阅读说明：本技术 用于控制持续电流开关的温度的系统 (System for controlling temperature of persistent current switch ) 是由 E·P·A·范拉内 P·A·门特乌尔 J·A·乌尔巴恩 于 2020-03-20 设计创作，主要内容包括：一种用于控制在背景磁场中操作的持续电流开关(120)的温度的系统(100)包括热交换器(138)、回路管(135)、球阀(245)和多个电磁体(251、252)。所述热交换器将热量消散到低温冷却器(106)。所述回路管使得冷却剂能够流动以将由所述持续电流开关生成的热能以对流方式传递到所述热交换器。所述球阀在所述持续电流开关与所述热交换器之间与所述回路管集成在一起,并且包含铁磁球(250)。所述电磁体邻近所述球阀被定位在所述回路管外部,其中,使所述多个电磁体中的第一电磁体通电将所述铁磁球以磁性方式移动到打开所述回路管并使得所述冷却剂能够流动的第一位置,并且使第二电磁体通电将所述铁磁球以磁性方式移动到关闭所述回路管并阻挡所述冷却剂的所述流动的第二位置。(A system (100) for controlling the temperature of a persistent current switch (120) operating in a background magnetic field includes a heat exchanger (138), a loop pipe (135), a ball valve (245), and a plurality of electromagnets (251, 252). The heat exchanger dissipates heat to a cryocooler (106). The loop pipe enables coolant to flow to convectively transfer thermal energy generated by the persistent current switch to the heat exchanger. The ball valve is integrated with the loop pipe between the persistent current switch and the heat exchanger and includes a ferromagnetic ball (250). The electromagnets are positioned outside the loop pipe adjacent the ball valve, wherein energizing a first electromagnet of the plurality of electromagnets magnetically moves the ferromagnetic ball to a first position that opens the loop pipe and enables the flow of the coolant, and energizing a second electromagnet magnetically moves the ferromagnetic ball to a second position that closes the loop pipe and blocks the flow of the coolant.)

1. A system for controlling the temperature of a persistent current switch operating in a background magnetic field, the system comprising:

a heat exchanger configured to dissipate heat to a cryocooler;

a loop pipe configured to enable a coolant to flow to convectively transfer thermal energy generated by the persistent current switch to the heat exchanger; and

a thermal switch, comprising:

a ball valve integrated with the loop pipe between the persistent current switch and the heat exchanger, the ball valve including a ferromagnetic ball having a diameter greater than an inner diameter of an opening of the loop pipe or an inner diameter of an orifice in the ball valve adjacent the opening of the loop pipe; and

a plurality of electromagnets positioned outside the loop pipe adjacent the ball valve, wherein energizing a first electromagnet of the plurality of electromagnets magnetically moves the ferromagnetic ball to a first position that opens the loop pipe and enables the flow of coolant, and energizing a second electromagnet of the plurality of electromagnets magnetically moves the ferromagnetic ball to a second position that closes the loop pipe and blocks the flow of coolant.

2. The system of claim 1, wherein the ball valve defines the aperture and further includes a notch adjacent the aperture, and

wherein energizing the first electromagnet magnetically moves the ferromagnetic ball to the notch to enable the coolant to flow and energizing the second electromagnet magnetically moves the ferromagnetic ball to the orifice to block the flow of the coolant, the ferromagnetic ball being retained in one of the notch and the orifice by gravity when the first and second electromagnets are de-energized.

3. The system of claim 2, wherein each of the first and second electromagnets is configured to create a magnetic force strong enough to overcome the gravitational force and a force resulting from the background magnetic field acting on the ferromagnetic ball.

4. The system of claim 1, wherein the loop pipe includes a first end portion formed of a ferromagnetic material and extending partially into a first side of the ball valve and a second end portion formed of the ferromagnetic material and extending partially into a second side of the ball valve, the first end portion defining one or more through holes within the ball valve,

wherein the first end portion and the second end portion are magnetized by the background magnetic field when the first electromagnet and the second electromagnet are not energized,

wherein energizing the first electromagnet at least partially demagnetizes the first end portion, causing the ferromagnetic ball to move to the magnetized second end portion, thereby covering the opening of the loop pipe and blocking the flow of the coolant, and

wherein energizing the second electromagnet at least partially demagnetizes the second end portion, causing the ferromagnetic ball to move to the magnetized first end portion, thereby covering another opening of the loop pipe and enabling the coolant to flow through the one or more through holes.

5. The system of claim 4, wherein each of the first end portion and the second end portion has substantially the same orientation as the background magnetic field.

6. The system of claim 4, wherein when the first electromagnet is energized to at least partially demagnetize the first end portion, the second electromagnet is energized with a reverse voltage relative to a voltage used to energize the first solenoid, further causing the ferromagnetic ball to move to the magnetized second end portion.

7. The system of claim 6, wherein when the second electromagnet is energized to at least partially demagnetize the second end portion, the first electromagnet is energized with a reverse voltage relative to a voltage used to energize the first electromagnet, further causing the ferromagnetic ball to move to the magnetized first end portion.

8. The system of claim 1, wherein energizing the first electromagnet or the second electromagnet comprises pulsing the first electromagnet or the second electromagnet with a voltage.

9. The system of claim 1, wherein the gaseous or liquid coolant comprises helium gas or liquid helium.

10. The system of claim 1, wherein the persistent current switch enables energization of a superconducting magnet.

11. The system of claim 1, wherein the loop pipe comprises a non-magnetic metal.

12. The system of claim 1, wherein the heat exchanger dissipates heat to a cryocooler.

13. A system for controlling the transfer of thermal energy of a persistent current switch to a heat exchanger in thermal contact with a cryocooler, the system comprising:

a loop pipe positioned between the persistent current switch and the heat exchanger, wherein coolant selectively flows through the loop pipe;

a first ball valve on a first portion of the loop pipe between the persistent current switch and the heat exchanger, the first ball valve including a first ferromagnetic ball, a first orifice abutting a first opening of the first portion of the loop pipe, and a first notch adjacent the first orifice;

a second ball valve on a second portion of the loop pipe between the persistent current switch and the heat exchanger, the second ball valve including a second ferromagnetic ball, a second orifice abutting a second opening of the second portion of the loop pipe, and a second notch adjacent the second orifice;

a first solenoid and a second solenoid positioned outside the first portion of the loop pipe adjacent the first ball valve; and

a third solenoid and a fourth solenoid positioned outside the second portion of the loop pipe adjacent the second ball valve,

wherein the coolant can be flowed through the loop pipe by: energizing the first and third solenoids such that the first and second ferromagnetic balls move to the first and second notches, respectively, thereby opening the first and second portions of the loop pipe, and

wherein the coolant is blocked from flowing through the loop pipe by: energizing the second and fourth solenoids such that the first and second ferromagnetic balls move to the first and second orifices, respectively, thereby closing the first and second portions of the loop pipe.

14. The system of claim 13, wherein each of the first, second, third, and fourth solenoids is configured to create a magnetic force strong enough to overcome gravity and a force resulting from a background magnetic field acting on the first and second ferromagnetic balls, respectively.

15. The system of claim 13, wherein the loop pipe is formed of a non-magnetic metal.

16. A system for controlling the transfer of thermal energy of a persistent current switch operating in a background magnetic field to a heat exchanger in thermal contact with a cryocooler, the system comprising:

a loop pipe positioned between the persistent current switch and the heat exchanger, wherein coolant selectively flows through the loop pipe;

a ball valve in the loop pipe between the persistent current switch and the heat exchanger, the ball valve including a ferromagnetic ball having a diameter greater than an inner diameter of the loop pipe;

a first solenoid positioned outside the loop pipe adjacent a first side of the ball valve; and

a second solenoid positioned outside the loop pipe adjacent a second side of the ball valve,

wherein the loop pipe comprises a first end portion formed of a ferromagnetic material extending partially into the first side of the ball valve and a second end portion formed of the ferromagnetic material extending partially into the second side of the ball valve, the first end portion defining one or more through-holes in a sidewall of the first end portion located within the ball valve,

wherein the first end portion and the second end portion are magnetized by the background magnetic field when the first solenoid and the second solenoid are not energized,

wherein energizing the first solenoid at least partially demagnetizes the first end portion, causing the ferromagnetic ball to move to the magnetized second end portion, thereby covering the opening of the return tube within the ball valve and blocking the flow of the coolant, and

wherein energizing the second solenoid at least partially demagnetizes the second end portion, causing the ferromagnetic ball to move to the magnetized first end portion, thereby covering another opening of the return tube within the ball valve and enabling the coolant to flow through the one or more through holes.

17. The system of claim 16, wherein each of the first end portion and the second end portion has substantially the same orientation as the background magnetic field.

18. The system of claim 16, wherein when the first solenoid is energized to at least partially demagnetize the first end portion, the second solenoid is energized with a reverse voltage relative to a voltage used to energize the first solenoid, further causing the ferromagnetic ball to move to the magnetized second end portion.

19. The system of claim 18, wherein when the second solenoid is energized to at least partially demagnetize the second end portion, the first solenoid is energized with a reverse voltage relative to a voltage used to energize the first solenoid, further causing the ferromagnetic ball to move to the magnetized first end portion.

20. The system of claim 16, wherein the loop pipe is formed of a non-magnetic material except for the first end portion and the second end portion.

Background

Superconducting magnets may be used in systems requiring strong magnetic fields, for example, Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR) spectroscopy. To achieve superconductivity, the magnet comprises a superconducting wire formed of one or more electrically conductive coils and is maintained in a low temperature environment at a temperature close to absolute zero during operation. In the superconducting state, the conductive coils are referred to as superconducting coils, which have virtually no resistance, and therefore conduct much larger currents to create a strong magnetic field. Operation of a superconducting magnet in a superconducting state may be referred to as a persistent current mode. That is, the persistent current mode is a state in which the circuit (e.g., including superconducting coils) is able to carry current substantially indefinitely and does not require an external power source due to the absence of resistance.

To operate in persistent current mode, the superconducting magnet provides a closed superconducting circuit with a superconducting circuit. The circuit is interrupted to allow the power supply to drive current into the coil. Interrupting the circuit typically involves heating portions of the superconducting loop so that the superconducting loop develops electrical resistance. The components of the superconducting circuit responsible for switching between the superconducting state and the normal (non-superconducting) resistance are referred to as magnet Persistent Current Switches (PCS). When the voltage source is connected across the PCS, most of the current will flow in the coil and only a small current will flow through the now resistive line of the PCS. The act of turning off the PCS and the act of applying a voltage across the PCS both cause the PCS to generate heat. When the cooling system has limited ability to absorb or carry away the additional heat generated by the PCS, the cryogenic cooling system (cryostat), which also cools the superconducting coils, cannot handle the additional heat. This is the case for so-called no cryogen or sealed systems, which require the PCS to be thermally disconnected from the cooling system when the magnet is energized or de-energized.

Therefore, there is a need for a cooling system that allows the temperature of the magnet PCS to rise and fall as needed within seconds without damaging the cooling system for the superconducting coils.

Disclosure of Invention

According to a representative embodiment, a system for controlling the temperature of a persistent current switch operating in a background magnetic field includes a heat exchanger, a loop pipe, and a thermal switch. The heat exchanger is configured to dissipate heat. The loop pipe is configured to enable a coolant to flow to convectively transfer thermal energy generated by the persistent current switch to the heat exchanger. The thermal switch includes a ball valve integrated with the loop pipe between the persistent current switch and the heat exchanger, the ball valve including a ferromagnetic ball having a diameter greater than an inner diameter of an opening of the loop pipe or an inner diameter of an orifice in the ball valve that abuts the opening of the loop pipe, and a plurality of electromagnets positioned outside the loop pipe adjacent the ball valve. Energizing a first electromagnet of the plurality of electromagnets magnetically moves the ferromagnetic ball to a first position that opens the loop pipe and enables the coolant to flow. Energizing a second electromagnet of the plurality of electromagnets magnetically moves the ferromagnetic ball to a second position that closes the loop pipe and blocks the flow of the coolant. The background magnetic field in which the system operates may interfere with the functioning of the system. Thus, the system may be located in a region of the background magnetic field that is small enough to overcome any magnetic force on the ferromagnetic ball when the electromagnet is energized. Alternatively or additionally, an optional ferromagnetic shield may be installed around the ball valve and electromagnet if the system and/or other device is not positioned such that it is sufficiently immune to the background magnetic field.

According to another representative embodiment, a system for controlling the transfer of thermal energy of a persistent current switch to a heat exchanger in thermal contact with a cryocooler is provided. The system comprises: a loop pipe positioned between the persistent current switch and the heat exchanger, wherein coolant selectively flows through the loop pipe; a first ball valve on a first portion of the loop pipe between the persistent current switch and the heat exchanger, the first ball valve including a first ferromagnetic ball, a first orifice abutting a first opening of the first portion of the loop pipe, and a first notch adjacent the first orifice; a second ball valve on a second portion of the loop pipe between the persistent current switch and the heat exchanger, the second ball valve including a second ferromagnetic ball, a second orifice abutting a second opening of the second portion of the loop pipe, and a second notch adjacent the second orifice; a first solenoid and a second solenoid positioned outside the first portion of the loop pipe adjacent the first ball valve; and third and fourth solenoids positioned outside the second portion of the loop pipe adjacent the second ball valve. Enabling the coolant to flow through the loop pipe by: energizing the first and third solenoids such that the first and second ferromagnetic balls move to the first and second notches, respectively, thereby opening the first and second portions of the loop pipe. Blocking the flow of coolant through the loop pipe by: energizing the second and fourth solenoids such that the first and second ferromagnetic balls move to the first and second orifices, respectively, thereby closing the first and second portions of the loop pipe.

According to another representative embodiment, a system for controlling the transfer of thermal energy of a persistent current switch operating in a background magnetic field to a heat exchanger in thermal contact with a cryocooler is provided. The system comprises: a loop pipe positioned between the persistent current switch and the heat exchanger, wherein coolant selectively flows through the loop pipe; a ball valve in the loop pipe between the persistent current switch and the heat exchanger, the ball valve including a ferromagnetic ball having a diameter greater than an inner diameter of the loop pipe or an inner diameter of an orifice adjoining an opening of the loop pipe; a first solenoid positioned outside the loop pipe adjacent a first side of the ball valve; and a second solenoid positioned outside the loop pipe adjacent a second side of the ball valve. The loop pipe includes a first end portion formed of a ferromagnetic material that extends partially into the first side of the ball valve and a second end portion formed of the ferromagnetic material that extends partially into the second side of the ball valve, the first end portion defining one or more through-holes in a sidewall of the first end portion that is located within the ball valve. The first end portion and the second end portion are magnetized by the background magnetic field when the first solenoid and the second solenoid are not energized. Energizing the first solenoid at least partially demagnetizes the first end portion, causing the ferromagnetic ball to move to the magnetized second end portion, thereby covering the opening of the loop pipe and blocking the flow of the coolant. Energizing the second solenoid at least partially demagnetizes the second end portion, causing the ferromagnetic ball to move to the magnetized first end portion, thereby covering another opening of the loop pipe and enabling the coolant to flow through the plurality of through holes.

Drawings

The example embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements.

Fig. 1 is a simplified block diagram of a superconducting magnet system according to a representative embodiment.

Fig. 2A is a simplified cross-sectional view of a thermal switch in an open position in a cooling circuit of a superconducting magnet system according to a representative embodiment.

Fig. 2B is a simplified cross-sectional view of a thermal switch in a closed position in a cooling circuit of a superconducting magnet system according to a representative embodiment.

Fig. 3A is a simplified cross-sectional view of a thermal switch in an open position in a cooling circuit of a superconducting magnet system according to another representative embodiment.

Fig. 3B is a simplified cross-sectional view of a thermal switch in a closed position in a cooling circuit of a superconducting magnet system according to another representative embodiment.

Fig. 4 is a simplified block diagram of a superconducting magnet system according to another representative embodiment.

FIG. 5 is a simplified state flow diagram for operation of a superconducting magnet system in accordance with a representative embodiment.

Detailed Description

In the following detailed description, for purposes of explanation and not limitation, representative embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. Descriptions of well-known systems, devices, materials, methods of operation, and methods of manufacture may be omitted so as to not obscure the description of the representative embodiments. Nonetheless, systems, devices, materials, and methods that are within the knowledge of one of ordinary skill in the art are also within the scope of the present teachings and may be used in accordance with the representative embodiments. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The defined terms are complementary to the scientific and technical meaning of the defined terms as commonly understood and accepted in the technical field of the present teachings.

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements or components, these elements or components should not be limited by these terms. These terms are only used to distinguish one element or component from another element or component. Thus, a first element or component discussed below could also be termed a second element or component without departing from the teachings of the present inventive concept.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the specification and in the claims, the singular form of the terms "a", "an" and "the" are intended to include both the singular and the plural, unless the context clearly dictates otherwise. In addition, the terms "comprises" and/or "comprising," and/or the like, when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude 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.

Unless otherwise indicated, when an element or component is referred to as being "connected to," "coupled to," or "adjacent to" another element or component, it is to be understood that the element or component can be directly connected or coupled to the other element or component or intervening elements or components may be present. That is, these and similar terms encompass the case where one or more intermediate elements or components may be employed to connect two elements or components. However, when an element or component is considered to be "directly connected" to another element or component, this only covers the case where the two elements or components are connected to each other without any intervening or intermediate elements or components.

"computer-readable storage medium" encompasses any tangible storage medium that can store instructions that are executable by a "processor" of a "computing device". The computer-readable storage medium may be referred to as a non-transitory computer-readable storage medium to distinguish it from a transitory medium (e.g., a transitory propagating signal). The computer readable storage medium may also be referred to as a tangible computer readable medium.

In some embodiments, the computer-readable storage medium is also capable of storing data that is accessible by a processor of the computing device. Examples of computer-readable storage media include, but are not limited to: a floppy disk, a magnetic hard drive, a solid state disk, flash memory, a USB thumb drive, Random Access Memory (RAM), Read Only Memory (ROM), an optical disk, a magneto-optical disk, and a register file for a processor. Examples of optical disks include Compact Disks (CDs) and Digital Versatile Disks (DVDs), e.g., CD-ROMs, CD-RWs, CD-R, DVD-ROMs, DVD-RWs, or DVD-R disks. The term computer readable storage medium also refers to various types of recording media that can be accessed by a computer device via a network or a communication link. For example, the data may be retrieved over a modem, the internet, or a local area network. References to a computer-readable storage medium should be interpreted as possibly being a plurality of computer-readable storage media. Various executable components of one or more programs may be stored in different locations. The computer-readable storage medium may be, for example, multiple computer-readable storage media within the same computer system. The computer-readable storage medium may also be a computer-readable storage medium distributed among multiple computer systems or computing devices.

"memory" is an example of a computer-readable storage medium. Computer memory is any memory that can be directly accessed by a processor. Examples of computer memory include, but are not limited to: RAM memory, registers, and register files. References to "computer memory" or "memory" should be interpreted as possibly being multiple memories. The memory may be, for example, multiple memories within the same computer system. The memory may also be multiple memories distributed among multiple computer systems or computing devices. Computer storage is any non-volatile computer-readable storage medium. Examples of computer storage include, but are not limited to: hard drives, USB thumb drives, floppy drives, smart cards, DVDs, CD-ROMs, and solid state hard drives. In some embodiments, the computer storage may also be computer memory, and vice versa. References to "computer storage" or "storage" should be read as possibly including a plurality of storage devices or components. For example, a storage may comprise multiple storage devices within the same computer system or computing device. The storage may also include multiple storages distributed among multiple computer systems or computing devices.

As used herein, a "processor" encompasses an electronic component capable of executing software, programs, and/or machine-executable instructions, for example, stored in memory and/or on a computer-readable medium. References to a "computing device" including a "processor" should be interpreted as possibly containing more than one processor or processing core and possibly containing one or more Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), or a combination thereof. The processor may be, for example, a multi-core processor. A processor may also refer to a collection of processors within a single computer system or distributed among multiple computer systems. The term "computing device" should also be read to possibly refer to a collection or network of multiple computing devices, each of which includes one or more processors. Many programs have instructions that are executed by multiple processors that may be within the same computing device or even distributed across multiple computing devices.

As used herein, a "user interface" or "user input device" is an interface that allows a user or operator to interact with a computer or computer system. The user interface may provide information or data to and/or receive information or data from an operator. The user interface may enable input from an operator to be received by the computer and may provide output from the computer to the user. In other words, the user interface may allow an operator to control or manipulate the computer, and the interface may allow the computer to indicate the effect of the operator's control or manipulation. Displaying data or information on a display or graphical user interface is an example of providing information to an operator. Receiving data through a touch screen, keyboard, mouse, trackball, touch pad, pointing stick, tablet, joystick, game pad, web camera, head-mounted device, gear shift lever, steering wheel, wired glove, wireless remote control, and accelerometer are all examples of user interface components capable of receiving information or data from a user.

"hardware interface" encompasses an interface that enables a processor of a computer system or computer device to interact with and/or control an external computing device and/or apparatus. The hardware interface may allow the processor to send control signals or instructions to an external computing device and/or apparatus. The hardware interface may also enable the processor to exchange data with external computing devices and/or apparatus. Examples of hardware interfaces include, but are not limited to: a universal serial bus, an IEEE1394 port, a parallel port, an IEEE1284 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 MIDI interface, an analog input interface, and a digital input interface.

In view of the foregoing, the present disclosure, through one or more of its various aspects, embodiments, and/or specific features or sub-components, is therefore intended to present one or more of the advantages as specifically noted below. For purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, other embodiments consistent with the present disclosure that depart from the specific details disclosed herein are still within the scope of the claims. Moreover, descriptions of well-known apparatus and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparatus are also within the scope of the present disclosure.

Thus, the system for controlling the temperature of the magnet Persistent Current Switch (PCS) enables efficient cooling of the PCS separately from the cooling system (e.g., cryostat) for the superconducting coil(s). In general, embodiments described herein relate to a thermal switch that thermally disconnects a PCS from a cooling system to enable energization of, for example, superconducting coils in a superconducting magnet (e.g., an MRI magnet). A thermal disconnect from the cooling system is required to prevent heat from the PCS from overwhelming the cooling system which also maintains the cryogenic temperature of the superconducting coils. The thermal switch may be used with a low-cryogen superconducting magnet, in particular, a low-cryogen superconducting magnet having a relatively small helium volume for cooling the magnet by convective helium flow (rather than conductive cooling of the magnet in a conventional helium bath). As mentioned above, the thermal switch prevents the excess heat generated by the PCS when energizing the magnet from overloading the cryostat, which cools the superconducting coils of the magnet. The thermal switch also enables the PCS to maintain the same temperature as the superconducting coil when the magnet is operating in the persistent current mode. Thus, various embodiments provide a temperature control system that allows the temperature of the PCS to rise and fall as needed within seconds without damaging the cryostat used to cool the superconducting coils. In addition, the energy required to operate the thermal switch is limited to switching operations that occur within a few milliseconds, thus further limiting the amount of heat input to the cryostat.

Fig. 1 is a simplified block diagram of a superconducting magnet system according to a representative embodiment.

Referring to fig. 1, superconducting magnet system 100 includes superconducting coils 110 of a superconducting magnet connected in parallel with a magnet PCS120 and a power supply 180 (shown as a current source for illustration purposes). Superconducting coils 110 are in cryostat 105 of superconducting magnet system 100 in order to limit the heat input to superconducting coils 110. Superconducting coils 110 may be maintained at cryogenic temperatures by cryocooler 106 in cryostat 105 (and attached to cryostat 105), wherein cryocooler 106 has a first stage 107 and a second stage 108, first stage 107 maintaining the temperature of a thermal shield (not shown) enclosing superconducting coils 110 at about 40 kelvin, second stage 108 maintaining the temperature of superconducting coils 110 at about 4 kelvin. The portion of cryocooler 106 can be accessed from outside cryostat 105. Heat exchanger 138 of convective cooling loop 130 is permanently connected to second stage 108 of cryocooler 106 or is in thermal contact with second stage 108 of cryocooler 106. Power supply 180 may be permanently or temporarily connected to electrical contacts external to cryostat 105.

The controller 170 may be implemented by a computer system or computer device, for example, having one or more processors executing instructions, for example, stored in memory and/or on a computer-readable medium, as described above. In the depicted embodiment, the controller 170 controls the state of the power supply 180 and the PCS120 (indicated by dashed lines) to enable the magnet to be placed in a continuous current mode and the magnet to be ramped down, for example, in response to an instruction given by an operator to ramp up the magnet. The controller 170 also controls operation of a thermal switch 131 (indicated by dashed lines) in the convective cooling loop 130 to control the temperature of the PCS120 by selectively blocking coolant flow through the loop tube 135 in the convective cooling loop 130 and enabling coolant flow through the loop tube 135 in the convective cooling loop 130. It should be understood that the controller 170 includes one or more processors and other components of a computer system, as described above. The instructions stored in the memory and/or on the computer readable medium and executed by the processor(s) include instructions for opening and closing the PCS120, opening and closing the thermal switch 131, and changing the voltage/power output by the power supply 180.

More specifically, the controller 170 controls the PCS120 to selectively enter a closed state (superconducting state) and an open state (non-superconducting state). PCS120 comprises a composite superconducting wire made of superconducting filaments inside a copper matrix, similar to the superconducting wire used in superconducting coil 110. Like other superconducting wires, the composite superconducting wire functions as a "normal" conductor at high temperatures and as a "superconductor" at cryogenic temperatures. When PCS120 is in the closed (superconducting) state, it can carry the main magnet current, and the superconducting magnet can enter a persistent current mode. PCS120 may be switched to the closed state by cooling, for example, using cryocooler 106. When the PCS120 is in the off (non-superconducting or normal) state, it cannot carry the main magnet current. The PCS120 may be switched to the closed state by heating, for example, using a PCS heater (not shown). However, the PCS120 has a small (normal) resistance in the off state that is high enough that when the magnet is connected to the power supply 180, only a small amount of current flows through the PCS120, and the rest of the current flows in the superconducting coil 110.

Thus, when the PCS120 is off, the magnet may be in a ramping state during which the PCS120 dissipates power because the ramping voltage across the PCS120 generates a current that flows through its normal resistivity. When PCS120 is closed, there is no ramping voltage and no power dissipation. The PCS120 transitions from the open state to the closed state by means of cooling via the convective cooling loop 130 discussed below, and the power supply 180 maintains the magnet operating current during the transition. When the PCS120 is in a fully closed state (rather than transitioning between open and closed), the power supply 180 ramps down the current. The high self-inductance of the superconducting coils 110 ensures that the coil current does not change, so as a result (e.g., according to kirchhoff's current law), the current through the PCS120 ramps up as the power supply 180 current ramps down.

In addition, the controller 170 controls the thermal switch 131 in the convective cooling loop 130 to be turned on and off according to the action required by the operator. For example, when PCS120 is in the open state and the magnet needs to be placed in the continuous current mode after ramping activity, thermal switch 131 is opened to enable coolant to flow through convective cooling loop 130, thermally connecting PCS120 to heat exchanger 138 via loop pipe 135, thereby providing additional cooling for closing PCS 120. When PCS120 is in the closed state but needs to be opened, for example, to ramp up or ramp down the magnet, thermal switch 131 closes to stop coolant flow through convective cooling loop 130 (e.g., by blocking loop tube 138 as discussed below), thereby thermally disconnecting PCS120 from heat exchanger 138 and allowing it to warm up to open without overloading second stage 108 of cryocooler 106. When the magnet is in the ramping state and PCS120 is in the open state, thermal switch 131 is in the closed state to ensure that the power generated by PCS120 does not overload second stage 108 of cryocooler 106 (which keeps superconducting coil 110 in the cold state). When the magnet enters the continuous current state, the thermal switch 131 opens to keep the PCS120 thermally connected to the heat exchanger 138, ensuring that the PCS120 remains in the superconducting state.

In an embodiment, controller 170 may pulse an electromagnet (e.g., a solenoid) in thermal switch 131 to move a ferromagnetic ball in thermal switch 131 to a flow blocking position, as discussed below, to close thermal switch 131. The controller 170 system then powers an electric heater (not shown) to heat the PCS120, driving the PCS120 out of the superconducting (closed) state and into the resistive (open) state. The PCS120 in the closed state enables the power supply 180 to generate a current through the superconducting coil 110 while keeping the superconducting magnet in a cold state, as discussed above. Similarly, controller 170 can pulse the electromagnet in thermal switch 131 to move the ferromagnetic ball in thermal switch 131 out of the flow-blocking position, thereby opening thermal switch 131 and providing additional cooling to PCS 120.

The second stage 108 of cryocooler 106 is capable of bringing the superconducting coils 110 of the magnet system to a desired cryogenic temperature of about 4 kelvin, but it has limited power absorption capability. Thus, heat from PCS120 in the off state would otherwise overload cryocooler 106. As discussed above, when the power supply 180 is connected across the PCS120 in the off state, most of the current will flow into the superconducting coil 110, and only a small current will flow through the normal resistance line of the PCS 120. Once the current flowing through the superconducting coil 110 has reached its target value (target current), the controller 170 controls the PCS120 to enter the closed state so that the superconducting coil 110 can operate in a continuous current mode with virtually zero resistance after ramping down the power supply 180. This may be referred to as a closed superconducting circuit. The target current is the current required to flow in the wire to form the target field at the center of the superconducting magnet.

In general, magnet PCS120 generates heat (thermal energy) due to current flow through a normal resistance when in the open state, and may also continue to generate heat when controlled to transition from the closed state to the open state or from the open state to the closed state. When the current in the superconducting coils 110 has reached the target current, the controller 170 turns off the voltage of the power supply 180, but the high inductance of the superconducting coils 110 causes the current to continue to flow through the power supply 180. In this condition, there is no more power dissipation in the PCS120, and the PCS120 is ready to be cooled down to switch from the open state to the closed state. Cooling PCS120 is accomplished in part by: thermal switch 131 is controlled to allow coolant to flow in loop pipe 135 of convective cooling loop 130 and thus thermally connect PCS120 to second stage 108 of cryocooler 106.

The loop pipe 135 may be formed of a non-magnetic metal (e.g., copper, aluminum, titanium, zinc, tin, or lead) or other non-magnetic material. The loop pipe 135 is hermetically sealed, and the coolant contained in the loop pipe 135 may be, for example, helium gas or liquid helium for enabling convective transfer of thermal energy between the PCS120 and the heat exchanger 138. Other types of gaseous and/or liquid coolants may be included without departing from the scope of the present teachings.

The thermal switch 131 is configured to open and close the loop pipe 135 so as to selectively enable and block the flow of the coolant, respectively. When the thermal switch 131 is open, coolant can flow through the loop pipe 135 between the PCS120 and the heat exchanger 138 to dissipate the heat being generated. When the thermal switch 131 is closed, coolant is blocked from flowing through the loop pipe 135. In various embodiments, the thermal switch 131 may be implemented using a ball valve (not shown in fig. 1) containing a ferromagnetic ball having a diameter greater than the inner diameter of the opening of the loop pipe 135 and/or the inner diameter of the orifice adjoining the opening of the loop pipe 135, and an electromagnet configured to control placement of the ferromagnetic ball within the opening of the loop pipe 135 or the orifice within the ball valve to selectively block the loop pipe 135 by activating and deactivating a magnetic field, as discussed below. That is, the electromagnet is configured to control the placement of the ferromagnetic balls in the opening of the loop pipe 135 or the orifice within the ball valve to block the loop pipe 135 and to remove the ferromagnetic balls from the opening or orifice of the loop pipe 135 to open the loop pipe 135.

Fig. 5 is a simplified state flow diagram for operation of superconducting magnet system 100 in accordance with a representative embodiment. More particularly, for the purpose of illustrating the operation of the thermal switch 131 in the context of operating the PCS120, the state flow diagram shows the states of the thermal switch 131, the PCS heater for the PCS120, and the voltage level of the power supply 180 during the ramp-up operation. That is, fig. 5 shows a ramp-up process for ramping the current in the superconducting coils 110 to the target current and ultimately placing the magnet in a persistent current mode. The time line (horizontal axis) is arbitrary. As will be apparent to those skilled in the art, the ramp-down process is similar to the ramp-up process, but the inverse of the ramp-up process. Ramping up the superconducting coil 110 to place the magnet in the persistent current mode takes much longer than ramping down the power supply 180. The process may be controlled, for example, by controller 170.

Referring to the top portion of fig. 5 (top four traces), thermal switch 131 is controlled to transition from an open state to a closed state, blocking coolant flow through loop tube 135 in convective cooling loop 130, thereby preventing heat from PCS120 from overloading second stage 108 of cryocooler 106. The PCS heater is controlled to be on to heat the PCS120, and in response, the PCS120 transitions from the closed state to the open state. The power supply 180 is controlled to transition from 0 to a positive voltage to begin the ramping process. When the power supply 180 is controlled to transition back from a positive voltage to 0, the ramping process ends, at which time the PCS heater is also turned off. Thermal switch 131 is then controlled to transition from the closed state to the open state so that coolant can flow through loop pipe 135, thereby providing additional or supplemental cooling for PCS 120. The PCS120 cools down and enters a closed state and the power supply 180 is then controlled to temporarily transition from 0 to a negative voltage, causing the magnet to enter a continuous current mode.

Referring to the bottom portion of fig. 5 (bottom three traces), when the PCS heater is turned on and the PCS120 transitions to the off state, the temperature of the PCS120 starts to rise, and when the power supply 180 transitions from 0 to a positive voltage at the start of the ramp-up process, the temperature of the PCS120 further rises. During substantially the entire time that PCS120 is at an elevated temperature, thermal switch 131 is in a closed state to prevent heat from overloading second stage 108 of cryocooler 106. Meanwhile, the current passing through the superconducting coil 110 starts to increase at the beginning of the ramping-up process and reaches the target current at the end of the ramping process, which is maintained. The superconducting magnet is considered "off-field" prior to the ramp-up process, and is considered "on-field" once the current reaches the target. After the power supply 180 discharges, the magnet is in the persistent current mode and the target current is carried entirely by the coil 110 and PCS 120.

Fig. 2A and 2B are simplified cross-sectional views of a thermal switch in an open position and a closed position in a convective cooling loop of a superconducting magnet system according to a representative embodiment. The thermal switch depicted in fig. 2A and 2B and discussed below may be used as the thermal switch 131 in fig. 1.

Referring to fig. 2A and 2B, thermal switch 231 is positioned in a loop pipe 235, and loop pipe 235 is substantially identical to loop pipe 135 described above. The thermal switch 231 includes a ball valve 245 containing a ferromagnetic ball 250 and two electromagnets indicated by a first solenoid 251 and a second solenoid 252, the first solenoid 251 and the second solenoid 252 being positioned outside the loop pipe 235 adjacent to the ball valve 245. While the thermal switch 231 is described as including a first solenoid 251 and a second solenoid 252, it should be understood that other types of electromagnets may be incorporated without departing from the scope of the present teachings. First and second solenoids 251 and 252 are on opposite sides of the return tube 235 to control movement of the ferromagnetic ball 250 within the ball valve 245 by selectively energizing and de-energizing the first and second solenoids 251 and 252, as discussed below. The loop pipe 235 is formed of a non-magnetic metal (e.g., copper, aluminum, titanium, zinc, tin, or lead) or other non-magnetic material. Ferromagnetic ball 250 is formed of any compatible ferromagnetic material (e.g., iron, nickel, or cobalt).

In the depicted embodiment, the first and second solenoids 251, 252 surround the ball valve 245 such that, in cross-section, portions of each of the first and second solenoids 251, 252 appear above and below the ball valve 245. Thermal switch 231 is located in a region of the superconducting magnet system where the background magnetic field from the superconducting magnet itself and its spatial gradient are sufficiently small that first solenoid 251 and second solenoid 252, when energized, can overcome any magnetic force on ferromagnetic ball 250. In the depicted example, the direction of the background magnetic field is from left to right, as indicated by the arrows.

Ball valve 245 is integrated with return tube 235 such that return tube 235 effectively passes through ball valve 245 via a first (upstream) orifice 247 and a second (downstream) orifice 248 defined by ball valve 245. Ferromagnetic ball 250 has a diameter that is larger than the inner diameter of first aperture 247 (and return tube 235). The first and second apertures 247, 248 may coincide with the openings of the return tube 235 itself such that each of the first and second apertures 247, 248 abut a corresponding opening of the return tube 235. Ball valve 245 provides bi-stable operation because ferromagnetic ball 250 is in one of two possible positions: a first (open) position in which the ferromagnetic ball 250 is in the notch 246, shown in fig. 2A, and a second (closed) position in which the ferromagnetic ball 250 is in the first aperture 247, shown in fig. 2B. When the ferromagnetic ball 250 is in the first position, the thermal switch 231 is open and coolant can flow through the loop pipe 235, as indicated by the dashed arrow in fig. 2A. When ferromagnetic ball 250 is in the second position, thermal switch 231 is closed and coolant cannot flow through loop pipe 235 (since ferromagnetic ball 250 blocks first aperture 247 and thus blocks loop pipe 235). In alternative configurations, the coolant may flow in the opposite direction without departing from the scope of the present teachings.

As discussed above, the first and second solenoids 251 and 252 are selectively energized and de-energized under the control of a controller (e.g., controller 170 in fig. 1) to move the ferromagnetic ball 250 between the notch 246 and the first aperture 247. Energizing the first solenoid 251 or the second solenoid 252 may include pulsing the first solenoid 251 or the second solenoid 252 with a voltage from a voltage source (not shown) for a short period of time (e.g., about 1 millisecond to about 100 milliseconds). As shown in fig. 2A, when the first solenoid 251 is energized (e.g., pulsed), it generates a magnetic field in a direction that magnetically attracts the ferromagnetic ball 250 to the first solenoid 251, thereby moving the ferromagnetic ball 250 to a first position in the notch 246. When the first solenoid 251 is de-energized after a short period of time, the ferromagnetic ball 250 is held in the notch 246 by gravity. As shown in fig. 2B, when the second solenoid 252 is energized (e.g., pulsed), it generates a magnetic field in a direction that magnetically attracts the ferromagnetic ball 250 to the second solenoid 252, thereby moving the ferromagnetic ball 250 to a second position in the first aperture 247. When the second solenoid 252 is de-energized after a short period of time, the ferromagnetic ball 250 is held in the first aperture 247 by gravity.

The strength of the magnetic force on ferromagnetic ball 250 is a function of the volume of ferromagnetic ball 250 and the gradient of the magnetic field strength in ferromagnetic ball 250. That is, each of the first and second solenoids 251 and 252 is configured to create a magnetic force strong enough to overcome the force of gravity and the force due to the background magnetic field acting on and in the ferromagnetic ball 250 in order to magnetically move the ferromagnetic ball 250 within the ball valve 245.

Depending on the location of thermal switch 231 and/or convective cooling loop within the superconducting magnet system, the background magnetic field may disable or impair the functionality of thermal switch 231. In this case, an optional magnetic shield 270 formed of a ferromagnetic material (e.g., iron, nickel, or cobalt) may be included to divert field lines from the background magnetic field around the configuration of the thermal switch 231. The inclusion of magnetic shield 270 increases the space required to install thermal switch 231 inside a cryostat (e.g., cryostat 105).

Fig. 3A and 3B are simplified cross-sectional views of a thermal switch in an open position and a closed position in a convective cooling loop of a superconducting magnet system according to another representative embodiment. The thermal switch depicted in fig. 3A and 3B and discussed below may be used as the thermal switch 131 in fig. 1.

Referring to fig. 3A and 3B, the thermal switch 331 is positioned in the convective loop pipe 335, the convective loop pipe 335 being substantially identical to the loop pipe 135 described above. The thermal switch 331 includes a ball valve 345 containing a ferromagnetic ball 350 and two electromagnets indicated by a first solenoid 351 and a second solenoid 352, the first solenoid 351 and the second solenoid 352 being positioned outside the loop pipe 335 adjacent to the ball valve 345. Other types of electromagnets may be included without departing from the scope of the present teachings. Ferromagnetic ball 350 is formed of any compatible ferromagnetic material (e.g., iron, nickel, or cobalt). First and second solenoids 351 and 352 are on opposite sides of the ball valve 345 to control movement of the ferromagnetic ball 350 within the ball valve 345 by selectively energizing and de-energizing the first and second solenoids 351 and 352, as discussed below. In the depicted embodiment, the first and second solenoids 351, 352 encircle the loop pipe 335 such that, in cross-section, portions of each of the first and second solenoids 351, 352 appear above and below the loop pipe 335.

In the depicted embodiment, the loop pipe 335 includes a first (upstream) end portion 335a, the first (upstream) end portion 335a being formed of a ferromagnetic material (e.g., iron, nickel, or cobalt) and extending partially into a first side of the ball valve 345. The loop pipe 335 also includes a second (downstream) end portion 335b, the second (downstream) end portion 335b also being formed of ferromagnetic material and extending partially into the second side of the ball valve 345. The remainder of the loop pipe 335 is formed of a non-magnetic metal (e.g., copper, aluminum, titanium, zinc, tin, or lead) or other non-magnetic material, as discussed above with reference to loop pipe 135. In the ball valve 345, a first opening 347 of the loop pipe 335 is defined by the first end portion 335a, and a second opening 348 of the loop pipe 335 is defined by the second end portion 335 b. The first end portion 335a also defines one or more through-holes 333 located within the ball valve 345. The through holes 333 enable coolant to flow into the ball valve 345, as indicated by the dashed arrows in fig. 3A, even when the ferromagnetic ball 350 is blocking the first opening 347, as discussed below.

The thermal switch 331 is located in a region of the superconducting magnet system where the background magnetic field from the superconducting magnet itself and its spatial gradient are large enough that the field lines of the background magnetic field will be attracted by the first end portion 335a and the second end portion 335b of the loop pipe 335. In response, when the first and second solenoids 351, 352 are not energized, the first and second end portions 335a, 335b will create a field gradient at the first and second openings 347, 348, respectively. When the first and second solenoids 351, 352 are not energized, this causes the ferromagnetic ball 350 to be magnetically attracted to the first and second end portions 335a, 335 b. Even a low background magnetic field can create sufficient magnetic force on the ferromagnetic ball 350 to hold it in place at one of the first opening 347 and the second opening 348. In the depicted example, the direction of the background magnetic field is from right to left, as indicated by the arrow.

The ball valve 345 is integrated with the loop pipe 335 such that the loop pipe 335 effectively passes through the ball valve 345. The ferromagnetic ball 350 has a diameter larger than the inner diameters of the first opening 347 and the second opening 348 of the loop pipe 335. The ball valve 345 provides bi-stable operation because the ferromagnetic ball 350 is in one of two possible positions: in the first (open) position shown in fig. 3A, in which ferromagnetic ball 350 is magnetically attracted to first end portion 335a with sufficient force to block first opening 347, and in the second (closed) position shown in fig. 3B, in which ferromagnetic ball 350 is magnetically attracted to second end portion 335B with sufficient force to block second opening 348. When the ferromagnetic ball 350 is in the first position, the thermal switch 331 is open and coolant can flow through the loop pipe 335 via the through-hole(s) 333, as indicated by the dashed arrow in fig. 3A. When the ferromagnetic ball 350 is in the second position, the thermal switch 331 is closed and coolant cannot flow through the loop pipe 335 (since the ferromagnetic ball 350 blocks the first opening 347).

As discussed above, the first and second solenoids 351, 352 are selectively energized and de-energized under the control of a controller (e.g., controller 170 in fig. 1) to move the ferromagnetic ball 350 between the first and second openings 347, 348. Energizing the first solenoid 351 or the second solenoid 352 may include pulsing the first solenoid 351 or the second solenoid 352 with a voltage from a voltage source (not shown) for a short period of time (e.g., about 1 to about 100 milliseconds). When one of the first and second solenoids 351, 352 is energized, it generates a corresponding magnetic field having a direction opposite to the direction of the background magnetic field, thereby partially or completely demagnetizing the first end portion 335a or the second end portion 335b, respectively, of the loop pipe 335. As a result, the ferromagnetic ball 350 is magnetically drawn toward the other of the first solenoid 351 (and first end portion 335a) or the second solenoid 352 (and second end portion 335b) that is not yet energized, as the corresponding first end portion 335a or second end portion 335b continues to be magnetized by the background magnetic field.

More specifically, as shown in fig. 3A, when the second solenoid 352 is energized (e.g., pulsed), the second end portion 335b is demagnetized, and thus the ferromagnetic ball 350 is magnetically attracted to the first end portion 335a, and when the second solenoid 352 is pulsed, the first end portion 335a remains magnetized by the background magnetic field. Accordingly, the ferromagnetic ball 350 moves to the first position, blocking the first opening 347 of the magnetized first end portion 335a, while the second opening 348 is unobstructed. Accordingly, the thermal switch 331 is opened, and the coolant can flow through the loop pipe 335, as indicated by the dashed arrow in fig. 3A. When the second solenoid 352 is de-energized after a short period of time (e.g., once the ferromagnetic ball 350 has moved to the first position), the ferromagnetic ball 350 is held in the first position by the magnetized first end portion 335a even though the second end portion 335b is magnetized again. If the background magnetic field is not strong enough to hold the ferromagnetic ball 350, for example, at the beginning of energization of the superconducting magnet, a small amount of reverse voltage may be supplied to energize the first solenoid 351 to generate a magnetic field in a direction that increases the magnetic attraction, and/or a small amount of (forward) voltage may be applied to energize the second solenoid 352 to generate a magnetic field in a direction that again partially demagnetizes the second end portion 335b and reduces the opposite magnetic force, to hold the ferromagnetic ball 350 in the first position.

Similarly, as shown in fig. 3B, when the first solenoid 351 is energized (e.g., pulsed), the first end portion 335a is demagnetized, and thus the ferromagnetic ball 350 is magnetically attracted to the second end portion 335B, the second end portion 335B remaining magnetized by the background magnetic field. Accordingly, the ferromagnetic ball 350 moves to the second position, blocking the second opening 348 of the magnetized second end portion 335b, while the first opening 347 is unobstructed. Accordingly, the thermal switch 331 is closed and coolant cannot flow through the loop pipe 335. When the first solenoid 351 is de-energized after a short period of time (e.g., once the ferromagnetic ball 350 has moved to the second position), the ferromagnetic ball 350 is held in the second position by the magnetized second end portion 335b, even if the first end portion 335a is magnetized again. If the background magnetic field is not strong enough to hold the ferromagnetic ball 350, a small amount of reverse voltage may be supplied to energize the second solenoid 352 to generate a magnetic field in a direction that increases the magnetic attraction, and/or a small amount of (forward) voltage may be supplied to energize the first solenoid 351 to generate a magnetic field in a direction that again partially demagnetizes the first end portion 335a and decreases the opposite magnetic force, to hold the ferromagnetic ball 350 in the second position.

In an alternative embodiment, the cooling loop for individually controlling the temperature of the PCS in the superconducting magnet system may include a plurality of thermal switches, such as thermal switch 231 and/or thermal switch 331 discussed above. FIG. 4 is a simplified block diagram of a superconducting magnet system including a plurality of thermally controlled switches according to another representative embodiment.

Referring to fig. 4, superconducting magnet system 400 includes superconducting coils 110 connected in parallel with magnet PCS120 and power supply 180, as discussed above with reference to fig. 1. The heat generated by the PCS120 is dissipated primarily through the convective cooling loop 430 to control the temperature of the PCS120 alone. The convective cooling loop 430 includes the heat exchanger 138 and the loop pipe 135 and a first thermal switch 431 and a second thermal switch 432 integrated with the loop pipe 135 between the PCS120 and the heat exchanger 138. In the depicted example, a first thermal switch 431 (similar to thermal switch 131 in fig. 1) is positioned on the supply portion of loop pipe 135 that delivers coolant from PCS120 to heat exchanger 138, and a second thermal switch 432 is positioned on the return portion of loop pipe 135 that delivers coolant from heat exchanger 138 to PCS 120. The loop pipe 135 is hermetically sealed, and the coolant contained in the loop pipe 135 may be, for example, helium gas or liquid helium, so as to achieve convective transfer of thermal energy between the PCS120 and the heat exchanger 138.

The first and second thermal switches 431 and 432 are configured to open and close the loop pipe 135 under the control of the controller 170 so as to selectively enable and block the flow of the coolant, respectively. For example, first thermal switch 431 and second thermal switch 432 are closed to allow PCS120 to generate heat without thermally overloading second stage 108 of cryocooler 106, e.g., when PCS120 is in an open state and/or when PCS120 transitions from a closed state to an open state or from an open state to a closed state. Otherwise, the first and second thermal switches 431 and 432 are opened, for example, when the PCS120 is in a closed state, so that the coolant can flow through the loop pipe 135 to keep the PCS120 in a cold state. Examples of such conditions are the very beginning and very end of the traces in fig. 5.

In various embodiments, each of the first and second thermal switches 431 and 432 may be implemented using a ball valve, as described above with respect to the thermal switches 231 and 331 in fig. 2 and 3, respectively. Therefore, a description of the structure and operation of each of the first and second thermal switches 431 and 432 will not be repeated here. In an embodiment, the first and second thermal switches 431 and 432 operate substantially simultaneously, which increases the efficiency of the convective cooling loop 430 because the substantially simultaneous operation eliminates the possibility of convective flow between the PCS120 and the heat exchanger 138 inside only one of the two legs of the cooling loop 430. It also improves the reliability of the system in which both thermal switches are redundant, which avoids the potentially costly and time-consuming repairs in the event of failure of one of the first and second thermal switches 431, 432.

While 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 which have been used are words of description and illustration, rather than words of limitation. Changes may be made within the purview of the claims, as presently stated and as amended, without departing from the scope and spirit thereof in aspects of the system for controlling the temperature of a persistent current switch. Although the system for controlling the temperature of a persistent current switch has been described with reference to particular means, materials and embodiments, the system for controlling the temperature of a persistent current switch is not intended to be limited to the details disclosed; rather, the system for controlling the temperature of a persistent current switch extends to all functionally equivalent structures, methods and uses, such as are within the scope of the claims.

Although this specification describes components and functions that may be implemented in particular embodiments with reference to particular standards and protocols, this disclosure is not limited to these standards and protocols. Such standards are periodically superseded by more efficient equivalents having essentially the same function. Accordingly, replacement standards and protocols having the same or similar functions are considered equivalents thereof.

The illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. These illustrations are not intended to be a complete description of all of the elements and features of the disclosure described herein. Many other embodiments will be apparent to those of skill in the art upon reviewing the disclosure. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. Additionally, the illustrations are merely representational and may not be drawn to scale. Some proportions may be exaggerated in the drawings, while other proportions may be minimized. The present disclosure and figures are, therefore, to be regarded as illustrative rather than restrictive.

The term "invention" may be used herein, individually and/or collectively, to refer to one or more embodiments of the disclosure for convenience only and is not intended to limit the scope of the disclosure to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the description.

The abstract of the present disclosure is provided to comply with 37c.f.r. § 1.72(b), and should be understood at the time of filing not to be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing detailed description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure should not be read as reflecting the intent: 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 of the features of any of the disclosed embodiments. Thus, the following claims are hereby incorporated into the detailed description, with each claim standing on its own as defining separately claimed subject matter.

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. As such, the above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.