JPS5968910A - Superconductive coil - Google Patents

Abstract

PURPOSE:To obtain a supreconductive coil which can generate high uniform magnetic field by a method wherein the superconductive coil is divided into a plurality of blocks and different exciting current is applied to a winding in each block and the space distribution of the magnetic field is changed optionally. CONSTITUTION:A plurality of protruded dividing strips 13a with a constant thickness S are provided around a drum 13 with a constant block length l and main coil windings 11a are wound between those dividing strips 13a individually. If there is a space remained in each block, it is filled by a filler 15 of a length DELTAl. A jumper wire 11b is connected to the winding 11a and, if necessary, connected to the adjacent winding 11a through a jumper notch 13b provided to the protruded dividing strip 13a. With this constitution, the windings 11a are composed of a required number of independent windings and the current applied to each winding is controlled individually so that the uniformity of the magnetic field generated by the main coil is improved one figure up.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting coil, and particularly to a superconducting coil with high spatial uniformity of magnetic field.

Conventionally, there has been a device of this type as shown in FIG.

In the figure, a main coil 1 and a magnetic field correction coil 2 are wound around a winding frame 3 to form a highly uniform magnetic field region 1. Here, the axial direction 2. The radial direction r is also shown. The main coil / is a coil that generates a main magnetic field, and also includes a coil that corrects a large non-uniform magnetic field that occurs because the coil has a finite length.

The magnetic field correction coil is also called a shim coil, and is a group of coils for improving the spatial uniformity of the magnetic field in the highly uniform magnetic field region q by correcting a small non-uniform magnetic field.

With this configuration, when a constant current that does not change over time is passed through the main coil 1, a highly uniform magnetic field is generated in the highly uniform magnetic field region DA. In order to improve the uniformity of the magnetic field, that is, the uniformity of the spatial distribution of the magnetic field, compared to the dimensions of the highly uniform magnetic field area,
The diameter and length of the main coil l are increased. However, the current density distribution of the main coil cannot be made completely uniform within the cross section of the main coil, the main coil cannot be made completely cylindrical, and the length of the main coil l is finite.
For these reasons, it has been difficult to improve the uniformity of the magnetic field generated only by the main coil l. Therefore, in order to improve the uniformity of the magnetic field, a magnetic field correction coil 2 is generally used. The magnetic field correction coil 2 is composed of a large number of coils of various shapes such as a circular coil, a saddle-shaped coil, and a rectangular coil. The magnetic field generated by the correction coil 2 is adjusted to improve the uniformity of the magnetic field within the highly uniform magnetic field region. However, in the output magnetic field of the magnetic field correction coil 2, in addition to the magnetic field component that cancels out the non-uniform magnetic field generated by the main coil 1, a small amount of error magnetic field component that is not involved in the correction of the non-uniform magnetic field is included. When the output magnetic field of the magnetic field correction coil λ is increased, such error magnetic field components also increase. Therefore, unless the uniformity of the magnetic field generated by the main coil l is not good to some extent, it is difficult to improve the uniformity of the magnetic field even if a magnetic field correction coil is used.

Next, the influence of the distribution of the current density of the main coil within the cross section of the main coil on the uniformity of the magnetic field will be considered. Second
The figure shows the actual measured value of the variation ΔW of the superconducting wire used for the winding of the main coil l. Here, the cross-sectional dimension of the wire is on the order of 1 m, and the wire length is on the order of km. The range of variation in the width of the wire is 20 μm, and the variation is determined by the finishing accuracy of the wire itself and the accuracy of the thickness of the electrical insulator applied to the surface of the wire. It is difficult to reduce the variation in wire width shown in FIG. 2 to a value smaller than this in view of wire manufacturing technology. The variation in the thickness of the wire is similar to the variation in the width. FIG. 3' schematically shows a cross-section of the winding when a wire rod having varying widths is wound around the main coil. /a is a coil winding, and the figure shows only a cross section of the winding for one layer, indicating that the number of turns per unit length in the Z-axis direction varies depending on the location.

Since the same current flows through each turn, the current density differs depending on the location in the Z-axis direction.

Now, the current density (W) in the Z direction is defined by the following equation.

L(△-)-(wo+~) Here, I: main coil current value, wo: standard width of wire, ΔW: deviation of wire width from standard width WO, now wire width is W(7=/' 1m, deviation of wire width ΔW = ±5μg
, L(, When calculating the current density using l as the reference current value, L(+yoml/spider=/-1×10-' ” (-rp,) / L(1) = t + s x
It becomes t o-'. In other words, when the main coil l is wound using a practically obtained coil winding wire as shown in Figure 2, the current density will vary depending on the location from the reference value L ((4). The magnetic field generated by the main coil l changes in accordance with the current density. It will fluctuate on the order of lθ.

Also, a similar problem occurs due to variations in the thickness of the wire. It is said that the uniformity of the magnetic field in a high uniform magnetic field superconducting coil required for NMR (nuclear magnetic resonance) phenomena etc. needs to be less than io at the sample position. Therefore, in order to realize such a highly uniform magnetic field, it is necessary to use the correction coil 2 to correct the magnetic field created by the main coil.

Conventional high-uniform magnetic field superconducting coils are wound with wires whose cross-sectional dimensions vary as described above, so the current density distribution within the cross-section of the main coil is not uniform, and the magnetic field generated by the main coil l is As the uniformity decreases, the amount of correction of the magnetic field by the base field correction coil increases, which has the disadvantage of increasing the size of the magnetic field correction coil 2. Ta.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and uses a winding structure in which the winding frame is divided into a large number of blocks of fixed dimensions, and the number of turns in each block is set to a predetermined value. The object of the present invention is to provide a superconducting coil that can generate a highly uniform magnetic field.

Another object of the invention is to divide the coil into a plurality of blocks and make each block electrically independent so that different excitation currents can flow through the windings of each block, thereby arbitrarily controlling the spatial distribution of the magnetic field. It is an object of the present invention to provide a superconducting coil that can significantly improve magnetic field uniformity in a highly uniform magnetic field region by changing the magnetic field uniformity.

The present invention will be described below with reference to an embodiment shown in FIG. The figure shows one layer of coil winding //9- of the main coil, and the winding is performed from left to right in the figure. A plurality of divided protrusions 13a having a thickness of S are formed on the outer circumferential surface of the winding frame 13, and a coil winding of 1/2 length //& is wound between adjacent divided protrusions 13a. All coils are 1 length
It is divided into blocks. Also, if there is any remaining space in each block, fill it with /3 and increase its length by Δ1.
It is expressed as The number of turns within one block is constant. Therefore, since the filling width Δ1 changes depending on the variation in the width of the wire, it is usually each.

Width Δ of filling 15 with blocks of! is different. However, the block length and dividing protrusion/? The thickness S of a is a constant value.

FIG. 5 shows the winding state near the winding transition portion between each block. In the figure, //b is the crossover wire of coil winding 1/a, /, ? b is a transition groove provided on the split protrusion/3eL. The coil winding 1/a, which has been wound by the required number of turns in a certain block, reaches the winding start position of the coil winding tia of the adjacent block via the crossover wire (//1). Winding l/a
and crossover wire//b are the names of different positions of the same wire, and there may or may not be a point where the wire is connected after being cut between winding l/a and crossover wire//l). Good too. Further, the connecting wire 71b passes through the dividing groove /jl) which is partially formed in the divided protrusion 7a. Crossing ditch/? b is each divided protrusion/
There are l locations in Ja, the groove width is wide enough for one crossover wire //1) to pass through, and the groove depth is less than the diameter around which the outermost coil of winding frame /3 is wound. Also, crossing ditch/3b
is parallel to the Z axis.

Next, the action and effects will be described. In the main coil configured as described above, the current density of the coil as seen per block is constant and does not change depending on the location in the Z-axis direction.

If the block length 1 is made sufficiently smaller than the radius R of the main coil, the distribution of current density within the winding cross section of the main coil can be considered to be substantially uniform. As a result, the uniformity of the magnetic field generated by the main coil is improved. Here, sufficiently small means
70 minutes/or less. In addition, J-/R and Δφ
.

The smaller the values of s and l are, the more desirable it is from the point of view of improving the uniformity of the magnetic field.
Appropriate dimensions may be determined based on the workability during manufacturing and the degree of improvement in magnetic field uniformity.

Here, since the connecting wire //b shown in Fig. 3 has a different winding direction from the winding wire //a, the magnetic field generated by the current flowing in the connecting wire //b is an unnecessary magnetic field. . However, the first
Layer crossover wire 1lblC current flowing and first layer crossover wire/
Since the current flowing through /l) has the same absolute value and opposite direction, the magnetic fields generated by each crossover wire //b are almost canceled out.

Therefore, the unrestricted magnetic field component generated due to the presence of the crossover wire //b does not pose any problem at all in the highly uniform magnetic field region located away from the water turbine and the crossover wire //b.

Further, in the above embodiment, the groove/3 extends across each divided protrusion 13a.
b was provided at l locations, but there were multiple crossings.
/ 3 b may be present. In this case, if the connecting wires 71b are passed in such a way that the sum of the currents with positive and negative signs is θ depending on the direction of the current of all the connecting wires llb in one connecting groove /7b, The non-uniform magnetic field generated at the connecting wire//b section is almost flattened, resulting in a high uniform magnetic field region lI
In this case, the influence of crossover wire //b is not a problem at all.

Also, one split protrusion /,? aK Multiple crossing grooves/Jb
, the transition grooves /3b may be arranged at equal intervals on the circumference of the divided protrusions /3&. In this case, it is possible to disperse the slight non-uniform -m different component generated by the crossover wire //b on the circumference, and the crossover wires //b located near the symmetrical position with respect to the Z axis are The influences on the uniform magnetic field region q can be canceled out. Therefore, the influence of the magnetic field generated by the crossover wire /lb on the highly uniform magnetic field region is even greater than when the sum of the currents of the multiple crossover wires //l) in the same crossover groove /3b is set to θ. It has the unique effect of becoming smaller.

As described above, the present invention makes it possible to improve the uniformity of the magnetic field generated by the main coil by more than one order of magnitude compared to the conventional method by making the current density distribution within the winding cross section of the main coil uniform. It is possible. Therefore, the amount of correction of the magnetic field by the magnetic field correction coil may be small, and there is a special effect that the magnetic field correction coil is unnecessary in some cases.

Next, other embodiments will be described. In the above embodiment, the coil windings //a of all blocks are connected via the crossover wire //b, but here the crossover wire //b is eliminated and the coil windings lla in each block are made independent from each other. The windings mti = in each block are made independent of each other, and the windings //a in each block are each independent divided coils.7 In this case,
There is no need to cut a groove in the split protrusion /3a, which was necessary to pass the crossover wire /b. In this way, different currents can be applied to the divided coils of each block, making it possible to change the spatial distribution of the magnetic field in various ways. In other words, it is possible to select a combination of current values that provides the highest degree of magnetic field uniformity within the highly uniform magnetic field region. Another advantage is that the coils can be excited completely independently for each block. The main coil used to obtain a highly uniform magnetic field generally consists of a simple solenoid coil and one pair of notch coils attached to the outer periphery of the coil at both ends. As mentioned here, the coil configuration is such that a different excitation current can be passed through each divided coil, by making the excitation current of the divided coils at both ends of the main coil larger than the excitation current of the other divided coils. , it is possible to perform the same role as installing l pairs of notch coils. Therefore, a highly uniform magnetic field can be obtained with a very simple coil shape that does not require a notch coil.

In addition, the split protrusion /,? If a is manufactured by machining with a lathe, the dimensional accuracy is high and the thickness is sufficiently thin. a can be obtained very easily.

Further, the winding frame 13 is generally a simple cylinder, but in this invention, a divided protrusion/, ? a is added, so that the mechanical strength of the winding frame can be increased. Accordingly, even if the thickness of the base of the winding frame 13 is made thinner, mechanical strength similar to or greater than that of the conventional method can be obtained.Furthermore, the total weight of the coil can be reduced. As a result, the weight of the liquid helium necessary to create a superconducting state that must be cooled, that is, the weight to be cooled, can be reduced, making it possible to realize an economical superconducting coil that consumes less liquid helium when cooling the coil. effective.

In all of the above embodiments, the main coil is wound by providing a dividing protrusion on the winding frame to serve as a winding reference surface, so that during winding,
Block length! There is no need to wind the coil while measuring it, and it is sufficient to simply wind the coil along the side surface of the divided protrusion, making the winding work extremely easy.

Further, although the above embodiments have been described using superconducting coils, normal conducting coils may be used, and similar effects can be obtained.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of a conventional product, Fig. 2 is a line diagram showing variations in the width of generally obtained coil wires, Fig. 3 is a partial longitudinal cross-sectional view of a conventional product, and Fig. The longitudinal cross-sectional view of the embodiment and FIG. 5 are the same (partially a perspective view).
/3... winding frame, /,? 'a... split ridge, /,? b...
Crossing groove, G... Highly uniform magnetic field region, 15... Filling. In addition, in each figure, the same reference numerals indicate the same - or the corresponding parts are indicated by the previous two figures. 14!
No. 2, Name of the invention Superconducting coil 3, To the snow representative Hitoshi Katayama who makes the amendment Part 4, Agent Column for detailed explanation of the invention in the specification Contents of the amendment (11 Specification, page 19, Hiroyuki) Correct "just winding" to "just winding."

Claims (3)

[Claims] (1) A winding frame, a plurality of dividing ridges formed on the outer peripheral surface of the winding frame and divided into equal lengths in the axial direction of the winding frame, and each block divided by the dividing ridges having the same number of windings. A superconducting coil comprising a main coil wound with an I-coil winding. (2) The superconducting coil according to claim 7, wherein the remaining space of the block on which the coil winding has been applied is filled with a filler. (3) Claim 1, which is provided with a crossover groove formed in the divided protrusion and through which a crossover wire is passed between the coil windings of adjacent blocks.
Superconducting coil described in Section 1. (i) A winding frame, a plurality of dividing ridges formed on the outer peripheral surface of the winding frame and dividing the winding frame into nine equal lengths in the axial direction, and each block divided by the dividing ridges having the same number of windings. 1. A super 1°C conductive coil comprising a main coil which is wound and is electrically divided into independent divided coils. (j) The superconducting coil according to claim q, wherein the divided coils at both ends of the winding frame are each notch coils.