JP3147577B2 - Superconducting magnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is provided to suppress a temperature rise due to an AC loss of a superconducting magnet, particularly a superconducting coil, in which an electric current used for an energy storage device or a superconducting transformer is changed with time. Related to cooling ducts.

[0002]

2. Description of the Related Art In order for a superconducting magnet to maintain a superconducting state, it is required that temperature, current, and generated magnetic flux density are each smaller than a critical value. These critical values are critical temperature, critical current, and critical magnetic flux density, respectively. is called. temperature,
The superconducting state is maintained only when both the current and the generated magnetic flux density are below the respective critical values, and when one exceeds the critical value, the transition from the superconducting state to the normal conducting state occurs, so-called quench occurs. I do. When the quench occurs, the magnetic energy stored in the superconducting magnet is released as Joule heat due to the resistance of the superconducting wire in a normal conducting state, causing a large amount of expensive liquid helium as a refrigerant to evaporate. In addition, the temperature of the superconducting wire constituting the superconducting magnet may increase due to the above-described Joule heat, which may cause burnout. For these reasons, quench is well known to be detrimental to superconducting magnets.

[0003] In recent years, superconducting magnets have been actively applied to AC applications, particularly pulse applications, in various places. It is known that when a time-varying current such as an alternating current or a pulse flows through a superconducting wire and a magnetic field is generated along with the current, a loss generally called an AC loss occurs. AC loss consists of three losses: hysteresis loss, coupling loss and eddy current loss. Hysteresis loss is proportional to the magnitude of the generated magnetic flux density and does not depend on its temporal change.Coupling loss is proportional to the square of the temporal change in the generated magnetic flux density, and does not depend on the magnitude of the current density. ing. The eddy current loss occurs in a normal conductor as a stabilizing material in which a superconducting element wire is embedded. The occurrence of these AC losses raises the temperature of the superconducting wire and increases the possibility of occurrence of quench when the temperature exceeds the above-mentioned critical temperature. Therefore, various measures are taken to reduce the AC loss.

One is a method of reducing hysteresis loss. The hysteresis loss has a characteristic that it is proportional to the diameter of the superconducting element wire constituting the superconducting wire in addition to the magnitude of the generated magnetic flux density. Therefore, the superconducting element wire is made as thin as possible to reduce the hysteresis loss. Next, a method of reducing the coupling loss is to reduce the twist pitch as much as possible because the coupling loss is proportional to the twist pitch that periodically changes the cross-sectional position of the superconducting element wire along the length direction. In addition, a structure in which a superconducting wire is embedded in a stabilizing material is generally adopted in order to allow a current to pass when the superconducting wire is quenched. Is inversely proportional to the resistivity. Therefore, in order to reduce the coupling loss and the eddy current loss, a metal having a high resistivity, for example, a copper-nickel alloy may be used as the stabilizing material. However, if a metal with too high resistivity is used as the stabilizing material, the generated heat and temperature rise will increase when the superconducting wire is quenched and current flows through the stabilizing material,
Because of the problem that the risk of burning the superconducting wire increases, it is not possible to easily use a stabilizing material having a high resistivity. In particular, the stabilizing material of the superconducting wire of the superconducting magnet having a large conduction current of 1 kA or more is actually limited to copper or aluminum which is a good conductive metal.

Therefore, a superconducting wire having a three-layer structure in which the periphery of the superconducting wire is covered with copper and the space between the wires covered with copper is further covered with a copper-nickel alloy as a metal barrier may be adopted. However, even if the superconducting element wire is made thinner or a three-layer structure is adopted, there is a limit in reducing the AC loss. Therefore, in order to realize a superconducting magnet having a large value and capable of generating a magnetic flux density that changes rapidly with time, a spacing piece is provided between the layers of the superconducting windings that is parallel to the axis of symmetry and is evenly distributed in the circumferential direction. In addition, a configuration is adopted in which a cooling duct through which liquid helium or helium gas passes through a gap between adjacent spacing pieces is formed to actively cool the inside of the superconducting magnet to suppress a temperature rise due to AC loss.

FIG. 2 is a cross-sectional view of a conventional superconducting magnet taken along a plane perpendicular to the axis of symmetry, and FIG. 3 is a cross-sectional view taken along line AA of FIG. In these figures, the bobbin 1 and the superconducting coil 2 have a cylindrical shape, and the bobbin 1 has a cylindrical portion 11 around which the superconducting wire 20 is wound.
And a flange 12 provided at both ends thereof for fixing an end of the superconducting coil 2. Superconducting coil 2
Is composed of four layers. The superconducting wire 20 is wound two layers on the spacing piece 31 provided on the outer diameter surface of the cylindrical portion 11 of the winding frame 1 to form the inner diameter side coil 21. A spacing piece 32 is provided on the outer side, and two layers of outer diameter side coils 22 are formed on the outer diameter side. In this figure, the superconducting wire 20 is shown as a round wire, but may be a square wire. Also, in the case of a round wire, the cross-sectional dimension of the superconducting wire 20 is actually smaller than that shown in the figure, and the number of turns is much larger. The axis of symmetry 100 is shown in FIG.
And the center point of the concentric circle of the superconducting coil 2 and is a line running left and right in the center of the upper and lower cross-sections shown by the dashed line in FIG.

There is a gap between the brim portions 12 at both ends and the end portion of the superconducting coil 2, and an insulating plate 33 is inserted as a spacing piece in this portion. Radial duct 4 through which fluid can flow
3 are formed. Therefore, the cooling ducts 41, 4
2 is connected to the outside via these radial ducts 43.

In FIG. 3, the superconducting magnet is shown as being installed horizontally so that the magnetic field is generated in the horizontal direction. However, the superconducting magnet may be installed vertically so that the magnetic field is generated in the vertical direction depending on the application. FIG. 4 is a perspective view of a part of the bobbin 1 of FIG. In this figure, the spacing pieces 31 are in the shape of a strip, and are attached to the cylindrical portion 11 in predetermined equal numbers so as to be parallel to the axis of symmetry. The radial duct 43 provided on the insulating plate 33 is also provided radially so as to be parallel to the radial direction. Of course, the cooling duct 41 and the radial duct 43 are arranged so as to communicate with each other. The cooling duct 42 not shown in this figure is located on the outer diameter side of the spacing piece 31 as can be seen from FIG. One cooling duct 41 and one spacing piece 31 are provided so that both cooling ducts 41 and 42 communicate with the radial duct 43.
Two radial ducts 43 are provided.

The superconducting magnet is used in a state where it is housed in a liquid helium container and immersed in liquid helium as a cooling medium. Therefore, in the normal case, the cooling duct 41,
The liquid duct 42 and the radial duct 43 are filled with liquid helium. Since the liquid helium maintains the boiling temperature, when an AC loss occurs in the superconducting coil 2, the liquid helium evaporates and is absorbed by the heat of vaporization, and helium gas is generated instead. The helium gas is discharged outside the superconducting magnet through the cooling ducts 41, 42, 43.

[0010]

When the superconducting magnet is installed vertically, the cooling ducts 41 and 42 are oriented vertically, and the helium gas generated in the cooling ducts 41 and 42 depends on the difference in specific gravity from liquid helium. There is no problem because buoyancy is generated, and the buoyancy moves upward and is discharged outside the superconducting magnet through the radial duct 43. However, in the case of a horizontal installation, even if buoyancy occurs, a phenomenon occurs in which the helium gas cannot move upward and stays in the cooling ducts 41 and 42.
As described above, since the superconducting wire 20 is cooled by evaporating liquid helium, if a part of the helium gas stagnates, the temperature of the superconducting wire 20 in that portion is not directly in contact with the liquid helium, and quench may occur. There is a problem that the property becomes high.

An object of the present invention is to solve such a problem and to provide a superconducting magnet in which helium gas does not stagnate in cooling ducts 41 and 42 that cause quench.

[0012]

According to the present invention, in order to solve the above-mentioned problem, a cylindrical winding frame and a superconducting wire are arranged on the outer diameter side of the winding frame in a direction of a symmetric axis to a predetermined number of turns. In a superconducting magnet in which a predetermined number of superconducting coils are formed by laminating layers formed by winding only in the radial direction, at least one layer provided between the winding frame and the innermost layer or an adjacent layer Is formed at a predetermined angle to a straight line parallel to the axis of symmetry.

[0013]

In the structure of the present invention, the superconducting coil is generated by forming the cooling duct provided between the winding frame and the innermost layer or the adjacent layer obliquely to a straight line parallel to the axis of symmetry. The generated helium gas is absorbed by the heat of vaporization of the liquid helium, and the generated helium gas can rise along the oblique cooling duct, so that the helium gas does not stay locally.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
FIG. 1 is a perspective view showing a winding frame showing an embodiment of the present invention and a part of a spacing piece provided on the winding frame.
The same members are denoted by the same reference numerals, and detailed description is omitted. Also, members similar to those in FIG. 4 are denoted by a subscript A to indicate that they are similar. The spacing piece 31A is arranged obliquely at a certain angle with respect to the axis of symmetry, and has a shape in which strips are spirally attached. As described above, since the FRP is used for the spacing piece 31A to secure the mechanical strength, it is usually difficult to bend a strip-shaped plate into a spiral shape as shown in the figure. However, it can be easily manufactured by obliquely cutting a cylindrically shaped FRP at a desired angle.

By making the spacing piece 31A helical, the cooling duct 41A formed between the adjacent spacing pieces 31A also becomes helical, and its circumferential position changes according to the axial position. Therefore, the helium gas generated locally can move upward along the spacing piece 31A. Therefore, the helium gas does not stay locally. When the stagnation of the helium gas is eliminated, the superconducting wire 20 shown in FIG. 3 is always cooled directly in contact with the liquid helium, so that the possibility of occurrence of quench due to local overheating is significantly reduced.

In FIG. 1, the spacing piece 32 and the cooling duct 4 shown in FIG.
Although the spacing piece 32A and the cooling duct 42A corresponding to 2 are not shown, the spacing piece 42A is arranged so as to be spiral in parallel with the spacing piece 41A. Therefore, the sectional view perpendicular to the axis of the superconducting magnet corresponding to FIG. 1 is similar to FIG. 2, and the circumferential positions of the spacing pieces 41A and 42A corresponding to the spacing pieces 41 and 42 differ depending on the axial position where the section is taken. Only.

Spacing pieces 41A, 42A and cooling duct 31
The values of the widths of A, 32A, the number in the circumferential direction, the angle with respect to the axis of symmetry, and the like are determined according to the cross-sectional dimensions of the superconducting wire 20, the number of layers, the number of turns, the radius, and the like. is there.

[0018]

According to the present invention, as described above, the helium gas generated by evaporating the liquid helium is formed in the oblique cooling duct by forming the cooling duct obliquely with respect to the axis of symmetry. Helium gas does not stagnate locally, so the superconducting wire is always in direct contact with liquid helium, which can suppress local temperature rise and result in quench The effect is that the possibility of the superconducting magnet becomes highly reliable and the reliability becomes high.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a winding frame and a part of a spacing piece cut out and showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a plane perpendicular to a symmetry axis of a conventional superconducting magnet.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a perspective view showing a part of a winding frame and a spacing piece shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 winding frame 11 cylindrical portion 12 flange portion 2 superconducting coil 21 inner diameter side coil 22 outer diameter side coil 31A spacing piece 41A cooling duct 33A insulating plate 43A radius duct

Claims (3)

(57) [Claims] A cylindrical winding frame and a layer formed by arranging superconducting wires on the outer diameter side of the winding frame in the direction of the symmetry axis and winding them by a predetermined number of turns in the radial direction to form a predetermined number of layers. In a superconducting magnet in which a superconducting coil is formed, at least one layer of cooling duct provided between the winding frame and the innermost layer or an adjacent layer is inclined at a predetermined angle with respect to a straight line parallel to the axis of symmetry. A superconducting magnet characterized in that it is formed on a superconducting magnet. 2. The superconducting magnet according to claim 1, wherein the spacer is made of an insulating material. 3. The superconducting magnet according to claim 2, wherein the spacer is made of glass fiber reinforced synthetic resin.