System for controlling superconducting coils using magnetic persistent current switches
Patent Information
- Application Number
- JP2023575573
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2021-06-11
- Filing Date
- 2022-06-02
- Publication Date
- 2025-06-05
AI Technical Summary
Existing cooling systems for superconducting coils struggle to manage the heat generated by magnetic persistent current switches without overburdening the cryogenic cooling system, particularly in cryogen-free systems where thermal isolation is required.
A system utilizing a magnetic persistent current switch with a thermal switch that includes a movable shaft controlled by a solenoid and a latching device, allowing coolant flow through a loop tube to a heat exchanger, where the shaft position is maintained by magnetic forces, requiring power only for switching and not for stabilization.
Enables rapid temperature adjustment of the magnetic persistent current switch without overloading the cooling system, maintaining efficient operation of superconducting coils in persistent and ramp modes by minimizing power consumption during stable positions.
Smart Images
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Abstract
Description
[Technical field]
[0001] The present invention relates to the field of superconducting coils, and in particular to a magnetic persistent current switch for switching a superconducting coil between persistent and ramp modes. [Background technology]
[0002] Superconducting magnets are sometimes used in systems requiring strong magnetic fields, such as magnetic resonance imaging (MRI) and nuclear magnetic resonance spectroscopy (NMR). To achieve superconductivity, magnets contain one or more conductive coils formed from superconducting wire. To maintain superconductivity, a cryogenic environment near absolute zero is required during operation. In the superconducting state, the conductive coils, called superconducting coils, have virtually no electrical resistance and therefore can conduct larger electric currents and generate stronger magnetic fields.
[0003] The operation of a superconducting magnet in the superconducting state is sometimes called the persistent current mode. That is, the persistent current mode is a state in which an electrical circuit (e.g., including a superconducting coil) can carry an electrical current for practically an indefinite period of time without the need for an external power source due to the lack of electrical resistance. To operate in the persistent current mode, a superconducting magnet provides a closed superconducting circuit with a superconducting loop. This circuit is interrupted in order for a power source to pass an electrical current through the coil. Interrupting the circuit typically involves heating a portion of the superconducting loop to create an electrical resistance in the superconducting loop. The component of the superconducting circuit responsible for switching between the superconducting state and the normal (non-superconducting) resistance is called the magnet persistent current switch (MPCS). The superconducting state is also called the persistent state, and the normal state is called the ramp state, i.e., the state for ramping up or down the superconducting coil.
[0004] When a voltage source is connected across the MPCS, most of the current flows through the coils and only a small amount of current flows through the resistive wires of the MPCS. Both the actions of opening the MPCS and applying a voltage across it cause the MPCS to heat up. The low-temperature cooling system (also called a cryostat) that cools the superconducting coils is usually unable to cope with the additional heat generated by the MPCS (given the limited ability of the cooling system to absorb or remove that heat). This is the case in so-called cryogen-free, or sealed, systems, which require the MPCS to be thermally isolated from the cooling system while the magnet is energized or de-energized.
[0005] In this regard, International Patent Publication WO2020 / 193415A1 describes a system for controlling the temperature of a persistent current switch operating in a background magnetic field, including a heat exchanger, a loop tube, a ball valve, and a plurality of electromagnets. The heat exchanger dissipates heat to a cryocooler. The loop tube allows the thermal energy generated by the persistent current switch to be transferred to the heat exchanger by a flow of coolant. The ball valve is integrated with the loop tube between the persistent current switch and the heat exchanger, and includes a ferromagnetic ball. The electromagnet is disposed outside the loop tube adjacent to the ball valve. Here, when a first electromagnet of the plurality of electromagnets is energized, the ferromagnetic ball is magnetically moved to a first position that opens the loop tube, allowing the coolant to flow. When a second electromagnet is energized, the ferromagnetic ball is magnetically moved to a second position that closes the loop tube, blocking the flow of the coolant. Summary of the Invention [Problem to be solved by the invention]
[0006] An object of the present invention is to provide a cooling system capable of raising and lowering the temperature of a magnet persistent current switch as desired in a short period of time without placing a burden on the cooling system for a superconducting coil. [Means for solving the problem]
[0007] According to the invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the invention are set out in the dependent claims.
[0008] Thus, in accordance with the present invention, there is provided a system for controlling a superconducting coil, the system comprising: a magnetic persistent current switch for switching the superconducting coil between a persistent mode and a ramp mode; a heat exchanger to distribute the heat to the cryocooler; a loop tube that allows a flow of coolant to transfer the thermal energy generated by the magnetic persistent current switch to a heat exchanger; A thermal switch including a valve integrated with a loop tube between a magnetic persistent current switch and a heat exchanger, the valve comprising: a valve body having an inlet and an outlet, the outlet being connected to a loop tube; a movable shaft disposed within the valve body and including a permanent rod magnet; a latching device including a permanent magnet or a ferromagnetic or paramagnetic retaining element; a solenoid; and a thermal switch, the shaft is movable between a closed position in which the shaft closes an inlet or an outlet of the valve body such that no coolant flows through the valve body, and an open position in which the inlet and outlet of the valve body are open such that coolant flows through the valve body; the solenoid is positioned relative to the shaft such that application of a current pulse having a first polarity to the solenoid moves the shaft to a closed position, and application of a current pulse having a second polarity opposite the first polarity to the solenoid moves the shaft to an open position; The latch device is arranged relative to the shaft such that the magnetic force acting from the permanent magnet of the latch device to the permanent magnet of the shaft causes the shaft to remain in the closed or open position, unless a current pulse is applied to the solenoid to switch the shaft from the closed position to the open position (or vice versa). Alternatively, the latch device is provided with a ferromagnetic or paramagnetic retaining element, which is magnetized by a permanent rod magnet of the shaft in the vicinity of the retaining element. The retaining element may be formed as a ferromagnetic or paramagnetic insert. The magnetic force between the permanent rod magnet and the induced magnetization of the retaining element keeps the movable shaft in its currently stable position (open or closed) when the solenoid is not actuated.
[0009] The present invention relates to a system for controlling a superconducting coil using a magnetic persistent current switch for ramping (up / down) the superconducting coil and operating the superconducting coil in a persistent mode. A loop tube through which a coolant flows is provided between the magnetic persistent current switch and a heat exchanger to carry away heat from the magnetic persistent current switch during ramping of the superconducting coil. The cooling circuit is controlled using a valve with a permanent magnetic movable shaft that is moved using a solenoid electromagnet coil.
[0010] According to one aspect of the invention, the shaft is locked in its current position using a latching device having a permanent magnet or a ferromagnetic or paramagnetic retaining element. The latching device causes the shaft to remain in a stable stop position formed by the closed position or in an open position as long as a current pulse is not applied to the solenoid. Thus, when a current pulse of the appropriate polarity is applied to the solenoid, the magnetic field of the solenoid moves the permanent magnetic shaft to its current position. After the current pulse, the latching device maintains the shaft in its current position without the need to keep the solenoid activated. Thus, the invention moves the shaft between the open and closed positions by the magnetic field of the solenoid and without the need for mechanical contact to the shaft. The shaft is maintained in its current position (i.e., the position to which the shaft was last moved) by the latching device without the need to apply power to the latching device. Thus, operation of the valve requires power only to switch the valve between its open and closed positions, and no power is required to keep the shaft in its current stable stop position.
[0011] The push / pull capability of the solenoid in conjunction with a permanent magnet allows the valve to be operated with only one pulsing solenoid, which is nearly independent of gravity as a stable stop position (open or closed) is maintained by the locking force provided by the magnet in the latching device.
[0012] With regard to the solenoid, it is essential in the present invention that the solenoid is arranged relative to the shaft such that applying a current pulse with a first polarity to the solenoid moves the shaft to a closed position, and applying a current pulse with a second polarity opposite to the first polarity to the solenoid moves the shaft to an open position. Therefore, the design, orientation and location of the solenoid may be different in different designs of the system for controlling the superconducting coil. For example, the solenoid may be arranged laterally next to the valve body, or the solenoid may be wrapped around the valve body. Furthermore, other designs and arrangements are possible. Furthermore, interference with existing background magnetic fields must be taken into account. Such existing background magnetic fields may exert a force or torque on the solenoid when powered, which is undesirable and should be countered, for example, by a different orientation of the solenoid.
[0013] According to a preferred embodiment of the invention, the shaft includes a sealing element in one of its two end regions, which seals the inlet or outlet in the closed position by pressing against a valve seat arranged in the inlet or outlet.
[0014] In general, the shaft may be movable within the valve body in a variety of ways. According to a first preferred embodiment of the invention, the shaft is arranged within the valve body such that it is rotatable along an axis of rotation perpendicular to the longitudinal axis of the shaft.
[0015] As is customary, the longitudinal axis is to be understood as the longest extension axis of the shaft. In this first preferred embodiment of the invention, the sealing element is preferably a sealing ball in an internal bore, by means of which the sealing ball is movably arranged on the shaft. In this respect, the valve body preferably comprises a groove for guiding the sealing bore ball during rotation of the shaft. Generally, the other end of the shaft is a free end, but preferably the shaft comprises a balance ball in the other end region. The balance ball has an internal bore, by means of which the balance ball is also movably arranged on the shaft. Furthermore, in this respect, the valve body preferably comprises a groove for guiding the balance bore ball during rotation of the shaft. In this way, a stable design is achieved, which allows the valve to be reliably switched from the open state to the closed state or from the closed state to the open state.
[0016] Generally, according to the first embodiment of the invention, in which the shaft is rotatable, the rotation range of the shaft is not limited to a specific value. However, according to a preferred embodiment of the invention, the rotation range of the shaft is limited to less than 90°, and the permanent magnet of the latching device is a permanent rod magnet, which is arranged such that one of its two ends is directed toward the central region of the rotation range, and the polarity of the one end is the same as the polarity of the permanent rod magnet of the shaft in the rotation range. This provides the following operation: the shaft is brought into a position related to the open state or to the closed state by the repulsive magnetic forces between the same polarities. Furthermore, switching from the open state to the closed state or vice versa can only be achieved by applying a current pulse with the corresponding polarity to the solenoid in order to bring about an attractive or repulsive magnetic force on the shaft. In this regard, according to a preferred embodiment, the permanent magnet of the latching device is fixed and only serves to maintain the open or closed state as long as no current is applied to the solenoid. In contrast, according to another embodiment, the permanent magnet of the latching device is pivotally fixed to the valve body. Here, the permanent magnet of the latch device is pivotably arranged in the valve body such that when the shaft is moved to the closed position, the end facing the rotation range pivots away from the closed position, and when the shaft is moved to the open position, the end facing the rotation range pivots away from the open position. In this regard, according to a preferred embodiment of the invention, two changeover contacts are provided such that one of these changeover contacts is actuated by the permanent rod magnet of the latch device by pivoting away from the closed state to indicate a closed state of the valve, and the other one is actuated by the permanent rod magnet of the latch device by pivoting away from the open state to indicate an open state of the valve.
[0017] According to a second preferred embodiment of the present invention, the shaft is arranged in the valve body such that it is not rotatable but is linearly movable along a shaft channel provided in the valve body. In this regard, instead of using a separate sealing element, it is preferred that the shaft itself seals the inlet or outlet in the closed position by pressing against a valve seat arranged in the inlet or outlet. Furthermore, for the second preferred embodiment of the present invention, it is further preferred that the valve body includes a flow channel extending parallel to the shaft channel from the inlet to the outlet. Here, the shaft is arranged in the valve body such that the flow channel is open in the open position and the coolant flows through the valve body from the inlet to the outlet. Also, for the second preferred embodiment of the present invention, it is preferred to have a latch device. In this regard, a first permanent magnet is arranged in one end region of the shaft channel and a second permanent magnet is arranged in the other end region of the shaft channel. The polarity of the first permanent magnet is opposite to that of the end of the permanent rod magnet on the shaft that faces the first permanent magnet, and the polarity of the second permanent magnet is opposite to that of the end of the permanent rod magnet on the shaft that faces the second permanent magnet. The latching arrangement also ensures that the valve remains open or closed unless a current pulse is provided to the solenoid.
[0018] The present invention also relates to a method of operating a system for controlling a superconducting coil, the system comprising: A magnetic persistent current switch; a heat exchanger to distribute the heat to the cryocooler; A loop tube connecting the magnetic persistent current switch to a heat exchanger; A thermal switch including a valve integrated with a loop tube between a magnetic persistent current switch and a heat exchanger, the valve comprising: a valve body having an inlet and an outlet, the outlet being connected to a loop tube; a movable shaft disposed within the valve body and including a permanent rod magnet; a latch device including a permanent magnet; and a thermal switch including a solenoid. switching the superconducting coil between a persistent mode and a ramp mode; dissipating heat from the heat exchanger to a cryocooler; enabling a flow of coolant to transfer the thermal energy generated by the magnetic persistent current switch to a heat exchanger; moving the shaft between a closed position in which the shaft closes an inlet or an outlet of the valve body such that no coolant flows through the valve body and an open position in which the inlet and outlet of the valve body are open such that coolant flows through the valve body; applying a current pulse having a first polarity to the solenoid to move the shaft to a closed position or applying a current pulse having a second polarity opposite the first polarity to the solenoid to move the shaft to an open position; A magnetic force acting from a permanent magnet in the latch device to a permanent magnet in the shaft causes the shaft to remain in the closed or open position unless a current pulse is applied to the solenoid which switches the shaft from the closed position to the open position or vice versa.
[0019] Moreover, the present invention also relates to a non-transitory computer readable medium having stored thereon instructions which, when executed on a processor, cause the system for controlling a superconducting coil as described above to perform the method as described above. [Brief description of the drawings]
[0020] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, although such embodiments do not necessarily represent the full scope of the invention, and therefore, reference should be made to the claims and this specification for interpreting the scope of the invention.
[0021] [Figure 1]FIG. 1 shows a schematic block diagram of a superconducting magnet system according to a preferred embodiment of the present invention. [Diagram 2] FIG. 2 shows diagrammatically a valve of a superconducting magnet system according to a preferred embodiment of the present invention in an open position. [Diagram 3] FIG. 3 shows diagrammatically the valve of the superconducting magnet system according to the preferred embodiment of the present invention of FIG. 3 in a closed position. [Figure 4] FIG. 4 shows diagrammatically a valve of a superconducting magnet system according to another preferred embodiment of the present invention in an open position. [Diagram 5] FIG. 5 shows diagrammatically the valve of the superconducting magnet system according to the preferred embodiment of the invention of FIG. 4 in a closed position. [Figure 6] FIG. 6 shows diagrammatically a valve of a superconducting magnet system according to yet another preferred embodiment of the present invention in an open position. [Figure 7] FIG. 7 shows diagrammatically the valve of the superconducting magnet system according to the preferred embodiment of the present invention of FIG. 6 in a closed position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] FIG. 1 shows a schematic block diagram of a superconducting magnet system according to a preferred embodiment of the present invention. According to this preferred embodiment, the superconducting magnet system 1 includes a superconducting coil 6 of a superconducting magnet connected in parallel with a magnet permanent current switch (MPCS) 7, and a power supply 11, shown as a current source for illustrative purposes. The superconducting coil 6 is within a cryostat 2 of the superconducting magnet system 1 to limit heat input to the superconducting coil 6. The superconducting coil 6 is maintained at a low temperature in a cryocooler 3 attached to the cryostat 2. The cryocooler 3 has a first stage 4 that maintains the temperature of a thermal shield (not shown in FIG. 1) encasing the superconducting coil 6 at about 40 Kelvin, and a second stage 5 that maintains the temperature of the superconducting coil 6 at about 4 Kelvin. A portion of the cryocooler 3 is accessible from outside the cryostat 2. A heat exchanger 10 of a convection cooling loop 8 is permanently connected to or in thermal contact with the second stage 5 of the cryocooler 3. A power supply 11 is permanently or temporarily connected to electrical contacts on the outside of the cryostat 2 .
[0023] The controller 12 is implemented by a computer system or device having one or more processors executing instructions stored on a memory and / or computer readable medium, for example, as described above. In the illustrated embodiment, the controller 12 controls the state of the power supply 11 and the MPCS 7 (shown in dotted lines) to allow, for example, ramping up the magnet, placing the magnet in persistent current mode, and ramping down the magnet in response to operator-issued instructions. The controller 12 also controls the operation of a thermal switch 9 in the convection cooling loop 8 (shown in dotted lines) to selectively block or enable the flow of coolant through a loop tube 13 in the convection cooling loop 8, thereby controlling the temperature of the MPCS 7. The MPCS 7 is thermally coupled to the loop tube 13 via a second heat exchanger 34. It is understood that the controller 12 includes one or more processors and other components of a computer system, as described above. The instructions stored in the memory and / or computer readable medium and executed by the processor include instructions for opening and closing the MPCS 7, opening and closing the thermal switch 9, and changing the voltage / power output of the power supply 11.
[0024] More specifically, the controller 12 controls the MPCS 7 to selectively enter a closed state, i.e., a superconducting state, and an open state, i.e., a normal state, i.e., a non-superconducting state. The MPCS 7 includes a composite superconducting wire made of superconducting filaments in a copper matrix, similar to the superconducting wire used in the superconducting coil 6. Like other superconducting wires, this composite superconducting wire functions as a normal conductor at high temperatures and as a superconductor at cryogenic temperatures. When the MPCS 7 is in the closed (superconducting) state, the main magnet current can be passed and the superconducting magnet can enter a persistent current mode. The MPCS 7 can be switched to the closed state by cooling it, for example, using the cryocooler 3. When the MPCS 7 is in the open state (non-superconducting state or normal state), the main magnet current cannot be passed. The MPCS 7 can be switched to the closed state by heating it, for example, using the MPCS heater (not shown). However, the MPCS 7 has a small (normal) resistance in the open state. This is high enough that when the magnet is connected to the power supply 11, only a small amount of current flows through the MPCS 7, with the remaining current flowing through the superconducting coil 6. Thus, when the MPCS 7 is open, the magnet is in a ramping state during which the MPCS 7 consumes power because the ramping voltage across the MPCS 7 creates a current flowing through its normal resistivity. When the MPCS 7 is closed, there is no ramping voltage and no power consumption. The MPCS 7 transitions from an open to a closed state by cooling via the convection cooling loop 8, described below, and the power supply 11 maintains the operating current of the magnet during the transition. When the MPCS 7 is fully closed (rather than transitioning between open and closed states), the power supply 11 ramps down the current. Due to the high self-inductance of the superconducting coil 6, the coil current does not change, so the current through the MPCS 7 ramps up as the current in the power supply 11 ramps down.
[0025] Additionally, the controller 12 controls a thermal switch 9 in the convection cooling loop 8 to open or close depending on the action desired by the operator. For example, when the MPCS 7 is in an open state, such as when the magnet needs to be placed in persistent current mode after a ramping activity, the thermal switch 9 is opened to allow coolant flow through the convection cooling loop 8, thereby thermally connecting the MPCS 7 to the heat exchanger 10 via the loop tube 13 to provide additional cooling for closing the MPCS 7. When the MPCS 7 is in a closed state, but needs to be opened, such as to ramp up or down the magnet, the thermal switch 9 is closed to stop the flow of coolant through the convection cooling loop 8 (for example, by blocking the loop tube 10, as described below), thereby thermally disconnecting the MPCS 7 from the heat exchanger 10 and allowing the MPCS to warm up and open without overloading the second stage 5 of the cryocooler 3. When the magnet is in the ramping state and the MPCS 7 is open, the thermal switch 9 is closed so that the power generated by the MPCS 7 does not overload the second stage 5 of the cryocooler 3 (which keeps the superconducting coils 6 cold). When the magnet enters the persistent current state, the thermal switch 9 is opened to keep the MPCS 7 thermally connected to the heat exchanger 10 so that the MPCS 7 remains in the superconducting state.
[0026] The second stage 5 of the cryocooler 3 has a limited power absorption capacity but is able to bring the superconducting coils 6 of the magnet system to the desired cryogenic temperature of about 4 Kelvin. Thus, the heat coming from the MPCS 7 in the open state would otherwise overload the cryocooler 3. As mentioned above, when the power supply 11 is connected across the MPCS 7 in the open state, most of the current flows in the superconducting coils 6 and only a small amount of current flows in the normal resistance wire of the MPCS 7. When the current through the superconducting coils 6 reaches a target value (target current), the controller 12 controls the MPCS 7 to enter a closed state, allowing the superconducting coils 6 to operate in a persistent current mode with substantially zero resistance after ramping down the power supply 11. This is called a closed superconducting circuit. The target current is the current that needs to flow in the wire to create the target magnetic field in the center of the superconducting magnet.
[0027] In general, the magnet MPCS 7 generates heat, i.e., thermal energy, when in an open state due to current flowing through a normal resistance, and continues to generate heat when controlled to transition from a closed state to an open state (or vice versa). When the current in the superconducting coil 6 reaches a target current, the controller 12 turns off the voltage to the power supply 11, but the high inductance of the superconducting coil 6 allows current to continue to flow through the power supply 11. In this situation, the MPCS 7 no longer consumes power and is ready to cool and switch from an open state to a closed state. Cooling of the MPCS 7 is achieved in part by controlling the thermal switch 9 to allow coolant to flow through the loop tube 13 of the convection cooling loop 8 to thermally connect the MPCS 7 to the second stage 5 of the cryocooler 3.
[0028] The loop tube 13 is made of a non-magnetic metal, such as copper, aluminum, titanium, zinc, tin, or lead, or other non-magnetic material. The loop tube 13 is sealed, and the coolant contained within the loop tube 13 can be, for example, helium gas or helium liquid to allow for convective transfer of thermal energy between the MPCS 7 and the heat exchanger 10. Other types of gas or liquid coolants may also be incorporated.
[0029] The thermal switch 9 opens and closes the loop tube 13 to selectively enable and block the flow of coolant. When the thermal switch 9 is open, coolant flows through the loop tube 13 between the MPCS 7 and the heat exchanger 10 to dissipate generated heat. When the thermal switch 9 is closed, the flow of coolant through the loop tube 13 is blocked.
[0030] According to preferred embodiments of the present invention, which will be further described below with reference to Figures 2-7, the thermal switch 9 comprises a valve 14 integrated with the loop tube 13 between the magnetic persistent current switch 7 and the heat exchanger 10. Each of the valves 14 of the different preferred embodiments of the present invention comprises a valve body 15 having an inlet 16 and an outlet 17, at which the valve body 15 is connected to the loop tube 13, a movable shaft 18 disposed within the valve body 15 and including a permanent rod magnet 19, a latch device 20 including a permanent magnet 21, and a solenoid 22. The shaft 18 is movable between a closed position in which the shaft 18 closes the inlet 16 or the outlet 17 of the valve body 15, thereby preventing coolant from flowing through the valve body, and an open position in which the inlet 16 and the outlet 17 of the valve body 15 are open, thereby allowing coolant to flow through the valve body 15. Further, the solenoid 22 is positioned relative to the shaft 18 such that application of a current pulse having a first polarity to the solenoid 22 moves the shaft 18 to a closed position, and application of a current pulse having a second polarity opposite to the first polarity to the solenoid 22 moves the shaft 18 to an open position. Such current pulses are initiated by the controller 12, which is connected to the thermal switch by a control line shown in dotted lines in FIG. 1. The latching device 20 is positioned relative to the shaft 18 such that a magnetic force acting from the permanent magnet 21 of the latching device 20 to the permanent magnet 19 of the shaft 18 causes the shaft 18 to remain in a closed or open position, unless a current pulse is applied to the solenoid 22 to switch the shaft 18 from a closed position to an open position (or vice versa). In this way, the latching device maintains the valve 14 in a stable open or closed state, unless an active switching from an open state to a closed state (or vice versa) is performed by the controller 12.
[0031] As shown in figures 2 to 5, the shaft 18 comprises a sealing element 24 in one of its two end regions. The sealing element seals the inlet 16 or the outlet 17 in the closed position by pressing against a valve seat 23 arranged in the outlet 17. The sealing element 24 is a sealing ball having an internal bore by means of which the sealing ball is movably arranged on the shaft 18. According to the embodiment shown in figures 2 to 5, the shaft 18 is arranged in the valve body 15 so as to be rotatable along a rotation axis perpendicular to the longitudinal axis of the shaft 18. The longitudinal axis of the shaft 18 is the longest extension axis of the shaft. Furthermore, the valve body 15 comprises a groove 25 for guiding the sealing element 24 during the rotation of the shaft 18. On the opposite side, the shaft 18 comprises a balance ball 26 having an internal bore by means of which the balance ball is also movably arranged on the shaft 18. The balance ball 26 rolls in another groove 33.
[0032] According to the embodiment shown in Figures 2 to 5, the rotation range of the shaft 18 is limited to an angle slightly smaller than 90°. The permanent magnet 21 of the latch device 20 is a permanent rod magnet arranged such that one of its two ends is directed towards the central region of the rotation range. The polarity of this end is the same as the polarity of the permanent rod magnet 19 of the shaft 18 in this rotation range. In this way, the shaft 18 is brought into a position related to the open state or into a position related to the closed state by the repulsive magnetic forces between the same polarities. Switching from the open state to the closed state or vice versa can only be achieved by applying a current pulse with the corresponding polarity to the solenoid 22 in order to bring about an attractive or repulsive magnetic force on the shaft 18.
[0033] According to the embodiment shown in Figures 2 and 3, the permanent magnet 21 of the latch device 20 is fixed and functions only to maintain the open or closed state as long as no current is applied to the solenoid 22. In contrast, according to the embodiment shown in Figures 4 and 5, the permanent magnet 21 of the latch device 20 is pivotally fixed to the valve body 15. In this regard, the permanent magnet 21 of the latch device 20 is pivotally arranged such that when the shaft 18 moves to the closed position, the end facing the rotation range pivots away from the closed position, and when the shaft 18 moves to the open position, the end facing the rotation range pivots away from the open position. Furthermore, two changeover contacts 27, 28 are provided such that one of these changeover contacts 27, 28 is actuated by the permanent rod magnet 21 of the latch device 20 by pivoting in a first direction away from the permanent rod magnet 21 to indicate a closed state of the valve 14, and the other is actuated by the permanent rod magnet 21 of the latch device 20 by pivoting in a second direction, opposite to the first direction, away from the permanent rod magnet 21 to indicate an open state of the valve 14. By contacting one or the other changeover contact 27, 28, a current starts to flow through the permanent magnet 21 and the corresponding changeover contact 27, 28 providing the possibility to indicate the state of the valve 14 (i.e. closed or open).
[0034] Figures 6 and 7 show another embodiment of the invention in which the shaft 18 is arranged in the valve body 15 so that it is linearly movable along a shaft channel 29 provided in the valve body 15. The general principle of operation of this valve 14, shown in the open state in Figure 6 and in the closed state in Figure 7, is very similar to that of the valve of Figures 2 to 5. By applying a current pulse to the solenoid 22, the permanent rod magnet 19 of the shaft 18 moves towards or away from the solenoid 22 depending on the polarity of the current pulse. In this way, the left end of the permanent rod magnet 19 of the shaft can be moved into or away from the valve seat 23 which opens and closes the valve 14. Here, instead of using a separate sealing element, the permanent rod magnet 19 of the shaft 18 itself seals the outlet 17 in the closed position by pressing against a valve seat 23 arranged in the outlet. According to this embodiment of the invention, the valve body 15 includes a flow channel 30 that extends parallel to the shaft channel 29 from the inlet 16 to the outlet 17. The shaft 18 is arranged within the valve body 15 such that in the open position, the flow channel 30 is open and coolant flows through the valve body 15 from the inlet 16 to the outlet 17. Furthermore, this embodiment also includes a latching arrangement 20 that maintains the valve 14 in an open or closed state unless a current pulse is applied to the solenoid 22 to change from the open state to the closed state (and vice versa). To realize this latching arrangement 22, a first permanent magnet 31 is arranged in one end region of the shaft channel 29 and a second permanent magnet 32 is arranged in the other end region of the shaft channel 29. The polarity of the first permanent magnet 31 and the polarity of the end of the permanent rod magnet 19 of the shaft 18 facing the first permanent magnet 31 are opposite to each other, and the polarity of the second permanent magnet 32 and the polarity of the end of the permanent rod magnet 19 of the shaft 18 facing the second permanent magnet 32 are opposite to each other. In this way, the permanent rod magnet 19 of the shaft 18 remains in the open or closed state of the valve 14 due to the magnetic force between the first permanent magnet 31 on the right side or the second permanent magnet 32 on the left side and the corresponding end of the permanent rod magnet 19 of the shaft.Alternatively, the latching device may include a set of ferromagnetic or paramagnetic retaining elements positioned at each end region of the shaft channel.
[0035] While the present invention has been illustrated and described in detail in the drawings and the above description, such illustration and description should be considered as illustrative or exemplary, and not restrictive. The present invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and singular elements do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope. Moreover, for the sake of clarity, not all elements in the drawings have been provided with reference signs. [Explanation of symbols]
[0036] Superconducting magnet system 1 Cryostat 2 Cryocooler 3 Cryocooler first stage 4 Cryocooler second stage 5 Superconducting coil 6 Magnetic persistent current switch 7 Cooling Loop 8 Thermal Switch 9 First heat exchanger 10 power supply 11 Controller 12 Loop Tube 13 Valve 14 Valve body 15 Inlet 16 Outlet 17 Shaft 18 Shaft Permanent Rod Magnets 19 Latch device 20 Permanent magnets in latching devices 21 Solenoid 22 Valve seat 23 Sealing element 24 groove 25 Balance ball 26 Contact for open state 27 Contact for closed state 28 Shaft Channel 29 Flow Channel 30 First permanent magnet 31 Second permanent magnet 32 groove 33 Second heat exchanger 34
Claims
1. 1. A system for controlling a superconducting coil, the system comprising: a magnetic persistent current switch for switching the superconducting coil between a persistent mode and a ramp mode; a heat exchanger to distribute the heat to the cryocooler; a loop tube allowing the flow of a coolant to transfer the thermal energy generated by the magnetic persistent current switch to the heat exchanger; A thermal switch including a valve integrated with the loop tube between the magnetic persistent current switch and the heat exchanger, the valve comprising: a valve body having an inlet and an outlet, the valve body being connected to the loop tube at the outlet; a movable shaft disposed within the valve body and including a permanent rod magnet; a latching device including a permanent magnet or a ferromagnetic or paramagnetic retaining element; a thermal switch including a solenoid; Including, the shaft is movable between a closed position in which the shaft closes the inlet or the outlet of the valve body, thereby preventing coolant from flowing through the valve body, and an open position in which the inlet and the outlet of the valve body are open, thereby allowing coolant to flow through the valve body; the solenoid is positioned relative to the shaft such that application of a current pulse having a first polarity to the solenoid moves the shaft to the closed position, and application of a current pulse having a second polarity opposite the first polarity to the solenoid moves the shaft to the open position; A system for controlling a superconducting coil, wherein the latch device is positioned relative to the shaft such that a magnetic force acting from the permanent magnet of the latch device or the ferromagnetic or paramagnetic retaining element of the latch device to the permanent magnet of the shaft causes the shaft to remain in a stable rest position formed by the closed position or in the open position, unless a current pulse is applied to the solenoid to switch the shaft from the closed position to the open position or vice versa.
2. 2. The system for controlling a superconducting coil as described in claim 1, wherein the shaft includes a sealing element at either of its two end regions, the sealing element sealing the inlet or the outlet in the closed position by pressing against a valve seat disposed at the inlet or the outlet.
3. 3. The system for controlling a superconducting coil as described in claim 1 or 2, wherein the shaft is disposed within the valve body so as to be linearly movable along a shaft channel provided in the valve body.
4. 4. The system for controlling a superconducting coil as described in claim 3, wherein the valve body includes a flow channel extending parallel to the shaft channel from the inlet to the outlet, and the shaft is disposed within the valve body such that the flow channel is open in the open position and coolant flows through the valve body from the inlet to the outlet.
5. 5. The system for controlling a superconducting coil according to claim 3 or 4, wherein a first permanent magnet is disposed in one end region of the shaft channel and a second permanent magnet is disposed in the other end region of the shaft channel, the polarity of the first permanent magnet and the polarity of the end of the permanent rod magnet of the shaft facing the first permanent magnet are opposite to each other, and the polarity of the second permanent magnet and the polarity of the end of the permanent rod magnet of the shaft facing the second permanent magnet are opposite to each other.
6. 1. A system for controlling a superconducting coil, the system comprising: a magnetic persistent current switch for switching the superconducting coil between a persistent mode and a ramp mode; a heat exchanger to distribute the heat to the cryocooler; a loop tube allowing the flow of a coolant to transfer the thermal energy generated by the magnetic persistent current switch to the heat exchanger; A thermal switch including a valve integrated with the loop tube between the magnetic persistent current switch and the heat exchanger, the valve comprising: a valve body having an inlet and an outlet, the valve body being connected to the loop tube at the outlet; a movable shaft disposed within the valve body and including a permanent rod magnet; a thermal switch including a solenoid; Including, the shaft is movable between a closed position in which the shaft closes the inlet or the outlet of the valve body, thereby preventing coolant from flowing through the valve body, and an open position in which the inlet and the outlet of the valve body are open, thereby allowing coolant to flow through the valve body; 1. A system for controlling a superconducting coil, wherein the solenoid is positioned relative to the shaft such that application of a current pulse having a first polarity to the solenoid moves the shaft to the closed position and application of a current pulse having a second polarity opposite to the first polarity to the solenoid moves the shaft to the open position, and the shaft is disposed within the valve body so as to be rotatable along a rotational axis perpendicular to a longitudinal axis of the shaft.
7. 7. The system for controlling a superconducting coil as described in claim 6, wherein the system includes a latch device arranged relative to the shaft such that a magnetic force acting from the permanent magnet or the ferromagnetic or paramagnetic retaining element of the latch device on the permanent magnet of the shaft causes the shaft to remain in a stable rest position formed by the closed position or in the open position, unless a current pulse is applied to the solenoid to switch the shaft from the closed position to the open position or vice versa.
8. 8. The system for controlling a superconducting coil of claim 7, wherein the rotation range of the shaft is limited to less than 90 degrees, the permanent magnet of the latch device is a permanent rod magnet, and the permanent magnet of the latch device is arranged such that one of its ends is oriented toward a central region of the rotation range, and the polarity of the one end is the same as the polarity of the permanent rod magnet of the shaft in the rotation range.
9. 8. The system for controlling a superconducting coil as described in claim 7, wherein the permanent magnet of the latch device is pivotally arranged such that when the shaft moves to the closed position, the end facing the rotation range pivots away from the shaft in a first direction, and when the shaft moves to the open position, the end facing the rotation range pivots away from the shaft in a second direction opposite to the first direction.
10. 1. A method of operating a system for controlling a superconducting coil, the system comprising: A magnetic persistent current switch; a heat exchanger to distribute the heat to the cryocooler; a loop tube connecting the magnetic persistent current switch to the heat exchanger; A thermal switch including a valve integrated with the loop tube between the magnetic persistent current switch and the heat exchanger, the valve comprising: a valve body having an inlet and an outlet, the valve body being connected to the loop tube at the outlet; a movable shaft disposed within the valve body and including a permanent rod magnet; a latching device including a permanent magnet or a ferromagnetic or paramagnetic retaining element; a thermal switch including a solenoid; Including, The method comprises: switching the superconducting coil between a persistent mode and a ramp mode; dissipating heat from the heat exchanger to a cryocooler; enabling a flow of coolant to transfer thermal energy generated by the magnetic persistent current switch to the heat exchanger; moving the shaft between a closed position in which the shaft closes the inlet or the outlet of the valve body, thereby preventing coolant from flowing through the valve body, and an open position in which the inlet and the outlet of the valve body are open, thereby allowing coolant to flow through the valve body; applying a current pulse having a first polarity to the solenoid to move the shaft to the closed position or applying a current pulse having a second polarity opposite to the first polarity to the solenoid to move the shaft to the open position; a magnetic force acting from the permanent magnet of the latch device to the permanent magnet of the shaft causes the shaft to remain in the closed or open position unless a current pulse is applied to the solenoid to switch the shaft from the closed position to the open position or vice versa; A method comprising:
11. A non-transitory computer readable medium having instructions stored thereon that, when executed on a processor, cause a system for controlling a superconducting coil as described in claim 1 to perform the method of claim 10.