JPH0555032A - Crystal for superconducting magnet use - Google Patents

Abstract

PURPOSE:To obtain the title crystal wherein the vibration of the pressure of an evaporated gas is restrained, the quantity of heat creeping to a refrigerant due to a change in the pressure is reduced and the amount consumed of the refrigerant is reduced by a method wherein a fluid resistance which restrains the vibration of the pressure of the evaporated gas is installed, so as to be in parallel with a safety value, in the evaporation passage of the evaporated gas. CONSTITUTION:The crystal is provided with an inner container 15 which houses a superconducting magnet 11 and a refrigerant 3; an outer container 17 which holds the inner container 15 at the inside in a heat-insulating state; and an evacuation passage 25 which discharges, to the outside, the evaporated gas, of the refrigerant 13, generated inside the inner container 15. In addition, a fluid resistance 35 which restrains the vibration of the pressure of an evaporated gas is installed in the evacuation passage 25 so as to be in parallel with a safety valve 19 which is opened automatically when the pressure inside the inner container 15 becomes a first set pressure or higher which is higher than atmospheric pressure. In addition, for example, the following inner-pressure holding valve 31 is installed in the evacuation passage 25 so as to be in parallel with the fluid resistance 35: it is opened automatically when the pressure inside the inner container 15 becomes a second set pressure or higher which is lower than the first set pressure and higher than atmospheric pressure; and it is shut automatically when the pressure inside the inner container becomes the second set pressure or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryostat used for cooling a superconducting magnet.

[0002]

2. Description of the Related Art A general structure of a conventional cryostat for a superconducting magnet is shown in FIG. Reference numeral 11 is a superconducting magnet wound in a coil shape, 13 is a cryogen such as liquid helium that cools the superconducting magnet 11, 15 is an inner container for containing the superconducting magnet 11 and the cryogen 13, and 17 is an adiabatic enclosure for the inner container 15. Then, the outer container forming a vacuum layer between the inner container 15 and 19, the heat insulating shield layer provided between the inner container 15 and the outer container 17, 21 is provided between the heat insulating shield layer 19 and the outer container 17. A multi-layered heat insulating material layer, 23 is a support material for supporting the inner container 15 and the heat insulating shield layer 19 at a predetermined position with respect to the outer container 17, and 25 is an exhaust gas that connects the inner container 15 and the outer container 17 to each other. aisle,
27 is an injection pipe for injecting a cryogen into the inner container 15.

The exhaust passage 25 is divided into three branches outside the outer container 17, and the first branch pipe 25a breaks or breaks the thin plate when the pressure in the inner container 15 exceeds a first set pressure higher than atmospheric pressure. A destructive safety valve 29 that releases the vaporized gas in the inner container 15 by deformation is connected, and the second branch pipe 25b has a second pressure in the inner container 15 lower than the first set pressure and higher than atmospheric pressure. The internal pressure holding valve 31 is automatically opened when the pressure becomes equal to or higher than the set pressure of, and the valve is automatically closed when the pressure becomes equal to or lower than the second set pressure. The opening / closing valve 33 is connected to the third branch pipe 25c. ..

The on-off valve 33 is always closed except when the cryogen is injected, and the safety valve 29 does not open as long as the superconducting magnet 11 maintains a normal superconducting state. Therefore, only the internal pressure holding valve 31 operates in the normal operating state.

The internal pressure holding valve 31 is composed of, for example, a spring type check valve, which opens when the inside of the inner container 15 is pressurized by the evaporation gas of the cryogen and evaporates to keep the pressure inside the inner container 15 constant. It releases gas. As a result, the inside of the inner container 15 is maintained at a pressure slightly higher than the atmospheric pressure, and the outside air is prevented from flowing into the inner container 15 due to the fluctuation of the atmospheric pressure.

The safety valve 29 is activated when the superconducting magnet 11 causes a superconducting breakdown. That is, when the superconducting magnet 11 causes a superconducting breakdown, the electric energy that it possesses becomes thermal energy and is released in a short time.
The cryogen 13 that has cooled the superconducting magnet 11 is rapidly gasified, and the internal pressure of the inner container 15 is rapidly increased. If the inner pressure of the inner container 15 becomes too high, the inner container 15 may be destroyed. Therefore, when the inner pressure of the inner container 15 rises above a specified value (first set pressure), the thin plate of the safety valve 31 is destroyed. The evaporative gas is released from the inner container 15 to the atmosphere to protect the inner container 15 from pressure breakdown.

Further, the opening / closing valve 33 is for opening the cryogen when injecting the cryogen into the inner container 15 to release the vaporized gas. That is, when injecting the cryogen, in the initial stage, evaporation of the cryogen in the injection pipe 27 and flash loss cause evaporation of a large amount of the cryogen and increase the pressure in the inner container 15, so open the on-off valve 33. The vaporized gas generated at the time of injection is released to prevent the pressure in the inner container 15 from rising.

[0008]

According to the measurements made by the present inventors, it has been found that the conventional cryostat causes self-excited oscillation of the vaporized gas pressure in a steady operation state. This self-excited vibration is below 30K above the cryogen level, especially
The low temperature region below 10K is considered to be the generation source, and the vibration frequency is several
It is from Hz to several tens of Hz. When such self-excited vibration occurs, a large amount of heat enters the cryogen and increases the evaporation amount of the cryogen. Since cryogens such as liquid helium are extremely expensive,
It is desirable to minimize the amount of evaporation, and the fact that self-excited oscillation of the evaporative gas pressure occurs in the steady operation state indicates that there is evaporation of the cryogen due to it,
The problem is how to suppress this self-excited vibration.

The present invention has been made in order to solve the above-mentioned problems, and suppresses the vibration of the evaporative gas pressure, reduces the amount of heat entering the cryogen due to pressure fluctuation, and consumes less cryogen. It is intended to provide a cryostat for a magnet.

[0010]

To achieve this object, the present invention is carried out in an inner container for containing a superconducting magnet and a cryogen, an outer container for holding the inner container in a heat-insulated state, and an inner container. Equipped with an exhaust passage for discharging the cryogen's evaporative gas to the outside, and the evaporative gas pressure in parallel with the safety valve that automatically opens when the pressure inside the inner container becomes higher than the first set pressure higher than atmospheric pressure. Is provided with a fluid resistor for suppressing the vibration of the. As a fluid resistor,
Flow control valves such as needle valves and orifices are used.

[0011]

In this cryostat, when the superconducting magnet maintains the superconducting state, the vaporized gas generated in the inner container is discharged to the outside through the fluid resistor.
At this time, the safety valve is of course closed. When self-excited vibration occurs in the pressure of evaporative gas discharged from the inner container to the outside through the exhaust passage, the fluid resistor acts as a resistance to the flow of evaporative gas, so the amplitude of self-excited oscillation is the fluid resistance. It is smaller than the case without a vessel, and the heat flow into the cryogen due to self-excited vibration can be reduced.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. This conventional cryostat for a superconducting magnet has an inner container 15 and an outer container 1 for accommodating the superconducting magnet 11 and the cryogen 13, as in the conventional case.
7, the heat insulating shield layer 19, the multilayer heat insulating material layer 21, the support material 23, the exhaust passage 25, the first to third branch pipes 25a to 25c, the cryogen injection pipe 27, the safety valve 29, the internal pressure holding valve 31, the open / close valve 33. I have it.

The feature of this cryostat is that the exhaust passage is
The second branch pipe 25b of 25 is provided with a flow control valve 35 including a needle valve or the like in series with the internal pressure holding valve 31.
This flow rate control valve 35 is a fluid resistance that suppresses self-excited oscillation of evaporative gas pressure by narrowing the opening to such an extent that the pressure inside the inner container 15 does not rise abnormally when the superconducting magnet 11 maintains the superconducting state. It functions as a container.

In this embodiment, the flow control valve 35 is replaced with the internal pressure holding valve.
Although it was connected to the downstream side of 31, the flow control valve 35 and the internal pressure holding valve 31
Even if the positions of are replaced, there is no functional change.

Next, the operation will be described. When the superconducting magnet 11 normally maintains the superconducting state, the cryogen 13 in the inner container 15 is radiated by heat from the heat insulating shield layer 19 or the like, or the supporting material.
It always evaporates due to the heat that enters through the heat conduction through 23. The pressure in the inner container 15 rises due to this vaporized gas, and when it rises above a certain limit, the internal pressure holding valve 31 opens, so the vaporized gas is released into the atmosphere through the internal pressure holding valve 31 and the flow rate control valve 35. ..

When the flow control valve 35 is fully opened and the pressure in the inner container 15 is observed with a high-precision pressure gauge, pressure oscillation is observed, and self-excited oscillation of the vaporized gas pressure occurs in the exhaust passage 25. Can be confirmed. It can be seen that when the opening degree of the flow rate control valve 35 is gradually reduced and the flow rate is reduced, the pressure vibration eventually subsides and the amplitude of the self-excited vibration decreases. The flow rate control valve 35 adjusts the opening so that the amplitude of the self-excited vibration in the exhaust passage 25 becomes small and the pressure in the inner container 15 does not rise, and the opening is fixed in that state. This makes it possible to construct a cryostat in which less heat flows due to self-excited oscillation of the pressure of the evaporative gas, and thus less cryogen consumption.

If the amplitude of the self-excited vibration becomes small and the opening of the flow control valve 35 at which the pressure in the inner container 15 does not rise abnormally is known by measurement, etc., the flow control is performed. Instead of the valve 35, an orifice or the like having the same fluid resistance as the opening can be used.

Since the functions of the safety valve 29 and the opening / closing valve 33 are the same as those of the conventional one, the description thereof will be omitted. Open / close valve
33 can be omitted if, for example, the upstream side of the safety valve 29 can be opened when the cryogen is injected. Further, the safety valve 29 does not necessarily have to be a destructive-type opening valve. It is also possible to use a pressure type on-off valve that can secure a sufficient opening degree for releasing.

Next, another embodiment of the present invention will be described with reference to FIG. This cryostat is different from the cryostat in FIG. 1 in that the internal pressure holding valve 31 in FIG. 1 is omitted, and the second branch pipe 25b has a flow rate control valve as a fluid resistor.
Only 35 are connected. According to the experiment, if the opening degree of the flow rate control valve 35 is narrowed down to the extent that it functions as a fluid resistor for vibration suppression, the inside of the inner container 15 is higher than atmospheric pressure even if the inner pressure holding valve is opened. It was confirmed that the pressure was maintained and no inflow of outside air occurred. Therefore, the internal pressure holding valve can be omitted. Since the configuration other than the above is the same as that of the cryostat in FIG. 1, the same portions are denoted by the same reference numerals and the description thereof will be omitted.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 3, only the evacuation system for evaporating gas is shown, and the other parts are the same as in FIG. This cryostat is different from the cryostat shown in FIG. 1 in that the pressure fluctuation of the evaporative gas due to the fluctuation of the atmospheric pressure is further absorbed on the downstream side of the flow rate control valve 35 as a fluid resistor for suppressing the self-excited oscillation of the evaporative gas pressure. That is, another set of the flow rate control valve 37 and the gas container 39 is connected in series. The gas container 39 is located between the two flow control valves 35 and 37.

The pressure of the evaporative gas in the inner container also fluctuates due to changes in atmospheric pressure (changes due to weather, changes due to air conditioning, changes due to opening and closing of doors, etc.), which increases the evaporation amount of the cryogen. is there. Since the fluctuation cycle of atmospheric pressure is much longer than the self-excited vibration cycle of the evaporative gas, it is difficult for the flow control valve 35 for suppressing self-excited vibration to absorb the influence of the fluctuation of atmospheric pressure.

Therefore, in this embodiment, a flow rate control valve 37 functioning as a fluid resistor against atmospheric pressure fluctuations and a gas container 39 for a buffer are connected to the downstream side of the flow rate control valve 35 to change the atmospheric pressure fluctuations. The pressure fluctuation of the evaporative gas based on the above is absorbed. The other structure is the same as that of the embodiment of FIG.

According to this structure, both the self-excited oscillation of the pressure of the evaporative gas and the pressure fluctuation of the evaporative gas due to the fluctuation of the atmospheric pressure are suppressed, so that the evaporation amount of the cryogen is more than that in the embodiment of FIG. Less. Instead of the flow rate control valve 37, an orifice or the like having the same fluid resistance as the flow rate control valve 37 can be used.

[0024]

As described above, according to the present invention, the vibration of the evaporative gas pressure can be suppressed, so that the heat quantity penetrating into the inner container due to the vibration of the evaporative gas pressure can be reduced and the cryogen consumption can be reduced. You can get less economical cryostats.

[Brief description of drawings]

FIG. 1 is a sectional view of a cryostat for a superconducting magnet according to an embodiment of the present invention.

FIG. 2 is a sectional view of a cryostat for a superconducting magnet according to another embodiment of the present invention.

FIG. 3 is an explanatory diagram of a main part of a cryostat for a superconducting magnet according to still another embodiment of the present invention.

FIG. 4 is a sectional view of a conventional cryostat for a superconducting magnet.

[Explanation of symbols]

11: Superconducting magnet 13: Cryogen 15: Inner container
17: Outer container 19: Insulation shield layer 21: Multi-layer insulation layer 23: Support material 25: Exhaust passage 27: Cold agent injection pipe 29: Safety valve 31: Internal pressure holding valve
33: Open / close valve 35: Flow rate control valve (fluid resistor for suppressing self-excited vibration) 37: Flow rate control valve (fluid resistor for absorbing atmospheric pressure fluctuation)
39: Gas container

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Furuto 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. An inner container for accommodating a superconducting magnet and a cryogen, an outer container for holding the inner container in a heat-insulated state therein, and an exhaust passage for discharging evaporative gas of the cryogen generated in the inner container to the outside. It is equipped with a fluid resistor in the exhaust passage in parallel with a safety valve that opens automatically when the pressure inside the inner container rises above a first set pressure, which is higher than atmospheric pressure. Cryostat for superconducting magnet. 2. An exhaust passage, in series with a fluid resistor, automatically opens when the pressure in the inner container becomes equal to or higher than a second set pressure lower than the first set pressure and higher than atmospheric pressure, and then set to the second set. The cryostat for a superconducting magnet according to claim 1, further comprising an internal pressure holding valve that automatically closes when the pressure falls below a pressure. 3. A set of a fluid resistor and a gas container, which absorbs the pressure fluctuation of the evaporative gas due to the fluctuation of the atmospheric pressure, is provided downstream of the fluid resistor, and the gas container is located between the two fluid resistors. 1 or 2 is provided in series as described above.
Cryostat for the superconducting magnet described.