JP2025518044A - Quench detection in superconductors - Google Patents

Abstract

A method and system for quench detection in high temperature superconductors such as REBCO (rare earth barium copper oxide) prior to thermal runaway. The REBCO superconducting tape is excited as a transmission line to form a standing wave. A quench can then be detected in response to detecting a disturbance in the standing wave. In this manner, a quench in a high temperature superconductor such as REBCO is rapidly detected prior to thermal runaway.
[Selected figure] Figure 2

Description

Government Rights
[0001] This invention was made with government support under Grant No. N00014-21-1-2429 awarded by the Office of Naval Research. The United States Government has certain rights in this invention.

Technical Field
[0002] The present disclosure relates generally to superconductors, and more particularly to detecting quenches in high temperature superconductors (e.g., rare-earth barium copper oxide (REBCO)).

[0003] Superconductivity is a set of physical properties observed in certain materials in which electrical resistance disappears and magnetic flux fields are eliminated from the material. Any material that exhibits these properties is a superconductor.

[0004] A superconducting material is expected to behave as a superconductor in a region defined by the superconductor's critical temperature (the highest temperature at which the material is a superconductor at zero applied magnetic field) and the superconductor's critical magnetic field (the highest magnetic field at which the material is a superconductor at 0 K). The temperature of the superconductor and the magnetic field present limit the current that can be carried by the superconductor without it becoming resistive or "normal". "Normal" as used herein refers to "not superconducting".

[0005] Superconducting materials are typically divided into "high temperature superconductors" (HTS) and "low temperature superconductors" (LTS). LTS materials, such as Nb and NbTi, are metals or metal alloys whose superconductivity can be explained by the Bardeen-Cooper-Schrieffer (BCS) theory. All low temperature superconductors have a critical temperature below about 30 K (the temperature above which the material does not become superconducting, even in zero magnetic field). The behavior of HTS materials is not explained by the BCS theory, but such materials may have critical temperatures above about 30 K (note, however, that it is the behavior at superconductivity and physical differences in composition, rather than the critical temperature, that define HTS materials). The most commonly used HTS are "copper oxide superconductors", which correspond to ceramics based on copper oxides (compounds containing the copper oxide group), such as bismuth strontium calcium copper oxide (BSCCO) or rare earth barium copper oxide (REBCO), where examples of rare earth elements can be Y or Gd. Other high temperature superconductors include iron pnictides (e.g., FeAs and FeSe) and magnesium diboride ( _MgB2 ).

[0006] Of all superconductors, REBCO exhibits the best performance at high magnetic fields over a wide temperature range. Due to their stronger magnetic fields and relatively high superconducting critical temperatures, these materials have been proposed for future magnetic confinement fusion reactors, such as the Affordable, Robust, and Compact (ARC) fusion reactors, which would allow for more compact and economical construction, and also for new generations of magnets for use in particle accelerators such as the Large Hadron Collider (LHC) at CERN.

[0007] Any rare earth element may be used in REBCO. Some popular choices include yttrium (YBCO), dysprosium (DyBCO), samarium (Sm123), neodymium (Nd123), gadolinium (Gd123) and europium (Eu123), where the numbers in parentheses indicate the molar ratio of the rare earth, barium and copper.

[0008] These types of materials are brittle, making wires out of them has been difficult. Since 2005, industrial manufacturers have started producing tapes with various layers encapsulating the REBCO material, paving the way for its commercial use. For example, REBCO tapes can be fabricated using a reel-to-reel process, where the superconductor is coated as a thin film onto a flexible metal substrate with a dielectric buffer layer in between.

[0009] The excellent current density of REBCO tapes allows for highly efficient electric machines with high power density. At such high current densities, superconductors are susceptible to localized heating at defective spots ("hot spots") that are always present in long tapes. Because each tape bend in the coil containing the superconducting device is usually insulated, the hot spots do not dissipate easily, thus causing thermal runaway (a process driven by an increase in temperature, which in turn releases energy that further increases the temperature) and catastrophic failure (termination of operation in resistive normal conditions). Such a localized buildup of heat leading to thermal runaway can also be referred to as a "quench." That is, a quench refers to an abnormal termination of operation that occurs during the transition of a superconductor from a superconducting state to a resistive normal state. Thus, quenches or normal zones (i.e., hot spots) need to be detected quickly to protect the superconducting device.

[0010] Thermal runaway leading to catastrophic failure in HTS materials such as REBCO in particular is caused by a low normal zone propagation (NZP) velocity (e.g., 0.01-0.1 m/sec). By having such a low NZP velocity, the normal zone spreads slowly, thus causing a slow increase in the fault-induced voltage. At the same time, the slow spread of heat results in high temperatures before the voltage has increased enough for external detection. These two combined effects can cause thermal runaway and catastrophic failure of the coil prior to quench detection.

[0011] Currently, numerous methods for quench detection are under development, including modifications to HTS coil designs for quench resistance. Examples of these include acoustic emission detection, acoustic temperature measurement, Rayleigh scattering based fiber optics, various quench antennas, ultrasonic based detection, various laminations, non-insulated coils, various insulating materials and epoxies. However, all solutions have drawbacks such as susceptibility to vibration, low signal to noise ratio, external sensors wrapped with tape, which increase the complexity of coil fabrication or reduce the overall current density.

[0012] As a result, there are currently no means for rapid quench detection in high temperature superconductors such as REBCO prior to thermal runaway.

[0013] In one embodiment of the present disclosure, a method for quench detection in a superconductor includes exciting a REBCO (rare earth barium copper oxide) superconducting tape as a transmission line to form a standing wave. The method further includes detecting a quench in response to detecting a disturbance of the standing wave.

[0014] In another embodiment of the present disclosure, a system for quench detection in a superconductor includes a REBCO (rare earth barium copper oxide) superconducting tape architecture including a substrate, a buffer layer stack present on the substrate, the buffer layer stack including one or more dielectric layers, and a first REBCO layer on the buffer layer stack, the first REBCO layer being used to transport current and form a transmission line with the substrate. The system further includes a first device for exciting the REBCO superconducting tape architecture to form a standing wave in the transmission line. The system additionally includes a first device or a second device for detecting a quench in response to detecting a disturbance of the standing wave.

[0015] The foregoing has outlined, rather generally, the features and technical advantages of one or more embodiments of the present disclosure in order that the detailed description of the present disclosure that follows may be better understood. Additional features and advantages of the present disclosure that may form the subject of the claims of the present disclosure will be described below.

[0016] A better understanding of the present disclosure can be obtained when the following detailed description is considered in conjunction with the following drawings, in which:

[0017] FIG. 1 illustrates an embodiment of the present disclosure of a schematic layout of a REBCO superconducting tape. [0018] Figure 2 is a flow chart of a method for rapid quench detection in high temperature superconductors according to an embodiment of the present disclosure. [0019] FIG. 3A illustrates a system for quench detection in a REBCO superconducting tape with integrated transmission line according to an embodiment of the present disclosure. [0020] FIG. 3B illustrates an alternative system for quench detection in a REBCO superconducting tape with integrated transmission line according to an embodiment of the present disclosure. [0021] FIG. 3C illustrates a further alternative system for quench detection in a REBCO superconducting tape with integrated transmission line according to an embodiment of the present disclosure.

[0022] As mentioned in the background section, the excellent current density of REBCO tapes allows for highly efficient electric machines with high power density. At such high current densities, superconductors are susceptible to localized heating at defective spots ("hot spots") that are always present in long tapes. Because each tape bend in the coil containing the superconducting device is usually insulated, the hot spots do not dissipate easily, thus causing thermal runaway (a process driven by an increase in temperature, which in turn releases energy that further increases the temperature) and catastrophic failure (termination of operation in resistive normal conditions). Such a localized buildup of heat leading to thermal runaway can also be referred to as a "quench." That is, a quench refers to an abnormal termination of operation that occurs during the transition of a superconductor from a superconducting state to a resistive normal state. Thus, quenches or normal zones (i.e., hot spots) need to be detected quickly to protect the superconducting device.

[0023] In particular, thermal runaway leading to catastrophic failure in HTS materials such as REBCO is caused by a low normal zone propagation (NZP) velocity (e.g., 0.01-0.1 m/sec). By having such a low NZP velocity, the normal zone spreads slowly, thus causing a slow increase in the fault-induced voltage. At the same time, the slow spread of heat results in high temperatures before the voltage has increased enough for external detection. These two combined effects can cause thermal runaway and catastrophic failure of the coil prior to quench detection.

[0024] Numerous methods for quench detection are currently under development, including modifications to HTS coil designs for quench resistance. Examples of these include acoustic emission detection, acoustic temperature measurement, Rayleigh scattering based fiber optics, various quench antennas, ultrasonic based detection, various laminations, non-insulated coils, various insulating materials and epoxies. However, all solutions have drawbacks such as susceptibility to vibration, low signal to noise ratio, external sensors wrapped with tape, which increase the complexity of coil fabrication or reduce the overall current density.

[0012] As a result, there is currently no means for rapid quench detection in high temperature superconductors such as REBCO prior to thermal runaway.
[0025] As a result, there is currently no means for rapid quench detection in high temperature superconductors such as REBCO prior to thermal runaway.

[0026] The disclosed embodiments of the present invention provide a means for rapid quench detection in high temperature superconductors such as REBCO prior to thermal runaway by utilizing high temperature superconductor (e.g., REBCO) tape architectures as transmission lines at high frequencies for rapid quench detection as discussed herein.

[0027] Although the following discusses the use of REBCO tape architectures as transmission lines at high frequencies for rapid quench detection, it should be noted that the principles of the present disclosure are not intended to be limited in this manner, and any high temperature superconductor tape architecture can be used as a transmission line at high frequencies for rapid quench detection. One of ordinary skill in the art will be able to apply the principles of the present disclosure to such implementations. Moreover, embodiments that apply the principles of the present disclosure to such implementations are expected to be within the scope of the present disclosure.

[0028] In some embodiments of the present disclosure, the present disclosure includes methods and systems for quench detection in high temperature superconductors such as REBCO prior to thermal runaway. In one embodiment, a REBCO superconducting tape is excited as a transmission line to form a standing wave. A quench can then be detected in response to detecting a disturbance in the standing wave. In this manner, the principles of the present disclosure provide a means for rapid quench detection in high temperature superconductors such as REBCO prior to thermal runaway.

[0029] Referring now in detail to the drawings, FIG. 1 illustrates an embodiment of the present disclosure of a schematic layout of a REBCO superconducting tape 100.
[0030] As shown in Figure 1, REBCO (rare earth barium copper oxide) superconducting tape 100 includes a substrate 101 of structural material (e.g., Hastelloy, stainless steel, or nickel alloy). In one embodiment, a metal oxide layer (buffer layer stack 102) and a superconducting REBCO layer 103 are deposited on the substrate 101 with a two-dimensional texture by chemical or physical means. In one embodiment, a stabilizing silver (e.g., Ag cap layer 104) is deposited on the superconducting REBCO layer 103. In one embodiment, tape 100 is copper stabilized with a surrounding copper layer (e.g., Cu stabilization layer 105', 105"). In one embodiment, the copper stabilization layer 105', 105" is optional.

[0031] In one embodiment, the thickness of the copper stabilization layer 105' is approximately 20 μm. In one embodiment, the thickness of the substrate 101 is approximately 50 μm. In one embodiment, the thickness of the buffer layer stack is less than 0.2 μm. In one embodiment, the thickness of the REBCO layer 103 is approximately 1 μm. In one embodiment, the thickness of the Ag cap layer 104 is approximately 2 μm. In one embodiment, the thickness of the copper stabilization layer 105" is approximately 20 μm. In one embodiment, the total thickness of the REBCO superconducting tape 100 is less than 0.1 mm. In one embodiment, the total thickness of the REBCO superconducting tape 100, not including the copper stabilization layers 105', 105", is less than 0.06 mm.

[0032] In one embodiment, REBCO superconducting tape 100 is a high temperature superconducting tape that operably operates as a superconductor at temperatures above 77 K. In one embodiment, REBCO superconducting tape 100 conducts electricity with zero electrical resistance.

[0033] As discussed above, the principles of the present disclosure provide a means for rapid quench detection in high temperature superconductors such as REBCO prior to thermal runaway. In one embodiment, quenches can be rapidly detected in REBCO (e.g., REBCO layer 103) by utilizing a REBCO tape architecture (e.g., REBCO superconducting tape 100) as a transmission line at high frequencies for rapid quench detection, as discussed below in connection with FIG. 2.

[0034] Figure 2 is a flow chart of a method 200 for rapid quench detection in high temperature superconductors according to an embodiment of the present disclosure.
[0035] Referring to FIG. 2 in conjunction with FIG. 1, in step 201, a REBCO superconducting tape, such as REBCO superconducting tape 100, is excited as a transmission line to form a standing wave.

[0036] In one embodiment, the tape 100 is treated as a microstrip-like transmission line in which TEM (transverse electromagnetic) modes are excited. In one embodiment, such excitation of the tape 100 creates standing waves of a particular Q (quality) factor that is characteristic of the elements contained in the circuit.

[0037] In step 202, a quench is detected in response to detecting a disturbance in the standing wave.
[0038] It should be noted that the transmission line is susceptible to any change in uniformity along its length, either dimensional changes or property changes, such as changes in the permittivity of the dielectric layer or the conductivity of the conductive layer. Since the REBCO film (e.g., REBCO layer 103) is a nonlinear device in the transition between the superconducting and normal states, a large change in resistivity is expected to occur if a quench occurs locally. Unlike voltage detection, where the signal is proportional to the length of the normal zone, a 100 m long transmission line is expected to effectively become two 50 m transmission lines if a quench occurs in the middle of the tape and is coupled by a resistive transmission segment. The standing wave formed in the transmission line is instantly disturbed, which can be easily detected in one embodiment by a frequency analyzer in a sweep mode acting as a source of excitation and a detection circuit (used to detect disturbances in the standing wave). Thus, the disturbance of the standing wave is due to a change in resistivity of the REBCO superconducting tape 100. Furthermore, in one embodiment, dual mode can be achieved if two excitation circuits are connected at each end of the tape 100 (or coil), or if the tape 100 is used as a transmitter (so that excitation is performed at one end but the signal is sensed at both ends). Such a signal change is expected to be detected nearly instantaneously.

[0039] In one embodiment, standing wave disturbances are detected by detecting multiple reflections over a frequency sweep with the standing wave occurring at multiple wavelengths over some characteristic length of the transmission line (e.g., the length of the transmission line itself, or the length of a segment of the transmission line from one end to the quenched location).

[0040] In another embodiment, a disturbance of the standing wave is detected by detecting a change in the frequency of the reflection, for example when a disturbance along the transmission line changes the characteristic length or introduces a new characteristic length.

[0041] In a further embodiment, the disturbance of the standing wave is detected by detecting a change in the quality factor, for example a change in the quality factor of a resonant peak.
[0042] In one embodiment, a disturbance of the standing wave is detected by detecting a change in the quality factor when a portion of the superconductor becomes normal (a quench).

[0043] In a further embodiment, the disturbance of the standing wave is detected by detecting a change in the magnitude of the resonant peak.
[0044] It should be noted that standing wave disturbances may be detected using a combination of the embodiments discussed above.

[0045] Because the REBCO film, e.g., REBCO layer 103, and the metal substrate, e.g., substrate 101, are separated by a thin dielectric layer, e.g., the dielectric layer of the buffer layer stack 102, the REBCO superconducting tape 100 can be excited by an alternating current (AC) source that produces a signal that is a function of the total capacitance or transmission line characteristics at high frequencies.

[0046] In one embodiment, a high temperature superconductor (HTS) tape used in a transmission line mode, such as REBCO superconducting tape 100, is excited in a non-contact manner. For example, a capacitor plate in the vicinity of REBCO superconducting tape 100 introduces an electromagnetic wave (EM) that is expected to propagate along the entire length of REBCO superconducting tape 100 (e.g., the entire length of REBCO layer 103).

[0047] In another embodiment, the REBCO superconducting tape 100 is excited with an inductive loop, again creating EM waves if the frequency and coupling are properly chosen.
[0048] In one embodiment, the configuration of the capacitor and/or inductor excitations is modified to introduce different wave modes (e.g., shear waves, longitudinal waves with different polarizations, etc.) These features provide great flexibility and multiple options for circuit optimization to create the most sensitive quench detection system to disturbances.

[0049] Below is provided a discussion of various embodiments of quench detection systems that employ method 200. In particular, such embodiments utilize quench detection integrated within REBCO superconducting tape 100.

[0050] Referring now to FIG. 3A, FIG. 3A illustrates a system 300 for quench detection in a REBCO superconducting tape with integrated transmission line in accordance with an embodiment of the present disclosure.

[0051] As shown in FIG. 3A, the system 300 includes a substrate 101, which corresponds to a metal substrate (conductor) having a thickness of approximately 50 μm. Further, as shown in FIG. 3A, the system 300 includes a buffer layer stack 102 present on the substrate 101, the buffer layer stack 102 including a plurality of dielectric layers, such as a dielectric layer 301 (e.g., alumina) and a dielectric layer 302 (e.g., magnesium oxide (MgO) and lanthanum manganate (LMO)). In one embodiment, the thickness of the dielectric layer 301 is approximately 80 nm. In one embodiment, the thickness of the dielectric layer 302 is approximately 80 nm.

[0052] Additionally, as shown in FIG. 3A, the system 300 includes a REBCO layer 103 present on the buffer layer stack 102. In one embodiment, the thickness of the REBCO layer 103 is approximately 1 μm.

[0053] As further shown in FIG. 3A, the system 300 includes an excitation device 303 configured to excite the REBCO layer 103 as a transmission line to form a standing wave. In one embodiment, the excitation device 303 corresponds to an alternating current (AC) source having terminals between the substrate 101 and the REBCO layer 103. In one embodiment, the AC source produces a signal that is a function of the transmission line characteristics.

[0054] In one embodiment, the excitation device 303 excites the REBCO layer 103 in a contactless manner. In such an embodiment, the excitation device 303 corresponds to a capacitor plate or an inductor loop. Moreover, in such an embodiment, such excitation introduces an electromagnetic wave that propagates along the REBCO superconducting tape 100, e.g., the REBCO layer 103.

[0055] Additionally, as shown in FIG. 3A, the system 300 includes a detection device 304 configured to detect a quench in response to detecting a disturbance in the standing wave.
[0056] In one embodiment, the excitation device 303 and the detection device 304 are the same device, for example a frequency analyzer, in which the frequency analyzer acts as both a source of excitation and a detection circuit for detecting disturbances of the standing wave in a sweep mode.

[0057] In one embodiment, the detection device 304 detects disturbances of the standing wave via one or more of the following means: detecting multiple reflections in a frequency sweep, detecting changes in the frequency of the reflections, detecting changes in the quality factor, and detecting changes in the magnitude of the resonant peak, as previously discussed.

[0058] Additionally, the detection device 304 is configured to detect disturbances in the standing wave via one or more of the following techniques:
[0059] For example, in one embodiment, the detection device 304 detects standing wave disturbances using capacitance measurements. For example, when a section of a superconducting coil quenches, the capacitance of the HTS tape, e.g., tape 100, changes from a superconducting capacitor of length L to two segments of lengths (1-f)L-s/2 and fL+s/2 joined by a normal capacitor of length s, where f indicates the location of the quench. Both the amplitude and phase of the AC signal are affected.

[0060] In one embodiment, the detection device 304 detects standing wave disturbances using a single-ended radio frequency sweep using contact coupling. For example, with a single-ended sweep, a transmission line study of RF/microwave resonances in a tape structure such as the tape structure 100 is expected to use contacts or capacitive coupling implemented on top of such a finite length transmission line. Additionally, with a single-ended sweep, the Q factor and resonant frequency value of the resonances generated in the reflection (s11) mode are monitored.

[0061] In one embodiment, the detection device 304 detects standing wave disturbances using a double-ended radio frequency (RF) sweep. For example, a double-ended RF sweep offers the potential advantage of obtaining both reflected (s11) and transmitted (s12) signals and superimposing them as a function of time. Thus, reflection and propagation are correlated with the location and size of the quenched section of the coil. Phase shifts and Q-factors are also correlated, providing increased spatial resolution of the quenched region. Furthermore, correlation between detected modes provides an additional level of information not available in single-ended modes, resulting in more detailed information about the nature of the disturbance.

[0062] In one embodiment, the detection device 304 detects standing wave disturbances using intermodulation detection. For example, an HTS tape, such as a YBCO tape, is driven with a signal containing two frequencies _f1 and _f2 to detect the presence of non-linearities in the output signal, i.e., intermodulation distortion (IMD) peaks. In such an embodiment, the YBCO tape acts as an RCL resonator. In one embodiment, such frequencies are generated by a two-tone generator.

[0063] Typically, in the nonlinear case, the IMD spectrum contains many higher order peaks; however, to conserve bandwidth, in one embodiment, only the fundamental ( _f1 and _f2 ) and third order IMD peaks ( _2f1 - _f2 and _2f2 - _f1 ) are measured as a function of input power, e.g., via a spectrum analyzer.

[0064] Moreover, an additional advantage of IMD technology, in terms of its sensitivity, is its ability to account for non-linearities at extremely low power levels, thereby allowing the avoidance of any thermal effects.

[0065] Referring again now to FIG. 3A, a REBCO layer 103 is used to transport the current (such a REBCO layer is referred to herein as "T-REBCO") and forms a transmission line with the substrate 101. In one embodiment, a small high frequency signal is superimposed on the transporting current through the T-REBCO 103. Because the transmission line is only very sensitive to high frequency signals, an effective detection circuit is formed. Unlike voltage detection methods where the signal during a quench is proportional to the length of the normal zone (which is small for REBCO), a 100m long transmission line would be expected to effectively become two 50m lines if a quench occurs halfway along the tape. The standing wave formed in the transmission line is instantly disturbed, which can be easily detected by the detection device 304 as a change in the frequency of reflection and a change in the Q factor of the resonant peak.

[0066] Referring now to FIG. 3B, FIG. 3B illustrates an alternative system 300' for quench detection in a REBCO superconducting tape with integrated transmission line in accordance with an embodiment of the present disclosure.

[0067] As shown in FIG. 3B, system 300' differs from system 300 in that a second REBCO layer 305 is present on buffer layer stack 102. In one embodiment, REBCO layer 305 has a thickness of approximately 100 nm. In one embodiment, REBCO layer 305 has a thickness of 10-100 nm. Such a layer is referred to herein as "S-REBCO" and is used solely for sensing as part of a transmission line. In one embodiment, S-REBCO layer 305 is electrically floating with respect to all other layers and can be excited separately to serve as a sensing circuit.

[0068] As further shown in FIG. 3B, the system 300' further includes a dielectric layer 306 (e.g., LMO) overlying the REBCO layer 305. In one embodiment, the thickness of the dielectric layer 306 is approximately 40 nm.

[0069] Additionally, as shown in FIG. 3B, the system 300' includes a REBCO layer 103 present on the dielectric layer 306.
[0070] In one embodiment, excitation device 303 corresponds to multiple AC sources, such as a first AC source having terminals connected between substrate 101 and REBCO layer 305, and a second AC source having terminals connected between REBCO layer 305 and REBCO layer 103.

[0071] Referring now to FIG. 3C, FIG. 3C illustrates a further alternative system 300" for quench detection in a REBCO superconducting tape with integrated transmission line according to an embodiment of the present disclosure.

[0072] As shown in FIG. 3C, system 300" differs from system 300' in that a third REBCO layer 307 is present on dielectric layer 306. In one embodiment, REBCO layer 307 has a thickness of approximately 100 nm. In one embodiment, REBCO layer 307 has a thickness of 10-100 nm. In one embodiment, REBCO layer 307 corresponds to an "S-REBCO" layer.

[0073] Additionally, in one embodiment, REBCO layer 305 has a thickness of approximately 100 nm. In one embodiment, REBCO layer 305 has a thickness of 10-100 nm. In one embodiment, REBCO layer 305 corresponds to an "S-REBCO" layer. Alternatively, in another embodiment, REBCO layer 305 corresponds to an S normal conductor (e.g., TiN).

[0074] As further shown in FIG. 3C, the system 300" includes a dielectric layer 308 (e.g., LMO) overlying the REBCO layer 307. In one embodiment, the thickness of the dielectric layer 308 is approximately 40 nm.

[0075] Additionally, as shown in FIG. 3C, the system 300" includes a REBCO layer 103 present on the dielectric layer 308.
[0076] In one embodiment, system 300" includes two floating layers (layers 305, 307) (e.g., S-REBCO/S-REBCO or S-REBCO/S normal conductor) grown for sensing/transmission line. In one embodiment, multiple bonds are expected to form characteristic peaks of different Q factors in the frequency sweep. During the quench, new reflections are expected to form and existing reflections are expected to change frequency, Q factor and intensity. The spread of heat from the quench in the T-REBCO film (layer 103) to the S-REBCO film (layer 307) is expected to be nearly instantaneous, easily transitioning the S-REBCO layer (layer 307) to its normal state and forming a signal change in the transmission line.

[0077] Note that the sensing layers 305, 307 form an independent floating circuit with respect to the transport REBCO layer 103. Thus, the sensing circuit is completely isolated/floating and forms a very high Q line.

[0078] As a result of the foregoing, embodiments of the present disclosure provide a means for rapidly detecting quenches in high temperature superconductors (HTS) by utilizing the HTS tape architecture itself as a transmission line at high frequencies. For example, in one embodiment, the HTS tape is treated as a microstrip-like transmission line, where TEM modes are excited to form noise-free standing waves. Quenches can be rapidly detected in response to the detection of disturbances in such standing waves.

[0079] For example, even in the case of a 10 km length of REBCO tape in the form of a coil with an unrealistically high dielectric constant of the dielectric layer (e.g., 500 F/m), the signal propagation speed in the transmission line can be 10,000 km/sec, which results in a quench response time of 0.5 ms. In another example, using the principles of the present disclosure, a quenched zone size of 10 cm is detected over a 1 km length of tape with no noise interference to the measured signal. As a result, the principles of the present disclosure provide a rapid quench detection system.

[0080] Additionally, by utilizing such an embodiment, significant modifications to the HTS coil construction are avoided. For example, co-wound additional sensors for quench detection are avoided. In another example, no modifications to the coil design are required to address insulation, stability, available current density, or lateral heat transfer.

[0081] For illustrative purposes, descriptions of various embodiments of the present disclosure have been presented, but are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations that do not depart from the scope and essence of the described embodiments will be apparent to those skilled in the art. The terms used in this specification are selected to best explain the principles of the embodiments, practical applications or technical improvements to the technology found in the market, or to enable those skilled in the art to understand the embodiments disclosed herein.

100 REBCO superconducting tape 102 Buffer layer stack 103 Superconducting REBCO layer 104 Ag cap layer 105', 105 Copper stabilization layer 300 System 301 Dielectric layer 302 Dielectric layer 303 Excitation device 304 Detection device 305 Second REBCO layer 306 Dielectric layer 307 Third REBCO layer 308 Dielectric layer

Claims (28)

1. A method for quench detection in a superconductor involving a transition between a superconducting state and a resistive normal state, comprising:
The method includes exciting a REBCO (rare earth barium copper oxide) superconducting tape as a transmission line to form a standing wave; and detecting a quench in response to detecting a disturbance of the standing wave. The method of claim 1, wherein the disturbance of the standing wave is due to a change in resistivity of the REBCO superconducting tape. The disturbance of the standing wave is:
Detecting multiple reflections in a frequency sweep;
detecting a change in frequency of the reflection;
Detecting a change in the quality factor; and
detecting a change in the magnitude of the resonance peak;
The method of claim 1 or 2, wherein the detection is via one or more of the following: The disturbance of the standing wave may be achieved by the following techniques:
Capacitance measurements, single-ended radio frequency sweep with contact coupling, single-ended radio frequency sweep with capacitive coupling, single-ended radio frequency sweep with electromagnetic coupling, double-ended radio frequency sweep, and intermodulation detection,
The method of claim 1 or 2, wherein the detection is via one or more of the following: The method according to any one of claims 1 to 4, wherein the standing wave is formed with a specific quality factor. The method according to any one of claims 1 to 5, wherein the REBCO superconducting tape is a high-temperature superconducting tape operable as a superconductor at temperatures above 77K. The method of claim 1 or 2, wherein the disturbances of the standing wave are detected in a sweep mode by a frequency analyzer that acts both as a source of excitation and as a detection circuit. The method of any one of claims 1 to 7, wherein the excitation is performed by an alternating current source. The method of claim 8, wherein the AC source produces a signal that is a function of transmission line characteristics. The method of any one of claims 1 to 7, wherein the REBCO superconducting tape is excited in a non-contact manner. The method according to any one of claims 1 to 7, wherein the excitation is performed via a capacitor plate or an inductive loop. The method of any one of claims 1 to 7, wherein the excitation introduces an electromagnetic wave that propagates along the REBCO superconducting tape. 13. A system for detecting quenches in a superconductor involving a transition between a superconducting state and a resistive normal state using the method of claim 1, the system comprising:
said REBCO superconducting tape architecture conducting electricity with zero electrical resistance;
a first device for exciting the REBCO superconducting tape architecture in the transmission line to form the standing wave;
wherein the REBCO superconducting tape architecture comprises:
substrate;
a buffer layer stack overlying the substrate, the buffer layer stack including one or more dielectric layers; and a first REBCO layer over the buffer layer stack, the first REBCO layer being used to transport electrical current and form the transmission line with the substrate;
wherein the first device or the second device is for detecting the quench in response to detecting the disturbance of the standing wave. The REBCO superconducting tape architecture comprises:
a second REBCO layer overlying the buffer layer stack;
a first dielectric layer overlying the second REBCO layer; and the first REBCO layer overlying the first dielectric layer;
The system of claim 13 further comprising: The system of claim 14, wherein the second REBCO layer is used for sensing as part of the transmission line. The system of claim 14 or 15, wherein the second REBCO layer is electrically floating with respect to other layers of the REBCO superconducting tape architecture. The REBCO superconducting tape architecture comprises:
a second REBCO layer overlying the buffer layer stack;
a first dielectric layer overlying the second REBCO layer;
a third REBCO layer overlying the first dielectric layer;
a second dielectric layer overlying the third REBCO layer; and the first REBCO layer overlying the second dielectric layer;
The system of claim 13 further comprising: The system of claim 17, wherein the second and third REBCO layers include two sensing layers that form independent floating circuits with respect to the first REBCO layer. The system of any one of claims 13 to 18, wherein the disturbance of the standing wave is due to a change in resistivity of the REBCO superconducting tape architecture. The first device or the second device comprises:
Detecting multiple reflections in a frequency sweep;
detecting a change in frequency of the reflection;
Detecting a change in the quality factor; and
detecting a change in the magnitude of the resonance peak;
19. The system of claim 13, further comprising: The first device or the second device is provided with the following technology:
Capacitance measurements, single-ended radio frequency sweep with contact coupling, single-ended radio frequency sweep with capacitive coupling, single-ended radio frequency sweep with electromagnetic coupling, double-ended radio frequency sweep, and intermodulation detection,
19. The system of claim 13, further comprising: The system of any one of claims 13 to 18, wherein the standing wave is formed with a specific quality factor. The system of any one of claims 13 to 18, wherein the first device includes a frequency analyzer configured for both exciting the REBCO superconducting tape architecture and detecting the disturbance of the standing wave. The system of any one of claims 13 to 18, wherein the first device includes an alternating current source configured to excite the REBCO superconducting tape architecture. The system of claim 24, wherein the AC source produces a signal that is a function of transmission line characteristics. The system of any one of claims 13 to 18, wherein the first device excites the REBCO superconducting tape architecture in a non-contact manner. The system of any one of claims 13 to 18, wherein the first device excites the REBCO superconducting tape architecture via a capacitor plate or an inductive loop. The system of any one of claims 13 to 18 and 27, wherein the excitation introduces an electromagnetic wave that propagates along the first REBCO layer.

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