JPH057598B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a cryogenic container used in skid magnetometers and the like.

(B) Prior Art In general, the detection unit (probe) of a skid magnetometer that performs weak magnetic measurements is housed in a cryogenic container containing liquid helium because the measurement principle is such that the measurement is performed at a cryogenic temperature. As shown in FIG. 1, this cryogenic container has a double structure formed by an inner shell 1 and an outer shell 2, and a vacuum part 3 of a predetermined width is formed between the inner shell 1 and the outer shell 2. Furthermore, liquid helium 4 is stored as a cryogen in the inner shell 1, and the probe 5 of the Skitt magnetometer is immersed in this liquid helium 4. The inner shell 1 and outer shell 2 are made of FRP (glass fiber reinforced plastic). Conventionally, in this type of cryogenic container, as the liquid helium 4 in the inner shell 1 evaporates and approaches the empty state, the temperature of the inner shell 1 rises, and the temperature rise causes the FRP to form the inner shell 1. The permeability of helium gas increases, and the helium gas that fills the inner shell 1 enters the vacuum section 3, reducing the degree of vacuum in the vacuum section 3. Therefore, even if new liquid helium is filled, evaporation does not occur. This had the drawback of increasing the amount of liquid helium, leading to early loss of expensive liquid helium, and reducing the functionality of the cryogenic container itself.

(C) Purpose In view of the above, the purpose of the present invention is to maintain the degree of vacuum in the vacuum section even if the liquid helium in the inner shell evaporates and becomes completely empty, that is, even if the temperature in the inner shell increases. It is an object of the present invention to provide a cryogenic container that does not deteriorate.

(D) Structure In order to achieve the above object, the cryogenic container of the present invention is provided with a liquid nitrogen storage section at the bottom of the inner shell, which has a communication part between the inner shell and the lower layer of a cryogen such as liquid helium. A small amount of liquid nitrogen is stored in the inner shell, and when the cryogen such as liquid helium evaporates and becomes empty, the inner shell is filled with nitrogen gas.

(E) Examples The present invention will be explained in more detail below with reference to Examples.

FIG. 2 is a sectional view of a cryogenic container showing one embodiment of the present invention. The cryogenic container of this embodiment has the same basic structure as that shown in FIG. 1, consisting of an inner shell 1, an outer shell 2, and a vacuum section 3. However, this cryogenic container has a ring-shaped groove 1b formed on the periphery of the flat bottom 1a of the inner shell 1,
It is distinctive in that liquid nitrogen 6 is stored in this groove 1b. After filling the groove 1b with liquid nitrogen 6, liquid helium 4 is injected into the inner shell 1. Of course, liquid nitrogen 6 is created when liquid helium 4 is injected and stored and the inside of inner shell 1 is kept at an extremely low temperature.
Exists in solid form. The volume of the groove 1b may be about 1/700 of the storage volume of the liquid helium 4.
Therefore, the shape of the groove 1b is not limited to a ring shape,
Any device that can store an appropriate amount of liquid nitrogen 6 may be used.
Of course, it is desirable that the groove 1b be formed in a location where the probe 5 of the skid magnetometer can be inserted into the groove 1b without any hindrance.

In this cryogenic container, as the liquid helium 4 evaporates and becomes empty, the temperature rises. Therefore, the solidified liquid nitrogen 6 evaporates, and the inner shell 1 is filled with the gas. Then, the helium gas in the inner shell 1 is expelled to the outside. Therefore, it is possible to prevent helium gas from entering the vacuum section 3. Of course, nitrogen gas does not pass through the inner shell 1 formed of FRP. Therefore, the degree of vacuum in the vacuum section 3 can be maintained.

FIG. 3 is a sectional view of a cryogenic container showing another embodiment of the present invention. This example cryogenic container is
The bottom part 1a of the inner shell 1 is formed into a downwardly convex curved surface, and between the lower ends of the side plates 1c, 1c of the inner shell 1,
The device is characterized in that a partition plate 7 having small holes 7a is provided, and nitrogen gas 6 is stored between the partition plate 7 and the bottom portion 1a. The partition plate 7 is provided for holding and positioning the inserted probe. The effect of liquid helium 4 after evaporation is similar to that shown in FIG.

FIG. 4 is a sectional view of a cryogenic container showing still another embodiment of the present invention. In the cryogenic container of this embodiment, the bottom 1a of the inner shell 1 is formed into an upwardly convex curved surface, and liquid nitrogen 6 is stored in a recess 1d formed at the periphery of the bottom 1a. In this embodiment, since the central convex portion of the bottom portion 1a has the function of holding and positioning the probe to be inserted, a partition plate as shown in FIG. 3 is not necessary.

(F) Effect According to the cryogenic container of the present invention, liquid nitrogen gas is stored at the bottom of the inner shell, and when the liquid helium is emptied, the inner shell is filled with nitrogen gas and the helium gas is expelled to the outside. Therefore, it is possible to prevent helium gas from entering the vacuum section, and to prevent deterioration of the vacuum section. Therefore, the stored liquid helium can be used for a long time. Furthermore, the number of times the vacuum section must be vacuumed can be reduced.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional cryogenic container;
The figure is a sectional view of a cryogenic container showing one embodiment of the invention, and FIGS. 3 and 4 are sectional views of cryogenic containers showing other embodiments of the invention. 1... Inner shell, 1a... Bottom of inner shell, 1b...
Groove, 1d... recess, 2... outer shell, 3... vacuum part,
4...Liquid helium, 6...Liquid nitrogen, 7...Partition plate.

Claims (1)

[Scope of Claims] 1. A double structure is formed by an inner shell and an outer shell formed of glass fiber reinforced plastic, a vacuum section is formed between the inner shell and the outer shell, and the inner shell is filled with liquid helium. In a cryogenic container in which a cryogen such as the above is stored and a member to be kept at a cryogenic temperature is immersed in this cryogen, a liquid nitrogen storage part having a communication part with the inner shell is provided at the bottom of the inner shell. . A cryogenic container, characterized in that a small amount of liquid nitrogen is stored in a layer below the cryogen. 2. The cryogenic container according to claim 1, wherein the liquid nitrogen storage section is a groove formed in the peripheral edge of the inner shell bottom plane. 3. The liquid nitrogen storage section is configured such that the bottom of the inner shell has a downwardly convex curved surface, a horizontal partition plate having small holes is provided above the curved bottom, and the liquid nitrogen storage section is formed by the partition plate and the curved bottom. A cryogenic container according to claim 1, characterized in that it is a portion. 4. The pole according to claim 1, wherein the liquid nitrogen storage portion is a concave portion formed at the periphery of the curved bottom portion of the inner shell having an upwardly convex curved bottom portion. cryogenic container.