阅读说明：本技术 用于使用双冷却路径来冷却超导开关的系统和方法 (System and method for cooling superconducting switches using dual cooling paths ) 是由 三根进 白烨 武安波 徐民风 P.S.M.S.汤普森 于 2020-02-28 设计创作，主要内容包括：本发明涉及用于使用双冷却路径来冷却超导开关的系统和方法。提出了一种持续电流开关系统。持续电流开关系统的一个实施例包括具有绕组单元和双冷却路径的真空室。双冷却路径构造成使冷却剂流循环。双冷却路径由第一冷却路径和第二冷却路径限定。第一冷却路径包括设置成与绕组单元直接接触的固体热构件,并且第二冷却路径包括冷却管,该冷却管设置成与绕组单元直接接触并且构造成使冷却剂在冷却管中循环。双冷却路径将绕组单元的温度冷却成低于阈值温度,以使持续电流开关系统从第一模式转换到第二模式。还公开了一种用于冷却持续电流开关系统中的绕组单元的方法和一种包括双冷却路径的切换系统。(The invention relates to a system and a method for cooling a superconducting switch using dual cooling paths. A persistent current switching system is presented. One embodiment of a persistent current switching system includes a vacuum chamber having a winding unit and dual cooling paths. The dual cooling paths are configured to circulate a coolant flow. The dual cooling path is defined by a first cooling path and a second cooling path. The first cooling path includes a solid thermal member disposed in direct contact with the winding unit, and the second cooling path includes a cooling pipe disposed in direct contact with the winding unit and configured to circulate a coolant in the cooling pipe. The dual cooling paths cool the temperature of the winding unit below a threshold temperature to transition the persistent current switching system from the first mode to the second mode. A method for cooling a winding unit in a continuous current switching system and a switching system comprising dual cooling paths are also disclosed.)

1. A persistent current switching system comprising:

a vacuum chamber;

a winding unit disposed in the vacuum chamber and configured to switch the persistent current switching system from a first mode to a second mode when a temperature associated with the winding unit is below a threshold temperature;

a first cooling path including a solid thermal member in direct contact with the winding unit and a second cooling path including a cooling tube disposed in direct contact with the winding unit and configured to circulate a coolant therein, the first and second cooling paths defining dual cooling paths to cool the temperature of the winding unit below the threshold temperature to transition the persistent current switching system from the first mode to the second mode.

2. The continuous current switching system of claim 1, further comprising a flow control member configured to control the flow of the coolant in the cooling tube.

3. The continuous current switching system of claim 2, wherein the flow control member is a cryogenic valve.

4. The continuous current switching system of claim 3, wherein the cryogenic valve is a latching valve.

5. The persistent current switching system of claim 2 wherein the flow control member is an orifice flow restrictor.

6. The persistent current switching system of claim 1 further comprising at least one of a buffer mass and a buffer tank of boil-off gas configured to absorb heat from the coolant.

7. The persistent current switching system of claim 1 wherein the cooling tube circulates the coolant therein to absorb heat generated by the winding unit.

8. The persistent current switching system of claim 1 wherein the solid thermal member comprises one of a thermally conductive metal rod, a thermally conductive metal plate, and a thermally conductive metal bar in direct contact with each of the winding unit and the cooling tube.

9. The persistent current switch system of claim 1 further comprising an additional cooling tube disposed in direct contact with the solid thermal member and configured to circulate a coolant therethrough.

10. The persistent current switch system of claim 1 wherein the cooling tube comprises:

an inlet coupled to a coolant reservoir and configured to receive the coolant from the coolant reservoir; and

an outlet coupled to the coolant reservoir and configured to deliver vaporized coolant from the cooling tube to the coolant reservoir.

Technical Field

The present disclosure relates generally to superconducting systems, and more particularly to systems and methods for cooling a persistent current switch when operating between resistive and superconducting modes in a cryogenic environment.

Background

Superconducting magnets are used in a variety of devices such as, but not limited to, superconducting generators and motors, Magnetic Resonance Imaging (MRI) systems for medical diagnostics, magnetic levitation devices for train transportation and nuclear fusion.

Superconducting magnets are used to generate magnetic fields in superconducting devices. In some methods, current from a power supply is continuously applied to a superconducting magnet to generate a magnetic field. However, the generation of such a strong magnetic field requires a continuous supply of current in the range of several hundred amperes. This constant supply of current to the superconducting magnet increases the operating cost of the superconducting apparatus.

On the other hand, in certain other techniques, the superconducting magnet is energized to operate in a continuous current mode in which current continuously flows in the superconducting loop without any current supply from the power supply. Initially, an external power supply is used to excite the magnetic field of one or more superconducting electrically conductive coils. After the desired magnetic field is achieved and the power supply is disconnected from the magnet, the magnet maintains the current and magnetic field through a persistent current switch coupled in parallel to the superconducting magnet and the power supply. The persistent current switch alternately switches from a normal state to a superconducting state to cause the superconducting magnet to operate in a persistent current mode. These techniques are widely used in magnetic devices such as superconducting generators, motors, and MRI systems. However, when the persistent current switch is operated in the normal state, a certain amount of heat is generated at the persistent current switch. It is desirable to optimally dissipate this heat from the persistent current switch to transition the switch from the normal state to the superconducting state without high vaporization of the cryogen in the superconducting system.

In conventional systems, the superconducting magnet is contained in a helium vessel containing approximately 2000 liters of liquid helium (He). Furthermore, a persistent current switch is fitted around the superconducting magnet, wherein the persistent current switch is immersed in such a helium vessel. Since this arrangement employs a large vessel with thousands of liters of liquid He, the arrangement is not only expensive to manufacture, but is also cumbersome to transport and install at the desired location (e.g., a diagnostic center). In addition, after completing the travel (ride) up to the customer, refilling thousands of liters of liquid He for delivery to a remote location can be inconvenient.

In addition, the liquid He in these systems can sometimes vaporize during a quench (queue) event. The vaporized helium escapes from the cryogen bath in which the magnetic coil is immersed. Thus, each quench event is followed by a refill of liquid He and a re-tilt of the magnet, which is an expensive and time consuming event.

On the other hand, conduction cooled magnet systems require less helium inventory than conventional systems. However, when the persistent current switch main body is in the off state (normal state), the design temperature is high, and therefore the cooling time from the off state to the on state (superconducting state) becomes longer. Such long cooling times are not preferred for system operation. To reduce the time to cool down, one can increase the conductivity of the heat conduction path, however, this will conduct excess heat to the cryogenic tank when the switch is in the off state (and higher temperature) for superconducting coil tilting. During the ramp-up of the superconducting coil, excess heat conduction from the persistent current switch may consume all of the stored liquid cryogen (e.g., liquid helium) before the ramp-up is completed.

Accordingly, there is a need for a superconducting switch and cooling method that provides increased switch cooling rates, increased system reliability, and reduced system thermal instability.

Disclosure of Invention

Aspects and advantages of the disclosure are set forth in the following description, or may be obvious from the description, or may be learned through practice of the disclosure.

Briefly, in accordance with one aspect of the present technique, a persistent current switching system is presented. The persistent current switch includes a vacuum chamber, a winding unit disposed in the vacuum chamber, a first cooling path, and a second cooling path. The winding unit is configured to cause the persistent current switching system to switch from the first mode to the second mode when a temperature associated with the winding unit is below a threshold temperature. The first cooling path includes a solid thermal member in direct contact with the winding unit. The second cooling path includes a cooling pipe disposed in direct contact with the winding unit and configured to circulate a coolant in the cooling pipe. The first cooling path and the second cooling path define a dual cooling path to cool the temperature of the winding unit below a threshold temperature to transition the persistent current switching system from the first mode to the second mode.

In accordance with further aspects of the present technique, a method for cooling a winding unit in a persistent current switch. The method comprises the following steps: disposing the winding unit and the dual cooling paths within a vacuum chamber; switching the continuous current switching system from the first mode to the second mode by reducing the temperature of the winding unit below a threshold temperature; and switching the continuous current switching system from the second mode to the first mode by stopping circulation of the coolant in the cooling tube, thereby increasing the temperature of the winding unit above the threshold temperature. The winding unit is thermally coupled to the dual cooling paths. The dual cooling path includes a first cooling path and a second cooling path. The first cooling path includes a solid thermal member directly connected to the winding unit. The second cooling path includes a cooling pipe directly connected to the winding unit and having a coolant disposed therein. The temperature is lowered below the threshold temperature by circulating a coolant in the cooling tube and by removing heat from the winding unit by direct cooling with a solid thermal member.

In accordance with another aspect of the present technique, a handover system is presented. The switching system includes: a persistent current switch comprising a persistent current switching system; and a superconducting magnet coupled to the persistent current switch system, wherein the superconducting magnet is configured to generate a magnetic field based on the switching. The persistent current switch is disposed in the low magnetic field region and is configured to alternately switch between a first mode and a second mode. The persistent current switch includes a vacuum chamber, a winding unit disposed in the vacuum chamber, a first cooling path, and a second cooling path. The winding unit is configured to cause the persistent current switching system to switch from the first mode to the second mode when a temperature associated with the winding unit is below a threshold temperature. The first cooling path includes a solid thermal member disposed in direct contact with the winding unit. The second cooling path includes a cooling pipe disposed in direct contact with the winding unit and configured to circulate a coolant in the cooling pipe. The first cooling path and the second cooling path define a dual cooling path to cool the temperature of the winding unit below a threshold temperature to transition the persistent current switching system from the first mode to the second mode.

Technical solution 1. a persistent current switching system includes:

a vacuum chamber;

a winding unit disposed in the vacuum chamber and configured to switch the persistent current switching system from a first mode to a second mode when a temperature associated with the winding unit is below a threshold temperature;

a first cooling path including a solid thermal member in direct contact with the winding unit and a second cooling path including a cooling tube disposed in direct contact with the winding unit and configured to circulate a coolant therein, the first and second cooling paths defining dual cooling paths to cool the temperature of the winding unit below the threshold temperature to transition the persistent current switching system from the first mode to the second mode.

Solution 2. the persistent current switching system according to solution 1, characterized in that the persistent current switching system further comprises a flow control member arranged to control the flow of the coolant in the cooling tube.

Claim 3. the persistent current switch system according to claim 2, wherein the flow control member is a cryogenic valve.

Claim 4. the persistent current switch system according to claim 3, wherein the cryogenic valve is a latching valve.

Claim 5. the persistent current switch system according to claim 2, wherein the flow control member is an orifice flow restrictor.

Solution 6. the persistent current switch system according to solution 1, characterized in that the persistent current switch system further comprises at least one of a buffer mass and an evaporation gas buffer tank arranged to absorb heat in the coolant.

The persistent current switch system according to claim 1, wherein the cooling pipe circulates the coolant in the cooling pipe to absorb heat generated by the winding unit.

Claim 8. the persistent current switch system according to claim 1, wherein the solid thermal member comprises one of a heat conductive metal rod, a heat conductive metal plate, and a heat conductive metal rod, which is in direct contact with each of the winding unit and the cooling tube.

The persistent current switch system of claim 9, wherein the persistent current switch system further comprises an additional cooling tube disposed in direct contact with the solid thermal member and configured to circulate a coolant therethrough.

The persistent current switch system according to claim 1, wherein the cooling tube includes:

an inlet coupled to a coolant reservoir and configured to receive the coolant from the coolant reservoir; and

an outlet coupled to the coolant reservoir and configured to deliver vaporized coolant from the cooling tube to the coolant reservoir.

The continuous current switching system of claim 11, wherein the inlet is configured to receive the coolant from the coolant reservoir when the winding unit is above the threshold temperature, and wherein the outlet is configured to deliver the vaporized coolant to the coolant reservoir.

Claim 12 the persistent current switching system according to claim 1, wherein the coolant includes liquid helium (LHe) and Liquid Hydrogen (LH)₂) Liquid neon (LNe) and Liquid Nitrogen (LN)₂) At least one of (1).

A method for cooling a winding unit in a continuous current switching system, the method comprising:

disposing a winding unit and a dual cooling path within a vacuum chamber, the winding unit thermally coupled to the dual cooling path, the dual cooling path including a first cooling path and a second cooling path, wherein the first cooling path includes a solid thermal member directly connected to the winding unit and the second cooling path includes a cooling tube directly connected to the winding unit and having a coolant disposed therein;

switching the persistent current switching system from a first mode to a second mode by reducing a temperature of the winding unit below a threshold temperature, wherein the temperature is reduced below the threshold temperature by circulating the coolant in the cooling tube and by removing heat from the winding unit by direct cooling with the solid thermal member; and

switching the continuous current switching system from the second mode to the first mode by stopping the circulation of the coolant in the cooling tube, thereby increasing the temperature of the winding unit above the threshold temperature.

The method of claim 14, the circulating the coolant in the cooling tube including circulating the coolant to reduce the temperature of the winding unit below the threshold temperature.

The method of claim 15, wherein the coolant is configured to absorb heat generated by the winding unit to reduce the temperature of the winding unit below the threshold temperature.

The method of claim 16, the method further comprising receiving the coolant from a coolant reservoir to cause the persistent current switching system to switch from a first mode to a second mode.

The method of claim 13, further comprising delivering the vaporized coolant from the cooling tube to the coolant reservoir via a recondenser.

The invention according to claim 18 provides a handover system comprising:

a persistent current switching system disposed in a low magnetic field region and configured to alternately switch between a first mode and a second mode, wherein the persistent current switching system comprises:

a vacuum chamber;

a winding unit disposed in the vacuum chamber and configured to switch the persistent current switching system from a first mode to a second mode when a temperature associated with the winding unit is below a threshold temperature;

a first cooling path and a second cooling path, the first cooling path including a solid thermal member disposed in direct contact with the winding unit, the second cooling path including a cooling tube disposed in direct contact with the winding unit and configured to circulate a coolant therethrough, the first cooling path and the second cooling path defining dual cooling paths to cool the temperature of the winding unit below the threshold temperature to transition the persistent current switching system from the first mode to the second mode; and

a superconducting magnet coupled to the persistent current switch system, wherein the superconducting magnet is configured to generate a magnetic field based on the switching of the persistent current switch system between the first mode and the second mode.

The switching system according to claim 18, characterized in that the switching system further comprises a flow control member arranged to control the flow of the coolant in the cooling pipe.

Solution 20. the switching system according to solution 18, wherein the solid thermal member and the winding unit are each in thermal communication with the coolant to absorb heat generated by the winding unit.

These and other features, aspects, and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the principles of the disclosure.

Drawings

A full and enabling disclosure of the present disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures wherein:

fig. 1 is a schematic cross-sectional side view of a persistent current switching system including dual cooling paths in accordance with one or more embodiments of the present disclosure;

fig. 2 is a schematic cross-sectional side view of a persistent current switching system including dual cooling paths in accordance with one or more embodiments of the present disclosure;

fig. 3 is a schematic cross-sectional side view of a persistent current switching system including dual cooling paths in accordance with one or more embodiments of the present disclosure;

FIG. 4 is a graphical comparison of a persistent current switch cooling system utilizing a solid cooling path and a persistent current switch system utilizing a dual cooling path in accordance with one or more embodiments of the present disclosure; and

fig. 5 is a flow diagram illustrating a method for alternately switching a persistent current switch including dual cooling paths between a first mode or normal state and a second mode or superconducting state in accordance with one or more embodiments of the present disclosure.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Detailed Description

One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

When introducing elements of various embodiments of the present invention, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

Embodiments of the present disclosure provide a superconducting switch with an increased cooling rate. In particular, embodiments of the present disclosure provide a superconducting switching system, and more particularly, a persistent current switch that utilizes dual cooling paths to provide an increased cooling rate of the persistent current switch.

Various examples are provided by way of illustration of the present disclosure and not by way of limitation thereof. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present disclosure without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment. Accordingly, the disclosure is intended to cover such modifications and variations as fall within the scope of the appended claims and their equivalents. Although for purposes of illustration, exemplary embodiments of the present disclosure will generally be described in the context of superconducting generators and motors, one of ordinary skill in the art will readily recognize that embodiments of the present disclosure may be used in combination with any component for heating and/or cooling (such as components associated with CT scanners, MRI systems, etc.), and are not intended to be limited to cooling implementations having superconducting components.

As will be described in detail below, various embodiments of an exemplary persistent current switch system including dual cooling paths and methods for cooling a persistent current switch to alternately switch between a first mode and a second mode are presented. By employing the methods described below, as well as various embodiments of persistent current switches and switching systems, the size of the magnetic device, manufacturing costs, installation costs, cooling time to effect switching, and costs of operating the magnetic device can be significantly reduced.

Turning now to the drawings and referring to fig. 1, a cross-sectional side view of a persistent current switching system 10 is depicted in accordance with aspects of the present technique. The persistent current switching system 10 may be configured to alternately switch between a first mode and a second mode. The first mode may represent a normal state in which the persistent current switch winding unit (described so far) provides a high resistance. Similarly, the second mode may represent a superconducting state, in which the persistent current switch winding unit provides zero resistance. It may be noted that the terms "normal state", "resistive state" and "first mode" may be used interchangeably, and the terms "superconducting state" and "second mode" may be used interchangeably. Persistent current switching system 10 is typically used to operate superconducting magnet 98 in a persistent current mode.

In the presently contemplated configuration, the continuous current switching system 10 includes a vacuum chamber 12, a winding unit 14 (also referred to herein as a "switch"), dual cooling paths 16, and a reservoir 18. The vacuum chamber 12 may be provided as a unit in a magnetic device such as a superconducting generator or motor. The vacuum chamber 12 has defined therein a vacuum space 13. It may be noted that embodiments of persistent current switch system 10 are not limited to this embodiment, and may be implemented in other devices, such as other types of superconducting electrical machines, superconducting magnet energy storage systems, MRI systems, and the like. In one embodiment, a vacuum chamber/environment may already exist in the system, and the magnet and persistent current switch system may be implemented in an existing vacuum environment.

During operation, and optionally by means of a heater (not shown), the temperature of the winding unit 14 is heated above a threshold temperature. The threshold temperature may be represented as a critical design temperature of the winding unit 14 above which the winding unit 14 transitions from a superconducting state to a normal or resistive state.

In the presently contemplated configuration, the persistent current switching system 10 is configured to alternately switch the winding unit 14 between the normal state and the superconducting state. In an exemplary embodiment, the winding unit 14 may be a linear structure wound on the outer circumference of a bobbin or the like. In one embodiment, the winding unit 14 may be wound on a bobbin in two wires to minimize the inductance of the winding unit 14.

The winding unit 14 and the dual cooling path are disposed in the vacuum chamber 12, and more particularly, within the vacuum space 13. The dual cooling paths 16 are configured to cool the winding unit 14 below a threshold temperature. To provide such cooling, the dual cooling paths 16 are thermally coupled to the winding unit 14 and configured to cool the temperature of the winding unit 14 below a threshold temperature (T;)_c) To switch the winding unit 14 from the first mode to the second mode. The dual cooling path 16 is constituted by a first cooling path 20 and a second cooling path 22. The first cooling path 20 is configured as a solid cooling path, wherein the solid thermal member 24 is thermally coupled to both the winding unit 14 and the cooling tube 26. More particularly, the solid thermal member 24 is in direct contact with both the winding unit 14 and the cooling tube 26. In an embodiment, a first end 23 of the solid thermal member 24 is in direct contact with the winding unit 14 and an opposite second end 25 of the solid thermal member 24 is in direct contact with the cooling tube 26. In contrast to the first cooling path 20, the second cooling path 22 does not employ a solid thermal member and is configured as a tube cooling path that provides a cooling tube 26 to be thermally coupled to the winding unit14 and more particularly, the cooling tube 26 is disposed in direct contact with the winding unit 14.

During the on-off cooling process (described presently), the cooling tube 26 is configured to circulate a coolant 28 through the cooling tube 26. Coolant 28 may include liquid helium LHe, Liquid Hydrogen (LH)₂) Liquid neon (LNe) or Liquid Nitrogen (LN)₂). In one embodiment, the winding unit 14 may be a low temperature superconductor, a medium temperature superconductor, or a high temperature superconductor. Also, the coolant may be selected based on the type of superconductor used for the winding unit 14. For example, persistent current switching systems with cryogenic superconductors may employ liquid helium (LHe) as a coolant. Similarly, for intermediate temperature superconductors, LHe, liquid neon (LNe), or Liquid Hydrogen (LH)₂) Can be used as a coolant. In addition, for high temperature superconductors, LNe or Liquid Nitrogen (LN)₂) May be used as a coolant in the system.

As indicated previously, in the exemplary embodiment, dual cooling paths 16 are configured to reduce the temperature of winding unit 14 below the threshold temperature at an accelerated rate that is faster than the rate at which cooling is achieved by using only a single cooling path. According to embodiments, the solid thermal member 24 of the first cooling path 20 may be any thermally conductive member, such as a metal plate, rod, or bar. In embodiments, the solid thermal member 24 may be, for example, brass, aluminum, and/or a copper plate, rod, or bar. As previously described, the solid thermal member 24 is in direct contact with the winding unit 14 and the cooling tube 26. The solid thermal member 25 provides conduction of heat from the winding unit 14 to the coolant 28 in the cooling tube 26. As previously described, the winding unit 14 is in direct contact with the cooling tube 26 and provides for conduction of heat from the winding unit 14 to the coolant 28 in the cooling tube 26.

The cooling tube 26 may include an inlet 30 at one end of the cooling tube 26 and an outlet 32 at the other end. Further, the inlet 30 is operatively coupled to an outlet 34 of the reservoir 18. It may be noted that the terms "reservoir" and "coolant reservoir" may be used interchangeably. The inlet 30 is configured to receive the coolant 28 from the reservoir 18. The cooling tube 26 defines a passage 36 therein, the passage 36 operatively coupling the cooling tube 26 and the reservoir 18 to convey the coolant 28 from the reservoir 18 through the cooling tube 26 for cooling the winding unit 14. Flow control members 38 are disposed along the cooling tubes 26 to regulate the flow of coolant 28 from the reservoir 18 through the cooling tubes 26. In one embodiment, the flow control member 40 is a cryogenic valve 40 (such as a latching valve) that is capable of controlling the flow of the coolant 28 within the cooling tube 26, and thus the rate at which heat is removed from the winding unit 14. In an embodiment, cryogenic valve 40 generates no heat other than transient heat during a change in valve state between open and closed states (and vice versa). In one embodiment, the inlet 30 of the cooling tube 26 is configured to receive the coolant 28 from the reservoir 18 when the winding unit 14 is on (superconducting state). The reservoir 18 may also be referred to as a storage unit for storing the coolant 28 and/or condensing the coolant 28. In certain embodiments, the reservoir 18 may include a release valve (not shown). The relief valve may be configured to help control any pressure build-up within the reservoir 18. The release valve may be configured to automatically and/or manually release any pressure buildup within the reservoir 18.

In a similar manner, the cooling tube 26 is operatively coupled to the inlet 44 of the recondenser 46 and is configured to convey the vaporized coolant 28 from the cooling tube 26 to the reservoir 18. In the illustrated embodiment, the recondenser 46 is coupled to a cryocooler 48. The outlet 52 of the recondenser is coupled to the reservoir 18. The outlet 32 of the cooling tube 26 is configured to deliver the vaporized coolant 28 from the cooling tube 26 to the reservoir 18 via the recondenser 46 when the winding unit 14 is off (normal state).

Superconducting (SC) switches (and more particularly, winding units 14) typically operate in a resistive state at temperatures well above a critical temperature (e.g., 50K-60K) during the magnet tilting process. After the magnet is energized to full current and the flow control means 38 are turned on, the winding unit 14 is cooled (to a superconducting state). During this cooling process, the coolant 28 will vaporize and be heated before it returns to the cryocooler reservoir 18. To minimize the potential impact of the heated coolant 28 on the cooling tubes 26 and the winding units 14, an optional buffer mass (such as a copper block, copper and epoxy composite, etc.) 50 and/or an optional boil-off gas buffer tank 56 are thermally attached to the return path of the cooling tubes 26 to cool the vaporized coolant 28 and reduce its impact on the overall cooling system. In the embodiment of fig. 1, an optional buffer mass 50 is provided between the winding unit 14 and the recondensor 46 to avoid heating the recondensor 46 too quickly when the flow control member 38 is open for on-off cooling. In another embodiment, the return gas (and more particularly, the vaporized coolant 28) may enter a vaporized gas buffer tank 56 disposed between the winding unit 14 and the recondenser 46.

As noted previously, in conventional bath cooling systems, the persistent current switch is typically submerged in a coolant vessel containing liquid He. When the switch is cooled, the liquid He evaporates and can be discharged from the system to the external environment. Furthermore, to compensate for this discharged liquid He, the coolant vessel is refilled with new liquid He, an expensive and time consuming event. In addition, this arrangement requires several liters of liquid He to refill the coolant container. Some or all of these disadvantages of currently available persistent current switches may be avoided via the use of embodiments consistent with the example persistent current switch system 10 that incorporates the disclosed dual cooling path 16.

In accordance with aspects of the present technique, the vaporized coolant 28 from the cooling tube 26 is delivered to the recondenser 46, where the vaporized coolant 28 recondenses and is delivered back to the reservoir 18 and ultimately to the cooling tube 26. This recondensing or recirculation of the vaporized coolant 28 substantially minimizes or in some cases eliminates the need for refilling the coolant reservoir 18, which in turn reduces the size and weight of the reservoir 18. Also, the use of liters of coolant in the system can be avoided since the coolant is recondensed and reused in the cooling tubes 26. This in turn reduces the manufacturing cost and weight of the system.

It may be noted that the persistent current switch system 10 is assumed to be operating in a normal state at the beginning. The normal state represents a state in which the winding unit 14 provides a high resistance to the superconducting magnet. Also, in order for the persistent current switching system 10 to operate in a normal state, the temperature of the winding unit 14 is maintained above the threshold temperature.

To switch the persistent current switching system 10 from the normal state to the superconducting state, the winding unit 14 (and more particularly, an optional associated heating unit (not shown)) is de-energized or turned off, and the cooling tube 26 is filled with coolant 28 received from the reservoir 18. A coolant 28 is circulated in the cooling tube 26 to maintain and/or reduce the temperature of the winding unit 14 below a threshold or critical temperature via the first and second cooling paths 20, 22. During the cooling process, the cooling tube 26 is in direct thermal contact with the solid thermal member 24 and the winding unit 14 and provides heat absorption from the winding unit 14 via the dual cooling paths 16. If the temperature of the winding element 14 is below the threshold temperature, the winding element 14 switches from the normal state to the superconducting state. As noted previously, the superconducting state may represent a state in which the winding unit 14 provides zero resistance to the superconducting magnet. Such zero resistance of the winding unit 14 helps to form a continuous loop in which current circulates between the winding unit 14 and the superconducting magnet without any further supply of current from a power supply (not shown in fig. 1). In one embodiment, when the persistent current switching system 10 is operating in a superconducting state, it may be noted that the external thermal load on the persistent current switching system 10 is relatively small. The source of the external thermal load may include thermal radiation. MLI-extended multilayer insulation may be used around the persistent current switching system 10 to further reduce such small thermal loads. In another embodiment, the persistent current switch system 10 may be a stand-alone entity with its own reservoir and may be placed anywhere around the superconducting magnet in the vacuum space 13.

Typically, the persistent current switching system 10 operates in a superconducting state if the temperature of the winding unit 14 is below a threshold temperature. Otherwise, the persistent current switch system 10 operates in a normal state. To switch the persistent current switch system 10 from the superconducting state to the normal state, the flow control member 38 disposed in the cooling tube 26 in fluid communication is closed. The flow control member 38 is designed to block or obstruct the flow of coolant 28 from the reservoir 18 through the cooling tubes 26, and also to prevent backflow of coolant 28 from the cooling tubes 26 to the reservoir 18. During operation or heating of the winding unit 14, the temperature of the winding unit 14 increases or rises above a threshold temperature. This increased temperature of the winding unit 14 causes the persistent current switching system 10 to transition from the superconducting state to the normal state.

During the transition of the persistent current switching system 10 (and more particularly, the winding unit 14) to the normal state, the vaporized coolant 28 is delivered out of the cooling tube 26 via the cooling tube outlet 32 to reach the reservoir 18 via the inlet 44 and outlet 52 of the recondenser 46 and the inlet 54 of the reservoir. In one embodiment, the density difference of the refrigerant (such as the coolant 28) may be used to drive the vaporized coolant 28 out of the cooling tube 26 to the reservoir 18 via the recondenser 46. After recondensation in recondensor 48, recondensed coolant 28 is stored in reservoir 18. During switching of the persistent current switching system 10 (and more particularly, the winding unit 14) from the normal state to the superconducting state, this recondensed coolant is circulated back to the cooling tube 26.

Thus, by employing the persistent current switch system 10 of fig. 1, the coolant 28 in the cooling tube 26 is efficiently utilized when used in a system having a low cryogen volume in a vacuum environment, and provides additional cooling beyond systems that utilize only a single cooling path (such as a solid thermal component). In addition, since the persistent current switch system 10 has its own low temperature environment or dual path cooling system, the persistent current switch system 10 can be used as a stand-alone entity. More specifically, the persistent current switch system 10 may be placed in close proximity to the superconducting magnet, or may be conveniently disposed at a distance from the superconducting magnet in the low magnetic field region. The exemplary persistent current switching system 10 allows for improved response times relative to known systems while alternately switching between a normal state and a superconducting state. The persistent current switching system 10 is configured to switch from the normal state to the superconducting state (see fig. 4) for a period of time in the range of about 1 minute to about 15 minutes. In one embodiment, the persistent current switch system 10 (and more particularly, the winding unit 14) may be disposed in a horizontal position, a vertical position, or a tilted position on the superconducting magnet.

Referring to fig. 2, a cross-sectional view of a persistent current switch system 60 is depicted in accordance with another embodiment of the present technique. The embodiment of FIG. 2 is similar to the embodiment of FIG. 1, except that the flow control device 38 is configured as an orifice flow restrictor 62, the orifice flow restrictor 62 being disposed in fluid communication with the cooling tube 26 to regulate the flow of coolant 28 from the reservoir 18 through the cooling tube 26. In addition, a flow control device 38 is arranged in the cooling tube 26 between the winding unit 14 and the recondenser 46. Additionally, as previously mentioned, the reservoir may also include a relief valve 64, the relief valve 64 being used to relieve any pressure build up within the reservoir 18. In the embodiment depicted in FIG. 2, the orifice flow restrictor 62 functions as a flow restrictor within the cooling tube 26 for the coolant 28 flowing through the cooling tube 26. It should be understood that alternative types of flow control components other than cryogenic latching valves and orifice flow restrictors are contemplated herein, such as, but not limited to, a long stem cryogenic valve.

In the presently contemplated configuration, the continuous current switching system 60 includes the vacuum chamber 12, the winding unit 14, the reservoir 18, and the dual cooling paths 16. As previously described, the dual cooling path 16, which is comprised of the first cooling path 20 and the second cooling path 22, is configured to reduce the temperature of the winding unit 14 below a threshold temperature. The cooling tube 26 includes an inlet 30 and an outlet 32. The inlet 30 is configured to receive the coolant 28 from the reservoir 18 via a passage 36 defined within the cooling tube 26, and the outlet 32 is configured to deliver vaporized coolant from the cooling tube 26 to the reservoir 18. Additionally, a flow control member 38 is disposed in fluid communication with the passage 36 to regulate the flow of the coolant 28 from the reservoir 18 through the cooling tubes 26.

In accordance with aspects of the present technique, the persistent current switching system 60 (and more particularly, the winding unit 14) is configured to alternately switch between a normal state and a superconducting state. As previously described with reference to fig. 1, by employing the persistent current switch system 60 of fig. 2, the coolant 28 in the cooling tube 26 is efficiently utilized when used in a system having a low cryogen volume in a vacuum environment, and provides additional cooling beyond systems that utilize only a single cooling path (such as a solid thermal component).

Turning now to fig. 3, a cross-sectional side view of a persistent current switching system 70 is depicted in accordance with yet another embodiment of the present technique. The embodiment of fig. 3 is similar to the embodiment of fig. 1, except that while the dual cooling path 16 of fig. 1 employs the solid thermal member 24 of the first cooling path 20 coupled to the same cooling tube 26 of the second cooling path 22, in the embodiment of fig. 3, the first cooling tube 72 is in direct contact with the solid thermal member 24 for removing heat from the winding unit 14, and the second cooling tube 74 is positioned in direct contact with the winding unit 14 and provides for heat removal from the winding unit 14. The coolant 28 flows through the passages formed in each of the first cooling pipe 72 and the second cooling pipe 74. It should be noted that in the embodiment of fig. 3, the coolant 28 in the first cooling tube 72 is output into the second cooling tube 74 at the outlet 78 before reaching the recondenser 46. In an alternative embodiment, the coolant 28 in the first cooling tube 72 may be output from the outlet 78 directly into an inlet (not shown) of the recondenser 46.

In addition, the persistent current switch system 70 also includes a winding unit 14 and a reservoir 18 that are arranged and operated in a manner substantially similar to the persistent current switch system 10 of fig. 1.

Similar to the previously disclosed embodiments, the dual cooling paths 16 are configured to reduce the temperature of the winding unit 14 below the threshold temperature in a shorter amount of time than if a single cooling path were used. According to embodiments, the solid thermal member 24 of the first cooling path 20 may be any thermally conductive member, such as a metal plate, rod, or bar. The solid thermal member 24 may be, for example, brass, aluminum, and/or a copper plate, rod, or bar. The solid thermal member 24 is in direct contact with the winding unit 14 and the first cooling tube 72. The solid thermal member 25 provides conduction of heat from the winding unit 14 to the coolant 28 in the first cooling tube 72.

The first cooling tube 72 may include an inlet 76 at one end of the cooling tube 72 and an outlet 78 at the other end. Further, the inlet 76 is operatively coupled to an outlet 80 of the reservoir 18. The inlet 76 is configured to receive the coolant 28 from the reservoir 18. The first cooling tube 72 defines a channel 82 therein, the channel 82 operatively coupling the first cooling tube 72 and the reservoir 18 to convey the coolant 28 from the reservoir 18 through the first cooling tube 72 for cooling the winding unit 14 via the solid thermal member 24.

The second cooling tube 74 is positioned in direct contact with the winding unit 14 and provides heat removal from the winding unit 14. The second cooling tube 74 may include an inlet 84 at one end of the second cooling tube 74 and an outlet 86 at the other end. Further, the inlet 84 is operatively coupled to the outlet 88 of the reservoir 18. The inlet 84 is configured to receive the coolant 28 from the reservoir 18. The second cooling tube 74 defines a passage 90 therein, the passage 90 operatively coupling the second cooling tube 74 and the reservoir 18 to convey the coolant 28 from the reservoir 18 through the second cooling tube 74 for cooling the winding unit 14.

The flow control member 38 is disposed along the second cooling tube 74 to regulate the flow of the coolant 28 from the reservoir 18 through the second cooling tube 74. In one embodiment, the flow control member 38 is a cryogenic valve 40 that is capable of controlling the flow of the coolant 28 within the second cooling tube 74, and thus the rate at which heat is removed from the winding unit 14. In an alternative embodiment, one or more additional flow control members may be disposed in fluid communication with first cooling tube 72 to control the flow of coolant 28 through first cooling tube 72.

In one embodiment, the inlets 76, 84 of the first and second cooling tubes 72, 74, respectively, are configured to receive the coolant 28 from the reservoir 18 when the persistent current switching system 70 is de-energized or off (superconducting state).

The first and second cooling tubes 72, 74 are operatively coupled to the inlet 44 of the recondenser 46 and are configured to deliver the vaporized coolant 28 from the first and second cooling tubes 72, 74 to the reservoir 18. In the illustrated embodiment, the recondenser 46 is coupled to a cryocooler 48. The respective outlets 78, 86 of the first and second cooling tubes 72, 74 are configured to deliver vaporized coolant 28 from the respective cooling tubes 72, 74 to the reservoir 18 when the persistent current switching system 70 (and more particularly, the winding unit 14) is energized or turned on.

Further, in accordance with aspects of the present technique, the winding unit 14 is configured to alternately switch the persistent current switching system 70 between the normal state and the superconducting state. The coolant 28 in the first cooling tube 72 and the second cooling tube 74 absorbs heat generated by the winding unit 14. As the heat is absorbed by the coolant 28, the winding unit 14 is cooled, and the temperature of the winding unit 14 falls below the threshold temperature. This temperature drop helps to switch the winding unit 14 from the normal state to the superconducting state. As previously described with reference to fig. 1, by employing the persistent current switching system 70 of fig. 3, the coolant 28 in the first and second cooling tubes 72, 74 is efficiently utilized when used in a system having a low cryogen volume in a vacuum environment, and provides faster and additional cooling over systems that utilize only a single cooling path (such as a solid thermal member).

Further, to switch the persistent current switching system 70 (and more particularly, the winding unit 14) from the normal state to the superconducting state, the heating unit (not shown) is de-energized or turned off, and the first and second cooling tubes 72, 74 are filled with the coolant 28 received from the reservoir 18. The coolant 28 circulates in the first cooling tube 72 and the second cooling tube 74 to maintain or reduce the temperature of the winding unit 14 below a threshold or critical temperature. If the temperature of the winding element 14 is below the threshold temperature, the winding element 14 switches from the normal state to the superconducting state. The superconducting state represents a state in which the winding unit 14 provides zero resistance to the superconducting magnet. Such zero resistance of the winding elements 14 helps to form a continuous loop in which current circulates between the winding elements 14 and the superconducting magnet without any supply of current from a power supply (not shown in fig. 3).

Typically, the persistent current switching system 10, 60, 70 of fig. 1-3 will operate in a superconducting state if the temperature of the winding unit 14 is below a threshold temperature. In some cases, the persistent current switch system 10, 60, 70 switches to a normal state. For example, in the event that the magnet must be ramped down, it may be desirable to switch the persistent current switch system 10, 60, 70 to a normal state. In order to switch the winding unit 14 from the superconducting state to the normal state, the flow control means 38 arranged in fluid communication with the cooling pipe is closed. In particular, flow control member 38 is closed to block or reduce the inflow of coolant 28 from reservoir 18 to the cooling tube(s), and also to prevent backflow of coolant 28 from the cooling tube(s) to reservoir 18. In addition, an optional heating unit (not shown) is energized or turned on to heat the winding unit 14. By heating the winding unit 14, the temperature of the winding unit 14 is increased or raised above a threshold temperature, which causes the winding unit 14 to transition from the superconducting state to the normal state. This transition of the persistent current switch system 10, 60, 70 to the normal state switches the magnetic device (such as a magnetic coil) for de-energizing the magnet.

The vaporized coolant is conveyed out of the cooling tube(s) to the reservoir 18 via the recondenser 46. In addition, the vaporized coolant is recondensed and stored in the reservoir 18. During switching of the persistent current switching system 10, 60, 70 (and more particularly, the winding unit 14) from the normal state to the superconducting state, this recondensed coolant is circulated back to the cooling tube(s) 26, 72, 74. The persistent current switch 616 is operatively coupled to the superconducting MRI magnet 602.

Referring now to fig. 4, a comparative cooling time achieved between a known continuous switching system using solid thermal members for direct cooling and a continuous current switching system including dual cooling paths in accordance with an exemplary embodiment is illustrated in an exemplary graphical representation generally designated 100. More specifically, graph 100 illustrates a temperature (K) (plotted on y-axis 102) versus time (plotted on x-axis 104) for a known continuous current switching system (shown by plot line 106) utilizing a thermal shunt of 2W at 60K as the solid cooling path, as compared to a continuous current switching system (shown by plot line 108) utilizing dual cooling paths (and more particularly, a first cooling path including a solid thermal component directly connected to the winding unit to define the solid cooling path and a second cooling path including a cooling tube of liquid helium directly connected to the winding unit) as disclosed herein.

As graphically demonstrated, the switch cooling time may be reduced from approximately 300 minutes for a conventional persistent current switching system to approximately 20 minutes for a novel persistent current switching system including dual cooling paths as disclosed herein. A reduction in time for switch cooling is achieved by using dual cooling paths.

Referring to fig. 5, a flow diagram 110 is depicted, the flow diagram 110 illustrating a method for alternately switching winding units between a first mode or normal state and a second mode or superconducting state using dual cooling paths (such as the persistent current switching system 10 of fig. 1) in accordance with aspects of the present technique. To facilitate an understanding of the present technique, the method is described with reference to the components of FIG. 1. It may be noted that the first mode represents the normal state of the persistent current switch, while the second mode represents the superconducting state. Also, in the normal state, the persistent current switch provides a high resistance to the current flowing in the associated magnetic device. In the superconducting state, however, the persistent current switch winding unit 14 provides zero resistance to the current flowing in the magnetic device.

The method begins at step 112, where dual cooling paths (such as the dual cooling path 16 of fig. 1, and more particularly, the first cooling path 20 and the second cooling path 22 of fig. 1) and winding units (such as the winding unit 14 of fig. 1) are disposed within a vacuum chamber (such as the vacuum chamber 12 of fig. 1) at step 112. In particular, the dual cooling paths are arranged within the vacuum chamber in the following manner: the first cooling path (and more particularly, a solid thermal member, such as the solid thermal member 24 of fig. 1) is disposed in direct contact with the winding unit and the cooling tube (such as the cooling tube 26 of fig. 1), and the second cooling path (and more particularly, the cooling tube) is disposed in direct contact with the winding unit. In one embodiment, the first cooling path and the second cooling path utilize a single cooling tube. The cooling tubes include inlets and outlets, such as inlet 30 and outlet 32 of FIG. 1. The inlet is operatively coupled to an outlet of a reservoir, such as outlet 34 of reservoir 18 of fig. 1, via a passage defined in the cooling tube, such as passage 36 of fig. 1. Similarly, the outlet of the cooling tube is operatively coupled to an inlet of a reservoir, such as inlet 54 of fig. 1, via a recondenser (such as recondenser 46 of fig. 1). In another embodiment, the first cooling path and the second cooling path utilize separate cooling tubes (and more particularly, a first cooling tube (such as the first cooling tube 72 of fig. 3) and a second cooling tube (such as the second cooling tube 74 of fig. 3)), respectively.

Subsequently, the cooling tube circulates a coolant (such as coolant 28 of fig. 1) to remove heat from the winding unit by absorption by the solid thermal member and directly from the winding unit. Since the cooling tube is coupled to the reservoir, coolant is initially received from the reservoir and circulated in the cooling tube to absorb heat generated by the winding unit, which in turn reduces the temperature of the winding unit. In one embodiment, the coolant is received from the reservoir when the heating unit is de-energized or turned off and at least a portion of the coolant is evaporated.

Further, at step 114, the persistent current switch (and more particularly, the winding unit) is switched from the first mode or normal state to the second mode or superconducting state by lowering the temperature of the winding unit below a threshold temperature. The temperature of the winding unit is lowered below the threshold temperature by circulating a coolant in a cooling pipe in contact with the winding unit and by directly cooling the winding unit with a solid thermal member. In particular, the coolant circulating in the cooling pipe may be used to absorb heat generated by the winding unit via the dual cooling paths, thereby cooling the winding unit. The heat absorption by the coolant causes the temperature of the winding unit to drop below the threshold temperature. The persistent current switch switches from the normal state or first mode to the superconducting state or second mode as the temperature drops below the threshold temperature. In addition, during the process of cooling the temperature of the winding unit, a portion of the coolant in the cooling pipe may evaporate. More specifically, the heat generated by the winding unit is absorbed by the coolant in the cooling pipe, which in turn evaporates the coolant. The vaporized coolant is then conveyed out of the cooling tube via the outlet of the cooling tube. Furthermore, the evaporated coolant is conveyed to the reservoir via a recondenser. At the recondenser, the vaporized coolant recondenses to a liquid coolant and is delivered back to the reservoir.

In addition, at step 116, circulation of coolant in the cooling pipe is stopped, thus increasing the temperature of the winding unit to a temperature higher than the threshold temperature. The persistent current switching system transitions from the second mode to the first mode by increasing the temperature above a threshold temperature. Initially, when the persistent current switching system is operated in the superconducting state or the second mode, the dual cooling paths (and more particularly, the first cooling path and the second cooling path) are utilized to maintain the temperature of the winding unit below the threshold temperature. Subsequently, in order to make the persistent current switching system transition from the superconducting state to the normal state, the temperature of the winding unit is allowed to rise above the threshold temperature. In order to increase or raise the temperature, an optional heating unit may be used to heat the winding unit. Thus, by employing the above-described method, the persistent current switching system alternately switches between the first mode and the second mode in a manner that reduces the switching cooling time relative to a manner that typically employs a single cooling path of a single solid thermal member.

Accordingly, various embodiments provide a persistent current switch, and more particularly, a persistent current switch system, that utilizes dual cooling paths for cooling, whereby a solid thermal member directly connected to a winding unit at a first end and directly connected to a cooling tube at a second end provides cooling along a first cooling path, and a cooling tube directly connected to a winding unit provides cooling along a second cooling path. Furthermore, implementation in superconducting systems provides a reduction in the time required to cool the winding unit below the threshold temperature and a reduction in magnet weight by eliminating the large liquid He storage vessels typically used in superconducting magnets and recirculating the liquid He as a coolant. In various embodiments, no maintenance or addition of refrigerant is required, and the overall system weight may be reduced.

The systems and methods described above for alternately switching systems (and more particularly, winding units) utilizing dual cooling paths help reduce the required switching time and reduce the manufacturing cost and weight of the magnetic device. In addition, a reduction in the preparation/lead time for operation of the system and a reduction in thermal instability of the system may be achieved. As a result, labor for preparation and system maintenance may be reduced, the operating rate of the system may be increased, and system reliability may be increased. Also, thousands of liters of coolant or liquid He in a reservoir or storage vessel can be prevented from being used since the vaporized coolant is recondensed and circulated back to the cooling unit of the persistent current switching system. Further, the arrangement of the present technique provides a very fast response time, such as a fast cool down time, for the persistent current switch.

While only certain features of the disclosure have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.