JPH0563246A - Superconducting magnet for magnetic leviation railway - Google Patents

Abstract

PURPOSE:To obtain a heat shield plate which suppressed the vibration due to eddy current and in addition is served as an AC magnetic field shield by providing a heat shield plate composed of 2 layers, i.e., aluminum nitride and pure-aluminum-based metal on the to-ground coil side of the heat shield. CONSTITUTION:A heat shield 5 between a liquid helium vessel 3 and a vacuum vessel 4 is made of a aluminum nitride and the section thereof corresponding to a ground coil is composed of 2 layers consisting of an aluminum nitride 8 and a pure-aluminum-based metal 2. A liquid helium vessel 3 involving a superconducting coil 1 in cryogenic status is housed in the vessel 4 to shield the external heat and further is enclosed with the shield 5 to prevent the radiant heat. Thus, the plate 5 can serve a heat shield and an AC magnetic field shield simultaneously, and the vibration can be reduced owning to high rigidity of aluminum nitride, thereby suppressing the generation of eddy current to the utmost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet for a magnetic levitation railway.

[0002]

2. Description of the Related Art A conventional superconducting magnet will be described with reference to FIG. The magnetic levitation railway requires a strong magnetic field for the levitation of the vehicle and the driving source for the propulsion guide, and therefore uses superconducting magnets. In order to obtain the superconducting phenomenon, it is necessary to bring the superconducting coil to an extremely low temperature, and the structure is usually as shown in FIG. That is, the superconducting coil 1 is soaked in liquid helium 2 and stored in the liquid helium container 3, and the liquid helium container 3 is further housed in the vacuum container 4 for thermal insulation.

A heat shield 5 composed of a heat shield plate is used between the vacuum container 4 and the liquid helium 3 to shield radiant heat, and the heat shield 5 is cooled by liquid nitrogen or a small refrigerator 6. It When this superconducting magnet is used in a magnetic levitation railway or the like, a ground coil 7 is installed near the superconducting magnet 1 and an AC current is passed through the ground coil to propel the superconducting magnet.

[0004]

When an alternating current is passed through the ground coil 7, an eddy current including a harmonic current flows through the heat shield 5 and the like. Since the heat shield 5 is usually made of aluminum having good heat conduction, it is soft and vibrates by an electromagnetic force due to an eddy current. In particular, the vibration becomes remarkable near a certain frequency, and the eddy current due to the vibration causes the liquid helium container 3 to generate heat. However, there is a problem that the evaporation of the liquid helium 2 is significantly increased. Further, if a material having a high electric resistance is used for the heat shield plate, there is a problem that the eddy current flowing in the heat shield plate increases and the evaporation of liquid helium increases.

In order to solve such a problem, the present invention is intended to obtain a heat shield plate which has little vibration due to eddy current and which serves as both a heat shield and an AC magnetic field shield.

[0006]

In the present invention, a heat shield plate composed of two layers of aluminum nitride (AlN) and pure aluminum metal (Al) is provided on the ground shield side of the heat shield.

[0007]

Function: Aluminum nitride AlN has good thermal conductivity, but is an insulating material against electricity. Therefore, with such a structure, heat shield is performed with AlN, and magnetic flux intrusion into the liquid helium container is prevented against AC magnetism from the ground coil due to the eddy current generated in Al.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on the embodiment shown in FIG.

The heat shield 5 between the liquid helium container 3 and the vacuum container 4 is made of aluminum nitride, and the portion corresponding to the ground coil has a two-layer structure of aluminum nitride 8 and pure aluminum-based metal 9. The pure aluminum-based metal 9 has the same shape (racetrack type) as the plan view of the superconducting coil 1.

The liquid helium container 3 containing the superconducting coil 1 in the cryogenic state is shielded from external heat by the vacuum container 4.
And is surrounded by a heat shield 5 to further reduce radiant heat.

Since the heat shield 5 is cooled by the refrigerator 6,
A material with good thermal conductivity is desirable. However, in order to eliminate the generation of eddy current due to vibration, an insulating material having high rigidity is preferable for electricity.

Therefore, in the present invention, aluminum nitride (Al
N) 8 is used. Further, an eddy current is generated by the alternating current of the ground coil 7, but when the electric resistance of the heat shield 5 is high, the eddy current flows in the liquid helium container 3, and the heat generated thereby causes significant evaporation of the liquid helium 2. Therefore,
Since an eddy current is not generated in the liquid helium container 3, it is necessary to consume the eddy current in the heat shield 5. Therefore, as shown in FIG. 1, the heat shield 5 on the ground coil side has a pure aluminum-based metal plate having a small electric resistance. 9 is joined, where eddy currents are consumed. The pure aluminum metal plate 9 has the same shape as the plan view of the superconducting coil 1 in order to minimize the eddy current.

As described above, the heat shield plate is made of an aluminum nitride plate which is an electrically insulating material and has good heat conduction and high rigidity, and an aluminum plate for eddy current consumption is joined on the ground coil side. The layered structure can serve as both a heat shield and an AC magnetic shield. Further, since the rigidity of AlN is high, the amount of vibration is reduced, which prevents the generation of eddy currents due to vibration.

As another embodiment of the present invention, a vacuum container can be constructed in the same manner as the heat shield plate described above. That is, the same effect can be obtained even if the vacuum container is made of aluminum nitride and aluminum is attached to the ground coil side.

[0015]

According to the present invention, a two-layer structure of aluminum nitride, which is an electrically insulating material, has good heat conduction, and has high rigidity, and pure aluminum-based metal, serves as both a heat shield and an electromagnetic shield. Can, in addition,
There is an effect that the generation of eddy current due to vibration can be prevented. Further, since the pure aluminum-based metal is used only in the portion of the superconducting coil that needs the magnetic shield, the generation of eddy current can be minimized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a superconducting magnet and a ground coil according to the present invention,

FIG. 2 is a cross-sectional view of a conventional superconducting magnet and a ground coil.

[Explanation of symbols]

 1 ... Superconducting coil 3 ... Liquid helium container 4 ... Vacuum container 5 ... Heat shield 7 ... Ground coil 8 ... Aluminum nitride plate 9 ... Pure aluminum metal plate

Claims (1)

[Claims] 1. A low-temperature liquid helium container containing a superconducting coil, a vacuum container containing the same, and a superconducting magnet provided with a heat shield between the liquid helium container and the vacuum container. A superconducting magnet for a magnetic levitation railway, characterized in that an aluminum plate is joined to the side of the constructed heat shield that corresponds to the ground coil to form a two-layer structure.