JPH06185844A - Cryostat for superconductive magnet integrated with precooler - Google Patents

Abstract

PURPOSE:To minimize heat invasion from a piping system and to improve cooling efficiency by a method wherein a superconductive magnet precooler to make a precooling by circulating helium gas of low temperature is built in a cryostat for superconductive magnet. CONSTITUTION:A superconductive magnet 11 is arranged inside a cryostat 10 and mounted on a center part of a top flange 18 to carry out a vacuum evacuation of the inside of the cryostat 10. After the evacuation is finished, helium gas is introduced from a gas bomb 20 through a reducing valve 22 to a helium gas line which leads to an inside space 21 and a low temperature helium blower 12 to carry out helium replacement. At this time, temperature of precooling gas which is supplied to the inside space 21 of the cryostat 10 is kept constantly at 80K. A control of precooling time of the superconductive magnet 11 can be realized easily by controlling the rotation number of the low temperature helium blower 12. Accordingly, as the helium gas is circulated within the cryostat 10, invasion heat can be largely prohibited, and therefore cooling efficiency can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryostat for a superconducting magnet integrated with a precooling device.
More specifically, the present invention saves space and
The present invention relates to a new cryostat for a superconducting magnet integrated with a precooling device, which can suppress heat entering from a system such as a pipe and improve cooling efficiency.

[0002]

2. Description of the Related Art Conventionally, a superconducting magnet which has been routinely used on a laboratory scale is generally housed in a cryostat having a liquid nitrogen heat insulation tank,
Pre-cooling, liquid helium injection, excitation test, etc. are performed. In the pre-cooling operation, liquid nitrogen is directly injected into the cryostat to cool / freeze the superconducting magnet to about 80K. After this, the injected liquid nitrogen is evacuated so that the nitrogen does not remain in the cryostat. If liquid helium is injected while nitrogen remains, the nitrogen solidifies and may damage the magnet or the like. Therefore, performing the pre-cooling with the low-temperature helium gas leads to preventing the magnet damage in the above work and reducing the labor and time for the pre-cooling.

Recently, a device called a superconducting magnet precooling device has been developed which supplies low-temperature helium gas into the cryostat for precooling. A method of connecting this to the cryostat and automatically performing the above-described precooling work has been proposed. It is also proposed. This superconducting magnet precooling device generally has a configuration including a liquid nitrogen dewar, a heat exchanger, a helium blower, and the like.

[0004]

However, in this conventional superconducting magnet precooling device, it is necessary to externally connect a precooling device having a size equal to or larger than that to the cryostat in which the superconducting magnet is housed. In addition, two low temperature transfer pipes (transfer tubes) that are vacuum-insulated in order to connect both of them and to supply and recover the low temperature pre-cooled gas.
Must be used. Therefore, there is a drawback that the entire system becomes large-scale.
Also, in the superconducting magnet precooling device,
Since a separate loop must be formed for the precooling gas, the bypass line, bypass valve, and
It is also necessary to install a line safety valve, liquid nitrogen injection / discharge line, etc. separately from the cryostat side. The above points are
There is an inherent economic problem as a pre-cooling device.

Further, the invasion heat in the transfer tube portion connecting the cryostat and the precooling device leads to a reduction in the precooling efficiency of the precooling device. On the other hand, the low-temperature helium blower, which is a gas drive source, is a device that compresses helium gas. However, since helium has a smaller molecular weight than general gas, it is not possible to secure a compression ratio that is too high. Therefore, the line that circulates the precooled gas is forced to have a severe design in terms of pressure loss, and in particular,
It is necessary to increase the inner tube diameter of the transfer tube on the recovery side.

The present invention has been made in view of the above circumstances, and solves the drawbacks of the conventional superconducting magnet precooling device, saves space, and suppresses heat entering from a piping system or the like to cool the device. Can improve efficiency,
It is intended to provide a new cryostat for a superconducting magnet integrated with a precooling device.

[0007]

In order to solve the above problems, the present invention provides a superconducting magnet precooling device for precooling by circulating low-temperature helium gas, wherein the precooling device is built in a cryostat for the superconducting magnet. Provided is a cryostat for a superconducting magnet integrated with a precooling device.

[0008]

[Operation] In the cryostat for a superconducting magnet integrated with a precooling device of the present invention, by incorporating the precooling device in the cryostat for a superconducting magnet, the entire device can be made compact and space saving can be achieved. Further, an external piping system with the conventional precooling device and a piping system independent of the precooling gas can be omitted, and the device configuration becomes simple. Since no external piping system is required, the precooling gas does not have to be exposed to the room temperature part, and the ingress heat can be suppressed. The cooling efficiency of the device is improved.

[0009]

Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. FIG. 1 is a sectional view showing an embodiment of a cryostat for a superconducting magnet integrated with a precooling device of the present invention.

In the example of FIG. 1, a cryostat (10) is provided with a liquid nitrogen heat insulating tank (17), and an internal space (21) thereof has a superconducting magnet (11).
To be able to place. The liquid nitrogen heat insulation tank (17) has a supply side heat exchanger (14) inside thereof.
And a suction side heat exchanger (13), and a low temperature helium blower (12) is connected to each of them. The low temperature helium blower (12) has a suction gas state of about 80K.
This is a device for boosting the atmospheric pressure helium gas up to about 1.2 atm. In this example, the drive unit is a room temperature motor type designed to be a room temperature part.

The helium gas whose pressure has been increased from atmospheric pressure to about 1.2 atm by the low-temperature helium blower (12) exchanges heat with the liquid nitrogen outside the pipe in the heat exchanger (14) on the supply side inside the liquid nitrogen tank (17). After being cooled to about 80K, it is directly supplied as a precooling gas to the bottom of the cryostat internal space (21) in which the superconducting magnet (11) is housed. The helium gas, which has exchanged heat with the superconducting magnet (11) in the cryostat internal space (21) and whose temperature has risen, is collected from the upper part of the space and is again transferred to the heat absorption side exchanger (13) in the liquid nitrogen tank (17) for about 80 K After being cooled to, the low temperature helium blower (12) is returned to the suction side.

The internal space (21) of the cryostat is directly connected to the precooling gas supply pipe, and the work of connecting an external low temperature transfer pipe (transfer tube) or the like is completely unnecessary. The nitrogen gas that has undergone heat exchange with the pre-cooling helium gas and has evaporated is discharged directly from the top of the cryostat (10) to the outside of the device.

Conventionally, a bypass valve (15) line connecting the intake and exhaust lines was required, but in the present invention, the cryostat internal space (21) also functions as an appropriate gas buffer, so the bypass valve (15) is used. 15) No line is required. Further, in this example, as a hardware protection of the apparatus, a safety valve (16) is attached in consideration of the case where the liquid nitrogen is exhausted and the internal helium gas rises. Pre-cooling of the superconducting magnet (11) is completed,
At the time of entering the excitation test, the internal space (21) is in a state of being filled with liquid helium, and the safety valve (16) is
It also has a function of preventing a rapid pressure increase in the internal space (21) during quenching of the superconducting magnet (11).

As other hardware components, a helium gas cylinder (20) for filling the inside with helium gas at the start of precooling operation and a pressure reducing valve (22) for reducing the pressure to atmospheric pressure are provided. Next, a specific precooling procedure will be described below. As a pre-stage of precooling the superconducting magnet (11), first, the superconducting magnet (11) is arranged inside the cryostat (10) and attached to the center portion of the top flange (18) to evacuate the inside. After the evacuation is completed, helium gas is introduced from the gas cylinder (20) through the pressure reducing valve (22) into the internal space (21) and the helium gas line leading to the low temperature helium blower (12) to replace the system with helium.

After the system is filled with helium gas, the liquid nitrogen tank (17) is started to be filled with liquid nitrogen. Liquid nitrogen shall always be automatically replenished only in the amount consumed during the pre-cooling operation. When the liquid level of the liquid nitrogen reaches a sufficiently high level, the low temperature helium blower (12) is activated to start circulation of the precooling gas. The temperature of the precooled gas supplied to the cryostat internal space (21) is always maintained at 80K by the supply-side heat exchanger (14). Therefore, the precooling time control of the superconducting magnet (11) can be easily performed by controlling the flow rate of the precooling gas, that is, the rotation speed of the low temperature helium blower (12).

At the beginning of precooling of the superconducting magnet (11), the temperature of the magnet and the supporting structure is at room temperature (about 300
K), the temperature of the recovered gas (inlet gas of the suction side heat exchanger (13)) is close to room temperature. However, as precooling progresses, the magnet temperature gradually drops from 300K to 80K. Moreover, although the temperature of the recovered gas also gradually drops, the heat absorption side heat exchanger (13) has a maximum load (about 30
By designing for 0 K helium gas), the endothermic temperature of the low-temperature helium blower (12) can be kept constant at all times, and stable operation is possible.

The typical temperature of the superconducting magnet (11) is about
Low temperature helium blower (1
2) is stopped and the supply of precooling gas is stopped. After that, finally, the cryostat internal space (21) is filled with liquid helium, and the superconducting magnet (11) is brought to a pool cooling state at a 4K level, and the precooling work is completed.

FIG. 2 is a sectional view showing another example of the apparatus of the present invention which employs a low temperature helium blower adopting a low temperature motor. In the example of FIG. 2, the nitrogen evaporative gas is guided to the blower motor (52) to cool the motor drive. Therefore, in the low-temperature motor type, the heat entering the drive unit is greatly reduced, and the blower (5
The adiabatic compression efficiency of 2) can be increased and the enthalpy of exhaust gas can be reduced. As a result, the consumption of liquid nitrogen is reduced as compared with the room temperature motor type illustrated in FIG.

Of course, the present invention is not limited to the above examples. It goes without saying that various details are possible.

[0020]

As described above in detail, according to the present invention, space saving such as elimination of the liquid tank for the precooling device, the transfer tube, the bypass line, and the individual relief valve, and simplification of the flow are realized. . Further, since the low-temperature precooling gas does not flow in the room temperature portion outside the system and is entirely circulated inside the cryostat, the heat of invasion in the process is significantly reduced, and the consumption amount of liquid nitrogen can be reduced. The cooling efficiency of the system is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a cryostat for a superconducting magnet integrated with a precooling device of the present invention.

FIG. 2 is a sectional view showing another example of the present invention.

[Explanation of symbols]

 10,50 Cryostat 11,51 Superconducting magnet 12,52 Low temperature helium blower 13,53 Suction side heat exchanger 14,54 Supply side heat exchanger 15 Bypass valve 16,55 Safety valve 17,57 Liquid nitrogen insulation tank 18,58 Top flange 19,59 Baffle plate 20,60 Helium gas cylinder 21,61 Internal space 22,62 Pressure reducing valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Hiyama, No. 801, Mukayama, Naka-cho, Naka-machi, Naka-gun, Ibaraki Prefecture, Japan 1) Inside the Naka Institute of the Japan Atomic Energy Research Institute (72) Inventor Jun Yoshida, 794 Higashitoyo, Higashitoyo, Yamaguchi (72) Inventor, Kozo Matsumoto, Higashi-Toyoi, Shimomatsu City, Yamaguchi Prefecture

Claims (2)

[Claims] 1. A superconducting magnet precooling device for precooling by circulating low-temperature helium gas,
A cryostat for a superconducting magnet integrated with a precooling device, characterized in that the precooling device is built in the cryostat for the superconducting magnet. 2. A precooled helium gas circulation line is provided in which a liquid nitrogen heat insulation tank is disposed inside the cryostat, and a helium gas supply source and an internal space in which a superconducting magnet is arranged are connected via this liquid nitrogen heat insulation layer. The cryostat for a superconducting magnet integrated with a precooling device according to claim 1, wherein the cryostat is provided inside the cryostat.