Queue protection for high-temperature superconducting (HTS) leads

Abstract

An apparatus (200) includes a cryostat (202) containing a volume of cryogenic fluid. One or more superconducting coils (204) are disposed within the cryostat. The one or more superconducting coils are configured to generate a magnetic field when current passes through them. One or more high-temperature superconducting (HTS) current leads (206) are permanently disposed within the cryostat and coupled to the one or more superconducting coils. One or more sensors (222) are positioned at or near one or more HTS current leads to monitor the state of the HTS current leads. An HTS protection switch (208) is selectively coupled to the one or more HTS current leads. A magnet controller (220) controls the HTS protection switch to divert current from the one or more HTS current leads when a quench is detected via the sensors.

Description

Technical Field

[0001] The following generally relates to superconducting permanent magnets, and more specifically, to systems and methods for preventing damage to high-temperature superconducting current leads in superconducting permanent magnets used for magnetic resonance imaging, and related fields. Background Technology

[0002] Magnetic resonance imaging (MRI) scanners typically use superconducting magnets to generate a static (BO) magnetic field. The superconducting windings are typically constructed as superconducting fibers embedded in a copper matrix and immersed in liquid helium to hold the windings below the superconducting critical temperature under operating current. The liquid helium is contained in a vacuum-jacketed cryostat with a cold head operated by a compressor, which maintains the helium at a low temperature (e.g., 4K or lower).

[0003] One drawback of this design is that some helium evaporation typically occurs, and sometimes it may be necessary to replenish the helium supply. Furthermore, if the magnet is brought to room temperature for maintenance, the entire helium supply is usually lost and must be replenished.

[0004] Some newer superconducting magnet designs employ a hermetically sealed cooling system filled with gaseous helium under high pressure (e.g., 1000 psi in some systems) and housed in a vacuum cryostat. A cold head operates to cool the hermetically sealed cooling system to a cryogenic temperature (e.g., 4 K or lower), at which point the helium filler is at least partially liquefied. The magnet windings are in a vacuum within the cryostat and are outside the hermetically sealed cooling system, but in thermal contact with it. Compared to conventional superconducting magnet designs where the magnet windings are immersed in liquid helium, this “hermetically sealed” superconducting magnet is less prone to helium loss and requires a significantly smaller helium filler.

[0005] One potential drawback of sealed superconducting magnets is that they are more prone to quenching due to temporary loss of cold head function (e.g., due to power outages). However, modern superconducting magnet windings are able to undergo quenching without damage because the copper matrix provides high conductivity when the superconducting fibers are in normal operation, and the winding design promotes a relatively uniform distribution of quenching from the point of quench initiation and heat dissipation.

[0006] In immersion or hermetically sealed superconducting magnet designs, current contact is made with the terminals of the superconducting winding to excite or de-excite the magnet. Ports in a cryostat are typically used for this purpose, through which metal leads can be inserted to contact the magnet terminals. Due to heat transfer from the leads to the superconductor surrounding the terminals of the superconducting winding, a non-superconducting region (i.e., a conventionally conductive region) can be created near the current contact point. The current in this conventionally conductive region is carried by the copper substrate. WO2017 / 178560A1, published October 19, 2017 by Urbahn et al., discloses an alternative design using high-temperature superconducting (HTS) leads, such as those made of HTS materials like bismuth strontium calcium copper oxide (BSCCO), yttrium barium copper oxide (YBCO), or magnesium diboride (MgB2). HTS leads have superconducting critical temperatures ranging from 25 K to up to 90 K or higher, depending on the HTS material and the current magnitude. HTS leads advantageously provide a smoother transition from room temperature outside the cryostat to 4K or lower temperatures of the superconducting magnet windings.

[0007] The following improvements are disclosed to overcome these and other issues. Summary of the Invention

[0008] In one aspect, an apparatus includes a cryostat containing a volume of cryogenic fluid. One or more superconducting coils are disposed within the cryostat. The one or more superconducting coils are configured to generate a magnetic field when current flows through them. One or more high-temperature superconducting (HTS) current leads are permanently disposed within the cryostat and coupled to the one or more superconducting coils. One or more sensors are located at or near the one or more HTS current leads to monitor the state of the HTS current leads. An HTS protection switch is selectively coupled to the one or more HTS current leads. A magnet controller controls the HTS protection switch to divert current from the one or more HTS current leads when a quench is detected via the sensors.

[0009] In another aspect, an apparatus for a medical imaging device includes at least one superconducting current lead. At least one voltage sensor is configured to measure the voltage in the at least one superconducting current lead. A protective switch is operable to transfer current from the at least one superconducting current lead. Electronic devices are configured to control the protective switch to disconnect a power circuit in response to a disconnection condition including the voltage sensor detecting that the voltage in the at least one superconducting current lead exceeds a disconnection threshold.

[0010] In another aspect, a method for protecting a high-temperature superconducting (HTS) lead in a medical imaging device from quenching includes: measuring a voltage across at least one HTS lead; determining whether the measured voltage is outside a corresponding predefined threshold; and when the measured voltage is outside the predetermined threshold, disconnecting the at least one HTS lead from the electronics of the medical imaging device.

[0011] Some of the illustrative embodiments disclosed herein address the issue of requiring professional personnel to be present at the superconducting magnet site through permanently installed power and current leads. Control equipment monitors the cryogenic conditions inside the magnet and uses a decision tree to determine whether to automatically de-excite the magnet or automatically excite it back to the nominal field. Furthermore, a user interface is provided to allow authorized users (e.g., operators) to automatically de-excite the magnet or automatically excite it back to the nominal field when needed or desired.

[0012] For example, stimulating a conventional magnet requires maintenance personnel and specialized equipment. If a magnetized foreign object (such as a hospital bed or floor buffer) gets stuck on the magnet, the time and cost of removing it can be a significant burden for users (e.g., hospitals, clinics, etc.). For newer “sealed” magnets, which have only a small fraction of the original helium stockpile, automatic magnet stimulating becomes more desirable. Unlike helium bath magnets, the small helium stockpile can only support a few hours of cooling failure. Afterward, residual heat entering the cryostat causes the coil temperature to rise to a level where superconductivity is no longer sustainable, and the magnet “goes quench” (thermal runaway causes rapid decay of the magnetic field and a rise in coil temperature). Maintenance personnel are unlikely to arrive on-site in time and prepare the magnet for destimulation. For automatic or user-initiated slewing (e.g., stimulating, destimulating), this state can be prevented by releasing the magnet’s energy to an external dump. Cooling failures can occur due to on-site destimulation of the MRI scanner. After power is restored, automatic power can re-stimulate the magnet without manual intervention. Similarly, when a foreign object gets stuck in the magnet, or for any other desired purpose, the user can de-energize the magnet. When the foreign object is removed from the magnet or the user determines that the magnet needs to be re-energized, the user can re-energize the magnet. This maximizes uptime, thereby increasing the system's value to the customer.

[0013] One advantage is that the HTS leads protect the superconducting magnet in the event of HTS lead quench.

[0014] Another advantage is that it prevents the HTS leads of the superconducting magnet from losing quench.

[0015] Another advantage is that it reduces maintenance time and costs by preventing damage to the HTS leads.

[0016] Another advantage is that it transfers current from the HTS leads to prevent lead failure, or to prevent damage to the HTS leads if HTS failure occurs.

[0017] Another advantage is that it provides an MRI device employing a superconducting magnet having one or more of the aforementioned advantages.

[0018] The given embodiments may not provide the aforementioned advantages, may provide one, two, more or all of the aforementioned advantages, and / or may provide other advantages, as will become apparent to those skilled in the art upon reading and understanding this disclosure. Attached Figure Description

[0019] This disclosure may take the form of various components and their arrangements, as well as various steps and their arrangements. The accompanying drawings are for illustrative purposes only and should not be construed as limiting this disclosure.

[0020] Figure 1 An exemplary embodiment of a magnetic resonance imaging (MRI) device is illustrated.

[0021] Figure 2 An exemplary embodiment of a superconducting magnet system that can be used in an MRI device according to aspects of the present invention is illustrated.

[0022] Figure 3 It shows Figure 2 Another embodiment of the system.

[0023] Figure 4 It shows Figure 2 and Figure 3 An exemplary flowchart of the system's operation. Detailed Implementation

[0024] HTS leads offer advantages over other solutions because of the electrical connections between parts of a magnet that operate at low but different temperatures. When used to transfer current between magnet parts, the near-zero resistance of components incorporating HTS significantly reduces ohmic heating, while the high thermal resistance reduces heat transfer between these parts.

[0025] On the other hand, low-temperature superconductor (LTS) leads, such as those used in superconducting magnet windings, employ superconducting metal wires within a copper substrate. When the critical temperature of these filaments is exceeded (e.g., the filament "desuperconducts"), the surrounding copper substrate begins to conduct electricity, diverting current around the now resistive (normal) portion of the filament. This prevents permanent damage to the delicate filament because ohmic heating within the filament is reduced, and any heat generated is rapidly conducted away from the normal area through the copper.

[0026] In contrast, HTS components are typically superconducting ceramic materials bonded to a relatively small metal volume. Therefore, the current shunted around the normal region and the heat carried away from the normal region during quench are usually insufficient to prevent permanent damage to the delicate ceramic. Depending on the current carried by the HTS during this quench period, permanent damage can occur within hundreds of milliseconds.

[0027] This situation should be distinguished from that of superconducting magnet windings, which have a copper matrix that provides low (though limited) resistance when the superconducting fibers are in normal operation; in contrast, HTS materials are typically ceramics that exhibit high resistance and cannot withstand current loads if the HTS leads fail to quench. Therefore, HTS leads can suffer irreparable damage rapidly, for example within one second of the onset of quench, and in reality, it could be much faster, such as 100 milliseconds or hundreds of milliseconds.

[0028] This paper discloses a permanent superconducting magnet with excitation current leads permanently mounted and connected to a power source. The temperature of the coil magnet needs to be kept below a cryogenic temperature to maintain superconductivity. The permanent electrical connection between the superconducting coil and the external world minimizes heat leakage from the outside to the superconducting coil. Furthermore, they should not generate excessive Joule heating (ohmic heating) when carrying current, otherwise the heat would cause the coil to lose its superconductivity.

[0029] This paper discloses a permanent superconducting magnet that employs an HTS lead assembly as part of the electrical connection between the superconducting coil and the equipment outside the vacuum space of the magnet. Specifically, the HTS is used to transmit high (hundreds of amperes) currents between the LTS coil and the high-temperature (i.e., LTS-prohibited, but HTS-adapted) section of the magnet.

[0030] Alternatively, rare-earth barium copper oxide (ReBCO) leads are used because they cover both regions; they can carry high currents at higher temperatures without Joule losses, and they can be manufactured with particularly low thermal conductivity. To further reduce heat leakage into the magnet, mechanical switches (thermal switches) are installed inside the magnet between the HTS current leads and external current terminals. These switches close only when current needs to flow through the HTS leads; otherwise, they are open. HTS is well-suited for this application. The heat transferred to the LTS from the high-temperature magnet regions and the ohmic heating within the HTS is small enough that the LTS can be maintained at superconducting temperatures during various magnet operating modes.

[0031] In some embodiments disclosed herein, an automatic current-cutting system is provided for abruptly disconnecting current in the event of initial HTS lead quench. The system includes voltage sensors located at both ends of the HTS lead, electrically connected to rack-mounted electronics, including differential voltmeters with high common-mode rejection. If the measured differential voltage across the HTS lead exceeds a specific threshold (e.g., 50 mV in one embodiment; note that this voltage is theoretically zero for an HTS lead in a superconducting state), an actuated (e.g., solenoid-driven) shut-off switch is then opened to disconnect the current. In variant embodiments, the current-cutting logic includes noise delays, low-pass filters, etc., to avoid unnecessary current cut-off due to noise. In some embodiments, the electronics are analog (e.g., using analog operational amplifier circuitry) to be insensitive to computer malfunctions. Although one HTS lead has been described above, it is preferable to monitor two HTS leads similarly, and if either HTS lead exhibits a voltage exceeding a trigger threshold, indicating initial quench of the HTS lead, the current-cut-off switch is triggered. As used herein, the term “initial loss of superconductivity” is intended to indicate that the HTS lead or a portion thereof is transitioning from a superconducting state to a normal state or has just transitioned to a normal state, but before the generated Joule heat reaches a level sufficient to damage the HTS lead.

[0032] In some embodiments disclosed herein, an automated system is provided to interrupt the current flowing through a superconducting heat exchanger (HTS). Superconducting materials exhibit very low (theoretically zero) resistance. Therefore, a significant voltage generated across the HTS carrying current indicates that some portion of the HTS has gone superconducting. The system monitors the voltage across all components containing the HTS and electrically disconnects the current loop containing any voltage generated by the HTS exceeding a threshold. This prevents further heating and damage within the HTS. The low differential-mode voltage (tens of millivolts) and high common-mode voltage (hundreds of volts) measured are noteworthy. In some variations, the monitored voltage is filtered by a noise filter (e.g., a low-pass filter or time delay) to prevent malfunctions. In some variations, the protection system is implemented entirely in analog (i.e., without software) circuitry for the purpose of immunity to computationally-induced faults.

[0033] In other embodiments disclosed herein, a temperature sensor (e.g., a thermistor or temperature-sensitive diode) is provided. Temperature may be a lagging indicator compared to differential voltage, and relying on detecting a temperature rise in the HTS lead to trigger a current-shutdown switch may be too slow to prevent damage to the HTS lead. A temperature sensor at the hot end of the HTS lead (i.e., near the connection to the current lead) can be used to implement less aggressive repairs, such as reducing the current amplitude in response to the HTS temperature at the hot end approaching a critical temperature (Tc). Reducing the current increases Tc (because it depends on the current amplitude) and may also reduce the rate of temperature rise if it is due to Joule heating of the metal conductor connected to the HTS lead.

[0034] In some embodiments disclosed herein, an automated system is provided to prevent the HTS from quenching due to temperature. This system monitors the temperature of all components containing the HTS and safely adjusts the system current to a level within a critical current corresponding to the measured temperature. Note that the temperature rise of the HTS components due to ohmic heating within the ceramic is a hysteresis indicator of quenching and is unlikely to provide a response time sufficient to prevent damage to a quenched HTS.

[0035] This paper discloses a system for proactively preventing damage to HTS current leads in the event of thermal runaway when they are carrying current. These current leads are permanently mounted within the cryostat of the magnet and can only be replaced by removing the magnet from its field and returning it to the factory where it was manufactured or a similar facility.

[0036] These systems are implemented to prevent damage to the HTS (High-Speed ​​Transmission System) components of the magnet. Repairing or replacing HTS components in a magnet requires returning the magnet to its factory or similar facility, specialized labor, and a considerable amount of time, making it highly undesirable.

[0037] Figure 1 An exemplary embodiment of a magnetic resonance imaging (MRI) apparatus 100 is illustrated. The MRI apparatus 100 may include, for example: a magnet 102; a patient stage 104 configured to hold a patient 10; a gradient coil 106 configured to at least partially surround at least a portion of the patient 10, for which the MRI apparatus 100 generates an image; a radio frequency coil 108 configured to apply radio frequency signals at least to the imaged portion of the patient 10 and to alter the alignment of the magnetic field; and a scanner for detecting changes in the magnetic field caused by the radio frequency signals. General operation of MRI apparatus is well known and therefore will not be described further herein.

[0038] refer to Figure 2The illustration shows an exemplary system or apparatus 200. System 200 includes a cryostat 202, which is a vacuum container containing superconducting coils (also called windings) 204, a closed cooling system (not shown) with a small amount of cryogenic fluid (e.g., helium), and other components for operating a magnet. One or more electric superconducting coils 204 are disposed within the cryostat 202, wherein the one or more electric superconducting coils 204 are configured to generate a magnetic field when an electric current passes through them;

[0039] The cryostat 202 is also configured to house one or more high-temperature superconducting current leads (i.e., one or more HTS leads) 206. The high-temperature superconducting current leads 206 are permanently disposed within the cryostat and coupled to one or more superconducting coils 204. The one or more high-temperature superconducting current leads 206 are formed of rare-earth-barium-copper oxide (ReBCO). High-temperature superconducting (HTS) ReBCO leads are used instead of conventional leads because they can carry high currents at higher temperatures without Joule losses, and they can be manufactured with particularly low thermal conductivity, thereby minimizing any heat transfer from the surrounding atmosphere into the temperature-sensitive superconducting coils.

[0040] A high-temperature superconducting protection switch (i.e., HTS protection switch) 208 is selectively coupled to one or more high-temperature superconducting current leads and external devices (e.g., excitation device 212, de-excitation device 214). The high-temperature superconducting protection switch 208 is preferably located outside the cryostat 202. When the high-temperature superconducting protection switch 208 is in a first state (i.e., open), one or more electric superconducting coils 204 are in a continuous state, and when the high-temperature superconducting protection switch 208 is in a second state (i.e., closed), the high-temperature superconducting current lead 206 is configured to excite or de-excite one or more electric superconducting coils 204. In one embodiment, a thermal switch 210 is configured to electrically couple one or more high-temperature superconducting current leads 206 to devices located outside the cryostat (e.g., excitation device 212, de-excitation device 214). Figure 2 As can be seen, the high-temperature superconducting protection switch 208 must also be closed to electrically couple the excitation and de-excitation devices 212, 214 to the high-temperature superconducting current lead 206; in other words, if either the protection switch 208 or the thermal switch 210 is opened, the excitation and de-excitation devices 212, 214 are electrically decoupled from the high-temperature superconducting current lead 206. The thermal switch 210 can be a latching thermal switch or any other desired switch. In one embodiment, the first state is an open state and the second state is a closed state.

[0041] System 200 includes a magnet controller 220, which typically controls and / or monitors various components of the system, including controlling the state of the high-temperature superconducting protection switch 208. For example, the magnet controller 220 is coupled to a voltage and temperature sensor 222, which is located at or near one or more of the high-temperature superconducting current lead 206, the excitation device 212, and the de-excitation device 214. Such a voltage and temperature sensor is configured to monitor the state of the high-temperature superconducting current lead 206.

[0042] The magnet controller 220 monitors signals from one or more sensors 222 of the system 200. The magnet controller 220 can determine, for example, by analyzing the signals from the one or more sensors 222 to determine if a fault or malfunction has been detected. Specifically, the magnet controller 220 can identify faults or malfunctions indicating that a quench is occurring or may be imminent. If the magnet controller 220 detects a fault or malfunction in the system 200, particularly a fault or malfunction indicating that the superconducting coil 204 is quenching or may be imminent, the magnet controller 220 switches the high-temperature superconducting protection switch 208 from a continuous state to a second state to transfer current from the high-temperature superconducting leads 206 to the energy storage unit (de-excitation unit) 214, which is located outside or on the exterior of the cryostat, via a pair of high-temperature superconducting leads 206 at opposite ends of the conductive coils of the superconducting magnet.

[0043] Magnet controller 220 monitors one or more fault conditions. In operation, magnet controller 220 determines, for example, by analyzing one or more sensor signals 222 whether a fault or malfunction has been corrected. If the fault has been corrected, so that superconducting coil 204 is no longer at risk of quenching, the magnet leads are disconnected from energy storage unit 212 and coupled to excitation device 212 to return the electric superconducting coil to a continuous state. Once the electric superconducting coil 204 is in or near a continuous state, a high-temperature superconducting protection switch and one or more high-temperature superconducting current leads are switched to a continuous state. System 200 operates in a continuous state until magnet controller 220 detects a fault or malfunction in the magnet system, as described above.

[0044] This process prevents quenching in the cryogenic thermostat 202 and damage to the high-temperature superconducting current lead 206, thereby avoiding damage to the cryogenic materials and / or the superconducting coil 204.

[0045] One aspect of the invention applies to a continuous superconducting magnet having an excitation current lead permanently installed and connected to a power source. The temperature of the coil magnet needs to be kept below a low temperature to maintain superconductivity. A permanent electrical connection between the superconducting coil and the external environment is required to allow the magnet to be automatically energized and de-energized without intervention from field service personnel. Furthermore, they cannot generate excessive Joule heating (ohmic heating) when carrying current, otherwise the heat would cause the coil to lose its superconductivity. To further reduce heat leakage into the magnet, mechanical switches (thermal switches) are installed inside the magnet between the HTS current lead and the external current terminal. These switches are closed only when current needs to flow through the HTS lead; otherwise, they are open.

[0046] Another problem addressed in this paper (i.e., failure mode) is that if the high-temperature superconducting current leads 206 are driven into a normal state (quenching failure) for any reason while carrying current, damage caused by Joule heating may render them inoperable. Another failure mode is that if any thermal switch 210 trips while carrying current, arcing will damage its contacts, and it will also require replacement. The problem is that both the high-temperature superconducting leads 206 and the thermal contacts are within the vacuum of the sealed cryogenic thermostat 202. Therefore, maintenance can only be performed at specialized locations, such as their original manufacturing facility or a similar facility. This incurs considerable cost and inconvenience for users due to the downtime of the MRI scanner and the refurbishment work required to replace the magnets.

[0047] As mentioned above, Figure 2 The embodiment includes additional hardware 222 and control software to monitor the state of the high-temperature superconducting lead 206 and to divert current from the HTS lead 206 by disconnecting the HTS protection switch 208 once a quench is detected in the HTS. This may cause the magnet itself (i.e., the superconducting coil 204) to quench, but a passive quench protection circuit (not shown) inside the magnet ensures that Joule heating does not cause damage to the internal components of the magnet. Upon detection of a high-temperature superconducting quench, the excitation controller also immediately closes the power supply, and the current in the high-temperature superconducting current lead 206 between the magnet and the power supply is almost immediately disconnected by the HTS protection switch 208.

[0048] In one embodiment, one or more thermal switches 210 are latched. For example, they require only an electrical pulse to switch between an open and closed state or between a closed and open state. This means that even if the MRI site experiences a power outage during magnet excitation or de-excitation, the switches will remain closed. The control software further ensures that these contactors are not disconnected when they are carrying current. The latching operation of the switches 210 ensures that the switches 210 do not change their state (whether open or closed) in response to de-excitation. Therefore, if the switch 210 is closed and carrying current during a power outage, the switch 210 will remain closed. In contrast, if a non-latched conventional disconnect solenoid-driven switch is used, and then power is lost during a power outage, the current to the solenoid will be lost, causing the switch to return to its normally open state, which may result in an arc, potentially damaging the HTS lead 206 and / or other components in the circuit.

[0049] Conversely, if a non-locking conventional solenoid is used to drive the switch, loss of power during a power outage will cause the switch to close, potentially creating an undesirable short circuit. On the other hand, the latching switch 210 retains its current state (open or closed) unless and until the magnet control electronics 220 sends an electrical pulse to the latching switch 210, causing the latching switch 210 to switch its state (from open to closed, or from closed to open). The control software appropriately ensures that the latching switches 210 do not open when they are carrying current—for example, the magnet control electronics 220 may include an ammeter that measures the current flowing to / out of the circuit of the latching switch 210 and sends an electrical pulse to switch the latching state of the latching switch 210 only if the measured current is zero.

[0050] In another embodiment of the invention, software is provided for processing signals and sending commands to open and close the HTS protection circuit. Furthermore, control of the magnet controller can be performed on-site at the MR scanner or remotely from a computer communicatively coupled to the MR scanner via a network (e.g., the Internet, cloud, remote server, service provider, etc.).

[0051] Figure 3 The illustration shows a medical imaging device according to another aspect (e.g., Figure 1 A more detailed embodiment of the superconducting magnet 300 of the MRI device 100. It should be understood that... Figure 2 and Figure 3 Common components will be indicated by "similar" reference numerals between the figures; therefore, for brevity, descriptions of these common components will not be repeated. Figure 3As shown, the superconducting magnet 300 includes a cryostat 202 and a closed cooling system 302 containing a small amount of cryogenic fluid (e.g., helium). The cryostat 202 is a vacuum container containing a superconducting coil 204. A cold head 304, driven by a compressor (not shown), operates to cool the helium in the closed cooling system 302 to approximately 4 K or lower. The illustrative cold head 304 is a two-stage cold head with a first cold station CS1 and a second cold station CS2, wherein the second cold station CS2 (e.g., at approximately 4 K or lower) is colder than the first cold station CS1 (e.g., typically tens of Kelvin). The at least one electrically superconducting coil 204 is disposed within the cryostat 202, in thermal contact with the closed cooling system 302, so as to also be cooled to a cryogenic temperature of approximately 4 K or lower, and is configured to generate a magnetic field when an electric current passes through it.

[0052] Figure 3 A device for preventing lead quenching in the MRI apparatus 100 is also shown. The device includes at least one HTS lead 206, 206' (e.g., a first HTS lead 206 and a second lead HTS 206'); Figure 2 The voltage and temperature sensor 222 in Figure 3 The following are shown respectively: at least one voltage sensor 322 monitoring the first HTS lead 206, at least one voltage sensor 322' monitoring the second HTS lead 206', at least one temperature sensor 324 monitoring the first HTS lead 206, and at least one temperature sensor 324' monitoring the second HTS lead 206'; HTS protection switch 208 and magnet control electronics 220. The signals from the various sensors 322, 322', 324, 324' to the electronics 220 are connected in... Figure 3 The dashed lines schematically indicate that these signal connections can be physically implemented as wired or wireless connections. The at least one HTS lead 206, 206' is disposed within the cryostat 202 and coupled to the at least one electrically superconducting coil 204. Figure 3 As shown, a first HTS lead 206 is disposed at the first “top” end of the at least one electric superconducting coil 204, and a second HTS lead 206' is disposed at the second “bottom” end of the at least one electric superconducting coil.

[0053] Each HTS lead 206, 206' has a first end, marked E1, electrically connected to a metallic conductor (e.g., copper, aluminum, their alloys, etc.), and a corresponding second end, marked E2, electrically connected to the terminals of the superconducting winding 204. Typically, the second end E2 is at or near the superconducting winding 204, i.e., at an operating temperature of approximately 4K or lower. In contrast, the first end E1 is at significantly higher temperatures, such as tens of Kelvin to approximately 70K to 80K, depending on the specific configuration. In a suitable method, the first cold station CS1 of the cold head 304 is thermally connected to the first end E1 or to the corresponding electrically connected metallic conductor to help maintain the first end E1 at the desired temperature. Note that... Figure 3 No thermal connection to the cold station CS1 is illustrated. In a typical arrangement, such as that described in WO2017 / 178560, a thermal shield (not shown) surrounds the cold, closed cooling system 302 and the superconducting winding 204, and is in thermal contact with the first cold station CS1 to maintain the thermal shield at a temperature of approximately 100 K or lower, and the thermal shield provides at least a portion of the thermal path between the first end E1 and the cold station CS1. Figure 3 As shown, a first end of the first HTS lead 206 is operably connected to a protective switch 208, and a second end of the first HTS lead 206 is operably connected to a terminal of at least one superconducting coil 304. A first end E1 of the second HTS lead 206' is operably connected to excitation / de-excitation devices 212, 214, and a second end E2 of the second HTS lead 206' is operably connected to another terminal of at least one superconducting coil 304.

[0054] The at least one voltage sensor 322, 322' is configured to measure the voltage in the at least one HTS lead 306, 306'. (See figure) Figure 3 In this configuration, each voltage sensor 322, 322' is a differential voltage sensor configured to measure the differential voltage of the corresponding HTS leads 206, 206'. Figure 3 As further shown, the at least one voltage sensor 322, 322' includes a first differential voltage sensor 322 configured to measure the differential voltage across the first HTS lead 206 and a second differential voltage sensor 322' configured to measure the differential voltage across the second HTS lead 206. Each illustrative temperature sensor 324, 324' is arranged to measure the temperature of the first end E1 of the respective HTS lead 206, 206'. Because of the reasons stated above, the first end E1 of each HTS lead is expected to be at a higher temperature than the second end E2 of the HTS lead—therefore, as long as the first end E1 is at the superconducting critical temperature T... C Below this, the entire HTS lead should be at the critical temperature T.C under.

[0055] like Figure 3 As shown, the protective switch 208 is disposed outside the cryogenic thermostat 202. The protective switch 208 is used to divert current from at least one HTS lead 206, 206'. In other words, the protective switch 208 operates when open to disconnect the current path from the excitation / de-excitation devices 212, 214 to at least one superconducting coil 204.

[0056] Electronic device 220 is configured to control protection switch 208 to disconnect a power circuit in response to an interruption condition. The interruption condition may include at least voltage sensors 322, 322' detecting that the voltage in the at least one HTS lead 206, 206' exceeds an interruption threshold. To do this, when at least one differential voltage sensor 322, 322' measures a differential voltage across the at least one HTS lead 206, 206', electronic device 220 detects whether the amplitude of the measured differential voltage has increased above a predetermined voltage threshold (e.g., 50 mV). When this occurs, electronic device 220 is configured to disconnect protection switch 208 to divert current from the at least one HTS lead 206, 206'. In one example, if the amplitude of the differential voltage after being filtered by a low-pass filter is above the predetermined voltage threshold, then electronic device (220) detects that the amplitude of the differential voltage has increased above the predetermined voltage threshold. In another example, if the amplitude of the differential voltage remains above a predetermined voltage threshold for a predetermined time interval, the electronic device (220) detects that the amplitude of the differential voltage has increased above the predetermined voltage threshold.

[0057] This method reduces the likelihood of noise causing the HTS protection switch 208 to be thrown and unnecessarily disconnected, potentially leading to quenching of the superconducting winding 204. If a predetermined time interval is used, it should be selected to be short enough to ensure that the current is interrupted before the HTS leads 206, 206' can be damaged by Joule heating. Generally, the predetermined time interval is expected to be 1 second or less, and more preferably, 100 milliseconds or less; the selection of the predetermined time interval should take into account any time delays in the process of initiating the disconnection of the HTS protection switch 208, as well as other factors such as the type, length, geometry, etc. of the HTS. Similar factors should also be appropriately considered when selecting the time constant or transient behavior of the low-pass filter used to suppress noise—its response time should be sufficient to avoid damage to the HTS leads due to Joule heating.

[0058] In some instances, at least one temperature sensor 324, 324' detects the temperature leads 306, 306' of the at least one HTS. If the temperature exceeds a threshold, electronics 322 can disconnect protection switch 308 to divert current from at least one HTS lead 306, 306'. However, as previously mentioned, since temperature tends to be a hysteresis indicator of quenching compared to differential voltage, it is more preferable that the temperature sensor is not used to trigger the disconnection of the HTS protection switch 208 (or at least not relied upon as the primary trigger for this). Instead, in some preferred embodiments, the temperature sensors 324, 324' are used when the temperature at one or both first terminals E1 begins to approach the HTS superconducting temperature T. C This triggers a less aggressive remedial action. For example, the remedial action could be to reduce the current flowing through the HTS leads 206, 206' by operating the control or de-energizing devices 212, 214. This will reduce Joule heating in the metal conductor electrically connected to the first terminal E1 and also increase the HTS superconducting critical temperature T, which typically decreases with increasing current magnitude. c .

[0059] refer to Figure 4 An illustrative embodiment of the magnet protection method is shown. In 400, the current in various protection sensors (e.g., sensors 222, 232, 232', 234, 234') and the superconducting winding 204 is monitored. At 402, if a quench is detected in the magnet winding 204 (e.g., by detecting a non-zero voltage across the terminals of the magnet winding 204), then at 404, electronics 220 operates to close switches 208, 210 (if they are not already closed) and connects de-excitation device 214 to transfer the continuous current in winding 204 to de-excitation device 214 to perform controlled magnet closure (to the extent possible, as long as a quench is already in progress; however, the non-passive overrun protection circuitry of winding 204, including the copper substrate of the winding, provides protection against damage to the coil during winding quench. It should be noted that this fault path is triggered by winding 204 rising to around 4K—therefore, the probability that this would trigger a quench in HTS leads 206, 206' is very low, as their T C The values ​​are on the order of tens of Kelvin. Additionally, the HTS protection monitoring can optionally employ temperature sensors 324 and 324' to detect the rising temperature of the first terminal E1 and take less aggressive remedial measures as previously described; this is in Figure 4 It is not described in the text.

[0060] Under various possible fault conditions (shown at 412), an initial quench of one or both HTS leads 206, 206' is detected, for example based on the voltage measured across leads 206, 206' by the at least one voltage sensor 222, 222'. In this case, at 412, electronics 220 is configured to determine whether the measured voltage (which may be a differential voltage as previously described) is outside a corresponding predefined threshold. If so, then at 414, when the measured voltage is outside the predetermined threshold, electronics 220 operates to interrupt the current flowing in at least one HTS lead 206, 206' by opening the HTS protection switch 208. As previously described, this may result in a quench of the magnet winding 204; however, it is recognized here that a quench of the winding generally does not lead to damage to the winding and is preferred over uncontrolled Joule heating of the HTS leads, which is likely to cause costly damage to the HTS leads.

[0061] Under another possible fault condition (shown at 422), a call is generated to switch the latching thermal switch 210. This call can be generated automatically by the electronics 220 or manually by the user. In this case, at 424, this call to switch the latching thermal switch 210 is executed only if the current amplitude in the HTS leads 206, 206' is zero (or, for simplicity, below a certain threshold). This ensures that switch 210 is not disconnected while carrying current, thus preventing a destructive arc. It can be noted that the fault recovery paths 422, 424 do not interfere with either the winding quench recovery paths 402, 404 or the HTS lead quench recovery paths 412, 414 for the following reasons: First, if the latching switch 210 is in the open state, the current will be zero; therefore, recovery paths 422, 424 never prevent switching the latching switch 210 from the open state to the closed state. Next, if the latching switch 210 is closed and a winding overrun is detected at 402, operation 404 will not require switching the latching switch 210, as they are already closed. Finally, if the latching switch 210 is closed and an HTS lead overrun is detected at 412, the remedial action is to disconnect the HTS protection switch 208, which will not generate a call to trigger the latching switch 210.

[0062] This disclosure has been described with reference to preferred embodiments. Various modifications and variations can be made by those skilled in the art upon reading and understanding the foregoing detailed description. This disclosure is intended to be understood to include all such modifications and variations, provided they fall within the scope of the appended claims or their equivalents.

Claims

1. A magnetic device (200), comprising: A cryogenic thermostat (202) containing a volume of cryogenic fluid; One or more superconducting coils (204) are disposed within the cryostat, wherein the one or more superconducting coils are configured to generate a magnetic field when current passes through them; One or more high-temperature superconductors, hereinafter referred to as HTS, current leads (206), which are permanently disposed within the cryostat and coupled to the one or more superconducting coils; One or more sensors (222) are located at or near the one or more HTS current leads and are configured to monitor the state of the HTS current leads; HTS protection switch (208) for protecting one or more HTS current leads, the HTS protection switch being selectively coupled to one or more HTS current leads; A magnet controller (220) is configured to control the HTS protection switch; The magnet controller is configured to control the HTS protection switch to transfer current from one or more HTS current leads when a quench is detected via the sensor; and The device is characterized in that it further includes: A locking mechanical switch (210), which is installed inside the cryostat between one or more HTS current leads and external current terminals and configured to electrically couple the one or more HTS current leads to one or more devices disposed outside the cryostat; and The locking mechanical switch (210) has an open state and a closed state, and is configured to switch between the open state and the closed state or between the closed state and the open state in response to an electrical pulse.

2. The apparatus (200) according to claim 1, wherein, The one or more HTS current leads (206) are formed of rare earth-barium-copper oxide ReBCO.

3. The apparatus (200) according to any one of claims 1-2, wherein, The locking mechanical switch (210) in the closed state is configured to remain closed during power outages.

4. The apparatus (200) according to any one of claims 1-3, wherein, The magnet controller (220) is configured to prevent the locking mechanical switches (210) from opening when they are carrying current by not running a call to switch the locking mechanical switches (210).

5. The apparatus (200) according to any one of claims 1-4, wherein, The one or more sensors (220) include voltage sensors and / or temperature sensors.

6. An apparatus for a medical imaging device (100), the apparatus comprising: At least one superconducting current lead (306, 306'); At least one voltage sensor (322, 322') is configured to measure the voltage in said at least one superconducting lead; A protective switch (308) is configured to operate to transfer current from the at least one superconducting current lead; Electronic device (320) configured to control the protective switch to disconnect the power circuit in response to a disconnection condition, the disconnection condition including the voltage sensor detecting that the voltage in the at least one superconducting lead exceeds a disconnection threshold; as well as A locking mechanical switch, which electronically connects the at least one superconducting current lead to the electronic device, wherein disconnection includes switching the locking mechanical switch from a closed state to an open state; The at least one voltage sensor (322, 322') is a differential voltage sensor configured to measure the differential voltage across the at least one superconducting current lead (306, 306'); Wherein, when the electronic device (320) detects that the amplitude of the differential voltage measured by the differential voltage sensor (322, 322') has increased above a predetermined voltage threshold, the electronic device is configured to disconnect the protection switch to transfer current from the at least one superconducting current lead.

7. A superconducting magnet (300) for a medical imaging device (100), said superconducting magnet comprising: A cryogenic thermostat (302) containing a volume of cryogenic fluid; At least one electric superconducting coil (304) is disposed within the cryostat and configured to generate a magnetic field when current passes through it; as well as The apparatus according to claim 6; The at least one superconducting current lead (306, 306') is disposed inside the cryostat and coupled to the at least one electric superconducting coil, and the protection switch (308) is disposed outside the cryostat.

8. The superconducting magnet (300) according to claim 7, wherein, The cryogenic thermostat (302) includes a vacuum container containing at least one superconducting coil (304) and a closed cooling system containing a volume of cryogenic fluid.

9. The superconducting magnet (300) according to any one of claims 7-8, wherein, The protection switch (308) is operable to disconnect the current path from the excitation / de-excitation devices (312, 314) to the at least one superconducting coil (304).

10. The superconducting magnet (300) according to any one of claims 7-8, wherein, The at least one superconducting current lead (306, 306') includes a first superconducting current lead (306) and a second superconducting current lead (306'), wherein: A first end of the first superconducting current lead is operatively connected to the protective switch (308), and a second end of the first superconducting current lead is operatively connected to the at least one electric superconducting coil (304); and / or The differential voltage sensor (XX) includes a first differential voltage sensor (322') configured to measure the differential voltage across the first superconducting lead and a second differential voltage sensor (322') configured to measure the differential voltage across the second superconducting lead.

11. The superconducting magnet (300) according to any one of claims 7-8, wherein, The predetermined voltage is approximately 50mV.

12. The superconducting magnet (300) according to any one of claims 7-8, wherein, The electronic device (320) is configured to detect that the amplitude of the differential voltage increases above the predetermined voltage threshold when the amplitude of the differential voltage remains above the predetermined voltage threshold for a predetermined time interval.

13. The superconducting magnet (300) according to any one of claims 7-8, wherein, The electronic device (320) is configured to detect that the amplitude of the differential voltage increases above the predetermined voltage threshold when the amplitude of the differential voltage after being filtered by the low-pass filter is above the predetermined voltage threshold.

14. A method (400) for protecting an HTS current lead in the device according to claim 1 from quenching, the method comprising: Measure the voltage across one or more HTS current leads; Determine whether the measured voltage is outside the corresponding predefined threshold; When the measured voltage is outside the predefined threshold, disconnect the connection between one or more HTS current leads and the external current terminal. Furthermore, the cut-off is characterized in that the cut-off includes switching the locking mechanical switch (210) from a closed state to an open state, wherein the locking mechanical switch electronically connects one or more HTS current leads to an external current terminal.

15. The method (400) according to claim 14, wherein, The cutting also includes: Control the HTS protection switch used to protect one or more HTS current leads to transfer current from one or more HTS current leads.

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