JP2021093440A - Superconducting magnet device and superconducting magnet control method - Google Patents

Abstract

To reduce possibility of compulsive current interruption of a superconducting coil to improve operation continuity of a superconducting magnet device.SOLUTION: A superconducting magnet device 10 comprises: a superconducting coil 12; a cryogenic refrigerator 16 for cooling the superconducting coil 12; an excitation power supply 18 for supplying excitation current to the superconducting coil 12; a temperature sensor 22 for measuring a temperature of the superconducting coil 12 or a temperature of a portion cooled together with the superconducting coil 12 by the cryogenic refrigerator 16 to output a measurement signal indicating the measured temperature; and a control unit 24 for receiving the measurement signal from the temperature sensor 22, comparing the measured temperature with a temperature threshold, and controlling the excitation power supply 18 so as to adjust excitation current to a target current value smaller than a rated current value when the measured temperature exceeds the temperature threshold.SELECTED DRAWING: Figure 1

Description

The present invention relates to a superconducting magnet device and a superconducting magnet control method.

It is known that the superconducting coil is immersed in liquid helium to cool it, and the power lead is cooled by the low-temperature helium gas vaporized from the superconducting coil. The helium gas that cooled the power lead is discharged from the air release valve. In order to prevent overheating and burning of the power lead due to poor cooling, emergency degaussing is performed to forcibly cut off the current of the superconducting coil based on the open / closed state of the air release valve and the temperature of the power lead (for example). See Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-252085

The exciting power supply of the superconducting coil is required to apply a voltage to the coil, which is determined by the product of the time change rate of the current flowing through the coil and the inductance of the coil. When the superconducting coil is normally operated at the rated current, the current value itself is large, for example, reaching at least several hundred amperes (ampere), but the fluctuation is small, so it is sufficient for the exciting power supply to be able to output a relatively low voltage. is there. On the other hand, in emergency degaussing, the current is rapidly reduced from such a large current to zero, and a high voltage corresponding to this current reduction rate is required for the power supply. In other words, the voltage capacity of the power supply limits the rate of decrease in possible current, which increases the time required for emergency degaussing. Similarly, when exciting a superconducting coil for recovery from emergency degaussing or for starting normal operation of a superconducting magnet device, a high-voltage power supply is required to perform it in a short time. Some superconducting coils have a large increase in inductance when the current is near zero, in which case the required voltage is higher and the problem can be even more pronounced. However, if a high voltage excitation power supply is adopted, the manufacturing cost will be correspondingly high.

One of the exemplary objects of an aspect of the present invention is to reduce the possibility of forced current interruption of the superconducting coil and improve the operational continuity of the superconducting magnet device.

According to an aspect of the present invention, the superconducting magnet device includes a superconducting coil, a cryogenic refrigerator that cools the superconducting coil, an exciting power supply that supplies an exciting current to the superconducting coil, and the temperature of the superconducting coil. A temperature sensor that measures the temperature of the part cooled together with the superconducting coil by a cryogenic refrigerator and outputs a measurement signal indicating the measurement temperature, receives the measurement signal from the temperature sensor, and compares the measurement temperature with the temperature threshold. A control unit that controls the exciting power supply so as to adjust the exciting current to a target current value smaller than the rated current value when the measured temperature exceeds the temperature threshold is provided.

According to an aspect of the present invention, the superconducting magnet control method measures the temperature of a superconducting coil or the temperature of a portion cooled together with the superconducting coil by a cryogenic refrigerator, and uses the measured temperature as a temperature threshold. It includes comparison and adjustment of the exciting current of the superconducting coil to a target current value smaller than the rated current value when the measured temperature exceeds the temperature threshold.

It should be noted that any combination of the above components or components and expressions of the present invention that are mutually replaced between methods, devices, systems, and the like are also effective as aspects of the present invention.

According to the present invention, the possibility of forced current interruption of the superconducting coil can be reduced, and the operation continuity of the superconducting magnet device can be improved.

It is the schematic sectional drawing which shows the superconducting magnet apparatus and the cyclotron which concerns on embodiment. It is a graph which shows an example of the current inductance characteristic of the superconducting coil which concerns on embodiment. It is a flowchart which illustrates the control method of the superconducting magnet apparatus which concerns on embodiment. It is a flowchart which illustrates the control method of the superconducting magnet apparatus which concerns on embodiment.

Hereinafter, 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 designated by the same reference numerals, and duplicate description will be omitted as appropriate. The scales and shapes of the illustrated parts are set for convenience of explanation and are not to be interpreted in a limited manner unless otherwise specified. Embodiments are exemplary and do not limit the scope of the invention in any way. Not all features and combinations thereof described in the embodiments are essential to the invention.

FIG. 1 is a schematic cross-sectional view showing a superconducting magnet device and a cyclotron according to an embodiment. The cyclotron 100 is a circular accelerator that accelerates charged particles and outputs a charged particle beam. Examples of charged particles include protons, heavy particles (heavy ions), and electrons. Charged particles are supplied from an ion source (not shown). The cyclotron 100 is used, for example, as an accelerator for charged particle beam therapy.

The cyclotron 100 includes a superconducting magnet device 10, a yoke 102, and a pair of poles 104. The superconducting magnet device 10 includes a superconducting coil 12, a cryostat 14 having a cryogenic refrigerator 16, an exciting power supply 18, a vacuum exhaust system 20, a temperature sensor 22, and a control unit 24.

In the following description, an example in which the central axis of the cyclotron 100 (that is, the central axis of the superconducting magnet device 10) C is arranged in a posture extending in the vertical direction (horizontal posture) will be described. Expressions such as "top", "bottom", "left", and "right" are sometimes used to describe the positional relationship between the components, unless the cyclotron 100 is placed in a specific position. It doesn't mean that it doesn't become. The cyclotron 100 may be arranged, for example, in a posture in which the central axis C extends in the horizontal direction (vertical posture).

The superconducting coil 12 has an annular shape and is arranged in the cryostat 14 so that its central axis coincides with the central axis C. The superconducting coil 12 has two air-core coils and a metal coil support frame 13. The two air-core coils are juxtaposed in the direction of the central axis C, and are attached to the coil support frame 13 and integrally supported. The coil support frame 13 includes an upper flange attached to the upper part of the upper air core coil, a central flange sandwiched between the two air core coils, and a lower flange attached to the lower part of the lower air core coil. Has. Further, the superconducting coil 12 is supported by the cryostat 14 by a pair of supports 26. The pair of supports 26 are arranged vertically so as to sandwich the superconducting coil 12, and are attached to the upper flange and the lower flange of the coil support frame 13, respectively.

The cryostat 14 is a vacuum vessel that provides an environment for putting the superconducting coil 12 into a superconducting state. The cryostat 14 has a hollow annular shape, is arranged coaxially with the central axis C, and houses the superconducting coil 12 inside.

The yoke 102 is a hollow disk-shaped block in which the cryostat 14 is arranged. The position of the cryostat 14 in the yoke 102 is maintained by the block body 102a inserted so as to close the hole in which the cryostat 14 is arranged. Further, the pair of poles 104 are arranged at the air core portion of the cryostat 14 (the air core portion of the superconducting coil 12). In this way, the superconducting coil 12 and the pole 104 form a superconducting electromagnet with an iron core. A pair of dee electrodes (acceleration electrodes) (not shown) are arranged in the space G between the pair of poles 104.

The cryogenic refrigerator 16 is installed in the cryostat 14 and is thermally coupled to the superconducting coil 12 so as to cool the superconducting coil 12 by conduction cooling. For example, the low temperature portion of the cryogenic refrigerator 16 is directly attached to the coil support frame 13 (for example, the lower flange) or connected via an appropriate heat transfer member, and the cryogenic refrigerator 16 is a superconducting coil 12 Cools directly. When the cryogenic refrigerator 16 is a two-stage cryogenic refrigerator, the superconducting coil 12 can be cooled by the low temperature portion of the second stage. In the superconducting magnet device 10, a cryogenic refrigerant such as liquid helium is not used for cooling the superconducting coil 12. A plurality of cryogenic refrigerators 16 are typically installed in the cryostat 14, but only one is shown in the figure for the sake of simplicity.

The cryogenic refrigerator 16 includes a compressor for working gas (for example, helium gas) (not shown) and an expander also called a cold head, and the compressor and the expander constitute a refrigeration cycle of the cryogenic refrigerator 16. This cools the cold part to the desired cryogenic temperature. The cryogenic refrigerator 16 is, for example, a single-stage or two-stage Gifford-McMahon (GM) refrigerator, but is a pulse tube refrigerator, a Stirling refrigerator, or another type of cryogenic refrigerator. It may be a refrigerator.

The exciting power supply 18 is connected to the superconducting coil 12 via the current introduction line 19 and is configured to supply the exciting current to the superconducting coil 12. The exciting power supply 18 is communicably connected to the control unit 24, and the exciting current can be adjusted under the control of the control unit 24. For example, the exciting power supply 18 increases the exciting current from zero to the rated current value of the superconducting coil 12 at a predetermined current increasing rate (for example, a constant current increasing rate) when the superconducting magnet device 10 is started. Further, the exciting power supply 18 predetermined the exciting current of the superconducting coil 12 from the rated current value to zero when the operation of the superconducting magnet device 10 is stopped (for example, an emergency stop when an abnormality such as a superconducting quench occurs). The current is reduced at a current reduction rate (for example, a constant current reduction rate).

As will be described later, the exciting power supply 18 is located at, for example, the temperature of the superconducting coil 12 or a portion cooled together with the superconducting coil 12 by the cryogenic refrigerator 16 (for example, a current introduction line 19 or a portion to be cooled in the cryostat 14). It is configured to adjust the exciting current of the superconducting coil 12 to the target current value based on the temperature. The target current value may be greater than zero and less than the rated current value. The predetermined current increase rate described above may be used to increase the exciting current from the current current value to the target current value. The predetermined current reduction rate described above may be used to reduce the exciting current from the current current value to the target current value.

The current introduction line 19 has a superconducting current lead made of a superconducting material and other conductive members such as copper. When the cryogenic refrigerator 16 is a two-stage cryogenic refrigerator, the current introduction line 19 can be cooled by the low temperature portion of the first stage. Alternatively, the current introduction line 19 may be cooled by a cryogenic refrigerator different from the cryogenic refrigerator 16 that cools the superconducting coil 12.

The vacuum exhaust system 20 is configured to evacuate the cryostat 14. The vacuum exhaust system 20 has a vacuum pump 20a, a vacuum valve 20b, and a vacuum gauge 20c, and is connected to the connection port 21 of the cryostat 14. The vacuum pump 20a may be, for example, a turbo molecular pump, a rotary pump, or any other suitable vacuum pump, or a combination thereof. The vacuum valve 20b may be, for example, an on / off valve, and the vacuum exhaust system 20 can evacuate the cryostat 14 when both the vacuum pump 20a and the vacuum valve 20b are on. The connection port 21 may have a vacuum valve different from the vacuum valve 20b. During operation of the superconducting magnet device 10, the vacuum valve at the connection port 21 may be closed, thereby maintaining the vacuum inside the cryostat 14.

The vacuum gauge 20c is configured to measure the pressure of the vacuum exhaust system 20. The vacuum gauge 20c can be installed in, for example, a vacuum exhaust flow path or a vacuum pipe connecting the vacuum pump 20a to the vacuum valve 20b and can measure the pressure thereof. However, the vacuum gauge 20c may be installed, for example, in the vacuum exhaust flow path or the vacuum pipe connecting the vacuum valve 20b to the connection port 21, or in another place of the vacuum exhaust system 20. Alternatively, the vacuum gauge 20c may be installed inside the cryostat 14 to measure the pressure inside the cryostat 14. When required, the pressure gauge 20c generates a measurement signal indicating the measurement pressure (for example, the pressure of the vacuum exhaust system 20 or the pressure in the cryostat 14), and outputs the measurement signal to the control unit 24. You may.

The temperature sensor 22 measures and measures the temperature of the superconducting coil 12 or the temperature of a portion cooled together with the superconducting coil 12 by the cryogenic refrigerator 16 (for example, a current introduction line 19 or a portion to be cooled in the cryostat 14). It is configured to output the measurement signal S1 indicating the temperature. The temperature sensor 22 is communicably connected to the control unit 24 so as to output the measurement signal S1 to the control unit 24.

The temperature sensor 22 may be attached to the surface of the superconducting coil 12 or embedded inside the superconducting coil 12. For example, the temperature sensor 22 is attached to the surface of the coil support frame 13 as shown in FIG. Alternatively, the temperature sensor 22 may be attached to the current introduction line 19.

The temperature sensor 22 may be installed in various places as long as it is cooled by the cryogenic refrigerator 16. For example, the temperature sensor 22 may be installed in a low temperature portion of the cryogenic refrigerator 16 or a heat transfer member that connects the low temperature portion to the superconducting coil 12. The temperature sensor 22 may be installed in a portion of the superconducting coil 12 far from the low temperature portion (or heat transfer member) of the cryogenic refrigerator 16. The temperature sensor 22 may be installed on the inner peripheral portion of the superconducting coil 12. The temperature sensor 22 may be installed on the cryostat 14, or may be attached, for example, to the heat shield plate of the cryostat 14 surrounding the superconducting coil 12. The superconducting magnet device 10 may be provided with a plurality of temperature sensors 22.

Although the details will be described later, the control unit 24 receives the measurement signal S1 from the temperature sensor 22, compares the measurement temperature with the temperature threshold, and when the measurement temperature exceeds the temperature threshold, the exciting current reaches the target current value. It is configured to control the exciting power supply 18 so as to adjust the temperature. The control unit 24 generates a power supply control signal S2 based on the measurement signal S1 and outputs the power supply control signal S2 to the exciting power supply 18.

The control unit 24 may be configured to monitor the state of the exciting power supply 18. The exciting power supply 18 may generate a power supply status signal S3 and output the power supply status signal S3 to the control unit 24. The power supply status signal S3 may indicate the voltage and / or current of the exciting power supply 18.

The control unit 24 may be configured to receive the input signal S4 and control the superconducting magnet device 10 (and the cyclotron 100) based on the input signal S4. The input signal S4 is generated by the user operating an input means such as a mouse or a keyboard for receiving an input from the user, and / or is generated by another device communicably connected to the control unit 24. Can be done.

For example, the input signal S4 may be a control signal instructing the emergency degaussing of the superconducting magnet device 10. When the quenching of the superconducting coil 12 occurs, the control unit 24 may control the exciting power supply 18 so as to forcibly cut off the current to the superconducting coil 12 in response to this signal. Alternatively, the input signal S4 may be a control signal instructing the restart of the superconducting magnet device 10. When the operation of the superconducting magnet device 10 is stopped due to some abnormality, the input signal S4 may be input to the control unit 24 based on, for example, a user's operation when the cause is resolved. The control unit 24 may start restarting the superconducting magnet device 10 in response to the input signal S4.

Further, the control unit 24 is configured to store data related to the control of the superconducting magnet device 10 (and the cyclotron 100), and may include, for example, a semiconductor memory or other data storage medium.

The control unit 24 is realized by elements and circuits such as a computer CPU and memory as a hardware configuration, and is realized by a computer program or the like as a software configuration, but is appropriately realized by cooperation thereof in the figure. It is drawn as a functional block. Those skilled in the art will understand that these functional blocks can be realized in various ways by combining hardware and software.

In the superconducting magnet device 10, the superconducting coil 12 in the cryostat 14 in a vacuum state is cooled by the ultra-low temperature refrigerator 16, and a strong magnetic field is formed by passing a current through the superconducting coil 12 from the exciting power supply 18. .. Charged particles are supplied to the cyclotron 100 from an ion source (not shown), and the charged particles are accelerated by the action of a pair of poles 104 and a dee electrode (not shown). As a result, a charged particle beam is output from the cyclotron 100.

FIG. 2 is a graph showing an example of the current inductance characteristics of the superconducting coil 12 according to the embodiment. The horizontal axis shows the current flowing through the superconducting coil 12, and the vertical axis shows the inductance of the superconducting coil 12. The current on the horizontal axis is shown logarithmically.

In the case of the superconducting coil 12 with an iron core, the inductance of the superconducting coil 12 is large when the exciting current is small and the iron core is not magnetically saturated, and when the exciting current increases and the iron core is magnetically saturated, the inductance greatly decreases. The inductance of the superconducting coil 12 when the iron core is magnetically saturated is about the same as that of the air core coil. In the example shown in FIG. 2, the inductance reaches about 800H (Henry) in the small current region of less than 10A, but the inductance drops to less than about 100H in the large current region of more than 10A.

In the following, for convenience of explanation, a large current region in which the inductance decreases due to magnetic saturation of the iron core is referred to as a “first current region”, and a transient intermediate current region in which the inductance rapidly increases as the current decreases is referred to as a “second current region”. The small current region in which the inductance is large due to the fact that the current is further reduced and the iron core is not magnetically saturated is referred to as the "third current region". FIG. 2 shows a first current region 31, a second current region 32, and a third current region 33. In the first current region 31, the inductance gradually increases or is substantially constant as the exciting current decreases. Even in the third current region 33, the inductance gradually increases or is substantially constant as the exciting current decreases. However, as described above, since the inductance rapidly increases as the exciting current decreases in the second current region 32, the inductance in the third current region 33 is considerably larger than that in the first current region 31.

Here, consider the voltage required for the exciting power supply 18. The voltage is determined by the product of the time change rate of the current flowing through the superconducting coil 12 and the inductance of the superconducting coil 12. When the superconducting coil 12 is normally operated at the rated current, the current value is large, reaching at least several hundred amperes, for example (first current region 31). In a steady operation situation, the current value can be kept constant. Alternatively, even if the current value fluctuates, the fluctuation range is small (in normal operation of the superconducting coil 12, it is not necessary to significantly reduce the current value so as to deviate from the first current region 31). Since the time change rate of the current of the superconducting coil 12 is small and the inductance is small in the large current region as described above, it is sufficient for the exciting power supply 18 to be able to output a relatively low voltage.

On the other hand, when the current of the superconducting coil 12 is forcibly cut off, the current is rapidly reduced from a large current to zero. The exciting power supply 18 is required to have a high voltage corresponding to the current reduction rate. In particular, when the current decreases to a small current region near 0 A, the inductance also increases rapidly as shown in FIG. 2 (second current region 32, third current region 33), so that the exciting power supply 18 is considerably used. High voltage will be required. Since the exciting power supply 18 to which a high voltage is applied is more expensive than the one having a low voltage, if the high voltage exciting power supply 18 is adopted, the manufacturing cost of the superconducting magnet device 10 increases.

Therefore, from the viewpoint of reducing the manufacturing cost, it is desired to adopt a low-voltage exciting power supply 18 suitable for the first current region 31. It is possible to design such a low voltage exciting power supply 18 so as not to cause any inconvenience during steady operation in which the superconducting coil 12 is stably excited.

However, when the current is dropped from the first current region 31 to the third current region 33, the voltage of the exciting power supply 18 may be insufficient. In particular, considering the rapid increase in inductance that occurs at this time, the required voltage may exceed the maximum voltage of the exciting power supply 18 unless the current of the superconducting coil 12 is reduced extremely slowly. To avoid this, if the current reduction rate is made sufficiently small, the time required for degaussing may become longer than the permissible range. Similarly, when exciting the superconducting coil 12 for recovery from emergency degaussing or for starting normal operation of the superconducting magnet device 10, if the rate of increase of the exciting current is small, it takes a long time, which is desirable. Absent.

By the way, for some reason, local heat generation may occur in the superconducting coil 12 and the temperature may rise, which may eventually progress to superconducting quenching if left unattended. Therefore, when a cooling failure of the superconducting coil 12 is detected, the superconducting coil 12 is typically forcibly degaussed immediately. However, when a low-voltage exciting power supply 18 is adopted, as described above, the current reduction rate of the superconducting coil 12 is limited, and it is difficult to degauss the superconducting coil 12 in a short time. Further, when the superconducting coil 12 is excited again, the current increase rate is small and it takes time to complete the excitation. In some cases, it may take, for example, a day or more.

In addition, the cooling of the superconducting coil 12 is weakened by a factor other than heat generation that can be directly linked to quenching, for example, some fluctuation in the operation of the cryogenic refrigerator 16, an increase in heat input from the outside, or other circumstances. Some temperature rise may be seen in the superconducting coil 12. Such an increase in temperature can occur occasionally in the long-term operation of the superconducting magnet device 10, but in most cases it can be a temporary phenomenon. After a while, the temperature rise may disappear naturally and return to the original normal state. That is, the superconducting coil 12 does not need to be forcibly degaussed. If the superconducting coil 12 is degaussed in such a case, as a result, it merely interferes with the operation of the superconducting magnet device 10, which is not desired.

Therefore, the superconducting magnet device 10 according to the embodiment is equipped with three control modes: a normal mode, a forced degaussing mode, and a temporary standby mode. The normal mode is used while the superconducting coil 12 is normally cooled and stably excited by the cryogenic refrigerator 16, and the superconducting coil 12 has an exciting current of a rated current value or a magnitude close to the rated current value. Is supplied. The forced degaussing mode is used when a cooling failure of the superconducting coil 12 is detected, and the current of the superconducting coil 12 is immediately forcibly cut off. The temporary standby mode is used when the superconducting coil 12 is in the temperature range between the normal mode and the forced degaussing mode, and the superconducting coil 12 has a relatively small current value adjusted to maintain the magnetic saturation of the iron core. The supply of exciting current is continued at.

FIG. 3 is a flowchart illustrating a control method of the superconducting magnet device according to the embodiment. This method is performed in normal mode. Therefore, when this method is started, the superconducting coil 12 is cooled to an extremely low temperature by the cryogenic refrigerator 16 and excited to the rated current by the exciting power supply 18, and a high magnetic field is normally generated. As an example, the superconducting coil 12 is cooled to a normal cooling temperature of 4K or less (for example, 3K to 4K), and a current of, for example, 400A to 500A is flowing through the superconducting coil 12.

First, the temperature of the superconducting coil 12 is measured (S10). The temperature sensor 22 measures the temperature of the installation location, generates a measurement signal S1 indicating the measured temperature, and outputs the measurement signal S1 to the control unit 24. The control unit 24 acquires the measurement signal S1. As described above, the temperature sensor 22 may be installed at various locations on the superconducting coil 12, or on the cryostat 14 which is cooled together with the superconducting coil 12 by the cryogenic refrigerator 16 such as the current introduction line 19. When a plurality of temperature sensors 22 are provided, the control unit 24 can receive the measurement signal S1 from each temperature sensor 22 and grasp the measured temperature of the plurality of cooled parts.

The control unit 24 compares the measured temperature with the allowable upper limit temperature value (S12). The allowable upper limit temperature value is a preset temperature value as a reference temperature for degaussing the superconducting coil 12, and may be selected from, for example, a temperature range of 7K to 10K. When the measured temperature exceeds this temperature value, it is determined that the operation of the superconducting magnet device 10 should be stopped, for example, a superconducting quench is predicted.

When the measurement temperature exceeds the allowable upper limit temperature value (Y in S12), the control unit 24 controls the exciting power supply 18 so as to cut off the exciting current of the superconducting coil 12 (S20). That is, it is considered that the cooling failure of the superconducting coil 12 is detected, and the control mode is switched from the normal mode to the forced degaussing mode. The control unit 24 generates a power supply control signal S2 instructing to reduce the exciting current of the superconducting coil 12 from the current current value (for example, the rated current value) to zero, and outputs the power supply control signal S2 to the exciting power supply 18. To do. In this way, the superconducting coil 12 is forcibly degaussed, and this process is completed.

On the other hand, when the measurement temperature does not exceed the allowable upper limit temperature value (N in S12), the control unit 24 compares the measurement temperature with the temperature threshold value (S14). This temperature threshold is set to a temperature higher than the normal cooling temperature of the superconducting coil 12. Further, the temperature threshold value is set to a temperature lower than the allowable upper limit temperature value. The temperature threshold may be selected from, for example, a temperature range of 5K to 8K.

When the measurement temperature exceeds the temperature threshold value (Y in S14), the control unit 24 controls the exciting power supply 18 so as to adjust the exciting current to the target current value (S30). That is, the control mode is switched from the normal mode to the temporary standby mode. The control unit 24 generates a power supply control signal S2 instructing that the exciting current of the superconducting coil 12 is reduced from the current current value (for example, the rated current value) to the target current value, and the power supply control signal S2 is used as the exciting power supply 18 Output to.

As shown in FIG. 2, the target current value I ₀ is smaller than the rated current value I _{max of the superconducting coil 12.} The target current value I ₀ is selected from the first current region 31. The lower limit of the first current region 31 may be regarded as a current value in which the inductance is, for example, twice or 1.5 times the inductance at the _{rated current value I max in the current inductance characteristic.} Although it depends on the shape of the curve showing the current inductance characteristic, the lower limit value of the first current region 31 may be, for example, 10A. Therefore, the target current value I ₀ may be, for example, at least 10A. The rated current value I _max may be, for example, greater than 100 A or greater than 500 A. The rated current value I _max may be, for example, less than 10 kA or less than 1 kA. As described above, the rated current value I _max may be in the range of, for example, 400A to 500A.

Therefore, even if the exciting current of the superconducting coil 12 _{is lowered from the rated current value I max} to the target current value I ₀ , the magnetic saturation of the iron core of the superconducting coil 12 is maintained, and the inductance of the superconducting coil 12 is maintained. It remains small. Therefore, even with the low-voltage exciting power supply 18, it is possible to quickly reduce the exciting current _{from the rated current value I max} to the target current value I _0. In this way, in the temporary standby mode, the superconducting coil 12 is continuously supplied with the exciting current at a relatively small current value adjusted to maintain the magnetic saturation of the iron core. This process ends.

On the other hand, when the measurement temperature does not exceed the temperature threshold value (N in S14), the superconducting coil 12 is evaluated to be normally cooled, so that the normal mode is continued as it is. In this case, after this process is completed once, it may be executed again at the next timing to monitor the measurement temperature (S10 to S14) and switch the control mode (S20, S30).

FIG. 4 is a flowchart illustrating a control method of the superconducting magnet device according to the embodiment. This method is performed in temporary standby mode. Therefore, the method shown in FIG. 3 has already been executed before the method is started. The exciting current of the superconducting coil 12 has changed to the target current value or matches the target current value under the control of the control unit 24.

Similar to the control method shown in FIG. 3, the temperature of the superconducting coil 12 is monitored. That is, the temperature of the superconducting coil 12 or other parts to be cooled is measured (S10), and the measured temperature is compared with the allowable upper limit temperature value (S12). When the measurement temperature exceeds the allowable upper limit temperature value (Y in S12), the control unit 24 controls the exciting power supply 18 so as to cut off the exciting current of the superconducting coil 12 (S20). That is, the control mode is switched from the temporary standby mode to the forced degaussing mode. In this way, the superconducting coil 12 is forcibly degaussed, and this process is completed.

When the measured temperature does not exceed the permissible upper limit temperature value (N in S12), the measured temperature is compared with the temperature threshold (S14). When the measurement temperature does not exceed the temperature threshold value (N in S14), the control unit 24 controls the exciting power supply 18 so as to return the exciting current of the superconducting coil 12 toward the rated current value (S40). That is, the control mode is switched from the temporary standby mode to the normal mode. The control unit 24 generates a power supply control signal S2 instructing to increase the exciting current of the superconducting coil 12 from the current current value (for example, the target current value) to the rated current value, and the power supply control signal S2 is used as the exciting power supply 18 Output to. The superconducting coil 12 is excited again to the rated current value.

In this way, when the measured temperature drops toward the normal cooling temperature in the temporary standby mode, the temporary standby mode can be released and the normal mode can be restored. This process ends in this way. Even if some temperature rise is observed in the superconducting coil 12, the operation of the superconducting magnet device 10 can be continued without immediately forcibly degaussing the superconducting coil 12.

When the measurement temperature exceeds the temperature threshold value (Y in S14), the temperature rise of the superconducting coil 12 has not been resolved yet, so that the temporary standby mode is continued as it is. In this case, after this process is completed once, it may be executed again at the next timing to monitor the measurement temperature (S10 to S14) and switch the control mode (S20, S40).

A plurality of temperature threshold values and a plurality of target current values may be set in advance, and an appropriate target current value may be selected according to the measurement temperature. The control unit 24 includes a coil current setting having a plurality of temperature thresholds determined in stages and a plurality of target current values determined in stages corresponding to the plurality of temperature thresholds. May be good. The control unit 24 selects one of a plurality of target current values according to the measurement temperature based on the coil current setting, and controls the exciting power supply so as to adjust the exciting current to the selected target current value. You may. The control unit 24 generates a power supply control signal S2 instructing to increase or decrease the exciting current of the superconducting coil 12 from the current target current value to the newly selected target current value, and excites the power supply control signal S2. It may be output to the power source 18.

As an example, the control unit 24 adjusts the exciting current to the rated current value (for example, 500A) when the measurement temperature is at the normal cooling temperature or is equal to or less than the first temperature threshold (for example, 5.5K), and measures the measurement. When the temperature exceeds the first temperature threshold and is equal to or less than the second temperature threshold (for example, 6.5K), the exciting current is adjusted to the first target current value (for example, 200A), and the measurement temperature becomes the second temperature. When the threshold value is exceeded and the temperature is below the third temperature threshold (for example, 7.5K), the exciting current is adjusted to the second target current value (for example, 50A), and the measured temperature exceeds the third temperature threshold and is the allowable upper limit. The exciting power supply 18 may be controlled so as to adjust the exciting current to the third target current value (for example, 20A) when the temperature value (for example, 8K) or less.

As described above, in the superconducting magnet device 10 according to the embodiment, the control unit 24 receives the measurement signal S1 from the temperature sensor 22, compares the measurement temperature with the temperature threshold value, and the measurement temperature is heated. If it exceeds the threshold value, the exciting power supply 18 is controlled so as to adjust the exciting current to a target current value smaller than the rated current value. In this way, the possibility of forced current interruption of the superconducting coil 12 can be reduced, and the operation continuity of the superconducting magnet device 10 can be improved.

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 embodiment, various design changes are possible, various modifications are possible, and such modifications are also within the scope of the present invention. By the way. The various features described in relation to one embodiment are also applicable to other embodiments. The new embodiments resulting from the combination have the effects of each of the combined embodiments.

In the above embodiment, the exciting current is adjusted based on the measured temperature, but the exciting current may be adjusted based on other measured values, for example, the measured vacuum degree. The degree of vacuum may be measured by, for example, the above-mentioned pressure gauge 20c. In this case, in the above description, "measurement temperature" and "temperature threshold value" may be read as "measurement vacuum degree" and "vacuum degree threshold value", respectively. For example, the control unit 24 compares the measured vacuum degree with the vacuum degree threshold value, and when the measured vacuum degree exceeds the temperature threshold value, excites the exciting current so as to adjust the exciting current to a target current value smaller than the rated current value. The power supply 18 may be controlled.

Although the present invention has been described using specific terms and phrases based on the embodiments, the embodiments show only one aspect of the principles and applications of the present invention, and the embodiments are claimed. Many modifications and arrangement changes are permitted within the range not departing from the idea of the present invention defined in the scope.

10 Superconducting magnet device, 12 Superconducting coil, 16 Cryogenic refrigerator, 18 Excitation power supply, 22 Temperature sensor, 24 Control unit, 31 First current region, 32 Second current region.

Claims (5)

With superconducting coil
A cryogenic refrigerator that cools the superconducting coil,
An exciting power supply that supplies an exciting current to the superconducting coil,
A temperature sensor that measures the temperature of the superconducting coil or the temperature of the part cooled together with the superconducting coil by the cryogenic refrigerator and outputs a measurement signal indicating the measured temperature.
The measurement signal is received from the temperature sensor, the measurement temperature is compared with the temperature threshold value, and when the measurement temperature exceeds the temperature threshold value, the excitation current is adjusted to a target current value smaller than the rated current value. A superconducting magnet device including a control unit that controls the exciting power supply so as to perform the above. In the first current region including the rated current value, the inductance of the superconducting coil gradually increases or is substantially constant as the exciting current decreases, and in the second current region smaller than the first current region, the inductance is described. It has a current inductance characteristic in which the inductance increases rapidly as the exciting current decreases.
The superconducting magnet device according to claim 1, wherein the target current value is selected from the first current region. When the exciting current changes to the target current value or matches the target current value, the control unit compares the measured temperature again with the temperature threshold value, and the measured temperature becomes the measured temperature. The superconducting magnet device according to claim 1 or 2, wherein when the temperature is lower than the temperature threshold value, the exciting power source is controlled so as to restore the exciting current toward the rated current value. The temperature threshold is set to a temperature lower than the allowable upper limit temperature value.
The control unit compares the measured temperature with the allowable upper limit temperature value, and controls the exciting power supply so as to cut off the exciting current when the measured temperature exceeds the allowable upper limit temperature value. The superconducting magnet device according to any one of claims 1 to 3. To measure the temperature of the superconducting coil or the temperature of the part cooled together with the superconducting coil by the cryogenic refrigerator,
Comparing the measured temperature with the temperature threshold
A superconducting magnet control method comprising: adjusting the exciting current of the superconducting coil to a target current value smaller than the rated current value when the measured temperature exceeds the temperature threshold value.

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