Superconducting coil and manufacturing method for superconducting coil

In a superconducting coil used in an MRI apparatus, it is necessary to arrange a superconducting wire at a desired position to obtain a desired coil shape in order to obtain a temporally stable static electromagnetic field with high strength and high uniformity. A superconducting coil includes a winding frame, a spacer disposed on an outer periphery of winding frame and including a winding groove having a spiral shape and a communication groove provided between winding grooves, and includes a coil group having a superconducting wire wound in winding groove. It is therefore possible to obtain superconducting coil having a desired coil shape.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on PCT filing PCT/JP2020/001947, filed Jan. 21, 2020, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a superconducting coil used in a magnetic resonance imaging (MRI) apparatus (hereinafter, referred to as an MRI apparatus) and a manufacturing method for the superconducting coil.

BACKGROUND ART

It is known that by using a superconducting coil as a static electromagnetic field generation source of an MRI apparatus, a temporally stable static electromagnetic field with high strength and high uniformity can be obtained.

In order to capture a precise human body tomographic image with high contrast, a superconducting coil used in an MRI apparatus is required to have a magnetic field intensity of about 0.5 Tesla to 3 Tesla and a temporally stable static magnetic field characteristic of about 0.05 ppm/h with a magnetic field uniformity of about 1 ppm to 10 ppm in a spherical space having a diameter of about 30 cm to 45 cm from a magnetic field center.

With advancing development of a superconducting coil satisfying the above conditions, it has been considered to wind, around an imaging space, a superconducting wire in a desired coil shape for obtaining the above characteristics. For example, a method of winding a superconducting wire around a winding frame while inserting a member that adjusts a shape has been disclosed (see, for example, PTL 1).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, in the conventional method, when the superconducting wire is laminated and wound, it is difficult to arrange the superconducting wire at a desired position and provide a winding space, and thus there is a problem that a desired coil shape cannot be obtained.

The present disclosure has been made to solve the above problem, and an object of the present disclosure is to provide a superconducting coil having a coil group whose coil shape is a desired shape.

Solution to Problem

A superconducting coil of the present disclosure includes a winding frame, a first spacer disposed on an outer periphery of the winding frame and including a first winding groove having a spiral shape and disposed in a peripheral direction of the winding frame, a second winding groove having a spiral shape and disposed apart from the first winding groove, and a first communication groove provided between the first winding groove and the second winding groove, a second spacer disposed on an upper layer of the first spacer and including a third winding groove having a spiral shape and disposed above the first winding groove, a fourth winding groove having a spiral shape and disposed apart from the third winding groove and above the second winding groove, and a second communication groove provided between the third winding groove and the fourth winding groove, a first coil group including a first layer of a superconducting wire having the superconducting wire wound in the first winding groove, and a second layer of the superconducting wire having the superconducting wire wound in the third winding groove, and a second coil group communicated with the first coil group by the superconducting wire on the first communication groove and the second communication groove and including a first layer of the superconducting wire having the superconducting wire wound in the second winding groove, and a second layer of the superconducting wire having the superconducting wire wound in the fourth winding groove.

A manufacturing method for a superconducting coil of the present disclosure includes a first spacer arrangement step of arranging, on an outer periphery of a winding frame, a first spacer including a first winding groove having a spiral shape and disposed on the outer periphery of the winding fame, a second winding groove having a spiral shape and disposed apart from the first winding groove, and a first communication groove to communicate the first winding groove with the second winding groove, a first layer formation step of forming a first layer of a first coil group by winding a superconducting wire in the first winding groove and forming a first layer of a second coil group by winding the superconducting wire in the first communication groove and the second winding groove, a second spacer arrangement step of arranging, on the first spacer, a second spacer including a third winding groove disposed on the first spacer and having a spiral shape, a fourth winding groove disposed apart from the third winding groove and having a spiral shape, and a second communication groove to communicate the third winding groove with the fourth winding groove such that the third winding groove is disposed above the first winding groove, and the fourth winding groove is disposed above the second winding groove, and a second layer formation step of forming a second layer of the second coil group by winding the superconducting wire in the fourth winding groove and forming a second layer of the first coil group by winding the superconducting wire in the second communication groove and the third winding groove.

Advantageous Effects of Invention

The present disclosure makes it possible to obtain a superconducting coil having a coil group whose coil shape is a desired shape.

DESCRIPTION OF EMBODIMENTS

First Embodiment

FIG.1is a schematic sectional view illustrating a part of a superconducting coil1according to a first embodiment. Superconducting coil1is used in, for example, a solenoid MRI apparatus. Superconducting coil1is provided in a substantially cylindrical vacuum heat insulation container (not shown), and is immersed in liquid helium or the like to have a low temperature. Superconducting coil1includes a spacer3disposed on an outer periphery of a winding frame2disposed on an inner wall of the vacuum heat insulation container and provided with a winding groove5and a communication groove6, and includes a coil group C formed by a superconducting wire4being wound in winding groove5, with a center of winding frame2as a rotation axis (Z axis inFIG.1).

Winding frame2includes, for example, metal, fiber-reinforced plastic, or the like, has a cylindrical shape, and is disposed in the vacuum heat insulation container. Here, the cylindrical shape includes a non-concentric shape, and may be any shape as long as winding frame2can be disposed in the vacuum heat insulation container.

Spacer3has a sheet shape and includes, for example, glass epoxy, and a plurality of layers of sheets are disposed on the outer periphery of winding frame2. Spacer3having a sheet shape is disposed on winding frame2and has, for example, a cylindrical shape in accordance with an outer shape of winding frame2. Spacer3is provided with winding groove5and communication groove6, and superconducting wire4is wound in these grooves to form coil group C having an annular shape.

A plurality of coil groups C are provided on winding frame2. The number of coil groups C varies depending on coil design, and thus may be a desired number. Each coil group C includes a plurality of folded superconducting wires4. Similarly to the number of coil groups, the number of layers varies depending on the coil design, and thus each coil group C may be constituted by a desired number of layers of superconducting wire4. Hereinafter, for ease of description, coil group C on the right side inFIG.1is referred to as a first coil group C1, and coil group C on the left side inFIG.1is referred to as a second coil group C2.

FIG.2is a schematic perspective view illustrating a part of spacer3.FIG.2illustrates, in an upper part, a first spacer31in which first layers of first coil group C1and second coil group C2are formed, and, in a lower part, a second spacer32in which second layers of first coil group C1and second coil group C2are formed. Winding groove5is a groove in which superconducting wire4having a diameter of about 2 mm obtained by coating, for example, Nb—Ti with Cu and an insulating material is disposed, and winding groove5is spirally continuous when spacer3is disposed in winding frame2. The groove has a width and a depth of, for example, about 2 mm, and is formed such that superconducting wire4can be disposed in the groove. Here, a direction in which winding groove5is formed, that is, a direction in which superconducting wire4is wound is referred to as a peripheral direction.

Hereinafter, inFIG.2, winding groove5formed on the right side of first spacer31is referred to as a first winding groove51, winding groove5formed on the left side of first spacer31is referred to as a second winding groove52, winding groove5formed on the right side of second spacer32is referred to as a third winding groove53, and winding groove5formed on the left side of second spacer32is referred to as a fourth winding groove54. First winding groove51, second winding groove52, third winding groove53, and fourth winding groove54are provided with a space therebetween. Then, the first layer of coil group C is formed by winding superconducting wire4in first winding groove51and second winding groove52, and the second layer of coil group C is formed by winding superconducting wire4in third winding groove53and fourth winding groove54.

Spacer3is provided with communication groove6. In an example inFIG.2, communication groove6is provided between first winding groove51and second winding groove52, and between third winding groove53and fourth winding groove54, and superconducting wire4is disposed. Superconducting wire4disposed in communication groove6communicates with coil group C. For example, in a case where superconducting wire4is wound in a direction from first coil group C1toward second coil group C2in a single layer, an end point of first coil group C1and a start point of second coil group C2are communicated by superconducting wire4. Communication groove6provided in first spacer31is referred to as a first communication groove61, and communication groove6provided in second spacer32is referred to as a second communication groove62.

In this manner, a single layer of coil group C is formed on one spacer3, and the single layer is laminated to form a plurality of layers of the plurality of coil groups C.

Superconducting coil1in which first coil group C1and second coil group C2are formed will be described with reference toFIGS.1and2. First spacer31includes a first winding groove51and a second winding groove52which are disposed apart from each other so as to be spirally continuous, and first winding groove51and second winding groove52are communicated by first communication groove61. The first layer of first coil group C1is formed in first winding groove51, and the first layer of second coil group C2is formed in second winding groove52. By arranging superconducting wire4on first communication groove61, the first layer of first coil group C1and the first layer of second coil group C2are communicated by continuous superconducting wire4.

Second spacer32is provided on first spacer31, and the second layers of first coil group C1and second coil group C2are formed on second spacer32. Second spacer32includes third winding groove53disposed on first winding groove51and fourth winding groove54disposed on second winding groove52. Third winding groove53and fourth winding groove54are formed so as to be spirally continuous. Second communication groove62is provided between third winding groove53and fourth winding groove54to communicate these winding grooves with each other. Similarly to the first layers of first coil group C1and second coil group C2, superconducting wire4is wound in third winding groove53to form the second layer of first coil group C1, and superconducting wire4is wound in fourth winding groove54to form the second layer of second coil group C2.

By arranging superconducting wire4on second communication groove62, the second layer of first coil group C1and the second layer of second coil group C2are communicated by continuous superconducting wire4. The same applies to a case of increasing coil groups C including, for example, a third coil group C3and a fourth coil group C4. In this case, in the same layer, each coil group C is communicated with adjacent coil group C by adjacent communication groove6.

Here, since superconducting wire4is folded back between the first layer and the second layer of coil group C, superconducting wire4constituting the first layer and the second layer is continuous. The direction in which superconducting wire4is wound is opposite between the first layer and the second layer.

As described above, by repeatedly winding superconducting wire4in winding groove5of spacer3and arranging spacer3for each layer, the plurality of coil groups C can be formed, and the coil shape of coil group C can be made as desired.

For example, in order to obtain a non-rectangular coil sectional shape, spacer3only needs to be designed such that the number of turns of coil group C decreases toward an upper layer, that is, the number of grooves constituting winding groove5in sectional view (in a view ofFIG.1from the front side of the sheet) decreases toward the upper layer. In this design, the cross section of coil group C can be a non-rectangular shape whose width decreases toward outside. In a design of spacer3in which the number of turns of coil group C decreases toward a lower layer, that is, the number of grooves constituting winding groove5in sectional view decreases toward the lower layer, the cross section of coil group C can be a non-rectangular shape whose width of the cross section decreases toward inside.

In spacer3, by varying distances between the grooves constituting winding groove5, superconducting wire4can be disposed discretely. For example, by forming a part in which distances between some of the grooves are larger in winding groove5, it is possible to form a coil sectional shape in which a space7is provided by the distances between the grooves of winding groove5as in coil group C illustrated inFIG.3, and superconducting wire4can be disposed discretely.

As described above, by arranging spacer3provided with winding groove5in which superconducting wire4is wound and communication groove6communicating with winding groove5on the outer periphery of winding frame2, and by designing the number of grooves of winding groove5and the distances between the grooves appropriately, the coil sectional shape can be made as desired.

Next, description will be made of a manufacturing method for superconducting coil1according to the present embodiment.

First, first winding groove51having a spiral shape, second winding groove52disposed apart from first winding groove51and having a spiral shape, and first communication groove61communicating first winding groove51with second winding groove52are provided on an insulating sheet of glass epoxy or the like to form first spacer31. Here, a thickness from a bottom surface of first spacer31to a bottom surface of winding groove5and a bottom surface of communication groove6is, for example, less than or equal to 1 mm, and depths and widths of winding groove5and communication groove6are, for example, about 2 mm.

Next, similarly to first spacer31, third winding groove53having a spiral shape, fourth winding groove54disposed apart from third winding groove53and having a spiral shape, and second communication groove62communicating third winding groove53with fourth winding groove54are provided on an insulating sheet to form second spacer32. Similarly to first spacer31and second spacer32, a plurality of spacers3having communication groove6communicating winding groove5with adjacent winding groove5are formed.

Then, first spacer31is disposed on the outer periphery of winding frame2(first spacer arrangement step).

The following will be description of a step of winding superconducting wire4in first winding groove51and second winding groove52to form the first layers of first coil group C1and second coil group C2(first layer formation step).

First, superconducting wire4is wound in first winding groove51to form the first layer of first coil group C1. Next, with the center of winding frame2as the rotation axis, superconducting wire4is wound in first communication groove61to communicate first coil group C1with second coil group C2in the first layer by continuous superconducting wire4(coil group communication step), and superconducting wire4is wound in second winding groove52to form the first layer of second coil group C2. In this way, the first layers of first coil group C1and second coil group C2are formed. In a case where three or more coil groups C are formed in first spacer31, adjacent winding grooves5are similarly communicated with each other by first communication groove61to form the first layer of each coil group C.

Then, second spacer32is provided on first spacer31in which the first layers of first coil group C1and second coil group C2are formed (second spacer arrangement step). In the second spacer arrangement step, third winding groove53is disposed on first winding groove51of first spacer31, and fourth winding groove54is disposed on second winding groove52of first spacer31.

The following will be description of a step of winding superconducting wire4in third winding groove53and fourth winding groove54to form the second layers of first coil group C1and second coil group C2(second layer formation step).

First, superconducting wire4constituting the first layer of second coil group C2is extended to fourth winding groove54of second spacer32. In a case where three or more coil groups C are formed, superconducting wire4only needs to be extended from the end point of the first layer to the start point of the second layer.

First, superconducting wire4is wound in fourth winding groove54to form the second layer of second coil group C2. Next, superconducting wire4is wound in second communication groove62to communicate second coil group C2with first coil group C1in the second layer by continuous superconducting wire4, and superconducting wire4is wound in third winding groove53to form the second layer of first coil group C1. In this way, the second layers of first coil group C1and second coil group C2are formed. In a case where three or more coil groups C are formed in second spacer32, adjacent winding grooves5only needs to be similarly communicated with each other by second communication groove62to form the second layer of each coil group C.

Further, a step of arranging one spacer3, a step of forming single layers of first coil group C1and second coil group C2, and a step of extending superconducting wire4to the upper layer are repeated until a desired number (N) of layers is obtained to obtain superconducting coil1. Here, N is an integer greater than 1.

That is, spacer3having a plurality of winding grooves5and communication groove6communicating adjacent winding grooves5with each other is disposed on the outer periphery of winding frame2, and superconducting wire4is wound in winding grooves5and communication groove6to form a single layer of continuous coil group C. Next, spacer3is disposed in the upper layer of the single layer of coil group C thus formed, and superconducting wire4constituting coil group C of the lower layer is extended to spacer3in the upper layer. Thereafter, superconducting wire4is wound in winding groove5and communication groove6in the upper layer to form a single layer of continuous coil group C and obtain coil group C including a plurality of layers.

As described above, by repeatedly arranging spacer3for each layer, the plurality of coil groups C can be formed, and the coil shape of coil group C can be made as desired. Superconducting wire4does not need to be folded back for each layer of one coil group C of superconducting wire4, the plurality of coil groups C can be continuously wound in a single layer without being folded back, and production efficiency of superconducting coil1is improved. In addition, since superconducting wire4is wound in winding groove5, superconducting wire4can be accurately wound.

In the present embodiment, an example has been described in which glass epoxy is used as a material of spacer3, but for example, a prepreg sheet in which reinforcing fibers such as aramid fibers are impregnated with an epoxy resin may be used. In this case, after the prepreg sheet is grooved, spacer3is heated to about 80° C. to be softened when spacer3is disposed on the outer periphery of winding frame2, the winding of superconducting wire4is completed, and coil group C is formed, spacer3only needs to be exposed to an environment of about 120° C. for about 30 minutes to be cured. Spacer3may be cured every time the winding of one layer of superconducting wire4is completed. In this way, strength of spacer3can be secured. Winding groove5and communication groove6in which superconducting wire4is wound may be sealed with an insulating resin such as an epoxy resin. In this way, deformation of superconducting wire4due to an action of an electromagnetic force can be suppressed, and strength of superconducting coil1can be secured.

An example has been described in which the depths of the grooves of winding groove5and communication groove6are set to be substantially the same as those of superconducting wire4. However, the depths of the grooves of winding groove5and communication groove6may be set to be small as long as superconducting wire4can be disposed.

In the present embodiment, an example has been described in which two coil groups C are provided in spacer3, but the number of coil groups C is not limited. In this case, winding grooves5only needs to be provided such that a desired number (i) of coil groups C can be disposed. Communication grooves6only needs to be provided corresponding to the number of winding grooves5. In a case where three or more coil groups C are provided in spacer3, as illustrated inFIG.4, superconducting wire4is wound to form a single layer of coil group C, and in each layer, superconducting wire4is extended to the upper layer to provide i coil groups C1to Ci. Here, i is an integer greater than 1. In this case, by forming coil groups C symmetrically at the center of winding frame2, magnetic field uniformity is improved.

Second Embodiment

FIG.5is a schematic top view illustrating a part of spacer3of superconducting coil1according to a second embodiment. As in the first embodiment, superconducting coil1according to the present embodiment includes coil group C in which spacer3having winding groove5and communication groove6is disposed on winding frame2, and superconducting wire4is wound in winding groove5. Further, in the present embodiment, communication groove6of spacer3disposed in the upper layer intersects communication groove6of spacer3disposed in the lower layer in top view. The same components as those in the first embodiment are denoted by the same reference signs, and the description thereof will be omitted.

In spacer3inFIG.5, second spacer32in the upper layer is disposed on first spacer31in the lower layer, and first spacer31is seen through from second spacer32. First communication groove61of first spacer31indicated by a broken line inFIG.5and second communication groove62of second spacer32indicated by a solid line are disposed so as to intersect each other.

A broken line arrow inFIG.5indicates a direction of a current flowing through superconducting wire4disposed in first communication groove61, and a solid line arrow indicates a direction of a current flowing through superconducting wire4disposed in second communication groove62. Since coil group C is formed by folding superconducting wire4in each layer, directions in which superconducting wire4is wound in communication groove6are opposite between adjacent layers. In an example inFIG.5, when superconducting wire4is wound in a direction from first winding groove51toward second winding groove52in the first layer, superconducting wire4is wound in a direction from fourth winding groove54toward third winding groove53in the second layer.

Therefore, when the direction in which superconducting wire4is wound is opposite between adjacent layers, the direction of the flowing current can also be opposite between adjacent layers. Accordingly, when communication grooves6cross each other between adjacent layers, a magnetic field component orthogonal to the Z axis inFIG.5is canceled, and generation of an unnecessary magnetic field component can be suppressed.

Alternatively, first communication groove61and second communication groove62may overlap each other in an identical direction in top view. Similarly, since the currents flowing through communication grooves6between adjacent layers are opposite to each other, the magnetic field component orthogonal to the Z axis can be canceled, and generation of an unnecessary magnetic field component can be suppressed.

As described above, when vertically adjacent first spacer31and second spacer32included in first communication groove61and second communication groove62, respectively, are disposed so as to intersect each other or overlap each other in the same direction in top view, the directions of currents flowing through superconducting wires4disposed in first communication groove61and second communication groove62are opposite to each other, and uniformity of a magnetic field generated by superconducting coil1is improved.

First communication groove61and second communication groove62are preferably disposed substantially symmetrically in top view. In this way, a magnetic field component orthogonal to the Z axis can be suppressed by a magnetic field component generated in superconducting wire4disposed in first communication groove61and a magnetic field component generated in superconducting wire4disposed in second communication groove62.

In the present embodiment, an example has been described in which first communication groove61and second communication groove62intersect each other. The same applies to a case where another spacer3is disposed in the lower layer of first spacer31or in the upper layer of second spacer32. Communication groove6in the upper layer and communication groove6in the lower layer only need to intersect each other or overlap each other in parallel in top view.

Third Embodiment

FIG.6is an explanatory view for describing a manufacturing method for superconducting coil1according to a third embodiment. As in the first embodiment, the manufacturing method for superconducting coil1according to the present embodiment includes arranging, on winding frame2, spacer3having winding groove5and communication groove6communicating with adjacent winding groove5, and winding superconducting wire4in winding groove5and communication groove6and forming a single layer of coil group C. The present embodiment is different from the first embodiment in that superconducting wire4is automatically wound in winding groove5and communication groove6to form coil group C. The same components as those in the first embodiment are denoted by the same reference signs, and the description thereof will be omitted.

In the present embodiment, superconducting wire4is wound in spacer3using a winding guide20and a position detector30to form coil group C. Winding guide20around which superconducting wire4is wound is disposed so as to be movable in a horizontal direction (Z axis direction inFIG.6) on the outer periphery of winding frame2. A position and orientation of winding guide20are controlled on the basis of position information of winding groove5and communication groove6of spacer3measured by position detector30.

Position detector30includes a laser displacement meter, an image measurement device, and the like. In a case where a laser displacement meter is used for position detector30, the displacement can be acquired by measuring heights of bottoms and peaks between the grooves of winding groove5and communication groove6of spacer3. When an image measurement device such as a CCD camera is used as position detector30, positions of winding groove5and communication groove6can be acquired by automatically focusing focal positions of the bottoms and the peaks between the grooves of winding groove5and communication groove6of the spacer3. The position information such as the displacement, the positions of winding groove5and communication groove6is transmitted to a control device (not shown). Further, by using the position information, the control device performs control to arrange winding guide20on the grooves of winding groove5and communication groove6.

Winding frame2is provided in a rotating device (not shown) so as to be rotatable about the Z axis as a rotation center. When spacer3is provided on winding frame2and spacer3is rotated together with winding frame2, superconducting wire4can be wound from winding guide20and disposed in winding groove5and communication groove6.

Winding guide20is controlled to be disposed on the grooves of winding groove5and communication groove6detected by position detector30, winding frame2is rotated, winding guide20is sequentially moved on the grooves where superconducting wire4is not disposed, and a single layer of coil group C is automatically wound. After the single layer of coil group C is formed, spacer3is newly disposed, and a single layer of coil group C is similarly formed. By repeating the above processing, coil group C can be automatically wound and formed on the basis of the design of winding groove5and communication groove6.

In this way, by forming coil groups C of a plurality of layers on the basis of the design of winding groove5and communication groove6, superconducting wire4can be accurately wound using the position information, and the coil shape can be made as desired. Furthermore, since coil group C can be automatically wound, the production efficiency is improved.

In the present embodiment, a laser displacement meter may be used as position detector30to detect the bottoms between the grooves of winding groove5and communication groove6while slightly vibrating the laser displacement meter in the Z axis direction. This improves accuracy of the position information of winding groove5and communication groove6acquired by position detector30.

REFERENCE SIGNS LIST