JP7242580B2 - superconducting electromagnet - Google Patents

Description

Embodiments of the present invention relate to conductively cooled superconducting electromagnets.

Conventionally, liquid helium immersion has been the mainstream method for cooling superconducting electromagnets that generate an induced magnetic field by circulating a persistent current. In recent years, a heat conduction method for directly cooling a superconducting electromagnet with cold heat supplied by a cryogenic refrigerator has been studied. In either of these two schemes, a persistent current switch (PCS) is used when starting the superconducting electromagnet. That is, the persistent current switch is set to OFF, and an excitation current is supplied from the power source to generate an induced magnetic field in the main coil (driven mode). After that, the persistent current switch is switched to the ON setting, and the supply of the excitation current is gradually reduced to shift to the persistent current mode (PC mode).

The persistent current switch includes a non-inductive coil of superconducting wire and a heater wire. Then, by heating/removing the heat from the non-inductive winding coil in the cooled state, the normal conducting state/superconducting state is switched, and the persistent current switch is set to OFF/ON.

In the case of cooling by the liquid helium immersion method, the heat generated when the persistent current switch is turned off is dissipated into liquid helium, which is a coolant, except for raising the temperature of the non-inductive winding coil. Therefore, there was no particular need to consider the influence of the heat generated when the persistent current switch is turned off on the main coil.

JP 2018-010948 A

However, in the case of cooling by heat conduction, part of the heat generated when the persistent current switch is turned off reaches the main coil. There is concern that the temperature of the main coil will rise due to this reaching heat, and that the critical point of superconductivity will be exceeded, leading to a normal conduction transition (quench).

Further, while pure copper is used for the matrix of the superconducting wire of the main coil, a high-resistance alloy (CuNi) is used for the matrix of the superconducting wire of the persistent current switch. A wire having a CuNi matrix is less stable than a superconducting wire having a copper matrix, and is likely to be quenched due to magnetic instability. For this reason, it can be said that the superconducting electromagnet cooled by the heat conduction method has the risk of quenching in the persistent current switch and its surroundings.

The embodiments of the present invention have been made in consideration of such circumstances, and it is an object of the present invention to provide a superconducting electromagnet that reduces the risk of quenching when cooled by heat conduction.

In the superconducting electromagnet according to the embodiment, a main coil around which a first superconducting wire is wound to generate an induced magnetic field, a second superconducting wire of non-inductive winding, and a heat generating portion for switching the second superconducting wire from a superconducting state to a normal conducting state. a connecting member for connecting in parallel a pair of said first superconducting wires drawn out as first lead wires from said main coil and a pair of said second superconducting wires drawn out as second lead wires from said persistent current switch in parallel. a first heat transfer member that supports the main coil and the connecting member and transfers cold heat supplied from the cryogenic refrigerator; and a first heat transfer member that transfers the cold heat to the persistent current switch. and a second heat transfer member that supports the second lead wire, wherein the second heat transfer member is an intermediate member that contacts the second lead wire and is separated from the intermediate member and positioned at both ends thereof. and an electrical insulating material disposed on the connection surface of the intermediate member and the end member and the contact surface of the second lead line and the end member, or the second heat transfer member a groove having a reversed shape of one side surface of the outer periphery of the second lead wire is engraved, or the second heat transfer member has a wire shape, and the second heat transfer member is the second lead wire Circumscribe each other linearly.

Embodiments of the present invention provide a superconducting electromagnet that reduces the risk of quenching when cooled in a thermal conduction fashion.

1 is a longitudinal sectional view of a superconducting electromagnet according to an embodiment of the present invention; FIG. FIG. 2 is a partially enlarged view of the superconducting electromagnet indicated by symbol A in FIG. 1; 1 is a circuit diagram of a superconducting electromagnet according to an embodiment; FIG. (A) A conceptual diagram showing a cross section of a first superconducting wire forming a main coil and a first lead wire, (B) A conceptual diagram showing a cross section of a second superconducting wire forming a persistent current switch and a second lead wire. A graph showing changes in electrical resistance values of superconductors and matrix bodies constituting the first superconducting wire and the second superconducting wire with respect to temperature. Graph explaining the three critical points of the superconducting state (critical current Ic, critical temperature Tc, critical magnetic field Hc). (A), (B), (C), and (D) are graphs for explaining the excitation process of the superconducting electromagnet. (A), (B), (C), and (D) are cross-sectional views showing an embodiment of a support mechanism for the second lead wire in the second heat transfer member. FIG. 11 is a side sectional view showing another embodiment of the second heat transfer member; FIG. 11 is a side sectional view showing another embodiment of the second heat transfer member; (A) A side sectional view showing another embodiment of the second heat transfer member, (B) a BB sectional view thereof. FIG. 4 is a partially enlarged view of a superconducting electromagnet according to a comparative example; A circuit diagram of a superconducting electromagnet according to a comparative example. 4 is a graph showing quench current values of a superconducting electromagnet according to a comparative example; (a), (b), and (c) are partial cross-sectional views of experimental samples for confirming the effect of thermal contact performance between the second heat transfer member and the second lead wire. FIG. 16 is a graph showing quench current values at various set temperatures for the experimental sample of FIG. 15;

(First embodiment)
An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view of a superconducting electromagnet 10 according to an embodiment. FIG. 2 is a partial enlarged view of the superconducting electromagnet 10 indicated by symbol A in FIG.

Thus, the superconducting electromagnet 10 includes the main coil 15 wound with the first superconducting wire 11 to generate an induced magnetic field, the non-inductive second superconducting wire 12, and the second superconducting wire 12 from the superconducting state to the normal conducting state. A persistent current switch 17 including a switching heating portion 16, a pair of first superconducting wires 11 drawn out from the main coil 15 as first lead wires 11a, and a pair of second superconducting wires drawn out from the persistent current switch 17 as second lead wires 12a. A connection member 18 that connects the wires 12 in parallel, a first heat transfer member 21 that supports the main coil 15 and the connection member 18 and transfers cold heat supplied from the cryogenic refrigerator 30, and from the first heat transfer member 21 A second heat transfer member 22 that transfers cold heat to the persistent current switch 17 and supports the second lead wire 12a.

The above-described main coil 15, persistent current switch 17, first heat transfer member 21, and second heat transfer member 22 must be kept below the critical temperature Tc of superconducting transition, so they are housed in a heat insulating vacuum vessel 28. there is The heat insulating vacuum container 20 further has a radiation shield 29 in order to reduce the effect of heat intrusion from the environment (room temperature: about 300K) in which the superconducting electromagnet 10 is installed. The weights of the radiation shield 29, the first heat transfer member 21 and the persistent current switch 17 are supported from the heat insulating vacuum vessel 28 by supporting members (not shown).

A GM refrigerator 30 is exemplified as the cryogenic refrigerator 30 in the embodiment. The first freezing stage 31 and the radiation shield 29 of the GM refrigerator 30 are connected, and the second freezing stage 32 and the first heat transfer member 21 are connected. The radiation shield 29 is cooled to about 40K and the first heat transfer member 21 is cooled to about 4K due to the effect of adiabatic compression of the working gas (such as He gas) enclosed in the GM refrigerator 30 from the compressor (not shown). .

The adopted cryogenic refrigerator 30 is not limited to the GM refrigerator described above. Pulse tube refrigerators, Claude refrigerators, Stirling refrigerators, and the like, which can generate extremely low temperatures, are appropriately employed.

FIG. 3 is a circuit diagram of the superconducting electromagnet 10 according to the embodiment. As described above, in the superconducting electromagnet 10, the excitation power supply 35 is connected to the persistent current switch 17 and the main coil 15 which are connected in parallel. By forming the circuit in this way, the excitation power supply 35 and the main coil 15 form a closed circuit in the driven mode, and the main coil 15 and the persistent current switch 17 form a closed circuit in the persistent current mode (PC mode). .

The main coil 15 is formed by winding the first superconducting wire 11 in one direction, and generates an induced magnetic field when a current flows. The persistent current switch 17 is provided with a non-inductive wound coil that does not generate an induced magnetic field even when a current flows, and two coils each having the second superconducting wire 12 wound in opposite directions are connected in series. The heat generating portion 16 of the persistent current switch 17 includes an electric resistor 37 arranged close to the non-inductive winding coil, and controlling the electric power supplied to the electric resistor 37 to heat the non-inductive winding coil in a superconducting state. and a power controller 36 that changes to a conducting state.

Terminal ends of a pair of first lead wires 11 a (first superconducting wires 11 ) drawn from the main coil 15 are connected to connecting members 18 . Terminations of a pair of second lead wires 12 a (second superconducting wires 12 ) drawn from persistent current switch 17 are also connected to connecting member 18 . Thus, the main coil 15 and the persistent current switch 17 are connected in parallel to form a closed circuit.

FIG. 4A is a conceptual diagram showing a cross section of the first superconducting wire 11 forming the main coil 15 and the first lead wire 11a. FIG. 4B is a conceptual diagram showing a cross section of the second superconducting wire 12 forming the persistent current switch 17 and the second lead wire 12a.

In this way, the first superconducting wire 11 and the second superconducting wire 12 are composed of the superconductor 41 that switches between the superconducting state and the normal conducting state depending on the set temperature, and the matrix body 42 (42a, 42b) that shows the normal conducting state regardless of the set temperature. ) and Although the matrix body 42 and the superconductor 41 are formed in a sea-island shape when viewed in cross section, the structure is not limited to such a structure, and may be formed in layers, for example.

FIG. 5 is a graph showing changes in electrical resistance with respect to temperature of the superconductors 41 and the matrix bodies 42 (42a, 42b) that constitute the first superconducting wire 11 and the second superconducting wire 12. As shown in FIG. At a temperature lower than the critical temperature Tc, the superconductor 41 has zero electrical resistance and can pass a persistent current. On the other hand, when the superconductor 41 exceeds the critical temperature Tc, the electrical resistance value rises abruptly, and the electrical resistance value further rises as the temperature rises. In the embodiment, a widely used NbTi alloy is exemplified as the superconductor 41, but the material is not limited to this.

The matrix body 42a of the first superconducting wire 11 is made of an oxygen-free shell having a small electrical resistance, and the matrix body 42b of the second superconducting wire 12 is made of a copper alloy having a larger electrical resistance than that of the oxygen-free shell. The reason why the electrical resistance value of the matrix body 42b of the second superconducting wire 12 is increased in this way is that in the driven mode in which the persistent current switch 17 is set to OFF (the electrical resistor 37 generates heat), as will be described later, This is because it must have a large electrical resistance value.

FIG. 6 is a graph explaining the three critical points (critical current Ic, critical temperature Tc, critical magnetic field Hc) of the superconducting state. If even one of these critical points is exceeded, the superconducting wires 11 and 12 may transition (quench) from the superconducting state to the normal conducting state and burn out. Moreover, as can be seen from this graph, even if the temperature of the superconducting wires 11 and 12 is lower than the critical temperature Tc, the critical current drops from _I1 to _I2 when the set temperature rises from _T1 to _T2 . . Therefore, it is necessary to prevent the heat generated by the electrical resistor 37 from being transmitted to the main coil 15 when the persistent current switch 17 is turned off.

The excitation process of the superconducting electromagnet 10 will be described based on the graph of FIG. 7 (see FIG. 3 as necessary). First, both the main coil 15 and the persistent current switch 17 are cooled to a temperature _T1 indicating a superconducting state. Next, as shown in FIG. 7(A), the control of the heating unit 16 is activated to cause the electric resistor 37 to generate heat, and as shown in FIG. The temperature is raised to the indicated temperature _T3 . In the heating process starting from time _t1 , at time _t2 when the coil temperature exceeds the critical temperature _Tc , the persistent current switch 17 is turned off, and a closed circuit including the excitation power source 35 and the main coil 15 is formed. . It should be noted that the heat transfer to the first heat transfer member 21 is suppressed by a structure described later so that the heat generated by the electric resistor 37 forming this closed circuit does not contribute to an unwanted temperature rise of the main coil 15 .

As shown in FIG. 7(C), the excitation power supply 35 is activated at time _t2 when the persistent current switch 17 is turned OFF, and the main coil 15 is closed so that the excitation current value _A1 has a positive slope. Pass current through the circuit. Then, when the excitation current value _A1 reaches the rated value, the current flowing through the closed circuit of the main coil 15 is made constant, and the driven mode is achieved.

After reaching the driven mode, the control of the heating unit 16 is disabled at time _t3 as shown in FIG. 7(A). Then, the temperature of the persistent current switch 17 drops as shown in FIG. 7(B). In the cooling process started from time _t3 , the persistent current switch 17 is turned ON at time _t4 when the coil temperature drops below the critical temperature _Tc . It should be noted that rapid heat transfer from the persistent current switch 17 to the first heat transfer member 21 in this temperature lowering process shortens the time difference between the time _t3 and the time _t4 , and the ON setting of the persistent current switch 17 is early. can be achieved. This requirement is in a trade-off relationship with the above-described requirement for suppressing the temperature rise of the main coil 15, but the design is made in consideration of the balance.

At time _t4 when persistent current switch 17 returns to the ON setting, a closed circuit of main coil 15 and persistent current switch 17 is formed. Then, as shown in FIG. 7C, the excitation power source 35 is controlled so that the excitation current value _A1 has a negative slope. In this process, based on Lenz's law, a persistent current is induced in the closed circuit of the main coil 15 and the persistent current switch 17 so as not to change the induced magnetic field penetrating the main coil 15, as shown in FIG. 7(D). The current value _A2 of this persistent current increases in inverse proportion to the decrease in the exciting current value _A1 , and reaches a constant value at time _t5 when the exciting current value _A1 becomes zero. At this time _t5 , a persistent current mode is achieved in which steady current continues to flow through the main coil 15 without electromotive force.

Returning to FIG. 1, the description continues. The first heat transfer member 21 is made of a material having high mechanical rigidity, non-magnetization, and high thermal conductivity, such as copper, copper alloy, aluminum, and aluminum alloy. The first heat transfer member 21 is supported by a support member (not shown) from the inside of the heat insulating vacuum vessel 28 and receives cold heat from the cryogenic refrigerator 30 in contact therewith. Cold heat supplied from the cryogenic refrigerator 30 is supplied to the main coil 15, the first lead wire 11a, and the connection member 18 which are supported by transmitting the first heat transfer member 21. As shown in FIG. Furthermore, cold heat supplied from the cryogenic refrigerator 30 is transmitted to the second heat transfer member 22 via the first heat transfer member 21 and supplied to the persistent current switch 17 .

The second heat transfer member 22 has a base end fixed to the first heat transfer member 21 and a tip end supporting the persistent current switch 17 . Furthermore, the second heat transfer member 22 forms a transition section of the second lead wire 12 a that continues from the connection member 18 to the non-inductive coil of the persistent current switch 17 . Thus, the second heat transfer member 22 transfers cold heat from the first heat transfer member 21 to the persistent current switch 17 and supports the second lead wire 12a.

In some cases, the weight of the persistent current switch 17 is entirely borne by the second heat transfer member 22, and part of the weight is a support member (not shown) extending directly from the heat insulating vacuum vessel 28 or the first heat transfer member 21. ) may be supported by Cold heat supplied to the persistent current switch 17 may also be transmitted through other heat transfer members (not shown) extending from the first heat transfer member 21 other than via the second heat transfer member 22 .

The copper alloy, which is the matrix body 42b of the second lead wire 12a (second superconducting wire 12), is more heat resistant than the oxygen-free copper (pure copper), which is the matrix body 42a of the first lead wire 11a (first superconducting wire 11). Lower conductivity by one order of magnitude or more. For this reason, the heat transfer between the first heat transfer member 21 and the persistent current switch 17 is so small that it can be ignored through the second lead wire 12 a , and almost all of it is through the second heat transfer member 22 .

The second lead wire 12 a is supplied with cold heat from the cryogenic refrigerator 30 by being in contact with the second heat transfer member 22 . The second lead wire 12a and the second heat transfer member 22 are brought into good thermal contact with each other by mechanical means such as pressing with a jig or fixing with an adhesive or brazing material.

Further, the second lead wire 12a and the second heat transfer member 22 may be brought into contact with each other with an electrical insulating material 24 interposed therebetween. By interposing the sheet-like electrical insulating material 24, thermal contact with small conductance can be achieved while electrically insulating. The electrical insulating material 24 may be, for example, a thin sheet of polyimide or the like, fiber-reinforced plastic, aluminum nitride, boron nitride, alumina, polyamide (nylon), polyethylene, vinyl chloride, fluororesin, or materials containing these as components. is mentioned.

The second heat transfer member 22 is provided with a constricted portion 26 whose cross section is reduced compared to the end portions 25 and 27 in the midway path along the second lead wire 12a. That is, compared with the heat transfer portion 25 in thermal contact with the first heat transfer member 21 and the heat transfer portion 27 in thermal contact with the persistent current switch 17, the narrowed portion 26 has a reduced cross-sectional area perpendicular to the longitudinal direction. part. Although the figure shows an aspect in which the dimension in the vertical direction is narrowed down, there is also an aspect in which the dimension in the depth direction is narrowed down.

By adjusting the design dimensions of the constricted portion 26 in this way, it is possible to control the rate of part of the heat generated when the persistent current switch 17 is turned off, which causes heat to be conducted to the first heat transfer member 21 . In other words, it facilitates equipment design that suppresses heat conduction in the opposite direction without impeding good heat conduction of cold heat from the first heat transfer member 21 to the persistent current switch 17 .

That is, in actual equipment design, it is inevitable that the second heat transfer member 22 has a complicated curved shape, and it is difficult to perform electrical heat calculations assuming a constant cross-sectional area. However, by providing the constricted portion 26 as described above, the electrothermal calculation is facilitated. It should be noted that the present invention does not exclude the application of the second heat transfer member 22 that does not have the constricted portion 26 and has a constant cross-sectional area.

8A, 8B, 8C, and 8D are sectional views showing an embodiment of a support mechanism for the second lead wires 12a in the second heat transfer member 22. FIG. By adopting such a support mechanism, the thermal contact performance between the second lead wire 12a and the second heat transfer member 22 is improved, and the cooling of the second lead wire 12a is promoted. As a result, even if some instability factors such as mechanical disturbances or changes in the distribution of the intruding magnetic flux occur in the second lead wire 12a, the heat generated by these factors can be released quickly.

In FIG. 8A, the second lead wire 12a is fixed to the surface of the second heat transfer member 22 with a fixing material 46 such as epoxy resin. Furthermore, an insulating layer 47 may be interposed between the second lead wire 12 a and the second heat transfer member 22 . Also, the fixing member 46 may be a mechanical component such as a holding jig.

In FIG. 8B, the surface of the second heat transfer member 22 is engraved with a groove 48 having an inverted shape of one side surface of the outer circumference of the second lead wire 12a. The groove 48 is engaged with the second lead wire 12a.

In FIG. 8C, the second heat transfer member 22 is provided so as to cover the entire outer circumference of the second lead wire 12a. In this case, the second heat transfer member 22 has a split structure, and the surface of each split body is provided with a groove having an inverted shape of the outer peripheral surface facing the second lead wire 12a. These divided bodies are configured to sandwich the second lead wire 12a. This improves the thermal contact performance of the second lead wire 12a with the second heat transfer member 22 over the entire outer peripheral surface, further promoting cooling.

In FIG. 8D, the second heat transfer member 22 has the same wire shape as the second lead wire 12a. The wire-shaped second heat transfer member 22 and the second lead wire 12a are linearly in contact with each other. Good linear thermal contact between the two is ensured by soldering, brazing, fixing with resin, or the like. The illustrated second heat transfer member 22 is exemplified as having a circular cross section, but may also have a rectangular cross section, and the cross-sectional shape of the second heat transfer member 22 is not particularly limited.

Note that in FIGS. 8A to 8D described above, if the insulation between the second lead wire 12a and the second heat transfer member 22 is maintained by other means, the insulating layer 47 is omitted. may Further, the illustrated second lead wire 12a is exemplified as having a circular cross section, but the cross-sectional shape of the second lead wire 12a is not particularly limited.

By the way, the length of the second superconducting wire 12 wound as a non-inductive coil inside the persistent current switch 17 is much longer than the length of the second lead wire 12a. However, the second superconducting wire 12 wound as a non-inductive coil can easily dissipate heat to the adjacent wire even if signs of quenching appear. It can be said that it is stable to

9, 10 and 11A are side sectional views showing other embodiments of the second heat transfer member 22. FIG. FIG. 11(B) is a cross-sectional view taken along line BB of FIG. 11(A). In FIGS. 9 to 11, portions having configurations or functions common to those in FIG. 2 are denoted by the same reference numerals, and overlapping descriptions are omitted.

The second heat transfer member 22 in FIG. 9 is composed of two or more types of members 25, 38, 27 having different thermal conductivities along the second lead line 12a. Specifically, the members 25 and 27 are made of oxygen-free copper, and the member 38 is made of a material having a lower thermal conductivity than that of oxygen-free copper. Such materials include copper or copper alloys with a volume resistivity of 2×10 ⁻⁴ Ωm or more. The effects obtained with the second heat transfer member 22 configured as shown in FIG. 9 are similar to those of the second heat transfer member 22 configured as shown in FIG. Further, the components of the second heat transfer member 22 shown in FIG. 2 may be added to the second heat transfer member 22 shown in FIG.

The second heat transfer member 22 in FIG. 10 includes an intermediate member 39 that contacts the second lead wire 12a, end members 25 and 27 that are separated from the intermediate member 39 and positioned at both ends thereof, the intermediate member 39 and the end members. It has an electrical insulating material 24 arranged on the connection surface of the members 25 and 27 and the contact surface of the second lead wire 12 a and the end members 25 and 27 .

With this configuration, heat can be efficiently released from the second lead wire 12a to the intermediate member 39, and short-circuiting of the current flowing through the second lead wire 12a can be prevented. The thermal contact between the second lead wire 12a and the intermediate member 39 may be achieved by fixing them with resin, or by soldering or brazing. The effect obtained with the second heat transfer member 22 configured as shown in FIG. 10 is similar to that of the second heat transfer member 22 configured as shown in FIG. 2 or 9 . Further, the components of the second heat transfer member 22 shown in FIG. 2 or 9 may be added to the second heat transfer member 22 shown in FIG.

In FIG. 11, a contact member 23 is provided so as to sandwich the second heat transfer member 22 and the second lead wire 12a. The contact surface between the second lead wire 12a and the contact member 23 does not need to be electrically insulated. With this configuration, heat can be efficiently released from the second lead wire 12 a to the contact member 23 . 2, 9 or 10 may be added to the second heat transfer member 22 shown in FIG.

Next, an example for confirming the effect of the present embodiment will be described. FIG. 12 is a partially enlarged view of a superconducting electromagnet according to a comparative example. A superconducting electromagnet according to a comparative example (FIG. 12) does not have a component corresponding to the second heat transfer member 22 in the embodiment. Furthermore, cooling of the persistent current switch 17 in the comparative example is achieved by extending the first heat transfer member 21 and bringing it into contact with the first heat transfer member 21 to directly supply cold heat.

FIG. 13 is a circuit diagram of a superconducting electromagnet according to a comparative example. This demonstration experiment was conducted without the main coil 15 (FIG. 12). In the circuit diagram expressed in this way, the excitation power source 35 is controlled so that the current value A increases at a speed of 100 A/min. Then, by measuring the potential difference in the sections defined by the _Vp , _V1 , _V2 , _V5 , _V6 , _V3 , _V4 , _{and Vn} contacts shown in the circuit diagram (FIG. 13), the Detect signs of quenching in the interval.

The second superconducting wire 12 and the second lead wire 12a wound around the persistent current switch 17 are composed of an NbTi superconductor 41 and a Cu-10% Ni matrix 42b. The first lead wire 11a is composed of an NbTi superconductor 41 and a Cu matrix body 42a. All of them had a diameter of 0.9 mm and a matrix/superconductor ratio of 1.3.

FIG. 14 is a graph showing the quench current value _Iq of the superconducting electromagnet according to the comparative example. In the region indicated by the broken line in FIG. 13, the temperature was changed to 4.2K, 5K, 6K, 7K and 8K, and the external magnetic field was changed to 1.2T, 2.0T and 3.0T. A sign of quench is taken at the time when a rise in the potential difference is detected in any section defined by the contacts _Vp , _V1 , _V2 , _V5 , _V6 , _V3 , _V4 and _Vn . Then, the current value A at the time of detection is plotted on a graph as the quench current value I _q together with the attribute information of the section. Then, the output of the excitation power supply 35 was returned to 0, the temperature and/or the external magnetic field were changed, the current value A was increased again at a rate of 100 A/min, and the above test was repeated.

The critical current value expected from the filament cross-sectional area of the first lead wire 11a and the second lead wire 12a is estimated to be around 1,100 A at a temperature of 4.2 K and a magnetic field of 1.2 T, for example. In contrast to this value, in the comparative example, the quench current value I _q was about 300 A to 400 A, which is about 40% lower than the expected value, under any conditions.

The tests described above were then performed on the embodiment of FIG. It was then confirmed that no sign of quenching was detected even when the current value was increased to 600A. This demonstrated that the embodiment reduces the risk of quenching.

15A, 15B, and 15C are partial cross-sectional views of experimental samples for confirming the effect of thermal contact performance between the second heat transfer member 22 and the second lead wire 12. FIG. Each experimental sample was produced by winding the second superconducting wire 12 around a cylindrical holder 51 made of stainless steel, which was likened to the second heat transfer member 22 . Then, the experimental samples (a), (b), and (c) are attached to the tip of the cryogenic refrigerator 30 (Fig. 1), conductively cooled in a vacuum vessel, energized in an external magnetic field, and the quench current value I _q is It was measured.

The second superconducting wire 12 wound around each of the experimental samples (a), (b), and (c) is composed of an NbTi superconductor 41 and a Cu-30% Ni matrix 42b. All of them had a diameter of 0.5 mm and a matrix/superconductor ratio of 1.24.

Experimental sample (a) is obtained by winding a second superconducting wire 12 around a cylindrical holder 51 made of stainless steel and fixing it with an epoxy resin 52 . Experimental sample (b) is obtained by winding the second superconducting wire 12 around a cylindrical holder 51 made of stainless steel and fixing it with solder 53 . Experimental sample (b) is obtained by fixing the second superconducting wire 12 to oxygen-free copper 54 having a cross-sectional area of about 1.5 mm ² with solder 53 and winding it around a cylindrical holder 51 made of stainless steel. The experimental samples (a), (b), and (c) produced in this way are excellent in thermal contact performance of the second superconducting wire 12 in this order.

FIG. 16 is a graph showing the quench current values _Iq at various set temperatures for the experimental samples (a), (b), and (c) of FIG. The external magnetic field is set at 1.2 Tesla. From FIG. 16, the temperature dependent tendency of the quench current value _Iq is similarly observed in any of the experimental samples (a), (b) and (c). Furthermore, it is also observed that the detected quench current value _Iq increases in the order of the experimental samples (a), (b) and (c) having excellent thermal contact performance. Further, the dispersion of the quench current value _Iq detected under the same temperature and magnetic field conditions is about 1 to 2 A, and the reproducibility is good. This demonstrated that the risk of quenching was reduced in the embodiment in which the cooling performance of the second lead wire 12a was improved.

According to the superconducting electromagnet of at least one embodiment described above, quenching occurs by supporting the second lead wire 12a of the persistent current switch 17 with the second heat transfer member 22 that transfers cold heat from the cryogenic refrigerator 30. It is possible to provide a superconducting electromagnet that reduces the risk of

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 10... Superconducting electromagnet, 11... 1st superconducting wire, 11a... 1st lead wire, 12... 2nd superconducting wire, 12a... 2nd lead wire, 15... Main coil, 16... Heat generation part, 17... Permanent current switch, 18 Connection member 20 Thermal insulation vacuum container 21 First heat transfer member 22 Second heat transfer member 23 Abutting member 24 Electrical insulating material 26 Constricted portion 28 Thermal insulation vacuum container 29 Radiation shield 30 Cryogenic refrigerator (GM refrigerator) 31 First refrigerating stage 32 Second refrigerating stage 35 Excitation power supply 36 Power controller 37 Electric resistor 38 Member , 39... Intermediate member 41... Superconductor 42 (42a, 42b)... Matrix body 46... Fixing material 47... Insulating layer 48... Groove 51... Cylindrical holder 52... Epoxy resin 54... Oxygen-free copper .

Claims (7)

a main coil around which the first superconducting wire is wound to generate an induced magnetic field;
a persistent current switch including a second superconducting wire with non-inductive windings and a heating portion for switching the second superconducting wire from a superconducting state to a normal conducting state;
a connection member that connects in parallel a pair of the first superconducting wires drawn out from the main coil as first lead wires and a pair of the second superconducting wires drawn out from the persistent current switch as second lead wires;
a first heat transfer member that supports the main coil and the connection member and transfers cold heat supplied from a cryogenic refrigerator;
a second heat transfer member that transfers the cold heat from the first heat transfer member to the persistent current switch and supports the second lead wire ;
The second heat transfer member includes an intermediate member that contacts the second lead wire, end members that are separated from the intermediate member and positioned at both ends thereof, a connection surface between the intermediate member and the end member, and the second heat transfer member. 2 electrical insulation disposed on the lead wires and the contact surfaces of the end members . a main coil around which the first superconducting wire is wound to generate an induced magnetic field;
a persistent current switch including a second superconducting wire with non-inductive windings and a heating portion for switching the second superconducting wire from a superconducting state to a normal conducting state;
a connection member that connects in parallel a pair of the first superconducting wires drawn out from the main coil as first lead wires and a pair of the second superconducting wires drawn out from the persistent current switch as second lead wires;
a first heat transfer member that supports the main coil and the connection member and transfers cold heat supplied from a cryogenic refrigerator;
a second heat transfer member that transfers the cold heat from the first heat transfer member to the persistent current switch and supports the second lead wire ;
A superconducting electromagnet in which the second heat transfer member is provided with a groove having a reverse shape of one side surface of the outer periphery of the second lead wire . a main coil around which the first superconducting wire is wound to generate an induced magnetic field;
a persistent current switch including a second superconducting wire with non-inductive windings and a heating portion for switching the second superconducting wire from a superconducting state to a normal conducting state;
a connection member that connects in parallel a pair of the first superconducting wires drawn out from the main coil as first lead wires and a pair of the second superconducting wires drawn out from the persistent current switch as second lead wires;
a first heat transfer member that supports the main coil and the connection member and transfers cold heat supplied from a cryogenic refrigerator;
a second heat transfer member that transfers the cold heat from the first heat transfer member to the persistent current switch and supports the second lead wire ;
The second heat transfer member is a superconducting electromagnet in which the wire-shaped second heat transfer member linearly circumscribes the second lead wire . In the superconducting electromagnet according to claim 1 or claim 2 ,
A superconducting electromagnet in which the second heat transfer member is provided with a constricted portion having a reduced cross section along the route along the second lead wire. In the superconducting electromagnet according to any one of claims 1, 2 and 4 ,
The second heat transfer member is a superconducting electromagnet composed of two or more members having different thermal conductivities along the second lead wire. In the superconducting electromagnet according to any one of claims 1, 2, 4 and 5 ,
A superconducting electromagnet comprising a contact member arranged to sandwich the second heat transfer member and the second lead wire. In the superconducting electromagnet according to any one of claims 1 to 6 ,
A superconducting electromagnet in which the matrix body of the second lead wires is made of a material having a lower thermal conductivity than the matrix body of the first lead wires.

Images