JPH08148327A - Superconducting magnet and particle accelerator with the superconducting magnet - Google Patents

Abstract

PURPOSE: To enhance the quench characteristics while reducing power consumption by employing a superconductor having such cross-section as reducing the coupling loss between the superconducting strands while taking account of the effect of correlation, between the aspect ratio of the cross-section of superconductor and the magnetic field and the inner resistance of the superconductor, on the coupling loss. CONSTITUTION: The superconductor 1 in the cross-section 2 of a superconducting electromagnet comprises a set of a plurality of superconducting strands 4 stranded with a predetermined transposition where superconducting filaments are arranged in a stabilization material. Assuming the flux density 3 of a magnetic field, to which the superconductor 1 is exposed, has a component Ba normal to the longitudinal direction of the superconductor 1 and a component Bb in parallel with the longitudinal direction of the superconductor 1 and the electric resistances in these two directions are ρa and ρb , respectively, the aspect ratio b/a of the cross-section of the conductor 1 is previously designed to minimize the total loss Pa+Pb between the superconducting strands thus reducing the total loss Pa+Pb between the superconducting strands 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting conductor which is a main component of a superconducting magnet, and in particular, a superconducting conductor formed by twisting the strands at a predetermined pitch in order to reduce the coupling loss between the strands. AC superconducting power used for particle deflection dipole magnets such as accelerators, particle converging quadrupole magnets, superconducting large solenoid devices, fusion poloidal coil pulse magnets, superconducting generators, transformers, etc. It is about equipment.

[0002]

2. Description of the Related Art Among the superconducting conductors of this type, as a production example of the one mainly characterized by being used for a particle accelerator, as a production example of ICFA Proceedings of Workshop on AC Superconductivity, KE Broodings 92-
14 (1992) 100 to 108 (ICFAPr
oceedings of Workshop on AC SUPERCONDUCTIVITY, KEK
Proceedings 92-14December 1992 A).

Originally, superconducting magnets are roughly classified into two types according to the purpose of use. That is, an electromagnet that operates while maintaining a constant energizing current and an electromagnet that operates such that a varying magnetic field is provided by exciting and demagnetizing the electromagnet by changing the energizing current. In the latter, in the electromagnet that operates by changing the energizing current, especially in the superconducting magnet for alternating current characterized by being excited and demagnetized at a high speed, in the superconducting magnet that constitutes the superconducting magnet, the chains between filaments and strands in the superconducting conductor Induced current due to changes in the alternating magnetic field (This induced current is combined with the filament in the superconducting wire to form a loop,
It is conventionally called the coupling current. ) Of the asymmetric magnetic field, or due to the Joule heat generated by the generation of the coupling current (the loss due to this Joule heat is conventionally called the coupling loss) deterioration of the quench current and increase of the load of the refrigerator. As a means for solving the above, there are many examples in which an insulating coating layer is provided around the wire or the stabilizing material of the superconducting wire is covered with a metal having high electric resistance to interrupt the coupling current. , One of them is Shokoku Sho5
It is described in JP-A-3-56997.

In addition, the filaments are transpositioned at a predetermined pitch to make it more effective to interrupt the coupling current between the filaments, that is, between the filaments. There are many examples in which the asymmetric magnetic field and the coupling loss are reduced by more effectively blocking the coupling current. An example of a combination of two of these is Japanese Patent Publication No. 6
It is described in Japanese Patent Publication No. 4-24314. There, an alternating current is made to flow by devising the method of arranging the superconducting element wire and the high electric resistance metal or the low electric resistance metal in the superconducting conductor, or by twisting the element wire at a predetermined pitch. It describes a superconducting conductor with a relatively low AC loss that can be used both for the purpose and for the purpose of generating a magnetic field.

Further, by winding such that the wider surface of the cross section of the superconducting conductor is parallel to the flow direction of the magnet wire inside the superconducting electromagnet, fluctuation of interlinking magnetic field between filaments and strands in the superconducting conductor. Japanese Patent Publication No. 58-66311 discloses a method of reducing the induced current by the method, but it does not describe the aspect ratio of the cross section of the superconducting conductor itself and the effect of the correlation between this aspect ratio and the magnetic field on the coupling loss. No, it can be seen that it has not been considered.

In particular, in a superconducting magnet used in a device of a relatively large scale, such as a particle accelerator, a superconducting magnet is constructed in order to reduce the total amount of expensive superconducting conductors such as NbTi. It is desired to operate at an extremely high load factor (85% or more) for the short length characteristics of the superconducting conductor, and furthermore, when quenching occurs, a high heat load or a potential difference is locally applied to the superconducting conductor in the superconducting magnet. It is desired that all superconducting conductors within the superconducting magnet be operated at similar load factors to avoid possible damage.

Here, the load factor indicates a value defined as follows. In FIG. 4, the horizontal axis represents the magnetic field experienced by the superconducting conductor that constitutes the superconducting magnet, and the vertical axis represents the density of the current flowing in the superconducting conductor, that is, the cross-sectional area of the current flowing in the superconducting conductor. Indicates the value divided by. Line 8 represents the relationship between the magnetic field experienced by the superconducting conductor and the critical current density in that magnetic field. Further, the line 9 represents the relationship between the density of the current flowing in the superconducting conductor and the magnetic field generated at that time, and the point A represents the operating condition required for the superconducting conductor. Now, when the density of the current flowing through the superconducting conductor is increased from the required operating condition, the state of the superconducting conductor moves from the point A along the line 9 in the direction of the arrow in the figure, and the line 8 The current density reaches a critical state when the point A ′ is reached. Here, line segment OA and line segment O
The ratio of the length with A'is defined as the load factor. For the above reasons, in order to reduce the number of current introducing terminals by causing the inner layer and the outer layer to carry the same transport current, in a superconducting dipole electromagnet in which two layers of the inner layer and the outer layer are superposed and connected in the middle, The outer superconducting conductor has a higher current density, that is, a smaller cross-sectional area.
At the same time, the number of superconducting wires has been increasing in response to the demand for higher current as the performance of the equipment improves, and in a superconducting conductor wound in a flat wise manner, the bending radius is proportional to a / r. The thickness of the superconducting conductor cross section must be reduced in order to reduce the deterioration of the performance of the superconducting conductor due to the filament breakage caused by the strain at the end winding. The result is that superconducting conductors with a large aspect ratio are used.

The aspect ratios of the cross sections of the superconducting conductors of the world's main superconducting dipole magnets summarized in the above-mentioned document (T.F.A. Proceedings) are shown below.

-Tevatron of the United States about 6.2-Herla of Germany about 6.8-Rick of the United States about 8.3-Europe L Etch about 7.6 (for inner layer / planned) -Europe L Etch about 11 .5 (for outer layer / planned) ・ US SSC approximately 8.4 (for inner layer / plan discontinued) ・ US SSC approximately 10.1 (for outer layer / plan discontinued)

[0010]

By the way, in the particle accelerator, the beam life depends on the vacuum degree of the beam tube, the number of collisions should be large in order to accumulate events, and the power consumption should be small. For reasons such as good performance, it is required that the time for accelerating the particles to the required speed be short. Therefore, it is pointed out that the AC loss of the superconducting magnet is not negligible, as symbolized by the particle accelerator operated in the bipolar cycle for the sake of reduction of construction cost and location and space. Has been done. On the other hand, in terms of manufacturing, in order to match the required magnetic field shape and the cross-sectional shape required to obtain the magnetic field accuracy in the superconducting magnet, the thickness 2a of the superconducting conductor as shown in FIG. In addition to being twisted and molded to have a value (86% to 93%) smaller than twice the diameter d of the superconducting element wire (2d), a superconducting conductor carrying a large current acts on itself. In order to prevent quenching due to frictional heat when moving by force, a strong lateral pre-pressure is applied to the superconducting conductor during manufacturing. Is easily induced and the contact resistance between the superconducting wires becomes a small value, so that the coupling loss between the superconducting wires due to the cross-sectional shape of the superconducting conductor is accounted for in the AC loss of the superconducting magnet. That proportion that has also been pointed out that is larger.

Various measures have been taken to solve this problem. If the transposition pitch of the superconducting wire is shortened, there is a risk of filament breakage,
In a superconducting conductor that requires a rectangular cross-sectional shape, it is naturally difficult to set the twist pitch limit of the wire. By arranging a composite of high resistance metal such as CuNi in the stabilizing material of the superconducting element wire, the thermal properties of the stabilizing material, that is, thermal conductivity and heat capacity are not impaired,
A method of increasing only the electric resistance, a superconducting element wire whose surface is subjected to copper oxide blackening treatment, etc. is arranged in parallel with a normal superconducting element wire and twisted alternately in general.
The method called a), in which the surface of the superconducting element wire is plated with an alloy of silver and tin, is generally Stabilite.
The method called te) has been attempted to reduce the coupling loss between the superconducting wires.

The present invention has been made in view of the above technical background, and a first object thereof is to provide a superconducting magnet having a superconducting conductor having a cross-sectional shape in which the coupling loss between the superconducting element wires is small. It is in. A second object is to provide a particle accelerator using a superconducting magnet having a superconducting conductor having a cross-sectional shape with a small coupling loss between superconducting element wires.

[0013]

Means for Solving the Problems In order to achieve the first object, each means is constructed as follows.

That is, the first means is based on the variation of the interlinking magnetic field between the strands with respect to the uniform varying magnetic field applied perpendicularly to the superconducting conductor formed by bundling a plurality of superconducting element wires. A magnetic field is generated by winding a superconducting conductor formed by twisting the superconducting element wires at a predetermined pitch so that a coupling current does not easily flow. In a superconducting magnet, a value obtained by dividing the length of the wide side of the cross section of the superconducting conductor by the length of the narrow side (hereinafter referred to as “aspect ratio”) is taken into consideration between the superconducting element wires in consideration of the magnetic field distribution of the fluctuating magnetic field. It is characterized in that the superconducting conductor is wound so that it is partially selected so as to minimize the coupling loss.

A second means is an AC superconducting magnet based on the same premise as the first means, wherein the aspect ratio makes the absolute value of the fluctuating magnetic field orthogonal to the narrow side of the superconducting conductor to the wide side of the superconducting conductor. It is characterized in that the superconducting conductor is formed so as to be larger than a square root of a value obtained by dividing an absolute value of an orthogonal fluctuating magnetic field and smaller than twice the square root.

A third means is an AC superconducting magnet on the same premise as the first means, wherein the aspect ratio is such that the absolute value of the fluctuating magnetic field orthogonal to the narrow side of the superconducting conductor is set to the wide side of the superconducting conductor. The square root of the value obtained by dividing by the absolute value of the changing magnetic field orthogonal to each other, and the value obtained by dividing the electrical resistivity in the direction orthogonal to the wide side of the superconducting conductor by the electrical resistivity in the direction orthogonal to the narrow side of the superconducting conductor. It is characterized in that the superconducting conductor is formed so as to be larger than the square root of the multiplied value and smaller than three times the square root.

In the first to third means, the superconducting conductor may be formed by twisting a plurality of twisted wires at least once with the twisted superconducting element wires as a unit. In this case, it is preferable that the twisted superconducting element wire and the twisted strand of the superconducting element wire have the same twist direction. Further, the superconducting element wire undergoes a normal conduction transition, and an element wire made of a low-resistance metal that causes a current to flow when the energizing current is shunted from the superconducting element wire is arranged in parallel with the superconducting element wire, and A wire made of a resistance metal may be twisted in the opposite direction to the superconducting wire and the stranded wire. A member having a high resistivity may be further arranged in the central portion of the assembled stranded wire, or a metal having a higher resistivity may be combined in the superconducting wire or the wire made of the low resistance metal. You may arrange. As the arranged member having high resistivity, CuN is used.
A material containing at least one of i and CuSn as a main component can be used, and an insulating material made of synthetic resin can also be used. The metal having a high resistivity can be formed of a material containing at least one of CuNi and CuSn as a main component.

The fourth means is that the maximum load factor during operation of the AC superconducting magnet using the superconducting magnet is 85%.
It is characterized by the above settings.

Further, in order to achieve the second object, the fifth object
This means is characterized in that the AC superconducting magnets of the first to third means are used in the particle accelerator.

In this case, the AC superconducting magnet having an aspect ratio of 3 or less may be used, and an iron core may be provided. In addition, the generated magnetic field has a 2n-order component (n
Is a natural number). Further, this kind of particle accelerator is used for nuclear fusion, electric power storage, or physical property research.

The superconducting magnet is set to either a solenoid or a toroid, and the aspect ratio on both ends of the axis of the magnet in the magnetic field direction in the cross section of the superconducting magnet of either the solenoid or the toroid is the center of the axis of the magnet. It may be set to be smaller than the aspect ratio on the copy side. In addition, here, when the aspect ratio extends from 1 or less to 1 or more, the length of the side parallel to the reference is based on the longer side of the cross section of the superconducting conductor at the center of the magnet. And divide it by the length of the side that is not parallel and consider it as the aspect.

[0022]

The above-mentioned means are basically intended to minimize the AC loss of the AC superconducting conductor. The AC loss of a superconducting conductor for alternating current depends on its loss mechanism: hysteresis loss in the superconducting filament, eddy current loss in the normal conducting metal or stabilizing material, coupling loss between the superconducting filaments through the stabilizing material, and stabilization. It is roughly classified into the coupling loss between the superconducting wires through the material. Among them, regarding the coupling loss between the superconducting wires which is known to depend on the cross-sectional shape of the superconducting conductor, Campbell, A. M. Based on the consideration in Cryogenics (1982) 3 to 16 (Campbell, AM Cryogenics.JANUARY (1982) 3), the magnetic flux density B (hereinafter, the magnetic flux density is expediently limited by the notational limitation " B ).). For a superconducting conductor in which the transposition pitch of the superconducting element wire is Lp, if the average electrical resistivity between the superconducting element wires is ρ, the width of the superconducting conductor in the direction perpendicular to the magnetic flux density B is 2a and the magnetic flux density B is B. When the width of the superconducting conductor in the direction parallel to is 2b (see FIG. 1), the following equation is obtained. Denoting the coupling loss per unit volume calculated by the ^{P, P = (B 2 /} ρ) · {Lp 2/16 (a + b) 2} · ^{[a 2 + b 2 {(7a} 4 / 30b 4) + a 2 / 6b ² } + ab (2a ² / 3b ² )] (1) In this equation (1), the electrical resistivity between the superconducting element wires in the direction orthogonal to the narrow side of the conductor and the electrical resistivity in the direction orthogonal to the wide side of the conductor (assumed to be ρ _{a and} ρ _b , respectively) Treated as equal.

Now, considering the difference between ρ _{a and} ρ _b ,
As shown in FIGS. 1 and 2, consider a case where the superconducting conductor 1 is exposed to _a magnetic flux density B _{a in} a direction orthogonal to a narrow side of the conductor and a magnetic flux density B _{b in} a direction orthogonal to a wide side of the conductor. And the coupling losses P _{a and} P _b corresponding to the changes over time of the respective magnetic flux densities are as shown in equations (2) and (3).

[0024] ^{_{P a = B a 2 {Lp}} 2/16 (a + b) 2} · {(1 / ρ a) · (a 2 + 2a 3 / 3a + 7b 4 / 30b 2) + (1 / ρ b) (a 2 / 6} ··· (2) P b = B b 2 {Lp 2/16 (a + b) 2} · {(1 / ρ b) · (b 2 + 2b 3 / 3a + 7b 4 / 30a 2) + (1 / ^{_{ρ a) (b 2/6}} } ··· (3) is coupling loss between both of the superconducting wire, respectively P _a, P _b
Therefore, the total coupling loss between superconducting wires is P _a +
_Will be given by P _b . Therefore, the aspect ratio b / a of the cross section that approximately minimizes the total coupling loss P _a + P _b will be examined.

Considering a superconducting conductor having a cross-sectional shape such that 3a <b, P _{a and} P _b are respectively defined by the following (4)
And the equation (5) is approximated. These are P
Expressed in ^{_{a 'P b', P a}} '= B a 2 {Lp 2/16 (a + b) 2 · a 2 (1 / ρ a) + (1 / 6ρ b)} ··· (4) P b '= become ^{_{B b 2 {Lp 2/16}} (a + b) 2} · (7b 4 / 30a 2) (1 / ρ b) ··· (5). At this time, total coupling loss between the superconducting wires P _a + P
The minimum value of _b is as shown in equation (6).

[0026] ² B _a B _{b b} 2 _{[(7 / 30ρ b) {1} / ρ a) + (1 / 6ρ b)} ] ^{1/2 × {Lp 2/16 (} a + b) 2} ··· ( 6) The aspect ratio b / a of the cross section when this minimum value is obtained is given by the following equation (7).

B / a = ( B _a / B _b ) ^1/2 · {(30/7) (ρ _b / ρ _a +1/6)} ^1/4 (7) Further, equation (7) On the right side, ρ _{b is a} typical value
/ Ρ _a ≒ 1 and when, b / a = 1.5 (B a / B b) 1/2 a (8). In other words, it is possible to obtain the effect by making the aspect ratio _{b / a (B a / B} b) 1/2 <b / a <2 (B a / B b) 1/2 ··· (9) it can.

When ρ _b / ρ _a >> 1/6, b / a≈2.1 ( B _a / B _b (ρ _b / ρ _a ) ^1/2 ) ^1/2 ... (10 ), and the aspect ratio _{b / a, (B a /} B b (ρ b / ρ a) 1/2) 1/2 <b / a <3 (B a / B b (ρ b / ρ a) 1 The effect can be obtained by setting ^{/ 2} ) ^1/2 ... (11).

[0029]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is an explanatory view showing a sectional shape of a superconducting conductor of a superconducting dipole electromagnet for a particle accelerator according to an embodiment of the present invention, and FIG. 2 is a perspective view showing an appearance of the superconducting dipole magnet for a particle accelerator. In these figures, the superconducting conductor 1 in the cross section of the superconducting dipole electromagnet is made of an assembly in which a plurality of superconducting element wires 4 in which a superconducting filament is arranged in a stabilizing material are twisted in a predetermined transposition. The superconducting dipole electromagnet has an iron core 7, and each superconducting conductor is wound so as to bring the current close to an ideal cos θ distribution. As the stabilizer, for example, a low resistance metal such as copper or aluminum is used. In addition, the strand which becomes the stabilizing material is composed of a strand made of a low-resistance metal that causes a current to flow when the superconducting strand undergoes normal conduction transition and the energizing current is shunted from the superconducting strand, with respect to the superconducting strand. Are arranged in parallel with each other, and the wires made of a low resistance metal are twisted in the opposite direction to the superconducting wires and the assembled stranded wires.

The cross section 2 of the superconducting dipole electromagnet is formed by a group of superconducting conductors 1 through which a current for producing a central magnetic field 5 flows, and is exposed to different magnetic fields depending on the place. Therefore, consider a specific superconducting conductor 1 in the cross section of the electromagnet.

The superconducting conductor 1 in the cross section of the superconducting electromagnet is a superconducting element wire 4 in which a superconducting filament is arranged in a stabilizing material.
It is made up of an aggregate of a plurality of twisted strands in a predetermined transposition. This twist is formed by twisting a plurality of twisted wires at least once, using the twisted (hereinafter referred to as “twisted”) superconducting element wires as a unit. In that case, the twisted direction of the twisted superconducting element wire and the collective twisted wire of this superconducting element wire are the same. A component of the magnetic flux density 3 of the magnetic field to which the superconducting conductor 1 is exposed, which is perpendicular to the longitudinal direction (longitudinal direction) of the superconducting conductor 1, is B _a , and a component parallel to the longitudinal direction of the superconducting conductor 1 is B _b . Letting the electrical resistivities in these two directions be ρ _{a and} ρ _{b ,} respectively _, the cross-sectional aspect ratio b / a of the superconducting conductor 1 is set so that the coupling loss P _a + P _b between the superconducting element wires becomes the minimum (minimum By designing in advance so that the coupling loss P _a + P _b between the superconducting wires 4 can be reduced. here,
The value of ρ _b / ρ _a can be determined by calculation or measurement, and the value of B _a / B _b is known to be the maximum empirical field 6
The method of independently using the calculated value of the magnetic field to which the superconducting conductor 1 is exposed, and the method of calculating the magnetic field to which the individual superconducting conductors 1 forming the cross section of the electromagnet are exposed can be considered. In the latter case, the cross-sectional aspect ratio b / a of the superconducting conductor can be determined so as to minimize the total of the coupling loss P _a + P _b of the superconducting element wires 4 of the entire superconducting electromagnet.

Hereinafter, in the cross section of the superconducting dipole electromagnet,
Assuming that the superconducting conductor 1 is wound so that the current for producing the central magnetic field 5 has an ideal cos θ distribution, the coupling loss P _a + P _b between the superconducting element wires 4 of the entire superconducting electromagnet.
The cross-sectional aspect ratio b / a of the superconducting conductor 1 that minimizes the total of

In FIG. 3A, a portion indicated by reference numeral 21 is a cross section of the superconducting dipole electromagnet wound so that the current simulated in this evaluation has an ideal cos θ distribution, and FIG. The part indicated by reference numeral 22 in) indicates the layered current of the cos θ distribution used in the actual calculation.
For simplification, the superconducting dipole electromagnet is provided with an iron core 7, the magnetic flux density 3 of the magnetic field has only its Y component in the region where the superconducting conductor 1 is wound, and each superconducting conductor 1 is It is assumed that the winding is located radially with respect to the origin O. The winding density n of the superconducting conductor 1 for making the current have a cos θ distribution is defined by the angle θ from the X axis in FIG. 3B.
, N (θ) = (N / 2) cos θ (12) (N is the total number of turns), the coupling loss dP _a " _, dP between the superconducting element wires corresponding to each value of θ. _b ", ^{_{respectively, dP a" = {Lp 2}} /16 (a + b) 2} · · {(1 / ρ a) (a 2 + 2a 3 / 3b + 7a 4 / 30b 2) + (1 / ρ b) a 2 / ^{6} B y 2 (N /} 2) sin 2 θcosθdθ ··· (13) dP b "= {Lp 2/16 (a + b) 2} · {(1 / ρ b) (b 2 + 2b 3 / 3a + 7b 4 / ^{30a 2) + (1 / ρ} a) b 2/6} B y 2 (N / 2) cos 2 θdθ ··· (14) becomes, by summing them from theta = 0 to θ = π / 2 Get the total coupling loss.

[0035] That ^{_{is, P a "= ∫ 2 dP}} a" = (1/3) B y 2 (N / 2) {Lp 2/16 (a + b) 2} · {(1 / ρ a) (a 2 + 2a ^{3 / 3b + 7a 4 / 30b} 2) + (1 / ρ b) a 2/6} ··· (15) P b "= ∫ 2 dP b" = (2/3) B y 2 (N / 2) { ^{lp 2/16 (a + b} ) 2} · {(1 / ρ b) become ^{(b 2 + 2b 3 / 3a} + 7b 4 / 30a 2) + (1 / ρ a) b 2/6} ··· (16). However, B y is the Y component of the magnetic flux density.

The coefficients 1/3 and 2/3 in the above equations (15) and (16) are called the vertical magnetic field factor and the horizontal magnetic field factor for the superconducting conductor of the superconducting dipole electromagnet, respectively. It is a feature of the present invention that the cross-sectional aspect ratio b / a of the superconducting conductor is optimized by the magnetic field factor corresponding to the magnetic field distribution of each superconducting electromagnet.

The superconducting dipole electromagnet has been described above as an example. Generally, in a 2n-pole superconducting electromagnet, when the superconducting conductor 1 is wound so that the current has an ideal cos θ distribution, the above-mentioned longitudinal magnetic field factor, It is similarly shown that the lateral magnetic field factors are 1 / 3n and 2 / 3n, respectively.

FIG. 5 shows ρ _b / ρ _a = 1 of the total coupling loss (normalized loss) P _a "+ P _b " when the longitudinal magnetic field factor and the lateral magnetic field factor are 1/3 and 2/3, respectively. In the case of, the change of the aspect ratio b / a is shown. From this figure, the superconducting conductor 1 is wound so that the current has an ideal cosnθ distribution, and only the ideal component of the magnetic coil internal region is wound in the region where the superconducting conductor 1 is wound due to the effect of the iron core 7. , The cross-sectional shape of the superconducting conductor 1 of the existing superconducting electromagnet for particle accelerator (b / a
= 6 to 12), it can be seen that the coupling loss between superconducting element wires P _a "+ P _b " is large. In FIG. 5, the illustration is omitted when the aspect ratio b / a is about 8 or more.

FIG. 6 shows _a change in the value of the cross-section aspect ratio b / a which gives the minimum value of the coupling loss P _a "+ P _b " between the superconducting wires with respect to the change of ρ _b / ρ _a . Considering the value of ρ _b / ρ _a of the current superconducting electromagnet for particle accelerator as 1 or less, FIG.
As a result, the cross-sectional aspect ratio of the superconducting conductor that minimizes the sum of the coupling loss P _a "+ P _b " between the superconducting element wires is approximately 1 in consideration of the manufacturing and finished product shape restrictions. I can say.

That is, the fact that the aspect ratio is small means that a is relative to the bending radius r wound in a flatwise manner.
It means that the distortion at the end winding, which is proportional to / r, becomes large. As a countermeasure, we consider a superconducting conductor in which a member with high resistivity is placed in the center of the stranded wire. In this case, ρ
_It is considered that the value of _b / ρ _a becomes large. Ρ at this time
Considering the value of _b / ρ _a to be about 3 to 10, according to FIG.
Coupling loss P _a "+ P between superconducting wires when ρ _b / ρ _a > 1
_It can be seen that the optimum cross-sectional aspect ratio b / a of the superconducting conductor 1 that minimizes the sum of " _b " is about 1 to 2. The cross-sectional aspect ratio b / a that is actually adopted is the influence of the above strain, Considering the manufacturability and the cost, a slightly larger value of about 3 is desirable, which is 1/2 to any of the above-mentioned cross-sectional aspect ratios b / a of actual superconducting dipole electromagnets. The value is 1/4.
The member having a high resistivity is, for example, CuNi or Cu.
It is formed of a material containing at least one of metals having a high resistivity such as Sn as a main component, or an insulating material made of a synthetic resin having a high resistivity.

The optimization of the cross-sectional aspect ratio b / a of the superconducting conductor 1 by the magnetic field factor corresponding to the magnetic field distribution of each superconducting electromagnet, which is a feature of the present invention, is applicable to superconducting electromagnets other than the superconducting electromagnet for the particle accelerator. Easy to adapt. As an example, the states of the magnetic field distributions of typical solenoid coils and toroid coils and the schematic cross-sectional shapes when the present invention is applied are shown in FIGS. 7 and 8.

In FIG. 7, (a) shows the state of the magnetic field distribution of the solenoid coil, (b) shows the sectional shape when the present invention is applied, and (c) shows the appearance of the solenoid coil device. Represent Solenoid coil is the entire cross section 2
For the purpose of optimizing the cross-sectional aspect ratio b / a of the superconducting conductor 1 at each part by using the magnetic field distribution, the whole is divided into three stages and wound. In this example, the magnetic flux density ratio B _a /
In the axial center portion 10 of the magnet where B _b has a large value, the cross-sectional aspect ratio b / a of the superconducting conductor 1 is set to 4, B _a /
The aspect ratio b / a is set to about 1 at both ends 11 of the shaft center portion of the magnet whose B _b value is close to 1. Further, at the shaft end 12 closer to the end than that, the cross-sectional aspect ratio b of the superconducting conductor corresponds to the fact that the value of B _a / B _b becomes smaller than 1.
/ A is set to about 0.4 and becomes smaller than the aspect ratio of the central portion of the coil axis as it moves toward both ends of the coil axis. Here, when the aspect ratio b / a extends from 1 or less to 1 or more, the reference is displayed in the same direction.

Further, in FIG. 8, (a) shows the sectional shape of the toroid coil when the present invention is applied, and (b) shows the appearance of the toroid coil device. The toroid coil is divided into two stages and wound for the purpose of optimizing the cross-sectional aspect ratio b / a of the superconducting conductor in each part by using the magnetic field distribution of the whole cross-section 2. In this example, the cross-sectional aspect ratio b / a of the superconducting conductor 1 is set to 4 in the axial center portion 10 of the magnet where the magnetic flux density ratio B _a / B _b takes a large value, and the value of B _a / B _b is set to 1. The aspect ratio b / a is set to about 1 at both ends 11 of the central portion of the nearby magnet.

[0044]

According to the present invention, in the superconducting conductor which is a main constituent element of the superconducting magnet, the superconducting conductor formed by twisting the strands at a predetermined pitch in order to reduce the coupling loss between the strands, and Considering the effect of the correlation between the aspect ratio of the cross section of the superconducting conductor, the magnetic field, and the resistance in the superconducting conductor on the coupling loss in the AC superconducting power equipment using this superconducting conductor, consider that the coupling loss between the superconducting wires is small. By using a superconducting conductor with a unique cross-sectional shape, it has excellent quench characteristics and low overall power consumption.
It is possible to provide an AC superconducting magnet having high magnetic field homogeneity and a power device such as a particle accelerator using the superconducting magnet.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a cross-sectional shape of a superconducting conductor of a superconducting dipole electromagnet according to an embodiment of the present invention.

FIG. 2 is a perspective view showing an appearance of a superconducting dipole magnet for a particle accelerator according to an example.

FIG. 3 is an explanatory diagram showing a cross-sectional shape of a superconducting dipole electromagnet wound so that an electric current has an ideal cos θ distribution and a layered current having a cos θ distribution.

FIG. 4 is an explanatory diagram showing a definition of a load factor of a superconducting conductor.

FIG. 5 is a diagram showing a change in total coupling loss of a superconducting magnet with respect to a cross-sectional aspect ratio of a superconducting conductor.

FIG. 6 is a diagram showing a change in the total coupling loss of superconducting magnets with respect to the electrical resistivity ratio of the minimum value of the cross-sectional aspect ratio of the superconducting conductor.

FIG. 7 is an explanatory view showing a superconducting solenoid electromagnet to which the present invention is applied.

FIG. 8 is an explanatory view showing a superconducting toroid electromagnet to which the present invention is applied.

[Explanation of symbols]

1 superconducting conductor 2 cross section of superconducting dipole magnet 3 magnetic flux density of magnetic field 4 superconducting element wire 5 central magnetic field 6 site where the magnetic field is exposed to the superconducting conductor 7 iron core 8 magnetic field experienced by the superconducting conductor and critical current in the magnetic field Relationship with density 9 Relationship between density of current flowing in superconducting conductor and magnetic field generated at that time 10 Superconducting conductor in central part of solenoid or toroid electromagnet shaft 11 Superconducting conductor at both ends of central part of solenoid or toroid electromagnet 12 Solenoid or Superconducting conductors on both ends of the shaft of the toroid electromagnet

Claims (18)

[Claims] 1. With respect to a uniform fluctuating magnetic field applied perpendicularly to a superconducting conductor formed by bundling a plurality of superconducting element wires, it becomes difficult for a coupling current to flow due to interlinking magnetic field fluctuation between the element wires. As described above, in the superconducting magnet for alternating current, which generates a magnetic field by winding a superconducting conductor formed by twisting the superconducting element wires at a predetermined pitch, and gives a fluctuating magnetic field by deenergizing a flowing current, the superconducting magnet A value obtained by dividing the length of the wide side of the conductor cross section by the length of the narrow side is partially selected in consideration of the magnetic field distribution of the fluctuating magnetic field so that the coupling loss between the superconducting wires is minimized,
A superconducting magnet for alternating current, wherein the superconducting conductor is wound. 2. With respect to a uniform fluctuating magnetic field applied perpendicularly to a superconducting conductor formed by bundling a plurality of superconducting element wires, it becomes difficult for a coupling current to flow due to an interlinking magnetic field fluctuation between the element wires. As described above, in the superconducting magnet for alternating current, which generates a magnetic field by winding a superconducting conductor formed by twisting the superconducting element wires at a predetermined pitch, and gives a fluctuating magnetic field by deenergizing a flowing current, the superconducting magnet The value obtained by dividing the length of the wide side of the conductor cross section by the length of the narrow side is the absolute value of the varying magnetic field orthogonal to the narrow side of the superconducting conductor and the absolute value of the varying magnetic field orthogonal to the wide side of the superconducting conductor. A superconducting magnet for alternating current, wherein the superconducting conductor is formed so as to be larger than a square root of a divided value and smaller than twice the square root. 3. A coupling current based on a variation in interlinking magnetic field between strands becomes difficult to flow against a uniform varying magnetic field applied perpendicularly to a superconducting conductor formed by bundling a plurality of superconducting element wires. As described above, in the superconducting magnet for alternating current, which generates a magnetic field by winding a superconducting conductor formed by twisting the superconducting element wires at a predetermined pitch, and gives a fluctuating magnetic field by deenergizing a flowing current, the superconducting magnet The value obtained by dividing the length of the wide side of the conductor cross section by the length of the narrow side is the absolute value of the varying magnetic field orthogonal to the narrow side of the superconducting conductor and the absolute value of the varying magnetic field orthogonal to the wide side of the superconducting conductor. Greater than the square root of the product of the divided value and the square root of the value obtained by dividing the electrical resistivity in the direction orthogonal to the wide side of the superconducting conductor by the electrical resistivity in the direction orthogonal to the narrow side of the superconducting conductor. , AC superconducting magnet, characterized in that said superconducting conductors are formed to be less than 3 times the square root. 4. The superconducting conductor is formed by twisting a plurality of twisted wires at least once by using a set twisted wire of the twisted superconducting element wires as a unit. The superconducting magnet for alternating current according to any one of 2 and 3. 5. The superconducting magnet for alternating current according to claim 4, wherein the twisted superconducting element wires and the collective twisted wire of the superconducting element wires have the same twist direction. 6. An element wire made of a low-resistance metal that causes a current to flow when the superconducting element wire undergoes a normal conduction transition and an energizing current is shunted from the superconducting element wire, is further arranged in parallel with the superconducting element wire. The superconducting magnet for alternating current according to claim 4 or 5, wherein the element wire made of the low-resistance metal is twisted in a direction opposite to the superconducting element wire and the assembled stranded wire. 7. A member having a high resistivity is further arranged in the central portion of the assembled stranded wire.
1. A superconducting magnet for alternating current according to any one of 1. 8. A superconducting magnet for alternating current according to claim 6, wherein a metal having a higher resistivity is arranged in combination in the superconducting element wire or the element wire made of the low resistance metal. . 9. The superconducting magnet for alternating current according to claim 7, wherein the member having a high resistivity is formed of a material containing at least one of CuNi and CuSn as a main component. 10. The superconducting magnet for alternating current according to claim 7, wherein the member having a high resistivity is formed of an insulating material made of synthetic resin. 11. The AC superconducting magnet according to claim 8, wherein the metal having a high resistivity is formed of a material containing at least one of CuNi and CuSn as a main component. 12. A superconducting magnet for alternating current, wherein the maximum load factor during operation of the superconducting magnet for alternating current according to claim 1 is set to 85% or more. 13. A particle accelerator equipped with the superconducting magnet for alternating current according to claim 1. Description: 14. The particle accelerator according to claim 13, wherein an AC superconducting magnet having a value obtained by dividing a length of a wide side of a cross section of the superconducting conductor by a length of a narrow side of 3 or less is used. 15. The particle accelerator according to claim 13, further comprising an iron core. 16. The magnetic field to be generated is a 2n-order component (n is a natural number), 13, 14, and 15.
2. The particle accelerator according to any one of 1. 17. The AC superconducting magnet according to claim 1, wherein the superconducting magnet is either a solenoid or a toroid. 18. A value obtained by dividing a wide side length of a superconducting conductor cross section on both axial ends of the magnet in a magnetic field direction in a cross section of the superconducting magnet of the solenoid or the toroid by a narrow side length, 18. The AC superconducting magnet according to claim 17, wherein the length is set smaller than a value obtained by dividing the length of the wide side of the cross section of the superconducting conductor on the axial center side of the magnet by the length of the narrow side.