Superconducting magnet device

Abstract

To cope with polarity erroneous connection between a superconducting coil and its power supply.SOLUTION: A superconducting magnet device 10 comprises: a superconducting coil 12; a quench protection circuit 22 that is connected in parallel to the superconducting coil 12 and permits current in a single direction; and an excitation power supply 24 that is connected to the superconducting coil 12 in a normal polarity determined so that current flows in the single direction in the quench protection circuit 22 at the time of quench generation of the superconducting coil 12 to excite the superconducting coil 12. The excitation power supply 24 is configured to detect erroneous connection with the superconducting coil 12 in the case of being connected to the superconducting coil 12 in a polarity reverse to the normal polarity.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a superconducting magnet device. [Background technology]

[0002] One undesirable phenomenon that can occur during the operation of a superconducting magnet device is thermal runaway (quench) of a superconducting coil. When a quench occurs, the superconducting coil transitions from superconductivity to normal conductivity, generating resistance inside the coil. A large amount of Joule heat can be generated from the large current that flowed through the coil in the previous superconducting state. A voltage rise in the coil and a resulting discharge may also occur. In addition, a large electromagnetic force can act on the superconducting coil due to the transient current imbalance that occurs when a quench occurs. Eddy currents can also be generated in conductors placed near the coil, generating electromagnetic forces. The heat, discharge, and electromagnetic forces that can be generated in this way can damage the superconducting coil and its surrounding structures and equipment.

[0003] Generally, a superconducting magnet device is provided with a protection circuit to protect the superconducting coil when a quench occurs. An example of the protection circuit is a pair of diodes connected in parallel with the superconducting coil, each diode connected in parallel with the superconducting coil and having opposite polarity. The protection circuit is usually placed in a cryogenic environment together with the superconducting coil and cooled to the same temperature. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-234689 A Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors of the present invention have intensively studied the protection circuit of a superconducting magnet device and have come to recognize the following problems. Diodes that are guaranteed to operate at extremely low temperatures are more expensive than general-purpose diodes that are not guaranteed to operate at extremely low temperatures. If the above-mentioned pair of diodes is replaced with a single diode in the quench protection circuit, the number of diodes used will be halved, which is advantageous for reducing the cost of the device. In this case, the design of the superconducting magnet device should be such that the direction of the current flowing through the superconducting coil in normal operation (i.e., when no quench has occurred in the superconducting coil) is predetermined so that when a quench occurs, the current flows from the coil to the diode in the forward direction. The superconducting coil and its power supply must be connected with the correct polarity to operate in this way.

[0006] However, the inventors have noticed that there is a risk of connecting the superconducting coil and the power supply in the wrong polarity when manufacturing the superconducting magnet device or when installing the device at the site of use. If such a wrong connection occurs, a current flows in the superconducting coil in the opposite direction to the correct direction during normal operation. Then, when a quench occurs, the current from the superconducting coil to the diode will try to flow in the opposite direction to the diode. In other words, the wrong connection may prevent the operation of the quench protection circuit. If the protection circuit does not operate, the risk of damage to the superconducting magnet device when a quench occurs increases, which is undesirable, as described above.

[0007] One exemplary purpose of certain aspects of the present invention is to address polarity misconnection between a superconducting coil and its power source. [Means for solving the problem]

[0008] According to an aspect of the present invention, a superconducting magnet device includes a superconducting coil, a quench protection circuit connected in parallel to the superconducting coil and allowing a current to flow in a single direction, and an excitation power supply connected to the superconducting coil with a normal polarity determined so that a current flows in a single direction in the quench protection circuit when a quench occurs in the superconducting coil, and configured to detect a misconnection with the superconducting coil when the excitation power supply is connected with a polarity opposite to the normal polarity.

[0009] According to one aspect of the present invention, a superconducting magnet device includes a superconducting coil, a quench protection circuit connected in parallel to the superconducting coil and allowing a current to flow in one direction, an excitation power supply connected to the superconducting coil with a normal polarity determined so that a current flows in one direction in the quench protection circuit when a quench occurs in the superconducting coil and excites the superconducting coil, and a coil-side positive terminal and a coil-side negative terminal connected to the superconducting coil. The excitation power supply includes a power supply-side positive terminal connected to the coil-side positive terminal and a power supply-side negative terminal connected to the coil-side negative terminal. The coil-side positive terminal is configured so as to be unconnectable to the power supply-side negative terminal, and the coil-side negative terminal is configured so as to be unconnectable to the power supply-side positive terminal. Effect of the Invention

[0010] According to the present invention, it is possible to deal with the case where the polarity of a superconducting coil is connected to its power supply in an incorrect manner. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a schematic diagram of a superconducting magnet device according to an embodiment. [Diagram 2] 1 is a diagram illustrating a schematic diagram of a superconducting magnet device according to an embodiment. [Diagram 3] 1 is a diagram showing a schematic diagram of an erroneous connection of an excitation power supply in a superconducting magnet apparatus according to an embodiment. FIG. [Figure 4] 4(a) to 4(c) are diagrams illustrating an example of electrical connection between an excitation power supply and a superconducting coil according to an embodiment. [Diagram 5] 5(a) to 5(c) are diagrams illustrating another example of electrical connection between an excitation power supply and a superconducting coil according to an embodiment. [Figure 6] 6(a) and 6(b) are diagrams illustrating an example of a countermeasure against erroneous connection between an excitation power supply and a superconducting coil according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience in order to facilitate the description, and are not to be interpreted as being limiting unless otherwise specified. The embodiments are merely examples, and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0013] 1 and 2 are schematic diagrams showing a superconducting magnet device 10 according to an embodiment. The superconducting magnet device 10 is mounted in high magnetic field equipment as a magnetic field source for, for example, a single crystal pulling device, an NMR (Nuclear Magnetic Resonance) system, an MRI (Magnetic Resonance Imaging) system, an accelerator such as a cyclotron, a high energy physics system such as a nuclear fusion system, or other high magnetic field equipment (not shown), and can generate a high magnetic field required for the equipment.

[0014] The superconducting magnet device 10 includes a superconducting coil 12, a vacuum vessel 14, a cryogenic refrigerator 16, a heat shield 18, a current supply line 20, a quench protection circuit 22, and an excitation power supply 24.

[0015] The superconducting coil 12 is disposed within a vacuum vessel 14, and is configured to generate a strong magnetic field when current is applied while the coil is cooled to an extremely low temperature below the superconducting transition temperature. The superconducting coil 12 may be a known superconducting coil (for example, a so-called low-temperature superconducting coil). The superconducting coil 12 is connected to an excitation power supply 24 disposed outside the vacuum vessel 14 via a current introduction line 20. An excitation current is supplied from the excitation power supply 24 to the superconducting coil 12 via the current introduction line 20. This enables the superconducting magnet device 10 to generate a strong magnetic field.

[0016] The vacuum vessel 14 is an insulated vacuum vessel that provides an extremely low temperature vacuum environment suitable for bringing the superconducting coil 12 into a superconducting state, and is also called a cryostat. Typically, the vacuum vessel 14 has a cylindrical shape or a cylindrical shape with a hollow space at the center. Thus, the vacuum vessel 14 has a top plate 14a and a bottom plate 14b that are generally flat and circular or annular, and a cylindrical side wall (a cylindrical outer wall, or a cylindrical outer wall and an inner wall that are coaxially arranged) that connect the top plate 14a and the bottom plate 14b. The cryogenic refrigerator 16 may be installed on the top plate 14a of the vacuum vessel 14. The vacuum vessel 14 is formed of a metal material such as stainless steel or other suitable high-strength material so as to withstand the ambient pressure (e.g., atmospheric pressure).

[0017] The cryocooler 16 is configured to cool the thermal shield 18 and the quench protection circuit 22 to a first cooling temperature, and to cool the superconducting coil 12 to a second cooling temperature lower than the first cooling temperature. In this embodiment, the cryocooler 16 is a two-stage Gifford-McMahon (GM) cryocooler, and includes a first cooling stage 16a and a second cooling stage 16b. The first cooling stage 16a and the second cooling stage 16b are provided to surround the first expansion space and the second expansion space in the cryocooler 16, respectively, and are formed of a metal material such as copper or other material having a high thermal conductivity. The first cooling temperature may be in a temperature range of about 20K to about 100K, for example, in a temperature range of about 30K to about 50K, and the second cooling temperature may be in a temperature range of about 3K to about 20K, for example, about 4K.

[0018] The heat shield 18 is disposed so as to surround the superconducting coil 12 within the vacuum vessel 14. The heat shield 18 is formed of a metal material such as copper or other material having high thermal conductivity. The heat shield 18 is directly attached to the first cooling stage 16a of the cryogenic refrigerator 16 and is thermally coupled to the first cooling stage 16a. Alternatively, the heat shield 18 may be attached to the first cooling stage 16a via a flexible or rigid heat transfer member. During operation of the superconducting magnet device 10, the heat shield 18 is cooled to a first cooling temperature by the first cooling stage 16a. The heat shield 18 can thermally protect low-temperature parts, such as the second cooling stage 16b of the cryogenic refrigerator 16, which is disposed inside the heat shield 18 and is cooled to a lower temperature than the heat shield 18, and the superconducting coil 12, from radiant heat from the vacuum vessel 14.

[0019] The superconducting coil 12 is thermally coupled to the second cooling stage 16b via a heat transfer member 26. The heat transfer member 26 is formed of a metal material such as copper or other material with high thermal conductivity, and connects the superconducting coil 12 to the second cooling stage 16b. The heat transfer member 26 may be a rigid member that rigidly connects the superconducting coil 12 to the second cooling stage 16b, or may be flexible and connect the superconducting coil 12 to the second cooling stage 16b to allow relative displacement between them. Alternatively, the superconducting coil 12 may be directly attached to the second cooling stage 16b and thermally coupled to the second cooling stage 16b. During operation of the superconducting magnet device 10, the superconducting coil 12 is cooled to the second cooling temperature by the second cooling stage 16b.

[0020] The current introduction line 20 includes an external wiring 20a, a feed-through portion 20b, an outer current lead portion 20c, and an inner current lead portion 20d, and forms a current path from the excitation power supply 24 to the superconducting coil 12. Typically, one current introduction line 20 on the positive electrode side and one current introduction line 20 on the negative electrode side are provided.

[0021] An external wiring 20a arranged outside the vacuum vessel 14 connects an excitation power supply 24 to a feed-through portion 20b provided on the wall of the vacuum vessel 14. The external wiring 20a may be an appropriate power supply cable. The feed-through portion 20b is an airtight terminal for introducing current into the vacuum vessel 14, and connects the external wiring 20a to internal wiring (i.e., the outer current lead portion 20c and the inner current lead portion 20d) inside the vacuum vessel 14. The current introduction line 20 can penetrate the wall of the vacuum vessel 14 while maintaining the airtightness of the vacuum vessel 14 by the feed-through portion 20b.

[0022] The outer current lead portion 20c is disposed outside the heat shield 18 in the vacuum vessel 14, and connects the feed-through portion 20b to the inner current lead portion 20d. The outer current lead portion 20c is formed of a metal material having excellent electrical conductivity, such as pure copper, such as oxygen-free copper. The end portion of the outer current lead portion 20c connected to the inner current lead portion 20d is thermally coupled to the heat shield 18. This end portion of the outer current lead portion 20c is fixed to the heat shield 18 or connected to the heat shield 18 via an appropriate heat transfer member, and is cooled to the first cooling temperature in the same manner as the heat shield 18. However, the outer current lead portion 20c is electrically insulated from the heat shield 18. For example, the outer current lead portion 20c may be attached to a fixed portion such as the heat shield 18 or the heat transfer member by sandwiching an insulating material (e.g., a sheet of insulating resin material) between the outer current lead portion 20c and the fixed portion.

[0023] The inner current lead 20d is disposed inside the heat shield 18 and connects the outer current lead 20c to the superconducting coil 12. The inner current lead 20d may include a first terminal 20d1, a second terminal 20d2, and a high temperature superconducting current lead 20d3 connecting the two terminals. The first terminal 20d1 is connected to the outer current lead 20c, and the second terminal 20d2 is connected to the superconducting coil 12. The first terminal 20d1 is thermally coupled to the heat shield 18 and is cooled to a first cooling temperature in the same manner as the heat shield 18. The second terminal 20d2 is cooled to a second cooling temperature in the same manner as the superconducting coil 12.

[0024] The high temperature superconducting current lead 20d3 may be formed of, for example, a copper oxide superconductor or other high temperature superconducting material. Such a material of the high temperature superconducting current lead has thermal insulation properties. Therefore, compared to when the inner current lead portion 20d is made of metal, it is possible to reduce heat that may be transferred from the quench protection circuit 22 to the superconducting coil 12 through the inner current lead portion 20d as a heat transfer path. This can reduce the heat load on the second cooling stage 16b of the cryocooler 16 and help to improve cooling of the superconducting coil 12.

[0025] The quench protection circuit 22 is connected in parallel to the superconducting coil 12. One end of the quench protection circuit 22 is connected to one (e.g., positive pole) current introduction line 20, and the other end is connected to the other (e.g., negative pole) current introduction line 20, thereby being connected in parallel to the superconducting coil 12. For example, the quench protection circuit 22 may be connected to the current introduction line 20 using a bus bar made of a metal material having excellent conductivity such as copper.

[0026] The quench protection circuit 22 is capable of generating heat when energized, and may comprise a typical linear (i.e., obeying Ohm's law) resistive element, or may comprise a nonlinear resistor. The nonlinear resistor may have a nonlinear characteristic in which the resistance value is high when the voltage across the nonlinear resistor is small, and the resistance value is low when the voltage across the nonlinear resistor is large (the nonlinear resistor may have a first resistance value when the voltage across the nonlinear resistor is a first value, and a second resistance value smaller than the first resistance value when the voltage across the nonlinear resistor is a second value larger than the first value).

[0027] The nonlinear resistor may be, for example, a rectifying element such as a diode or a thyristor. In this embodiment, the quench protection circuit 22 includes, for example, a diode 28. Alternatively, the nonlinear resistor may be a varistor. Note that the quench protection circuit 22 may include both a linear resistor and a nonlinear resistor, and these may be connected in series, for example.

[0028] Unlike a typical existing quench protection circuit having a pair of diodes connected in parallel with opposite polarity, in this embodiment, the quench protection circuit 22 allows current to flow only in a single direction, which corresponds to the forward direction of the diode 28, and blocks current in the reverse direction. Such a quench protection circuit 22 is more advantageous in reducing the cost of the superconducting magnet device 10 than existing ones, because the number of diodes used in the quench protection circuit 22 can be reduced by half because a single diode 28 is used instead of a pair of diodes. Diodes guaranteed to operate at cryogenic temperatures are more expensive than general-purpose diodes that are not guaranteed to operate at cryogenic temperatures, so reducing the number of diodes used is a great help in reducing costs.

[0029] As described above, the quench protection circuit 22 is cooled to a higher cooling temperature than the superconducting coil 12 during operation of the superconducting coil 12. The quench protection circuit 22 may be thermally coupled to the first cooling stage 16a of the cryogenic refrigerator 16 and cooled to a first cooling temperature. For convenience, in FIG. 2, a first portion cooled to the first cooling temperature is shown surrounded by a dashed line 30, and a second portion cooled to the second cooling temperature is shown surrounded by a dashed line 32. As shown in the example, the quench protection circuit 22 may be connected between the outer current leads 20c and installed in a portion cooled to the first cooling temperature, such as the heat shield 18. The quench protection circuit 22 may be connected to the superconducting coil 12 via the inner current lead 20d (i.e., the high temperature superconducting current lead 20d3).

[0030] If the temperature rise of the superconducting coil 12 due to a quench is large, the time required for recooling to recover will be extended, which may lead to an increase in downtime of the superconducting magnet device 10. In existing designs, the protection circuit for the superconducting coil is often cooled to the same temperature as the superconducting coil. In this embodiment, the quench protection circuit 22 is cooled to a higher cooling temperature than the superconducting coil 12, so recooling can be performed in a shorter time than in existing designs in which the protection circuit is cooled to the same temperature as the superconducting coil (i.e., the second cooling temperature). The time required to recover the superconducting magnet device 10 from a quench can be shortened.

[0031] Since the quench protection circuit 22 is cooled by the first cooling stage 16a of the cryocooler 16, the heat generated by the quench protection circuit 22 can be efficiently removed. This is because the cooling capacity of the first stage of the cryocooler 16 is usually larger (for example, several tens of times) than that of the second stage, and has a relatively large margin. This is also advantageous in shortening the time required to restore the superconducting magnet device 10 from a quench.

[0032] When the quench protection circuit 22 is connected to the superconducting coil 12 via the high temperature superconducting current lead 20d3, the heat that may be transferred from the quench protection circuit 22 to the superconducting coil 12 through the inner current lead portion 20d as a heat transfer path can be reduced, compared to when the inner current lead portion 20d is made of metal. This can reduce the heat load on the second cooling stage 16b of the cryogenic refrigerator 16, and can help to efficiently cool the superconducting coil 12.

[0033] As shown in Fig. 2, the superconducting coil 12 may be divided into a plurality of (for example, N, where N is any natural number) superconducting coil portions 12a_1 to 12a_N, and these superconducting coil portions 12a may be connected in series. The quench protection circuit 22 includes a plurality of diodes 28, each of which is connected in parallel to a corresponding one of the plurality of superconducting coil portions 12a. The high temperature superconducting current lead 20d3 connects each diode 28 to the corresponding superconducting coil portion 12a. Such a divided coil configuration can reduce the voltage applied to both ends of the superconducting coil 12 when a quench occurs, compared to a non-divided coil configuration, and is therefore advantageous especially when the superconducting coil 12 is large.

[0034] The superconducting magnet device 10 may have a plurality of superconducting coils 12, and in this case, a quench protection circuit 22 may be provided for each superconducting coil 12. In other words, a plurality of quench protection circuits 22 may be provided, and each quench protection circuit 22 may be connected in parallel to a corresponding one of the plurality of superconducting coils 12. Each of the plurality of superconducting coils 12 may be divided into a plurality of superconducting coil portions 12a.

[0035] In this embodiment, the direction of the current that the excitation power supply 24 supplies to the superconducting coil 12 is predetermined in the design of the superconducting magnet device 10 so that this current does not flow to the quench protection circuit 22 during normal operation of the superconducting magnet device 10. The direction of the current that the excitation power supply 24 supplies to the superconducting coil 12 is fixed to a single direction. The excitation power supply 24 with a fixed current direction may be used in some applications of the superconducting magnet device 10, such as a single crystal pulling device. As illustrated by the arrow 34 in FIG. 2, the direction of the current flowing from the excitation power supply 24 to the superconducting coil 12 corresponds to the reverse direction for the diode 28 of the quench protection circuit 22, so that this current is blocked by the diode 28 and does not flow to the quench protection circuit 22.

[0036] On the other hand, when a quench occurs during the operation of the superconducting coil 12, the electrical connection between the excitation power supply 24 and the superconducting coil 12 is cut off, and a current from the superconducting coil 12 flows to the quench protection circuit 22. The direction of this current corresponds to the forward direction of the diode 28, as illustrated by the arrow 36 in FIG. 2. Thus, a current can be passed from the superconducting coil 12 to the quench protection circuit 22, and at least a part of the electromagnetic energy stored in the superconducting coil 12 can be converted to heat and consumed by the quench protection circuit 22. In this way, the quench protection circuit 22 extracts energy from the superconducting coil 12, thereby protecting the superconducting coil 12 when a quench occurs. By reducing the energy of the superconducting coil 12, it is possible to prevent or reduce damage to the superconducting coil 12 and its surroundings that may occur due to the reduction in the energy of the superconducting coil 12.

[0037] Fig. 3 is a schematic diagram showing an erroneous connection of the excitation power supply 24 in the superconducting magnet device 10 according to the embodiment. As mentioned at the beginning of this document, the inventors realized that there is a risk of erroneously connecting the superconducting coil 12 and the excitation power supply 24 in the case of manufacturing the superconducting magnet device 10 or installing it at the site where it will be used, and the like, in which case they may be connected in the opposite polarity. In Fig. 3, the excitation power supply 24 connected in the opposite direction in this way is shown by a dashed line.

[0038] If such a misconnection occurs, a current will flow in the superconducting coil 12 in a direction opposite to the correct direction during normal operation, as illustrated by arrow 38a in Fig. 3. Then, in the event of a quench, a current from the superconducting coil 12 toward the diode will attempt to flow in the reverse direction of the diode, as illustrated by arrow 38b in Fig. 3. In other words, the misconnection may prevent the operation of the quench protection circuit 22. If the quench protection circuit 22 does not operate, there is an undesirable increased risk of damage to the superconducting magnet device 10 in the event of a quench, as described above.

[0039] Therefore, in this document, several solutions for dealing with the incorrect polarity connection between the superconducting coil 12 and the excitation power supply 24 are proposed below.

[0040] 4(a) to 4(c) are diagrams illustrating an example of an electrical connection between the excitation power supply 24 and the superconducting coil 12 according to an embodiment. Fig. 4(a) shows a state before the excitation power supply 24 and the superconducting coil 12 are connected, and Fig. 4(b) shows a state in which the excitation power supply 24 and the superconducting coil 12 are correctly connected with the correct polarity. Fig. 4(c) shows a state in which the excitation power supply 24 and the superconducting coil 12 are erroneously connected with the polarity opposite to the correct polarity.

[0041] As described above, the superconducting coil 12 is connected to the excitation power supply 24 by the current introduction line 20. As shown in Fig. 4(a), the positive-side current introduction line 20 has a coil-side positive terminal 40a at its end, and the negative-side current introduction line 20 has a coil-side negative terminal 40b at its end, and this pair of coil-side terminals is connected to the superconducting coil 12 by the current introduction line 20. The excitation power supply 24 includes a power supply-side positive terminal 42a connected to the coil-side positive terminal 40a, and a power supply-side negative terminal 42b connected to the coil-side negative terminal 40b. The coil-side and power supply-side terminals are coupled to each other so as to be electrically connectable, for example, by fastening, crimping, or other appropriate fixing method.

[0042] The coil side positive terminal 40a is configured to be unconnectable to the power supply side negative terminal 42b, and the coil side negative terminal 40b is configured to be unconnectable to the power supply side positive terminal 42a. As an example of such an unconnectable configuration, the coil side positive terminal 40a and the coil side negative terminal 40b may be made different in shape from each other, and the power supply side positive terminal 42a and the power supply side negative terminal 42b may also be made different in shape from each other in response to the difference in shape between the coil side positive terminal 40a and the coil side negative terminal 40b.

[0043] For example, as shown in the figure, the coil side positive terminal 40a and the coil side negative terminal 40b may have different terminal lengths, and correspondingly, the power supply side positive terminal 42a and the power supply side negative terminal 42b may also have different terminal lengths. In other words, the coil side positive terminal 40a and the power supply side positive terminal 42a may have the same terminal length, the coil side negative terminal 40b and the power supply side negative terminal 42b may have the same terminal length, and the positive terminal length and the negative terminal length may be different.

[0044] 4(b), the coil side positive terminal 40a can be connected to the power supply side positive terminal 42a, and the coil side negative terminal 40b can be connected to the power supply side negative terminal 42b by matching the terminal shapes. In this way, the excitation power supply 24 and the superconducting coil 12 can be correctly connected with the normal polarity.

[0045] On the other hand, as shown in FIG. 4(c), if an operator mistakenly attempts to connect the excitation power supply 24 and the superconducting coil 12 with a polarity opposite to the normal polarity, the terminals on the coil side and the power supply side cannot be connected to each other at least on the positive and negative sides (the positive side in the illustrated example) due to incompatibility of the terminal shapes.

[0046] In this way, it is possible to physically prevent erroneous connection between the excitation power supply 24 and the current supply line 20 (and thus the superconducting coil 12). This makes it possible to avoid the risk that the quench protection circuit 22 will not operate as a result of erroneous connection. A single diode 28 can be used in the quench protection circuit 22 instead of a pair of diodes connected in reverse to each other, thereby realizing a reduction in the cost of the superconducting magnet device 10.

[0047] 5(a) to 5(c) are diagrams illustrating another example of electrical connection between the excitation power supply 24 and the superconducting coil 12 according to the embodiment. Fig. 5(a) shows a state before the excitation power supply 24 and the superconducting coil 12 are connected, and Fig. 5(b) shows a state in which the excitation power supply 24 and the superconducting coil 12 are correctly connected with the correct polarity. Fig. 5(c) shows a state in which the excitation power supply 24 and the superconducting coil 12 are erroneously connected with the polarity opposite to the correct polarity.

[0048] As in the above example, a set of coil side terminals (coil side positive terminal 40a and coil side negative terminal 40b) is provided on the current introduction line 20, and a set of power supply side terminals (power supply side positive terminal 42a and power supply side negative terminal 42b) is provided on the excitation power supply 24. The coil side positive terminal 40a is connected to the power supply side positive terminal 42a, and the coil side negative terminal 40b is connected to the power supply side negative terminal 42b, whereby the superconducting coil 12 is connected to the excitation power supply 24 via the current introduction line 20. In this example, these terminals can be connected to each other by inserting the coil side terminals into the power supply side terminals.

[0049] As shown in the figure, a detector 44 is provided that generates a detection signal S1 that indicates whether a pair of coil side terminals and a pair of power supply side terminals are connected in the normal polarity or in the reverse polarity. In this example, the detector 44 may be configured to generate the detection signal S1 when the coil side terminals and the power supply side terminals are connected in the normal polarity, but not to generate the detection signal S1 when they are connected in the reverse polarity to the normal polarity.

[0050] As an example, the detector 44 may include a detection signal generator 44a provided at a power supply side terminal (power supply side negative terminal 42b in the illustrated example) and an operation unit 44b provided at a coil side terminal (coil side negative terminal 40b in the illustrated example) for operating the detection signal generator 44a. The detection signal generator 44a may be configured to generate a detection signal S1 when operated by the operation unit 44b, and may be, for example, a push button that generates the detection signal S1 in this manner. The operation unit 44b may be configured to be out of contact with the detection signal generator 44a when the power supply side and coil side terminals are not connected, and to come into contact with and operate the detection signal generator 44a when both terminals are connected, and may be, for example, a collar attached to the terminal. Note that the detection signal generator 44a may be provided at the coil side terminal, and the operation unit 44b may be provided at the power supply side terminal.

[0051] The excitation power supply 24 is configured to detect a misconnection based on a detection signal S1. The excitation power supply 24 is connected to a detector 44 (specifically, a detection signal generator 44a) so as to receive the detection signal S1 from the detector 44. Therefore, the excitation power supply 24 can receive the detection signal S1 from the detector 44 and detect a misconnection in response to the detection signal S1.

[0052] The excitation power supply 24 may incorporate an interlock mechanism 46 as a safety device. When the detection signal S1 indicates a correct connection between the excitation power supply 24 and the superconducting coil 12, the excitation power supply 24 may be configured to release the interlock mechanism 46 on the condition that the detection signal S1 is received. As the interlock mechanism 46, a known interlock mechanism can be appropriately adopted. In this way, power supply from the excitation power supply 24 to the superconducting coil 12 is permitted when the connection is correct, while power supply can be prohibited by the interlock mechanism 46 when the connection is incorrect.

[0053] In addition, the excitation power supply 24 may be configured to notify the operator visually, audibly, or in any other suitable manner that a misconnection has been detected or that a misconnection has not been detected (i.e., the connection is correct).

[0054] In this example, as shown in FIG. 5(b), the coil side positive terminal 40a can be connected to the power supply side positive terminal 42a, and the coil side negative terminal 40b can be connected to the power supply side negative terminal 42b. At this time, the operation unit 44b attached to the coil side negative terminal 40b contacts the detection signal generator 44a attached to the power supply side negative terminal 42b (i.e., the collar presses the push button), and a detection signal S1 is generated. The detection signal S1 is input from the detector 44 to the excitation power supply 24. In this case, the excitation power supply 24 releases the interlock mechanism 46 based on the detection signal S1. The excitation power supply 24 may also notify the operator that the excitation power supply 24 and the superconducting coil 12 are correctly connected based on the detection signal S1.

[0055] On the other hand, as shown in Fig. 5(c), when an operator mistakenly connects the excitation power supply 24 and the superconducting coil 12 with a polarity opposite to the normal polarity, the coil side positive terminal 40a is not provided with an operation unit 44b, so the detection signal generator 44a of the power supply side negative terminal 42b is not operated. Therefore, the detector 44 does not generate the detection signal S1. In this case, the excitation power supply 24 maintains the interlock by the interlock mechanism 46.

[0056] In this way, it is possible to detect an erroneous connection between the excitation power supply 24 and the current introduction line 20 (and thus the superconducting coil 12). As a result, even if an erroneous connection occurs once, it can be reconnected correctly. It is possible to avoid the risk that the quench protection circuit 22 will not operate as a result of an erroneous connection. A single diode 28 can be used in the quench protection circuit 22 instead of a pair of diodes connected in reverse to each other, and it is possible to reduce the cost of the superconducting magnet device 10.

[0057] The detector 44 is not limited to the contact detector described above, but may be a non-contact detector such as an optical detector.

[0058] Instead of or in addition to the countermeasure against misconnection using the detector 44, it is also possible to detect misconnection between the excitation power supply 24 and the superconducting coil 12 by devising a way of changing the current when the excitation power supply 24 excites the superconducting coil 12. Here, the excitation of the superconducting coil 12 is a part of the preparation stage for the normal operation in which the superconducting magnet device 10 generates a magnetic field, and refers to the process of increasing the coil current supplied from the excitation power supply 24 to the superconducting coil 12 from zero to a predetermined current (for example, the rated current of the superconducting coil 12). An example of such misconnection detection is described below.

[0059] 6(a) and 6(b) are diagrams illustrating an example of a countermeasure against erroneous connection between the excitation power supply 24 and the superconducting coil 12 according to the embodiment. Fig. 6(a) shows a state in which the excitation power supply 24 and the superconducting coil 12 are correctly connected with the correct polarity. Fig. 6(b) shows a state in which the excitation power supply 24 and the superconducting coil 12 are erroneously connected with the polarity opposite to the correct polarity.

[0060] The excitation power supply 24 may be configured to control the rate of current increase when exciting the superconducting coil 12 so that the induced electromotive force generated in the superconducting coil 12 or a portion thereof (e.g., the superconducting coil portion 12a) by this current increase rate exceeds the threshold voltage of a rectifying element (e.g., the diode 28).

[0061] In other words, the excitation power supply 24 may be configured to control the current increase rate (dI / dt) during excitation of the superconducting coil 12 so as to satisfy the following equation: Vf <L(dI / dt) Here, Vf represents the threshold voltage of the rectifying element, and L represents the inductance of the superconducting coil 12 or a part of the superconducting coil 12 connected in parallel with the rectifying element.

[0062] 6(a), when the excitation power supply 24 and the superconducting coil 12 are connected with the normal polarity, while the superconducting coil 12 is excited by the excitation power supply 24, a current I from the excitation power supply 24 flows through the superconducting coil 12. The direction of this current I corresponds to the reverse direction of the diode 28, so the current I does not flow through the diode 28.

[0063] On the other hand, as shown in Fig. 6(b), if the excitation power supply 24 and the superconducting coil 12 are erroneously connected with a polarity opposite to the normal polarity, during excitation of the superconducting coil 12 by the excitation power supply 24, the current I from the excitation power supply 24 will flow not only to the superconducting coil 12 but also to the diode 28. This is because, as described above, the excitation power supply 24 controls the induced electromotive force L(dI / dt) generated in the superconducting coil 12 so as to exceed the threshold voltage Vf of the diode 28. At this time, the direction of the current I corresponds to the forward direction of the diode 28, so that the induced electromotive force L(dI / dt) causes the diode 28 to be energized (turned on), and a forward current flows through the diode 28 (indicated by an arrow 48 in Fig. 6(b)).

[0064] Therefore, the superconducting magnet device 10 may be provided with a sensor 50 that detects the flow of current through the rectifying element, the diode 28 in this example. For example, the sensor 50 may be a current sensor that measures the current flowing through the rectifying element, such as a non-contact current sensor. Alternatively, the sensor 50 may be a magnetic sensor that is placed near the rectifying element and measures the magnetic flux. The magnetic sensor can detect the magnetic flux that is generated when a current flows through the rectifying element. Alternatively, the sensor 50 may be a temperature sensor that measures the temperature of the rectifying element. The temperature sensor can detect the temperature rise of the rectifying element that occurs when a current flows through the rectifying element.

[0065] The excitation power supply 24 may be configured to control the current increase rate dI / dt so that the induced electromotive force L(dI / dt) exceeds the threshold voltage Vf of the rectifier element, and to detect a misconnection based on the output of the sensor 50. For example, the excitation power supply 24 may receive the output from the sensor 50 and compare the output of the sensor 50 with a certain threshold. The excitation power supply 24 may determine that the excitation power supply 24 and the superconducting coil 12 are correctly connected when the output of the sensor 50 is below the threshold, and may determine that the excitation power supply 24 and the superconducting coil 12 are misconnected when the output of the sensor 50 exceeds the threshold. The threshold for the determination can be appropriately set based on the empirical knowledge of the designer or experiments, simulations, etc. performed by the designer.

[0066] In this manner, by setting the current increase rate during excitation of the superconducting coil 12 by the excitation power supply 24 as described above, it is possible to detect an erroneous connection between the excitation power supply 24 and the current introduction line 20 (and thus the superconducting coil 12). As a result, even if an erroneous connection occurs once, it can be reconnected correctly. It is possible to avoid the risk that the quench protection circuit 22 will not operate as a result of an erroneous connection. A single diode 28 can be used in the quench protection circuit 22 instead of a pair of diodes connected in reverse to each other, and it is possible to reduce the cost of the superconducting magnet device 10.

[0067] For simplicity, Fig. 6(a) and Fig. 6(b) show one superconducting coil 12 and one rectifying element (diode 28) connected in parallel thereto. However, as described with reference to Figs. 1 to 3, the superconducting magnet device 10 may be provided with a plurality of superconducting coils 12 (or a plurality of superconducting coil portions 12a) and a corresponding plurality of rectifying elements. In this case, the above-mentioned misconnection detection method can be similarly applied. In other words, a misconnection can be detected based on the presence or absence of current flow through at least one of the plurality of rectifying elements.

[0068] Instead of the above-mentioned sensor 50, the excitation power supply 24 may be configured to measure the voltage across the excitation power supply 24 and detect the erroneous connection based on the measured voltage across the excitation power supply 24. When the excitation power supply 24 and the superconducting coil 12 are connected with the correct polarity, the excitation power supply 24 measures a voltage across its both ends that corresponds to the induced electromotive force L(dI / dt) during excitation of the superconducting coil 12 by the excitation power supply 24. On the other hand, when the excitation power supply 24 and the superconducting coil 12 are erroneously connected with a polarity opposite to the correct polarity, the voltage across the excitation power supply 24 becomes the threshold voltage Vf of the diode 28.

[0069] Therefore, a threshold value for the determination based on the voltage across the excitation power supply 24 may be set in advance to a value that is greater than the threshold voltage Vf of the rectifier element and less than the induced electromotive force L(dI / dt). The excitation power supply 24 may measure the voltage across the excitation power supply 24 while exciting the superconducting coil 12 by the excitation power supply 24, and compare the measured voltage across the excitation power supply 24 with this threshold value. When the voltage across the excitation power supply 24 exceeds the threshold value, the excitation power supply 24 may determine that the excitation power supply 24 and the superconducting coil 12 are correctly connected, and when the voltage across the excitation power supply 24 is less than the threshold value, the excitation power supply 24 may determine that the excitation power supply 24 and the superconducting coil 12 are incorrectly connected.

[0070] When multiple superconducting coils 12 (or multiple superconducting coil portions 12a) are provided, the threshold value for this determination may be greater than the sum of the threshold voltages of the corresponding multiple rectifying elements (ΣVf; for example, when N rectifying elements having the same threshold voltage are provided, N×Vf) and less than the sum of the induced electromotive forces (ΣL(dI / dt)).

[0071] The excitation power supply 24 may be configured to stop the excitation power supply 24 when the measured voltage across the excitation power supply 24 falls below a lower voltage limit. For example, the excitation power supply 24 may include an interlock mechanism 46 (see FIG. 5(a)), and the interlock mechanism 46 may stop the excitation power supply 24 when the voltage across the excitation power supply 24 falls below a lower voltage limit.

[0072] In this case, the excitation power supply 24 may be configured to control the current increase rate dI / dt so that the induced electromotive force (L(dI / dt) or ΣL(dI / dt)) exceeds a voltage lower limit, measure the voltage across the excitation power supply 24, and detect a misconnection based on the measured voltage across the excitation power supply 24. The voltage lower limit may be preset so as to exceed the threshold voltage (Vf or ΣVf) of the rectifier element.

[0073] In this way, when the excitation power supply 24 and the superconducting coil 12 are connected correctly, the voltage across the excitation power supply 24 exceeds the lower voltage limit, so that the interlock by the interlock mechanism 46 does not operate, and the superconducting coil 12 can be excited. On the other hand, in the case of an incorrect connection, the voltage across the excitation power supply 24 falls below the lower voltage limit, so that the interlock by the interlock mechanism 46 operates, and the excitation of the superconducting coil 12 by the excitation power supply 24 can be stopped.

[0074] Depending on the type and design of the superconducting coil 12, the current increase rate immediately after the start of excitation may be slow (or may need to be slowed down). To avoid erroneously determining this situation as an erroneous connection, the excitation power supply 24 may disable the voltage lower limit value (or the interlock mechanism 46) when the current increase rate falls below a certain level. In this case, the excitation power supply 24 may enable the voltage lower limit value (or the interlock mechanism 46) when the current increase rate reaches a certain level.

[0075] Even in this way, it is possible to detect an erroneous connection between the excitation power supply 24 and the current introduction line 20 (and thus the superconducting coil 12). As a result, even if an erroneous connection occurs once, it can be correctly reconnected. It is possible to avoid the risk that the quench protection circuit 22 will not operate as a result of an erroneous connection. A single diode 28 can be used in the quench protection circuit 22 instead of a pair of diodes connected in reverse to each other, and it is possible to reduce the cost of the superconducting magnet device 10.

[0076] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, that various design changes are possible, that various modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment resulting from a combination has the combined effects of each of the combined embodiments.

[0077] In the above embodiment, the cryocooler 16 is a GM refrigerator, but the present invention is not limited thereto. In an embodiment, the cryocooler 16 may be another type of two-stage cryocooler having a first cooling stage 16a and a second cooling stage 16b, such as a Solvay refrigerator, a Stirling refrigerator, or a pulse tube refrigerator.

[0078] FIG. 1 shows one cryogenic refrigerator 16 as an example, but if necessary, for example when the superconducting coil 12 is large, the superconducting magnet device 10 may be provided with multiple cryogenic refrigerators 16 each cooling one and the same superconducting coil 12.

[0079] In the above-described embodiment, the superconducting magnet device 10 is configured as a so-called conduction-cooled type in which the superconducting coil 12 is directly cooled by the cryogenic refrigerator 16, rather than as an immersion-cooled type in which the superconducting coil 12 is immersed in a cryogenic liquid refrigerant such as liquid helium. However, the superconducting magnet device 10 may be of an immersion-cooled type. In this case, the superconducting coil 12 may be immersed and cooled in a cryogenic liquid such as liquid helium, and the quench protection circuit 22 may be cooled using a refrigerant with a higher boiling point (such as liquid nitrogen). In this way, the quench protection circuit 22 may be cooled to a higher cooling temperature than the superconducting coil 12 during operation of the superconducting coil 12.

[0080] In the above embodiment, the quench protection circuit 22 is thermally coupled to the first cooling stage 16a of the cryogenic refrigerator 16 and cooled to the first cooling temperature, but the present invention is not limited to this. The quench protection circuit 22 may be thermally coupled to the second cooling stage 16b of the cryogenic refrigerator 16 and cooled to the second cooling temperature. Alternatively, the quench protection circuit 22 may be disposed in the ambient environment outside the vacuum vessel 14 and cooled to the ambient temperature (e.g., room temperature).

[0081] The present invention has been described using specific terms based on the embodiments, but the embodiments merely show one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments without departing from the spirit of the present invention as defined in the claims. [Explanation of symbols]

[0082] 10 superconducting magnet device, 12 superconducting coil, 22 quench protection circuit, 24 excitation power supply, 40a coil side positive terminal, 40b coil side negative terminal, 42a power supply side positive terminal, 42b power supply side negative terminal, 44 detector, 50 sensor.

Claims

1. A superconducting coil; a quench protection circuit connected in parallel with the superconducting coil and allowing current to flow in a single direction; an excitation power supply connected to the superconducting coil with a regular polarity determined so that a current flows in the unidirectional direction through the quench protection circuit when a quench occurs in the superconducting coil, and excites the superconducting coil; a first power supply for supplying a first polarity to the first superconducting coil, the first polarity being opposite to the first polarity of the first superconducting coil;

2. the quench protection circuit comprises a rectifier connected in parallel with the superconducting coil or a portion thereof; 2. The superconducting magnet device according to claim 1, wherein the excitation power supply is configured to control a current increase rate when exciting the superconducting coil so that an induced electromotive force generated in the superconducting coil or the portion thereof by the current increase rate exceeds a threshold voltage of the rectifying element.

3. A sensor for detecting the flow of current through the rectifying element is further provided.

3. The superconducting magnet apparatus according to claim 2, wherein the excitation power supply is configured to control the current increase rate so that the induced electromotive force exceeds a threshold voltage of the rectifying element, and to detect the improper connection based on an output of the sensor.

4. 3. The superconducting magnet apparatus according to claim 2, wherein the excitation power supply is configured to control the current increase rate so that the induced electromotive force exceeds a threshold voltage of the rectifying element, measure a voltage across the excitation power supply, and detect the misconnection based on the measured voltage across the excitation power supply.

5. The excitation power supply is configured to stop the excitation power supply when the measured voltage across the two terminals falls below a lower voltage limit value; the excitation power supply is configured to control the current increase rate so that the induced electromotive force exceeds the voltage lower limit value, measure a voltage across the excitation power supply, and detect the misconnection based on the measured voltage across the excitation power supply; 5. The superconducting magnet apparatus according to claim 4, wherein the lower limit voltage is preset so as to exceed a threshold voltage of the rectifying element.

6. A pair of coil side terminals connected to the superconducting coil, the excitation power supply includes a pair of power supply side terminals connected to the pair of coil side terminals, the superconducting magnet apparatus further includes a detector that generates a detection signal that indicates whether the set of coil side terminals and the set of power supply side terminals are connected in the normal polarity or in the reverse polarity; 6. The superconducting magnet apparatus according to claim 1, wherein the excitation power supply is configured to detect the erroneous connection based on the detection signal.

7. A superconducting coil; a quench protection circuit connected in parallel with the superconducting coil and allowing current to flow in a single direction; an excitation power supply that is connected to the superconducting coil with a regular polarity determined so that a current flows in the unidirectional direction through the quench protection circuit when a quench occurs in the superconducting coil, and that excites the superconducting coil; a coil-side positive terminal and a coil-side negative terminal connected to the superconducting coil; the excitation power supply includes a power supply side positive terminal connected to the coil side positive terminal and a power supply side negative terminal connected to the coil side negative terminal, The coil side positive terminal is configured to be unable to be connected to the power supply side negative terminal, 2. A superconducting magnet device, comprising: a coil-side negative terminal configured to be unable to be connected to the power supply-side positive terminal;

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