JPH06302869A - Superconducting magnet cooling system - Google Patents

Abstract

PURPOSE:To improve coil cooling efficiency in a superconducting magnet cooling system which cools multistage thermal stage due to thermal contact with a cold head. CONSTITUTION:A helium gas lead-in pipe 11 is thermally connected near a first cold head 5 and gas cooled here is used for cooling a coil 3. A coil cooling efficiency can be increased by jointly using the cooling due to contact with the cold head 6 and the cooling due to convection of helium gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling system for cooling a superconducting coil in a refrigerator.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
The cooling technology for superconducting coils is to immerse and cool the superconducting coil in a refrigerant such as liquid helium or liquid nitrogen.
There are two types of cooling by solid heat conduction, and one related to this is the one using a cryogenic container as shown in FIG.

This comprises a heat shield 2 and a superconducting coil 3 in a vacuum container 1, and the cold heads 5 and 6 of a refrigerator 4 are thermally connected to these to cool them to different temperature levels. In vacuum with shield 2 (10 ^-6 Torr
Installed).

Here, the coil 3 comes into contact with the second (final stage) cold head 6 to finally reach 4.2K to 20K.
It is cooled to the extremely low temperature of K, but this second cold head 6
The cooling by means exhibits the cooling ability at the temperature reached by the first cold head 6 (for example, 40 K) or less.

On the other hand, cooling from room temperature to 40K is performed by the first cold head 5, but the coil is in contact with only the second cold head 6, so the cooling capacity of the first cold head 5 is reduced. There was a problem that it could not be effectively used for cooling.

[0006]

In order to solve the above problems, the present invention utilizes cooling capacity other than that of the final stage cold head to cool the coil as well to enhance cooling efficiency. A helium gas introduction mechanism is provided near the head, and the helium gas cooled here is used for cooling the coil. In that case, in order to further enhance the cooling efficiency of the helium gas, it is preferable to provide cooling fins near the cold head other than the final stage cold head.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the system of the present invention comprises a vacuum container 1, a copper heat shield 2 and a superconducting coil 3 surrounded by the heat shield 2.
And a refrigerator 4 for cooling them.

The refrigerator 4 cools the heat shield 2 and the coil 3 to different temperature levels, and is thermally connected to the heat shield 2 and the coil 3 by the first and second (final stage) cold heads 5 and 6. In addition, it is connected to the compressor 7.

Further, the heat shield 2 is O of the flange portion of the lid.
A ring 8 is configured to be airtight to maintain a predetermined vacuum state, and an outer periphery thereof is surrounded by a heat insulating material (super insulation) 9 and housed in a vacuum container 1.

Then, a helium gas introducing pipe 11 was introduced into the heat shield 2 through a gas pressure controller 10 outside the vacuum container, and a gas outlet 12 was arranged below the first cold head 5. An enlarged view of the vicinity of the first cold head is shown in FIG.

As shown in the figure, cooling fins 13 are spirally provided on the outer circumference of the support pipe of the cold head, and the introduction pipe 11 is provided.
Is wound around the support tube along the cooling fins 13. Increasing the contact area by providing the cooling fins 13,
The introduction pipe 11 and the introduced helium gas were efficiently thermally connected to the first cold head 5.

In the system as described above, cooling of the coil is performed as follows. First, before cooling the coil 3 from room temperature, the outside of the heat shield 2 is evacuated well. The refrigerator 4 is operated to start cooling, the valve a is opened, and helium gas is introduced into the heat shield. At this time, the gas pressure is automatically adjusted by the gas pressure controller 10 so that the gas pressure does not decrease with cooling. Here, the helium gas introduction pipe 11 is thermally connected to the first cold head 5 by the cooling fins 13 to efficiently cool the helium gas. The coil is mainly the second cold head 6
However, the cooled helium gas descends and covers the entire surface of the coil 3, so that the coil can be cooled more efficiently. Since the cold head is in contact with only one end surface of the coil, the combined use of cooling with helium gas is particularly effective in the case of a large coil. Further, the coil 3 is cooled, and the warmed helium gas rises and is cooled again by the cooling fins 13, and convection acts on the coil. When the coil is cooled to near the temperature reached by the first cold head, the valve a is closed to stop the gas pressure control, and then the valve b is opened to evacuate the inside of the heat shield. Since the coil is placed in an adiabatic vacuum state due to the vacuum drawing in the heat shield, the cooling effect of the second cold head sufficiently functions to cool the coil to the minimum cooling temperature of the refrigerator.

[0013]

[Test Example] The superconducting coil was actually cooled using the above system, and the time required to cool the coil to the temperature reached by the second cold head was measured. For comparison, the system shown in FIG. 3 was also subjected to the same test to measure the cooling time. The test conditions are as follows.

(1) Coil structure Outer diameter: 100 mm Inner diameter: 40 mm Height: 60 mm Composition: Double pancake x 12 sheets Number of turns: 200 (2) Conductor material: Bi-based silver sheath wire Dimensions: 2 0.7mm square x 0.24mm silver ratio: 4

(3) Refrigerator type: Gifford McMahon type Achievement temperature: 1st cold head 80K, 35W 2nd cold head 20K, 4W Input: 2kW Cooling fin shape: 20mmh x 1mm thick x 20 sheets (4) Helium Gas pressure: 0.1 atmosphere

As a result, the cooling time of the conventional system was 15 hours, whereas the cooling of the system of the embodiment was as short as 5 hours, confirming the effectiveness of the present invention.

[0017]

As described above, the mechanism for introducing helium gas is provided, and the helium gas cooled by the cold head other than the final cold head is also used for cooling the coil, whereby the coil can be efficiently cooled. . In particular, even when the coil is large, the helium gas covers the surface of the coil thoroughly, so that even a small refrigerator can be efficiently cooled. Therefore, MRI, linear motor, DC motor, induction motor, high energy physical magnet, S
It can be expected to be applied to OR ring magnets.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of a system of the present invention.

FIG. 2 is an enlarged view of the vicinity of a first cold head in the system of FIG.

FIG. 3 is a schematic view showing a conventional cryogenic container.

[Explanation of symbols]

 1 Vacuum Container 2 Heat Shield 3 Coil 4 Refrigerator 5 First Cold Head 6 Second Cold Head 7 Compressor 8 O-ring 9 Heat Insulation Material 10 Gas Pressure Controller 11 Introducing Pipe 12 Gas Outlet 13 Cooling Fin 14 Current Lead a, b Valve

Claims (2)

[Claims] 1. A system in which a plurality of cold heads are brought into contact with a heat shield and a superconducting coil to cool to multiple temperature levels, and a helium gas introduction mechanism is provided near the cold heads other than the final cold head. A superconducting magnet cooling system characterized by being thermally connected. 2. The superconducting magnet cooling system according to claim 1, wherein cooling fins are thermally connected to and provided in the vicinity of the cold head other than the cold head at the final stage.