JP2013038262A - Superconducting magnetic shield body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconducting magnetic shield body which can be manufactured at a low cost by a simple method, and a method for manufacturing the same.SOLUTION: The cylindrical superconducting magnetic shield body including a normal conducting conductor and a superconductor is characterized in that the superconductor is divided into a plurality of pieces in the circumferential direction of the cylinder and continuously extends in the axial direction of the cylinder.

Description

  The present invention relates to a superconducting magnetic shield for preventing magnetic field intrusion from the outside or correcting magnetic field fluctuations from outside.

  Since the superconductor has a physical characteristic of preventing a magnetic field from entering the superconductor, it can be used as a magnetic shield against an external magnetic field. This is because a shielding current that cancels the penetration of the external magnetic field and the fluctuation of the magnetic field flows through the superconductor.

In general, since the physical properties of a superconductor cannot be exhibited unless cooled, NbTi and Nb ₃ Sn are cooled with liquid helium, and high-temperature superconductors are cooled with liquid nitrogen. In addition, it may be cooled using a refrigerator.

  However, the superconductor is thermally unstable, and a normal conduction transition called quench occurs due to the movement of itself or the removal of cooling, and the characteristics as a superconductor are lost. For this reason, in general, when a superconductor is used, it is necessary to provide thermal tolerance in combination with a stabilizer made of copper, aluminum, or an alloy thereof.

  As a superconducting material used for a superconducting magnetic shield often used for industrial applications, a metal superconductor such as NbTi is generally used. For the above reason, it is usually combined with a stabilizing material such as copper. As a composite method, a Nb alloy plate is bonded to a copper plate, or a plurality of Nb alloy plates 41 and a stabilized copper plate 42 are alternately laminated and clad as shown in FIG. 8 (Patent Document 1). Is taken. The superconducting magnetic shield manufactured by this method needs to prepare a thin plate-like body as a superconducting material, but the plate-like superconducting material is expensive, and in order to join the plates together, it is pressed at a high pressure. There is a need to.

  Further, in order to manufacture a cylindrical superconducting magnetic shield clad by alternately laminating a plurality of Nb alloys 51 and stabilizing copper 52 as shown in FIG. 9, it is clad as shown in FIG. In addition, a method of forming a cylinder by deep drawing the superconducting magnetic shield plate and machining an end portion thereof was adopted, and the manufacturing method thereof was complicated and expensive.

JP-A-5-243778

  The present invention has been made in view of such problems, and an object of the present invention is to provide a superconducting magnetic shield that can be manufactured by a simple method and at a low cost.

  In order to solve the above problems, a first aspect of the present invention is a cylindrical superconducting magnetic shield body comprising a normal conducting conductor and a superconducting conductor, and the superconducting conductor is provided in plural in the circumferential direction of the cylinder. A superconducting magnetic shield is provided which is divided and extends continuously in the axial direction of a cylinder.

  The superconducting conductor may be composed of a plurality of superconducting filaments and arranged along multiple rows of concentric circles in the radial direction of the cylinder. By arranging multiple rows of superconducting filaments, the magnetic shield characteristics can be improved.

  In such a superconducting magnetic shield body, the superconducting filaments can be arranged so that there is at least one row in any radial direction. Arrangement so that there is at least one row in any radial direction can effectively shield the intruding magnetic field from the radial direction, and the magnetic shield characteristics can be further improved.

  The superconducting conductor may be composed of a plurality of superconducting tapes and may be disposed along the inner surface and / or outer surface of the cylindrical normal conducting conductor. In this case, the superconducting conductor and the normal conducting conductor can be joined with a good heat conductive resin.

  According to a second aspect of the present invention, there is provided a normal conductor cylinder, a composite conductor layer comprising a plurality of superconducting filaments disposed on the outer periphery of the cylinder, and an outer periphery of the composite conductor layer. A step of forming a composite cylindrical body having a normal conducting conductor sheath disposed on the substrate, and cutting the composite to provide a normal conducting conductor and a superconducting conductor, wherein the superconducting conductor has a plurality in the circumferential direction of the cylinder. There is provided a method of manufacturing a superconducting magnetic shield body comprising a step of forming a superconducting magnetic shield body that is divided into pieces and continuously extends in the axial direction of a cylinder.

  In the method of manufacturing a superconducting magnetic shield body, the step of forming the composite cylindrical body is performed by inserting a rod made of a superconducting conductor into a pipe made of a normal conducting conductor and extruding the outer circumference of the normal conducting conductor cylinder. A plurality of primary strands are formed to form a composite composed of a normal conducting cylinder and a primary strand, and the composite is inserted into the normal conducting cylinder to form a composite billet. It is possible to include performing an extrusion process on the composite billet and performing a drawing process on the extruded composite billet.

  According to the present invention, there is provided a superconducting magnetic shield that is thermally stable and can be manufactured by a simple method and at a low cost.

It is sectional drawing which shows the cylindrical superconducting magnetic shield which concerns on the 1st Embodiment of this invention. It is a perspective view which shows the cylindrical superconducting magnetic shield which concerns on the 1st Embodiment of this invention. It is a figure which shows the partial cross section of the cylindrical superconducting magnetic shield which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the cylindrical superconducting magnetic shield which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the cylindrical superconducting magnetic shield which concerns on the 4th Embodiment of this invention. It is the fragmentary sectional view which made the superconducting magnetic shield which concerns on the 2nd Embodiment of this invention into plate shape. It is the fragmentary sectional view which made the superconducting magnetic shield which concerns on the 4th Embodiment of this invention into plate shape. It is sectional drawing which shows the conventional plate-shaped superconducting magnetic shield. It is sectional drawing which shows the conventional cylindrical superconducting magnetic shield.

  Hereinafter, embodiments of the present invention will be described in detail.

  A superconducting magnetic shield according to an embodiment of the present invention has a cylindrical shape, a hollow cylindrical normal conductive conductor as a stabilizing material, and is divided into a plurality in the circumferential direction of the cylinder, and is continuous in the axial direction of the cylinder. And a superconducting conductor that extends.

In such a superconducting magnetic shield, examples of the normal conductive conductor include metals that function as a stabilizer for the normal conductive conductor, such as Cu, Cu alloy, Al, Al alloy, Ag, and Ag alloy. . Further, the superconducting conductor is not particularly limited, and examples thereof include NbTi, Nb ₃ Sn, Nb ₃ Al, MgB ₂ , Bi2212, Bi2223, REBCO (RE: rare earth element, YBCO, etc.) and the like.

  The ratio (volume ratio or cross-sectional area ratio) between the superconducting conductor and the normal conducting conductor in the circumferential direction of the cylinder is preferably 5: 1 to 5: 3. When the ratio of the superconducting conductor is more than 5: 1, the ratio of the normal conducting conductor is small, so that it is likely to become thermally unstable. When the ratio is smaller than 5: 3, the ratio of the superconducting conductor is small. For this reason, the performance of the magnetic shield is lowered, which is not preferable.

  Hereinafter, superconducting magnetic shields according to various embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a sectional view showing a cylindrical superconducting magnetic shield according to the first embodiment of the present invention, and FIG. 2 is a perspective view thereof. The superconducting magnetic shield shown in FIGS. 1 and 2 is a cylindrical superconducting magnetic shield in which a plurality of filamentous superconducting conductors 2 are embedded in a cylindrical normal conducting conductor 1 that is a stabilizing material.

  This superconducting magnetic shield is formed with a plurality of axially extending holes in the circumferential direction of the cross section of the cylindrical normal conducting conductor. After inserting the rod-shaped superconducting conductor into this hole and then extruding it, the outer and inner sides Can be formed by cutting.

  FIG. 3 is a sectional view showing a part of a cylindrical superconducting magnetic shield according to the second embodiment of the present invention. In the superconducting magnetic shield shown in FIG. 3, a plurality of filamentous superconducting conductors 12 are arranged along the concentric circle in the radial direction in the circumferential direction of the cylinder, and stable between adjacent filamentous superconducting conductors 12. A normal conducting conductor layer 11 as a chemical material is interposed.

  The superconducting magnetic shield shown in FIG. 3 is formed by inserting a rod made of a superconducting conductor into a pipe made of a normal conducting conductor and extruding it to form primary strands. The composite conductor layer can be formed by disposing the cylindrical conductive conductor on the outside of the composite conductor layer, and the outer periphery and the inner side of the composite conductor layer can be formed by extruding and then cutting the outer periphery and the inner side.

  FIG. 4 is a cross-sectional view showing a cylindrical superconducting magnetic shield according to the third embodiment of the present invention. In the superconducting magnetic shield shown in FIG. 4, a composite conductor layer in which a plurality of tape-like superconducting conductors 23 are joined to the inner and outer surfaces of a cylindrical ordinary conducting conductor 22 that is a stabilizing material is embedded in a cylindrical ordinary conducting conductor 21. A cylindrical superconducting magnetic shield.

  This superconducting magnetic shield has a structure in which the tape-shaped superconducting conductors 23 are arranged in two rows in the radial direction along concentric circles in the normal conducting conductor sheath 21. The joining of the plurality of tape-shaped superconducting conductors 23 to the inner and outer surfaces of the cylindrical normal conducting conductor 22 is an extremely low temperature adhesive that does not cause cracks or the like even at a low temperature such as liquid nitrogen temperature and maintains the adhesive force. For example, an epoxy resin adhesive, a polyimide resin adhesive, a vinyl ester resin adhesive, or the like can be used. As the cryogenic adhesive, it is preferable to use a highly heat conductive adhesive. Examples of the good heat conductive adhesive include NF Nitofex SK-299 manufactured by Nitto Denko.

  FIG. 5 is a sectional view showing a cylindrical superconducting magnetic shield according to the fourth embodiment of the present invention. The superconducting magnetic shield shown in FIG. 5 is a cylindrical superconducting magnetic shield in which a plurality of tape-shaped superconducting conductors 32 are embedded in a cylindrical normal conducting conductor 31 that is a stabilizing material.

  In this superconducting magnetic shield, tape-shaped superconducting conductors 32 are embedded in cylindrical normal conducting conductors 31 along three concentric circles in the radial direction.

  In the superconducting magnetic shield according to the third and fourth embodiments, it is preferable to use a high temperature superconductor (tape shape or thin film element shape) rather than a low temperature superconductor such as NbTi. As the tape-shaped high-temperature superconductor, for example, an RE-based superconducting tape wire in which an intermediate layer and a superconducting layer are formed on a long metal substrate, or a Bi-based superconducting tape wire in which Bi2223 or the like is arranged in a silver matrix is used. be able to. As the high-temperature superconductor in the form of a thin film element, an RE-based superconducting thin film element in which an intermediate layer and a superconducting layer are formed on a plate-like substrate can be used. In the case of a high-temperature superconductor in the form of a thin film element, it is preferable to use a plate-shaped substrate formed in advance by bending.

  High-temperature superconductors exhibit performance with liquid nitrogen and are more stable than low-temperature superconductors, so that both manufacturing costs and running costs are excellent.

  The performance of the magnetic shield is determined by the critical current density (Jc) and volume (cross-sectional area) of the superconductor, and it is known that the higher (larger) both the better the magnetic shield performance. On the other hand, for thermal stability, it is preferable that the contact area (cooling circumference) with the normal conductor (stabilizing material) is large.

  Here, the thermal stability of the conventional conductive magnetic shield body and the superconducting magnetic shield body according to the present embodiment is examined. 8 using the conventional magnetic shield plate shown in FIG. 8, the superconducting magnetic shield plate according to the second embodiment shown in FIG. 6, and the superconducting magnetic shield plate according to the fourth embodiment shown in FIG. Consider the contact area (cooling circumference) with the chemical material.

  6 to 8 are plate-like superconducting shields for the sake of convenience, the cylindrical case also has the same effect in relation to the conventional example.

<Examination of thermal stability>
(1) Cooling circumference of the second embodiment The magnetic shield body according to the second embodiment shown in FIG. 6 has a width (circumferential length) L ₁ and a thickness t ₁ , and a thickness (diameter) d. ₁ of superconducting filaments and has _one N. The cross-sectional area ratio of the normal conducting conductor (stabilizing material) and the superconducting conductor in the magnetic shield body is λ ₁ : 1.

In this case, the total sectional area S ₁ of the superconducting conductor,

It becomes.

In addition, the number _{N 1} of the superconducting filaments,

It becomes.

From the above, the cooling circumference x ₁ in the second embodiment is the product of the circumference of the superconducting filament and the number of superconducting filaments.

It becomes.

(2) Cooling circumference of the fourth embodiment The magnetic shield body according to the fourth embodiment shown in FIG. 7 has a width (circumferential length) L ₂ and a thickness t ₂ , and has a thickness d ₂ and a width. It is assumed that there are n ₂ superconducting filaments of w ₂ per circumference and the total number of superconducting filaments is N ₂ . In this case, the size (width) ratio between the superconducting conductor and the normal conducting conductor in the circumferential direction is 5: a. Further, the cross-sectional area ratio of the normal conducting conductor (stabilizing material) and the superconducting conductor in the magnetic shield body is λ ₂ : 1.

In this case, the total sectional area S ₂ of the superconducting conductor,

It becomes.

The cross-sectional area s ₂ of the superconducting filament at this time is

Therefore, the number N _{2 of} superconducting filaments is

It becomes.

Thus, cooling perimeter x ₂ in the fourth embodiment,

It becomes.

(3) Cooling Perimeter of Conventional Example The conventional magnetic shield shown in FIG. 8 has a width (circumferential length) L ₃ and a thickness t ₃ , and has N ₃ superconducting layers with a thickness d _3. Suppose that Further, the cross-sectional area ratio of the normal conducting conductor (stabilizing material) and the superconducting conductor in the magnetic shield is λ ₃ : 1.

In this case, the total sectional area S ₃ of the superconducting conductor,

It becomes.

In addition, the number _{N 3} of the superconducting filaments,

It becomes.

From the above, the cooling circumference x ₃ in the conventional magnetic shield body is

It becomes.

(4) Comparison above type cooling circumference (1) to compare - cooling perimeter _x 1 ~x ₃ obtained in (3). The cross-sectional area (t × L = S) and the copper ratio (λ) of the entire magnetic shield body are the same for each shield body (t ₁ = t ₂ = t ₃ = t, L ₁ = L ₂ = L ₃ = L, λ ₁ = λ ₂ = λ ₃ = λ)
Equation (1) is

Equation (2) is

Equation (3) is

It becomes.

Here, with respect to the thickness (d _{1 to} d ₃ ) of the superconductor (superconducting filament, superconducting layer), as described above, a certain amount of thickness is required to maintain the magnetic shield characteristics. Therefore, here, the thickness of the superconducting conductor is also the same for each shield body (d ₁ = d ₂ = d ₃ = d).
Equation (1) is

Equation (2) is

Equation (3) is

It becomes.

From Expressions (4) to (6), the relationship between x ₁ , x ₂ , and x ₃ is as follows.

From the above, the magnetic shield body according to the second embodiment has about twice the thermal stability as compared with the conventional example, and the magnetic shield body according to the fourth embodiment is equivalent to the following formula compared with the conventional example. It can be seen that it has excellent thermal stability.

  By dividing the superconducting conductor in the circumferential direction in this manner, the contact area with the normal conducting conductor (stabilizing material) can be increased while having a superconducting conductor that can maintain the magnetic shield characteristics. Therefore, heat retention and cooling of the superconductor can be promoted while maintaining the magnetic shield characteristics, and quenching can be prevented.

Incidentally, the magnetic shield body according to a fourth embodiment, n ₂ is the number of filaments of the superconducting conductors in one turn, means a number of divisions in the circumferential direction. Therefore, although it is preferable that the number of divisions in the circumferential direction is large, the ratio of the superconducting conductor and the normal conducting conductor in the circumferential direction of the cylinder is in the range of 5: 1 to 5: 3 in order to maintain the magnetic shielding characteristics. It is preferable to divide into two.

  Further, higher thermal stability can be obtained by making the cross-sectional shape of the superconducting filament circular as in the magnetic shield body according to the second embodiment.

  A magnetic shield body having a superconducting filament with a circular cross-section like the magnetic shield body according to the second embodiment can be manufactured as follows.

  First, a NbTi rod is inserted into a copper tube to create a single-core billet, which is extruded to form a primary strand. Next, a primary strand is arranged around a copper cylinder, and this is inserted into a copper tube to create a multi-core billet. The multi-core billet is extruded and further drawn. Thereafter, the inside and the outer periphery of the extruded and drawn multi-core billet are cut.

  By manufacturing as described above, a cylindrical superconducting magnetic shield in which a plurality of rod-shaped superconducting conductors (NbTi filaments) 12 are embedded in a cylindrical normal conducting conductor (copper cylinder) 11 as shown in FIG. Can be manufactured.

  In the superconducting magnetic shield, it is necessary to make the superconducting conductor thin to some extent in order to effectively cool the superconducting conductor. However, the superconducting magnetic shield according to the first and second embodiments described above is manufactured by extrusion and drawing. Therefore, the superconducting conductor can be easily made thin by increasing the rolling reduction and the extrusion ratio. In addition, rolling and extrusion performed in the manufacturing process also has an advantage that the cost is lower than that of manufacturing a clad plate in a conventional superconducting magnetic shield.

  The superconducting magnetic shield described above can be suitably used for an MRI superconducting magnet which is a medical diagnostic imaging apparatus. For example, a GM type helium refrigerator is installed above the superconducting magnet to cool the internal members. The refrigerating machine contains a magnetic regenerator material, but this magnetic regenerator material moves with cooling, which causes disturbance in the magnetic uniformity of the superconducting magnet. On the other hand, by arranging the superconducting magnetic shield according to the present embodiment outside the regenerator moving part of the refrigerator, it is possible to reliably shield the superconducting magnet from the magnetic regenerator.

  The superconducting magnetic shield according to the present embodiment is particularly effective for shielding a magnetic field acting in a direction perpendicular to the axis of the superconductor rather than a magnetic field in the same direction as the axis. Therefore, the superconducting magnetic shield according to the present embodiment can be suitably used for the magnetic shield of the cryogenic refrigerator attached to the MRI.

  1, 2, 22, 31... Cylindrical normal conductor, 2, 12 Filament superconductor, 13 Normal conductor layer, 32 Tape superconductor.

Claims (7)

A cylindrical superconducting magnetic shield body comprising a normal conducting conductor and a superconducting conductor,
The superconducting magnetic shield is characterized in that the superconducting conductor is divided into a plurality of pieces in the circumferential direction of the cylinder and extends continuously in the axial direction of the cylinder.   The superconducting magnetic shield body according to claim 1, wherein the superconducting conductor is composed of a plurality of superconducting filaments, and is arranged along a plurality of rows in a concentric circle in the radial direction of the cylinder.   The superconducting magnetic shield body according to claim 2, wherein the superconducting filaments are arranged so as to exist in at least one row in any radial direction.   The superconducting conductor is composed of a plurality of superconducting tapes and / or superconducting thin film elements, and the superconducting tape and / or superconducting thin film elements are disposed along the inner surface and / or outer surface of a cylindrical normal conducting conductor. The superconducting magnetic shield body according to claim 1, wherein the superconducting magnetic shield body is provided.   The superconducting magnetic shield body according to claim 4, wherein the superconducting conductor and the normal conducting conductor are joined together by a highly heat conductive resin. A normal conductor cylinder, a composite conductor layer comprising a plurality of superconducting filaments, the outer peripheral surface of which is arranged on the outer periphery thereof, and a normal conductor sheath disposed on the outer periphery of the composite conductor layer; Forming a composite cylindrical body, and cutting the composite cylindrical body to provide a normal conducting conductor and a superconducting conductor, the superconducting conductor being divided into a plurality in the circumferential direction of the cylinder, and A method of manufacturing a superconducting magnetic shield comprising the step of forming a superconducting magnetic shield extending continuously in the axial direction. The step of forming the composite cylindrical body includes
A plurality of primary strands formed by inserting a rod made of a superconducting conductor into a pipe made of a normal conducting conductor and extruding the pipe are arranged on the outer periphery of the normal conducting conductor cylindrical body. And forming a composite composed of primary strands;
Inserting the composite into a normal conducting cylinder and forming a composite billet;
Extruding the composite billet;
The method for producing a superconducting magnetic shield body according to claim 6, further comprising a step of performing a drawing process on the extruded composite billet.

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