Superconducting magnet and method of operating the same

Abstract

To provide a superconducting magnet capable of promoting to perform maintenance in a period where there is no hindrance in normal operation of the superconducting magnet, and provide an operational method of the superconducting magnet.SOLUTION: A superconducting magnet comprises: a superconducting coil 1 that is arranged to a vacuum insulation container 8; an excitation power supply 3 that excites the superconducting coil; a refrigeration machine 9 that cools the superconducting coil; and an operation control device 50 that controls the excitation power supply and the refrigeration machine. The operation control device comprises: a coil temperature adjustment device 2; a coil voltage measurement device 4; a magnetic field measurement device 5; a magnetic field stable time storage deice 6; and a secure requirement determination device 7, where a temperature of the superconducting coil is changed via the refrigeration machine at a predetermined time, and excites the superconducting coil while measuring a voltage of the superconducting coil and measuring magnetic field strength of the superconducting coil, and a magnetic stable time required for satisfying a desired time stable level in the generation magnetic field of the superconducting coil after the excitation of the superconducting coil by the excitation power supply is stored, and a secure requirement is determined on the basis of a relationship between a coil temperature setting value of excitation at a plurality of times and the magnetic field stable time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a superconducting magnet and a method for operating a superconducting magnet. [Background technology]

[0002] Superconducting magnets with one or more superconducting coils have traditionally used low-temperature superconducting wires such as NbTi (niobium titanium) wire. The operating temperature of superconducting magnets using NbTi wire is approximately 4K, so they require cooling with expensive liquid helium. Note that "K" is the absolute temperature. However, in recent years, with the development of high-temperature superconducting materials, the operating temperature of superconducting magnets has been rising. For example, MgB2 (magnesium diboride) wire has a relatively low critical temperature among the superconducting wires currently under development, but MgB2 itself still achieves a high superconducting transition temperature of approximately 40K.

[0003] The practical operation temperature of a superconducting magnet using this MgB2 wire is about 10K to 20K. At such operating temperatures, superconducting magnets do not require liquid helium and can be maintained at that temperature by conduction cooling from a refrigerator. The specific heat of metal materials in the temperature range of about 10 K to 20 K is about one order of magnitude larger than the specific heat at 4 K. Therefore, the temperature rise for a given amount of heat generation is suppressed by one order of magnitude. By utilizing this large specific heat, the temperature rise of the superconducting coils during short-term excitation of the superconducting magnet is suppressed, making it possible to energize and demagnetize the superconducting magnet faster than before.

[0004] In conventional low-temperature superconducting magnets, the excitation speed is very slow to avoid the temperature rising above the critical temperature of superconductivity due to the temperature rise during excitation. For example, superconducting magnets used in MRI (Magnetic Resonance Imaging) take several hours to be excited. Furthermore, since it takes time for the magnetic field strength to stabilize after excitation, it is common to maintain the excited state unless demagnetization is required due to an emergency or maintenance. On the other hand, recent superconducting magnets, which do not require liquid helium and can be operated at temperatures above 10K, are capable of rapid excitation and demagnetization, making it possible to operate them by energizing them only when a magnetic field is needed and demagnetizing them at other times. This feature can be utilized to simplify the operation of mobile MRIs and MRIs for operating rooms. In the case of mobile MRIs, the MRI can be demagnetized during transport and energized only when MRI imaging is performed after the transport, while in the case of operating room MRIs, the MRI can be demagnetized during surgery and energized only when MRI imaging is performed to confirm the surgical results.

[0005] When the superconducting coil is excited only at the necessary time and place, the shielding current flowing in the superconducting wire of the superconducting magnet after excitation can cause problems in the operation of the superconducting magnet. The abstract of Patent Document 1 states, "Problem: To provide a method for operating a superconducting magnet, a superconducting magnet, and an inspection device that can ensure the stability of the magnetic field generated by the superconducting coil in a short time. Solution: The method for operating a superconducting magnet includes a step (S20) of adjusting the temperature of a superconducting coil formed by winding a superconducting wire to a predetermined target temperature, a step (S30) of repeatedly exciting and demagnetizing the superconducting coil after the temperature of the superconducting coil reaches the target temperature, and a step (S40) of maintaining the superconducting coil in a superconducting state during the execution of excitation and demagnetization of the superconducting coil. The target temperature is set to a temperature at which the superconducting coil reaches thermal equilibrium during the execution of excitation and demagnetization of the superconducting coil that has been cooled to a superconducting state." and discloses technology for the method for operating a superconducting magnet. Thus, Patent Document 1 describes an operating method in which, in order to suppress the influence of the shielding current, the superconducting coil is heated and then excited, and then cooled in the process of maintaining the operating current of the superconducting coil. This method utilizes the fact that the magnitude of the shielding current decreases as the operating condition approaches a certain level. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-12743 Summary of the Invention [Problem to be solved by the invention]

[0007] On the other hand, in superconducting magnets with higher operating temperatures, the number of times they are energized and deenergized can be increased, so the superconducting coils are repeatedly subjected to electromagnetic forces associated with energization.Furthermore, superconducting magnets that are intended to be transported daily or that are used in motors for moving objects are repeatedly subjected to vibrations associated with movement. Since superconducting magnets are mainly composed of superconducting coils, a vacuum insulation layer, and a cooling device, their cooling characteristics may change if they are subjected to repeated loads such as electromagnetic force or vibration.

[0008] For example, in a cooling method that does not use a refrigerant, the superconducting coil is cooled by conduction cooling from a cooling device, but if the fastening parts of the cooling path become loose, the thermal conduction performance of the cooling path may change, resulting in a change in the temperature distribution of the superconducting coil from that of a conventional method. Furthermore, if the degree of vacuum in the vacuum insulation layer decreases or a malfunction occurs in the cooling device, the superconducting coil may be operated at a temperature that is different from the conventional coil temperature setting value. Such changes in the cooling performance of superconducting magnets are difficult to detect during normal operation, and there is a possibility that a malfunction such as an inability to generate the rated magnetic field may suddenly occur.

[0009] The present invention aims to provide a superconducting magnet and an operating method for a superconducting magnet that can shorten the waiting time required for the magnetic field to stabilize after the excitation of the superconducting coil, and that can detect slight changes in the performance of the superconducting coil or the conduction cooling path, or slight changes in the cooling performance of the vacuum insulation layer or the refrigerator, and can prompt maintenance when normal operation is not affected. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention is configured as follows. That is, the superconducting magnet of the present invention comprises a superconducting coil disposed inside a vacuum insulated vessel, an excitation power supply that excites the superconducting coil, a refrigerator that cools the superconducting coil, and an operation control device that controls the excitation power supply and the refrigerator, wherein the operation control device is configured to comprise a coil temperature regulator, a coil voltage measurement device, a magnetic field measurement device, a magnetic field stabilization time storage device, and a maintenance necessity determination device, wherein the coil temperature regulator changes the temperature of the superconducting coil via the refrigerator a predetermined number of times, and while the coil voltage measurement device measures the voltage of the superconducting coil and the magnetic field measurement device measures the magnetic field strength of the superconducting coil, the operation control device excites the superconducting coil via the excitation power supply, and the magnetic field stabilization time storage device records the magnetic field stabilization time required from the excitation of the superconducting coil by the excitation power supply until the magnetic field generated by the superconducting coil satisfies a desired time stability, and the maintenance necessity determination device determines whether maintenance is necessary based on the relationship between the coil temperature setting value and the magnetic field stabilization time for multiple excitations recorded by the magnetic field stabilization time storage device.

[0011] Other means will be described in the description of the preferred embodiment of the invention. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a superconducting magnet and a method of operating a superconducting magnet that can shorten the waiting time required for the magnetic field to stabilize after the excitation of the superconducting coil, and that can detect slight changes in the performance of the superconducting coil or the conduction cooling path, or slight changes in the cooling performance of the vacuum insulation layer or the refrigerator, and can prompt maintenance when normal operation is not affected. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing an example of the configuration of a superconducting magnet according to a first embodiment of the present invention. [Figure 2] FIG. 4 is a diagram showing an example of measurement results of the relationship between the coil temperature setting value during excitation of the superconducting coil of the superconducting magnet according to the first embodiment of the present invention and the magnetic field stabilization time. [Figure 3] FIG. 1 is a diagram showing an example of a flowchart illustrating basic steps of a method for operating a superconducting magnet according to a first embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing an example of a case in which the magnetic field stabilization time in the N+1th period has changed to be shorter than that in the Nth period in the measurement results of the relationship between the coil temperature setting value during excitation of the superconducting coil of the superconducting magnet according to the first embodiment of the present invention and the magnetic field stabilization time. [Figure 5] FIG. 4 is a diagram showing an example of the configuration of a superconducting magnet according to a second embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing a configuration example of a superconducting magnet according to a third embodiment of the present invention. [Figure 7A] FIG. 10 is a diagram showing an example of a flowchart of a method for operating a superconducting magnet according to a fourth embodiment of the present invention. [Figure 7B] FIG. 10 is a diagram showing an example of a flowchart of specific steps constituting a coil Ic measurement step in a method for operating a superconducting magnet according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, modes for carrying out the present invention (hereinafter referred to as "embodiments") will be described with reference to the drawings as appropriate.

[0015] First Embodiment A superconducting magnet according to a first embodiment of the present invention will be described with reference to the drawings.

[0016] <Configuration of Superconducting Magnet 101> FIG. 1 is a diagram showing an example of the configuration of a superconducting magnet 101 according to a first embodiment of the present invention. In FIG. 1, a superconducting magnet 101 is configured to include a superconducting coil 1, an excitation power supply 3, a refrigerator 9, a cooling path 10, excitation wiring 11, and an operation control device 50. The superconducting coil 1 is disposed inside a vacuum insulating container 8. It is preferable that the superconducting coil 1 is made of a high-temperature superconducting material. The excitation power supply 3, refrigerator 9, and operation control device 50 are provided outside the vacuum insulated container 8. The refrigerator 9 is provided outside the vacuum insulated container 8 and cools the inside of the vacuum insulated container 8.

[0017] The superconducting coil 1 is connected to an excitation power supply 3 via an excitation wiring 11 and is excited by the excitation power supply 3 . The superconducting coil 1 is connected to a refrigerator 9 via a cooling path 10, and is cooled to a predetermined temperature by the refrigerator 9. Since the refrigerator 9 cools the superconducting coil 1 via the cooling path 10, the superconducting coil 1 can be cooled quickly. Moreover, the refrigerator 9 can cool the superconducting coil 1 so as to keep it within a predetermined low temperature range.

[0018] The operation control device 50 controls the excitation power supply 3 and the refrigerator 9 via control wiring (not shown). The operation control device 50 controls the excitation power supply 3 and the refrigerator 9, thereby controlling the superconducting coil 1. The operation control device 50 is configured to include a coil temperature adjustment device 2, a coil voltage measurement device 4, a magnetic field measurement device 5, a magnetic field stabilization time storage device 6, and a maintenance necessity determination device 7.

[0019] The superconducting coil 1 is cooled by the refrigerator 9 with the coil temperature designated by the coil temperature adjusting device 2 provided in the operation control device 50 as the target. If the temperature of the superconducting coil 1 when the refrigerator 9 is constantly operated is lower than the designated coil temperature value, the temperature of the superconducting coil 1 is adjusted by operating the refrigerator 9 intermittently or by heating a heater (not shown) provided in the refrigerator 9, the cooling path 10, or the superconducting coil 1. The heater is controlled by the operation control device 50.

[0020] The operation control device 50 controls the excitation power supply 3 while measuring the voltage value generated in the superconducting coil 1 with the coil voltage measuring device 4 provided in the operation control device 50. By this control, the excitation power supply 3 energizes the superconducting coil 1, and the value of the current flowing through the superconducting coil 1 is increased, thereby exciting the superconducting coil 1.

[0021] <AC loss and shielding current> When the superconducting coil 1 is excited, it is cooled by a refrigerator 9 and set to a superconducting state. However, heat called AC loss occurs inside the superconducting coil 1 during excitation. Therefore, when the superconducting coil 1 is cooled with a certain cooling capacity, the temperature of the superconducting coil 1 rises. Note that AC loss is a phenomenon that occurs due to a different factor even when the superconducting coil 1 is in a superconducting state and its electrical resistance is zero. The magnetic field strength generated by the superconducting coil 1 is measured by a magnetic field measuring device 5. The measured magnetic field strength is approximately proportional to the magnitude of the current supplied from the excitation power supply 3. When the current supplied from the excitation power supply 3 reaches a predetermined rated current, the increase in the current value is stopped and the current value is maintained, thereby maintaining the state in which the rated magnetic field is generated in the superconducting magnet 101.

[0022] When the shielding current caused by excitation in the superconducting wire that constitutes the superconducting coil 1 cannot be ignored, the direction of the magnetic field formed by this shielding current is opposite to the direction of the magnetic field generated by the current supplied from the excitation power supply 3. Therefore, the magnetic field of the superconducting magnet 101 changes with time, monotonically increasing immediately after excitation.

[0023] <Relationship between coil temperature setting during excitation and magnetic field stabilization time> Next, the relationship between the excitation coil temperature setting value and the magnetic field stabilization time will be described with reference to Figures 1 and 2. In the following description, superconducting magnet 101 is in a superconducting state. The time from when the rated current is applied by the excitation power supply 3 (FIG. 1) until the time when the time stability of the magnetic field generated by the superconducting magnet 101 reaches a predetermined value is defined as the magnetic field stabilization time. The superconducting magnet 101 of the present invention is characterized in that, under the control of the operation control device 50, the relationship between the coil temperature setting value during excitation and the magnetic field stabilization time is recorded and compared over multiple excitations.

[0024] For example, the coil temperature setting for the jth excitation is T j (K) and the magnetic field stabilization time is t j (s), i.e., t j (seconds), and the coil temperature setting value for the (j+1)th excitation is T j+1 (K) and the magnetic field stabilization time is t j+1 (s), etc., until the (j+n)th excitation, T j+n (K) j+n Measure (s). In addition, the coil temperature setting value T j In the notation (K), "T" stands for temperature, j " means the jth time, and "K" means absolute temperature.

[0025] For example, if the coil temperature setting value during excitation is increased in increments of 0.05 (K) and the coil is excited nine times, T j (K) to T j+0.4 The magnetic field stabilization time (K) is recorded relative to the coil temperature setting value during excitation. This gives the graph shown in Figure 2. FIG. 2 shows the coil temperature setting value (coil temperature setting value) T j (K) and magnetic field stabilization time t j FIG. 10 is a diagram showing an example of the measurement results of the relationship (s). In Figure 2, the horizontal axis represents the coil temperature setting value (coil temperature setting value) T j (K), and the vertical axis is the magnetic field stabilization time t j (s), i.e., t j (seconds). Also, the coil temperature setting value during excitation (coil temperature setting value) T j The graph shows the results of nine measurements (B9) with (K) simply increased in increments of 0.05 (K).

[0026] Coil temperature setting value during excitation (coil temperature setting value) T j If the actual coil temperature (K) is lower than a certain threshold, the excitation coil temperature setting (coil temperature setting) T j As the temperature increases, the magnetic field stabilization time t j (s) monotonically decreases. The reason is that the effect of the shielding current is weakened by the rise in the actual coil temperature (superconducting state), which results in a reduction in the time required for the magnetic field to stabilize. In other words, it is possible to shorten the waiting time until the magnetic field stabilizes.

[0027] Furthermore, as will be described later with reference to FIG. 4, by repeating periodic operation with n excitations as one cycle, it becomes possible to grasp the state of the superconducting magnet 101. Specifically, at the (j+n+1)th excitation, the coil temperature setting value at excitation is set to T j Return to (K) and T j+n By repeating the measurements of the excitation and magnetic field stabilization times up to (K), it becomes possible to compare the results with those from the previous period. If the measurement results in the Nth period and the (N+1)th period match within the measurement error range, superconducting magnet 101 is in a healthy state.

[0028] As will be described later with reference to Figure 4, if the measurement results in the (N+1)th cycle change more quickly than the measurement results in the Nth cycle, the difference between the excitation coil temperature setting value and the actual coil temperature (or part of the actual coil temperature) becomes large, which may indicate a change in performance of the vacuum insulated container 8, the refrigerator, or the cooling path 10, and the need for maintenance becomes apparent.

[0029] <Basic processes of excitation and demagnetization, and how to operate a superconducting magnet> The method of operating the superconducting magnet 101 of the first embodiment will be described with reference to FIG. 3 is a diagram showing an example of a flowchart of basic steps (basic operation steps) 80 of the method for operating the superconducting magnet 101 according to the first embodiment of the present invention. In FIG. 3, each step is carried out in order from step S60 to step S65. Among the steps in the flowchart shown in FIG. 3, the superconducting coil 1 is in a superconducting state at least in steps S61 to S65.

[0030] <Step S60> In step S60 (FIG. 3), "excitation coil temperature adjustment" of superconducting magnet 101 (FIG. 1) is performed. That is, the temperature of the superconducting coil 1 (FIG. 1) during excitation is set, and the temperature of the superconducting coil 1 is adjusted to a predetermined set value by the coil temperature adjusting device 2 (FIG. 1) and the refrigerator 9 (FIG. 1). Then, the process proceeds to step S61.

[0031] Step S61 In step S61 (FIG. 3), the superconducting coil 1 is "excited" by the excitation power supply 3 (FIG. 1). That is, the current supplied to the superconducting coil 1 is increased by the excitation power supply 3 until it reaches a predetermined current value. Then, the process proceeds to step S62. During this excitation process, if the coil voltage measuring device 4 (FIG. 1) detects an abnormal voltage in the superconducting coil 1, the excitation is stopped.

[0032] Step S62 In step S62 (FIG. 3), magnetic field measurement device 5 (FIG. 1) is used to measure the change over time in the magnetic field generated by superconducting magnet 101. Through this measurement, the magnetic field stabilization time is measured (magnetic field stabilization time measurement) and the magnetic field stabilization time is calculated. Then, the process proceeds to step S63.

[0033] Step S63 In step S63 (FIG. 3), the temperature of the superconducting coil 1 is adjusted to a predetermined set value by the coil temperature adjustment device 2 (FIG. 1) and the refrigerator 9. That is, the "normal coil temperature adjustment" step is performed. In this normal coil temperature adjustment step, the normal coil temperature is set to a temperature lower than the excitation coil temperature, as described above. Then, the process proceeds to step S64.

[0034] <Step S64> In step S64 (FIG. 3), the superconducting magnet 101 is put into "normal operation." That is, at a normal coil temperature that is lower than the excitation coil temperature, the superconducting magnet 101 operates to form a magnetic field in a stable superconducting state, and is operated in this state (normal operation). Then, the process proceeds to step S65.

[0035] Step S65 In step S65 (FIG. 3), when the operation (normal operation) of superconducting magnet 101 is to be ended, that is, when the use of the magnetic field of superconducting magnet 101 is completed, a "demagnetization" step is carried out. Specifically, the current supplied to the superconducting coil 1 by the excitation power supply 3 is gradually reduced. This reduction in the current flowing through the superconducting coil 1 causes the superconducting magnet 101 to be demagnetized. Even when the superconducting magnet 101 is demagnetized, the superconducting coil 1 is maintained in a superconducting state in terms of operation.

[0036] <Supplementary information on the basic process of magnetization and demagnetization> The above steps S60 to S65 constitute the basic process (basic operation process) 80 for one cycle of excitation to demagnetization. The operation of the superconducting magnet 101 according to the first embodiment of the present invention is premised on multiple excitation / demagnetization (excitation and demagnetization). As a result, the magnetic field stabilization time storage device 6 (FIG. 1) stores the relationship between the excitation coil temperature setting value (coil temperature setting value) and the magnetic field stabilization time as shown in FIG. Furthermore, when a display device 14 (FIG. 6) is provided as in the third embodiment described later, when the magnetic field stabilization time does not monotonically decrease but starts to increase midway while the excitation coil temperature setting value is within a predetermined range, it is also possible to display a maintenance reminder for the superconducting magnet 101 on the display device 14 (FIG. 6).

[0037] <When the magnetic field stabilization time in the N+1th cycle becomes shorter than that of the Nth cycle> When explaining the magnetic field stabilization time with reference to Fig. 2, it was explained that "superconducting magnet 101 is in a sound state when the measurement result in the Nth period and the measurement result in the (N+1)th period match within the range of measurement error" using Fig. 4 as an example, which will be described later. However, superconducting magnet 101 is not always in a sound state. Next, with reference to FIG. 4, a description will be given of "a case in which the magnetic field stabilization time in the (N+1)th period is changed to be shorter than that in the Nth period."

[0038] FIG. 4 shows the coil temperature setting value (coil temperature setting value) T j (K) and magnetic field stabilization time t j In the measurement results of the relationship between (seconds), the N+1th period (C N+1 ) is the magnetic field stabilization time in the Nth period (C N ) is a diagram showing an example of a case where the time has changed to be shorter than the time In Figure 4, the horizontal axis represents the coil temperature setting value (coil temperature setting value) T j (K), and the vertical axis is the magnetic field stabilization time t j (s), i.e., t jAlso, the nine basic steps (basic operation steps) 80 are shown as the measurement results of the Nth cycle (C N ) and the measurement result of the N+1th period (C N+1 ) is also shown. Note that on the horizontal axis of Figure 4, "excitation coil temperature setting value" is abbreviated to "coil temperature setting value."

[0039] In Fig. 4, the magnetic field stabilization time t j (s) exceeds the measurement error range and changes in less than the Nth period. In other words, the measurement result of the N+1th period (C N+1 ) is the measurement result of the Nth period (C N ) has changed to be shorter. In this way, the magnetic field stabilization time t j If (s) changes in less than the Nth period, the excitation coil temperature setting value T j (K) and the actual coil temperature (or some of the actual coil temperatures) is getting larger. If such measurement results are obtained, a change in the performance of the vacuum insulated container 8, the refrigerator 9, and the cooling path 10 in FIG. 1 is suspected, and the need for maintenance is evoked.

[0040] The magnetic field stabilization time t j In the operation of the superconducting magnet 101 after (s) has elapsed, the coil temperature setting value (normal coil temperature setting value) T j By operating the coil at a temperature (K) lower than the coil temperature setting during excitation, for example, minus 2 Kelvin, the possibility of the superconducting coil 1 suddenly becoming normal conducting (quenching) due to disturbances can be reduced to a negligible level. Furthermore, even if some performance change is suspected during the N+1th cycle, the operation of the superconducting magnet 101 will not be maintained at the excitation coil temperature setting value, so immediate maintenance is not required and the timing of maintenance can be set appropriately in accordance with the magnet operation schedule.

[0041] <Summary of the First Embodiment> When the superconducting magnet 101 according to the first embodiment of the present invention is constructed using a high-temperature superconducting material, a cooling path 10 is provided between the refrigerator 9 and the superconducting coil 1, enabling temperature control of the superconducting coil 1 in a relatively short time. Therefore, switching between excitation and demagnetization can be performed relatively quickly. When the superconducting magnet 101 is used, for example, for a medical MRI, it is possible to perform multiple excitation / demagnetization (excitation and demagnetization) tests to understand the characteristics of the superconducting magnet 101 between uses in medical procedures. As a result, under the control of the operation control device 50 of the superconducting magnet 101, the magnetic field stabilization time storage device 6 stores data on the relationship between the excitation coil temperature setting value and the magnetic field stabilization time. By analyzing such data, it is possible to obtain various information, such as whether immediate maintenance is necessary for the vacuum insulated vessel 8, refrigerator 9, cooling path 10, etc. in the superconducting magnet 101, or whether timely maintenance can be performed in accordance with the operating schedule.

[0042] <Effects of the first embodiment> According to the present invention, it is possible to reduce the waiting time required for the magnetic field to stabilize after the excitation of the superconducting coil. Furthermore, it is possible to provide a superconducting magnet and an operating method for a superconducting magnet that can detect slight changes in the performance of the superconducting coil or conduction cooling path, or slight changes in the cooling performance of the vacuum insulation layer or refrigerator, and can prompt maintenance when normal operation is not affected.

[0043] Second Embodiment A superconducting magnet 102 according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a diagram showing an example of the configuration of a superconducting magnet 102 according to the second embodiment of the present invention. In FIG. 5, a superconducting magnet 102 comprises a superconducting coil 1, an excitation power supply 3, a refrigerator 9, a cooling path 10, excitation wiring 11, an operation control device 50, a persistent current switch 12, and a heater 13 for the persistent current switch. The configuration of the superconducting magnet 102 in FIG. 5 differs from the superconducting magnet 101 in FIG. 1 in that a persistent current switch 12 and a heater 13 for the persistent current switch are newly provided in FIG.

[0044] The persistent current switch 12 and the heater 13 for the persistent current switch are controlled by an operation control device 50. The persistent current switch 12 is also controlled by the heater 13 for the persistent current switch. In the following description of the superconducting magnet 102 according to the second embodiment, differences from the first embodiment will be mainly described.

[0045] In the superconducting magnet 102 for MRI and other applications where magnetic field stability is important, persistent current operation is preferable. As shown in FIG. 5, the superconducting magnet 102 that performs persistent current operation includes a persistent current switch 12 and a heater 13 for the persistent current switch. The persistent current switch 12 is connected to both ends of the superconducting coil 1. When the persistent current switch 12 enters a superconducting state and the resistance becomes zero, the superconducting coil 1 enters a superconducting state, and a closed loop with zero resistance is formed in the closed loop consisting of the superconducting coil 1 and the persistent current switch 12. When a closed loop with zero resistance is formed, there is no need to supply current from the excitation power supply 3 (persistent current operation). Furthermore, when the heater 13 for the persistent current switch is overheated and the heat causes the persistent current switch 12 to deviate from the superconducting state and acquire a predetermined resistance, a predetermined resistance is generated in the closed loop consisting of the superconducting coil 1 and the persistent current switch 12.

[0046] In the second embodiment, similarly to the first embodiment, the magnetic field stabilization time in the superconducting magnet 102 is defined as the time required from the start of persistent current operation to the time required for the magnetic field to stabilize to a predetermined value. In the process of ensuring this predetermined magnetic field stability, persistent current operation is performed in a closed loop consisting of the superconducting coil 1 and the persistent current switch 12, eliminating the need for current supply from the excitation power supply 3, thereby making it possible to eliminate the influence of the excitation power supply 3 on the temporal stability of the magnetic field.

[0047] In other words, the superconducting magnet 102 according to the second embodiment, which is provided with the persistent current switch 12 and the heater 13 for the persistent current switch, makes it possible to maintain the temporal stability of the magnetic field required for MRI imaging while also monitoring the status of the superconducting magnet 102.

[0048] <Effects of the second embodiment> In the process of ensuring magnetic field stability, persistent current operation is performed in a closed loop consisting of the superconducting coil 1 and the persistent current switch 12, eliminating the need for current supply from the excitation power supply 3. This makes it possible to eliminate the influence of the excitation power supply 3 on the temporal stability of the magnetic field, thereby contributing to the temporal stability of the magnetic field. In addition, there is an effect that it is possible to simultaneously maintain the degree of temporal stability of the magnetic field required for MRI imaging and monitor the state of the superconducting magnet 102.

[0049] Third Embodiment The configuration of a superconducting magnet 103 according to a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram showing an example of the configuration of a superconducting magnet 103 according to the third embodiment of the present invention. In FIG. 6, in addition to the configuration of the superconducting magnet 101 shown in FIG. 1 as the first embodiment, a display device 14 is also provided. The display device 14 is connected to the operation control device 50. As explained in the <Supplementary Information on the Basic Processes of Excitation and Demagnetization> in the first embodiment, when the magnetic field stabilization time does not monotonically decrease but starts to increase midway through when the coil temperature setting value during excitation is within a predetermined range, maintenance of the superconducting magnet 101 may be necessary.

[0050] In this case, if it is determined that maintenance is necessary under the control of the operation control device 50, the maintenance necessity determination is displayed on the display device 14. Then, a maintenance request is made to the user (operator, manager) of the superconducting magnets (101, 103). Alternatively, a maintenance request may be sent to, for example, the manufacturer of the superconducting magnets (101, 103) by some communication means. The configuration of the superconducting magnet 103 according to the third embodiment of the present invention allows even a user who is not familiar with superconductivity and superconducting magnets to easily know whether or not maintenance of the superconducting magnets (101, 103) is required.

[0051] <Effects of the third embodiment> The configuration of the superconducting magnet 103 equipped with the display device 14 according to the third embodiment of the present invention allows even a user who is not familiar with superconductivity and superconducting magnets to easily know whether or not maintenance of the superconducting magnet is required.

[0052] Fourth Embodiment A method of operating a superconducting magnet according to a fourth embodiment of the present invention will be described with reference to FIGS. 7A and 7B. FIG. 7A is a diagram showing an example of a flowchart of a method (801) for operating a superconducting magnet according to the fourth embodiment of the present invention. FIG. 7B is a diagram showing an example of a flowchart of specific steps constituting the coil Ic measurement step (S81) in the method (801) of operating a superconducting magnet according to the fourth embodiment of the present invention.

[0053] The coil Ic measurement process (S81) is an intermediate process of repeating the basic operation process (S80) in the superconducting magnet operation method (801), in which the coil temperature setting value during excitation is increased by 1 Kelvin or more from the value in the basic operation process 80, and excitation is performed, and the current value at which a predetermined voltage is generated in the coil (superconducting coil 1) is measured.

[0054] <Operation method of superconducting magnet (801)> 7A, the method of operating a superconducting magnet (801) of the fourth embodiment comprises a basic operation process (step S80) and a coil Ic measurement process S81. Next, each process will be described in order.

[0055] Step S80 Step S80 is a basic operation process. The basic operation step (S80) corresponds to the basic operation step (basic operation step) 80 of the method of operating the superconducting magnet 101 explained in Fig. 3. However, in the basic operation step of step S80 in Fig. 7A, a loop L80 is shown, indicated by an arrow returning from the bottom of the block showing step S80 to the right. This process shown as loop L80 indicates that in step S80 in Fig. 7A, each of steps S60 to S65 of the basic operation step 80 of the method of operating the superconducting magnet 101 shown in Fig. 3 is repeatedly performed. Once the basic operation process of step S80 has been carried out, the process proceeds to the next step S81.

[0056] Step S81 Step S81 is a coil Ic measurement step. The coil Ic measuring step (S81) is a step of measuring a current value that generates a predetermined voltage in the coil (superconducting coil 1). However, the coil Ic measuring step (S81) further includes a plurality of steps. Next, the coil Ic measuring step (S81) will be described in detail.

[0057] <Coil Ic measurement process (S81)> 7B, the coil Ic measurement step (S81) includes a step of adjusting the coil temperature during excitation (coil temperature adjustment step during excitation) S70 and a step of excitation (excitation step) S71. Next, each step will be described in order.

[0058] Step S70 Step S70 is a coil temperature adjustment step during excitation. In this step S70, the temperature of the superconducting coil 1 (FIG. 1) is set to the coil temperature during Ic measurement, and the temperature of the superconducting coil 1 is adjusted toward the set value by the coil temperature adjustment device 2 (FIG. 1) and the refrigerator 9 (FIG. 1). The excitation coil temperature setting value is set to be 1 Kelvin or more higher than the value in the basic operation step S80.

[0059] Step S71 Step S71 is an excitation step. In step S71, the superconducting coil 1 whose temperature has been adjusted in step S70 is "excited." Specifically, in the excitation step (step S71), the value of the current passed from the excitation power supply 3 (FIG. 1) to the superconducting coil 1 is increased to a predetermined current value, while the coil voltage is measured by the coil voltage measuring device 4 (FIG. 1). When the coil voltage reaches a predetermined voltage, the current supplied from the excitation power supply 3 is returned to zero, and the excitation step S71 is completed.

[0060] <Correspondence between the operation control device 50 and the display device 14> In the method (801) for operating a superconducting magnet according to the fourth embodiment described above in Figures 7A and 7B, the operation control device 50 stores the current value at which a predetermined voltage is generated in the superconducting coil 1 as the coil Ic (coil current Ic). Then, the coil Ic measurement step S81 is repeated periodically, and the coil Ic (coil current Ic) relative to the coil temperature at the same time of coil Ic measurement is recorded. If the coil Ic relative to the coil temperature during this same Ic measurement drops, a signal to prompt maintenance of the superconducting magnets (101, 103) is sent to the display device 14 at the stage when the drop is observed. The display device 14 displays a maintenance reminder.

[0061] <Effects of the Fourth Embodiment> By periodically repeating the coil Ic measurement process S81, recording the coil Ic (coil current Ic) relative to the coil temperature at the same coil Ic measurement, and detecting when the coil Ic relative to the coil temperature at the same Ic measurement decreases, the need for maintenance of the superconducting magnets (101, 103) can be made known.

[0062] Other Embodiments The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with part of the configuration of another embodiment, and it is also possible to add, delete, or replace part or all of the configuration of another embodiment with the configuration of one embodiment. Other embodiments and modifications will be further described below.

[0063] <<Shortening the magnetic field stabilization time>> As a method for mitigating the influence of the shielding current after excitation and shortening the time required for the magnetic field to stabilize, there is a method for overshooting the current value applied to the superconducting coil 1. The method of overshooting the current value applied to the superconducting coil 1 is to once apply current to a value several percent higher than the rated current value, and then reduce the current value to the rated current value. In this magnet, the reduction in the magnetic field stabilization time due to this overshoot is also effective and feasible. In step S61 (FIG. 3) of the above-described method for operating a superconducting magnet, there is a process of "exciting" the superconducting coil 1 by the excitation power supply 3 (FIG. 1), and the above-described overshoot may be applied during this excitation process.

[0064] 《Display device 14》 The display device 14 can display not only the above-mentioned maintenance warning but also various information related to the superconducting magnets (101, 102) as needed. Although the display device 14 is described as a "display," it is not limited to text or images. For example, it may be a device that outputs a warning sound, human voice, or transmits a predetermined signal to another department.

[0065] <<Measurement of magnetic field stabilization time>> In Figures 2 and 4, the coil temperature setting value during excitation was simply increased in increments of 0.05 (K), and excitation was performed nine times, and the magnetic field stabilization time for the coil temperature setting value during excitation was recorded to measure and evaluate the stability of the magnetic field. However, nine times is just one example, and although the accuracy will change, it may be performed more or less than nine times.

[0066] <<Increase in the excitation coil temperature setting value during the excitation coil temperature adjustment process>> In the method (801) for operating a superconducting magnet in the fourth embodiment, in the step of adjusting the coil temperature during excitation (step S70: FIG. 7B), in which the temperature of the superconducting coil 1 is adjusted toward the set value, a method has been described in which the coil temperature set value during excitation is set to be 1 Kelvin or more higher than the value in the basic operation step (step S80: FIG. 7A), but is not limited to 1 Kelvin. Depending on the characteristics, configuration, or operation method of the superconducting magnet, the temperature may be adjusted in steps other than 1 Kelvin.

[0067] <Configuration of operation control device> With reference to Figure 1, the operation control device 50 in the superconducting magnet of the first embodiment has been described as being configured to include a coil temperature adjustment device 2, a coil voltage measurement device 4, a magnetic field measurement device 5, a magnetic field stabilization time storage device 6, and a maintenance necessity determination device 7, but is not limited to these configurations. Recording of the magnetic field stabilization time and the like may be performed in a storage device included in the magnetic field stabilization time storage device 6 (operation control device 50), or may be performed in an external storage device via a network or the like. Furthermore, the maintenance necessity determination device 7 and the like may exist on the network. Furthermore, the operation control device 50 may include devices with other characteristics as needed. Furthermore, the above-mentioned devices may be removed if they are not required for the intended use. Furthermore, the display device 14 shown in FIG. 6 may be incorporated as a component of the operation control device 50.

[0068] <Number of superconducting coils> In the description of the first embodiment, no explanation was given regarding the number of superconducting coils constituting the superconducting coil, but the superconducting coil may be constituted by a plurality of superconducting coils. [Explanation of symbols]

[0069] 1 Superconducting coil 2. Coil temperature control device 3 Excitation power supply 4. Coil voltage measuring device 5 Magnetic field measuring device 6 Magnetic field stabilization time memory device 7 Maintenance necessity determination device 8. Vacuum insulated container 9. Freezer 10 Cooling Paths 11 Excitation wiring 12 Persistent current switch 13 Heater for persistent current switch 14 Display device 50 Operation control device 60 (S60) Coil temperature adjustment process during excitation 61(S61) Excitation process 62(S62) Stability time measurement process 70(S70) Coil temperature adjustment process during Ic measurement 71(S71) Excitation process 80 (S80) Basic Operation Process, Basic Process 81 (S81) Coil Ic measurement process, 101,102,103 Superconducting magnets

Claims

1. a superconducting coil disposed inside a vacuum insulated container; an excitation power supply that excites the superconducting coil; a refrigerator for cooling the superconducting coil; an operation control device that controls the excitation power supply and the refrigerator; Equipped with The operation control device is configured to include a coil temperature adjustment device, a coil voltage measurement device, a magnetic field measurement device, a magnetic field stabilization time storage device, and a maintenance necessity determination device, the coil temperature adjusting device changes the temperature of the superconducting coil via the refrigerator a predetermined number of times, the operation control device excites the superconducting coil via the excitation power supply while the coil voltage measuring device measures the voltage of the superconducting coil and the magnetic field measuring device measures the magnetic field strength of the superconducting coil; The magnetic field stabilization time storage device records the magnetic field stabilization time required from the excitation of the superconducting coil by the excitation power supply until the magnetic field generated by the superconducting coil satisfies a desired time stability, The maintenance necessity determination device determines whether maintenance is necessary based on the relationship between the coil temperature setting value and the magnetic field stabilization time of the multiple excitations recorded by the magnetic field stabilization time storage device. A superconducting magnet characterized by:

2. In claim 1, The superconducting coil is made of a high-temperature superconducting material. A superconducting magnet characterized by:

3. In claim 1, The refrigerator cools the superconducting coil through a cooling path. A superconducting magnet characterized by:

4. In claim 1, a persistent current switch connected to both ends of the superconducting coil; a heater for the persistent current switch that destroys the superconducting state of the persistent current switch; Equipped with When the persistent current switch is brought into a superconducting state, the superconducting coil and the persistent current switch form a closed loop, and the switch is operated in a persistent current state. A superconducting magnet characterized by:

5. In claim 1, a display device that displays a determination of whether or not maintenance is required by the maintenance requirement determination device; A superconducting magnet characterized by:

6. In claim 5, The display device is provided in the operation control device. A superconducting magnet characterized by:

7. A method for operating a superconducting magnet using the superconducting magnet according to claim 1, comprising: a step of exciting the superconducting coil a predetermined number of times while changing the temperature of the superconducting coil; a step of recording a magnetic field stabilization time required for a magnetic field generated by the superconducting coil to satisfy a desired time stability after the superconducting coil is excited by the excitation power supply; a step of determining whether maintenance is necessary based on the relationship between the coil temperature setting value for exciting the superconducting coil a plurality of times and the magnetic field stabilization time; Equipped with A method for operating a superconducting magnet, comprising:

8. In claim 7, A predetermined number of times to excite the superconducting coil is defined as one cycle, The coil temperature setting value within one cycle is set within the range from standard temperature to standard temperature + 1 Kelvin. With the coil temperature setpoint set within the temperature range from the standard temperature to the standard temperature + 1 Kelvin, the superconducting coil is excited and the magnetic field stabilization time is recorded; The relationship between the coil temperature setting value and the magnetic field stabilization time in the Nth cycle is compared with the relationship between the coil temperature setting value and the magnetic field stabilization time up to the N-1th cycle. A method for operating a superconducting magnet, comprising:

9. In claim 7 or claim 8, The superconducting coil is excited multiple times with the coil temperature set value set to a temperature that is 1 K or more higher than the standard temperature, Measure and record the current value that generates a specified voltage in the superconducting coil. The measured current value at which a predetermined voltage is generated at the same coil temperature setting is compared with the measured current value. A method for operating a superconducting magnet, comprising:

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