Permanent current switch device and magnetic resonance imaging device

Abstract

To further improve the reliability of a superconducting magnet.SOLUTION: A persistent current switch device electrically connected to a superconducting coil via a superconducting wire includes a plurality of parallel structures in which thermal persistent current switches that can switch between conduction and interruption of the current flowing through the superconducting wire are connected in parallel. Also, the parallel structures are connected in series.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to a persistent current switch device and a magnetic resonance imaging device.

Background Art

[0002] In recent years, in a magnetic resonance imaging device, as a static magnetic field magnet that generates a static magnetic field in an imaging region where a subject is placed, a superconducting magnet, which is an electromagnet using a superconductor, is mounted. This superconducting magnet is generally manufactured by arranging a superconductor coil (hereinafter referred to as a "superconducting coil") in a refrigerant container filled with liquid helium as a refrigerant.

[0003] When the superconducting coil transitions to the superconducting state by being cooled with liquid helium, its electrical resistance becomes zero, and as a result, a large current can flow through it. Therefore, a superconducting magnet can generate a stronger magnetic field than an ordinary electromagnet.

[0004] However, in a superconducting magnet, a part of the superconducting coil may return from the superconducting state to the normal conducting state due to external or internal factors. Such an event where a part of the superconducting coil returns from the superconducting state to the normal conducting state is called a "quench".

[0005] By the way, the static magnetic field magnet includes a persistent current switch (hereinafter also referred to as PCS (Persistent Current Switch)) that switches between the normal conduction and superconductivity of a superconducting wire. When a quench occurs in this PCS, the superconducting coil cannot maintain the persistent current mode. Therefore, conventionally, even when a quench occurs in the PCS, in order to maintain the persistent current mode, a group of PCSs in one stage in which a plurality of PCSs are connected in series is connected in parallel in a plurality of stages.

[0006] However, with conventional technology, if one PCS in each stage quenched, it was possible that the persistent current mode could not be maintained. In other words, there is room for improvement in the reliability of the superconducting magnets. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Unexamined Patent Publication No. 63-299214 [Overview of the project] [Problems that the invention aims to solve]

[0008] One of the problems that the embodiments disclosed in this specification and drawings aim to solve is to further improve the reliability of superconducting magnets. However, the problems that the embodiments disclosed in this specification and drawings aim to solve are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0009] The perpetual current switch device according to this embodiment is a perpetual current switch device electrically connected to a superconducting coil via a superconducting wire, and comprises a plurality of parallel configurations in which thermal perpetual current switches capable of switching between conducting and interrupting the current flowing through the superconducting wire are connected in parallel. Furthermore, the parallel configurations are connected in series. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a configuration diagram showing the configuration of an MRI apparatus according to an embodiment. [Figure 2] Figure 2 is a block diagram showing an example of the configuration of a static magnetic field magnet according to the embodiment. [Figure 3] Figure 3 is a schematic diagram showing an example of the configuration of the PCS according to the embodiment. [Figure 4]Figure 4 is a schematic diagram showing an example of current change when a quench occurs in one of the thermal persistent current switches of the PCS according to the embodiment. [Figure 5] Figure 5 is a schematic diagram showing an example of current change when a quench occurs in two of the thermal persistent current switches of the PCS according to the embodiment. [Figure 6] Figure 6 is a schematic diagram showing an example of a case where a break occurs in the heater connection wire of the PCS according to the embodiment. [Figure 7] Figure 7 is a schematic diagram showing the configuration of a PCS other than the PCS according to the embodiment. [Figure 8] Figure 8 is a schematic diagram showing the current change when a quench occurs in one of the thermal persistent current switches of a PCS other than the PCS according to the embodiment. [Figure 9] Figure 9 is a schematic diagram showing the current change when a quench occurs in two thermal persistent current switches of a PCS other than the PCS according to the embodiment. [Figure 10] Figure 10 is a schematic diagram showing a case where a break occurs in the heater connection wire of a PCS other than the PCS according to the embodiment. [Modes for carrying out the invention]

[0011] Embodiments of a persistent current switch and a magnetic resonance imaging apparatus will be described in detail below with reference to the drawings. In the embodiments described below, the case in which the persistent current switch is applied to the static magnetic field magnet of a magnetic resonance imaging apparatus will be described, but the present invention is not limited to this embodiment. Furthermore, in the following, the magnetic resonance imaging apparatus will also be referred to as an "MRI (Magnetic Resonance Imaging) apparatus."

[0012] First, the configuration of the MRI apparatus 100 according to this embodiment will be described. FIG. 1 is a configuration diagram showing the configuration of the MRI apparatus 100 according to this embodiment. As shown in FIG. 1, the MRI apparatus 100 includes a static magnetic field magnet 10, a gradient magnetic field coil 20, an RF coil 30, a top plate 40, a gradient magnetic field power supply 50, a transmitter 60, a receiver 70, a sequence control device 80, and a computer system 90.

[0013] The static magnetic field magnet 10 generates a static magnetic field in the imaging region where the subject is placed. The static magnetic field magnet 10 is an example of a superconducting magnet. The static magnetic field magnet 10 includes a vacuum vessel 11, a refrigerant vessel 12, and a superconducting coil 13.

[0014] The vacuum vessel 11 is formed in a substantially cylindrical shape, and the inside of the cylinder wall is kept in a vacuum state. The space formed inside the cylinder of the vacuum vessel 11 becomes the imaging region where the subject is placed. The refrigerant vessel 12 is formed in a substantially cylindrical shape and is housed inside the vacuum vessel 11. The refrigerant vessel 12 stores a refrigerant such as liquid helium inside the cylinder wall. The superconducting coil 13 is disposed inside the refrigerant vessel 12 and is immersed in liquid helium. Then, the superconducting coil 13 generates a static magnetic field in the imaging region inside the cylinder of the vacuum vessel 11.

[0015] The gradient magnetic field coil 20 is formed in a substantially cylindrical shape and is fixed inside the static magnetic field magnet 10. The gradient magnetic field coil 20 generates a gradient magnetic field in the directions of the X-axis, Y-axis, and Z-axis set in the imaging region by the current supplied from the gradient magnetic field power supply 50.

[0016] The RF coil 30 is fixed inside the gradient magnetic field coil 20 so as to face each other with the subject P interposed therebetween. The RF coil 30 irradiates the subject P with an RF pulse transmitted from the transmitter 60, and also receives a magnetic resonance signal emitted from the subject P due to the excitation of hydrogen nuclei.

[0017] The top plate 40 is provided so as to be horizontally movable on a bed (not shown), and the subject P is placed thereon and moved into the imaging region during imaging. The gradient magnetic field power supply 50 supplies current to the gradient magnetic field coil 20 based on an instruction from the sequence control device 80.

[0018] The transmission unit 60 transmits an RF pulse to the RF coil 30 based on an instruction from the sequence control device 80. The reception unit 70 detects the magnetic resonance signal received by the RF coil 30, digitizes the detected magnetic resonance signal, and transmits the resulting raw data to the sequence control device 80.

[0019] The sequence control device 80 scans the subject P by driving the gradient magnetic field power supply 50, the transmission unit 60, and the reception unit 70 under the control of the computer system 90. Then, when raw data is transmitted from the reception unit 70 as a result of the scan, the sequence control device 80 transmits the raw data to the computer system 90.

[0020] The computer system 90 controls the entire MRI apparatus 100. Specifically, this computer system 90 includes an input unit that receives various inputs from an operator, a sequence control unit that causes the sequence control device 80 to execute a scan based on imaging conditions input by the operator, an image reconstruction unit that reconstructs an image based on the raw data transmitted from the sequence control device 80, a storage unit that stores the reconstructed image and the like, a display unit that displays various information such as reconstructed images, and a main control unit that controls the operations of each functional unit based on an instruction from the operator.

[0021] Here, the configuration of the static magnetic field magnet 10 will be described with reference to FIG. 2. FIG. 2 is a block diagram showing an example of the configuration of the static magnetic field magnet 10 according to the present embodiment. As shown in FIG. 2, the static magnetic field magnet 10 includes a vacuum vessel 11, a refrigerant vessel 12, a superconducting coil 13, a protection circuit 14, a current lead 15, a PCS 16, and a magnet excitation / demagnetization power supply 17.

[0022] The protection circuit 14 protects the superconducting coil 13 by consuming the current flowing through it when a quench occurs in the superconducting coil 13. This protection circuit 14 is, for example, a protective resistor element or a diode bank. The protection circuit 14 is installed in a room temperature environment outside the refrigerant container 12.

[0023] In this embodiment, when the superconducting coil 13 is energized, the magnet excitation / demagnetization power supply 17 is disconnected from the current lead 15. When the superconducting coil 13 is demagnetized, the magnet excitation / demagnetization power supply 17 is reconnected to the current lead 15.

[0024] The current lead 15 supplies current from the magnet excitation / demagnetization power supply 17, which is at room temperature (hereinafter also referred to as the ambient temperature environment), to the superconducting coil 13, which is cooled by a refrigerant such as liquid helium (hereinafter also referred to as the low-temperature environment). The current lead 15 also connects the superconducting coil 13 to the protection circuit 14. The current lead 15 is made of high-temperature superconductor. As a result, the conductivity of the current lead 15 is low at ambient temperature and high at low temperatures.

[0025] Therefore, during normal operation, the current lead 15 is less likely to conduct heat, thus reducing the amount of heat entering the refrigerant container 12 from the outside. In other words, the current lead 15 can suppress the evaporation of refrigerant caused by heat entering the refrigerant container 12 from the outside.

[0026] On the other hand, if a quench occurs in the superconducting coil 13, the current lead 15 is cooled by the vaporization of the refrigerant in the refrigerant container 12 and becomes superconducting. Therefore, when a quench occurs, current automatically flows from the superconducting coil 13 to the protection circuit 14 via the current lead 15, thus reliably protecting the protection circuit 14. In other words, the current lead 15 can act as a switch that allows current to flow from the superconducting coil 13 to the protection circuit 14 when a quench occurs.

[0027] PCS16 is an example of a persistent current switch device. PCS16 in this embodiment is a persistent current switch device having a superconducting wire 163 including a switch section 161 (described later) and a thermal persistent current switch 160 (see Figure 3). The switch section 161 is a part of the superconducting wire 163 that acts as a switch to switch between the superconducting state and the normal conducting state of the superconducting wire 163 by heat generated by a heater. PCS16 turns on when the switch section 161 is in the superconducting state and turns off when the switch section 161 is in the normal conducting state. PCS16 is connected in parallel with the superconducting coil 13.

[0028] Here, when PCS16 is turned on, for example, when the magnet excitation / demagnetization power supply 17 is disconnected, the superconducting coil 13 and PCS16 form a closed loop. Also, when PCS16 is turned off, for example, it becomes possible to supply current from the magnet excitation / demagnetization power supply 17 to the superconducting coil 13.

[0029] In this embodiment, when the PCS16 is turned on, the state of the magnet excitation / demagnetization power supply 17 is such that the magnet excitation / demagnetization power supply 17 is disconnected. However, the state of the magnet excitation / demagnetization power supply 17 is not limited to this. For example, the state of the magnet excitation / demagnetization power supply 17 may be such that the output is close to zero. In short, the state of the magnet excitation / demagnetization power supply 17 is such that the superconducting coil 13 and the PCS16 can form a closed loop.

[0030] Furthermore, PCS16 has a heater 162 (see Figure 3), which will be described later. The heater 162 is connected to an external power source located outside the static magnetic field magnet 10, and controls the on / off state of PCS16 by raising or lowering the temperature of the switch unit 161 when the superconducting coil 13 is excited or demagnetized. The configuration of PCS16 will be described later.

[0031] The magnet excitation / demagnetization power supply 17 is a power source used when the superconducting coil 13 is excited or demagnetized. The magnet excitation / demagnetization power supply 17 is installed in a room temperature environment outside the refrigerant container 12. When the superconducting coil 13 is excited or demagnetized, the magnet excitation / demagnetization power supply 17 is connected to the superconducting coil 13 via the current lead 15.

[0032] Furthermore, when the superconducting coil 13 is energized or demagnetized, the heater 162 generates heat to control the PCS 16, causing the refrigerant in the refrigerant container 12 to evaporate. Since refrigerants are generally expensive, the number of switch units 161 in the PCS 16 is determined considering the amount of refrigerant evaporation.

[0033] Furthermore, at this time, the current lead 15 is cooled by the evaporated coolant, causing the current lead 15 to become superconducting. Therefore, when the superconducting coil 13 is excited or demagnetized, a stable current is supplied to the superconducting coil 13 from the magnet excitation / demagnetization power supply 17 via the current lead 15.

[0034] Here, the configuration of PCS16 will be described in detail with reference to Figures 3 to 10. First, in order to compare it with the configuration of PCS16 of this embodiment shown in Figure 3, the configuration of PCS216, which is different from PCS16, will be described using Figure 7. Here, Figure 7 is a schematic diagram showing the configuration of PCS216, which is different from PCS16 in this embodiment.

[0035] As shown in Figure 7, the PCS216 includes, for example, thermal persistent current switches PC1 to PC8, superconducting wire SU, and heater connection wire HL. In the following description, unless otherwise specified, thermal persistent current switches PC1 to PC8 may simply be referred to as thermal persistent current switch PC.

[0036] Furthermore, the thermal persistent current switch PC1 includes a switch section SW1 and a heater HT1. In the following description, when no particular distinction is made between the switch sections SW1 to SW8, they may simply be referred to as the switch section SW. Similarly, when no particular distinction is made between the heaters HT1 to HT8, they may simply be referred to as the heater HT. The switch section SW is the part that acts as a switch, switching between the superconducting state and the normal conducting state of the switch section SW by the heat generated by the heater HT.

[0037] The thermal persistent current switch PC switches between conducting and interrupting the current flowing through the switch SW. Thermal persistent current switches PC1 to PC4 are connected in series to form a series switch unit IL1. Similarly, thermal persistent current switches PC5 to PC8 form a series switch unit IL2. Series switch units IL1 and IL2 are connected in parallel by a superconducting wire SU.

[0038] The heater HT heats the switch unit SW. The thermal persistent current switch PC adjusts the heating of the heater HT, thereby raising or lowering the temperature of the switch unit SW and switching between the superconducting and normal conducting states of the switch unit SW. The heater HT is connected in series with the external power supply PW via the heater connection wire HL.

[0039] Next, we will explain the current state when a quench occurs in the thermal persistent current switch PC while PCS216 is in a superconducting state. First, we will explain the case when no quench occurs in any of the thermal persistent current switches PC1 to PC8.

[0040] In this case, if the current flowing through PCS216 is Isc, then, as shown in Figure 7, the current Isc is divided between the parallel-connected series switches IL1 and IL2. Therefore, the current flowing through the series switch IL1 is approximately Isc / 2, and the current flowing through the series switch IL2 is approximately Isc / 2. Next, we will explain the case where a quench occurs in any one of the thermal permanent current switches PC1 to PC8.

[0041] Here, in order to compare with the configuration of PCS16 in this embodiment shown in Figure 4, Figure 8 shows the configuration of PCS216, which is separate from PCS16. Figure 8 is a schematic diagram showing the current state when a quench occurs in one of the thermal persistent current switches PC of PCS216, which is separate from PCS16 in this embodiment. Figure 8 shows the case when a quench occurs in the thermal persistent current switch PC2 that constitutes the series switch unit IL1 due to a fault FP1. In this case, the thermal persistent current switch PC2 becomes a resistor R.

[0042] When the thermal persistent current switch PC2 becomes resistor R, as shown in Figure 8, the entire current flowing through PCS216 is commutated to the series switch assembly IL2, which is composed of thermal persistent current switches PC5 to PC8, where no quench is occurring. Therefore, the current flowing to the series switch assembly IL1 becomes 0, and the current flowing to the series switch assembly IL2 becomes Isc.

[0043] This maintains the superconducting state of one of the paths, thus allowing the static magnetic field magnet 10 to operate in persistent current mode. In other words, even if a quench occurs in any one of the thermal persistent current switches PC1 to PC8, the static magnetic field magnet 10 can be maintained in persistent current mode, so in this case, PCS216 can be said to have redundancy.

[0044] Next, we will explain the case where a quench occurs in each of the switch series units IL1 and IL2.

[0045] Here, in order to compare with the configuration of PCS16 of this embodiment shown in Figure 5, the configuration of PCS216, which is different from PCS16, is shown in Figure 9. Figure 9 is a schematic diagram showing the current state when a quench occurs in each of the switch series units IL1 and IL2 of PCS216, which is different from PCS16 in this embodiment. Figure 9 shows a state in which a quench occurs in the thermal persistent current switch PC2 that constitutes the switch series unit IL1 due to fault FP1, and a quench occurs in the thermal persistent current switch PC8 that constitutes the switch series unit IL2 due to fault FP2.

[0046] In this case, thermal persistent current switches PC2 and PC8 become resistors R. When thermal persistent current switches PC2 and PC8 become resistors R, the redundancy of PCS216 is lost, and as shown in Figure 9, the current Isc flowing through PCS216 decays to 0.

[0047] In other words, if a quench occurs in the thermal persistent current switch PC in either the switch series unit IL1 or the switch series unit IL2, and a quench occurs in the thermal persistent current switch PC of the other switch series unit, the static magnetic field magnet 10 will no longer be able to maintain operation in persistent current mode.

[0048] Furthermore, in the configuration of PCS216, which is different from PCS16, if the heater connection wire HL becomes disconnected or otherwise unable to conduct electricity, a problem arises in that the superconducting coil 13 cannot be excited or demagnetized. The following describes the effects of a disconnection in the heater connection wire HL of PCS216, which is different from PCS16.

[0049] Here, in order to compare with the configuration of PCS16 in this embodiment shown in Figure 6, Figure 10 shows the configuration of PCS216, which is different from PCS16. Figure 10 is a schematic diagram showing a state in which a break has occurred in the heater connection line HL of PCS216, which is different from PCS16 in this embodiment. Figure 10 shows the case in which a break has occurred in a part of the heater connection line HL due to fault FH1.

[0050] Since heaters HT1 to HT8 are connected in series with the external power supply PW, if a break occurs in part of the heater connection wire HL, the heater current Ih cannot be supplied to heaters HT1 to HT8. As described above, the PCS216 adjusts the heating of heaters HT1 to HT8, thereby raising and lowering the temperature of the superconducting wire SU, and switching between the superconducting state and the normal conducting state of the switch SW.

[0051] In other words, if a break occurs in part of the heater connection wire HL, it becomes impossible to adjust the heating of the heater HT1 to raise or lower the temperature of the superconducting wire SU, and therefore the static magnetic field magnet 10 will no longer be able to excite or demagnetize the superconducting coil 13.

[0052] Therefore, the PCS16 according to this embodiment has a configuration that improves upon the problems of the PCS216 described above, which are different from the PCS16. Specifically, the PCS16 according to this embodiment has a configuration in which multiple switch parallel units, each consisting of multiple thermal persistent current switches connected in parallel, are connected in series. A switch parallel unit is an example of a parallel configuration. The configuration of the PCS16 according to this embodiment will be described below with reference to Figure 3.

[0053] Figure 3 is a schematic diagram showing an example of the configuration of PCS16 according to the embodiment. As shown in Figure 3, PCS16 has thermal persistent current switches 160a to 160h, superconducting wires 163, and heater connection wires 164. In the following description, unless otherwise distinguished, thermal persistent current switches 160a to 160h may simply be referred to as thermal persistent current switch 160.

[0054] The thermal persistent current switch 160, like the PCS216 which is separate from the PCS16, switches between conducting and interrupting the current flowing through the superconducting wire 163. The thermal persistent current switches 160a and 160b are connected in parallel by the superconducting wire 163, forming a switch parallel assembly JP1.

[0055] Similarly, thermal persistent current switches 160c and 160d constitute switch parallel assembly JP2, thermal persistent current switches 160e and 16f constitute switch parallel assembly JP3, and thermal persistent current switches 160g and 160h constitute switch parallel assembly JP4. Switch parallel assembly JP1, JP2, JP3, and JP4 are connected in series by superconducting wire 163.

[0056] In this embodiment, the superconducting wire 163 is composed of Cu / NbTi, but the material of the superconducting wire 163 is not limited to this. For example, the superconducting wire 163 may be composed of CuNi / NbTi.

[0057] Furthermore, the thermal permanent current switch 160a has a switch section 161a and a heater 162a. In the following description, when the switch sections 161a to 161h are not specifically distinguished, they may simply be referred to as the switch section 161. Similarly, when the heaters 162a to 162h are not specifically distinguished, they may simply be referred to as the heater 162.

[0058] The switch section 161, like the switch section SW of PCS216 which is separate from PCS16, is a part that acts as a switch to switch between the superconducting state and the normal conducting state of the switch section 161 by the heat generated by the heater 162.

[0059] In this embodiment, the switch portion 161 is formed by stripping Cu from the Cu / NbTi that constitutes the superconducting wire 163, but the configuration of the switch portion 161a is not limited to this. For example, it may be composed of CuNi / NbTi. The heater 162 heats the superconducting wire 163 in the same way as the heater HT of PCS216, which is separate from PCS16.

[0060] The heaters 162 are divided into multiple groups and connected in parallel to the external power supply PW. Furthermore, each heater 162 is connected such that the current flowing through it is equal. For example, PCS 16 ensures that the current flowing through each heater 162 is equal by making the number of heaters 162 connected in parallel to the external power supply PW via heater connection lines 164 equal.

[0061] This allows each heater to heat the superconducting wire 163 at its corresponding position without creating a temperature difference. As a result, each switch unit 161 can switch between the superconducting state and the normal conducting state of the switch unit 161 at its corresponding position at approximately the same time.

[0062] In this embodiment, heaters 162a, 162b, 162c, and 162d form heater group HG1. Heaters 162e, 162f, 162g, and 162h form heater group HG2. Heater groups HG1 and HG2 are connected in parallel to an external power supply PW by heater connection lines 164, which are independent of the superconducting wire 163.

[0063] Note that the parallel connection configuration of heater 162 is not limited to the above. For example, in the above example, the number of heaters 162 in heater group HG1 may be 2, and the number of heater groups in heater group HG2 may be 6. Also, the number of heater groups is not limited to 2. For example, the number of heater groups may be 3 or more.

[0064] Next, we will explain the current state when a quench occurs in the thermal persistent current switch 160 while the PCS 16 with the above configuration is in a superconducting state. First, we will explain the case when no quench occurs in any of the thermal persistent current switches 160a to 160h.

[0065] In this case, if we denote the current flowing through PCS16 as Isc, then, as shown in Figure 3, the current Isc is divided among the parallel-connected thermal permanent current switches 160. Therefore, the current flowing through thermal permanent current switch 160a of the switch parallel assembly JP1 is approximately Isc / 2, and the current flowing through thermal permanent current switch 160b is approximately Isc / 2.

[0066] Similarly, the current flowing through the thermal permanent current switch 160c of the switch parallel assembly JP2 is approximately Isc / 2, and the current flowing through the thermal permanent current switch 160d is approximately Isc / 2. Also similarly, the current flowing through the thermal permanent current switch 160e of the switch parallel assembly JP3 is approximately Isc / 2, and the current flowing through the thermal permanent current switch 160f is approximately Isc / 2. Also similarly, the current flowing through the thermal permanent current switch 160g of the switch parallel assembly JP4 is approximately Isc / 2, and the current flowing through the thermal permanent current switch 160h is approximately Isc / 2.

[0067] Next, we will explain the case where a quench occurs in any one of the thermal persistent current switches 160, referring to Figure 4.

[0068] Figure 4 is a schematic diagram showing an example of the current state when a quench occurs in one of the thermal persistent current switches 160 of the PCS16 according to the embodiment. Figure 4 shows a state in which a quench occurs in the thermal persistent current switch 160c constituting the switch parallel JP2 due to fault FP1. In this case, the thermal persistent current switch 160c becomes a resistor R.

[0069] When the thermal persistent current switch 160c becomes resistor R, as shown in Figure 4, all the current flowing through the switch parallel JP2 is commutated to the thermal persistent current switch 160d side where no quench occurs. Therefore, the current flowing through the thermal persistent current switch 160c side becomes 0, and the current flowing through the thermal persistent current switch 160d side becomes Isc. The current that flows through the thermal persistent current switch 160d side is then passed to the subsequent switch parallel JP3.

[0070] As a result, the superconducting state of the superconducting wire 163 is maintained, and the operation of the static magnetic field magnet 10 in persistent current mode can be maintained. In other words, even if a quench occurs in any one of the thermal persistent current switches 160a to 160h, the operation of the static magnetic field magnet 10 in persistent current mode can be maintained, so the PCS 16 can be said to have redundancy.

[0071] Next, we will explain the case where a quench occurs in any two of the thermal persistent current switches 160, referring to Figure 5.

[0072] Figure 5 is a schematic diagram showing an example of the current state when a quench occurs in two of the thermal persistent current switches in the PCS16 according to this embodiment. Figure 5 shows a state in which a quench occurs in the thermal persistent current switch 160c constituting the switch parallel JP2 due to fault FP1, and a quench occurs in the thermal persistent current switch 160h constituting the switch parallel JP4 due to fault FP2. In this case, the thermal persistent current switch 160h becomes a resistor R.

[0073] When the thermal persistent current switch 160h becomes resistor R, as shown in Figure 5, the entire current flowing through the switch parallel JP3 is commutated to the thermal persistent current switch 160g side where no quench occurs. Therefore, the current flowing through the thermal persistent current switch 160g side becomes Isc, and the current flowing through the thermal persistent current switch 160h side becomes 0.

[0074] As a result, PCS16 functions effectively, maintaining the superconducting state of the superconducting wire 163, and thus maintaining operation of the static magnetic field magnet 10 in persistent current mode. In other words, even if quenching occurs in both the thermal persistent current switches 160c and 160h, operation of the static magnetic field magnet 10 in persistent current mode can be maintained, so PCS16 can be said to have redundancy.

[0075] Although not shown in the diagram, if a quench occurs in the thermal persistent current switch 160d while a quench is occurring in the thermal persistent current switch 160c that constitutes the switch parallel assembly JP2, then the thermal persistent current switch 160d will become a resistor R. When both the thermal persistent current switches 160c and 160d become resistor R, the redundancy of PCS16 is lost, and the current Isc is attenuated by the resistance R and reaches 0.

[0076] Therefore, the PCS16 according to this embodiment can maintain operation of the static magnetic field magnet 10 in the permanent current mode even if a quench occurs in any two of the thermal permanent current switches 160 that constitute the same switch parallel JP, as long as a quench does not occur in either of the thermal permanent current switches 160.

[0077] Here, using a PCS216 different from the PCS16 described in Figures 7 to 10 and the PCS16 according to this embodiment described in Figures 3 to 6 as examples, the difference in reliability between the PCS216 different from the PCS16 described in Figures 7 to 10 and the PCS16 according to this embodiment will be explained. In this embodiment, the degree of unreliability represents the extent to which the permanent current mode cannot be maintained due to the quenching of two thermal permanent switches over an arbitrary period (e.g., 10 years).

[0078] For example, if the failure probability per unit of thermal persistent current switch PC or 160 in a 2-parallel configuration is F2, and the failure probability per unit of thermal persistent current switch PC or 160 in a 1-parallel configuration is F1, then the unreliability F of PCS216 is F = 8C1 × F2 × 4C1 × F1. On the other hand, the unreliability F of PCS16 is F = 8C1 × F2 × F1. Therefore, the unreliability of PCS16 is 1 / 4 that of PCS216.

[0079] In other words, the PCS16 according to this embodiment has improved reliability compared to a different PCS216.

[0080] Next, the effects of a break in the heater connection wire 164 of the PCS16 according to this embodiment will be explained with reference to Figure 6. Figure 6 is a schematic diagram showing an example of a break in the heater connection wire 164 of the PCS16 according to this embodiment.

[0081] Figure 6 shows the case where a break occurs in a portion of the heater connection line 164 due to fault FH1. If a break occurs at the location of fault FH1, the external power supply PW will be unable to supply heater current Ih to the heater 162 that constitutes the heater group HG1.

[0082] However, in PCS16, since heater group HG1 and heater group HG2 are connected in parallel to the external power supply PW, even if a break occurs at the location of fault FH1, the external power supply PW can still supply heater current Ih to heater group HG2. In other words, in this embodiment, the static magnetic field magnet 10 can energize and demagnetize the superconducting coil 13 even if a break occurs at one point in the heater connection wire 164.

[0083] As described above, the MRI apparatus 100 according to this embodiment includes a static magnetic field magnet 10 having a superconducting coil 13 and a PCS 16. The PCS 16 is connected in parallel with the superconducting coil 13 and has a superconducting wire 163. The PCS 16 also has a switch parallel assembly JP, which is made up of multiple thermal permanent current switches 160 connected in parallel to interrupt the current flowing through the superconducting wire 163. Multiple switch parallel assembly JPs are connected in series.

[0084] As a result, even if a quench occurs in one of the thermal persistent current switches 160 constituting the switch parallel JP, current flows to the other thermal persistent current switches 160 constituting the switch parallel JP, thus maintaining the superconducting state of the superconducting coil 13. In other words, the PCS 16 according to this embodiment has redundancy and can improve the reliability of the static magnetic field magnet 10 compared to when the thermal persistent current switches 160 are connected in series with the superconducting coil 13.

[0085] Furthermore, since the PCS16 according to this embodiment has a configuration in which multiple switch parallels JP are connected in series, even if one thermal persistent current switch 160 is quenched and another thermal persistent current switch quenches, the superconducting state of the superconducting coil can be maintained as long as not all thermal persistent current switches 160 constituting the same switch parallel JP quench. Therefore, the PCS16 according to this embodiment can increase the possibility of maintaining the superconducting state of the superconducting coil 13 even if two or more thermal persistent current switches 160 quench. In other words, the PCS16 according to this embodiment can further improve the reliability of the static magnetic field magnet 10.

[0086] Furthermore, the PCS16 according to this embodiment includes a plurality of heaters 162 that raise and lower the temperature of the switch section 161, and a heater connection line 164 that connects an external power supply PW that supplies power to each heater 162 and the plurality of heaters 162 in parallel.

[0087] As a result, the thermal permanent current switch 160 can adjust the heating of the heater 162 and raise or lower the temperature of the switch section 161, thereby switching between the superconducting state and the normal conducting state of the switch section 161. Therefore, in this embodiment, the static magnetic field magnet 10 can energize and demagnetize the superconducting coil 13 using the thermal permanent current switch 160.

[0088] Furthermore, since the PCS16 according to this embodiment has a configuration in which an external power supply PW and a plurality of heaters 162 are connected in parallel, even if a break occurs in one of the heater connection wires 164, current can still flow to the heaters 162 on the side where the break does not occur. In other words, the static magnetic field magnet 10 according to this embodiment can energize and demagnetize the superconducting coil 13 even if a break occurs in one of the heater connection wires 164.

[0089] Furthermore, in the PCS16 according to this embodiment, multiple heaters 162 are connected in parallel by heater connection lines 164 such that the current flowing through each heater 162 is equal. As a result, each heater can heat the superconducting wire 163 at the corresponding position without causing a temperature difference. Therefore, each switch unit 161 can switch between the superconducting state and the normal conducting state of the switch unit 161 at the corresponding position at approximately the same timing.

[0090] Furthermore, in the PCS16 according to this embodiment, the number of heaters 162 connected in parallel by the heater connection line 164 is equal. This makes it easy to equalize the current flowing through each heater 162.

[0091] The embodiments described above can also be modified and implemented as appropriate by changing some of the configurations or functions of each device. Therefore, several modifications of the embodiments described above will be described below as other embodiments. In the following, we will mainly describe the differences from the embodiments described above, and will omit detailed explanations of points that are common with what has already been described. Furthermore, the modifications described below may be implemented individually or in combination as appropriate.

[0092] (Variation 1) In the embodiment described above, a PCS16 was described in which four switch parallel units JP, each consisting of two thermal permanent current switches 160, were connected in series. However, the configuration of PCS16 is not limited to this. For example, PCS16 may be configured in which three switch parallel units JP, each consisting of three thermal permanent current switches 160, were connected in series.

[0093] Here, PCS16 can maintain the superconducting state of the superconducting coil 13 as long as not all of the thermal persistent current switches 160 constituting the same switch parallel JP quench. Therefore, by increasing the number of thermal persistent current switches 160 constituting the switch parallel JP, the possibility of maintaining the superconducting state of the superconducting coil 13 even if quenching occurs in multiple thermal persistent current switches 160 can be increased.

[0094] In other words, the PCS16 according to this modified example can further improve the reliability of the static magnetic field magnet 10.

[0095] (Modification 2) In the embodiment described above, a PCS16 was described in which two heater groups HG, each consisting of four heaters 162, were connected in parallel. However, the parallel connection configuration of the heaters 162 in the PCS16 is not limited to this. For example, the PCS16 may be configured in which four heater groups HG, each consisting of two heaters 162, are connected in parallel.

[0096] Here, since the PCS16 has multiple heaters 162 connected in parallel, even if a break occurs in the heater connection line 164, if there is a group of heaters HG that is not broken, current can still flow to the heaters 162 that make up that group of heaters HG. Therefore, by increasing the number of heaters 162 connected in parallel, the possibility of being able to energize and demagnetize the superconducting coil 13 even if a break occurs in the heater connection line 164 can be increased.

[0097] In other words, according to the PCS16 of this modified example, even if a break occurs in the heater connection wire 164, the possibility of excitation and demagnetization of the superconducting coil 13 can be increased.

[0098] According to at least the embodiments and modifications described above, the reliability of the static magnetic field magnet 10 can be further improved.

[0099] While several embodiments have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in a variety of other forms, and various omissions, substitutions, modifications, and combinations of embodiments are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0100] 100 MRI machines (Magnetic Resonance Imaging machines) 10 Static magnetic field magnet 11 Vacuum container 12 Refrigerant containers 13 Superconducting Coil 14 Protection circuit 15 Current Leads 16 PCS 17 Magnet excitation / demagnetization power supply 50 Gradient magnetic field power supply 60 Transmitter 70 Receiver 80 Sequence control device 90 Computer Systems 160A~160H Thermal Permanent Current Switch 161a~161h Switch section 162a~162h Heater 163 Superconducting wire 164 Heater connection wire

Claims

1. A permanent current switch device electrically connected in parallel with a superconducting coil via a superconducting wire, A first parallel configuration is formed by electrically connecting a first thermal persistent current switch, which is electrically connected in parallel to the superconducting coil and switches between a superconducting state and a normal conducting state, and a second thermal persistent current switch, which is electrically connected in parallel to the superconducting coil and switches between a superconducting state and a normal conducting state, to each other in a first parallel configuration. A second parallel configuration is formed by electrically connecting a third thermal persistent current switch, which is electrically connected in parallel with the superconducting coil and switches between a superconducting state and a normal conducting state, and a fourth thermal persistent current switch, which is electrically connected in parallel with the superconducting coil and switches between a superconducting state and a normal conducting state, to each other. Equipped with, The first thermal persistent current switch comprises a first heater, The second thermal permanent current switch comprises a second heater, The third thermal permanent current switch comprises a third heater, The fourth thermal permanent current switch comprises a fourth heater, The first parallel configuration and the second parallel configuration are electrically connected in series with respect to each other. Perpetual current switch device.

2. The first heater and the second heater constitute a first heater group, The third heater and the fourth heater constitute a second heater group. The first group of heaters and the second group of heaters are electrically connected in parallel to an external power supply that provides power to the first to fourth heaters. The permanent current switch device according to claim 1.

3. The first thermal persistent current switch includes a first switch unit that switches between the superconducting state and the normal conducting state by heat generated by the first heater, The second thermal persistent current switch includes a second switch section that switches between the superconducting state and the normal conducting state by heat generated by the second heater, The third thermal persistent current switch includes a third switch section that switches between the superconducting state and the normal conducting state by heat generated by the third heater, The fourth thermal persistent current switch includes a fourth switch section that switches between the superconducting state and the normal conducting state by heat generated by the fourth heater. The permanent current switch device according to claim 1.

4. A magnetic resonance imaging apparatus equipped with a superconducting magnet, The superconducting magnet is, It is equipped with a permanent current switch device that is electrically connected to a superconducting coil via a superconducting wire, The aforementioned permanent current switch device is A first parallel configuration is formed by electrically connecting a first thermal persistent current switch, which is electrically connected in parallel to the superconducting coil and switches between a superconducting state and a normal conducting state, and a second thermal persistent current switch, which is electrically connected in parallel to the superconducting coil and switches between a superconducting state and a normal conducting state, to each other in a first parallel configuration. A second parallel configuration is formed by electrically connecting a third thermal persistent current switch, which is electrically connected in parallel with the superconducting coil and switches between a superconducting state and a normal conducting state, and a fourth thermal persistent current switch, which is electrically connected in parallel with the superconducting coil and switches between a superconducting state and a normal conducting state, to each other. Equipped with, The first thermal persistent current switch comprises a first heater, The second thermal permanent current switch comprises a second heater, The third thermal permanent current switch comprises a third heater, The fourth thermal permanent current switch comprises a fourth heater, The first parallel configuration and the second parallel configuration are electrically connected in series with respect to each other. Magnetic resonance imaging device.

5. The first heater and the second heater constitute a first heater group, The third heater and the fourth heater constitute a second heater group. The first group of heaters and the second group of heaters are electrically connected in parallel to an external power supply that provides power to the first to fourth heaters. The magnetic resonance imaging apparatus according to claim 4.

6. The first thermal persistent current switch includes a first switch unit that switches between the superconducting state and the normal conducting state by heat generated by the first heater, The second thermal persistent current switch includes a second switch section that switches between the superconducting state and the normal conducting state by heat generated by the second heater, The third thermal persistent current switch includes a third switch section that switches between the superconducting state and the normal conducting state by heat generated by the third heater, The fourth thermal persistent current switch includes a fourth switch section that switches between the superconducting state and the normal conducting state by heat generated by the fourth heater. The magnetic resonance imaging apparatus according to claim 4.

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