JP2600195B2 - Method of flowing permanent current to superconducting coil and superconducting magnet device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for applying a permanent current to a superconducting coil, and a magnet device using the superconducting coil.

<Conventional technology> Magnets utilizing a magnetic field obtained by passing a permanent current through a superconducting coil, so-called superconducting magnets, have been conventionally used mainly in MRI apparatuses, and are mainly air-core type and have many thin wires. It has been put to practical use for generating a wound strong magnetic field.

When using ceramic superconductors, which have recently attracted attention for realizing room-temperature superconductors, for such applications, it is difficult to make them thinner, so it is necessary to pass a large current as a small number of turns. Then, because of its small size, it has not been put to practical use.

By the way, a magnet used for precision measurement, such as an electromagnetic force generator for an electromagnetic force balance type electronic balance, does not require a very large magnetic field, but rather the stability of the magnetic field created by a superconducting magnet against temperature is more important. It is. Therefore, if a ceramic superconductor is simply formed in a ring shape, a permanent current less than its critical current is passed, and a magnetic field of about several thousand gauss is obtained by using a magnetic circuit such as a yoke, it is immediately applicable to this application. It is expected that effective results will be obtained.

Here, a circuit and a method as shown in FIG. 3 have conventionally been adopted as a method of passing a permanent current to the superconducting coil, in other words, as a method of magnetizing the superconducting magnet. That is, a DC power supply 34 is connected to a superconductor circuit section 33 having a superconducting coil 31 and a superconducting switch 32 by a switch 35 and a current limiting resistor 36.
Connect through. Also, a resistor 37 is inserted in parallel as needed. In such a circuit, when the switch 35 is closed while the superconducting switch 32 is open, the DC power supply 34
, A current flows to the superconducting coil 31 through the current limiting resistor 36. When the superconducting switch 32 is closed in this state, a permanent current flows through the closed superconducting circuit section 33 including the superconducting coil 31 and the superconducting switch 32. The resistor 37 is used to prevent a high voltage from being generated when the superconducting switch 32 is opened or the superconducting state is broken and magnetic energy is released, thereby preventing dielectric breakdown and focal loss. It can be omitted for small capacity devices. The superconducting switch 32 can be turned ON / OFF by selecting a superconducting state and a normal conducting state by a method of mechanically contacting and separating from each other, and by selecting a superconducting state and a normal conducting state by a magnetic field and temperature.
The F method is used.

When an open magnetic field space is required as an actual superconducting magnet, a plurality of superconducting coils 31a and 31b are connected to a series as shown in FIG. There is also.

<Problems to be Solved by the Invention> As described above, a superconducting magnet using superconducting ceramics or the like is highly likely to be realized in the field of precision measurement and can be extremely effective. When the conventional method described above is adopted, a superconducting switch and a relatively large DC power supply are required. for that reason,
When a superconducting magnet is delivered to the user and once loses its function as a magnet due to a normal conduction state due to an increase in ambient temperature, etc., it is necessary to provide the function of the magnet again, that is, re-magnetization is troublesome. At the same time, disadvantages requiring large costs are expected.

An object of the present invention is to provide a method for easily passing a permanent current to a superconducting coil without the need for a superconducting switch or a large current source, and to easily magnetize and re-magnetize using the method. An object of the present invention is to provide a superconducting magnet device suitable for use in a balance or the like.

<Means for Solving the Problems> The first invention is an invention of a method of flowing a permanent current to a superconducting coil, and its configuration will be described with reference to FIG. 1 or FIG. 2 corresponding to the embodiment. After the superconducting coil 1 is brought into a normal conducting state by heating or applying a magnetic field, a magnetic flux B in a predetermined direction along the central axis is formed inside the superconducting coil 1, and the superconducting coil 1
Is returned to the superconducting state, and then the above-mentioned magnetic flux B is removed.

The second invention is a superconducting magnet device used directly for carrying out the first invention. As shown in FIG. 1 corresponding to the embodiment, a superconducting coil 1 and a superconducting coil 1 are arranged close to the superconducting coil 1. A beam 4 capable of heating the superconducting coil 1 by power supply to at least partially bring the superconducting coil 1 into a normal conducting state, and a pole piece made of a ferromagnetic material disposed inside the superconducting coil 1 along a central axis thereof. 2 and a magnetic circuit comprising a yoke 3 disposed so as to surround the outside of the superconducting coil 1, and wound coaxially with the superconducting coil 1 to form a magnetic flux in a predetermined direction in the magnetic circuit by power supply. It is characterized by having the coil 5 obtained.

<Operation> The superconducting coil 1 is heated by power supply to the heater 4 or the like.
At least a part of the superconducting coil 1 is in the normal conducting state by passing a current through the coil 5 or sandwiching the superconducting coil 1 from outside with the magnetizing magnets 6a and 6b. A magnetic flux B can be formed in the direction of the central axis. Next, when the superconducting coil 1 is returned to the superconducting state by preventing power supply to the heater 4 and the magnetic flux B is removed, a permanent current flows through the superconducting coil 1 by electromagnetic induction.

<Example> An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing the configuration of an embodiment of the present invention, in which (a) is a longitudinal sectional view at the center and (b) is a plan view of the superconducting coil 1.

Inside a superconducting coil 1 formed by firing a superconducting material such as ceramics in a ring shape, a pole piece 2 made of a ferromagnetic material is disposed at the center thereof. The yoke 3 is housed in the yoke 3. The axial length of the pole piece 2 is the superconducting coil 1
Longer than the axial length (ring width) of the superconducting coil 1
Larger than the large diameter portion 2a.
Are formed.

Inside the yoke 3, a coil 5 of a normal conducting material wound coaxially with the superconducting coil 1 is disposed between the inner peripheral surface of the superconducting coil 1 and the outer peripheral surface of the pole piece 2. . In addition, as shown in FIG.
Has a heater 4 wound therearound. Both ends of the heater 4 and the coil 5 are respectively led out of the apparatus, and are connected to a DC power source E ₁ and a switch, respectively.
S ₁ , or DC power supply E ₂ and switch S ₂ .

In the above configuration, a permanent current can flow through the superconducting coil 1 in the following procedure.

1 (a), (b), the direct current through the heater 4 and the switches S ₁ or S ₂ in the coil 5 Power
Connecting E ₁ or E _2.

First, heated by applying a current to the heater 4 by closing the switch S _1, at least a portion of the superconducting coil 1 was allowed to warm from normal use and normal conducting state. Then, closing the switch S ₂ in this state, an electric current is applied to the coil 5. This current forms a magnetic field, which forms a magnetic flux through a magnetic circuit formed by the pole piece 2 and the yoke 3. At this time, if only a part of the superconducting coil 1 is in the normal conducting state, the magnetic flux B can enter the inside of the superconducting coil 1.

To stop power supply to the heater 4 to open the switch S ₁ in a state in which the magnetic flux B is formed, by returning the superconducting coil 1 to the normal operating temperature, return the superconducting coil 1 in the superconducting state.

Then open the switch S _2, remove the magnetic flux B. here,
When the magnetic flux B decreases, an electromotive force is generated in the superconducting coil 1 by electromagnetic induction in a direction that hinders the decrease. However, since the superconducting coil 1 in the superconducting state has no resistance, eventually,
Current required to generate the same magnetic flux and the magnetic flux B which had been formed before opening the switch S ₂ flows to the superconducting coil 1. That is, a permanent current flows through the superconducting coil 1, and thereafter, a magnetic flux due to the permanent current flowing through the superconducting coil 1 is formed as a magnetic path in a magnetic circuit formed by the pole piece 2 and the yoke 3. The strength of this magnetic field is determined by the magnitude of the permanent current, and a magnet with extremely low temperature dependence can be obtained, making it a magnet suitable for precision measurement applications such as electronic balances.

Here, since the coil 5 may be made of a material such as a copper wire, a large number of fine wires can be wound. Therefore, a large magnetic field can be formed by flowing a relatively small current, and a magnetic field equal to the magnetic field is formed in the superconducting coil 1. since the permanent current flows, the DC power source E ₂ I present coupled with the magnetic circuit may be of small scale.

When the magnetic flux B is formed, if the upper opening of the yoke 3 is covered with a ferromagnetic short piece or the like, the magnetic resistance is further reduced and the magnetizing current can be further reduced.

FIG. 2 is an explanatory view of another embodiment of the first invention. In this example, the magnetic flux B is formed by applying a current to the coil 5 in the previous example, whereas the magnetic flux B is formed by sandwiching the superconducting coil 1 between the magnetizing magnets 6a and 6b separately from the outside. Is different. That is, after at least part of the superconducting coil 1 is brought into a normal conducting state, the magnetizing magnet 6
A magnetic flux B is formed by sandwiching the superconducting coil 1 so that the magnetic poles a and 6b face each other. The other procedure is the same. To remove the magnetic flux B, the magnets 6a, 6
b may be removed.

In the first invention, as a method of bringing at least a part of the superconducting coil 1 into a normal conducting state, a method of applying a magnetic field at a critical point or higher may be adopted in addition to a method of exceeding a critical temperature by heating.

In order to apply the superconducting magnet device of the second invention to an electromagnetic force generator such as an electronic balance, for example, in FIG. 1 (a), the outer peripheral surface of the large diameter portion 2a of the pole piece 2 and the yoke 3
A force coil, which is movable in engagement with a plate or the like and in which a control current is passed by a servo mechanism or the like, is disposed in a ring-shaped static magnetic field space formed on the inner peripheral surface of the plate, and acts on the plate or the like. What is necessary is just to comprise so that a load may be measured from the force coil electric current required to generate | occur | produce the electromagnetic force balanced with the load. However, the shape of the magnetic circuit is not limited to that shown in FIG. 1 (a), and various applications such as those used in known electromagnetic force generators using permanent magnets can be applied. Needless to say.

Further, as the material of the superconducting coil 1 constituting the superconducting magnet device, any material can be used in addition to a fired body of ceramics or the like, but one winding is sufficient for precision measurement of an electronic balance or the like. Therefore, it is particularly suitable for using a ceramic superconductor.

<Effects of the Invention> As described above, according to the present invention, a permanent current can flow through a superconducting coil without a current flowing directly from a current source. A superconducting magnet can be easily obtained without preparing. Further, according to the superconducting magnet device of the present invention, the heater 4
A power supply E ₁ for heating, it is possible magnetized at any time by simply providing a small DC power source E ₂ for supplying a current to the coil 5,
In particular, remagnetization can be easily and inexpensively performed at the time of demagnetization due to an accident, which is expected when a room-temperature superconducting material is used, and the effect is large for practical use. When this superconducting magnet device is used for precision measurement applications such as electronic balances, extremely high-precision measurement results are obtained because the temperature dependence of the magnetic field strength is minimal and the magnetic leakage due to the presence of the pole piece and yoke is small. Is obtained.

[Brief description of the drawings]

FIG. 1 is a structural diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of another embodiment of the method of the present invention, FIG. 3 is an explanatory diagram of a conventional method of passing a permanent current to a superconducting coil, and FIG. It is a figure showing the example of the conventional superconducting magnet. 1 ... superconducting coil 2 ... pole piece 3 ... yoke 4 ... heater 5 ... coil

Claims (4)

(57) [Claims] A superconducting coil is heated or a magnetic field is applied so that at least a part of the superconducting coil is in a normal conducting state, and a magnetic flux in a predetermined direction along a central axis is formed inside the superconducting coil. And returning the superconducting coil to the superconducting state in that state, and then removing the magnetic flux. 2. A superconducting coil, a heater disposed in close proximity to the superconducting coil, and capable of heating the superconducting coil by power supply to at least partially attain a normal conducting state; A magnetic circuit composed of a ferromagnetic material pole piece disposed along the center axis thereof and a ferromagnetic material yoke disposed so as to surround the outside of the superconducting coil; Wound around
A superconducting magnet device comprising a coil capable of forming a magnetic flux in a predetermined direction in the magnetic circuit by feeding power. 3. The superconducting magnet device according to claim 2, wherein said superconducting coil is formed of a normal temperature superconducting material. 4. The superconducting coil according to claim 2, wherein said superconducting coil is a ring-shaped fired body.
The superconducting magnet device according to the paragraph.