JPH06112040A - Superconductive magnet - Google Patents

Abstract

PURPOSE:To make a superconducting magnet stably operable meeting even electromagnetically strict requirements by a method wherein the thickness of a low electric resistance member is specified to be thicker than the surface depth in the frequency of the dimensional component of the AC magnetic field maximizing the eddy current loss of an inner vessel corresponding to the maximum velocity of a running device. CONSTITUTION:The thickness (d) of a low electric resistance member 6 is specified to be thicker than the surface depth in the frequency of the dimemsional component of the AC magnetic field maximizing the eddy current loss of an inner vessel 2 but not exceeding the twice value of the surface depth. Through these procedures, the superconducting magnet capable of stably operating meeting even electromagnetically strict requirements and yet not heavy in weight can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting magnet mainly used in a superconducting magnetic levitation vehicle.

[0002]

2. Description of the Related Art FIG. 4 is a partially sectional perspective view showing a conventional superconducting magnet. In FIG. 4, 1 is a superconducting coil made of a wound superconducting wire, 2 is an inner tank container that houses the superconducting coil 1 and is filled with liquid helium, and 3 is arranged so as to surround the inner tank container 2. A radiation shield plate cooled by nitrogen or vaporized helium gas. Reference numeral 4 denotes an outer tank container arranged outside the radiation shield plate 3, and the inside thereof is maintained in a vacuum in order to keep the superconducting coil 1, the inner tank container 2 and the radiation shield plate 3 in an adiabatic state from the outside. There is.

The superconducting magnet shown in FIG. 4 serves as a power source for a traveling device such as a superconducting magnetic levitation vehicle. Therefore, in the superconducting magnet, there are an AC magnetic field of higher harmonics from a ground coil (not shown) installed outside, and an inner tank container 2 and a radiation shield plate 3 or an outer tank container 4 generated with traveling. The alternating magnetic field generated due to the relative vibration between the two acts on the inner tank container 2.

FIG. 5 shows a structure for shielding these alternating magnetic fields from the inner container 2 to reduce the eddy current loss of the inner container 2. 2a is a plate member made of a stainless steel plate or the like serving as a strength member, and 5 is a low electric resistance material such as copper or aluminum that is integrally attached to the entire surface of the plate material 2a. Tank container 2
Shielded from.

Generally, there is a relationship between the thickness of the low electrical resistance material 5 and the eddy current loss of the inner tank 2 as shown in FIG. That is, when the low electrical resistance material 5 becomes thin, its electrical resistance is not sufficiently small and the alternating magnetic field cannot be sufficiently magnetically shielded, so that the eddy current loss of the inner vessel 2 increases. On the other hand, if the low electrical resistance material 5 is thickened, the eddy current loss can be reduced, but the weight of the inner tank container 2 increases. The low electric resistance material 5 is integrally joined to the surface of the plate material 2a in advance, and the inner tank container 2 is manufactured using such a composite material.

[0006]

The conventional superconducting magnet is
Since it is configured as described above, if the low electrical resistance material 5 is made thin, the eddy current loss generated in the inner tank container 2 increases, and stable operation cannot be performed under electromagnetically severe conditions. There was a problem. On the other hand, if the low electrical resistance material 5 is thickened, the weight of the inner tank container 2 increases, and thus the weight of the superconducting magnet also increases.

The present invention has been made in order to solve the above problems, and obtains a superconducting magnet which can be stably operated even under severe electromagnetic conditions and is not heavy. With the goal.

[0008]

In the superconducting magnet according to claim 1 of the present invention, the thickness of the low electric resistance material is such that the order component of the alternating magnetic field that maximizes the eddy current loss of the inner tank is that of the traveling device. It is thicker than the skin depth at the frequency that corresponds to the maximum speed.

Further, in the superconducting magnet according to claim 2 of the present invention, the thickness of the low electric resistance material is such that the order component of the alternating magnetic field that maximizes the eddy current loss of the inner tank corresponds to the maximum speed of the traveling device. The thickness is thicker than the skin depth at the frequency thus obtained and is twice the skin depth or less.

[0010]

In the superconducting magnet according to the first aspect of the present invention, the thickness of the low electric resistance material is set to a value that can effectively reduce the eddy current loss of the inner vessel.

Further, in the superconducting magnet according to the second aspect of the present invention, the thickness of the low electric resistance material can effectively reduce the eddy current loss of the inner vessel and the weight of the inner vessel does not increase. Value.

[0012]

【Example】

Example 1. First Embodiment FIG. 1 is a perspective view showing a part of a cross section showing a first embodiment of the present invention. The same or corresponding parts as in FIG. 6 is a low electric resistance material having a thickness different from the conventional one, and d is the thickness of the low electric resistance material 6.

Next, a method of determining the thickness d of the low electric resistance material 6 will be described. An alternating magnetic field interlinks in the inner container 2 as described above, resulting in eddy current loss. Generally, the eddy current loss occurs only near the surface of the conductor, but the skin depth δ where the eddy current occurs is expressed by the following equation.

Δ = √ (2ρ / μ ₀ ω) = √ {ρ / (μ ₀ πf)} ... where ρ: resistivity of the electric resistance material μ ₀ : permeability of vacuum ω: angular frequency f: frequency

As is clear from the equation, the skin depth δ depends on the frequency f. Therefore, when the low electrical resistance material 6 having a predetermined thickness d is used as the electrical resistance material, the magnetic shield effect, and thus the eddy current loss of the inner vessel 2 has frequency dependency.

FIG. 3 is an explanatory diagram of such frequency dependence, that is, an explanatory diagram of frequency characteristics of eddy current loss generated in the inner container 2 when an alternating magnetic field is linked to the inner container 2. . As the AC magnetic field, only the order component that maximizes the eddy current loss is considered. Solid lines (α ₁ , β ₁ ,
γ ₁ ) represents the eddy current loss generated in the inner tank container 2 due to the relative vibration between the inner tank container 2 and the radiation shield plate 3 or the outer tank container 4, and the broken lines (α ₂ , β ₂ , γ ₂ ) are It shows the eddy current loss generated in the inner tank container 2 due to an alternating magnetic field from a ground coil (not shown) provided outside the superconducting magnet.

Here, using the frequency f ₁ taken as the order component for maximizing the eddy current loss, which corresponds to the maximum speed of the traveling device having the superconducting magnet of the first embodiment as a power source, the skin is obtained from the equation. Determine the depth δ ₁ = √ {ρ / (μ ₀ πf ₁ )}. α ₁ and α ₂ are the thickness d when the skin depth δ ₁ is almost the same, β ₁ and β ₂ are the low electrical resistance materials, γ ₁ and
γ ₂ is data when the thickness d is as thin as about 1/6 of the skin depth δ ₁ .

As is clear from FIG. 3, the eddy current losses α ₁ , β ₁ , γ ₁ due to relative vibration increase with frequency, while the eddy current losses α ₂ , β ₂ , γ ₂ due to the ground coil increase with frequency. Decrease. This is because the radiation shield plate 3 magnetically shields the AC magnetic field from the ground coil. The eddy current loss due to the ground coil is smaller than the eddy current loss due to relative vibration, and the eddy current loss due to relative vibration is dominant.

When the thickness d is as thin as ⅙ of the skin depth δ ₁ (γ ₁ , γ ₂ ), the electric resistance of the low electric resistance material 6 does not become sufficiently small and the inner tank container 2 Since the fluctuating AC magnetic field outside the above can not be sufficiently magnetically shielded, the eddy current loss of the inner tank container 2 cannot be reduced. Therefore, when the low electrical resistance material 6 having a thickness of the skin depth δ ₁ is provided,
The electric resistance becomes sufficiently small to allow a sufficient eddy current to flow for the magnetic shield, and it is possible to prevent the fluctuating AC magnetic field from entering the superconducting coil 1.

By the way, when the thickness d is made much thicker than the skin depth δ ₁ , the eddy current flowing in the low electric resistance material 6 due to the alternating magnetic field is concentrated on the surface thereof, and the skin depth δ.
Almost no eddy currents flow in parts deeper than ₁ . Therefore, the magnetic shield effect is hardly improved further, and the weight of the inner tank container 2 increases, which is not a good idea.

From the above, if the thickness d is selected to be the skin depth δ ₁ or more, the eddy current loss generated in the inner tank container 2 becomes sufficiently small, and further, the thickness d is set to the skin depth δ ₁ . 1-2
If doubled, the weight of the inner tank container 2 is not increased and the eddy current loss is sufficiently reduced.

[0022]

As described above, according to the superconducting magnet according to claim 1 of the present invention, the thickness of the low electric resistance material is such that the order component of the alternating magnetic field that maximizes the eddy current loss of the inner vessel is Since it is thicker than the skin depth at the frequency that corresponds to the maximum speed of the traveling device, there is an effect that it can be stably operated even under electromagnetically severe conditions.

In the superconducting magnet according to the second aspect of the present invention, the order of the AC magnetic field that maximizes the eddy current loss of the inner tank is the maximum speed of the traveling device due to the thickness of the low electric resistance material. Since it is thicker than the skin depth at the frequency corresponding to, and less than twice the skin depth, it can be stably operated even under severe electromagnetic conditions, and the weight Has the effect of not being large.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a relationship between a thickness of a low electric resistance material and an eddy current loss.

FIG. 3 is an explanatory diagram of frequency dependence.

FIG. 4 is a perspective view showing a conventional superconducting magnet.

FIG. 5 is a structural diagram for reducing eddy currents.

[Explanation of symbols]

 1 Superconducting coil 2 Inner tank container 6 Low electrical resistance material d Low electrical resistance material thickness

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaru Iwamatsu 8-8 Hikarimachi, Kokubunji, Tokyo 38 Inside the Railway Technical Research Institute (72) Motoaki Terai 2-17-6 Higashi-Nakano, Nakano-ku, Tokyo −202 (72) Inventor Masatoshi Shinobu 787 Nakazawa, Kamagaya City, Chiba Prefecture (72) Inventor Koji Ikeshita 8-1-1 Tsukaguchi Honmachi, Amagasaki City Mitsubishi Electric Corporation Itami Works (72) Inventor Yoshihiro Jizo Tsukaguchi, Amagasaki City 8-1-1 Honmachi Mitsubishi Electric Corporation Itami Works

Claims (2)

[Claims] 1. A superconducting coil made of a wound superconducting wire, an inner vessel for accommodating the superconducting coil, and a low electric resistance material provided on the surface of the inner vessel for traveling. In a superconducting magnet that is a power source of a traveling device that generates an AC magnetic field due to the thickness of the low electric resistance material, the order component of the AC magnetic field that maximizes the eddy current loss of the inner vessel is the traveling. A superconducting magnet that is thicker than the skin depth at the frequency that corresponds to the maximum speed of the device. 2. A superconducting coil made of a wound superconducting wire, an inner vessel for housing the superconducting coil, and a low electric resistance material provided on the surface of the inner vessel for traveling. In a superconducting magnet that is a power source of a traveling device that generates an AC magnetic field, the thickness of the low electrical resistance material is the order component of the AC magnetic field that maximizes the eddy current loss of the inner vessel, A superconducting magnet, which is thicker than a skin depth at a frequency corresponding to a maximum speed of a traveling device and is twice the skin depth or less.