, in a refrigerator of around 50K, efficient heat transport can be realized by enclosing nitrogen or the like as a working fluid.
[0064]
At this time, when the temperature is too high, for example during the cooling process, a liquid phase is not formed, and efficient heat transport is not performed. Therefore, a gas having a higher boiling point is sealed or a gas species having a different boiling point is sealed. A plurality of heat pipes may be juxtaposed.
[0065]
A heat transfer tube with a wide temperature range can be realized if the juxtaposed heat pipes are thermally joined inside. On the other hand, cold transport to the cold exposed portion 18 is obstructed from the periphery of the heat transfer tube 15 by heat radiation or heat transfer by gas.
[0066]
For this reason, the surroundings of the cold generating part 13 and the heat transfer tube 15 are hermetically sealed by the upper vacuum container 12 and the lower vacuum container 17 to be thermally insulated by vacuum, and heat intrusion is prevented by the multilayer heat radiation shield foil 14. Furthermore, since the SUS pipe forming the upper and lower vacuum containers has low thermal conductivity, heat penetration due to conduction through the container is reduced. The tip of the SUS pipe is thin to reduce the thermal conductivity.
[0067]
With the above cooling tube structure, it is possible to transmit cold to a distant place. Therefore, if it is brought into thermal contact with a cold-necessary part such as a cryogenic cryostat for biomagnetic measurement, magnetic noise can be prevented and the amount of refrigerant evaporated can be reduced.
[0068]
FIG. 2A is a cross-sectional view showing a configuration of another embodiment in which the configuration of FIG. 1 is expanded, and FIG. 2B is a cross-sectional view taken along the line AA ′ of FIG. The structure which conveys the cold of the 2nd step | paragraph in FIG. 2 (a) and 2 (b), reference numeral 21 denotes a two-stage refrigerator, which includes a first-stage cold generator 24 connected to the lower part as a part thereof, and a second-stage cold generator 25 in the lower part thereof.
[0069]
  26 is a multilayer heat radiation shield foil.1st stageSurrounding the cold generation part 24, the second stage cold generation part 25 and the second heat transfer tube 31 described later,Prevents radiant heat transfer from outside the foil.
[0070]
Reference numeral 31 denotes a second heat transfer tube having a predetermined length. One end of the second heat transfer tube is connected to the second-stage cold-generating unit 25 inside the multilayer heat radiation shield foil 26, and the other end is exposed to the outside from the lower end of the lower vacuum vessel 32. An exposed portion 34 is formed.
[0071]
29 is a 3rd heat exchanger tube, and one end is connected to the 1st stage cold generating part 24 directly or through the below-mentioned thermal radiation shield network 30. The heat radiation shield network 30 extends to the lower part of the lower vacuum vessel 32 by concentrically surrounding the second heat transfer tube 31.
[0072]
In such a two-stage configuration, a low temperature of, for example, 50K is achieved in the first-stage cold generator 24 and an extremely low temperature of 4K is achieved in the second-stage cold generator 25, but two or more stages may be used. In general, since the amount of heat discharged is extremely low at an extremely low temperature of about 4K, the radiation shield must be made stricter than the cold transportation of the single-stage refrigerator shown in FIG.
[0073]
  A heat radiation shield network 30 formed in a concentric cylindrical shape (pipe shape) by braiding and insulating thin wires such as copper is brought into thermal contact with the first stage cold-generation unit 24, and the temperature of the heat radiation shield network 30 is further increased. Thermally shield low spaces. Since the shield network formed of the copper thin wire has low thermal conductivity, the cold transport from the first stage cold generation part 24 does not reach the end of the thermal radiation shield network 30.In order for the first heat transfer tube 27 made of a metal rod such as copper or a heat pipe to transmit cold downwardFor heat radiation shield net 30Connected.
[0074]
  Reference numeral 28 denotes a relay plate, which is a high thermal conductivity structure that transmits the cold of the first stage cold generator 24 to the third heat transfer tube 29 below. This may be metal or ceramic, but may be omitted and the first heat transfer tube 27 and the third heat transfer tube 29 may be integrated.The operating principle of the device does not change depending on the magnitude of each thermal conductivity of the plurality of heat transfer tubes.
[0075]
These outer layer structures 27, 28, and 29 in the vacuum vessel need to be thermally separated from the inner layer structure 31, and are not in contact with each other. A second heat transfer tube 31 is connected to the second stage cold generation part 25, and the cold is discharged at the cold exposure part 34 at the lower end.
[0076]
  The third heat transfer tube 29 is connected to the heat radiation shield network 30. Since the radiant heat shield net 30 made of a thin copper wire has low heat conduction, the third heat transfer pipe 29 is connected to the heat radiant shield net 30 in the same manner as the first heat transfer pipe 27, thereby connecting the second heat transfer pipe 31 inside. The radiant heat about to penetrate is efficiently transported to the first stage cold generating unit 24.
[0077]
The internal working fluid of the second heat transfer tube 31 connected to the second stage cold generator 25 is filled with a substance that generates a liquid-gas phase state at a very low temperature such as helium or hydrogen depending on the temperature. To do.
[0078]
Thus, since the heat radiation shield network 30 is connected to the first stage cold generator 24 of the two-stage refrigerator via the heat radiation shield network and the second heat transfer pipe 29 at the lower part, it is efficient. In addition, the temperature of the heat radiation shield net 30 is lowered.
[0079]
For this reason, heat intrusion into the internal space from the heat radiation shield network 30 can be suppressed, the temperature rise of the cryogenic part with a small heat discharge amount can be prevented, and the heat connected to the second stage cold generating part 25 For example, 4K of cold can be generated from the cold exposure portion 34 of the second heat transfer tube 31 such as a pipe.
[0080]
In a multistage refrigerator having two or more stages, a shield structure such as 30 heat radiation shield nets may be multilayered to further prevent heat intrusion. In addition, here, two heat transport units connected to each cold generating unit in the two-stage refrigerator are two systems, but a plurality of heat shield structures may be provided for each cold generating unit.
[0081]
The same applies to FIG. For example, in FIG. 1, a heat shield network (which has a small amount of heat transfer) that does not include a heat transfer tube is connected to one cold generator 13 to reduce the thermal conductivity, and this is provided separately for heat shield. Loss on the way is reduced by adopting a structure that transports in the cold with heat transfer tubes.
[0082]
  FIG. 3 shows a heat transfer tube 37 and a heat radiation shield network in the cold generator 36 coupled to the expander 35 in the case of the single-stage refrigerator described in FIG.38Is a simplified cross-sectional view showing a configuration of an embodiment in which the two are directly connected, and a vacuum vessel and a multilayer heat radiation shield foil are omitted.
[0083]
In this embodiment, there is a feature in the configuration of the radiant heat shield net, and a net-like metal such as copper, which has a relatively low thermal conductivity compared to a heat transfer tube such as a heat pipe, is connected to the cold generating part. The heat shield can be configured without taking excessive heat load, and heat intrusion into the heat transfer tube can be reduced.
[0084]
In the embodiment shown in FIG. 4 (a), the heat shield of the cryogenic cold transmission section from the second stage cold generation section in the two-stage refrigerator is not the heat shield by the heat radiation shield network but the first stage cold generation. This is realized by a hollow cylindrical heat pipe connected to the section, and this heat pipe combines cold conduction and heat shield.
[0085]
A first heat transfer pipe 42 is connected to the first stage cold generating section 40, and 43 heat radiation shield nets 43 are attached so as to be in contact with and surround the first heat transfer pipe 40. Shielded by cold. The heat radiation shield network 43 may be a cylindrical metal plate such as copper.
[0086]
  FIG. 4B is a cross-sectional view taken along the line AA ′ of FIG. 4A, and the second heat transfer tube 44 connected to the second stage cold generation part 41 surrounds the second heat transfer tube 44 made of a hollow cylindrical heat pipe. 3 Heat transfer tube 46 is thermally connected to relay plate 45DenselyIt touches. The heat pipe structure of the third heat transfer tube 46 includes a gas sealing portion 50 surrounded by an inner tube 49 and an outer tube 48 as shown in the cross-sectional view of FIG. 4C, and a gas such as nitrogen is sealed inside. ing.
[0087]
With such a configuration, since the volume of the gas sealing part 50 can be increased by the third heat transfer tube 46, the flow rate of the working gas can be increased and the cold transport amount can be increased. Since the amount of heat inflow due to radiation from the outside is proportional to the square of the length of the pipe, it is effective when the transport pipe length is long.
[0088]
If the heat transfer rate is slow, the temperature of the shield rises toward the end, and as a result, the temperature of the cold exposed portion 47 rises. This is effective in preventing this. In addition, structural stability and rigidity are increased compared to meshes and the like, which has the advantage of preventing accidents such as thermal shorts.
[0089]
5A and 5B show the heat transfer tube 15 shown in FIG. 1, the second heat transfer tube 31 shown in FIG. 2, the heat transfer tube 37 shown in FIG. 3, and the second heat transfer tube 44 shown in FIG. It is sectional drawing which shows the specific example of a structure.
In FIG. 5A, the end portion is not a uniform hollow pipe but a different material. The heat transfer tube 51 is a thin hollow pipe made of SUS with low thermal conductivity, and both ends are sealed with metal caps 52a and 52b made of copper or the like with high thermal conductivity. Etc. are sealed at an appropriate pressure.
[0090]
FIG. 5B shows an example in which the heat transfer tube 54 has a double structure of a thin hollow pipe made of SUS, and a vacuum heat insulating portion 57 is formed around the heat transfer tube. Both ends are sealed with metal caps 56a and 56b made of copper or the like having high thermal conductivity, and a gas such as nitrogen or helium is sealed in the internal gas sealing portion 55 with an appropriate pressure.
[0091]
In this case, the gas may be sealed with a high heat conductivity tube such as a copper tube as the heat transfer tube, but by configuring the long part with a material with low heat conductivity such as a SUS tube, the heat radiation shield foil or the like When the contact occurs, there is an effect of reducing conduction heat intrusion and preventing a reverse flow of cold when the refrigerator is turned off.
[0092]
Heat pipes are generally transported by heat or cold under conditions where the upper part is at a low temperature and the lower part is at a high temperature. However, when the operation of the refrigerator is stopped, the upper part becomes hot and the movement of the working fluid in the heat pipe stops. .
[0093]
However, the heat transfer through the tube wall of the heat transfer tube (not the internal working fluid) is irrelevant in direction, so the coldness at the bottom will rise. As shown in FIG. 5A, a material having a low thermal conductivity such as SUS is effective as the heat transfer tube 51 in order to reduce the conduction heat transfer.
[0094]
When the internal fluid is nitrogen or the like, resin or the like is also possible. On the other hand, in order to absorb and dissipate cold at the upper and lower ends, it is necessary to increase the mobility of heat conduction, and it is effective to seal the copper caps 52a and 52b having high thermal conductivity such as copper.
[0095]
In FIG. 5B, the vacuum heat insulating portion 57 is provided in the SUS tube portion of the heat transfer tube 54, so that it is possible to improve the lateral conduction heat penetration reduction performance, and at the same time, the rigidity by the double structure can be increased. .
[0096]
The same effect can be obtained in reducing the thermal conductivity even if the vacuum heat insulating portion 57 is replaced with glass, resin, heat insulating foam, or a metal spacer having low thermal conductivity. Thus, according to the configuration of FIG. 5, it is possible to reduce a loss due to heat entering from the middle of the conduction path.
[0097]
The example of FIG. 6 shows another embodiment of the cooling pipe, and is a view for explaining the means for connecting the heat transfer pipe by the leaf spring together with vibration insulation and electrical insulation. FIG. 6 (a) illustrates the thermoelectromotive force generated in the cooling pipe placed at a cryogenic temperature. The lower part is at a very low temperature and the upper part is at room temperature.
[0098]
The upper vacuum vessel to which the expander 60 of the refrigerator is attached is SUS, the lower vacuum vessel 58 is also SUS, the cold generation part 59 and the cold exposure part 57 are made of copper, and the electromotive force generation point 61 of the cold exposure part 57 is The thermoelectromotive force generation point 62 of the cold generation part 59 is substantially the same temperature.
[0099]
In addition, since different metals are connected in directions that generate electromotive forces in opposite directions, in principle, they should cancel each other and no internal current should be generated. However, since each structural material is not made of the same material, the unbalanced current 63 flows from the upper part to the lower part along the path indicated by the arrow. Since this is emitted as a magnetic field to the outside, it becomes electromagnetic noise.
[0100]
FIG. 6B shows a structure in which an insulating material such as insulating resin or insulating rubber is provided in the middle of the electrical path for electrical insulation. 64a is an insulating material provided at the connecting portion between the expander 60 of the refrigerator and the upper vacuum vessel, 64b is an insulating material provided at the connecting portion between the upper vacuum vessel and the lower vacuum vessel 58, and 64c is provided at the cold exposure portion 57. It is an insulating material. The insulating material may be provided somewhere, or a plurality of these different insertion positions may be used in combination.
[0101]
FIG. 6C shows another configuration of electrical insulation, in which a flange portion is formed in the middle of the lower vacuum vessel 58 and an insulating material (for example, rubber) 64d is sandwiched therebetween.
[0102]
As described above, according to the configuration of FIG. 6, since the current path of the circulating current is cut off by the insulating material made of the insulating resin or the insulating rubber, no temporal noise due to the thermoelectromotive force is generated outside.
[0103]
Further, by providing a leaf spring 65 inside or providing an elastic insulating material 64 such as rubber, a spring property can be provided between the internal structure and the external structure. It is also possible to prevent breakage during cooling due to the difference in the linear expansion coefficient.
[0104]
FIG. 7 is a cross-sectional view showing a configuration of another embodiment for providing a plurality of cold exposure portions in a cooling pipe. In this configuration, the cold is released to the outside from the cold exposure portion 67 formed of a high conductivity material such as copper while being in thermal contact with the third heat transfer tube 66 described in FIG. On the other hand, the cold at a lower temperature is led out from the cold exposure portion 68 of the second heat transfer tube.
[0105]
If the structure of FIG. 7 is spread, since the cold output of different temperature is possible with a some heat exchanger tube, the cold utilization method of a cryostat spreads. For example, as will be described later with reference to FIGS. 9 and 10, the cold exposure portion 67 on the high temperature side is supplied to the radiation shield, and the cold exposure portion 68 on the low temperature side is connected to the radiation shield at a lower temperature, or the gas phase temperature in the cryostat is changed. It can be used for liquefaction or the like when exposed to cooling or gas phase.
[0106]
FIG. 8 is a cross-sectional view showing a configuration of an embodiment in which two refrigerators serving as cold supply means are connected. In this configuration, the expander 70 of the first-stage refrigerator is installed on the expanded upper vacuum vessel 71 along with the expander 69 of the two-stage refrigerator. Reference numeral 72 denotes a vacuum sealing valve. The configuration on the two-stage refrigerator side is the same as that in FIG. 2, and includes a first-stage cold generator 73, a second-stage cold generator 74, a third heat transfer tube 75, a cold exposure section 76, and a heat radiation shield net 78.
[0107]
Reference numeral 79 denotes a cold generator that is coupled to the expander 70 of the first-stage refrigerator, and is thermally coupled to the third heat transfer tube 75 via the first heat transfer tube 80 and the relay plate 81. The relay plate 81 is made of a highly heat conductive material, and may be a metal such as copper or a heat pipe.
[0108]
A cold exposure part similar to the cold exposure part 67 shown in FIG. 7 may be formed in the vicinity of the lower end of the third heat transfer pipe 75 connected to the first heat transfer pipe 80 so that the cold is taken out to the outside. A multilayer heat radiation shield foil 82 is disposed so as to surround the cold generating portion 79.
[0109]
In the configuration of FIG. 7, since the heat load of the first stage cold generator is used for the heat shield and external cold supply, when the heat load is larger than the cold generation capacity, the temperature of the second cold generator increases. There is a problem.
[0110]
In the embodiment structure of FIG. 8, the third heat transfer tube 75 is not connected to the first stage cold generator 73 but is connected to the cold generator 79, so that the first stage cold generator 73 of the two-stage refrigerator is used. A large heat load is reduced, and the temperature of the second stage cold generation part 74 does not rise.
[0111]
On the other hand, when the cold is supplied to the outside other than the heat shield or the cold exposure unit 76, the cold supply source is the cold generation unit 79, and thus does not affect the cold generation unit 73 of the two-stage refrigerator. A sufficient cooling function can be achieved. In this embodiment, a configuration is shown in which two refrigerators with different numbers of stages are shown. However, two refrigerators with the same number of stages may be used, and if this configuration is used, two or more refrigerators can be added. It is.
[0112]
FIG. 9 is a cross-sectional configuration diagram showing an embodiment of a cryogenic cryostat to which the cooling pipe of the present invention described in FIGS. 1 to 8 is connected, and also shows a drive unit of the refrigerator. Gas is switched and supplied to the expander 86 of the refrigerator via a gas pipe 100 by a valve motor 89 via a high-pressure side pipe 91 and a low-pressure side pipe 92 of the compressor 90. The upper vacuum vessel 87 is fixedly installed on the upper part of the magnetic shield room 83 via a vibration isolation pedestal 88.
[0113]
The lower vacuum vessel 93 is attached through the wall of the magnetic shield room 83 and further through the heat insulating foam 94 at the neck portion of the cryogenic cryostat 84 in the magnetic shield room. The upper cold exposed portion 95 is in thermal contact with an isothermal surface formed near the upper or lower portion of the thermal anchor 98.
[0114]
The lower cold generating part 96 is coupled to a cold diverging part 97 exposed in a liquid reservoir gas phase part having liquid helium 83 at the bottom. The cold divergence portion 97 is formed of a member that easily radiates cold such as a copper mesh.
[0115]
In this embodiment, a method of exposing the cold in the gas phase portion of the cryogenic cryostat has been described. However, the structure for connecting the cold to the thermal anchor 88 may be one place or a plurality of places. Alternatively, the upper cold exposure portion 95 may not be provided, and only the lower cold exposure portion 96 may be configured.
[0116]
Furthermore, in this embodiment, the cold can be transmitted to the heat radiation shield network 99 by providing the upper cold exposure portion 95 in the vicinity of the thermal anchor 98. For this reason, the transmission of radiant heat to the liquid tank in which the liquid helium 85 is accumulated decreases, and the amount of helium evaporation decreases. Moreover, since it cools in the cold divergence part 97, since the temperature of the gaseous-phase part of a liquid tank upper part falls, an evaporation rate falls.
[0117]
When the cold divergence portion 97 is sufficiently cooled, liquefaction starts in the liquid reservoir gas phase portion of the cryostat, so that the evaporation amount can be further reduced. On the other hand, since the expander 86 of the refrigerator is provided outside the magnetic shield room 83, acoustic vibration and magnetic noise do not adversely affect the inside of the magnetic shield room 83. Moreover, since it is installed on the anti-vibration base 88, the influence of the propagation of vibration into the magnetic shield room 83 is not great.
[0118]
FIG. 10 is a cross-sectional configuration diagram showing still another embodiment of a cryogenic cryostat using the cooling pipe of the present invention.
The embodiment shown in FIG. 10 is a configuration example in which an expander 86 of a refrigerator is surrounded by a magnetic shield box 103 containing a sound and vibration isolator 102 and installed in a magnetic shield room 83. Here, the lower vacuum vessel 93 may be inserted into the neck portion of the cryogenic cryostat 84 as shown in FIG. 9, but a configuration example connected to the vacuum layer is shown.
[0119]
That is, the cold exposed portion 101 at the lower part of the lower vacuum vessel 93 is connected by the vacuum layer of the upper thermal anchor 98 and has a structure for efficiently transmitting the cold to the heat radiation shield net 99.
[0120]
In this embodiment, since it is directly connected to the upper thermal anchor 98 in the vacuum layer, the thermal resistance is low and the efficiency is high compared to cold transport via the gas phase or cryostat structure material. Therefore, it is possible to lower the shield temperature and to reduce the amount of helium evaporation. Although an example of connection to the upper thermal anchor is shown here, the same effect can be obtained even if it is connected to the lower thermal anchor.
[0121]
Moreover, even if two cold exposed parts with different temperatures in a two-stage refrigerator or the like are connected to two thermal anchors with different temperatures, the shield temperature can be lowered, further reducing the amount of helium evaporation. be able to. On the other hand, since the magnetic shield box 103 is used for connection in the magnetic shield room 83, the length of the lower vacuum vessel 93 can be shortened.
[0122]
Generally, since heat penetration increases in proportion to the square of the length of the heat transfer tube, less heat needs to be discharged from the refrigerator, and the temperature of the cold generating portion decreases. As a result, it is effective in reducing the amount of helium evaporation.
[0123]
In order to reduce the amount of cryogen cryogenic evaporation of the cryogenic cryostat of the SQUID magnetometer for biomagnetic measurement, the present invention provides a means for oscillating and re-liquefying the auxiliary cooling and cryogenic cryostat with a relatively weak heat shield. It was made for the purpose of providing without the influence of magnetic noise. However, it is clear that it is useful for other applications that want to avoid the effects of vibration and refrigerator noise, and the following development is expected.
[0124]
FIG. 11 is a configuration diagram showing an example in which the cooling pipe of the present invention is applied to a superconducting magnet for MRI, and is shown in a simplified manner. Reference numeral 201 denotes an outer shell that houses a magnet and supports the whole, and is made of a nonmagnetic material.
[0125]
The superconducting magnet 202 is wound around a gap in the outer shell, and the gap is filled with liquid helium. The surroundings are surrounded by a vacuum heat insulating layer 200. The heat insulating shield 204 is built in the vacuum heat insulating layer 200 to prevent heat from entering the superconducting magnet from the outside. 205 is a penetration part.
[0126]
When radiation shielding is performed with liquid nitrogen, a multi-layer structure is provided in which a vacuum layer is provided outside the superconducting magnet 202 filled with liquid helium and a liquid nitrogen tank is further provided outside. Reference numeral 203 denotes a cooling pipe of the present invention, which is connected to the heat radiation shield 204, but may be connected to a liquid nitrogen tank. Further, when connecting a cooling pipe having two or more cold exposure parts, each may be connected to a plurality of heat radiation shields or one may be exposed to the liquid helium tank.
[0127]
According to such a configuration, since the cooling pipe 203 can keep a distance from the magnet body, it is possible to take a soundproofing measure for the noise generating unit. In addition to preventing noise associated with pressure vibrations of the refrigerator, the amount of evaporation can be reduced regardless of the model by inserting a cooling pipe into the helium inlet for magnets that are not connected to existing refrigerators. There is an advantage of being able to plan.
[0128]
Furthermore, even in a device using liquid nitrogen as a shield, it is effective for reducing the amount of evaporation, as in the biomagnetic measurement cryostat.
[0129]
FIG. 12 is a connection diagram showing an application example of the cooling pipe of the present invention to an electron beam exposure apparatus as an application example to a general vacuum apparatus, and is an example used as a cryopump for obtaining a high vacuum. .
[0130]
206 is an anti-vibration table for blocking ambient vibrations, 207 is a stepper for moving a point to be exposed, 208 is an electron beam column, and an electron beam generation source for applying an electron beam to a target is built in. The inside is hollow and in a vacuum state.
[0131]
  Reference numeral 209 denotes a vacuuming pipe for maintaining a vacuum inside the electron beam column. The cold exposure part 210 of the cooling pipe 211 of the present invention is in contact with the cooling part.Yes. 212Is a shielded box that has a built-in refrigerator and shields the magnetic noise of the refrigerator from leaking outside.
[0132]
An electron beam column such as an electron microscope or an electron beam exposure apparatus requires a high vacuum, but at the same time it is extremely reluctant to vibration and magnetic noise. These use the effect of enlarging and reducing the image by taking advantage of the straightness of electrons flying in a vacuum, but magnetic noise and vibration of the equipment cause image blurring, which significantly impairs performance. .
[0133]
Cryogenic refrigerators are often used in high vacuum equipment for semiconductors as cryopumps for freezing and adsorbing gas molecules, but the structure that can be connected at a distance by the cooling pipe of the present invention is effective in reducing the distance of magnetic noise and absorbing vibration. This is advantageous in terms of vibration isolation.
[0134]
【The invention's effect】
As is clear from the above description, the following effects can be expected according to the present invention.
(1) It is possible to easily realize a cooling pipe and a cryogenic cryostat using the same without causing the blockage problem seen in the helium circulation.
(2) A cooling pipe that is not affected by magnetic noise and a cryogenic cryostat using the same can be easily realized by a small cooling means.
(3) A cooling pipe capable of reducing the consumption of helium with a small facility and a cryogenic cryostat using the same can be easily realized.
[0135]
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram showing a basic configuration of a cooling pipe to which the present invention is applied.
FIG. 2 is a cross-sectional configuration diagram showing another embodiment of the present invention.
FIG. 3 is a cross-sectional configuration diagram of a main part showing still another embodiment of the present invention.
FIG. 4 is a cross-sectional configuration diagram of a main part showing still another embodiment of the present invention.
FIG. 5 is a cross-sectional configuration diagram showing a configuration example of a heat transfer tube of the present invention.
FIG. 6 is a cross-sectional configuration diagram of a main part showing still another embodiment of the present invention.
FIG. 7 is a cross-sectional configuration diagram showing still another embodiment of the present invention.
FIG. 8 is a cross-sectional configuration diagram showing still another embodiment of the present invention.
FIG. 9 is a cross-sectional configuration diagram showing an embodiment of a cryogenic cryostat using the cooling pipe of the present invention.
FIG. 10 is a cross-sectional configuration diagram showing still another embodiment of a cryogenic cryostat using the cooling pipe of the present invention.
FIG. 11 is a connection diagram showing an application example of the cooling pipe of the present invention to an MRI superconducting magnet.
FIG. 12 is a connection diagram showing an application example of the cooling pipe of the present invention to an electron beam exposure apparatus.
FIG. 13 is a configuration diagram of a helium circulation system showing the prior art described in Non-Patent Document 1.
FIG. 14 is a cryostat connection configuration diagram of a cryogenic refrigerator showing a conventional technique described in Non-Patent Document 2.
[Explanation of symbols]
11 Expander
12 Upper vacuum vessel
13 Cold generation part
14 Multilayer thermal radiation shield foil
15 Heat transfer tube
16 Spacer
17 Lower vacuum container
18 Cold exposure area
19 Vacuum sealing valve
20 Sealing plate

Claims (14)

A refrigerator attached to the upper end of the cylindrical vacuum vessel, a cold generator of the refrigerator arranged in the vacuum vessel, one end connected to the cold generator, and the other end of the vacuum vessel A heat transfer tube having a predetermined length that is exposed to the outside and forms a cold exposure portion , wherein the cold generation portion is a first-stage cold generation portion (high temperature side) and a second-stage cold generation portion that are coupled to the refrigerator. A first heat transfer tube connected to the first stage cold generation part, and thermally connected to the first heat transfer pipe and surrounding the first stage and second stage cold generation part. A heat radiation shield member is provided, and one end of the heat radiation shield member is connected to the second stage cold generating portion, and the other end is exposed to the outside from the lower end of the vacuum vessel to form a cold exposed portion. A cooling pipe provided with the second heat transfer pipe. The cooling pipe according to claim 1, wherein nitrogen is contained in the first heat transfer pipe and helium is enclosed in the second heat transfer pipe. The third heat transfer pipe is provided with one end connected to the first stage cold generation part and the other end concentrically surrounding the second heat transfer pipe and extending to the lower part of the vacuum vessel. The cooling pipe according to any one of 1 to 2. 4. The cooling pipe according to claim 3, wherein the other end of the third heat transfer pipe is exposed to the outside in the middle of the vacuum vessel to form a cold exposure portion. The cooling pipe according to any one of claims 1 to 4, wherein a strain absorbing member is provided at both ends or one end of the heat transfer pipe. 6. The cooling pipe according to claim 1, wherein both ends or one end of the heat transfer pipe are made of a high heat conductive material, and the other pipe parts are made of a material having low heat conductivity. . The cooling pipe according to claim 6, wherein a vacuum heat insulating part is formed around the pipe part made of a material having low thermal conductivity in the heat transfer pipe. One or more additional refrigerators arranged in addition to the refrigerator at the upper end of the vacuum vessel, and an additional cold generator connected to the additional refrigerator in the vacuum vessel, the additional cold The cooling pipe according to any one of claims 1 to 7, wherein the generator is connected to the thermal radiation shield member or the first cold generator. The cooling pipe according to any one of claims 1 to 8 is connected to a vacuum part of a cryogenic cryostat, and the cold discharge part of the cooling pipe is connected to a high-temperature part of a heat radiation shield plate inside the cryogenic cryostat. A cryogenic cryostat characterized in that it is brought into contact with or in contact with a heat shield plate at a plurality of temperatures corresponding to a cryogenic cryostat in a cooling pipe having a plurality of cold exposure portions. The cooling pipe according to any one of claims 1 to 8 is inserted into an opening of a cryogenic cryostat, and near a base of a heat radiation shield plate connected in a vacuum layer near the opening of the cryogenic cryostat. A cryogenic cryostat characterized in that a cold exposure portion of the cooling pipe is disposed so as to be in contact with a generated isothermal surface. The coldest exposed portion of the coldest tube of the cooling pipe according to any one of claims 1 to 8 is positioned so as to be in contact with a cryogenic gas phase portion at an upper portion of a liquid reservoir of a cryogenic cryostat. A cryogenic cryostat characterized by that. The cryogenic cryostat according to any one of claims 9 to 11, further comprising separate cooling pipes respectively inserted into the heat radiation shield plate of the vacuum layer and the upper vapor phase of the liquid reservoir. 2. The cooling pipe or the cryogenic cryostat, wherein a magnetic shield is provided with a plate of a high magnetic permeability material so as to surround the refrigerator, and a vibration absorbing material is inserted into a weight holding portion of the cooling pipe. The cooling pipe according to any one of 1 to 12 or a cryogenic cryostat using the same. In the cooling pipe or the cryogenic cryostat, the refrigerator is taken out from a magnetic shield device having a through hole, and the cooling pipe is installed with a vibration-absorbing material provided with a weight holding part on the outside. The cooling pipe according to any one of claims 1 to 12, or a cryogenic cryostat using the cooling pipe.

Images