Magnetic valve and system including magnetic valve

Abstract

The magnetic valve controls the flow of fluid through a tube. The valve includes a first diode and a first solenoid connected between a first terminal and a second terminal, a second diode and a second solenoid connected in parallel with the first diode and the first solenoid between the first terminal and the second terminal, the second diode being disposed in anti-parallel with the first diode, and a ferrous ball moving between an open position and a closed position. The first solenoid generates a first magnetic field in response to a control signal having a first polarity applied to the first terminal and the second terminal to move the ferrous ball toward the first solenoid to an open position allowing fluid flow, and the second solenoid generates a second magnetic field in response to a control signal having a second polarity to move the ferrous ball toward the second solenoid to a closed position blocking coolant flow, the second polarity being opposite the first polarity.

Description

[Technical field]

[0001]

[0001] Superconducting magnets are used in systems requiring strong magnetic fields, such as magnetic resonance (MR) imaging and nuclear magnetic resonance (NMR) spectroscopy. Superconducting magnets contain one or more conductive magnet coils formed by superconducting wire. To achieve superconductivity, the magnet is maintained at a temperature near absolute zero in a cryogenic environment during operation. In the superconducting state, the magnet coils are called superconducting coils and have virtually no electrical resistance, thus conducting larger currents to generate strong magnetic fields for MR imaging. The operation of a superconducting magnet in the superconducting state is called persistent current mode. The persistent current mode is a state in which an electrical circuit (e.g., including a superconducting coil) can carry electrical current virtually indefinitely and without the need for an external power source due to the lack of electrical resistance. [Background technology]

[0002] To operate in persistent current mode, a superconducting magnet is first cooled to a superconducting state and then ramped to an operating current. Since current cannot simply be injected into the superconducting circuit due to the lack of electrical resistance, a portion of the superconducting circuit, called the magnet persistent current switch (PCS), is heated to create an electrical resistance, called the standard or resistive state. A voltage is then applied to the magnet PCS to inject current into the magnet coils. When a voltage is applied to the magnet PCS in its standard state, most of the current flows in the magnet coils, but a small amount of current flows in the now resistive wires of the magnet PCS. When heat is applied to the PCS to create a current flow through the PCS, the magnet PCS generates heat. The low temperature cooling system (cryostat) that cools the superconducting coils cannot accommodate the additional heat generated by the magnet PCS. Therefore, during ramping, the flow of coolant to the magnet PCS is interrupted, for example using a magnetically actuated valve, and the magnet PCS is thermally isolated from the cold material.

[0003]

[0003] A conventional magnetically actuated valve incorporates at least two actuator coils that can be pulled in either direction, and two pairs of electric wires to drive each of the two actuator coils, respectively. These electric wires must be fed into the cryostat and routed inside the superconducting magnet, which is problematic. For example, the electric wires are necessarily routed from the room temperature external environment into the supercooled magnet. Since the electric wires are good thermal conductors, the room temperature heat will pass through them into the cryostat, causing heat leakage. Therefore, reducing the number of electric wires will reduce the static heat load on the cryostat. Since the superconducting magnet must operate below the cryogenic temperature of, for example, 4 Kelvin (K), even the small amount of heat generated in the electric wires needs to be counteracted. Also, routing the electric wires inside the magnet is expensive and difficult; that is, the electric wires are shielded with reflective materials and fixed, for example, to the first stage of the cold head of the cooling system to keep the incoming heat load away. Also, the number of electric wires directly affects the number of connector pins. More electrical wires require more connector pins, reducing the limited number of available connector pins. Summary of the Invention [Problem to be solved by the invention]

[0004]

[0004] Therefore, there is a need for a cooling system that can flexibly and quickly raise / lower the temperature of the magnet PCS using fewer electrical wires so as not to put a strain on the cooling system of the superconducting coil. [Means for solving the problem]

[0005] According to an exemplary embodiment, a magnetic valve integrated with a fluid tube for controlling the flow of fluid through the fluid tube is provided. The magnetic valve includes a first diode and a first solenoid connected between a first terminal and a second terminal of the magnetic valve, a second diode and a second solenoid connected in parallel with the first diode and the first solenoid between the first terminal and the second terminal, the second diode being disposed in anti-parallel with the first diode, and a ferromagnetic ball moving between an open position that allows the flow of fluid through the loop tube and a closed position that blocks the flow of fluid through the loop tube. The first solenoid generates a first magnetic field in response to a control signal having a first polarity applied to the first and second terminals to move the ferrous ball toward the first solenoid to an open position, and the second solenoid generates a second magnetic field in response to a control signal having a second polarity applied to the first and second terminals to move the ferrous ball toward the second solenoid to a closed position, the second polarity being opposite to the first polarity of the control signal.

[0006] According to another representative embodiment, a magnetic resonance (MR) imaging system includes a superconducting magnet system for providing an MR magnetic field to enable MR imaging, a magnetic valve, and a control circuit. The superconducting magnet system includes a magnet coil for generating an MR magnetic field in a superconducting state, a magnet persistent current switch (PCS) for entering a standard state during ramping of the magnet coil to an operating current in the superconducting state, where the temperature of the magnet PCS increases in the standard state, and a cryostat for providing a cryogenic temperature to the magnet coil and the magnet PCS, the cryostat including a first loop tube for circulating a coolant at a cryogenic temperature through the magnet coil and a second loop tube for circulating a coolant at a cryogenic temperature through the magnet PCS. A magnetic valve is integrated with the second loop tube for selectively coupling and decoupling the magnet PCS from the second loop tube. The magnetic valve includes a first diode and a first solenoid connected between a first terminal and a second terminal, a second diode and a second solenoid connected in parallel with the first diode and the first solenoid between the first terminal and the second terminal, the second diode being arranged in anti-parallel with the first diode, and a ferromagnetic ball that moves between an open position and a closed position, where in the open position, coolant flow is permitted through the second loop tube in the magnet PCS to thermally couple the magnet PCS to the second loop tube, and in the closed position, coolant flow is blocked through the second loop tube in the magnet PCS to thermally decouple the magnet PCS from the second loop tube. The control circuit applies a control signal having a first polarity to the first terminal and the second terminal of the magnetic valve when the magnet PCS is in a closed state, and applies a control signal having a second polarity to the first terminal and the second terminal of the magnetic valve when the magnet PCS is in a normal state, the first polarity being opposite to the second polarity.The first solenoid generates a first magnetic field in response to a control signal having a first polarity to move the ferromagnetic ball toward the first solenoid to an open position allowing coolant flow to reduce a temperature of the magnet PCS, and the second solenoid generates a second magnetic field in response to a control signal having a second polarity to move the ferromagnetic ball toward the second solenoid to a closed position blocking coolant flow to prevent the magnet PCS from increasing the temperature of the coolant in the first loop tube.

[0007] According to another representative embodiment, a system for controlling a temperature of a magnet PCS operating in a superconducting magnet system is provided. The system includes a heat exchanger for dissipating heat to a cryocooler, a loop tube for allowing a flow of coolant to convectively transfer thermal energy generated by the magnet PCS and the magnet coil to the heat exchanger, a control circuit for generating a control signal having a first polarity and a second polarity opposite to the first polarity, a magnetic valve including a first diode and a first solenoid connected between a first terminal and a second terminal, a second diode and a second solenoid connected in parallel with the first diode and the first solenoid between the first terminal and the second terminal, the second diode being disposed in anti-parallel with the first diode, and a ferrous ball moving between an open position for allowing fluid flow through the loop tube and a closed position for blocking fluid flow through the loop tube. The first solenoid generates a first magnetic field in response to the control circuit applying a control signal having a first polarity to the first and second terminals to move the ferrous ball toward the first solenoid to an open position, and the second solenoid generates a second magnetic field in response to the control circuit applying a control signal having a second polarity to the first and second terminals to move the ferrous ball toward the second solenoid to a closed position. [Brief description of the drawings]

[0008]

[0008] Example embodiments are best understood when the following detailed description is read in conjunction with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, dimensions have been arbitrarily increased or decreased for clarity of discussion. Where applicable and practical, like reference numerals refer to like elements.

[0009] [Figure 1A] FIG. 1A is a simplified block diagram of a magnetic valve in an open position according to a representative embodiment. [Figure 1B]

[0010] FIG. 1B is a simplified block diagram of a magnetic valve in a closed position according to a representative embodiment. [Diagram 2]

[0011] FIG. 2 is a simplified circuit diagram of an H-bridge control circuit for a magnetic valve according to a representative embodiment. [Diagram 3]

[0012] FIG. 3 is a simplified block diagram of an MR imaging system including a superconducting magnet system incorporating a magnetic valve according to a representative embodiment. [Figure 4]

[0013] FIG. 4 is a simplified block diagram of a superconducting magnet system incorporating a magnetic valve according to a representative embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010]

[0014] In the following detailed description, for purposes of explanation and not limitation, representative embodiments disclosing specific details are described to provide a thorough understanding of the embodiments according to the present teachings. Descriptions of known systems, devices, materials, methods of operation, and methods of manufacture may be omitted so as not to obscure the description of the representative embodiments. However, systems, devices, materials, and methods within the purview of one of ordinary skill in the art are within the scope of the present teachings and may be used in accordance with the representative embodiments. It is to be understood that the terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting. Defined terms are to be given the technical and scientific meaning of the defined terms as commonly understood and accepted in the art of the present teachings.

[0011]

[0015] In this specification, terms such as "first," "second," and "third" are used to describe various elements or components, but it should be understood that these elements or components are not limited by these terms. These terms are used only to distinguish one element or component from another. Thus, a first element or component discussed below may be referred to as a second element or component without departing from the teachings of the inventive concept.

[0012]

[0016] The terms used herein are for the purpose of describing particular embodiments only and are not intended to be limiting. As used in this specification and the appended claims, singular terms are intended to include both the singular and the plural, unless the context clearly dictates otherwise. Additionally, as used herein, the terms "comprises," "comprising," and / or similar terms specify the presence of stated features, elements, and / or components, but do not exclude the presence or addition of one or more other features, elements, components, and / or groups thereof. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0013]

[0017] Unless otherwise noted, when an element or component is said to be "connected," "coupled," or "adjacent" to another element or component, it is understood that the element or component may be directly connected or coupled to the other element or component, or there may be intervening elements or components present. That is, these and similar terms encompass the cases where one or more intermediate elements or components may be used to connect the two elements or components. However, when an element or component is said to be "directly connected" to another element or component, this only encompasses the cases where the two elements or components are connected to each other without any intermediate or intervening elements or components.

[0014]

[0018] A "computer-readable storage medium" encompasses any tangible storage medium capable of storing instructions executable by a "processor" of a "computing system" or "controller." A computer-readable storage medium may also be referred to as a non-transitory computer-readable storage medium to distinguish it from a transitory medium such as a transitory propagating signal. A computer-readable storage medium may also be referred to as a tangible computer-readable medium. A "memory" is an example of a computer-readable storage medium. Examples of memory include, but are not limited to, RAM memory, registers, and register files.

[0015]

[0019] In some embodiments, the computer-readable storage medium may also store data that can be accessed by the processor of the computing system. The computer-readable storage medium may be implemented as any number, type, and combination of random access memory (RAM) and read-only memory (ROM), etc., and may store various types of information, such as software algorithms, artificial intelligence (AI) machine learning models, and computer programs, all of which are executed by the processor, as described below. The various types of ROM and RAM may include any number, type, and combination of non-transitory computer-readable storage media, such as disk drives, flash memory, electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, removable disks, tapes, compact disk read-only memory (CD-ROM), digital versatile disk (DVD), floppy disk, Blu-ray disk, universal serial bus (USB) drive, optical disk, magneto-optical disk, or any other form of storage medium known in the art. As used herein, the term "non-transitory" is to be interpreted as a characteristic of a state that persists for a period of time, rather than a permanent characteristic of a state. The term "non-transient" specifically negates momentary properties such as those of a carrier wave or signal or other type of property that exists only temporarily at any time and in any place.

[0016]

[0020] The term "computer-readable storage medium" also refers to various types of storage media that can be accessed by a computer system or controller via a network or communication link. For example, data is obtained via a modem, the Internet, or a local area network. Reference to a computer-readable storage medium should be interpreted as possibly being multiple computer-readable storage media. Various executable components of one or more programs may be stored in different locations. A computer-readable storage medium may be multiple computer-readable storage media, for example, within the same computer system. A computer-readable storage medium may also be a computer-readable storage medium distributed across multiple computer systems.

[0017]

[0021] As used herein, a "processor" encompasses electronic components capable of executing software, programs, and / or machine-executable instructions, e.g., stored in memory and / or computer-readable media. References to a "computing system," "controller," or "control circuitry" including a "processor" should be interpreted to include one or more processors and / or processing cores. A processor is implemented using hardware, software, firmware, hardwired logic circuitry, or a combination thereof, by a general purpose computer, a central processing unit, a computer processor, a microprocessor, a microcontroller, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), a state machine, a programmable logic device, or a combination thereof. For example, a processor may be a multi-core processor. A processor may also refer to a collection of processors within a single computer system or a collection of processors distributed across multiple computer systems. The term "computing system" also refers to a collection or network of computing devices, each possibly including one or more processors. Many programs have instructions executed by multiple processors, either within the same computing system or controller, or distributed among multiple computing devices or controllers. A processor may refer to a collection of processors within a single computer system, or a collection of processors distributed across multiple computer systems, such as in a cloud-based or other multi-site application.

[0018]

[0022] A "user interface" or "user input device" as used herein is an interface that allows a user to interact with a computer system, controller, and / or control circuitry. A user interface can provide information or data to a user or receive information or data from a user. A user interface can be used to receive input from a user at a computer, controller, and / or control circuitry and provide output from the computer, controller, and / or control circuitry to a user. That is, a user interface can be used to allow a user to control or operate a computer, controller, and / or control circuitry or to allow a computer, controller, and / or control circuitry to indicate the effect of a user's control or operation. Displaying data or information on a display or graphical user interface is an example of providing information to a user. User input devices of a user interface include, for example, one or more of a touch screen, keyboard, mouse, trackball, touchpad, pointing stick, graphics tablet, joystick, gamepad, webcam, headset, gear stick, steering wheel, wired gloves, wireless remote control, and accelerometer, all of which allow for receiving information or data from a user.

[0019]

[0023] A "hardware interface" encompasses an interface that allows a processor of a computer system or controller to interact with or control external devices and / or equipment. A hardware interface may be used to allow a processor to send control signals or instructions to, for example, an external computing system and / or equipment. A hardware interface may also be used to allow a processor to exchange data with an external computer system or controller. Examples of hardware interfaces include, but are not limited to, a universal serial bus, an IEEE 1394 port, a parallel port, an IEEE 1284 port, a serial port, an RS-232 port, an IEEE-488 port, a Bluetooth® connection, a wireless local area network connection, a TCP / IP connection, an Ethernet connection, a control voltage interface, a MID interface, an analog input interface, and a digital input interface.

[0020]

[0024] In view of the foregoing, the present disclosure is directed to providing one or more of the advantages specifically set forth below through one or more of its various aspects, embodiments, and / or specific features or subcomponents. For purposes of explanation and not limitation, example embodiments disclosing specific details are described to provide a thorough understanding of the embodiments according to the present teachings. However, other embodiments consistent with the present disclosure that depart from the specific details disclosed herein remain within the scope of the appended claims. Furthermore, descriptions of well-known devices and methods may be omitted so as not to obscure the description of the example embodiments. Such methods and devices are within the scope of the present disclosure.

[0021]

[0025] A system for controlling the temperature of a magnet persistent current switch (PCS) allows for efficient cooling of the magnet PCS separately from the cooling of the superconducting magnet coils. The cooling system (such as a cryostat) can provide cryogenic temperatures to the superconducting magnet coils in, for example, a superconducting magnet. The cooling system has a first part (first stage of the cold head) operating at, for example, 40K and a second part (second stage of the cold head) operating at 4K. Generally, embodiments described herein are directed to a magnetic valve that thermally isolates the magnet PCS from the second part of the cooling system during energization (ramping) of the superconducting magnet coils, such as, for example, an MR imaging magnet. The thermal isolation from the second part of the cooling system is necessary to ensure that heat from the magnet PCS does not overwhelm the cooling system that maintains the low temperature of the superconducting magnet coils. The magnetic valve is used in low-cryogenic temperature superconducting magnets where a relatively small helium volume is used to cool the superconducting magnet by convective helium flow as opposed to, for example, conventional conduction cooling of the magnet in a helium bath.

[0022]

[0026] As described above, the magnetic valve prevents excess heat generated by the magnet PCS when ramping the superconducting magnet from overloading the cryostat for cooling the superconducting magnet coils. Additionally, the magnetic valve allows the magnet PCS to maintain the same temperature as the superconducting magnet coils when the superconducting magnet is operating in persistent current mode. Thus, various embodiments provide a temperature control system that can freely raise or lower the temperature of the magnet PCS without burdening the cryostat for cooling the superconducting magnet coils.

[0023]

[0027] Additionally, operation of embodiments of the magnetic valve requires only two electrical wires, instead of at least four for conventional valves. This reduces the amount of heat entering the superconducting magnet due to heat leakage from the room temperature ends of the electrical wires. Also, the valve is operated between open and closed positions by simply changing the polarity of a control signal. Additional advantages over conventional valves include reduced connector pin count, reduced electrical wiring for the superconducting magnet, and reduced wiring complexity.

[0024]

[0028] 1A and 1B are simplified block diagrams of a magnetic valve in open and closed positions according to a representative embodiment, the magnetic valve shown in Fig. 1A and 1B may be used in a superconducting magnet system to control coolant flow, for example, as described below with reference to Fig. 3.

[0025]

[0029] 1A and 1B, a magnetic valve 100 is shown integrated with a fluid tube 116 to control the flow of fluid through the tube 116. The fluid within the tube 116 can be a liquid or a gas, such as liquid or gaseous helium.

[0026]

[0030] The magnetic valve 100 includes a housing 105 containing a ferromagnetic ball 108 and two electromagnets, indicated as a first solenoid 114 and a second solenoid 124, located outside a tube 116. Although the magnetic valve 100 is described as including a first solenoid 114 and a second solenoid 124, it is understood that other types of electromagnets may be incorporated without departing from the scope of the present teachings. The first solenoid 114 and the second solenoid 124 are disposed on opposite sides of the tube 116 to control the movement of the ferromagnetic ball 108 within the housing 105 in response to the first solenoid 114 and the second solenoid 124 being selectively energized. The ferromagnetic ball 108 has a diameter larger than an inner diameter of at least a portion of the tube 116 and moves between an open position that allows fluid flow through the tube 116 (indicated by the dashed arrow) and a closed position that blocks fluid flow through the tube 116.

[0027]

[0031] In the illustrated configuration, the ferromagnetic ball 108 moves to an open position in response to the first solenoid 114 being energized, as indicated by the dashed upward arrow in FIG. 1A, and the ferromagnetic ball 108 moves to a closed position in response to the second solenoid 124 being energized, as indicated by the downward arrow in FIG. 1B. In the closed position, the ferromagnetic ball 108 rests on a convex seat 109 or the like to hold the ferromagnetic ball 108 in place. The tube 116 may be made of a non-magnetic metal, such as copper, aluminum, titanium, zinc, tin, or lead, or other non-magnetic material. The ferromagnetic ball 108 may be made of any suitable ferromagnetic material, such as iron, nickel, or cobalt.

[0028]

[0032] In the illustrated embodiment, the magnetic valve 100 is bistable, i.e., when the ferromagnetic ball 108 moves to either the open or closed position, the first solenoid 114 and the second solenoid 124 are de-energized and the ferromagnetic ball 108 rests in place (e.g., by gravity) on the convex seat 109.

[0029]

[0033] The magnetic valve 100 further includes a first circuit path 110 and a second circuit path 120, the first circuit path 110 and the second circuit path 120 being connected in parallel with each other. The first circuit path 110 includes a first diode 112 and a first solenoid 114 connected in series across terminals A and B, and the second circuit path 120 includes a second diode 122 and a second solenoid 124 also connected in series across terminals A and B. A control circuit 140 for the magnetic valve 100 applies a voltage between terminals A and B as a control signal to selectively energize the first solenoid 114 and the second solenoid 124 to position the ferromagnetic ball 108, as described below. For example, the control signal has a current of about 100 mA to about 10 A.

[0030]

[0034] In particular, the magnetic valve 100 operates with only two terminals, terminal A and terminal B. In contrast, conventional magnetic valves have at least four terminals, i.e., two terminals for operating each of a plurality of electromagnets. As discussed above, this requires at least twice the amount of electrical wiring required through the system of which the magnetic valve is a part. Thus, stated another way, the illustrated embodiment reduces the amount of wiring by at least half. This not only simplifies the design and reduces costs, but also reduces the amount of heat leakage into the system of which the magnetic valve 100 is a part (e.g., a superconducting magnet) through the wires connected to each terminal.

[0031]

[0035] The second diode 122 is arranged in anti-parallel with the first diode 112, meaning that they allow current to flow in the opposite directions. That is, in the configuration shown, the first diode 112 has an anode connected to terminal A and a cathode connected to the first solenoid 114, such that current flows only from terminal A through the first solenoid 114 to terminal B, thereby energizing the first solenoid 114 (generating a first magnetic field) and de-energizing the second solenoid 124. The second diode 122 has an anode connected to terminal B and a cathode connected to the second solenoid 124, such that current flows only from terminal B through the second solenoid 124 to terminal A, thereby energizing the second solenoid 124 (generating a second magnetic field) and de-energizing the first solenoid 114.

[0032]

[0036] Whether the current flows through the first diode 112 or the second diode 122 depends on the polarity of the control signal output by the control circuit 140. In the illustrated configuration, when the control circuit 140 outputs a control signal of a first polarity 141 (e.g., applying a positive (+) to terminal A and a negative (-) to terminal B), current flows through the first diode 112 and the first solenoid 114, generating a first magnetic field in response to the control signal. This causes the ferromagnetic ball 108 to move toward the first solenoid 114 to the open position shown in FIG. 1A. Because the second diode 122 is arranged in anti-parallel with the first diode 112, no current flows through the second solenoid 124, and therefore it remains in a non-conductive state. When the control circuit 140 outputs a control signal of a second polarity 142 (e.g., applying a positive (+) to terminal B and a negative (-) to terminal A), current flows through the second diode 122 and the second solenoid 124 to generate a second magnetic field in response to the control signal. This causes the ferromagnetic ball 108 to move toward the second solenoid 124 to the closed position shown in FIG. 1B. Because the first diode 112 is arranged in anti-parallel with the second diode 122, no current flows through the first solenoid 114, and therefore it remains in a non-conductive state. Thus, the magnetic valve 100 operates between an open position and a closed position based on the polarity of the control signal provided by the control circuit 140.

[0033]

[0037] As mentioned above, because the magnetic valve 100 is bistable, both the first solenoid 114 and the second solenoid 124 become de-energized following a change in position of the ferromagnetic ball 108. In another configuration, one of the first solenoid 114 and the second solenoid 124 may remain energized to hold the ferromagnetic ball 108 in place without departing from the scope of the present teachings.

[0034]

[0038] The control circuit 140 can be implemented with any circuit capable of changing the polarity of an output signal. For example, the control circuit 140 is an H-bridge. However, any suitable circuit for changing polarity can be incorporated without departing from the scope of the present teachings.

[0035]

[0039] FIG. 2 is a simplified circuit diagram of an H-bridge control circuit for a magnetic valve according to a representative embodiment.

[0036]

[0040] 2, the control circuit 140A includes an exemplary H-bridge circuit. In particular, the control circuit 140A includes a first transistor 211 and a second transistor 212 connected between a positive voltage V+ and a negative voltage V- (e.g., common or ground), and a third transistor 213 and a fourth transistor 214 also connected between the positive voltage V+ and the negative voltage V-. Each of the first through fourth transistors 211-214 is represented as a metal oxide silicon field effect transistor (MOSFET), but it is understood that they may be any type of compatible FET or other types of transistors, such as bipolar junction transistors (BJT), without departing from the scope of the present teachings. A flyback diode is connected between the source and drain of each of the first through fourth transistors 211-214. That is, a first diode 221 is connected between the source and drain of the first transistor 211, a second diode 222 is connected between the source and drain of the second transistor 212, a third diode 223 is connected between the source and drain of the third transistor 213, and a fourth diode 224 is connected between the source and drain of the fourth transistor 214. To control the states of the transistors, the gates of the first transistor 211, the second transistor 212, the third transistor 213, and the fourth transistor 214 are respectively connected to a first control signal CS1, a second control signal CS2, a third control signal CS3, and a fourth control signal CS4. The first control signal CS1 to the fourth control signal CS4 are provided by a control logic, for example, from a state machine realized by a controller (not shown), such as a microcontroller, a field programmable gate array (FPGA), an erasable programmable logic device (EPLD), and / or an application specific integrated circuit (ASIC), as will be apparent to those skilled in the art.

[0037]

[0041] The control circuit 140A is connected to terminal A of the magnetic valve 100 between the first transistor 211 and the fourth transistor 214, and to terminal B of the magnetic valve 100 between the second transistor 212 and the third transistor 213. Changing the polarity of the control signal at terminals A and B is achieved by turning on / off different pairs of transistors. For example, in the illustrated configuration, the first polarity 141 is output by turning on the first transistor 211 and the third transistor 213 and turning off the second transistor 212 and the fourth transistor 214. The second polarity 142 is output by turning on the second transistor 212 and the fourth transistor 214 and turning off the first transistor 211 and the third transistor 213.

[0038]

[0042] Due to the reduced number of terminals (terminals A and B) and therefore the corresponding reduction in the number of electrical wires required to operate the magnet valve 100, the magnet valve 100 is useful in systems that require very low operating temperatures (e.g. cryogenic temperatures) since fewer electrical wires result in less heat leakage, other factors being equal. For example, as mentioned above, a superconducting magnet system is required to maintain a cryogenic temperature of about 4K in the superconducting state. Such a superconducting magnet system is incorporated into a magnetic resonance (MR) imaging system, an example of which is described with reference to Figs. 3 and 4. When the magnet valve 100 is implemented in such an MR imaging system, electrical wires conducting high (room) temperatures are threaded through the superconducting magnet. Therefore, fewer electrical wires are better.

[0039]

[0043] 3 is a simplified block diagram of an MR imaging system including a superconducting magnet system incorporating a magnetic valve according to a representative embodiment. The following description of the MR imaging system is intended to be illustrative and not limiting.

[0040]

[0044] 3, the MR imaging system 300 includes a superconducting magnet system 310 including a superconducting magnet 312 with a bore 313. The superconducting magnet 312 may be, for example, a cylindrical magnet, but may incorporate different types of superconducting magnets, such as a split cylindrical magnet or an open magnet, without departing from the scope of the present teachings. The bore 313 is provided with an imaging zone 314, in which the magnetic field generated by the operation of the superconducting magnet 312 is strong and uniform enough to perform magnetic resonance imaging. The subject 301 is placed on a support 303 and positioned within the bore 313 to be imaged during an MR imaging procedure. The support 303 is attached to an actuator 304 (optional) that moves the support 303 so that the subject 301 is moved within the imaging zone 314. Thus, a larger portion of the subject 301 or the entire subject 301 can be imaged.

[0041]

[0045] The superconducting magnet 312 includes a set of magnet coils 316, which may be magnetic field gradient coils for acquiring magnetic resonance data for spatially encoding magnetic spins in the imaging zone 314. In the illustrated embodiment, the magnet coils 316 are similarly cylindrical and are therefore shown above and below the bore 313 in a cross-sectional format. A magnet coil power supply 318 provides current to the magnet coils 316. The current from the power supply 318 is controlled as a function of time, e.g., ramped or pulsed. It is to be understood that the superconducting magnet 312 may include one or more magnet coils 316 in various implementations, such as to enable spatial encoding in three orthogonal spatial directions, without departing from the scope of the present teachings.

[0042]

[0046] To operate in persistent current mode, the superconducting magnet 312 includes a closed superconducting circuit with a superconducting loop. The superconducting circuit is broken to allow a power supply 318 to drive a current to the magnet coils 316. This is sometimes referred to as ramping the superconducting magnet 312 (or the magnet coils 316) to an operating at-field state. To this end, the superconducting magnet 312 further includes a magnet persistent current switch (PCS) 320 operable to break the superconducting circuit to ramp the superconducting magnet 312. To reach a cryogenic temperature, the superconducting magnet 312 including the magnet PCS 320 is cooled by a cryostat 410 including a convection cooling loop 411 for circulating a coolant, as described below with reference to FIG. 4.

[0043]

[0047] The magnet PCS 320 is heated by a PCS heater (not shown) to a resistance state referred to as the standard state. In the standard state, the magnet PCS 320 still has a relatively small electrical resistance, which is substantially open compared to the lack of resistance of the superconducting magnet 312 in the superconducting state. Only when the magnet PCS 320 is in the standard state can a voltage be developed across it to allow current to flow in the magnet coil 316. The electrical resistance of the magnet PCS 320 in the standard state, together with the heat added to bring the magnet PCS 320 to the standard state, increases the temperature of the magnet PCS 320 during the ramping process. To prevent this increased temperature from being transferred to the magnet coil 316 via the coolant circulating in the convection cooling loop 411, the magnetic valve 100 is disposed with the magnet PCS 320 and, under the control of the control circuit 140, removes (thermally disconnects) the magnet PCS 320 from the convection cooling loop 411 during the ramping process.

[0044]

[0048] The MR imaging system 300 further includes an RF coil 317 located within the bore 313. The RF coil 317 manipulates the orientation of magnetic spins within the imaging zone 314 and receives RF transmissions from spins within the imaging zone 314. The RF coil 317 may represent a dedicated transmit and receive antenna or may include multiple transmit and receive coil elements. The RF coil 317 is shown connected to an RF transceiver 319. The RF transceiver 319 transmits and receives RF signals to and from the RF coil 317 during an MR imaging procedure. In various configurations, the RF coil 317 and the RF transceiver 319 may be replaced by separate transmit and receive coils, separate transmitters and receivers, etc.

[0045]

[0049] The actuator 304, power supply 318, and RF transceiver 319 are connected to a hardware interface 331 and a controller 330. The controller 330 includes a processor 334, a memory 336, and a user interface 338. The memory 336 represents one or more of the non-transitory memories and / or computer-readable storage media described above. The memory 336 stores pulse sequence instructions that are executed by the processor 334 to perform an MR imaging procedure, as will be apparent to one of ordinary skill in the art. The memory 336 may also include data storage for storing magnetic resonance image data and / or reconstructed magnetic resonance images acquired during an MR imaging procedure.

[0046]

[0050] Hardware interface 331 allows controller 330 to interact with, control, and / or exchange data with at least actuator 304, power source 318, and RF transceiver 319. Processor 334 is representative of one or more of the processors discussed above. User interface 338 allows a user to interact with controller 330 and receives input from the user that is received by processor 334 and provides output from processor 334 to the user. That is, user interface 338 can provide information or data to and receive information or data from a user, as discussed above.

[0047]

[0051] FIG. 4 is a simplified block diagram of a superconducting magnet system incorporating a magnetic valve according to a representative embodiment.

[0048]

[0051] Referring to Figure 4, a portion of a superconducting magnet system 310 is shown, including a magnet coil 316, a magnet PCS 320 connected in parallel with the magnet coil 316, and a power supply 318 (shown as a current source for illustration purposes). The magnet coil 316 and the magnet PCS 320 are in a cryostat 410 of the superconducting magnet system 310 to limit temperature. That is, the magnet coil 316 and the magnet PCS 320 are maintained at a low temperature by a cryocooler 412 in (attached to) the cryostat 410. The cryocooler 412 has a first stage 413 that maintains the temperature of a thermal shield (not shown) that encases the magnet coil 316 and the magnet PCS 320 at about 40K, and a second stage 414 that maintains the temperature of the magnet coil 316 and the magnet PCS 320 (closed state) at about 4K. A portion of the cryocooler 412 is accessible from outside the cryostat 410. A power supply 318 is permanently or temporarily connected to electrical contacts on the outside of the cryostat 410 .

[0049]

[0052] The cryostat 410 includes a convection cooling loop 411, which includes a heat exchanger 418 and a first loop tube 415 and a second loop tube 416. The first loop tube 415 and the second loop tube 416 carry a coolant, such as liquid or gaseous helium, at a temperature of about 4K. The first loop tube 415 passes through the magnet coil 316 to cool the magnet coil 316 to a superconducting state. The second loop tube 416 is substantially similar to the tube 116 described above, and passes through the magnet PCS 320 and the magnetic valve 100. The heat exchanger 418 is permanently connected to or in thermal contact with the second stage 414 of the cryocooler 412 and distributes heat to the cryocooler 412. The cryostat 410 may include another convection cooling loop (not shown) including another loop tube and another heat exchanger, which is permanently connected or in thermal contact with the first stage 413 of the cryocooler 412 for carrying a coolant at the aforementioned temperature of about 40K. The other convection cooling loop is typically more robust than the convection cooling loop 411 and thus is responsible for the majority of the cooling of the superconducting magnet system 310 to the superconducting temperature, as will be apparent to those skilled in the art. This convection cooling loop does not need to be thermally isolated from the 40K convection cooling loop during ramping, since it handles the elevated temperature of the magnetic valve 100.

[0050]

[0053] The controller 330 is implemented by 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 330 controls the power supply 318 and the state of the magnet PCS 320 via signals indicated by dashed lines to, for example, enable ramping of the magnet coils 316, place the superconducting magnet 312 in persistent current mode, and ramp down the superconducting magnet 312 in response to user-issued commands.

[0051]

[0054] The control circuit 140 controls the operation of the magnetic valve 100 to control the temperature of the magnet PCS 320 by selectively blocking and enabling the flow of coolant (e.g., gaseous helium or liquid helium) through the second loop tube 416. The control circuit 140 is connected to the magnetic valve 100 through a pair of electrical wires, shown as electrical wires 143 and 144, which run through the cryostat 410. Because there are only two electrical wires 143 and 144, there is less heat leakage through the electrical wires 143 and 144 compared to conventional systems that require multiple pairs of electrical wires as discussed above. Thus, the two electrical wires 143 and 144 have less impact on the temperature of the cryostat 410. It is to be understood that the functionality of the control circuit 140 may be incorporated into the controller 330 or implemented separately from the controller 330 without departing from the scope of the present teachings.

[0052]

[0055] More specifically, the controller 330 controls the magnet PCS 320 to selectively enter a normal state for ramping the superconducting magnet 312 to the operating current and to selectively enter a closed state for maintaining the operating current (in persistent current mode). The magnet PCS 320 includes a composite superconducting wire made of superconducting filaments in a copper matrix, similar to the superconducting wire used in the magnet coils 316. As described above, in one embodiment, the magnet PCS 320 is one of the magnet coils 316. 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 magnet PCS 320 is in the closed (superconducting) state, the magnet current can flow while the superconducting magnet system 310 is in persistent current mode. When the magnet PCS 320 is in the normal state, the magnet current cannot flow and it is controlled to break the superconducting circuit. The magnet PCS 320 can be switched to the standard state by, for example, heating it using a PCS heater (not shown). However, as described above, in the standard state, the magnet PCS 320 has a small (standard) resistance that is high enough to allow a ramping voltage to be applied across the magnet PCS 320 to ramp the magnet coil 316 to an operating current. When the magnet PCS 320 transitions from the closed state to the standard state, an operating current flows through the magnet coil 316 and the PCS 320.

[0053]

[0056] Further, the control circuit 140 controls the magnetic valve 100 to open or close depending on, for example, the operation requested by the user. For example, when the magnet PCS 320 is in the normal state where the superconducting magnet 312 is ramping up to the operating current of the superconducting state, the magnetic valve 100 closes to stop the flow of coolant through the second loop tube 416 and thermally isolates the magnet PCS 320 from the heat exchanger 418. As described above, the magnet PCS 320 heats up to enter the normal state and generates heat by conducting some current in the normal state without overloading the second stage 414 of the cryocooler 412. That is, by stopping the flow of coolant through the magnet PCS 320, the increased temperature of the magnet PCS 320 does not increase the temperature of the coolant in the second loop tube 416 and the heat exchanger 418 does not need to remove this additional heat to maintain the temperature of 4K. When the magnet PCS 320 is closed to operate the superconducting magnet 312 in a persistent current mode or to ramp down the superconducting magnet 312, the magnetic valve 100 is opened to allow the flow of coolant from the second loop 416 through the magnet PCS 320, thermally connecting the magnet PCS 320 to the heat exchanger 418 via the second loop tube 416 to provide additional cooling to ensure that the magnet PCS 320 remains in a superconducting state.

[0054]

[0057] In one embodiment, the control circuit 140 sends a control signal having different polarities to open and close the magnet valve 100, as described above. When the control signal has a first polarity 141, it passes through the first diode 112 and the first solenoid 114, and energizes the first solenoid 114. The energized first solenoid 114 generates a first magnetic field that attracts the ferromagnetic ball 108 to the first solenoid 114, opens the magnet valve 100, and allows the coolant in the second loop tube 416 to flow through the magnet PCS 320. When the control signal has a second polarity 142, it passes through the second diode 122 and the second solenoid 124, and energizes the second solenoid 124. The energized second solenoid 124 generates a second magnetic field that attracts the ferromagnetic ball 108 to the second solenoid 124, closes the magnet valve 100 so that coolant in the second loop tube 416 does not flow through the magnet PCS 320, and thermally isolates the magnet PCS 320 from the second loop tube 416 and the heat exchanger 418.

[0055]

[0058] The second stage 414 of the cryocooler 412 has limited power absorption capacity but can bring the magnet coil 316 and the magnet PCS 320 to the desired cryogenic temperature of about 4K. Thus, the heat coming from the magnet PCS 320 in normal conditions would otherwise overload the cryocooler 412. As mentioned above, when the power supply 318 is connected across the magnet PCS 320 in normal conditions, most of the current flows through the magnet coil 316 and some current flows through the normal resistive wire of the magnet PCS 320. When the current through the superconducting magnet coil 316 reaches a target value (target current), the controller 330 controls the magnet PCS 320 to enter a closed state, such as by turning off the PCS heater, to allow the magnet PCS 320 to conduct the operating current after ramping down the power supply 318 while the magnet coil 316 operates in a substantially zero resistance persistent current mode. This is called a closed superconducting circuit.

[0056]

[0059] As described above with respect to tube 116, second loop tube 416 (and first loop tube 415) may be made of a non-magnetic metal, such as copper, aluminum, titanium, zinc, tin, or lead, or other non-magnetic material. Second loop tube 416 is sealed, and the coolant contained therein may be helium gas or helium liquid, for example, to allow for convective transfer of thermal energy between magnet PCS 320 and heat exchanger 418. Other types of gas and / or liquid coolants may be incorporated without departing from the scope of the present teachings. Magnetic valve 100 opens and closes second loop tube 416 to selectively enable or block the flow of coolant. When magnetic switch 100 is open, coolant flows through second loop tube 416, magnet PCS 320, and heat exchanger 418 to dissipate generated heat. When magnetic valve 100 is closed, the flow of coolant through second loop tube 416 is blocked. In various embodiments, the magnetic valve 100 is implemented using a ball valve including a ferromagnetic ball 108 having a diameter larger than the inner diameter of the opening of the second loop tube 416. The first solenoid (electromagnet) 114 and the second solenoid (electromagnet) 124 control the placement of the ferromagnetic ball 108 within the opening of the second loop tube 416 or other orifice in the ball valve to selectively block the second loop tube 416 by activating and deactivating the magnetic field based on the polarity of the control signal, as described above.

[0057]

[0060] In one embodiment, the superconducting magnet system 310 includes an additional magnetic valve (not shown) integrated with the second loop tube 416 between the magnet PCS 320 and the heat exchanger 418. The additional magnetic valve is positioned in the return portion of the second loop tube 416, such that the additional magnetic valve selectively blocks the flow of coolant through the second loop tube 416 when ramping the superconducting magnet 312, for example, as described above with respect to the magnetic valve 100. The magnetic valve 100 and the additional magnetic valve can be operated substantially simultaneously, which increases the efficiency of the convection cooling loop 411, since the possibility of convection between the magnet PCS 320 and the heat exchanger 418 within only one of the two legs of the second cooling tube 416 is eliminated. Also, the reliability of the system with two redundant magnetic valves is improved, since costly and time-consuming repairs are avoided if the magnetic valve 100 fails.

[0058]

[0061] Although the system for controlling the temperature of a persistent current switch has been described with reference to several exemplary embodiments, it is to be understood that the words used herein are words of description and illustration, rather than words of limitation. Changes may be made within the scope of the appended claims, as currently presented and as amended, without departing from the scope and spirit of the system for controlling the temperature of a persistent current switch in its aspects. Although the system for controlling the temperature of a persistent current switch has been described with reference to specific means, materials, and embodiments, the system for controlling the temperature of a persistent current switch is not intended to be limited to the disclosed particulars, but rather the system for controlling the temperature of a persistent current switch extends to all functionally equivalent structures, methods, and uses within the scope of the appended claims.

[0059]

[0062] Although components and functions that may be implemented in particular embodiments are described herein with reference to particular standards and protocols, the disclosure is not limited to such standards and protocols. Such standards are periodically superseded by more efficient equivalents having essentially the same functions. Accordingly, substitute standards and protocols having the same or similar functions are considered equivalents.

[0060]

[0063] The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of various embodiments. The illustrations do not completely describe all elements and features of the disclosure described herein. Many other embodiments will be apparent to those skilled in the art upon review of the present disclosure. Other embodiments can be utilized and derived from the present disclosure, such as structural and logical substitutions and changes can be made without departing from the scope of the present disclosure. Moreover, the illustrations are merely representative and may not be to scale. Certain proportions in the illustrations may be exaggerated and other proportions may be minimized. Thus, the present disclosure and the figures should be considered illustrative and not restrictive.

[0061]

[0064] One or more embodiments of the present disclosure may be referred to herein, individually and / or collectively, by the term "invention", for convenience only and without any intention to spontaneously limit the scope of the present application to any particular invention or inventive concept. Also, although specific embodiments are illustrated and described herein, it should be understood that subsequent arrangements designed to achieve the same or similar purpose may be substituted for the specific embodiment shown. The present disclosure is intended to cover any and all subsequent adaptations or variations of the various embodiments. Combinations of the above embodiments with other embodiments not specifically described herein will be apparent to one of ordinary skill in the art upon review of the description.

[0062]

[0065] The Abstract of the Disclosure is provided to comply with 37 CFR Rule 1.72(b) and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, the above Detailed Description may group or describe various features in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all features of any of the disclosed embodiments. Accordingly, the following claims are incorporated into the Detailed Description, with each claim standing on its own as defining separate claimed subject matter.

[0063]

[0066] The foregoing description of the disclosed embodiments is provided to enable any person skilled in the art to practice the concepts described in the present disclosure. Therefore, the above disclosed subject matter is considered to be illustrative and not restrictive. Moreover, the appended claims are intended to cover all such modifications, enhancements, and other implementations that fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent permitted by law, the scope of the present disclosure shall be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be limited or restricted by the foregoing detailed description.

Claims

1. A magnetic valve integrated with a tube, for controlling the flow of fluid through the tube, A first diode and a first solenoid are connected between the first terminal and the second terminal, A second diode and a second solenoid are connected in parallel with the first diode and the first solenoid between the first terminal and the second terminal, wherein the second diode is arranged in antiparallel to the first diode. A ferromagnetic ball moves between an open position that allows the fluid to flow through the tube and a closed position that blocks the fluid flow through the tube. Equipped with, The first solenoid, in response to a control signal having a first polarity being applied to the first and second terminals, generates a first magnetic field to move the ferromagnetic ball toward the first solenoid so that it is in the open position. The second solenoid, in response to a control signal having a second polarity being applied to the first and second terminals, generates a second magnetic field to move the ferromagnetic ball toward the second solenoid so that it is in the closed position. A magnetic valve in which the second polarity is opposite to the first polarity of the control signal.

2. The magnetic valve according to claim 1, wherein the fluid comprises liquid helium or gaseous helium.

3. The magnetic valve according to claim 1, wherein each of the control signals has a current of about 100 mA to about 10 A.

4. The magnetic valve according to claim 1, wherein the tube comprises at least one of copper, aluminum, titanium, zinc, tin, or lead, and the ferromagnetic ball comprises at least one of iron, nickel, or cobalt.

5. The magnetic valve according to claim 1, further comprising a seat disposed within the tube, wherein the ferromagnetic ball is positioned on the seat when in the closed position, and so the ferromagnetic ball is properly held on the seat by gravity when the second solenoid stops generating the second magnetic field.

6. (i) A superconducting magnet system that provides a magnetic resonance field to enable magnetic resonance imaging, Multiple magnet coils that generate the MR magnetic field in a superconducting state, A magnet permanent current switch configured to enter a standard state while ramping the plurality of magnet coils up to the operating current of the superconducting state, wherein the temperature of the magnet permanent current switch rises in the standard state, A superconducting magnet system comprising a cryostat that provides cryogenic temperatures to the plurality of magnet coils and the magnet permanent current switch, the cryostat including a first loop tube for circulating a coolant at the cryogenic temperature through the plurality of magnet coils and a second loop tube for circulating the coolant at the cryogenic temperature through the magnet permanent current switch, (ii) A magnetic valve according to any one of claims 1 to 5, which is integrated with the second loop tube, wherein the magnetic permanent current switch selectively couples with and selectively disconnects from the second loop tube, In the open position of the magnetic valve, the flow of the coolant through the second loop tube in the magnetic permanent current switch is permitted in order to thermally couple the magnetic permanent current switch to the second loop tube, and in the closed position of the magnetic valve, the flow of the coolant through the second loop tube in the magnetic permanent current switch is blocked in order to thermally disconnect the magnetic permanent current switch from the second loop tube. (iii) A control circuit that applies a control signal having a first polarity to the first terminal and the second terminal of the magnetic valve when the magnetic permanent current switch is closed, and applies a control signal having a second polarity to the first terminal and the second terminal of the magnetic valve when the magnetic permanent current switch is in the standard state, wherein the first polarity is the opposite of the second polarity, A magnetic resonance (MR) imaging system comprising, In the open position, the ferromagnetic ball of the magnetic valve allows the flow of the coolant to lower the temperature of the magnetic permanent current switch. A magnetic resonance imaging system in which the ferromagnetic ball of the magnetic valve in the closed position blocks the flow of the coolant so that the magnetic permanent current switch does not raise the temperature of the coolant in the first loop tube.

7. The magnetic resonance imaging system according to claim 6, wherein the control circuit includes an H-bridge that provides a first drive signal and a second drive signal having opposite polarities.

8. The magnetic resonance imaging system according to claim 6, wherein the magnetic permanent current switch includes one magnetic coil among the plurality of magnetic coils.

9. The magnetic resonance imaging system according to claim 6, wherein the loop tube circulates the coolant at a coolant temperature of approximately 4K.

10. The magnetic resonance imaging system according to claim 9, wherein the cryostat further includes another loop tube for circulating additional coolant through the plurality of magnet coils and the magnet permanent current switch at a coolant temperature of approximately 40 K, the other loop tube not being integrated with the magnetic valve, so that the other loop tube continues to remove heat from the magnet permanent current switch via the additional coolant during ramping of the plurality of magnet coils up to the operating current.

11. The magnetic resonance imaging system according to claim 6, wherein the ferromagnetic ball is positioned on a convex seat when in the closed position, and so that when the second solenoid is controlled to stop generating the second magnetic field, the ferromagnetic ball is properly held on the convex seat by gravity.

12. The magnetic resonance imaging system according to claim 6, further comprising a permanent current switch heater for heating the magnet permanent current switch to bring the magnet permanent current switch into the standard state, wherein the superconducting magnet system further includes a permanent current switch heater.

13. A system for controlling the temperature of a magnetic persistent current switch operating in a superconducting magnet system, A heat exchanger that distributes heat to the cryocooler, A loop tube that allows the flow of a coolant in order to convectively transfer the thermal energy generated by the magnetic permanent current switch and the plurality of magnetic coils to the heat exchanger, A control circuit that generates a control signal having a first polarity or a second polarity opposite to the first polarity, A system comprising a magnetic valve according to any one of claims 1 to 5, which is integrated with the loop tube.

14. The system according to claim 13, wherein the loop tube circulates the coolant at a coolant temperature of approximately 4K.

15. The system according to claim 13, wherein the magnetic permanent current switch includes one magnetic coil among the plurality of magnetic coils.

Images