JP5366391B2 - Superconducting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a superconductive element whose problem is solved that part of a superconductive wire is subjected to a normal electrical conduction transition and quenching is generated. <P>SOLUTION: In a permanent current switch (PCS) 10 shown in Fig.1, its superconductive wire 11 contains a hardened organic macromolecule 13. The organic macromolecule is prepared by impregnating hardening organic macromolecule whose viscosity is 200 (mPa S) or lower at 25&deg;C before hardening and thereafter being hardened at 60&deg;C or lower. A bending elastic modulus at 25&deg;C is 3 GPa or lower and no crack is created by a thermal shock of quenching from 25&deg;C to 77K. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a superconducting element, and more particularly to a superconducting element suitable as a magnetic field generating coil, a permanent current switch, or the like.

  A superconducting element is a superconducting coil for generating a magnetic field in a superconducting device such as a magnetic resonance diagnostic imaging apparatus, an NMR analyzer, a single crystal pulling apparatus, a magnetic levitation train, a magnetic separation apparatus, a SMES (superconducting power storage system), It is used as a permanent current switch (PCS).

  The superconducting coil is for outputting a high magnetic field with low loss, and has a structure in which a superconducting wire using a superconducting material such as a niobium-titanium alloy is wound many times. A superconducting electromagnet that outputs a high magnetic field can be obtained by cooling this to a superconducting state and passing a current.

  PCS is a switch that opens and closes by switching between the normal conducting state (resistance state) and the superconducting state (non-resistance state) of the superconducting wire by temperature control. The heater is in thermal contact with the wound superconducting wire. It has the structure to do. The superconducting wire can be switched from the normal conducting state to the superconducting state or vice versa by turning on / off the power to the heater with the PCS cooled, and the superconducting electromagnet can be operated in the permanent current mode. it can.

  In these superconducting elements, if the thermal disturbance is slight, a part of the superconducting wire easily undergoes normal conduction transition, and further, due to heat generation, the normal conduction transition spreads over the entire superconducting element. There is a situation to avoid that a quench occurs. When quenching occurs in a superconducting element, it loses a magnetic field as well as consumes a large amount of liquid helium. Even an indirect cooling coil that does not use a refrigerant takes a long time to cool to a temperature at which it returns to superconductivity again. Therefore, in order to prevent such a problem from occurring, various measures have been taken in this field to make it difficult for quenching to occur in superconducting elements.

  For example, a superconducting wire used in a superconducting element is firmly molded with resin so that it does not move due to electromagnetic force. In most cases, the superconducting element is used in such a way that a large current is applied in a high magnetic field environment, so that a large electromagnetic force acts on the superconducting wire through which the current flows. When the superconducting wire moves due to this electromagnetic force, heat is generated, and this heat may cause quenching. In order to prevent such movement of the wire, the superconducting wire is generally impregnated with a cured organic polymer such as a cured epoxy resin and fixed so as not to move inside the superconducting element.

JP-A-4-206506 JP-A-11-140415 JP 2005-322831 A JP 2003-267766 A

  As described above, the superconducting element has a structure in which a superconducting wire is molded with a cured organic polymer, but the curable organic polymer that has been used in the field has a high viscosity before curing. For this reason, there is a problem that air bubbles (voids) remain between the superconducting wires. Since there is a difference in thermal shrinkage between the cured organic polymer and the superconducting wire, an internal stress is generated when the superconducting element is cooled, and a large electromagnetic force acts on the internal superconducting wire when the superconducting element is used. For this reason, voids are generated in the cured organic polymer, and if they remain, minute cracks are generated in the organic polymer fixing the superconducting wire. When a crack occurs, heat is generated by the open energy, the temperature of the surrounding organic polymer and the superconducting wire rises, and a part of the superconducting wire undergoes a normal conducting transition to develop into a quench. As described above, the conventional superconducting element has a problem that quenching is likely to occur due to the occurrence of cracks.

An object of the present invention is to provide a superconducting element that suppresses the generation of voids inside the superconducting element and is difficult to quench, with the object of solving the above-described problems in the prior art, and the superconducting element has a bobbin shape. A superconducting element made of a superconducting wire wound around a winding frame and a cured organic polymer that fills the space between the superconducting wires, the cured organic polymer having an uncured organic viscosity of 190 mPa · S at 25 ° C. The cured organic polymer having a thickness of 5 mm, which is cured at 50 ° C. with the polymer impregnated between the lines of the superconducting wire, has a flexural modulus of 3 GPa at 25 ° C. , and a temperature of 25 ° C. is liquid. It is characterized in that no cracks are generated when it is introduced into nitrogen .

Since the space between the superconducting wires can be satisfactorily filled with the resin, it is possible to manufacture a superconducting element in which quenching hardly occurs.
Hereinafter, the present invention will be specifically described by way of embodiments, examples, and comparative examples.

Embodiment 1 FIG.
FIG. 1 and FIG. 2 explain Embodiment 1 of the present invention. FIG. 1 is a cross-sectional view of a permanent current switch 10 (PCS 10) as an example of a superconducting element of the present invention. It is the example of a circuit diagram which incorporated PCS10 in the superconducting electromagnet. In FIG. 1, a PCS 10 is composed of a superconducting wire 11 wound around a PCS winding frame 12, a cured organic polymer 13 filling the space between the superconducting wires 11, and a heater 14 (elongated white background portion). As the superconducting wire 11, for example, a superconducting material such as niobium / titanium alloy is used. As the cured organic polymer 13, for example, a cured product of an epoxy resin described later is used to fix the superconducting wire 11. It is electrically insulated. The PCS reel 12 is made of a nonmagnetic material such as glass, epoxy, or stainless steel, and functions as the core of the superconducting wire 11. The heater 14 is in thermal contact with the superconducting wire 11 and is embedded in the cured organic polymer 13 together with the superconducting wire 11.

  The PCS 10 according to the first embodiment is manufactured through the following steps. That is, the superconducting wire 11 is wound with tension to make the superconducting wire 11 firmly fixed with the PCS reel 12 as a core, and the heater 14 is attached after the winding. They are then placed in a suitable container and evacuated to remove the air between the windings. On the other hand, the uncured product of the organic polymer for impregnation is separately evacuated in the storage tank, and air or other dissolved gas dissolved in the uncured product is degassed.

  After removal of the dissolved gas, the uncured material is poured into the container held in a vacuum, and the uncured material is infiltrated into and between the windings. At that time, in order to achieve good impregnation with the uncured product, a vacuum pressure impregnation method in which pressurization and depressurization are repeated as necessary is recommended. Further, if moisture is mixed in or remains in the uncured material before curing, poor curing occurs. Therefore, prior to curing, the uncured material, the superconducting wire 11 and the PCS reel 12 are heated, vacuumed, or vacuumed under heating. It is preferable to dry by, for example. After the above impregnation, the uncured material is cured by heating as necessary, thus completing the superconducting element. In the present invention, since the uncured product is cured at a relatively low temperature of 60 ° C. or less, the curing treatment is preferably performed at 50 ° C. for about 12 hours under vacuum. If the resin that has permeated during the heating leaks, there is a problem that voids are generated inside the winding. In order to prevent this, it is preferable to impregnate and heat in an appropriate mold or container before impregnation. If molds or containers are used, they are removed after curing.

  In the present invention, if the viscosity of the cured organic polymer when it is uncured is excessive, it is difficult to fill the gap between the superconducting wires or between the superconducting wire and the winding frame with the organic polymer before curing, and voids after curing. If the curing temperature is too high, the difference in thermal shrinkage between the organic polymer and the superconducting wire will be large, resulting in a large residual internal stress. The bending organic modulus of the cured organic polymer will be excessive at room temperature. There is a problem that cracks are likely to occur when stress is applied, and among the hardened organic polymers that crack when they are put into liquid nitrogen, cracks occur even when used at extremely low temperatures. There is an easy problem.

  In the present invention, in order to solve the above problems, as the cured organic polymer, a polymer having a viscosity at 25 ° C. of 200 mPa · S or less when uncured is used. What was hardened | cured at 60 degrees C or less in the state impregnated at the wire | line 11 is used, and the above-mentioned hardening organic polymer is a thing whose bending elastic modulus in 25 degreeC is 3 GPa or less, and temperature is 25 degreeC When the cured organic polymer having a predetermined thickness is introduced into liquid nitrogen, one that does not generate cracks, that is, one having thermal shock resistance is used. The thermal shock resistance described above can be examined by checking whether or not a cured organic polymer piece to be tested having a thickness of about 1 mm kept at room temperature is placed in liquid nitrogen, and cracks are observed by visual observation. it can. Examples of the curable organic polymer and the curable organic polymer (hereinafter collectively referred to as the organic polymer of the present invention) include properties before and after curing among various conventionally known curable organic polymers. Can be selected and adopted that meets the above requirements.

  Examples of the above-described organic polymer of the present invention include, for example, epoxy resins obtained by curing a bisphenol A type epoxy resin mixed with a diluent such as butyl glycidyl ether using a modified aliphatic polyamine as a curing agent. . In addition, it is good to mix an antifoamer and a penetration support agent before hardening of the said epoxy resin. Examples of the antifoaming agent include silicone antifoaming agents such as dimethyl silicone oil and fluorine-modified silicone oil. Examples of penetration aids include higher alcohol ethylene oxide adducts, alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts, higher alkylamine ethylene oxide adducts, sorbitol and sorbitan fatty acid esters, sucrose fatty acid esters, and fluorine-based interfaces. Examples of the surfactant include surfactants.

  When a diluent such as butyl glycidyl ether is mixed with bisphenol A type epoxy resin, the viscosity of the uncured resin is lowered to prevent voids from occurring in the resin and between the wires after curing. Therefore, it is possible to obtain a material having excellent thermal shock resistance. Further, the antifoaming agent suppresses the generation of voids, and the permeability aid has an effect of improving the adhesion between the superconducting wire and the epoxy resin. Epoxy resins containing such additives have high thermal shock resistance as compared with conventional epoxy resins due to the above-mentioned effects, and as a result, a PCS that hardly causes quenching can be produced.

  Next, application of the PCS 10 in the first embodiment to a superconducting electromagnet will be described. FIG. 2 is a circuit diagram in which the PCS 10 according to the first embodiment is incorporated into a superconducting electromagnet. In FIG. 2, the superconducting electromagnet includes a PCS 10 composed of a superconducting wire 11 and a heater 14, a superconducting coil 22, a diode 23, a cryogenic vessel 24, an excitation power supply 25, a PCS power supply 26, a PCS power switch 27, and a heater 14. It is configured. In FIG. 2, a plurality of superconducting coils 22 (two examples are shown in FIG. 2) are connected in series to generate a desired magnetic field. The PCS 10 and the diode 23 combined in antiparallel are connected to both ends of the series connection of the superconducting coil 22.

  The PCS 10, the superconducting coil 22, and the diode 23 are components inside the electromagnet, and are immersed in liquid helium in the cryogenic vessel 24. Although not shown, the cryogenic container 24 includes a helium tank for holding liquid helium, a heat shield for blocking external heat radiation, a vacuum tank for thermally insulating the whole, a heat shield, and a cryogenic refrigerator for cooling the helium tank. And has a structure that suppresses evaporation of liquid helium. The excitation power supply 25 supplies a direct current to the coil circuit of the superconducting electromagnet. The PCS power supply 26 is connected to the heater 14 of the PCS 10. When the PCS power switch 27 is turned on, a current is supplied to the heater 14, and the superconducting wire 11 in the PCS 10 changes to a normal conducting state.

  When exciting the superconducting magnet, first, the PCS power switch 27 is closed and a current is passed through the heater 14 of the PCS 10 to heat the superconducting wire 11, thereby bringing the PCS 10 into a normal conducting state. In this state, when a voltage equal to or lower than the turn-on voltage of the diode 23 is applied by the excitation power supply 25 and a current is passed, the superconducting coil 22 has zero electrical resistance, while the PCS 10 is in a high resistance state, so It flows to the coil 22. In this way, the current value flowing through the superconducting coil 22 is increased to a current value at which a desired magnetic field output can be obtained. After that, when the power switch 27 for the PCS 21 is opened and the energization of the heater 14 of the PCS 10 is stopped, the superconducting wire 11 of the PCS 10 changes from the normal conducting state to the superconducting state, and the electric resistance of the circuit connected to the superconducting coil 22 is reduced. It becomes zero.

  Here, when the output current of the excitation power supply 25 is lowered, the current flowing through the circuit of the excitation power supply 25 and the superconducting coil 22 is shunted to the PCS 10, and finally all the current of the excitation power supply 25 is a circuit composed of the PCS10 and the superconducting coil 22. Will flow over. Thus, the superconducting electromagnet enters an operation mode called a permanent current mode and continues to generate a magnetic field without external power supply. Usually, the superconducting electromagnet in the permanent current mode is operated with the excitation power supply 25 and the PCS power supply 26 disconnected.

  In order to demagnetize the superconducting electromagnet in the permanent current mode, the following steps (i) to (d) are performed in reverse to the above. A: Excitation power supply 25 and PCS power supply 26 are connected to the superconducting electromagnet. B: Current is supplied from the excitation power supply 25 to the current value flowing through the superconducting coil 22. C: The heater 14 of the PCS 10 is energized and PCS10 The superconducting wire 11 is transferred to the normal conducting state. D: The current value of the exciting power supply 25 is lowered, and the current flowing through the superconducting coil 22 is lowered.

  As described above, the PCS 10 is used in a superconducting electromagnet, and a large current flows through the superconducting wire 11 in a high magnetic field environment, and a large electromagnetic force works. For example, when a current of 500 amperes flows in a magnetic field of 5000 gauss, if the superconducting wire 11 is orthogonal to the direction of the magnetic field, the magnitude of the electromagnetic force acting on the superconducting wire 11 is 250 N per meter. . When such a large electromagnetic force works, the superconducting wire 11 moves, or when a crack occurs in the cured organic polymer 13 such as an epoxy resin (see FIG. 1) fixing the superconducting wire 11, the superconducting wire 11. As a result, the cured organic polymer 13 impregnated with the superconducting wire 11 is required to have as few gaps or voids as possible between the superconducting wires.

Embodiment 2. FIG.
The first embodiment relates to the PCS 10 including the hardened organic polymer 13 having high crack resistance. However, when applied to the manufacture of a superconducting coil having the same material as the hardened organic polymer 13, the quench is caused. Difficult magnetic field generating coils can be manufactured. 3 and 4 illustrate a magnetic field generating coil as another example of the superconducting element of the present invention as the second embodiment. FIG. 3 is a plan view of the magnetic field generating coil 30. FIG. 4 is a cross-sectional view taken along line AA of FIG. 3 and 4, the magnetic field generating coil 30 includes a magnetic field generating coil winding frame 31, a superconducting wire 33 wound around the winding frame 31, and a cured organic polymer that fills the space between the superconducting wires 33. 32.

  The reel 31 is a tubular body whose body is hollow as shown in the figure, and the arrow inside the hollow indicates the direction of the magnetic field generated by the magnetic field generating coil 30. The reel 31 is made of, for example, austenitic stainless steel so as not to affect the generated magnetic field, but may be made of aluminum, titanium, or other nonmagnetic material. In addition, when it is desired to function as a magnetic core, a ferromagnetic material such as iron may be employed. The superconducting wire 33 is wound around the reel 31 with a high tension of, for example, several tens of kg in order to withstand a large electromagnetic force, and the reel 31 is required to have a high mechanical strength.

The superconducting wire 33 has a structure in which a filament such as a niobium / titanium alloy is used as a superconductor and is embedded in a copper stabilizing material, but a stabilizing material such as Nb ₃ Sn or MgB ₂ is used as the superconductor. Aluminum or other materials may be used. An epoxy resin 32 is embedded in the gap around which the superconducting wire 33 is wound around the winding frame 31, and the superconducting wire 33 is firmly fixed. The space between the superconducting wires 33 is filled without gaps by vacuum impregnation with a cured organic polymer 32 such as an epoxy resin by the same procedure as in the first embodiment.

  Next, the operation of the magnetic field generating coil 30 according to the second embodiment will be described. The connection state and operation method of the superconducting coil, PCS, and other components are the same as those of the superconducting electromagnet in the first embodiment. When a current flows through the magnetic field generating coil 30, a high magnetic field is generated. At that time, a large electromagnetic force acts on the superconducting wire forming the magnetic field generating coil 30, so that stress is generated inside the coil 30. . When a crack occurs in the cured organic polymer 32 due to this stress, the coil 30 is quenched by releasing the energy of the crack. As the cured organic polymer 32 in the second embodiment, for example, as described in the first embodiment, a mixture of an epoxy resin with a curing agent, an antifoaming agent, a permeability aid, and the like is exemplified.

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. The characteristics of a mixture in which other components are mixed with an epoxy resin are measured by the following methods and conditions. Viscosity (mPa · S); JIS-C-2103, specific gravity (25 ° C.); JIS-C-2103, tensile strength (25 ° C., N / mm ² ); ASTM-D-638, tensile modulus (25 ° C., GP-A); ASTM-D-638, bending strength (25 ° C., N / mm ² ); ASTM-D-790, flexural modulus (25 ° C., GPa); ASTM-D-790, glass transition temperature (° C.); DSC method, linear expansion coefficient (× 10-5), adhesive strength (MPa); SUS-SUS adhesion, dielectric breakdown strength (kv / mm); JIS-C-2110, crack resistance; thickness 5 mm The presence or absence of visual cracking when the test specimen was put into liquid nitrogen (77K) from 25 ° C. and rapidly cooled.

Example 1.
Viscosity at 25 ° C. as main agent: 1000 mPa · S, specific gravity: 1.14, flash point: 100 parts by mass of 79 bisphenol A type epoxy resin and viscosity at 25 ° C. as curing agent: 9 mPa · S, specific gravity: 0.95, ignition Point: A mixture with 30 parts by mass of a modified aliphatic polyamine at 125 ° C. was used. The mixture had a viscosity of 190 mPa · S and 80 mPa · S at 25 ° C. and 40 ° C. when uncured, and was cured by holding at 50 ° C. for 12 hours. The obtained cured product has a tensile strength of 58 N / mm ² , a tensile elastic modulus of 2.6 GPa, a bending strength of 80 N / mm ² , a bending elastic modulus of 3 GPa, a glass transition temperature of 60 ° C., and a linear expansion coefficient of 7.5 ×. 10 ⁻⁵ , adhesive strength 15.7 MPa, dielectric breakdown strength 18 kv / mm, and no crack was generated in the crack resistance test.

  An uncured material having the same composition as the above mixture is employed as the epoxy resin of the first embodiment, and a superconducting wire having a critical current of 1000 A in an external magnetic field of 3T is employed in the method described in the present embodiment. The permanent current switch of Embodiment 1 was manufactured by holding at 50 ° C. for 12 hours and curing. When the permanent current switch thus manufactured was energized under the condition of the externally applied magnetic field 3T and the current was gradually increased, no quenching occurred until the energization current 910A (load factor 91%).

Example 2
An uncured material having the same composition as that of Example 1 is employed as the epoxy resin 3 of the second embodiment, and a superconducting wire having a critical current of 973A in a magnetic field of 5T and a critical current of 760A in a magnetic field of 6T is employed. The magnetic field generating coil of the first embodiment was manufactured by using the method described in the above embodiment, and curing it by holding at 50 ° C. for 12 hours. When the magnetic field generating coil thus manufactured was energized under the condition of the externally applied magnetic field 3T and the current was gradually increased, no quenching occurred until the energizing current 514A. The load factor with respect to the critical current of the superconducting wire at this time was 94%.

Comparative Example 1
Viscosity at 25 ° C. as main agent: 500 mPa · S, specific gravity: 1.14, flash point: 100 parts by mass of 226 ° C. bisphenol A type epoxy resin and viscosity at 25 ° C. as curing agent: 65 mPa · S, specific gravity: 1.21, Flash point: A mixture with 86 parts by weight of a modified aliphatic polyamine at 157 ° C. was used. The mixture had a viscosity of 500 mPa · S, 145 mPa · S, and 50 mPa · S at 25 ° C., 40 ° C., and 60 ° C. when uncured, and was cured by being held at 150 ° C. for 15 hours. The resulting cured product had a tensile strength; 70N / mm ^2, tensile modulus; 2.3 GPa, flexural strength; 130N / mm ^2, flexural modulus 3.5 GPa, a glass transition temperature of 93 ° C., the linear expansion coefficient 7.16 × 10 ⁻⁵ , adhesive strength 16.2 MPa, dielectric breakdown strength 25 kv / mm, and occurrence of cracks was observed in the crack resistance test.

  An uncured material having the same composition as the above mixture is employed as the epoxy resin of the first embodiment, and a superconducting wire having a critical current of 1000 A in an external magnetic field of 3T is employed in the method described in the present embodiment. The permanent current switch of Embodiment 1 was manufactured by holding at 50 ° C. for 12 hours and curing. When the permanent current switch thus manufactured was energized under the condition of the externally applied magnetic field 3T and the current was gradually increased, quenching occurred at an energizing current of 800 A (load factor 80%).

Comparative Example 2
An uncured material having the same composition as the above mixture is employed as the epoxy resin of the second embodiment, and a critical current of 973A at a magnetic field of 5T and a critical current of 760A at a magnetic field of 6T are employed. The coil for magnetic field generation according to the second embodiment was manufactured by using the method and curing by holding at 50 ° C. for 12 hours. When the current-generating coil thus manufactured was energized under the condition of the externally applied magnetic field 3T and the current was gradually increased, quenching occurred with the energizing current 355A. The load factor with respect to the critical current of the superconducting wire at this time was 65%.

  The superconducting element of the present invention is used as a permanent current switch or a magnetic field generating coil.

It is sectional drawing of the permanent current switch in Embodiment 1 of this invention. It is an example of a circuit diagram incorporating a permanent current switch in a superconducting electromagnet. It is a top view of the coil for magnetic field generation in Embodiment 2 of this invention. FIG. 4 is a sectional view taken along line AA in FIG. 3.

Explanation of symbols

10; PCS, 11; superconducting wire, 12; reel for PCS, 13; cured organic polymer,
14; heater, 22; superconducting coil, 23; diode, 24; cryogenic vessel,
25; excitation power supply, 26; power supply for PCS, 27; power switch for PCS,
30; Coil for magnetic field generation; 31; Winding frame for coil for magnetic field generation; 32; Cured organic polymer;
33; Superconducting wire.

Claims (7)

A superconducting element made of a superconducting wire wound around a bobbin-shaped winding frame and a cured organic polymer filling a space between the superconducting wires,
The cured organic polymer is cured at 50 ° C. with an uncured organic polymer having a viscosity of 190 mPa · S at 25 ° C. impregnated between the lines of the superconducting wire, and has a flexural modulus of 3 GPa at 25 ° C. A superconducting element characterized in that no crack is generated when the cured organic polymer having a thickness of 5 mm having a temperature of 25 ° C. is introduced into liquid nitrogen .   After the superconducting wire is wound with tension applied to the reel, it is placed in a container and the uncured organic polymer is infiltrated between the windings by vacuum pressure impregnation, and heated as necessary. The superconducting element according to claim 1, obtained by curing the organic polymer. The superconducting element according to claim 1, wherein the organic polymer is an epoxy resin. The superconducting element according to claim 3, wherein the epoxy resin is a mixture of a diluent. The superconducting element according to claim 4, wherein the diluent is butyl glycidyl ether. The superconducting element according to any one of claims 1 to 5 , wherein the superconducting element is a magnetic field generating coil. The superconducting element according to any one of claims 1 to 5 , wherein the superconducting element is a permanent current switch.

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