Temperature limiting fixed current ramp lead for sealed low refrigerant superconducting machine

Abstract

The invention relates to a temperature-limited fixed current ramp lead for a sealed low refrigerant superconducting machine. A superconducting machine system includes a superconducting electric machine and a freezing container surrounding the superconducting electric machine. A superconducting machine system includes a ramped lead assembly disposed within a vacuum vessel wall and having a first end and a second end. A first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and a second end is coupled to a high temperature superconductor supply lead coupled to the superconducting switch. The ramp lead assembly includes a non-conductive support and a metal rod. The ramp lead assembly includes a thermal storage device coupled to the metal rod. The heat storage device is configured to store heat, limit transfer of heat along the metal rod, and limit a temperature increase along the ramp lead assembly during energization of the superconducting machine.

Description

BACKGROUND OF THE INVENTION

[0001] The subject matter disclosed herein relates to a temperature-limited fixed current ramp lead for sealing a cryogenic superconducting machine.

[0002] Non-invasive imaging techniques allow for the acquisition of images of the internal structures or features of a patient / object without performing an invasive procedure on the patient / object. Specifically, such non-invasive imaging techniques rely on various physical principles (such as differential transmission of X-rays through a target volume, reflection of sound waves within a volume, paramagnetism of different tissues and materials within a volume, decomposition of a target radionuclide within the body, etc.) to collect data and construct images or otherwise represent the observed internal features of the patient / object.

[0003] During magnetic resonance imaging (MRI), when a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with the polarizing field, but precess around the polarizing field in a random order at their characteristic Larmor frequency. If the substance or tissue is subjected to a magnetic field (excitation field B1) in the x-y plane and near the Larmor frequency, the net alignment torque or "longitudinal magnetization" M z can be rotated or "tilted" into the x-y plane to produce a net transverse magnetic moment M t . After termination of the excitation signal B1, the spins emit a signal, which can be received and processed to form an image.

[0004] When using these signals to generate an image, magnetic field gradients (G x , G y and G z ) are employed. Typically, the region to be imaged is scanned in a series of measurement cycles, in which these gradient fields vary according to the particular positioning method used. The resulting set of received nuclear magnetic resonance (NMR) signals is digitized and processed to reconstruct an image using one of the well-known reconstruction techniques.

[0005] MRI systems can utilize superconducting magnets using NbTi conductors, and other superconductors can be employed at temperatures similar to or higher than NbTi. Moreover, MRI systems require a cooling system that can operate using a cryogen (a very cold liquid), but can use a conductive material (such as copper) to directly cool the magnet. Ramp leads are used to energize superconducting MRI magnets (as well as other types of superconducting machines, such as motors and generators). Typically, these ramp leads can be fixed (permanently in place) or separable / retractable (either method will disrupt the electrical and thermal connection between room temperature and the magnet), and thus have moving parts. Ramp leads that are not completely removed after use will result in parasitic heat leakage in the superconducting MRI magnet. SUMMARY OF THE INVENTION

[0006] An overview of certain embodiments disclosed herein is shown below. It should be understood that these aspects are provided merely to give the reader a brief overview of these particular embodiments and are not intended to limit the scope of the disclosure. Indeed, the disclosure may cover various aspects that may not be shown below.

[0007] In one embodiment, a superconducting machine system is provided. The superconducting machine system includes a superconducting machine. The superconducting machine system also includes a cryogenic vessel. The cryogenic vessel surrounds the superconducting machine. A vacuum vessel wall surrounds the cryogenic vessel. The superconducting machine system also includes a superconducting switch that is coupled to the superconducting machine and configured to switch between a resistive mode and a superconducting mode. The superconducting machine system further includes a ramp lead assembly that is disposed within the vacuum vessel wall and has a first end and a second end. The first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high-temperature superconductor power lead that is coupled to the superconducting switch. The ramp lead assembly includes a non-conductive support. The ramp lead assembly also includes a metal rod that is configured to minimize the static heat load, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end. The ramp lead assembly further includes a heat storage device that is coupled to the metal rod between the first end and the second end. The heat storage device is configured to store heat during energization of the superconducting machine to limit heat transfer along the metal rod to the second end during energization of the superconducting machine and to limit the temperature rise along the ramp lead assembly during energization of the superconducting machine. The high-temperature superconductor portion of the high-temperature superconductor power lead is disposed between the second end of the metal rod and the superconducting switch.

[0008] In another embodiment, a superconducting magnet system for a magnetic resonance imaging system is provided. The superconducting magnet system includes a superconducting magnet. The superconducting magnet system also includes a cryogenic vessel that surrounds the superconducting magnet. A vacuum vessel wall surrounds the cryogenic vessel. The superconducting magnet system further includes a superconducting switch that is coupled to the superconducting magnet and configured to switch between a resistive mode and a superconducting mode. The superconducting magnet system even further includes a ramp lead assembly that is disposed within the vacuum vessel wall and has a first end and a second end, wherein the first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high temperature superconductor power lead that is coupled to the superconducting switch. The ramp lead assembly includes a non-conductive support. The ramp lead assembly also includes a metal rod that is configured to minimize a static heat load, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end. The ramp lead assembly further includes a solid metal structure that is coupled to the metal rod between the first end and the second end, wherein the ramp lead assembly is configured such that heat preferentially flows to the solid metal structure during energization of the superconducting magnet rather than along the metal rod toward the second end. The high temperature superconductor portion of the high temperature superconductor power lead is disposed between the second end of the metal rod and the superconducting switch.

[0009] In another embodiment, a method for limiting the temperature of a ramp lead assembly coupled to a superconducting magnet of a magnetic resonance imaging system is provided. The method includes energizing a superconducting magnet disposed within a cryogenic vessel that is disposed within a vacuum vessel wall. The magnetic resonance imaging system includes a ramp lead assembly that is disposed within the vacuum vessel wall and has a first end and a second end, wherein the first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high temperature superconductor power lead that is coupled to a superconducting switch. The ramp lead assembly includes a non-conductive support. The ramp lead assembly also includes a metal rod that minimizes a static heat load during energization of the superconducting magnet, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end. The high temperature superconductor portion of the high temperature superconductor power lead is disposed between the second end of the metal rod and the superconducting switch, which is configured to further reduce heat transfer into the superconducting magnet. The ramp lead assembly further includes a heat storage device that is coupled to the metal rod between the first end and the second end. The method also includes storing heat during energization of the superconducting magnet, restricting heat transfer along the metal rod to the second end during energization of the superconducting magnet, and restricting a temperature rise along the ramp lead assembly during energization of the superconducting magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and other features, aspects, and advantages of the present disclosure will be better understood when the following detailed description is read with reference to the accompanying drawings, in which like reference symbols represent like parts throughout the drawings, wherein:

[0011] Figure 1 is a schematic diagram of an exemplary magnetic resonance system in accordance with aspects of the present disclosure;

[0012] Figure 2 is a schematic diagram of a current or power ramp lead coupled to a superconducting switch in accordance with aspects of the present disclosure;

[0013] Figure 3 is in accordance with aspects of the present disclosure for use with Figure 1 a schematic diagram of a current ramp lead for use with a superconducting magnet of a magnetic resonance system in;

[0014] Figure 4 is in accordance with aspects of the present disclosure for use with Figure 1 a schematic diagram of a current ramp lead (e.g., having a heat storage device) for use with a superconducting magnet of a magnetic resonance system in;

[0015] Figure 5 is a perspective view of a fixed ramp lead assembly for paired current ramp leads in accordance with aspects of the present disclosure;

[0016] Figure 6 is in accordance with aspects of the present disclosure Figure 5 a perspective view of the fixed ramp lead assembly in;

[0017] Figure 7 is in accordance with aspects of the present disclosure Figure 5 a top view of the fixed ramp lead assembly in;

[0018] Figure 8 is a schematic diagram of a reference fixed ramp lead assembly in accordance with aspects of the present disclosure;

[0019] Figure 9 is a schematic diagram of an improved fixed ramp lead assembly (e.g., having a heat storage device) according to a version of aspects of the present disclosure;

[0020] Figure 10 is a graph showing the heat entering a thermal anchor during a simulated ramp up / down process in accordance with aspects of the present disclosure;

[0021] Figure 11 is an end view and a side view of a heat storage device (e.g., a simple disk) in accordance with aspects of the present disclosure;

[0022] Figure 12 is an end view of a heat storage device (e.g., a disk with a tapered orifice) in accordance with aspects of the present disclosure;

[0023] Figure 13 is an end view of a heat storage device (e.g., a disk with a conical orifice and additional material) in accordance with aspects of the present disclosure;

[0024] Figure 14 is an end view of a heat storage device (e.g., a disk with a hybrid material) in accordance with aspects of the present disclosure;

[0025] Figure 15 is a schematic view of a heat storage device (e.g., a refrigerant tank) in accordance with aspects of the present disclosure; and

[0026] Figure 16 is a schematic view of a current or power ramp lead coupled to a superconducting switch, the superconducting switch being coupled to a superconducting machine, in accordance with aspects of the present disclosure. DETAILED DESCRIPTION

[0027] One or more specific embodiments will be described below. To provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be understood 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 developer's specific goals, such as compliance with system-related and business-related constraints that may vary from one implementation to another. Moreover, it should be understood that such development efforts may be complex and time-consuming, but would still be a routine task for those of ordinary skill in the art who would benefit from the present disclosure to design, make, and manufacture.

[0028] When introducing elements of various embodiments of the present inventive subject matter, the articles "a," "an," "the," and "said" are intended to mean that there is one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that additional elements may exist in addition to the listed elements. Further, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.

[0029] Although the following discussion presents various aspects in the context of medical imaging, it should be understood that the techniques disclosed herein are not limited to such medical contexts. Indeed, providing examples and explanations in such medical contexts is merely to facilitate explanation by providing instances of real-world implementations and applications. However, the techniques disclosed herein may also be used in other contexts, such as power generation using superconducting machines. Generally, the techniques may be used in all superconducting machines that require energy transfer to / from a much hotter environment.

[0030] The present disclosure provides a system and method for a current ramp lead assembly to limit the temperature of a superconducting machine (e.g., a superconducting magnet, motor, generator, etc. of a magnetic resonance imaging system) in a sealed cryogenic system or bath (e.g., containing a liquid cryogen such as liquid helium) during energization of the superconducting machine. Specifically, the superconducting machine system includes a superconducting machine. The superconducting machine system may also include a sealed cryogenic (e.g., helium) container that surrounds the superconducting machine. The superconducting machine system also includes a vacuum vessel wall that surrounds the sealed cryogenic container. The superconducting machine system also includes a superconducting switch that is coupled to the superconducting machine and configured to switch between a resistive mode and a superconducting mode. The superconducting machine system further includes a ramp lead assembly that is disposed within the sealed cryogenic container and has a first end and a second end. The first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high-temperature superconductor power lead that is coupled to the superconducting switch. The ramp lead assembly includes a non-conductive support. The ramp lead assembly also includes a metal rod that is configured to minimize a static heat load, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end. The ramp lead assembly further includes a heat storage device (e.g., a thermal battery) that is coupled to the metal rod between the first end and the second end. The heat storage device is configured to store heat during energization of the superconducting machine to limit heat transfer along the metal rod to the second end during energization of the superconducting machine and to limit a temperature rise along the ramp lead assembly during energization of the superconducting machine.

[0031] In some embodiments, both the first end and the second end of the stationary ramp lead assembly are made of copper, and the metal rod is made of a metal with relatively lower thermal conductivity such as brass. In some embodiments, both the first end and the second end of the stationary ramp lead assembly are made of brass. In some embodiments, a portion of the first end is located outside the vacuum vessel wall, wherein the temperature outside the vacuum vessel wall is the ambient temperature. In some embodiments, the second end is coupled to a heat anchor (e.g., a thermal shield within which the sealed cryogenic container is located).

[0032] In some embodiments, the heat storage device is configured to limit heat flow into the heat anchor during energization of the superconducting machine. In some embodiments, the ramp lead assembly is configured such that heat preferentially flows to the heat storage device rather than along the metal rod towards the second end during energization of the superconducting machine.

[0033] In certain embodiments, the heat storage device includes a refrigerant tank that is coupled to a metal rod. In certain embodiments, the heat storage device is a solid structure made of a solid material with a high heat capacity (e.g., a material with a heat capacity greater than 250 joules per kilogram per kelvin (J / kg-K) at a temperature of 100K), which limits the temperature rise by absorbing heat. In certain embodiments, the heat storage device is made of metal. In certain embodiments, the heat storage device is a metal disk that is arranged to surround the metal rod at a position between the first end and the second end of a fixed ramp assembly. In certain embodiments, the metal disk is made of brass or copper. In certain embodiments, the heat storage device includes a plurality of metal (e.g., brass or copper) disks that are arranged to be spaced apart from each other around the metal rod.

[0034] In certain embodiments, one or more of the metal disks of the heat storage device include a tapered orifice through which the metal rod passes, wherein the tapered orifice is configured to reduce axial conduction along the metal rod. In certain embodiments, one or more of the metal disks of the heat storage device include a central portion having a tapered orifice and an additional portion disposed along the perimeter of the central portion. The central portion extends in a first direction and the additional portion extends in a second direction that intersects the first direction. The additional portion is configured to increase the heat storage capacity of the corresponding metal disk compared to a metal disk having only the central portion. In certain embodiments, the central portion is made of a first metal and the additional portion is made of a second metal different from the first metal.

[0035] In certain embodiments, a superconducting magnet system for a magnetic resonance imaging system includes a superconducting magnet. The superconducting magnet system also includes a sealed cryogenic container that encloses the superconducting magnet. The superconducting magnet system also includes a vacuum vessel wall that encloses the sealed cryogenic container. The superconducting magnet system further includes a superconducting switch that is coupled to the superconducting magnet and is configured to switch between a resistive mode and a superconducting mode. The superconducting magnet system even further includes a ramp lead assembly that is disposed within the vacuum vessel wall and has a first end and a second end, wherein the first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high-temperature superconductor power lead that is coupled to the superconducting switch. The ramp lead assembly includes a non-conductive support. The ramp lead assembly also includes a metal rod that is configured to minimize the static heat load, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end. The ramp lead assembly further includes a solid metal structure that is coupled to the metal rod between the first end and the second end, wherein the ramp lead assembly is configured such that heat preferentially flows to the solid metal structure during energization of the superconducting magnet rather than along the metal rod toward the second end.

[0036] In some embodiments, a method for restricting the temperature of a ramp lead assembly coupled to a superconducting magnet of a magnetic resonance imaging system includes energizing a superconducting magnet disposed within a sealed cryogenic container, the sealed cryogenic container being disposed within a vacuum vessel wall. The magnetic resonance imaging system includes a ramp lead assembly that is disposed within the vacuum vessel wall and has a first end and a second end, wherein the first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high temperature superconducting power lead that is coupled to a superconducting switch. The ramp lead assembly includes a non-conductive support. The ramp lead assembly also includes a metal rod that minimizes a static heat load during energization of the superconducting magnet, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end. The ramp lead assembly further includes a heat storage device that is coupled to the metal rod located between the first end and the second end. The method also includes storing heat during energization of the superconducting magnet, restricting heat transfer along the metal rod to the second end during energization of the superconducting magnet, and restricting a temperature increase along the ramp lead assembly during energization of the superconducting magnet.

[0037] The disclosed embodiments of the present invention provide a fixed / permanent ramp lead assembly that can be mounted on a low cryogen superconducting machine (e.g., a superconducting magnet) that provides a continuously connected circuit path between an external power supply and the internal circuitry of the superconducting machine. Thus, the disclosed embodiments of the present invention are applicable to automatically or remotely ramp up / ramp down low cryogen sealed superconducting machines with very limited cryogen (e.g., a few liters of helium) as well as superconducting machines in conventional liquid cryogen containers. The disclosed embodiments of the present invention enable automatic ramp up / down of a superconducting magnet in the event of a power outage or natural disaster. The disclosed embodiments of the present invention can increase the availability of a superconducting magnet for scanning by avoiding a quench of the low cryogen (since it may take several days to recover from a quench). The disclosed embodiments of the present invention enable reduction of heat transfer during operation of the superconducting machine. The disclosed embodiments of the present invention allow heat energy to flow into a heat storage device to limit a temperature increase and to limit heat flow into a thermal anchor during a ramp up / down process. The disclosed embodiments of the present invention provide a simple, low-cost, and robust configuration for a ramp lead for energizing a superconducting machine.

[0038] Now refer to Figure 1, shows a schematic block diagram of an exemplary MR system 10. The MR system 10 is used to obtain images of a subject or to perform spectroscopy applications on a subject. In an exemplary embodiment, the MR system 10 includes a magnet assembly 12, which includes a magnet 14. In some embodiments, the magnet 14 is a superconducting magnet formed by a plurality of magnetic coils wound around a magnetic coil support or bobbin. The magnet 14 is configured to generate a polarized magnetic field. As described in more detail below, the MR system 10 includes a current ramp lead assembly to limit the temperature of the superconducting magnet 14.

[0039] The magnet assembly 12 may include a cryostat 18 surrounding the magnet 14. The cryostat container 18 is typically filled with a cryogenic fluid or refrigerant, which is used to cool the superconducting coil to an extremely low temperature (e.g., 4 Kelvin (K)) so that current continues to flow through the superconducting coil without resistance to maintain a uniform and static magnetic field after the power supply is disconnected. The refrigerant can be helium, hydrogen, neon, nitrogen, or any combination thereof in liquid form, gas form, or a combination of liquid and gas forms. Helium is described as an example refrigerant. Other refrigerants can be used in the superconducting magnet assemblies described herein.

[0040] In an exemplary embodiment, the magnet assembly 12 may also include a thermal shield assembly 16, which encloses the cryostat container 18 and the magnet 14 therein. In one embodiment, the thermal shield assembly 16 may include an inner thermal shield member 162 and an outer thermal shield member 164. The inner thermal shield member 162 is typically cylindrical in shape and is radially placed inside the magnet 14. The inner thermal shield member 162 is configured to prevent heat from radiating from the warm region where the subject is placed to the cold region where the magnet 14 is placed. The outer thermal shield member 164 is concentrically arranged relative to the inner thermal shield member 162. The outer thermal shield member 164 may also be generally cylindrical in shape and is radially placed outside the magnet 14. The outer thermal shield member 164 is configured to prevent heat from radiating into the magnet 14 from the environment. The thermal shield assembly 16 is made of a metallic material such as aluminum. In some embodiments, the magnet assembly 12 may also include a magnet vacuum container 19 (e.g., having a vacuum container wall 21), which surrounds the thermal shield assembly 16 and insulates the magnet 14 from the environment during operation.

[0041] In an example implementation, MR system 10 also includes a gradient coil assembly 22 placed inside the thermal shielding member 162. The gradient coil assembly 22 is configured to selectively apply one or more gradient magnetic fields along one or more axes such as the x-axis, y-axis, or z-axis. MR system 10 also includes an RF coil 24. The RF coil 24 can be a transmitter coil configured to transmit RF pulses. The RF coil 24 can be a receiver coil configured to detect MR signals from a subject. The RF coil 24 can be a transmit and receive coil that both transmits and detects MR signals. The magnet assembly 12, the gradient coil assembly 22, and the body RF coil 24 are collectively referred to as the scanner assembly 50 because the scanner assembly 50 is formed as a unit and is located in the scanner room. The scanner assembly 50 has an aperture 46 in which the subject is positioned during a scan. Figure 1 The illustrated scanner assembly 50 is a closed-bore system, where the aperture is cylindrical. The scanner assembly 50 can be a magnet assembly employing other designs, such as an open-bore system, a bipolar electromagnet configuration, or a Hallbach configuration.

[0042] In an example implementation, MR system 10 also includes a controller 30, a magnetic field control 32, a gradient field control 34, a memory 36, a display device 38, a transmit / receive (T / R) switch 40, an RF transmitter 42, and a receiver 44. In operation, a subject is placed in the aperture 46 on a suitable support (e.g., a motorized operating table (not shown) or other patient worktable). The magnet 14 generates a uniform and static magnetic field B0 across the aperture 46. The intensity and uniformity of the magnetic field B0 in the aperture 46 and correspondingly on the patient are controlled by the controller 30 via the magnetic field control 32, which also controls the supply of the energizing current to the magnet 14. The gradient coil assembly 22 is energized by the gradient field control 34 and is also controlled by the controller 30 such that one or more gradient magnetic fields are applied on the magnetic field B0. The RF coil 24 and the receive coil (if provided) are selectively interconnected to either the RF transmitter 42 or the receiver 44, respectively, via the T / R switch 40. The RF transmitter 42 and the T / R switch 40 are controlled by the controller 30 such that RF field pulses or signals are generated by the RF transmitter 42 and are selectively applied to the subject to excite magnetic resonance in the subject.

[0043] In an exemplary embodiment, after applying the RF pulse, the T / R switch 40 is actuated again to decouple the RF transmit coil 24 from the RF transmitter 42. The detected MR signal is then transmitted to the controller 30, which is capable of organizing the MR signal in a specific format for storage in the memory 36. The controller 30 includes a processor 48 that controls the processing of the MR signal to generate a signal representative of an image of the patient, which is transmitted to the display device 38 to provide a visual display of the image.

[0044] The magnet 14 of the magnet assembly 12 is used to generate a magnetic field in the MR system 10 by a current flowing through the magnet windings of the magnet 14. This current is in the range of several hundred amperes. In some known systems, the current from the power supply is constantly applied to the magnet to generate the magnetic field. A constant supply of high current would significantly increase the operating cost of the MR system. The magnet 14 is a superconducting magnet, where the magnet 14 operates at the superconducting temperature (such as 4K) of the wire windings of the magnet 14, such that the winding wires have no resistance to the current and do not require an external power supply. This mode of operation of the magnet 14 is referred to as the persistent current mode.

[0045] Figure 2 is a schematic diagram of a current or power ramp lead 52 coupled to a superconducting switch 54. As depicted, the superconducting switch 54 is located within a cryostat (e.g., a refrigerator) vessel 18. In certain embodiments, the superconducting switch 54 may be located between the outer thermal shield member 164 and the refrigerator vessel 18. The superconducting switch 54 is used to excite the magnet to operate in the persistent current mode. The superconducting switch 54 includes windings. The superconducting switch 54 switches between a resistive mode and a superconducting mode. In the resistive mode, the superconducting switch 54 operates at a temperature (such as 80K) above the superconducting temperature of the windings of the switch. In the superconducting mode, the superconducting switch 54 operates at the superconducting temperature (such as 4K) of the windings of the superconducting switch 54. During the ramp up of the magnet, the superconducting switch 54 is electrically connected in parallel with the power supply. To generate the magnetic field, the superconducting switch 54 operates in the resistive mode such that current is injected into the switch due to the resistance in the windings of the switch in the resistive mode. When the current flowing through the superconducting switch 54 reaches the desired level of field strength for generating the magnetic field, the external power supply is disconnected and the superconducting switch 54 is switched to operate in the superconducting mode. This switching is achieved by changing the temperature of the superconducting switch 54. A heater is used to heat the superconducting switch 54. The superconducting switch 54 is typically cooled by a cryogen such as liquid helium. Thus, heating of the superconducting switch 54 vaporizes the cryogen.

[0046] During the ramp down or quench of the magnet, the magnetic field generated by the magnet is reduced by switching the superconducting switch 54 from operating in the superconducting mode to operating in the resistive mode. The current flowing through the resistance generates heat, which also vaporizes the cryogen.

[0047] The current or power lead 52 includes a fixed (or permanent) ramp lead assembly 56 disposed within a space 58 between a vacuum vessel wall 21 of the magnet vacuum vessel 19 and an outer thermal shield member 164. A portion of the fixed ramp assembly is located outside the vacuum vessel wall (where its temperature is ambient temperature) and is coupled to an external power supply 60. The current or power lead 52 also includes a high temperature superconducting power lead 62 that is coupled to and supplies power to the superconducting switch 54.

[0048] Figure 3 is a schematic diagram of a current ramp lead 52 for use with the superconducting magnet of the magnetic resonance system 10 in Figure 1 . The current ramp lead 52 includes a fixed ramp lead assembly 56 and a high temperature superconducting power lead 62. The high temperature superconducting power lead 62 may include high temperature superconducting tape (e.g., yttrium barium copper oxide or RBCO) provided with wires. In certain embodiments, the fixed ramp lead assembly 56 includes a non-conductive support (see Figures 5 to 7 ).

[0049] As depicted, the fixed ramp lead assembly 56 includes a first end 64 and a second end 66 (e.g., metal ends). The first end 64 and the second end 66 are made of copper. In certain embodiments, the first end 64 and the second end 66 are made of brass. A metal rod 67 extends between the first end 64 and the second end 66. The metal rod 67 is made of a material with relatively lower thermal conductivity such as brass. The metal rod 67 is configured to minimize the static thermal load. During operation (e.g., when the superconducting magnet is energized), a temperature gradient is formed along the metal rod 67 (where the first end 64 is warmer and the second end 66 is colder). The cross-section of the metal rod 67 is smaller than the cross-sections of the metal ends 64, 66.

[0050] The first end 64 is coupled to the vacuum vessel wall 21. The fixed ramp lead assembly 56 is coupled to the vacuum vessel wall 21 in a fixed or permanent manner such that the current ramp lead 52 can provide a continuously connected circuit path between the external power supply and the internal circuit of the superconducting magnet. This eliminates the need for moving parts (e.g., as compared to separable / retractable ramp leads). A portion 68 of the first end 64 is located outside the vacuum vessel wall 21 where its temperature is ambient temperature. An electrical insulator 70 (e.g., a ceramic insulator) is provided at the location where a portion 68 of the first end 64 extends through the vacuum vessel wall 21. The remaining portion of the fixed ramp lead assembly 56 is disposed within the space between the vacuum vessel wall 21 and a thermal shield (e.g., Figure 1 the outer thermal shield member 164 in

[0051] The second end portion 66 is coupled to the high-temperature superconducting power lead 62 (e.g., to the high-temperature superconducting portion of the high-temperature superconducting power lead 62, which is coupled to the superconducting switch). The higher-temperature superconducting power lead 62 has a temperature limit for maintaining superconductivity (e.g., below the liquid nitrogen temperature, 77 K). Thus, the second end portion 66 is coupled to the thermal anchor 72 before the high-temperature superconducting power lead 62. Figure 1 and Figure 2 the thermal shield in

[0052] In Figure 3 the configuration of the current ramp lead 52 in

[0053] Figure 4 is for use with Figure 1 the superconducting magnet of the magnetic resonance system in Figure 3 is a schematic diagram of a current ramp lead 52 (e.g., having a heat storage device). The current ramp lead 52 is as

[0054] As depicted, the thermal energy storage device 76 includes a solid structure 78 having a solid material with a suitable high heat capacity (e.g., aluminum, brass, copper, etc.) (e.g., a material having a heat capacity greater than 250 joules per kilogram per kelvin (J / kg-K) at a temperature of 100K), which limits the temperature rise by absorbing heat. In some embodiments, the thermal energy storage device 76 includes a refrigerant tank thermally coupled to a metal rod 67. As depicted, the solid structure 78 is a disk 80 (e.g., a metal disk) having an aperture 81 through which the metal rod 67 passes. The disk 80 is arranged to surround the metal rod 67. As described in more detail below, the configuration of the disk 80 can vary. The thermal energy storage device 76 can include one or more disks 80. As depicted, the thermal energy storage device 76 includes a plurality of disks 80. Preferably, the disks 80 are made of copper or brass.

[0055] The thermal energy formed by resistive heating preferably flows into the disk 80 during the ramp-up / down process rather than along the higher thermal resistance brass lead material of the metal rod 67. The cross-section of the metal rod 67 of the metal ends 64, 66 connected between the ambient end (e.g., adjacent to the first end 64) and the high-temperature superconducting power lead 62 is smaller and the brass material is longer, resulting in a lower thermal conductivity, which reduces the heat transfer along the brass portion. Thus, when the superconducting magnet operates, the heat transfer is reduced. The thermal energy flowing into the disk 80 limits the temperature rise and restricts the heat from flowing into the thermal anchor 72 during the ramp-up / down process. The number, size, and position of the disks 80 (along the metal rod 67 between the first end 64 and the second end 66) can be optimized.

[0056] Figures 5 to 7 Are different views of the fixed portion of the ramp lead assembly 56 for the pair of current ramp leads (e.g., where the high-temperature superconducting power leads of the pair of current ramp leads are not shown). The fixed ramp lead assembly 56 includes a support structure 84 (e.g., made of carbon steel). The configuration of the support structure 84 can vary. As depicted, the support structure 84 includes a wall 86 (e.g., a vertical wall). The support structure 82 also includes a first pair of rails 88 (e.g., bottom support rails) coupled to and extending away from the bottom portion 90 of the wall 86. The support structure 82 further includes a second pair of rails 92 (e.g., top support rails) coupled to and extending away from the top portion 94 of the wall 86. The second pair of rails 92 extends at an angle towards the end 96 of the first pair of rails 88 (positioned away from the wall 86) and is coupled thereto.

[0057] The fixed ramp lead assembly 56 also includes a pair of non-conductive supports 98, 100 that are coupled to and supported by the first pair of rails 88. Both the first pair of rails 88 and the second pair of rails 92 are located on the flanks of the non-conductive supports 98, 100. The non-conductive supports 98, 100 are spaced apart from each other along the first pair of rails 88. The non-conductive support 98 is coupled to the first pair of rails 88 adjacent to the wall 86. The non-conductive support 100 is coupled to the second pair of rails 92 at the end 96. The non-conductive supports 98, 100 are configured to achieve electrical isolation and high mechanical strength at room temperature. In addition to being non-conductive, the non-conductive supports 98, 100 do not generate sparks. In some embodiments, the non-conductive supports 98, 100 are made of a thermosetting plastic (e.g., a glass-reinforced epoxy laminate such as G10-FR4).

[0058] As depicted, the pair of metal rods 67 (e.g., brass rods) are arranged in parallel and coupled to respective first ends 64 (e.g., metal ends made of copper). As Figure 4 shown, the first ends 64 are coupled to a vacuum vessel wall (not shown). Each first end 64 includes a first metal portion 102 (e.g., a copper metal portion) that extends through both the non-conductive support 98 and the wall 86. A vacuum feedthrough 106 is disposed between the wall 86 and the first metal portion 102. The vacuum feedthrough 106 is the location where the fixed ramp lead assembly 56 is coupled to the vacuum vessel wall (i.e., the vacuum vessel wall is arranged to surround the vacuum feedthrough 106). A corresponding electrical insulator 108 is disposed between the first metal portion 102 and the vacuum feedthrough 106. Except for the electrical insulator 108 and the first metal portion 102, each part of the fixed ramp lead assembly 56 is disposed within the space between the vacuum vessel wall and a thermal shield (e.g., Figure 1 the outer thermal shield member 164 in

[0059] The pair of metal rods 67 are coupled to respective second ends 66 (e.g., metal ends made of copper). As depicted, the second ends 66 are copper stranded wires that extend to a thermal anchor (thermal shield not shown). The second ends 66 extend from respective sockets 110 that are coupled to the metal rods 67 and extend through the non-conductive support 100.

[0060] Each metal rod 67 is associated with a corresponding heat storage device 76. Each corresponding heat storage device 76 includes one or more solid structures 78 having a solid material with a suitable high heat capacity (e.g., aluminum, brass, copper, etc.) (e.g., a material having a heat capacity greater than 250 joules per kilogram per kelvin (J / kg-K) at a temperature of 100K), which limits the temperature rise by absorbing heat. As depicted, the solid structure is a disk 80 (e.g., a metal disk) having corresponding apertures through which the corresponding metal rod 67 passes. The disk 80 is arranged to surround the metal rod 67. As described in more detail below, the configuration of the disk 80 can vary. The heat storage device 76 can include one or more disks 80. Preferably, the disk 80 is made of copper or brass.

[0061] The thermal energy formed by resistive heating preferably flows into the disk 80 during the ramp-up and ramp-down processes, rather than flowing along the higher thermal resistance brass lead material of the metal rod 67. The cross-section of the metal rod 67 of the metal ends 64, 66 connected between the ambient end (e.g., adjacent to the first end 64) and the high-temperature superconducting power lead 62 is smaller and the brass material is longer, resulting in a lower thermal conductivity, which reduces the heat transfer along the brass portion. Therefore, when the superconducting magnet is operating, the heat transfer is reduced. The thermal energy flowing into the disk 80 limits the temperature rise and limits the heat from flowing into the heat anchor 72 during the ramp-up and ramp-down processes. The number, size, and position of the disks 80 (along the metal rod 67 between the first end 64 and the second end 66) can be optimized. "Disk" is used here as a general term, and the heat storage device can be any shape that meets the design requirements.

[0062] Figure 10 The effect of adding a solid structure (e.g., a disk) of the heat storage device to a stationary ramp lead assembly is shown. Figure 8 and Figure 9 shows a stationary ramp lead assembly for obtaining Figure 10 the simulation data in. Figure 8 shows a stationary ramp assembly 110 referred to as a reference (e.g., similar to Figure 3 [[ID=!7]]the stationary ramp assembly 56 in). The stationary ramp assembly 110 includes a metal rod 67 (e.g., a brass rod lead) disposed between a first end 64 and a second end 66 (e.g., metal ends such as copper ends). The first end 64 is the warm end (e.g., located adjacent to the ambient temperature and adjacent to the vacuum vessel wall). The second end 66 is the cold end and is thermally coupled to the cold first stage and the thermal shield. The stationary ramp assembly 110 does not have a heat storage device. Figure 9 shows a stationary ramp assembly 112 referred to as an improved version (e.g., similar to Figure 4the fixed ramp assembly 56). The fixed ramp assembly 112 includes a metal rod 67 (e.g., a brass rod lead) disposed between a first end 64 and a second end 66 (e.g., a metal end such as a copper end). The first end 64 is the warm end (e.g., adjacent to the ambient temperature and adjacent to the vacuum vessel wall). The second end 66 is the cold end and is thermally coupled to the cold first stage and the thermal shield. The fixed ramp assembly 112 includes a heat storage device 76 in the form of a solid structure 78 (e.g., a disk 80) as described in Figure 4 The heat storage device 76 is described.

[0063] Figure 10 is a graph 114 showing the heat entering the thermal anchor during a simulated ramp-up process. The graph 114 includes an X-axis 116 representing time. The graph 114 also includes a Y-axis 118 representing the heat entering the thermal shield (TS). Curve 120 represents the applied current. Curve 122 represents Figure 8 the reference fixed ramp assembly 110 in Figure 9 An improved version of the fixed ramp assembly 112 with a heat storage device in Figure 10 As depicted, when using the fixed ramp assembly 12 with a heat storage device, the heat flowing to the thermal shield is significantly reduced.

[0064] Figures 11 to 15 shows different heat storage devices used with a fixed ramp lead assembly acting as a temperature limiter. It should be noted that the simple "disk" shape is only for illustrative purposes, and the heat storage device can have many different shapes to meet the design requirements. Figure 11 is an end view and a side view of the heat storage device 76. The heat storage device 76 is a solid structure 78 made of a suitable solid material with a high heat capacity (e.g., metals such as aluminum, brass, copper, etc.) (e.g., a material with a heat capacity greater than 250 joules per kilogram per kelvin (J / kg-K) at 100K temperature), which limits the temperature rise by absorbing heat. The solid structure 78 is a disk 80 with an orifice 81 (e.g., for the metal rod to pass through).

[0065] Figure 12 is an end view of the heat storage device 76. The heat storage device 76 is a solid structure 78 made of a suitable solid material with a high heat capacity (e.g., metals such as aluminum, brass, copper, etc.) (e.g., a material with a heat capacity greater than 250 joules per kilogram per kelvin (J / kg-K) at 100K temperature), which limits the temperature rise by absorbing heat. The solid structure 78 is a disk 80 with a tapered orifice 136 (e.g., for the metal rod to pass through). The tapered orifice 136 is configured to reduce axial conduction along the metal rod.

[0066] Figure 13 is an end view of the thermal energy storage device 76. The thermal energy storage device 76 is a solid structure 78 made of a suitable solid material with a high heat capacity (e.g., metals such as aluminum, brass, copper, etc.) (e.g., a material with a heat capacity greater than 250 joules per kilogram per kelvin (J / kg-K) at a temperature of 100K), which limits the temperature rise by absorbing heat. The solid structure 78 is a disk 80 having a tapered orifice 136 (e.g., for a metal rod to pass through). The tapered orifice 136 is configured to reduce axial conduction along the metal rod. The disk 80 includes a central portion 138 having the tapered orifice 136. The disk 80 also includes an additional portion 140 disposed along the perimeter of the central portion 138, wherein the central portion 138 extends in a first direction 142 (e.g., the vertical direction) and the additional portion 140 extends in a second direction 144 (e.g., the horizontal direction) that intersects the first direction 142. Compared to a metal disk having only the central portion 138 (e.g., Figure 12 the disk 80 in

[0067] Figure 14 is an end view of the thermal energy storage device 76. The thermal energy storage device 76 is a solid structure 78 made of a suitable solid material with a high heat capacity (e.g., metals such as aluminum, brass, copper, etc.) (e.g., a material with a heat capacity greater than 250 joules per kilogram per kelvin (J / kg-K) at a temperature of 100K), which limits the temperature rise by absorbing heat. The solid structure 78 is a disk 80 having a tapered orifice 136 (e.g., for a metal rod to pass through). The tapered orifice 136 is configured to reduce axial conduction along the metal rod. The disk 80 includes a central portion 138 having the tapered orifice 136. The disk 80 also includes an additional portion 140 disposed along the perimeter of the central portion 138, wherein the central portion 138 extends in a first direction 142 (e.g., the vertical direction) and the additional portion 140 extends in a second direction 144 (e.g., the horizontal direction) that intersects the first direction 142. Compared to a metal disk having only the central portion 138 (e.g., Figure 12 the disk 80 in

[0068] Figure 15 is a schematic view of the thermal energy storage device 76. The thermal energy storage device 76 includes a refrigerant tank 146 that is thermally coupled to the metal rod 67 of the fixed ramp lead assembly. The refrigerant tank 146 is configured to absorb thermal energy from the metal rod 67.

[0069] Figure 16 is a schematic diagram of a current or power ramp lead 52 coupled to a superconducting switch 54, which is coupled to a superconducting machine 148. The current or power ramp lead is as described above and interacts with the superconducting switch as described above (e.g., in Figures 4 to 7 ). The current or power ramp lead 52 also includes a stationary ramp assembly 56 and a heat storage device 76 as described above (e.g., in Figures 4 to 7 ). The current or power ramp lead 52 can be used with the superconducting machine 148. The superconducting machine 148 can be a superconducting magnet for magnetic resonance imaging as described above. In certain embodiments, the superconducting machine 148 can be a superconducting motor or a superconducting generator (e.g., for a wind turbine). These are non-limiting examples of the superconducting machine 148, and the current or power ramp lead described herein can be used with such a superconducting machine.

[0070] The technical effects of the subject matter disclosed herein include providing a ramp lead assembly that can be mounted on a low cryogen superconducting machine (e.g., a superconducting magnet), which provides a continuously connected circuit path between an external power supply and the internal circuit of the superconducting machine. Thus, the subject matter disclosed herein is applicable to automatically or remotely ramping up / ramping down a low cryogen sealed superconducting machine with very limited cryogen (e.g., a few liters of helium). The technical effects of the subject matter disclosed herein include enabling the superconducting magnet to automatically ramp up / down in the event of a power outage or natural disaster. The technical effects of the subject matter include improving the availability of the superconducting magnet for scanning by avoiding quenching of the low cryogen (since it may take several days to recover from a quench). The technical effects of the subject matter disclosed herein include enabling reduction of heat transfer during operation of the superconducting machine. The technical effects of the subject matter disclosed herein include allowing heat energy to flow into the heat storage device to limit temperature rise and to limit heat flow into the thermal anchor during the ramp up / down process. The subject matter disclosed herein includes providing a simple, low-cost, and robust configuration of a ramp lead for powering a superconducting machine.

[0071] Referring to the technology presented herein and claimed and applying it to physical objects and specific examples having practical nature, the practical nature clearly improves the current technical field and is thus not abstract, intangible, or purely theoretical. Further, if any claim appended to the end of this specification contains one or more elements designated as "means for [performing]... function" or "step for [performing]... function", such elements are intended to be construed in accordance with 35 U.S.C. 112(f). However, for any claim containing elements designated in any other way, such elements are not intended to be construed in accordance with 35 U.S.C. 112(f).

[0072] This written description uses examples to disclose the subject matter, including the best mode, and also enables those skilled in the art to practice the subject matter, including making and using any device or system and performing any included method. The patent scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. If such other examples have 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 language of the claims, then such other examples are intended to fall within the scope of the claims.

Claims

1. A superconducting machine system, the superconducting machine system comprising: A superconducting electric machine; A cryogenic vessel that surrounds the superconducting electric machine; A vacuum vessel wall that surrounds the cryogenic vessel; A superconducting switch coupled to the superconducting electric machine and configured to switch between a resistive mode and a superconducting mode; And A ramp lead assembly disposed within the vacuum vessel wall and having a first end and a second end, wherein the first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high temperature superconductor power lead, the high temperature superconductor power lead being coupled to the superconducting switch, wherein the ramp lead assembly comprises: A non-conductive support; A metal rod configured to minimize a static heat load, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end; and A heat storage device coupled to the metal rod between the first end and the second end, wherein the heat storage device is configured to store heat during energization of the superconducting electric machine to limit heat transfer along the metal rod to the second end during energization of the superconducting electric machine and to limit a temperature rise along the ramp lead assembly during energization of the superconducting electric machine, wherein the high temperature superconductor portion of the high temperature superconductor power lead is disposed between the second end of the metal rod and the superconducting switch.

2. The superconducting machine system according to claim 1, wherein Both the first end and the second end include copper, and the metal rod includes brass.

3. The superconducting machine system according to claim 2, wherein, The second end is coupled to a heat anchor.

4. The superconducting machine system according to claim 3, wherein, The heat storage device is configured to limit heat flow into the heat anchor during energization of the superconducting electric machine.

5. The superconducting machine system according to claim 1, wherein, A portion of the first end is located outside the vacuum vessel wall, wherein the temperature outside the vacuum vessel wall is ambient temperature.

6. The superconducting machine system according to claim 1, wherein, The ramp lead assembly is configured such that heat preferentially flows to the heat storage device during energization of the superconducting electric machine rather than along the metal rod toward the second end.

7. The superconducting machine system according to claim 1, wherein, The heat storage device includes a cryogen tank coupled to the metal rod.

8. The superconducting machine system according to claim 1, wherein, The heat storage device includes metal.

9. The superconducting machine system according to claim 8, wherein, The heat storage device includes a metal disk disposed around the metal rod.

10. The superconducting machine system according to claim 9, wherein, The metal disk includes brass or copper.

11. The superconducting machine system according to claim 9, wherein, The heat storage device includes a plurality of metal disks disposed spaced apart from each other around the metal rod.

12. The superconducting machine system according to claim 9, wherein, The metal disk includes a tapered orifice through which the metal rod passes, wherein the tapered orifice is configured to reduce axial conduction along the metal rod.

13. The superconducting machine system according to claim 12, wherein, The metal disk includes a central portion having the tapered orifice and an additional portion disposed along a perimeter of the central portion, wherein the central portion extends in a first direction and the additional portion extends in a second direction that intersects the first direction, and the additional portion is configured to increase a heat storage capacity of the metal disk compared to another metal disk having only the central portion.

14. The superconducting machine system according to claim 13, wherein, The central portion is made of a first metal, and the additional portion is made of a second metal different from the first metal.

15. A superconducting magnet system for a magnetic resonance imaging system, the superconducting magnet system comprising: A superconducting magnet; A cryogenic container surrounding the superconducting magnet; A vacuum vessel wall surrounding the cryogenic container; A superconducting switch coupled to the superconducting magnet and configured to switch between a resistive mode and a superconducting mode; And A ramp lead assembly disposed within the vacuum vessel wall and having a first end and a second end, wherein the first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high temperature superconductor power lead, the high temperature superconductor power lead being coupled to the superconducting switch, and wherein the ramp lead assembly comprises: A non-conductive support; A metal rod configured to minimize a static heat load, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end; and A solid metal structure coupled to the metal rod between the first end and the second end, wherein the ramp lead assembly is configured such that heat preferentially flows to the solid metal structure during energization of the superconducting magnet rather than along the metal rod towards the second end, wherein the high temperature superconductor portion of the high temperature superconductor power lead is disposed between the second end of the metal rod and the superconducting switch.

16. The superconducting magnet system according to claim 15, wherein, The second end is coupled to a heat anchor, and the solid metal structure is configured to store heat during energization of the superconducting magnet to limit heat transfer along the metal rod to the second end during energization of the superconducting magnet, to limit a temperature rise along the ramp lead assembly during energization of the superconducting magnet, and to limit heat flow into the heat anchor during energization of the superconducting magnet.

17. The superconducting magnet system according to claim 15, wherein, The solid metal structure includes a disk.

18. The superconducting magnet system according to claim 17, wherein, The disk includes a tapered aperture through which the metal rod passes, wherein the tapered aperture is configured to reduce axial conduction along the metal rod.

19. The superconducting magnet system according to claim 18, wherein, The disk includes a central portion having the tapered aperture and an additional portion disposed along a perimeter of the central portion, wherein the central portion extends in a first direction and the additional portion extends in a second direction that intersects the first direction, and the additional portion is configured to increase a heat storage capacity of the disk compared to a disk having only the central portion.

20. A method for limiting a temperature of a ramp lead assembly coupled to a superconducting magnet of a magnetic resonance imaging system, the method comprising: Energizing the superconducting magnet disposed within a cryogenic container disposed within a vacuum vessel wall, wherein the magnetic resonance imaging system comprises: Ramp lead assembly, the ramp lead assembly being disposed within the vacuum vessel wall and having a first end and a second end, wherein the first end of the ramp lead assembly is fixedly coupled to the vacuum vessel wall and the second end is coupled to a high temperature superconductor power lead, the high temperature superconductor power lead being coupled to a superconducting switch, and the ramp lead assembly comprising: Non-conductive support; A metal rod that minimizes the static heat load during energization of the superconducting magnet, wherein the metal rod is disposed on the non-conductive support and extends between the first end and the second end, and wherein the high temperature superconductor portion of the high temperature superconductor power lead is disposed between the second end of the metal rod and the superconducting switch, the superconducting switch being configured to further reduce heat transfer into the superconducting magnet; and A heat storage device coupled to the metal rod between the first end and the second end; and Stores heat during energization of the superconducting magnet, limits heat transfer along the metal rod to the second end during energization of the superconducting magnet, and limits the temperature rise along the ramp lead assembly during energization of the superconducting magnet.

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