RF electrical measurement for superconductor quench and temperature anomaly detection in magnets

Abstract

Quench detection apparatuses and methods for high-temperature-superconducting (HTS) cables are described. Electrical signals are transmitted along a metallic coolant-carrying waveguide of the HTS cable. The transmitted signals are detected and the transmission and / or absorption properties of the coolant-carrying cable determined. Changes in the properties indicative of heating of the HTS cable associated with quench are detected.

Description

RF ELECTRICAL MEASUREMENT FOR SUPERCONDUCTOR QUENCH AND TEMPERATURE ANOMALY DETECTION IN MAGNETSRELATED APPLICATIONS

[0001] The present application claims the benefit under 35 U.S.C. § 119(e) of U.S. Patent Application Number 63 / 608,186, entitled “RF ELECTRICAL MEASUREMENT FOR SUPERCONDUCTOR QUENCH AND TEMPERATURE ANOMALY DETECTION IN MAGNETS,” and filed December 9, 2023 under Attorney Docket No. C1599.70045US00, which is hereby incorporated by reference herein in its entirety.BACKGROUNDField

[0002] The present disclosure relates to quench detection in high-temperature- superconducting (HTS) cables such as those used in high temperature superconducting magnets.Related Art

[0003] High-temperature-superconducting (HTS) cables can experience quench.BRIEF SUMMARY

[0004] Some embodiments provide for a system for detecting quench in a high- temperature- superconducting (HTS) cable that itself includes a high-temperature- superconductor and a conductive former comprising a cooling channel tube configured to carry a coolant, wherein the high-temperature-superconductor is coupled to or embedded in the conductive former. The system comprises: an electrical signal transmitter coupled to a first location of the cooling channel tube; an electrical signal receiver coupled to a second location of the cooling channel tube and configured to receive electrical signals transmitted by the electrical signal transmitter and transmitted along the cooling channel tube; and a processor coupled to the electrical signal receiver and configured to process the electrical signals received by the electrical signal receiver.

[0005] Some embodiments provide for a method of operating a quench detection system for a high-temperature-superconducting (HTS) cable, the HTS cable comprising a high- temperature- superconductor and a conductive former comprising a cooling channel tube configured to carry a coolant, wherein the high-temperature superconductor is coupled to or embedded in the conductive former. The method comprises: transmitting, from a first location ofthe cooling channel tube, an electrical signal along the cooling channel tube; receiving the electrical signal with an electrical signal receiver coupled to a second location of the cooling channel tube; and processing the electrical signal with a processor coupled to the electrical signal receiver.BRIEF DESCRIPTION OF DRAWINGS

[0006] Various aspects and embodiments will be described with reference to the following exemplary and non-limiting figures. It should be appreciated that the figures are not necessarily drawn to scale. Items appearing in multiple figures are indicated by the same or a similar reference number in all the figures in which they appear.

[0007] FIG. 1 is a cross-sectional view of an example tokamak, according to some embodiments of the present disclosure.

[0008] FIG. 2 is a cross-sectional view of the central solenoid magnets of the tokamak of FIG. 1, including high-temperature-superconducting (HTS) cables, according to a non-limiting embodiment of the present disclosure.

[0009] FIG. 3 is a perspective view of the poloidal field magnets of the tokamak of FIG.1, including HTS cables, according to a non-limiting embodiment of the present disclosure.

[0010] FIG. 4A is a perspective view of an HTS cable, according to a non-limiting embodiment of the present disclosure.

[0011] FIG. 4B is a cross-sectional view of the HTS cable of FIG. 4A.

[0012] Figure 5 shows a schematic of a system for transmitting and receiving the signal that propagates through the coolant of an HTS cable, according to a non-limiting embodiment of the present disclosure.

[0013] Figure 6 shows a plot of the quench zone insertion loss (IL) (measured in dB) versus the quench temperature (measured in K), for different lengths of the quench hotspot in an HTS cable.

[0014] FIG. 7 illustrates plots of the temperature of a former the coolant and an HTS cable.

[0015] FIG. 8 presents plots of the molar density, refractive index, and sensitivity of the refractive index of a coolant of an HTS cable.

[0016] FIG. 9 is a plot which shows the minimum detectable quench temperature of the helium coolant (measured in Kelvin) of an HTS cable as a function of the pressure drop (measured in bar) over the length of the cooling channel caused by the helium flow.

[0017] FIG. 10 is a flowchart of a method of detecting a quench hotspot, according to certain embodiments of the technology disclosed herein.DETAILED DESCRIPTION

[0018] Aspects of the present disclosure provide methods and apparatuses for detecting quench in superconducting cables such as those that may be used in magnetic fusion energy devices (e.g., tokamaks), particle accelerators, or other large scale, high-power devices that may experience ionizing radiation. Quench is an abrupt, localized transition of a superconducting structure to a non-superconducting (resistive) state. In some instances, quench can be highly detrimental to device operation and long-term device health. For example, uncontrolled quench can cause undesirable damage to a device. Early and accurate detection of quench allows for preventative or corrective action to be taken. Aspects of the present disclosure provide electrical quench detection for high-temperature-superconducting (HTS) cables. An electrical quench detecting system according to some aspects of the present disclosure includes an electrical signal transmitter configured to input an electrical signal to a cooling tube of the HTS cable, an electrical signal receiver configured to receive the transmitted signal, and a processor configured to analyze the received electrical signal for its transmitted properties. The coolant within the cooling tube is used as a temperature-dependent signal transmission medium and the tube itself as a waveguide. Transmission of the signal through the coolant depends on the temperature of the coolant, and thus the processor may analyze the properties of the received signal and determine the temperature of the coolant and, therefore, the HTS cable.

[0019] Magnetic fusion energy devices (e.g., tokamaks), particle accelerators, and other large-scale, high-power devices may use long HTS cables to generate magnetic fields. Such devices often require sufficient electrical current to generate high magnetic field strength over relatively large areas (e.g., tens of square meters or more). The use of superconducting magnets facilitates creation of the needed magnetic fields, including magnetic fields of the needed strength. The superconducting magnets utilize HTS cables to carry field-generating electrical current. Such HTS cables can be tens of meters or hundreds of meters long.

[0020] A temperature sensor can be used to monitor temperature along an HTS cable to detect quench. Quench of an HTS cable that includes a superconductor and a non- superconducting component can occur when the temperature of the superconductor rises above its current sharing temperature, which is the temperature at which current may begin to pass through the non- superconducting component(s) of the HTS cable. The current sharingtemperature is lower than the critical temperature of the HTS cable. Positioning a temperature sensor along the HTS cable allows for detection of temperature increases indicative of a potential quench event.

[0021] The inventors recognize that the coolant of the HTS cable exhibits a temperaturedependent index of refraction and therefore can serve as a temperature-dependent signal transmission medium, with the cooling tube that contains the coolant serving as a waveguide. The intensity, frequency, and / or phase of signals propagating through the coolant will depend on the temperature of the coolant. Thus, the inventors have recognized that using the coolant as a signal transmission medium, and analyzing the signals received after propagating down the coolant tube of the HTS cable allows for determination of the temperature of the coolant, which is indicative of the temperature of the HTS cable itself. In this manner, temperature of the HTS cable may be monitored and quench events may be detected.

[0022] According to an aspect of the disclosure, a system is provided for detecting quench in a high-temperature-superconducting (HTS) cable that itself includes a high- temperature- superconductor and a conductive former comprising a cooling channel tube configured to carry a coolant, wherein the high-temperature-superconductor is coupled to or embedded in the conductive former. The system comprises an electrical signal transmitter coupled to a first location of the cooling channel tube, an electrical signal receiver coupled to a second location of the cooling channel tube and configured to receive electrical signals transmitted by the electrical signal transmitter and transmitted along the cooling channel tube, and a processor coupled to the electrical signal receiver and configured to process the electrical signals received by the electrical signal receiver.

[0023] According to an aspect of the disclosure, a method of operating a quench detection system for a high-temperature-superconducting (HTS) cable is provided, the HTS cable comprising a high-temperature-superconductor and a conductive former comprising a cooling channel tube configured to carry a coolant, wherein the high-temperature superconductor is coupled to or embedded in the conductive former. The method comprises transmitting, from a first location of the cooling channel tube, an electrical signal along the cooling channel tube, receiving the electrical signal with an electrical signal receiver coupled to a second location of the cooling channel tube, and processing the electrical signal with a processor coupled to the electrical signal receiver.

[0024] As used herein the phrases “HTS materials” or “HTS superconductors” refer to superconducting materials having a critical temperature above 30 °K at zero self-field.

[0025] The aspects and embodiments described above, as well as additional aspects and embodiments, are described further below. These aspects and / or embodiments may be used individually, all together, or in any combination of two or more, as the disclosure is not limited in this respect.

[0026] As described above, aspects of the present disclosure provide methods and apparatuses for detecting quench in superconducting cables such as those that may be used in magnetic fusion energy devices (e.g., tokamaks), particle accelerators, or other high-power devices. FIG. 1 depicts a cross-sectional view of an example tokamak (or, more generally, a fusion energy device), according to some embodiments of the present disclosure. As shown in FIG. 1, tokamak 100 generates a core plasma 110 that circulates within a vacuum vessel 120, which is shaped as a toroid. There are numerous ports integrally formed within, or otherwise coupled to, the vacuum vessel that provide access to the vacuum vessel from outside of the tokamak 100, including upper off-midplane ports 131, midplane ports 132, and lower off- midplane ports 133, which are situated at various points around the tokamak 100.

[0027] The tokamak 100 also includes a plurality of toroidal field (TF) magnets 140, a plurality of poloidal field (PF) magnets 150, and one or more central solenoid (CS) magnets 160. The TF magnets 140 are D- shaped (or approximately D- shaped) magnets that are configured to confine the core plasma 110 in a desired region of the vacuum vessel 120, and to generate flux within the core plasma. The PF magnets 150 are roughly ring-shaped magnets that are configured to shape and position the core plasma 110. The CS magnet(s) 160 are arranged in the center of the tokamak 100 and are configured to inductively drive the electrical current in the plasma.

[0028] Although not shown in FIG. 1, the TF magnet 140 includes one or more conductor windings within the housing. According to some embodiments, these conductors may include a high temperature superconductor, such as REBCO. In some embodiments, the TF magnet 140 may be configured to be cooled to around 8K during operation of the tokamak. However, this is an example, and the TF magnet 140 may be cooled to different temperatures.

[0029] TF magnet 140 may assume various potential forms. According to some embodiments, a TF magnet 140 may comprise a plurality of plates and one or more cooling channels. For example, the TF magnet 140 may include a plurality of plates arranged in a stack that includes a first plate, the first plate comprising a conducting channel on a first side of the first plate, at least part of the conducting channel being arranged in a spiral path, the conductingchannel comprising a (HTS) material and a conductive material, and a plurality of cooling channels on a second side of the first plate, the second side opposing the first side.

[0030] According to some embodiments, a TF magnet 140 may comprise a winding of a non-insulated conductor, the conductor comprising a stack of HTS tapes, wherein each of the HTS tapes comprises an HTS material and is clad in a conductive material, a co-conductor layer, and a layer of solder arranged between and in contact with the stack of HTS tapes and the coconductor layer.

[0031] According to some embodiments, a TF magnet 140 may comprise a winding of a non-insulated conductor, the conductor comprising a stack of HTS tapes, wherein each of the HTS tapes comprises a superconductor layer and is clad in a conductive material, wherein a ratio between a cross-sectional area of the conductive material and a cross-sectional area of the superconductor layer is at least 0.75.

[0032] According to some embodiments, a TF magnet may comprise a winding of a noninsulated conductor, the conductor comprising a stack of HTS tapes, wherein each of the HTS tapes comprises an HTS material and is clad in a conductive material, and a stack of conductive non-superconductor tapes arranged in contact with the stack of HTS tapes.

[0033] According to some embodiments, a TF magnet may comprise a winding of a noninsulated conductor, the conductor comprising a stack of high temperature superconductor (HTS) tapes, wherein each of the HTS tapes comprises an HTS material having a conductive material disposed over at least a portion thereof, a co-conductor layer arranged over the stack of HTS tapes, and solder disposed between and in electrical contact with the stack of HTS tapes and the co-conductor layer.

[0034] According to some embodiments, the on-axis toroidal magnetic field produced by the plurality of TF magnets 140 in the tokamak 100 may be greater than or equal to 8 Tesla (T), 9 T, 10 T, 11 T, 12 T or 13 T. According to some embodiments, the on-axis toroidal magnetic field produced by the plurality of TF magnets 140 in the tokamak 100 may be less than or equal to 15 T, 14 T, 13 T, 12 T, 11 T, or 10 T. Any suitable combination of the above ranges is also possible (e.g., an on-axis toroidal field of greater than or equal to 10 T and less than or equal to 15 T, or greater than or equal to 12 T and less than or equal to 13 T).

[0035] The PF magnets 150 and CS magnets 160 are superconducting magnets and include HTS cables. In FIG. 1, the HTS cables are illustrated in end-on view. PF magnets 150 include HTS cables 152 and CS magnets 160 include HTS cables 162. Further details of theHTS cables are illustrated in subsequent figures and described in further detail below. FIG. 1 illustrates a single HTS cable 152 per PF magnet 150 and a single layer (in the radial direction) of HTS cables 162 per CS magnet 160. The various aspects of the present disclosure are not limited in this respect. Any suitable number of HTS cables may be included in the PF magnets 150 and CS magnets 160. Optionally, the TF magnets 140 include HTS cables of the types described herein.

[0036] In some embodiments, the tokamak 100 may comprise, or may otherwise be coupled to, a source of auxiliary heating to bring the core plasma 110 to a desired temperature. In some embodiments, the auxiliary heating source may comprise an ion cyclotron resonance heating system (e.g., a 25 MW, 120 MHz heating system). Other auxiliary heating may include alpha particles produced during fusion, and / or ohmic power, which together may produce around 1 MW of further heating. In some embodiments, the tokamak 100 may comprise a glow discharge cleaning system.

[0037] During operation of the tokamak 100, an axisymmetric toroidal core plasma 110 is produced in the vacuum vessel 120. This plasma carries a toroidal electrical current, created by the CS magnets 160 by induction, which in turn creates a poloidal magnetic field, providing confinement of the core plasma 110. The toroidal field magnets 140 provide stability to the electrical current in the core plasma 110, with the PF magnets 150 and the CS magnets 160 shaping and controlling the position of the core plasma 110. The core plasma 110 may be heated by the central solenoid, radio frequency (RF) and / or high energy neutron beams to initiate fusion. The resulting energy from the resulting neutrons may be captured in a blanket.

[0038] The tokamak 100 may generate radiation in various ways. Radiation 164 is shown in simplified form by the arrows emitted by the core plasma 110. The radiation 164 may irradiate the cables 152 and / or the cables 162, among other components of the tokamak 100.

[0039] FIG. 2 depicts a cross-sectional perspective view of central solenoid (CS) magnets 160, according to some embodiments. The tokamak 100 may include any number of CS magnets 160 stacked in a column at or approximate to a central axis of the tokamak 100, such as between four (4) and eight (8) CS magnets (e.g., six CS magnets 160). The CS magnets 160 are configured to inductively drive the plasma current.

[0040] According to some embodiments, one or more of the CS magnets 160 may be formed from a HTS cable 162 — shown in cross-section in FIG. 2 — which may be wound around a central structure (e.g., a bobbin) 202 in one or more layers. For instance, a CS magnet maycomprise multiple electrically insulated cable turns grouped in a multi-layer or multi-pancake arrangement. This allows the magnet to be driven in an alternating current (AC) mode by changing the power supply current over time, which in turn causes the field produced by the magnet to change over time as well. In the illustrated example, the HTS cable 162 has two layers 163a and 163b of windings in the radial direction r. However, a single layer of windings (e.g., 163a), or three or more layers of windings may be implemented in alternative embodiments, and the number of windings is not limited to that illustrated in FIG. 2.

[0041] FIG. 3 depicts a perspective view of a set of poloidal field (PF) magnets 150 as included in the tokamak 100, according to some embodiments. The tokamak 100 may include any number of PF magnets 150 arranged proximate to the TF magnets 140. For instance, as shown the tokamak 100 may include four upper PF magnets and four lower PF magnets. The plurality of PF magnets 150 are configured to shape the core plasma in the vacuum vessel and maintain a desired position of the core plasma. According to some embodiments, one or more of the PF magnets 150 may be formed from a HTS cable 152 shown in dashed lines in FIG. 3 since they are within the illustrated PF magnets 150.

[0042] FIGs. 4A-4B illustrate a non-limiting example of an HTS cable 400 that may be used as any one or more of the HTS cables for PF and / or CS magnets (e.g., PF magnets 150 and CS magnet 160) of a tokamak according to various embodiments of the present disclosure. More generally, the illustrated HTS cable 400 may be used in any of the types of devices described herein as utilizing HTS cables. As may be seen in FIGs. 4A and 4B, a HTS cable 400 includes a former 416 having HTS tape stacks 418 disposed in channels provided in an exterior surface of and extending along a length of the former 416. The former 416 may be made of any suitable electrically conductive material. In some embodiments, the former 416 may be formed of copper. The former 416 may be a single piece or may be segments (e.g., formed in thirds or quarters) with insulating material between them which may, for example, reduce eddy current formation in the former. For example, in the embodiment illustrated in FIG. 4B, former 416 is partitioned into four quarters by insulating material 417. This, in at least some instances, causes the former temperature to rise more rapidly during a thermal runaway.

[0043] The former 416 may have a cooling channel 429 through which coolant 430 may flow to keep the temperature of the HTS cable lower than it would be otherwise. Coolant 430, illustrated by the dotted fill within cooling channel 429 in FIG. 4B, has a temperature-dependent index of refraction. Specifically, the index of refraction of coolant 430 may decrease as the temperature of coolant 430 rises. Quench events produce heat, and an increase in thetemperature of a region of coolant 430 may be a precursor to a quench event in that region. This increase in temperature would lower the index of refraction of the region. This in turn raises the minimum frequency of signals that may propagate through coolant 430, such that signals at certain frequencies which propagated through coolant 430 prior to the increase in temperature are no longer able to propagate through coolant 430 after the increase in temperature. Coolant 430 may be, but is not limited to being, supercritical helium. Cooling channel 429 may also be surrounded by insulating material 431, which in at least some embodiments may contact insulating material 417.

[0044] The HTS cable 400 includes several additional features. HTS tape stacks 418 are held in their respective channels via solder 419. An inner jacket 420 (e.g., a copper jacket) is disposed around the former 416 and HTS tape stacks 418 and a plating 422 (e.g., a silver plating) may be disposed over the inner jacket 420. Although the entire surface of inner jacket 420 may be plated, in some embodiments, only a portion of inner jacket 420 may be plated. Thus, as illustrated in FIG. 4A, only about one-half of the surface of inner jacket 420 has a plating 422 disposed thereover. An outer jacket 424 (e.g., a steel or stainless-steel jacket) is disposed around inner jacket 420. In this example embodiment, the cable 400 has multiple channels in an electrically conductive (e.g., copper) former surrounded by one or more jackets. In some embodiments, the inner jacket 420 may comprise copper and the outer jacket 424 may comprise stainless steel. However, this is merely by way of example, as other suitable materials for the jackets and former may be used.

[0045] The illustrated components may have any suitable dimensions for carrying sufficient current to generate the desired magnetic field strengths, such as those magnetic field strengths listed previously herein. As shown in FIG. 4B, the width of an illustrative HTS tape stack 418 is Wl, the diameter of the former 416 is DI, the diameter of the inner jacket 420 is D2, and the diameter of the outer jacket 424 is D3. The width of the channels in which the HTS tape stacks 418 fit may be substantially the same as the width of the HTS tape stacks themselves, being slightly larger to accommodate the HTS tape stacks. Wl may be between 2 mm and 5 mm in some embodiments. D3 may be between 25 mm and 35 mm. D2 is between DI and D3, and DI is between Wl and D2.

[0046] Figure 5 shows a schematic of system 500 for transmitting and receiving the signal that propagates through the coolant 430 of an HTS cable. In the example illustrated in Figure 5, coolant 430 is supercritical helium. The supercritical helium enters cooling channel 429 at helium inlet 510. It then flows from left to right through cooling channel 429 and exits cooling channel 429 at helium outlet 520. Cooling channel 429 is centered in HTS cable 400, asdiscussed earlier with reference to Figure 4. The helium inlet 510 and helium outlet 520 may be generalized simply to “inlet” and “outlet” as they apply to scenarios in which the coolant is something other than helium.

[0047] System 500 also includes transmitter 532 which transmits a signal 530. In some embodiments, signal 530 may be a microwave signal with a frequency between a few GHz (e.g., 5 GHz) and 70 GHz, including any frequency or range of frequencies within that range, such as around 40 GHz. The larger the cooling channel (e.g., the larger its diameter or other cross- sectional dimension depending on the shape of the cooling channel), the lower the frequencies that may be used. Transmitter 532 is connected to cooling channel 429 by coaxial cable 534. Coaxial cable 534 comprises an outer conductor 531 and an inner conductor 533. Coaxial cable 534 may be attached to cooling channel 429 through any suitable manner, such as by means of a clamped contact between outer conductor 531 and cooling channel 429 or by soldering outer conductor 531 to the cooling channel 429. When coaxial cable 534 is attached to cooling channel 429 in this way, inner conductor 533 protrudes into cooling channel 429 to form a stub antenna 535, as shown in the cross-sectional view of cooling channel 429 at the bottom of Figure 5. Stub antenna 535 may have a circular shape. It may be sized to fit within cooling channel 429, for example having a diameter less than those described in connection with the cooling channel for FIG. 4B. The stub antenna 535 may be configured to convey frequencies of interest. For example, it may be configured to convey signals with frequencies within the ranges listed above.

[0048] System 500 further includes receiver 536, configured to receive signal 530 after it has propagated through cooling channel 429. Similar to transmitter 532, receiver 536 is connected to cooling channel 429 by a coaxial cable 538. Coaxial cable 538 may be substantially identical to coaxial cable 534, and therefore may also comprise an outer conductor and an inner conductor like those of coaxial cable 534. Coaxial cable 538 may also be attached to cooling channel 429 by means of a clamped contact between the outer conductor and the cooling channel, soldering the outer conductor to the cooling channel, or in some other suitable manner. When coaxial cable 538 is attached to cooling channel 429 in this way, the inner conductor of the coaxial cable 538 protrudes into cooling channel 429 to form a stub antenna 535, as shown in the cross-sectional view of cooling channel 429 at the bottom of Figure 5. As mentioned above, stub antenna 535 may have a circular shape; may be sized to fit within cooling channel 429; and may be configured to convey frequencies of interest. For example, it may be configured to convey signals with any of the frequencies previous described herein, such asfrequencies around 40 GHz. Receiver 536 may also be coupled to processor 550, configured to process the signal received by receiver 536.

[0049] Coolant 430 is the medium through which signal 530 propagates. Transmitter 532 transmits signal 530 along inner conductor 533 of coaxial cable 534. Signal 530 travels along inner conductor 533 from transmitter 532 to stub antenna 535. Upon reaching stub antenna 535, signal 530 is launched into the coolant 430. At this point, signal 530 propagates through coolant 430 in the direction of its flow, which is from left to right in the example shown in Figure 5.

[0050] Signal 530 travels in this way along cooling channel 429 until it reaches stub antenna 540. Stub antenna 540 then picks up signal 530, causing signal 530 to travel along inner conductor 539 until it reaches receiver 536. Signal 530 may then be detected by receiver 536 and sent to processor 550 so that it may be processed by processor 550.

[0051] As signal 530 travels down cooling channel 429 by propagating through coolant 430, it may encounter a heated region, which may be a precursor to a quench event. Hereafter, such a heated region that could potentially result in a quench event is referred to as a quench hotspot, an example of which is illustrated by quench hotspot 560 in Figure 5. As explained above, the increased temperature of quench hotspot 560 would cause a decrease in the index of refraction of the surrounding coolant. This decrease in the index of refraction of the surrounding coolant may impact the transmitted signal 530 in various ways. For example, it might lead to absorption of at least some frequencies of signal 530 that are evanescent (i.e., those frequencies that are below the cutoff frequency). In such cases, signal 530 will have a decreased intensity upon being received by stub antenna 540 and reaching receiver 536. Alternatively or in addition, the decrease in the index of refraction of the surrounding coolant may impact the phase of transmitted signal 530.

[0052] Therefore, processor 550 may be configured to analyze signal 530 in various ways. For example, processor 550 may be configured to analyze the intensity of signal 530, or the range of frequencies included in signal 530. This would allow processor 550 to detect if evanescent frequencies had been absorbed due to quench hotspot 560. Processor 550 may be configured to analyze the phase of signal 530, allowing processor 550 to detect if the phase of signal 530 was impacted by quench hotspot 560.

[0053] As already noted, a quench hotspot 560 along cooling channel 429 may impact signal 530 by changing its intensity, frequency or phase. The magnitude of this impact can depend on the length of the quench hotspot 560. In particular, an increase in the length of quench hotspot 560 can result in an increase in the impact that traversing quench hotspot 560 has on signal 530. This means that, if signal 530 has traversed a longer quench hotspot 560,processor 550 may be able to detect the impact on signal 530 of smaller temperature deviations of quench hotspot 560. This is significant because, in order for processor 550 to effectively detect quench hotspot 560, the magnitude of the impact on signal 530 from the increased temperature of quench hotspot 560 must exceed the magnitude of the impact on signal 530 from typical operating variations. Thus, a quench hotspot with a small temperature deviation may not be detected by processor 550, because the impact of the small deviation on signal 530 does not exceed the impact from typical operation variations. However, if the length of the quench hotspot is increased, then even a small temperature deviation could be detected by processor 550, because the increased length will increase the impact on signal 530 such that it exceeds the impact from typical operating variations.

[0054] Figure 6 shows a plot 600 of the quench zone insertion loss (IL) (measured in dB) versus the quench temperature (measured in K), for different lengths of the quench hotspot. The simulation on which the plot is based assumes a cooling tube inner diameter (ID) of 4 mm and an operating frequency of 42.5 GHz, with non-quench operating conditions of 25 bar, 20K. Quench zone IL is a measure of the reduction of the intensity of the transmitted signal after it has traversed the quench hotspot. The solid line 610 in plot 600 shows the quench zone IL for a quench hotspot length of 10 cm. The short-dashed line 620 in plot 600 shows the quench zone IL for a quench hotspot length of 50 cm. The long-dashed line 630 in plot 600 shows the quench hotspot IL for a quench zone length of 100 cm.

[0055] Plot 600 shown in Figure 6 illustrates the point discussed above that an increase in the length of quench hotspot 560 over which the signal 530 traverses increases the impact on signal 530. In this case, an increase in length increases the impact on the intensity of signal 530. For example, the short-dashed line 620 demonstrates that a quench temperature of 22.5 K (which is 2.5 K above ambient) over a 50 cm length will cause a ~10 dB IL. This is a 90% reduction in the transmitted signal. Meanwhile, the long-dashed line 630 demonstrates that a 2.5 K hotspot of a meter or longer will result in >20 dB IL, a 99% reduction in the transmitted signal. Additionally, for all quench hotspot lengths, the IL increases as quench zone temperature increases, since higher temperature deviations of the quench hotspot result in a greater range of evanescent frequencies, which in turn results in a greater reduction of the intensity of the transmitted signal.

[0056] FIG. 7 shows plots 700 and 710. Plot 700 shows the temperature of former 416 (measured in Kelvin) as a function of the distance (measured in meters) from a quench event in HTS cable 400 occurring at 25 K, for different amounts of time (measured in seconds) from the quench event. Plot 710 shows the temperature (measured in Kelvin) of coolant 430 (in this casehelium) as a function of the distance (measured in meters) from a quench event in HTS cable 400 occurring at 25 K, for different amounts of time (measured in seconds) from the quench event.

[0057] Some conventional quench detection systems rely on measuring the temperature of former 416 in order to detect quench. For example, some conventional quench detection systems, such as those using fiber optics, are able to detect quench at a peak former temperature of 50 K. Comparing the small-dotted line on plot 700 with the small-dotted line on plot 710 shows that the same quench event which produces a peak former temperature of 50 K at the position of the quench event will result in a helium hotspot of 27.5 K that extends at least 1 meter from the position of the quench event. This means that, in order for the quench detection system disclosed herein to be as effective as such conventional quench detection systems, the system should be able to detect a helium hotspot with a temperature of 27.5 K and greater than 1 meter long. The magnitude of the requisite temperature increase to be detected in helium is smaller than the magnitude of the requisite temperature increase to be detected in the former because the heat from the quench is deposited in the former and takes time to propagate into the coolant in a configuration like that shown in the figures.

[0058] FIG. 8 shows plots 800 and 810. Plot 800 shows both the molar density of the helium coolant (measured in moles per cubic meter) and the refractive index of the helium coolant as a function of the temperature of the helium coolant (measured in Kelvin). Plot 800 illustrates how both the density and the refractive index of the helium coolant decrease as the temperature of the helium coolant rises. This explains why a quench hotspot may result in evanescent frequencies in the transmitted signal. Plot 800 also illustrates that the sensitivity increases at around 20K. Supercritical fluids, such as supercritical helium, exhibit a relatively large decrease in refractive index as the temperature increases, a property which facilitates use of the techniques disclosed herein, particularly at temperature ranges of interest for operation of fusion devices of the types described herein.

[0059] Plot 810 shows the sensitivity of the helium coolant (measured in percent change of refractive index per degree Kelvin) as a function of the temperature of the helium coolant (measured in Kelvin). Plot 810 shows that, for a non-quench operating temperature of around 20 K (which is the region of interest for many applications of the invention disclosed herein), the sensitivity of the helium coolant is about 0.15% / K. This level of sensitivity is an improvement over the level of sensitivity achieved at a non-quench operating temperature of 20K in certain other conventional quench detection systems, such as those that employ fiber optics.

[0060] FIG. 9 shows plot 900, which shows the minimum detectable quench temperature of the helium coolant (measured in Kelvin) as a function of the pressure drop (measured in bar) over the length of the cooling channel caused by the helium flow. As discussed above, in order to effectively detect a quench hotspot, the magnitude of the impact on the signal from the increased temperature of the quench hotspot should exceed the magnitude of the impact on the signal from typical operating variations, such as the pressure drop due to the helium flow. The minimum detectable quench temperature shown in plot 900 is the minimum temperature that the helium coolant should reach in order to be able to say that the temperature increase is due to factors other than the pressure drop due to the helium flow (factors such as, for example, a quench hotspot). This is equivalent to calculating the temperature increase at constant pressure necessary to achieve the same reduction in density caused by a given pressure drop (at constant temperature).

[0061] Plot 900 shows that with a pressure drop of 2.5 bar - 10% the operating pressure - a 2 K quench hotspot is still detectable. Most cooling systems operate with a much smaller pressure drop, such as around 0.0003 bar. Plot 900 shows that, with a pressure drop of 0.0003 bar, a quench hotspot with a temperature of about 20 mK is still detectable. This implies that quench detection according to the technique disclosed herein should in most cases be distinguishable from temperature deviations due to the pressure drop over the length of the cooling channel caused by the helium flow.

[0062] FIG. 10 is a flowchart of a method of detecting a quench hotspot, according to certain embodiments of the technology disclosed herein. The method 1000 begins at step 1002 with transmitting a signal. The signal may be transmitted using a transmitter such as transmitter 532 described above with reference to FIG. 5. The signal may be transmitted along a coaxial cable, such as coaxial cable 534 described above with reference to FIG. 5, until it enters the cooling channel in which the coolant is propagating. In some embodiments, the signal may be a microwave signal with a frequency of around 40 GHz or any other frequency described herein. In some embodiments, the signal may be swept over a range of frequencies, such as any of those ranges described previously herein in in connection with FIG. 5. In some embodiments, the signal may be pulsed.

[0063] The method next moves to step 1004, at which the signal is detected. The signal may be detected with a receiver such as receiver 536 described above with reference to FIG. 5. The receiver may provide its output signal to a processor, such as the processor 550 of FIG. 5, for analysis.

[0064] The method next moves to step 1006, at which the signal is processed. The signal may be processed with a processor such as processor 550 described above with reference to FIG. 5. Processing the signal may comprise analyzing various characteristics of the signal. For example, processing the signal may involve analyzing the intensity of the signal. As discussed above, the traversal of a quench hotspot by the signal as it propagates along the cooling channel would result in the absorption of evanescent frequencies, which would decrease the intensity of the signal. Therefore, at step 1006, the signal may be analyzed for a reduction in its intensity that would be indicative of a quench hotspot.

[0065] Processing the signal may involve analyzing the frequency of the signal. Since the traversal of a quench hotspot by the signal as it propagates along the cooling channel would result in the absorption of evanescent frequencies, a signal which had traversed a quench hotspot would consist of different frequencies than a signal which had not. Therefore, at step 1006, the frequency of the signal may be analyzed to detect a quench hotspot.

[0066] Processing the signal may involve analyzing the phase of the signal. As discussed above, the traversal of a quench hotspot by the signal as it propagates along the cooling channel may impact the phase of the signal. Specifically, a quench hotspot impacts the index of refraction of the coolant, which in turn impacts the wavelength of the signal as it travels through the coolant. This means that, having traversed the length of a quench hotspot, a signal will have a different phase than it would if it had traversed the same length through the coolant without the quench hotspot. This effect is greatly amplified by the strong dispersion of a waveguide operating at a frequency just above the cutoff frequency. This difference in phase may be able to be detected and would thus be indicative of a quench hotspot. Therefore, at step 1006, the phase of the signal may be analyzed to detect a quench hotspot.

[0067] In some embodiments, processing the signal may involve analyzing two or three of the signal characteristics listed above, including intensity, frequency, and phase. Analyzing multiple signal characteristics may provide increased confidence in the determination of a potential quench event. In some embodiments, processing the signal may additionally or alternatively involve compensating for variations in the electrical signal due to pressure fluctuations, mechanical strain on the HTS cable, and / or non-quench related temperature fluctuations.

[0068] According to an aspect of the present disclosure, a reflected signal may be detected and processed, with the processing involving analyzing any of the characteristics listed. For example, the system of FIG. 5 may be modified to place the receiver at the same end of the cooling channel as the transmitter. Alternatively, an additional receiver may be added to thesystem of FIG. 5, positioned near the transmitter. Either way, signals reflected by a heated region of the coolant may be detected and analyzed for intensity, frequency, and / or phase. The characteristics of the reflected signal may differ from those of the transmitted signal that propagates through the heated region of coolant, so that processing reflected signals may provide valuable alternative information.

[0069] According to an aspect of the present disclosure, a system is provided for detecting quench in a high-temperature-superconducting (HTS) cable that itself includes a high- temperature- superconductor and a conductive former comprising a cooling channel tube configured to carry a coolant. The high-temperature- superconductor is coupled to or embedded in the conductive former. According to one embodiment, the system comprises an electrical signal transmitter coupled to a first location of the cooling channel tube, an electrical signal receiver coupled to a second location of the cooling channel tube and configured to receive electrical signals transmitted by the electrical signal transmitter and transmitted along the cooling channel tube, and a processor coupled to the electrical signal receiver and configured to process the electrical signals received by the electrical signal receiver.

[0070] In some embodiments the cooling channel tube has a length greater than 50 meters.

[0071] In some embodiments the high-temperature- superconductor forms part of a HTS tape stack and the HTS tape stack is embedded in the conductive former.

[0072] In some embodiments the high-temperature- superconductor forms part of a HTS tape stack and the HTS tape stack is coupled to the conductive former.

[0073] In some embodiments the system further comprises a jacket surrounding the conductive former.

[0074] In some embodiments the coolant is supercritical helium and the cooling channel tube is configured to carry the supercritical helium at a temperature of between 20K and 30K.

[0075] In some embodiments the HTS cable comprises a plurality of HTS tape stacks disposed outwardly of the cooling channel tube and separated from the cooling channel tube and from each other by insulating material, at least one of the HTS tape stacks comprising the high- temperature- superconductor.

[0076] In some embodiments the cooling channel tube comprises a first end and a second end that protrude from the high temperature superconducting cable.

[0077] In some embodiments each of the electrical signal transmitter and the electrical signal receiver comprises an antenna that protrudes into the cooling channel tube.

[0078] In some embodiments the electrical signal transmitter is configured to transmit electrical signals having a frequency between 5 GHz and 70 GHz.

[0079] In some embodiments the electrical signal transmitter is configured to transmit electrical signals sweeping through a frequency range from 5 GHz to 70 GHz.

[0080] In some embodiments the processor is configured to analyze an intensity of the electrical signals received by the electrical signal receiver for a given frequency.

[0081] In some embodiments the processor is configured to analyze a frequency of the electrical signals received by the electrical signal receiver.

[0082] In some embodiments the processor is configured to analyze a phase of the electrical signals received by the electrical signal receiver.

[0083] In some embodiments the processor is configured to determine insertion loss of the electrical signals received by the electrical signal receiver.

[0084] In some embodiments the processor is configured to determine a temperature of the coolant based on the electrical signals received by the electrical signal receiver.

[0085] In some embodiments the processor is configured to detect a temperature change of the coolant of at least 0.5K from a reference temperature.

[0086] In some embodiments the transmitter is configured to transmit the electrical signals as pulses.

[0087] In some embodiments the processor is configured to generate an alert in response to detecting a quench event by processing the electrical signals received by the electrical signal receiver.

[0088] In some embodiments the electrical signal transmitter is configured to transmit the electrical signals as pulses and the processor is configured to analyze an intensity of the electrical signals received by the electrical signal receiver, determine a temperature of the coolant based on the electrical signals received by the electrical signal receiver, and generate an alert in response to detecting a quench event by processing the electrical signals received by the electrical signal receiver.

[0089] According to another aspect of this disclosure, a method is provided for operating a quench detection system for a high-temperature-superconducting (HTS) cable, the HTS cable comprising a high-temperature-superconductor and a conductive former comprising a cooling channel tube configured to carry a coolant, wherein the high-temperature superconductor is coupled to or embedded in the conductive former. According to one embodiment, the method comprises transmitting, from a first location of the cooling channel tube, an electrical signal along the cooling channel tube, receiving the electrical signal with an electrical signal receivercoupled to a second location of the cooling channel tube, and processing the electrical signal with a processor coupled to the electrical signal receiver.

[0090] In some embodiments transmitting the electrical signal along the cooling channel tube comprises transmitting the electrical signal greater than 50 meters.

[0091] In some embodiments transmitting the electrical signal comprises transmitting the electrical signal using a first antenna that protrudes into the cooling channel tube, the electrical signal receiver comprises a second antenna protruding into the cooling channel tube, and receiving the electrical signal comprises receiving the electrical signal using the second antenna.

[0092] In some embodiments transmitting the electrical signal comprises transmitting the electrical signal having a frequency between 5 GHz and 70 Hz.

[0093] In some embodiments transmitting the electrical signal comprises transmitting the electrical signal by sweeping through a frequency range from 5 GHz to 70 GHz.

[0094] In some embodiments processing the electrical signal comprises analyzing an intensity of the electrical signal received with the electrical signal receiver for a given frequency.

[0095] In some embodiments processing the electrical signal comprises analyzing a frequency of the electrical signal received with the electrical signal receiver.

[0096] In some embodiments processing the electrical signal comprises analyzing a phase of the electrical signal received with the electrical signal receiver.

[0097] In some embodiments processing the electrical signal comprises determining an insertion loss of the electrical signal received with the electrical signal receiver.

[0098] In some embodiments processing the electrical signal comprises determining a temperature of the coolant based on the electrical signal received with the electrical signal receiver.

[0099] In some embodiments the processor is configured to detect a temperature change of the coolant of at least 0.5K from a reference temperature.

[0100] In some embodiments determining the temperature comprises compensating for variations in the electrical signal due to pressure fluctuations, mechanical strain on the HTS cable, and / or non-quench related temperature fluctuations.

[0101] In some embodiments transmitting the electrical signal comprises transmitting pulses.

[0102] In some embodiments the method further comprises generating an alert in response to detecting a quench event by processing the electrical signal received with the electrical signal receiver.

[0103] Various aspects of the present disclosure may be used alone, in combination, or in a variety of arrangements not specifically described in the embodiments described in the foregoing and is therefore not limited in its disclosure to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

[0104] The systems and methods described herein may provide various benefits. For example, accurate detection of quench events, or the onset of quench events, may be performed, allowing action to be taken to avoid any damage from a potential quench event. The systems and methods described herein may avoid the need to integrate other materials into an HTS cable that are not already part of the HTS cable, which may simplify manufacture and reduce cost of the HTS cables compared to temperature detection systems involving the introduction of structures or materials not already part of the HTS cable.

[0105] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0106] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified.

[0107] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified.

[0108] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, butare used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0109] The terms “approximately” and “about” may be used to mean within ±20% of a target value in some embodiments, within ±10% of a target value in some embodiments, within ±5% of a target value in some embodiments, and yet within ±2% of a target value in some embodiments. The terms “approximately” and “about” may include the target value.

[0110] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

[0111] Having described above several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be object of this disclosure. Accordingly, the foregoing description and drawings are by way of example only.

Claims

CLAIMSWhat is claimed is:

1. A system for detecting quench in a high-temperature-superconducting (HTS) cable that itself includes a high-temperature- superconductor and a conductive former comprising a cooling channel tube configured to carry a coolant, wherein the high-temperature-superconductor is coupled to or embedded in the conductive former, the system comprising: an electrical signal transmitter coupled to a first location of the cooling channel tube; an electrical signal receiver coupled to a second location of the cooling channel tube and configured to receive electrical signals transmitted by the electrical signal transmitter and transmitted along the cooling channel tube; and a processor coupled to the electrical signal receiver and configured to process the electrical signals received by the electrical signal receiver.

2. The system of any preceding claim, wherein the cooling channel tube has a length greater than 50 meters.

3. The system of any preceding claim, wherein the high-temperature-superconductor forms part of a HTS tape stack, and wherein the HTS tape stack is embedded in the conductive former.

4. The system of any preceding claim, wherein the high-temperature-superconductor forms part of a HTS tape stack, and wherein the HTS tape stack is coupled to the conductive former.

5. The system of any preceding claim, further comprising a jacket surrounding the conductive former.

6. The system of any preceding claim, wherein the coolant is supercritical helium, and wherein the cooling channel tube is configured to carry the supercritical helium at a temperature of between 20K and 30K.

7. The system of any preceding claim, wherein the HTS cable comprises a plurality of HTS tape stacks disposed outwardly of the cooling channel tube and separated from the cooling channel tube and from each other by insulating material, at least one of the HTS tape stacks comprising the high-temperature-superconductor.

8. The system of any preceding claim, wherein the cooling channel tube comprises a first end and a second end that protrude from the high temperature superconducting cable.

9. The system of any preceding claim, wherein each of the electrical signal transmitter and the electrical signal receiver comprises an antenna that protrudes into the cooling channel tube.

10. The system of any preceding claim, wherein the electrical signal transmitter is configured to transmit electrical signals having a frequency between 5 GHz and 70 GHz.

11. The system of any preceding claim, wherein the electrical signal transmitter is configured to transmit electrical signals sweeping through a frequency range from 5 GHz to 70 GHz.

12. The system of any preceding claim, wherein the processor is configured to analyze an intensity of the electrical signals received by the electrical signal receiver for a given frequency.

13. The system of any preceding claim, wherein the processor is configured to analyze a frequency of the electrical signals received by the electrical signal receiver.

14. The system of any preceding claim, wherein the processor is configured to analyze a phase of the electrical signals received by the electrical signal receiver.

15. The system of any preceding claim, wherein the processor is configured to determine insertion loss of the electrical signals received by the electrical signal receiver.

16. The system of any preceding claim, wherein the processor is configured to determine a temperature of the coolant based on the electrical signals received by the electrical signal receiver.

17. The system of claim 16, wherein the processor is configured to detect a temperature change of the coolant of at least 0.5K from a reference temperature.

18. The system of any preceding claim, wherein the transmitter is configured to transmit the electrical signals as pulses.

19. The system of any preceding claim, wherein the processor is configured to generate an alert in response to detecting a quench event by processing the electrical signals received by the electrical signal receiver.

20. The system of claim 1, wherein the electrical signal transmitter is configured to transmit the electrical signals as pulses, wherein the processor is configured to analyze an intensity of the electrical signals received by the electrical signal receiver, determine a temperature of the coolant based on the electrical signals received by the electrical signal receiver, and generate an alert in response to detecting a quench event by processing the electrical signals received by the electrical signal receiver.

21. The system of any preceding claim, wherein the conductive former comprises a plurality of segments.

22. A method of operating a quench detection system for a high-temperature-superconducting (HTS) cable, the HTS cable comprising a high-temperature- superconductor and a conductive former comprising a cooling channel tube configured to carry a coolant, wherein the high- temperature superconductor is coupled to or embedded in the conductive former, the method comprising: transmitting, from a first location of the cooling channel tube, an electrical signal along the cooling channel tube; receiving the electrical signal with an electrical signal receiver coupled to a second location of the cooling channel tube; and processing the electrical signal with a processor coupled to the electrical signal receiver.

23. The method of any preceding claim, wherein transmitting the electrical signal along the cooling channel tube comprises transmitting the electrical signal greater than 50 meters.

24. The method of any preceding claim, wherein transmitting the electrical signal comprises transmitting the electrical signal using a first antenna that protrudes into the cooling channel tube, and wherein the electrical signal receiver comprises a second antenna protruding into thecooling channel tube, and wherein receiving the electrical signal comprises receiving the electrical signal using the second antenna.

25. The method of any preceding claim, wherein transmitting the electrical signal comprises transmitting the electrical signal having a frequency between 5 GHz and 70 Hz.

26. The method of any preceding claim, wherein transmitting the electrical signal comprises transmitting the electrical signal by sweeping through a frequency range from 5 GHz to 70 GHz.

27. The method of any preceding claim, wherein processing the electrical signal comprises analyzing an intensity of the electrical signal received with the electrical signal receiver for a given frequency.

28. The method of any preceding claim, wherein processing the electrical signal comprises analyzing a frequency of the electrical signal received with the electrical signal receiver.

29. The method of any preceding claim, wherein processing the electrical signal comprises analyzing a phase of the electrical signal received with the electrical signal receiver.

30. The method of any preceding claim, wherein processing the electrical signal comprises determining an insertion loss of the electrical signal received with the electrical signal receiver.

31. The method of any preceding claim, wherein the processing the electrical signal comprises determining a temperature of the coolant based on the electrical signal received with the electrical signal receiver.

32. The method of claim 31, wherein the processor is configured to detect a temperature change of the coolant of at least 0.5K from a reference temperature.

33. The method of any preceding claim, wherein determining the temperature comprises compensating for variations in the electrical signal due to pressure fluctuations, mechanical strain on the HTS cable, and / or non-quench related temperature fluctuations.

34. The method of any preceding claim, wherein transmitting the electrical signal comprises transmitting pulses.

35. The method of any preceding claim, further comprising generating an alert in response to detecting a quench event by processing the electrical signal received with the electrical signal receiver.

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