JP2014192182A - Permanent current switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a permanent current switch which has high quench resistance equal to or more than the prior arts and is reduced in cost.SOLUTION: The permanent current switch comprises: a reel; a superconducting coil 30 made of a superconducting wire wound around the reel; a heater for controlling a temperature of the superconducting wire; and a thermal diffusion sheet 502. The thermal diffusion sheet is formed by overlaying a thermal conductor layer 57 having a predetermined circuit shape on at least one surface of a resin sheet 55. The thermal conductor layer is disposed between the superconducting coil and the reel so as to be abutted with the superconducting wire of an innermost layer of the superconducting coil and/or the superconducting wire of an axial end face of the superconducting coil. The thermal conductor layer has a heat conductivity higher than that of a metal base material forming the superconducting wire and a thickness of 5 μm or more and 50 μm or less.

Description

  The present invention relates to a permanent current switch for operating a superconducting magnet in a permanent current mode, and more particularly to a permanent current switch having high quench resistance and low cost.

  Typical products using superconducting magnets (electromagnets wound with superconducting wires) include nuclear magnetic resonance analyzers (NMR) and nuclear magnetic resonance imaging devices (MRI), which are widely used in the biotechnology and medical fields. Yes. These devices are required to have a very small magnetic field attenuation rate of 0.1 ppm / h or less in magnetic field accuracy, and are normally operated in a permanent current mode. In order to achieve the permanent current mode operation of the superconducting magnet, a switch device called a permanent current switch (PCS) is used.

  The permanent current switch generally includes a superconducting winding (superconducting coil) in which a superconducting wire (superconducting wire for PCS) in which a superconducting filament is embedded in a metal base material having a high electrical resistivity is wound, and a heater. It has a configuration. Such a permanent current switch is turned on / off depending on the superconducting state (zero electric resistance) / normal conducting state (electrical resistance resulting from the shunting to the metal base material) of the superconducting wire by temperature control of the heater. In other words, since the electrical resistance gap is used to turn on / off the switch, in the superconducting wire for PCS, a metal base material of a normal superconducting wire (for example, a good conductor such as oxygen-free copper or pure aluminum, or a stabilizing material) It is preferable to use a metal base material (for example, copper nickel alloy) having a much higher electrical resistivity than

  On the other hand, because metals with high electrical resistivity have low thermal conductivity, superconducting wires for PCS have lower thermal diffusivity than ordinary superconducting wires, even when they have a metal base, and they have quench resistance. There is a tendency to decrease (a slight thermal disturbance can easily cause a quench). Therefore, PCS superconducting wires and permanent current switches with high quench resistance are strongly desired.

  When the fluctuation of the magnetic field applied to the superconducting wire is sufficiently small like a permanent current switch, the heat that causes the temperature rise of the superconducting wire is generally generated not near the superconducting wire but near the surface of the superconducting wire (for example, In most cases, heat is generated by friction between the superconducting winding and the winding frame, and heat is generated by cracking or peeling of the impregnated material. Rapid diffusion of these locally generated heats is an effective method for preventing quenching.

  As a superconducting wire capable of quickly diffusing locally generated heat, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 10-116722), a plurality of superconducting filaments are embedded in a matrix and the surface is insulated. A superconducting conductor having a diameter smaller than the diameter of the superconducting wire and having a plurality of insulated, heat-insulated conductors closely wound around a superconducting wire having a circular cross section. It is disclosed. According to Japanese Patent Laid-Open No. 2004-260260, the insulated good heat conductor wire wound around the superconducting wire is localized heat generated around the superconducting wire, for example, friction between superconducting conductors and cracking of the impregnating agent. Heat can be diffused in the length direction, local temperature rise can be prevented, quenching is not caused, and the good conductor wire of heat wrapped around the superconducting wire is thin, and Since insulation is applied, even if a fluctuating magnetic field is applied, heat generation due to generation of eddy current is very small, and there is little risk of quenching due to temperature rise.

  Non-Patent Document 1 discloses a wire structure (superconducting wire, insulation coating, and anisotropy provided with extreme anisotropy in the thermal conductivity in the linear and radial directions in order to reduce disturbances that cause instability of the superconducting wire. A copper-coated three-layer structure) is disclosed. In Non-Patent Document 2, in order to improve the transient stability of the wire for the superconducting winding of Non-Patent Document 1, the influence of the geometrical structure of the wire and the thermal characteristics of the winding structure has been studied and reported. Yes. According to Non-Patent Document 2, by providing a copper coating, heat can be easily transferred along the copper coating in the longitudinal direction of the wire, cooling efficiency with helium can be increased, and minimum quench energy (MQE) can be increased. It is supposed to be possible.

JP-A-10-116722

Toshiaki Onishi, Satoshi Ishii, Noboru Higuchi, Katsuyuki Kaiho, Haruhiko Nomura: "A Consideration on the Stability of Superconducting Wires", The 40th 1988 Fall Cryogenic Engineering and Superconductivity Society Preliminary Proceedings, page 82 Yutaka Ueno, Keisuke Aoki, Atsushi Ishiyama: “Improvement of transient stability of high current density superconducting magnets”, 51st 1994 Spring Cryogenic Engineering and Superconductivity Society Annual Meeting, 249 pages

  In the superconducting wire described in Non-Patent Document 1, electroless plating has been proposed as a method for forming a copper coating on an insulating coating (for example, formal (PVF) coating). However, the electroless plating of a copper thin film on a formal coating is not only a factor in increasing the manufacturing cost, but also there is a high possibility that sufficient adhesion cannot be secured between the formal coating and the copper thin film. There is a concern that the copper coating may peel off when winding the wire. Further, the superconducting wires described in Non-Patent Documents 1 and 2 are not actually prototyped (calculated design), and are not guaranteed to be practically used. Furthermore, it is described in Non-Patent Document 1 that an eddy current is generated through the copper coating.

  On the other hand, in the superconducting conductor described in Patent Document 1, a plurality of small-diameter wires serving as a heat diffusion medium are spirally formed around the PCS superconducting wire with almost or no gap over the entire length of the PCS superconducting wire. Since it is wound, an increase in cost associated with winding the thin wire is inevitable. Furthermore, since the superconducting conductor described in Patent Document 1 winds the thin wire over the entire length of the PCS superconducting wire, depending on the direction of the varying magnetic field applied to the superconducting wire, the influence of heat generation due to eddy current loss is exerted. May not be ignored.

  Also, superconducting products are still expensive, and cost reduction is an important issue for expanding the use of superconducting products.

  Accordingly, an object of the present invention is to provide a permanent current switch having a high quench resistance equal to or higher than that of the conventional one and having a lower cost than the conventional one.

One aspect of the present invention is a permanent current switch for a superconducting magnet to achieve the above object, wherein the permanent current switch includes a winding frame and a superconducting coil made of a superconducting wire wound around the winding frame. And a heater for controlling the temperature of the superconducting wire, and a thermal diffusion sheet,
In the thermal diffusion sheet, a good thermal conductor layer having a predetermined circuit shape is laminated on at least one surface of a resin sheet, and the good thermal conductor layer is the innermost layer of the superconducting coil. / Or disposed between the superconducting coil and the winding frame so as to come into contact with the superconducting wire on the axial end face of the superconducting coil,
The thermal good conductor layer has a higher thermal conductivity than the metal base material constituting the superconducting wire, and has a film thickness of 5 μm or more and 50 μm or less.

  According to the present invention, it is possible to provide a permanent current switch having a high quench resistance equal to or higher than that of the conventional one and having a cost lower than that of the conventional one.

It is a longitudinal cross-sectional schematic diagram which shows an example of the permanent current switch which concerns on this invention. It is a longitudinal cross-sectional schematic diagram which shows another example of the permanent current switch which concerns on this invention. It is a longitudinal cross-sectional schematic diagram which shows another example of the permanent current switch which concerns on this invention. It is a plane schematic diagram which shows an example of the circuit shape of the heat good conductor layer in the thermal diffusion sheet of this invention. It is a plane schematic diagram which shows another example of the circuit shape of the heat good conductor layer in the thermal diffusion sheet of this invention. It is a plane schematic diagram which shows another example of the circuit shape of the heat good conductor layer in the thermal diffusion sheet of this invention. It is a plane schematic diagram which shows another example of the circuit shape of the heat good conductor layer in the thermal diffusion sheet of this invention. It is an expanded section schematic diagram of an example of a permanent current switch concerning the present invention. 5 is a graph showing the relationship between the temperature of a metal base material and the distance from a heating point in a three-layer structure of a metal base material, an electrical insulating layer, and a good thermal conductor layer. It is a perspective schematic diagram which shows an example of the manufacture process of the permanent current switch which concerns on this invention.

  This inventor earnestly investigated about the heat penetration into the superconducting winding (superconducting coil) which becomes a quenching factor in order to provide a permanent current switch having high quench resistance equal to or higher than that of the conventional one and lower cost than the conventional one. . As a result, undesired heat generation that causes the permanent current switch to quench is caused by the interface region between the superconducting coil and other components (for example, the interface region between the superconducting coil and the winding frame, superconductivity, rather than inside the superconducting coil). It has been found that this occurs mainly in the interface region between the coil and the heater. In other words, it was considered that by selectively increasing the thermal diffusivity in a region where undesired heat generation is likely to occur, the cost can be reduced while maintaining the quench resistance equivalent to the conventional one.

  When the present inventor investigated the quenching factor in more detail, it was found that the influence of heat generation due to eddy current loss generated in the thermal diffusion layer imparted to enhance thermal diffusibility was larger than originally expected. . In other words, it was necessary to divide the loop of the eddy current generated in the heat diffusion layer as small as possible, and thus it was considered that the quench resistance could be improved more than before. That is, in order to achieve the object of the present invention, it has been found that it is important to achieve both improvement of thermal diffusivity in a selective region and suppression of eddy current loss. The present invention is based on this finding.

As described above, the permanent current switch according to the present invention includes a winding frame, a superconducting coil made of a superconducting wire wound around the winding frame, a heater for controlling the temperature of the superconducting wire, and a heat diffusion sheet. Equipped,
In the thermal diffusion sheet, a good thermal conductor layer having a predetermined circuit shape is laminated on at least one surface of a resin sheet, and the good thermal conductor layer is the innermost layer of the superconducting coil. / Or disposed between the superconducting coil and the winding frame so as to come into contact with the superconducting wire on the axial end face of the superconducting coil,
The good thermal conductor layer has a higher thermal conductivity than the metal base material constituting the superconducting wire, and has a film thickness of 5 μm or more and 50 μm or less.

The present invention can add the following improvements and changes to the permanent current switch according to the above invention.
(I) The predetermined circuit shape bridges the adjacent superconducting wires in the innermost layer of the superconducting coil, or bridges the adjacent superconducting wires every other layer on the axial end surface of the superconducting coil. It is formed to do.
(Ii) The resin sheet of the thermal diffusion sheet has flexibility.
(Iii) The permanent current switch further includes a third heat diffusion sheet, and the third heat diffusion sheet has a good thermal conductor layer having a predetermined circuit shape on at least one surface of the flexible resin sheet. The thermal conductive layer of the third heat diffusion sheet is disposed on the outer periphery of the superconducting coil so as to be in contact with the superconducting wire of the outermost layer of the superconducting coil. The heat good conductor layer of the heat diffusion sheet 3 has a higher thermal conductivity than the metal base material constituting the superconducting wire, and has a film thickness of 5 μm or more and 50 μm or less.
(Iv) In the permanent current switch, the superconducting coil is composed of a stack of a plurality of superconducting subcoils, and further includes a fourth heat diffusion sheet, and the fourth heat diffusion sheet has a predetermined circuit shape. The good conductor layer is laminated on both surfaces of the flexible resin sheet, and the heat good conductor layer of the fourth heat diffusion sheet is in contact with the superconducting wire of the plurality of superconducting subcoils. Each of the good thermal conductor layers of the fourth heat diffusion sheet is disposed between a plurality of superconducting subcoils, and has a higher thermal conductivity than the metal base material constituting the superconducting wire, and is not less than 5 μm and not more than 50 μm. It has the following film thickness.
(V) the predetermined circuit shape of the heat diffusion sheet, the predetermined circuit shape of the heat good conductor layer of the third heat diffusion sheet, and the predetermined circuit shape of the heat good conductor layer of the fourth heat diffusion sheet. The circuit shape is formed in at least one of a stripe shape, a mosaic shape, a meander shape, and a radial shape.
(Vi) The heat good conductor layer of the heat diffusion sheet, the heat good conductor layer of the third heat diffusion sheet, and the heat good conductor layer of the fourth heat diffusion sheet are made of copper or aluminum.
(Vii) The heat diffusion sheet, the third heat diffusion sheet, and the fourth heat diffusion sheet are provided with air vent holes.
(Viii) In the heat diffusion sheet and the third heat diffusion sheet, a heater circuit layer is laminated on the surface of the resin sheet and the flexible resin sheet opposite to the surface on which the heat good conductor layer is formed. And the heater circuit layer is the heater.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to a synonymous part and the overlapping description is abbreviate | omitted. Further, the present invention is not limited to the embodiments taken up here, and can be appropriately combined and improved without departing from the technical idea of the invention.

[Permanent current switch]
FIG. 1 is a schematic longitudinal sectional view showing an example of a permanent current switch according to the present invention. As shown in FIG. 1, the permanent current switch 10 according to the present invention includes a superconducting coil comprising a winding frame 20 (winding drum body portion 21 and winding frame flange portion 22) and a superconducting wire wound around the winding frame 20. 30, a heater 40 that controls the temperature of the superconducting wire, a thermal diffusion sheet 50 (in FIG. 1, a first thermal diffusion sheet 51 and a second thermal diffusion sheet 52), and a thermal insulating layer 60.

  The first heat diffusion sheet 51 is disposed between the superconducting coil 30 and the winding body part 21 so as to contact the innermost layer of the superconducting coil 30. The second heat diffusion sheet 52 is disposed between the superconducting coil 30 and the reel part 22 so as to contact the axial end surface of the superconducting coil 30. The heater 40 is disposed between the first heat diffusion sheet 51 and the reel body 21. The thermal insulating layer 60 is disposed so as to cover the outermost layer of the superconducting coil 30.

  When the superconducting coil 30 has an elongated shape (when “the axial length of the superconducting coil 30” is sufficiently larger than “the thickness in the radial direction of the superconducting coil 30”), the second thermal diffusion sheet 52 is disposed. It does not have to be done. Conversely, when the superconducting coil 30 is flat (when the “axial length of the superconducting coil 30” is sufficiently smaller than the “diameter thickness of the superconducting coil 30”), the first heat diffusion sheet 51 is disposed. It may not be provided. The shape of the superconducting coil 30 is a matter that is appropriately designed depending on the position and space where the permanent current switch is installed.

  FIG. 2 is a schematic longitudinal sectional view showing another example of the permanent current switch according to the present invention. As shown in FIG. 2, the permanent current switch 11 includes a winding frame 20 (winding frame body portion 21 and winding frame flange portion 22), a superconducting coil 30 made of a superconducting wire wound around the winding frame 20, and a superconducting switch. A heater 40 for controlling the temperature of the wire, a thermal diffusion sheet 50 (in FIG. 2, a first thermal diffusion sheet 51 and a third thermal diffusion sheet 53), and a thermal insulating layer 60 are provided.

  The third heat diffusion sheet 53 is disposed on the outer periphery of the superconducting coil 30 so as to be in contact with the outermost layer of the superconducting coil 30. The heater 40 is disposed on the outer periphery of the third heat diffusion sheet 53.

  FIG. 3 is a schematic longitudinal sectional view showing still another example of the permanent current switch according to the present invention. As shown in FIG. 3, the permanent current switch 12 includes a superconducting coil 30 (FIG. 3) made of a superconducting wire wound around the reel 20 (the reel body 21 and the reel frame 22) and the reel 20. Then, the first superconducting subcoil 31 and the second superconducting subcoil 32), the heater 40 for controlling the temperature of the superconducting wire, and the thermal diffusion sheet 50 (in FIG. 3, the first thermal diffusion sheet 51 and the fourth thermal diffusion sheet 54). And a heat insulating layer 60.

  In the permanent current switch 12, the superconducting coil 30 has a laminated structure of a first superconducting subcoil 31 and a second superconducting subcoil 32. The fourth thermal diffusion sheet 54 is disposed between the first superconducting subcoil 31 and the second superconducting subcoil 32 so as to come into contact with each of the first superconducting subcoil 31 and the second superconducting subcoil 32.

  In the permanent current switches 10 to 12, at least the winding frame 20, the superconducting coil 30, the heater 40, and the thermal diffusion sheet 50 may be integrated by vacuum pressure impregnation of resin (for example, epoxy resin). preferable.

  Hereinafter, each configuration of the permanent current switch according to the present invention will be described in more detail.

(Reel)
There is no particular limitation on the material of the reel 20 (the reel body 21 and the reel flange 22), and conventional materials can be used. For example, glass fiber reinforced plastic (GFRP) can be preferably used. Further, the reel 20 may be manufactured by machining a cylindrical material or a thick-walled pipe material as an integral part, or a reel frame body 21 and a reel flange portion 22 prepared separately are integrated. May be used.

(Superconducting coil / superconducting wire)
The configuration of the superconducting coil 30 is not particularly limited, and a conventional PCS superconducting coil (for example, a solenoid coil in which a superconducting wire is wound non-inductively) can be used. Moreover, as shown in FIG. 3, you may be comprised from the lamination | stacking of several superconducting subcoil. In the superconducting coil 30, the arrangement of the superconducting wires in the coil axial direction is referred to as “turn”, and the arrangement of the superconducting wires in the coil radial direction is referred to as “layer”.

  Further, the superconducting wire constituting the superconducting coil 30 is not particularly limited, and a conventional PCS superconducting wire can be used. As an example, a superconducting wire in which a plurality of superconducting filaments (for example, a niobium-titanium alloy superconductor) are embedded in a metal base material (for example, a copper-nickel alloy) having a high electrical resistivity can be preferably used. The superconducting wire preferably has an electrically insulating layer (for example, formal (PVF) coating) on its surface. Even if the superconducting wire is tightly wound, it is between adjacent turns and between adjacent layers in the superconducting coil 30. So that it is not short-circuited.

(heater)
The material of the heater 40 is not particularly limited, and a conventional material (for example, copper-manganese-nickel alloy) can be used. As shown in FIGS. 1 and 3, when the heater 40 is disposed between the superconducting coil 30 and the winding frame 20, the heater 40 is arranged so that the winding of the superconducting coil 30 is not disturbed. It is preferably formed over the entire circumference and length of the portion 21. On the other hand, as shown in FIG. 2, when the heater 40 is disposed on the outer periphery of the superconducting coil 30, the heater 40 may not be formed over the entire periphery of the superconducting coil 30.

(Thermal insulation layer)
The material of the heat insulating layer 60 is not particularly limited, and a conventional material (for example, a glass cloth is wound and then hardened with a resin) can be used. In the permanent current switch of the present invention, the heat insulating layer 60 may not be formed because it is not an essential component. However, in order to suppress excessive consumption (excess evaporation) of the refrigerant (for example, liquid helium) when the switch is turned off. Is preferably formed.

(Heat diffusion sheet)
The thermal diffusion sheet 50 (the first thermal diffusion sheet 51, the second thermal diffusion sheet 52, the third thermal diffusion sheet 53, the fourth thermal diffusion sheet 54) has a heat good conductor layer having a predetermined circuit shape as at least one of the resin sheets. The heat good conductor layer is disposed so as to come into contact with the superconducting wire of the superconducting coil 30. The good thermal conductor layer preferably has a higher thermal conductivity than the metal base material constituting the superconducting wire for PCS, and for example, copper or aluminum can be suitably used. The heat good conductor layer preferably has a thickness of 5 μm or more and 50 μm or less.

  The thermal diffusion sheet 50 (in particular, the first thermal diffusion sheet 51, the third thermal diffusion sheet 53, and the fourth thermal diffusion sheet 54) is provided between the superconducting coil 30 and the winding frame body 21, the outer periphery of the superconducting coil 30, Since the first superconducting subcoil 31 and the second superconducting subcoil 32 are disposed so as to be wound around, it is preferable to have flexibility. Therefore, it is preferable that the resin sheet which comprises these thermal diffusion sheets has flexibility and cold resistance, for example, can use a polyimide suitably. Further, the heat diffusion sheet (resin sheet) may be a wide sheet having the same width as the length of the winding drum body 21 (the axial length of the superconducting coil 30), or the length of the winding drum drum 21. It may be a ribbon sheet that is shorter (thin) than that.

  As described above, since the influence of the eddy current loss generated in the thermal diffusion layer applied to increase the thermal diffusibility in the prior art is very large, in order to increase the quench resistance of the permanent current switch, It is desirable to divide the resulting eddy current loop as small as possible.

  4A to 4D are schematic plan views illustrating examples of the circuit shape of the good thermal conductor layer in the thermal diffusion sheet of the present invention. FIG. 4A shows an example (thermal diffusion sheet 501) in which a stripe-shaped heat good conductor layer 56 is formed on a resin sheet 55. FIG. FIG. 4B shows an example (thermal diffusion sheet 502) in which a mosaic-shaped thermal good conductor layer 57 is formed on a resin sheet 55. FIG. 4C shows an example (thermal diffusion sheet 503) in which a meander-shaped thermal good conductor layer 58 is formed on a resin sheet 55. FIG. 4D shows an example of the second heat diffusion sheet 52, which is an example (thermal diffusion sheet 504) in which a radial good thermal conductor layer 59 is formed on a resin sheet 55. Thus, by forming the circuit shape of the good heat conductor layer thin and / or small, the loop of eddy current generated in the good heat conductor layer can be divided into small parts.

  The circuit shape of the good heat conductor layer is not limited to the above, and the width of the good heat conductor layer circuit in consideration of the magnitude and direction of the magnetic field fluctuation applied to the permanent current switch, the desired heat diffusion direction, etc.・ Design the length. Moreover, the shape which combined the circuit shape of FIG. 4A-FIG. 4D may be sufficient.

  In the first heat diffusion sheet 51, the third heat diffusion sheet 53, and the fourth heat diffusion sheet 54, the circuit shape of the heat good conductor layer is formed so as to bridge adjacent turns with the superconducting wire of the superconducting coil 30 that abuts. It is preferable that In the second heat diffusion sheet 52, the circuit shape of the heat good conductor layer is preferably formed so as to bridge the superconducting wires adjacent to each other on the axial end surface of the superconducting coil 30 that abuts. By thermally diffusing in a direction different from the winding direction of the superconducting wire (longitudinal direction of the superconducting wire), locally generated heat can be dispersed more widely and thinly.

  In addition, it is preferable that the good thermal conductor layers are formed on both surfaces of the resin sheet 55. Thereby, thermal diffusibility can further be improved. If a heat diffusion sheet having a good thermal conductor layer on both surfaces of the resin sheet 55 is disposed between the superconducting coil 30 and the heater 40, the heat from the heater 40 is transmitted to the superconducting coil 30 more evenly and in a shorter time. Since it can be heated, there is also a secondary effect that the switching speed of the permanent current switch is improved. In addition, when forming a heat good conductor layer on both surfaces of the resin sheet 55, the circuit shape of each heat good conductor layer may be the same, and may differ.

  As the thermal diffusion sheet 50 as described above, for example, a copper-clad laminate having a flexible resin sheet as a base material is etched to form a desired circuit shape (so-called flexible printed wiring board). Can be suitably used. In other words, by using a flexible printed wiring board with a desired circuit shape, the thermal diffusion sheet 50 can be prepared at low cost, and the thermal diffusion sheet 50 is disposed in the permanent current switch with good workability. can do.

  Note that the second heat diffusion sheet 52 is disposed between the axial end face of the superconducting coil 30 and the reel part 22 and therefore does not necessarily require flexibility. Therefore, from the viewpoint of reducing the number of components of the permanent current switch and the assembly workability of the permanent current switch, a desired circuit shape is directly formed on one surface of a glass fiber reinforced plastic substrate (so-called rigid printed wiring) The reel part 22 and the second heat diffusion sheet 52 may be integrated using a plate.

  Next, the reason why the permanent current switch according to the present invention can improve the quench resistance as compared with the prior art will be described.

  FIG. 5 is an enlarged schematic sectional view of an example of the permanent current switch according to the present invention, and shows the vicinity of the first heat diffusion sheet 51 of the permanent current switch 11 shown in FIG. As the first heat diffusion sheet 51, the heat diffusion sheet 502 shown in FIG. 4B is used.

  As shown in FIG. 5, in the first heat diffusion sheet 51 (heat diffusion sheet 502), a heat good conductor layer 57 is laminated on one surface of the resin sheet 55, and the heat good conductor layer 57 is formed in the superconducting coil 30. The superconducting coil 30 is disposed between the superconducting coil 30 and the winding body 21 so as to contact the innermost superconducting wire. The superconducting wire for PCS has an electrically insulating layer on its surface. The winding frame 20, the superconducting coil 30, and the first heat diffusion sheet 51 are integrated with an impregnating resin.

  As described above, undesired heat generation (for example, generation of cracks or peeling of the impregnated resin) that causes quenching tends to occur in the interface region between the superconducting coil and other components. FIG. 5 shows the case where heat is generated in the interface region between the first heat diffusion sheet 51 and the winding drum body 21. The generated heat diffuses in the winding drum body 21 and the resin sheet 55 of the thermal diffusion sheet 502, and part of the heat reaches the good thermal conductor layer 57 of the thermal diffusion sheet 502. Since the thermal conductivity of the good thermal conductor layer 57 is sufficiently high, the heat that has reached the good thermal conductor layer 57 quickly propagates and diffuses in the good thermal conductor layer 57, and the thin and widespread heat in the adjacent multi-turn PCS superconducting wire Penetrates through the electrical insulation layer. Compared to the case where the first thermal diffusion sheet 51 (thermal diffusion sheet 502) is not disposed, the volume of the PCS superconducting wire that intrudes heat increases, so that the temperature of the PCS superconducting wire at each turn increases. It is suppressed. As a result, the quench resistance of the permanent current switch is improved.

  Next, the film thickness of the good thermal conductor layer of the thermal diffusion sheet will be described.

  As the thickness of the thermal good conductor layer decreases, the thermal resistance increases and the thermal diffusibility decreases. As the thickness increases, the thermal diffusibility increases, but the eddy current loss increases and the thermal disturbance increases. Therefore, in order to estimate the optimum film thickness of the good thermal conductor layer, there are three virtual layers of the superconducting wire metal base material (Cu-Ni), electrical insulation layer (PVF), and thermal diffusion sheet thermal good conductor layer (Cu). In the structure, the relationship between the temperature of the metal base material of the superconducting wire and the distance from the heating point was calculated by the difference method.

  As the boundary conditions, the thickness of the metal base material is 0.4 mm, the thickness of the electrical insulation layer is 35 μm, and the thickness of the thermal conductor layer is 0, 0.1, 1, 2, 5, 10, 20, 50, 100 μm. did. “Thickness of good thermal conductor layer = 0 μm” means a case where no good thermal conductor layer is formed. The thermal conductivities of the metal matrix, electrical insulation layer, and good thermal conductor layer are 1,0.1 and 200 W / (m K). The initial temperature of the system was 4.2 K, and the exothermic point (temperature 20 K) was in contact with the outside of the good thermal conductor layer. The temperature change of specific heat was also taken into consideration. The calculation results are shown in FIG.

  FIG. 6 is a graph showing the relationship between the temperature of the metal base material and the distance from the heating point in a three-layer structure of the metal base material, the electrical insulating layer, and the good thermal conductor layer. As shown in FIG. 6, when the thickness of the heat good conductor layer is 0.1 μm, there is almost no effect of heat diffusion by the heat good conductor layer (this is almost the same as the case of the heat good conductor layer = 0 μm), and heat generation The temperature of the metal base material just above the point rose to over 7 K. At this temperature, there is almost no temperature margin with the critical temperature of Nb-Ti, so quenching is considered to occur. It can be seen that the maximum temperature of the metal base material decreases as the thickness of the good thermal conductor layer increases.

  Here, from the viewpoint of the thermal stability of the superconducting wire, it is desired that the temperature rise with respect to the thermal disturbance is within 1 K (that is, 5.2 K or less). In consideration of the standard, the thickness of the good thermal conductor layer is preferably 5 μm or more, and more preferably 10 μm or more. On the other hand, when the thickness of the good thermal conductor layer is 50 or 100 μm, there is almost no increase in temperature. Becomes larger. Therefore, the thickness of the heat good conductor layer is preferably 50 μm or less, and more preferably 20 μm or less.

  According to this calculation, it was found that the thermal diffusion length was about 10 mm, and the length mainly acting on the thermal diffusion was about 3 mm. From this, it can be said that the good thermal conductor layer is preferably configured to have a continuous length of 6 mm or more and 20 mm or less in consideration of symmetry.

  In the heat diffusion sheet 50 (in particular, the first heat diffusion sheet 51, the second heat diffusion sheet 52, and the third heat diffusion sheet 53), a predetermined circuit shape is formed on the surface of the resin sheet 55 on the side in contact with the superconducting coil 30. It is preferable that the heat good conductor layer is laminated and the heater circuit layer is laminated on the opposite surface of the resin sheet 55. By utilizing the heater circuit layer as the heater 30 of the permanent current switch, the conventional heater is not necessary, and the permanent current switch can be downsized.

  There is no particular limitation on the circuit shape of the heater circuit layer, but a non-inductive circuit shape is preferable. Also, the heater circuit layer material is not particularly limited. For example, using copper or copper-manganese-nickel alloy, the circuit dimensions (film thickness, width, length) are set so that a desired resistance value can be obtained. Just design.

  As described above, the permanent current switch is preferably integrated by vacuum pressure impregnation with resin (for example, epoxy resin). At this time, if bubbles remain in the impregnated resin, the bubbles are likely to become a starting point of cracks in the impregnated resin, so it is necessary to prevent the bubbles from remaining.

  FIG. 7 is a schematic perspective view showing an example of the manufacturing process of the permanent current switch according to the present invention. In the permanent current switch 11 shown in FIG. 2, a state in which the third heat diffusion sheet is wound around the outer periphery of the superconducting coil 30. It is shown. As shown in FIG. 7, the heat diffusion sheet 50 'of the present invention is provided with a hole 70 for venting air. Thereby, when resin impregnation is performed, no bubbles remain in the impregnated resin, and cracking of the impregnated resin due to the bubbles can be prevented.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, this invention is not limited to this Example.

(Production of permanent current switch)
As an example of the present invention, the permanent current switch shown in FIG. 1 (without the second thermal diffusion sheet 52) is manufactured, and as a comparative example, a permanent current switch without a thermal diffusion sheet and a heat good conductor layer A permanent current switch having a heat diffusion sheet not forming a circuit structure was produced.

  A GFRP reel is prepared as the reel 20, Nb-Ti superconducting wire coated with PVF is used as the superconducting wire for PCS (the metal base material is Cu-Ni alloy), and Cu-Mn- is used as the heater 40 Prepare Ni alloy wire, prepare flexible printed circuit board with 20μm thick Cu layer circuit on one surface of polyimide sheet as first heat diffusion sheet 51, and use glass cloth as thermal insulation layer 60 Prepared. The Cu layer circuit of the first heat diffusion sheet 51 was a circuit having a mosaic shape (6 mm square, 0.5 mm interval) as shown in FIG. 4B.

  First, a heater 40 was disposed by winding a Cu—Mn—Ni alloy wire on the reel body 21 of the reel 20. Next, the first heat diffusion sheet 51 was disposed on the heater 40 so that the Cu layer circuit of the heat diffusion sheet faces outward. Next, the superconducting coil 30 was formed by non-inductively winding a superconducting wire for PCS on the Cu layer circuit of the heat diffusion sheet. Next, six layers of glass cloth were wound to cover the outermost layer of the superconducting coil 30 to form a heat insulating layer 60. Finally, the whole was integrated by vacuum pressure impregnation of an epoxy resin to produce the permanent current switch of the example.

  A permanent current switch of Comparative Example 1 was produced in the same manner as in Example except that the first heat diffusion sheet 51 was not provided.

  Except for using a copper-clad laminate (with a 20 μm thick Cu layer laminated on the entire surface of one surface of the polyimide sheet) as a thermal diffusion sheet, without using a circuit structure. A permanent current switch of Comparative Example 2 was produced.

(Quench resistance evaluation)
The quench resistance of the permanent current switch produced above was evaluated as follows. The permanent current switch was fixed to a jig and installed in a cryostat filled with liquid helium. The permanent current switch to be measured was arranged so that the applied magnetic field was orthogonal to the axial direction of the superconducting coil 30. A 1.5 T magnetic field was applied to the permanent current switch to be measured, and the current-voltage characteristics of the superconducting coil 30 were measured by the four-terminal method. The energization current value at which the voltage of the superconducting coil 30 suddenly occurred was defined as a quench current. An energization test was performed 10 times or more on one permanent current switch, and the minimum quench current value was evaluated. In addition, the quench current of the superconducting wire for PCS alone (a linear short sample not wound in a coil shape) was separately measured.

  As a result of the measurement, the value of the minimum quench current of the permanent current switch of Comparative Example 1 manufactured without providing the thermal diffusion sheet is about 30% (about 60 A) with respect to the quench current 200 A of the PCS superconducting wire alone. there were. The value of the minimum quench current of the permanent current switch of Comparative Example 2 using a copper clad laminate having no circuit structure as the heat diffusion sheet was about 43% (about 85 A). On the other hand, the minimum quench current value of the permanent current switch of the example in which the first thermal diffusion sheet 51 is disposed is about 120 A, which is about twice that of Comparative Example 1 and about 1.4 times that of Comparative Example 2. Improved.

  As described above, according to the present invention, it has been proved that a permanent current switch having high quench resistance equal to or higher than that of the conventional one and having a lower cost than the conventional one can be provided.

  Note that the above-described embodiments and examples have been specifically described in order to help understanding of the present invention, and the present invention is not limited to having all the configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, a part of the configuration of each embodiment can be deleted, replaced with another configuration, or added with another configuration.

10, 11, 12 ... permanent current switch, 20 ... reel, 21 ... reel body, 22 ... reel frame,
30 ... Superconducting coil, 31 ... First superconducting subcoil, 32 ... Second superconducting subcoil,
40 ... Heater, 50, 50 '... Heat diffusion sheet,
51 ... 1st heat diffusion sheet, 52 ... 2nd heat diffusion sheet,
53 ... 3rd heat diffusion sheet, 54 ... 4th heat diffusion sheet, 55 ... Resin sheet,
56 ... Striped thermal conductor layer, 57 ... Mosaic thermal conductor layer,
58 ... Meander-shaped thermal conductor layer, 59 ... Radial-shaped thermal conductor layer,
501, 502, 503, 504 ... thermal diffusion sheet,
60 ... Heat insulation layer, 70 ... Hole for venting.

Claims (14)

A permanent current switch for a superconducting magnet,
The permanent current switch comprises a winding frame, a superconducting coil made of a superconducting wire wound around the winding frame, a heater for controlling the temperature of the superconducting wire, and a thermal diffusion sheet,
In the thermal diffusion sheet, a good thermal conductor layer having a predetermined circuit shape is laminated on at least one surface of a resin sheet, and the good thermal conductor layer is the innermost layer of the superconducting coil. / Or disposed between the superconducting coil and the winding frame so as to come into contact with the superconducting wire on the axial end face of the superconducting coil,
The permanent current switch, wherein the good thermal conductor layer has a higher thermal conductivity than a metal base material constituting the superconducting wire and has a film thickness of 5 μm or more and 50 μm or less. The permanent current switch according to claim 1,
The permanent current switch is characterized in that the predetermined circuit shape is formed in at least one of a stripe shape, a mosaic shape, a meander shape, and a radial shape. The permanent current switch according to claim 2, wherein
The predetermined circuit shape bridges the superconducting wires adjacent to each other in the innermost layer of the superconducting coil, or bridges the superconducting wires adjacent to each other in the axial end surface of the superconducting coil. A permanent current switch characterized by being formed. The permanent current switch according to any one of claims 1 to 3,
A permanent current switch, wherein the heat diffusion sheet is provided with a hole for venting air. The permanent current switch according to any one of claims 1 to 4,
A permanent current switch, wherein the resin sheet has flexibility. The permanent current switch according to any one of claims 1 to 5,
The permanent thermal switch, wherein the good thermal conductor layer is made of copper or aluminum. The permanent current switch according to any one of claims 1 to 6,
In the thermal diffusion sheet, a heater circuit layer is laminated on the surface of the resin sheet opposite to the surface on which the thermal conductor layer is formed,
The permanent current switch, wherein the heater circuit layer is the heater. The permanent current switch according to any one of claims 1 to 7,
The permanent current switch further comprises a third heat diffusion sheet,
The third heat diffusion sheet is obtained by laminating and forming a heat good conductor layer having a predetermined circuit shape on at least one surface of a flexible resin sheet, and the heat good conductor of the third heat diffusion sheet. Disposed on the outer periphery of the superconducting coil such that the layer contacts the superconducting wire of the outermost layer of the superconducting coil;
The thermal good conductor layer of the third heat diffusion sheet has a higher thermal conductivity than the metal base material constituting the superconducting wire and has a film thickness of 5 μm or more and 50 μm or less. switch. The permanent current switch according to claim 8,
The predetermined circuit shape of the thermal conductor layer of the third heat diffusion sheet is formed into at least one of a stripe shape, a mosaic shape, a meander shape, and a radial shape. switch. In the permanent current switch according to claim 8 or 9,
The permanent current switch according to claim 3, wherein the heat good conductor layer of the third heat diffusion sheet is made of copper or aluminum. The permanent current switch according to any one of claims 8 to 10,
In the third thermal diffusion sheet, a heater circuit layer is laminated on the surface of the flexible resin sheet opposite to the surface on which the thermal good conductor layer is formed,
The permanent current switch, wherein the heater circuit layer of the third heat diffusion sheet is the heater. The permanent current switch according to any one of claims 1 to 11,
In the permanent current switch, the superconducting coil is composed of a stack of a plurality of superconducting subcoils, and further includes a fourth heat diffusion sheet,
In the fourth heat diffusion sheet, a heat good conductor layer having a predetermined circuit shape is laminated on both surfaces of the flexible resin sheet, and the heat good conductor layer of the fourth heat diffusion sheet is Disposed between the plurality of superconducting subcoils so as to contact the superconducting wires of the plurality of superconducting subcoils;
Each of the good thermal conductor layers of the fourth thermal diffusion sheet has a higher thermal conductivity than the metal base material constituting the superconducting wire and has a film thickness of 5 μm or more and 50 μm or less. Permanent current switch. The permanent current switch according to claim 12,
The predetermined circuit shape of the good thermal conductor layer of the fourth heat diffusion sheet is formed into at least one of a stripe shape, a mosaic shape, a meander shape, and a radial shape. switch. The permanent current switch according to claim 12 or claim 13,
The permanent current switch according to claim 4, wherein the good thermal conductor layer of the fourth thermal diffusion sheet is made of copper or aluminum.

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