JPH0713922B2 - Cryostat - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cryostat provided with a heat shield plate including a circulation pipe for an evaporated refrigerant gas in a vacuum heat insulation layer between an inner container and an outer container, and in particular, an inner container. The present invention relates to a cryostat that automatically switches between a normal circulation path and a normal circulation path of evaporative gas so that the evaporative gas generated therein can flow through a circulation pipe without any shortage.

[Conventional technology]

Medical NMR (= MRI) -CT that uses a superconducting magnet
As a magnet container in (Nuclear Magnetic Resonance Computed Tomography), a model cryostat having a room temperature bore A is generally used as shown in FIG. This cryostat is a magnet B
In order to suppress the evaporation amount of the refrigerant C (generally, liquid helium) that cools the air from the viewpoint of maintenance and operation costs, the heat insulating structure is devised. That is, the radiant heat is generated at the outer circumference of the inner container 1 in the vacuum heat insulating layer 3 created between the hollow annular inner container 1 containing the magnet B and the refrigerant C and the outer container 2 concentrically surrounding the inner container 1. A heat shield plate 4 that shields the heat is provided. Further, the heat shield plate is attached by, for example, winding and soldering a circulation pipe 6 for letting the evaporative gas of the refrigerant flow in and out from the cylindrical port 5 portion of the inner container 1, and evaporating which flows in this circulation pipe. The heat shield plate 4 is forcibly cooled by the gas to enhance the heat insulation performance.

In an actual cryostat, in order to eliminate the invasion of the external heat transmitted through the circulation pipe, as shown in FIG. 5, the gas discharged from the outlet of the circulation pipe 6 is once returned to the inside of the port 5 and then the outlet 7 at the end of the port. To the outside, and in order to suppress the entry of radiant heat from the tip side of the port 5, a baffle plate 8 for heat shield is hung on the top flange 9 with a mounting rod 10 at the inlet of the port. It is supported and inserted.

Further, if the method of returning the gas after circulation into the port 5 once is adopted, it becomes difficult for the evaporative gas to flow into the pipe 6, so that the outlet of the pipe 6 is above the inlet, and the partition plate 11 is provided in the port 5 between the inlet and the outlet. I have Reference numeral 12 is a safety valve that opens when there is an abnormality or a fuse cap that bursts when there is an abnormality.

[Problems to be solved by the invention]

The baffle plate 8 and the partition plate 11 are provided with small holes 8a, 11a at corresponding positions for the purpose of passing a current lead wire through a magnet in the inner container and for the purpose of eliminating an abnormal increase in internal pressure of the inner container.
Since it is provided, it is not possible to prevent evaporative gas from passing through these holes and directly coming out to the outlet 7 after the lead wire is drawn out. Therefore, the gas pressure at the inlet side of the circulation pipe decreases. There is a problem that the amount of gas flowing into the pipe is insufficient, it is difficult to cool the heat shield plate to a desired temperature, and it takes time even if it can be cooled, and the amount of refrigerant consumed during that time increases.

[Means for solving problems]

In order to eliminate the above-mentioned problems, the present invention provides a cryostat equipped with the above-mentioned heat shield plate, partition plate and baffle plate, in which at least a shielding lid that can be inserted / removed from the outside of the port that closes the hole of the partition plate and its lid or partition. The closing lid of the hole separately provided in the plate serves as a valve element, and the valve element is displaced by a pressure difference received on one surface during abnormal evaporation of the refrigerant, and a valve mechanism for opening the closed hole of the valve element is provided. .

[Action]

In the above-mentioned valve mechanism, at least the hole of the partition plate is normally closed, so that the evaporated gas is forced to pass through the circulation pipe to the outlet, which increases the amount of circulation gas in the pipe.

Also, when a refrigerant abnormality occurs (when the magnet is quenched), the valve element is displaced by the pressure difference and the hole is opened, so that the inner side of the partition plate of the inner container is opened through the hole of the partition plate and the baffle plate. The chamber and the gas outlet provided in the port are short-circuited, and as a result, the vaporized gas passes through the short-circuiting path to the outlet, so that an abnormal increase in the internal pressure of the inner container can be eliminated.

〔Example〕

1 to 3 show a preferred embodiment of the present invention.

As shown in FIG. 1, the top flange 9 of the port 5 is provided with openings corresponding to the holes 8a, 11a of the baffle plate 8 and the partition plate 11 (the figure shows one of them). The opening is closed by a cap 14 sealed by the Wilson seal portion 13. The illustrated cryostat is required for suspending the support rod 16 using a string or thread 15 on the cap 14 and inserting it into the hole 11a of the partition plate at the lower end of the support rod which is penetrated through the hole 8a of the baffle plate. A shield lid 17 to be inserted with such a minimum clearance is attached by screw coupling or adhesion. In the middle of the support rod, a thin fin-shaped second shielding lid 18 which is inserted into the hole 11a of each baffle plate and closes the hole 11a with almost no gap is adjusted to the arrangement pitch of the baffle plate in the same manner as the lid 17. The support rod 16 at the position where the lids 17 and 18 are inserted into the holes 11a and 8a, and the length 17 of the string or thread 14 is fully extended from the hole 11a. The support rod is allowed to rise, but the lid 18 that closes the hole of the lower baffle plate is not allowed to rise to a position where it closes the hole of the upper baffle plate.

Each of the support rod 16 and the shielding lids 17 and 18 is made of glass fiber reinforced plastic having a low thermal conductivity, from the viewpoints of reducing the weight of the valve member 19 composed of the three members and preventing the heat from entering the valve member 19.
It is preferably formed of an organic material such as Teflon or carbon fiber reinforced plastic. However, the total weight of the valve member is determined such that the member cannot be pushed upward by the pressure difference of the vaporized gas under normal conditions. This weight adjustment may be performed by changing the volume of the lid 17. Since it is desirable for the lid 18 to be thinner in terms of heat penetration, it is not preferable to adjust the weight by changing its thickness.

As shown in FIGS. 2 and 3, the valve member 19 is partitioned by a partition plate.
An example cryostat is completed when holes are provided corresponding to all of 11 and the baffle plate 8.

By doing so, only when the refrigerant C in the inner container 1 evaporates abnormally and the inner pressure of the container suddenly rises, the difference in pressure acting on the both sides of the shielding lids 17 and 18 by the valve member 19 is increased. And first
The holes 8a and 11a are opened by being blown up as shown by the chain line in the figure. Therefore, the vaporized gas, as described in the section of action,
In the normal state, most of them flow into the circulation pipe 6, while in the abnormal state, the holes 8a and 11a open to the outlet through the short-circuit path created. Here, as shown in FIG. 3, there is a minute clearance g of, for example, about 0.1 to 0.2 mm, which is necessary for inserting and removing the baffle plate, between the inner surface of the baffle plate 8 and the port 5, so that the outlet of the pipe 6 is normally operated. Gas emitted from (the amount is 0 in the case of a normal horizontal cryostat.
2 l / hour) can be discharged from the clearance g even if the hole 8a is closed.

Although the valve member 19 is not so preferable in terms of preventing the entry of external heat, it may have the following structure. That is, the support rod 16 is fixed to the cap 14 and is suspended, and as shown in FIG. 4, the lid 17 and the lid 17 are slidably attached to the rod 16 preferably by downwardly urging them by a spring 20 to cause an abnormality. Sometimes only the lid is pushed up.

The object of the present invention can be achieved by opening and closing the hole 11a of the partition plate. Therefore, the second shield lid 18 is not essential, but the second shield lid 18 is not affected by the normal temperature portion that has passed through the baffle plate at the normal time. It is preferable that it works effectively to prevent heat infiltration of the. That is, the presence of the lid 18 makes it difficult for the evaporated gas in a normal state to escape from the hole of the baffle plate, and sufficiently cools the baffle plate before it escapes, so that the amount of external heat entering decreases.

Furthermore, when closing only the hole of the partition plate, the shielding lid 17 is inserted in a state of being held in the hole 11a even in the event of an abnormality, and the short circuit path is
The partition plate 11 may be provided with another hole, and a lid that closes the hole may be formed by a valve mechanism having a valve body. In this case, the valve mechanism is provided at a position separated from the hole 11a. Can be fastened to.

〔effect〕

As described above, according to the present invention, at the time of normal operation in which vaporized gas is naturally generated, at least most of the generated gas is forced to flow through the circulation pipe by closing the hole of the partition plate, so that the heat shield plate is cooled. The effect is enhanced and the radiant heat shielding performance is improved.

In addition, in the event of an abnormality, the lid that closes the hole of the partition plate serves as a valve body to short-circuit the inside of the inner container and the gas outlet of the port, so a dedicated safety gas that causes an increase in the diameter of the port It is possible to prevent an abnormal increase in internal pressure of the inner container without providing a vent passage.

Further, if the opening of the baffle plate is also closed by the opening / closing lid, the cooling effect of the baffle plate is improved, so that the radiant heat from the port entrance can be further reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing a part of a main part of a cryostat of an embodiment, FIG. 2 is a sectional view showing an entire port part, and FIG.
2 is a sectional view taken along the line III-III in FIG. 2, FIG. 4 is a front view showing a part of another embodiment of the valve member, FIG. 5 is a sectional view showing a known horizontal cryostat, and FIG. The figure is a detailed cross-sectional view of a port portion of a conventional cryostat. 1 ... inner container, 2 ... outer container, 3 ... vacuum heat insulating layer, 4 ...
… Heat shield plate, 5 …… cylindrical port, 6 …… circulation pipe, 7 …… gas outlet, 8 …… baffle plate, 8a …… hole, 9
…… Top flange, 10 …… Mounting rod, 11 …… Partition plate, 11
a …… hole, 12 …… safety valve or fuse cap, 13 ……
Wilson seal part, 14 ... Cap, 15 ... String or thread, 16 ... Support rod, 17, 18 ... Shielding lid, 19 ... Valve member,
20 …… Spring.

Claims (3)

[Claims] 1. A vacuum heat insulating layer between an inner container and an outer container has a heat shield plate around which a pipe for circulating an evaporative gas of a refrigerant in the inner container is circulated, and the port of the inner container has the port. A partition plate for partitioning the inside of the port between the inlet of the circulation pipe opened to the above and the outlet above it, and a baffle plate slightly smaller than the inner diameter of the port inserted into the port inlet portion. , In the cryostat having holes at corresponding positions in the partition plate and the baffle plate, at least a shielding lid that can be inserted / removed from the outside of the port that closes the hole of the partition plate and a hole separately provided in this lid or the partition plate. The closing lid serves as a valve body, and the valve body is provided with a valve mechanism that is displaced by a pressure difference applied to one surface and the other surface during abnormal evaporation of the refrigerant and opens the closed hole of the valve body. Cryostat. 2. The above-mentioned valve mechanism is a support rod which is hung in a closing cap of a hole formed in a top flange of a port and passes through a hole of a baffle plate, and is attached to a lower end of the support rod so as to be freely inserted into and removed from the hole of a partition plate. The shielding cover is provided, and the shielding cover is configured to move up and down together with a support rod to open and close a closed hole of the support rod. Cryostat. 3. The support bar comprises a thin plate having an outer diameter slightly smaller than the hole diameter of the baffle plate inserted into the hole of the baffle plate. The described cryostat.