JP4360037B2 - Cryostat - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, as a nondestructive biopsy system, cools and holds, for example, a measurement sensor used in a SQUID (Superconducting Quantum Interference Device) magnetic flux measurement system that measures biomagnetism such as the brain using the Josephson effect at cryogenic temperatures. It is related to the cryostat.
[0002]
[Prior art]
FIG. 2 is a longitudinal sectional view showing a configuration of a conventional cryostat. In FIG. 2 , the main body of the cryostat 1 is formed of an inner tank 2 and an outer tank 3, which are made of, for example, glass fiber reinforced plastics (hereinafter referred to as GFRP).
[0003]
The inner tub 2 includes a bottomed cylindrical main body 2a and a cylindrical neck portion 2b formed on the upper portion of the main body 2a with a diameter smaller than that of the main body 2a. The bottom of the main body 2a Is formed in an arc shape so as to fit the human head.
[0004]
A biopsy sensor (SQUID sensor array) 4 is inserted into the main body 2a of the inner tub 2 from the neck 2b and installed at the bottom of the arc shape. For example, liquid helium is used as a coolant for cooling the sensor 4. The main body 2a is filled from the neck 2b, and a heat insulating material 5 is provided inside the neck 2b.
[0005]
The outer tub 3 is disposed so as to surround the inner tub 2, and a vacuum layer 6 is formed between the inner wall of the outer tub 3 and the outer wall of the inner tub 2.
Further, a vacuum suction port 3a communicating with the vacuum layer 6 is formed on the side surface of the outer tub 3, and the bottom of the outer tub 3 is formed so as to surround the arc-shaped bottom of the inner tub 2. A measuring unit 3b is formed.
[0006]
Then, on the side surface of the neck portion 2b, for example, a doughnut-shaped first thermal anchor 7a for high temperature and a first thermal anchor 7b for low temperature made of copper, for example, are sequentially connected to the lower side of the inner tank 2 to form the vacuum layer 6 Is placed inside.
These thermal anchors 7a and 7b are heat reservoirs made of, for example, copper and having high thermal conductivity and high heat capacity.
[0007]
The thermal anchors 7a and 7b are connected to thermal shields 8a and 8b, for example, each made of a mesh made of copper and shielding radiant heat from the outside so as to be able to conduct heat to each other. It arrange | positions in the vacuum layer 6 so that the inner tank 2 may be surrounded sequentially as an outer side.
[0008]
In this case, the thermal shield 8b connected to the low-temperature thermal anchor 7b is formed in an arc shape suitable for the human head in the vacuum layer 6 near the arc-shaped bottom of the inner tank 2.
[0009]
Next, the thermal shield effect for preventing heat from entering from the outside in the cryostat shown in FIG. 2 will be described. The liquid helium in the inner tank 2 evaporates little by little by intrusion heat due to radiation and conduction from the outside, and the evaporated helium rises through the gap between the neck portion 2b and the heat insulating material 5, and at that time, the neck portion 2b is cooled, Gas absorbs heat and heat exchange takes place.
[0010]
Then, by cooling the two-stage thermal anchors 7a and 7b, the two-stage thermal shields 8a and 8b are similarly cooled to absorb the radiant heat entering from the outside of the outer tank 3. Thus, heat is prevented from being transmitted to the inner tank 2 and this is called a thermal shield.
[0011]
The high temperature thermal shield 8a has a relatively high temperature of, for example, 100 to 180K, and the low temperature thermal shield 8b has a low setting of 20 to 50K. Between the thermal shields 8a and 8b, the inner tank 2 and the outer tank. The gap between the wall and the wall 3 is built by sandwiching a large number of film-like thin films (not shown) called aluminum, which are vapor-deposited aluminum so as not to contact each other, and by implementing multiple heat shields, heat generated by radiation The intrusion is extremely low.
[0012]
[Problems to be solved by the invention]
However, such a cryostat has the following problems.
In a biomagnetism measuring device represented by a magnetoencephalograph, in order to measure a very weak signal, it is formed between the width of the vacuum layer 6 in the vicinity of the magnetoencephalogram measuring unit 3b (between the bottom of the inner tank 2 and the bottom of the outer tank 3). The width of the vacuum layer 6) is extremely thin, such as several mm.
For this reason, the thermal shield and the super insulator cannot be structurally sufficiently provided in the vacuum layer 6 in the vicinity of the magnetoencephalogram measuring unit 3b (in the vicinity of the bottom of the inner tank 2 and the bottom of the outer tank 3).
For example, the thermal shield 8a or the thermal shield 8b is omitted in the vacuum layer 6 in the vicinity of the magnetoencephalogram measurement unit 3b (the thermal shield 8a is omitted in FIG. 2), or the number of superinsulators is reduced to a fraction. Can only be inserted to the extent.
[0013]
Therefore, normally, the heat intrusion from the magnetoencephalogram measurement unit 3b is extremely large, a large temperature distribution is generated in the thermal shield 8b (the temperature becomes nonuniform), and the vicinity of the magnetoencephalogram measurement unit 3b is near the neck portion 2b even at a low temperature. Not only does the temperature of the thermal shield 8b rise, it also raises the heat intrusion of the entire cryostat 1 and increases the amount of refrigerant evaporated.
[0014]
Further, although the thermal shield 8b is made of a copper mesh, if the cross-sectional area is increased in order to ensure sufficient heat transfer, thermal noise increases and adversely affects measurement by the sensor 4.
Therefore, the thermal shield 8b cannot be provided with sufficient heat transfer capability, which also causes an increase in the evaporation amount of the refrigerant.
[0015]
The present invention has been made to solve the above-described problems, and is a thermal shield in the vicinity of the magnetoencephalogram measurement unit 3b (in the vicinity of the bottom of the inner tank 2 and the bottom of the outer tank 3) which is a large heat intrusion source. An object of the present invention is to realize a cryostat capable of efficiently cooling the copper mesh without increasing the cross-sectional area of the copper mesh and reducing the evaporation amount of the refrigerant.
[0016]
[Means for Solving the Problems]
In claim 1 of the present invention, a magnetoencephalogram measurement sensor for biopsy is installed inside, and a main body portion filled with a coolant for cooling the magnetoencephalogram measurement sensor, and a cylindrical shape connected to the main body portion. An inner tub having a neck portion, an outer tub disposed so as to surround the inner tub and forming a vacuum layer between the outer walls of the inner tub, and connected to the neck portion and disposed in the vacuum layer In a cryostat having a first thermal anchor and a thermal shield connected to the first thermal anchor and disposed in the vacuum layer,
The inner tank and the outer tank are cylindrical with a bottom, and the magnetoencephalographic sensor is installed at the bottom of the inner tank, and is connected to the thermal shield in the vacuum layer in the vicinity of the bottom. And a heat transport means connected to the first thermal anchor and the second thermal anchor .
[0017]
According to a second aspect of the present invention, in the cryostat according to the first aspect, the heat transporting means is a heat pipe.
[0018]
According to a third aspect of the present invention, in the cryostat according to the first aspect, the sensible heat of the gas evaporated from the refrigerant is heat-exchanged, and the first thermal is provided through the neck portion. A cryostat characterized by providing a soaking unit for exchanging heat with an anchor .
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
In addition, in the following drawings, the same part as FIG. 2 is attached with the same number, and the description is omitted as appropriate.
FIG. 1 is a longitudinal sectional view showing a configuration of a cryostat according to the present invention.
[0021]
In FIG. 1, 9 is a heat pipe as a heat transport means connected to the thermal anchor 7b and the thermal shield 8b. This heat pipe 9 is a liquid (nitrogen, hydrogen, argon, krypton, Heat is transported by absorbing heat from one end by evaporation of methane or the like and releasing heat from the other end by condensation of steam.
[0022]
Reference numeral 10 is provided so as to surround the inner tank 2 in the vacuum layer 6 in the vicinity of the bottom of the inner tank 2 and the outer tank 3 (near the magnetoencephalogram measuring unit 3b), and temporarily radiates heat from the outside near the bottom. It is a second thermal anchor for storing heat and improving the efficiency of heat transport by the heat pipe 9, and a thermal shield 8b in the vicinity of the bottom of the heat pipe 9, the inner tank 2 and the outer tank 3 (near the magnetoencephalogram measuring section 3b). And connected to.
[0023]
Reference numeral 11a denotes a heat equalizing means provided on the inner wall of the neck portion 2b, and 11b denotes a heat equalizing means provided around the heat insulating material 5 inside the neck portion 2b.
The soaking means 11b is connected to a disk-shaped radiation shield 12 made of a metal having high reflectivity such as aluminum or copper provided inside the heat insulating material 5.
[0024]
These soaking means 11a and 11b are provided to increase the effective area of heat exchange inside the neck portion 2b and to increase the ability to absorb heat flowing in from the outside, such as copper / aluminum having high thermal conductivity. These are made of a highly metal resin material or the like impregnated with a cylindrical metal band or net-like band, or a needle-shaped metal filler.
[0025]
Reference numeral 2c denotes a detour portion provided between the main body portion 2a and the neck portion 2b of the inner tank 2 in order to lengthen the heat conduction path of the neck portion 2b, and is formed with a diameter larger than the diameter of the neck portion 2b. Has been.
[0026]
Next, the operation of the cryostat shown in FIG. 1 will be described.
The heat that has entered from the outside near the bottom of the inner tub 2 and the outer tub 3 (near the magnetoencephalogram measuring unit 3b) is transferred to the second thermal anchor 10 from the thermal shield 8b and is stored, and a temperature gradient is formed. The heat pipe 9 heat transports to the first thermal anchor 7b at a high speed, the thermal shield 8b is cooled at a high speed, and the amount of heat entering the inner tank 2 is reduced, so that the amount of refrigerant evaporated is reduced.
[0027]
Further, the thermal shield 8b is separated into a part surrounding the side surface of the inner tank 2 and a part surrounding the bottom part of the inner tank 2 (near the magnetoencephalogram measuring unit 3b), and the heat pipe 9 is connected to the bottom part of the inner tank 2 (the magnetoencephalogram). It is possible to connect only to the part surrounding the measuring part 3b) and not to connect to the part surrounding the side surface of the inner tub 2. In this case, more efficiently (preferentially) through a large heat intrusion route The thermal shield 8b in the vicinity of a certain magnetoencephalogram measurement unit 3b can be cooled.
[0028]
The soaking zones 11a and 11b exchange heat (cooling) the sensible heat in the evaporated helium gas inside the neck portion 2b, cool the radiation shield 12 and absorb the radiant heat from the top of the neck portion 2b, Further, heat exchange is performed with the thermal anchor 7b via the neck portion 2b.
Further, since the temperature of the outflow gas has the property of maintaining the horizontal direction in the direction of gravity, the soaking zone 11a, 11b has the effect of increasing the effective contact area of the gas heat exchange section.
[0029]
And the detour part 2c detours the heat | fever which penetrate | invades into the inside of the inner tank 2 by heat conduction from the neck part 2b by taking long heat conduction path length, and reduces intrusion heat.
This detour portion 2c is effective particularly when the distance from the upper portion of the neck portion 2b cannot be obtained in order to reduce the size of the entire cryostat 1.
Further, a groove may be provided on the inner wall of the neck portion 2b in an oblique spiral shape to increase the surface area.
[0030]
In FIG. 1, the heat pipe 9 is connected only to the thermal anchor 7b and the thermal shield 8b, but another heat pipe may be connected to the thermal anchor 7a and the thermal shield 8a.
[0031]
In addition, the liquid sealed in the heat pipe is appropriately selected such that the liquid phase and the gas phase are mixed at the temperature set in the connected thermal anchor.
[0032]
Further, a plurality of heat pipes may be circumferentially provided on one thermal shield so that the thermal equalization in the circumferential direction of the thermal shield becomes efficient.
In addition, although the two-layer thermal shield is used here, the thermal anchor may be further subdivided into three or more layers, and the heat pipe and the thermal shield may be increased accordingly.
Although the cooling effect is lower than that of the heat pipe, a frame may be assembled with a rod such as copper instead of the heat pipe and connected to the thermal shield.
[0033]
Although so as to connect the thermal shield 8b copper mesh thermal anchor 10, omitted parts component surrounding the bottom of the inner tank 2 of the thermal shield 8b (the vicinity of magnetoencephalography measurement unit 3b), shown in the portion A plurality of super insulations that are not to be connected may be provided and connected to the thermal anchor 10.
[0034]
In addition, since the heat transfer speed increases, the number of super-insulations (not shown) inserted into the vacuum layer 6 can be reduced, the width of the vacuum layer 6 near the magnetoencephalogram measurement unit 3b can be reduced, and the signal source ( The SN ratio can be improved by bringing the sensor 4 closer to the head).
[0035]
In addition, since heat transfer (cooling) is performed by the heat pipe 9, it is not necessary to rely on warp yarns (in the direction from the thermal anchors 7a, 7b to the magnetoencephalogram measurement unit 3b) of the copper mesh constituting the thermal shields 8a, 8b. The copper mesh can be roughened or thinned, and the thermal noise caused by the copper mesh can be reduced.
[0036]
In addition, since the internal heat conduction of the vacuum layer 6 is performed at high speed by the heat pipe 9, what is conventionally required for stabilization of the heat inside the cryostat 1 main body for 6 to 12 hours becomes extremely short, and when helium is injected. Thereafter, the change in the amount of evaporation that has not been stabilized for a while is stabilized in a short time, and the noise generated by bubbling of liquid helium is reduced in a short time.
[0037]
Further, by providing the soaking zones 11a and 11b for heat exchange inside the neck portion 2b serving as a gas discharge path, the heat propagation resistance from the thermal anchor 7b is reduced, and the temperature of the entire thermal shield 8b is lowered. Can do.
Moreover, since the detour part 2c is provided in order to increase the effective length of the neck part 2b, it is possible to prevent an increase in heat penetration due to the provision of the soaking zones 11a and 11b.
[0038]
【The invention's effect】
As described above, according to the present invention, heat entering from the vicinity of the magnetoencephalogram measurement unit (in the vicinity of the bottom of the inner tank and the bottom of the outer tank) is rapidly heated by the heat pipe to the thermal anchor away from the heat intrusion unit. Since it is transported, the thermal shield is cooled at a high speed, the temperature is made uniform, and the evaporation amount of the refrigerant can be reduced.
[0039]
In addition, according to the present invention, the thermal shield is efficiently cooled by the heat pipe without increasing the cross-sectional area of the copper mesh, so that thermal noise due to the copper mesh can be suppressed and stable measurement can be performed. .
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a configuration of a cryostat according to the present invention.
FIG. 2 is a longitudinal sectional view showing a configuration of a conventional cryostat.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cryostat 2 Inner tank 2a Body part 2b Neck part 3 Outer tank 4 Sensor 6 Vacuum layer 7a, 7b Thermal anchor 8a, 8b Thermal shield 9 Heat pipe 10 Thermal anchor 11a, 11b, Soaking means

Claims (3)

And the inner tub having a main body portion and connected to a cylindrical neck portion to the body portion neuromagnetism coolant for cooling the measuring sensor is filled with magnetoencephalography measurement sensor for biopsy therein is placed, An outer tub disposed so as to surround the inner tub and forming a vacuum layer with an outer wall of the inner tub; a first thermal anchor connected to the neck portion and disposed in the vacuum layer; A cryostat having a thermal shield connected to one thermal anchor and disposed in the vacuum layer,
The inner tank and the outer tank are cylindrical with a bottom, and the magnetoencephalographic sensor is installed at the bottom of the inner tank, and is connected to the thermal shield in the vacuum layer in the vicinity of the bottom. And a heat transport means connected to the first thermal anchor and the second thermal anchor . The cryostat according to claim 1,
The cryostat, wherein the heat transport means is a heat pipe. The cryostat according to claim 1,
Provided inside the neck part is a heat equalizing means for exchanging heat between the sensible heat of the gas evaporated from the refrigerant and exchanging heat with the first thermal anchor via the neck part. A characteristic cryostat.

Images