JPS623561B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting magnet in which a superconducting coil is immersed in liquid helium.

In recent years, the development momentum for nuclear fusion devices has been increasing, but it is said that magnets for plasma confinement will not be realized at the stage of practical reactors unless they are made superconducting. In other words, with a normal copper coil, the excitation power exceeds the output of the furnace, so a lossless superconducting magnet is absolutely necessary.

The development of superconducting magnets for nuclear fusion devices begins with toroidal magnets, which are easy to start with, but the size of these magnets exceeds 10 m in length in experimental reactors, and reaches 20 m in commercial reactors, and the generated magnetic field is 8 to 12 Tesla. It is said to require a high magnetic field. The superconducting magnet, which is said to be the world's largest hydrogen bubble chamber for high-energy physics research achieved using conventional technology, has a diameter of about 4 meters and a magnetic field of about 3 to 4 Tesla, so a significant leap forward in technology is required. The main technical problems are a decrease in cooling characteristics and an increase in electromagnetic stress as the magnet becomes larger.

1 to 3 show cross sections of different conventional annular superconducting magnets.

Figure 1 shows a structure that increases the rigidity of the magnet against electromagnetic force. A groove is cut in a stainless steel disc 1, and a hollow superconducting conductor 2 is buried in this groove with electrical insulation 3 applied. . A dashed line 4 indicates the position of a bolt that fastens the disc 1. This structure is strong against the hoop force acting on the conductor 2 and the falling force between the coils when used as a toroidal coil.
Although attractive, so-called immersion cooling, in which the device is cooled by immersing it in liquid helium, is difficult to cool due to its structure, and is suitable for forced cooling in which liquid helium is passed inside as a hollow conductor.

FIG. 2 shows pancake-shaped coils 5 made of superconducting conductors 2 arranged in the central axis direction, inter-coil spacers 6 arranged radially between each coil 5 to ensure electrical insulation and cooling grooves 6a. is stored in a liquid helium container 7 and immersed in liquid helium (not shown). This structure is strong against electromagnetic force in both the circumferential direction and the axial direction, and the evaporation bubbles of liquid helium are released to the outer periphery of the coil 5 along the radially arranged spacers 6 between the coils, so the cooling is also comparable. It is suitable for immersion cooling.
However, there is a concern that the evaporation bubbles from below the coil 5 will adversely affect the cooling of the upper coil 5, which is particularly a problem for large coils for nuclear fusion devices. In addition, since the superconducting conductor 2 is rolled into a pancake shape, it is preferable that the superconducting conductor 2 is rectangular, but in this case, it is difficult to secure a cooling space on the long side of the conductor 2 for electromagnetic force support and electrical insulation, which limits the cooling circumference. There is. Also,
In the pancake-shaped coil 5, it is difficult to change the cross-sectional shape of the coil 5, and the connection portion (not shown) of the conductor 2 must also be located inside or outside the coil 5. When the length of the superconducting conductor 2 is limited due to manufacturing capacity, the position of this connection becomes a problem.

In order to solve these problems, the conductor 2 is made into a cylindrical coil 8, and this is constructed in multiple layers with a spacer 6 between the coils interposed therebetween, as shown in FIG. Since the vertically long superconducting conductor 2 is wound into a cylindrical shape, a connection part (not shown) is provided at the end in the axial direction of the coil, and although not shown, spacers are also placed between the conductors in the adjacent part of the conductor 2 for insulation. and ensure cooling grooves. In this case, since the long side of the conductor 2 is also cooled, the cooling circumference is improved. However, the evaporation bubbles of liquid helium have a negative effect on the cooling of other parts.
This is similar to the case of the pancake-shaped coil 5 shown in FIG. 2, and since the cooling grooves 6a have many horizontal parts, escape of evaporation bubbles is actually worse than in the pancake coil 5. Further, since the electromagnetic force is transmitted to the container 7 via the inter-coil spacer 6, a gap is likely to be formed between the coil 5 and the inter-coil spacer 6, making it difficult to reliably support the force.

The present invention has a coil structure in which the evaporation bubbles of liquid helium do not remain and are easily separated from the coil and do not adversely affect other coil parts, and there are few gaps between the coils, making it strong and easy to assemble the winding. The purpose of the present invention is to provide a superconducting magnet that has the following properties.

An embodiment of the present invention will be described below with reference to FIGS. 4 to 7.

In this embodiment, it is made of stainless steel (reinforced plastic reinforced with glass fibers may also be used), which has a ring shape with a groove 9 on the end surface, and one end is larger in diameter than the other, that is, one end is slightly open in the shape of a flap. A winding frame 10 is used. The superconducting conductor 2 is wound around the outer periphery of the winding frame 10 with a conductive spacer 12 having a protrusion 11 on the surface and an insulator 13 interposed therebetween to form a cylindrical coil 14. On the outer periphery of this cylindrical coil 14, a cooling groove 6a is formed through which air bubbles escape by interposing an inter-coil spacer 6 from one end of the cylinder to the other. The superconducting conductor 2 is also wound around this. This process is repeated to obtain the desired number of stages, which is then stored in the liquid helium container 7. The screws 16 are used to attach the inter-coil spacer 6 to the winding frame 10. The cooling groove 6a is surrounded by the superconducting conductor 2 at the bottom, the inner peripheral surface of the winding frame 10 at the top, and the spacer 6 at the side. The direction of the evaporation bubbles flowing through the cooling groove 6a is indicated by an arrow in FIG. 6, but since the coil 14 has a tufted shape, the flow direction of the evaporation bubbles is reversed at the lower side of the coil 14, so a deflector (not shown) is used. The evaporation bubbles may be guided by

In this way, since the cylindrical coils 14 wound around the wrapper-shaped winding frame 10 are stacked one on top of the other, the cylindrical coils 14 fit well together, and a wedge is also driven in between the container 7 and the entire coil. has high rigidity, and the electromagnetic force of the coil is reliably transmitted to the container 7.
Retained. Furthermore, the winding frame 10 is inclined with respect to the vertical direction, and the inter-coil spacer 6 is connected to the superconducting conductor 2.
Since the cooling grooves formed by the inter-coil spacers 6 are inclined toward the ends of the cylindrical coils 14, the cooling grooves formed by the inter-coil spacers 6 are inclined toward the ends of the cylindrical coils 14. The evaporated bubbles do not remain and are discharged to the side of the coil 14, forming the winding frame 10.
It escapes to the upper part through the groove 9 on the end face of. Moreover, since the interconductor spacer 12 has the protrusion 11 and the liquid helium is brought into contact with the side surface of the conductor 2, the heat transfer characteristics are further improved. Such a structure is
Particularly in a large vertical coil for a nuclear fusion device, the axial length of the coil does not increase so much even if its major axis increases, so it is particularly effective. This is because, in general, in boiling liquid helium cooling in a narrow cooling groove, the longer the vertical length of the cooling groove, the lower the cooling characteristics.

Next, another embodiment shown in FIG. 8 will be described.

This is similar to FIG. 4 in that the winding frame 10 is made into a flat shape, but when the central axis 17 is made horizontal,
The upper and lower slopes of the winding frame 10 are made almost parallel, so that the discharge of generated evaporation bubbles is rectified in the same direction both above and below the coil. In other words, the entire winding frame 10 is tilted at approximately the same angle, and the winding frame 10 is slightly tilted at approximately the same angle.
By opening one side in the shape of a flap, the fitting of the coil is improved and the evaporation bubbles are completely rectified to one side. Others are shown in Figures 4 to 7.
Since it is the same as the embodiment shown in the figure, the explanation will be omitted.

Incidentally, in the present invention, a plurality of coil groups may be stored in the same container 7, or a groove may be formed on the inside or outside of the winding frame 10 without using the inter-coil spacer 6, and this may be used as a cooling groove. 6a may be substituted and a perforated insulating plate may be inserted to discharge evaporation bubbles, etc., and is not limited to the embodiments described above and shown in the drawings, without changing the gist thereof. Of course, various modifications can be made within the scope of the invention.

As explained above, according to the present invention, the following effects can be obtained.

(1) The rigidity of the magnet can be increased to effectively transmit and support electromagnetic force.

(2) The evaporation bubbles of liquid helium do not accumulate and are rectified at the axial end of the coil, resulting in good heat transfer.

(3) The dimensions and configuration of the superconducting conductor can be selected relatively freely. In other words, unlike a pancake coil, there is no need to overwrap the conductor, and because it is wound directly onto the winding frame, the electromagnetic force that the conductor itself receives is small.
Free configuration.

(4) The connection part of the superconducting conductor can be provided at any position on the coil. In other words, if it is a pancake coil,
Although it is difficult to provide a connection part inside the pancake, we made it into a cylindrical coil and wound it around the winding frame.
Even if a connection part is provided in the middle of the cylinder, it does not affect the coil radial dimension.

(5) The coil assembly is easy, and the required dimensional accuracy can be relatively relaxed.

[Brief explanation of the drawing]

1 to 3 are sectional views of essential parts showing different conventional superconducting magnets, and FIG. 4 is a sectional view showing an embodiment of the superconducting magnet of the present invention.
Fig. 5 is a sectional view showing only the upper side of the coil, Fig. 6 is an enlarged perspective view with a cutaway of the main part thereof, Fig. 7 is a perspective view of the upper half of the coil with a partial cutaway, and Fig. 8 shows another embodiment. FIG. 2...Superconducting conductor, 6...Spacer, 6a...
Cooling groove, 10... Winding frame, 11... Protrusion, 12...
Insulator, 14... Coil, 17... Central axis.

Claims (1)

[Scope of Claims] 1. A plurality of superconducting conductors wound in a cylindrical shape are stacked and fitted onto a ring-shaped winding frame with one side open in the shape of a flap, and between the fitting surfaces there is a ring-shaped frame that is oriented toward the end of the cylinder. A superconducting magnet characterized by having a cooling groove through which evaporation bubbles escape and immersing it in liquid helium. 2. The superconducting magnet according to claim 1, wherein an insulator having protrusions is interposed between the layers of the superconducting conductor so that the liquid helium also comes into contact with the side surfaces of the superconducting conductor. 3. The superconducting magnet according to claim 1 or 2, characterized in that the winding frame is inclined upward and downward in substantially the same direction when its central axis is horizontal.