Patent Application
20090298697
1. Field of the Disclosure
The present disclosure is directed to multifilamentary superconducting articles, and is particularly directed to low AC loss multifilamentary superconducting articles.
2. Description of the Related Art
Superconductor materials have long been known and understood by the technical community. Low-temperature superconductors (low-Tc or LTS) exhibiting superconducting properties at temperatures requiring use of liquid helium (4.2 K), have been known since 1911. However, it was not until somewhat recently that oxide-based high-temperature (high-Tc) superconductors have been discovered. Around 1986, a first high-temperature superconductor (HTS), having superconducting properties at a temperature above that of liquid nitrogen (77 K) was discovered, namely YBa2Cu3O7-x (YBCO), followed by development of additional materials over the past 15 years including Bi2Sr2Ca2Cu3O10+y (BSCCO), and others. The development of high-Tc superconductors has created the potential of economically feasible development of superconductor components and other devices incorporating such materials, due partly to the cost of operating such superconductors with liquid nitrogen rather than the comparatively more expensive cryogenic infrastructure based on liquid helium.
Of the myriad of potential applications, the industry has sought to develop use of such materials in the power industry, including applications for power generation, transmission, distribution, and storage. In this regard, it is estimated that the inherent resistance of copper-based commercial power components is responsible for billions of dollars per year in losses of electricity, and accordingly, the power industry stands to gain based upon utilization of high-temperature superconductors in power components such as transmission and distribution power cables, generators, transformers, and fault current interrupters/limiters. In addition, other benefits of high-temperature superconductors in the power industry include a factor of 3-10 increase of power-handling capacity, significant reduction in the size (i.e., footprint) and weight of electric power equipment, reduced environmental impact, greater safety, and increased capacity over conventional technology. While such potential benefits of high-temperature superconductors remain quite compelling, numerous technical challenges continue to exist in the production and commercialization of high-temperature superconductors on a large scale.
Among the challenges associated with the commercialization of high-temperature superconductors, many exist around the fabrication of a superconducting tape segment that can be utilized for formation of various power components. A first generation of superconducting tape segment includes use of the above-mentioned BSCCO high-temperature superconductor. This material is generally provided in the form of discrete filaments, which are embedded in a matrix of noble metal, typically silver. Although such conductors may be made in extended lengths needed for implementation into the power industry (such as on the order of a kilometer), due to materials and manufacturing costs, such tapes do not represent a widespread commercially feasible product.
Accordingly, a great deal of interest has been generated in the so-called second-generation HTS tapes that have superior commercial viability. These tapes typically rely on a layered structure, generally including a flexible substrate that provides mechanical support, at least one buffer layer overlying the substrate, the buffer layer optionally containing multiple films, an HTS layer overlying the buffer film, and an optional capping layer overlying the superconductor layer, and/or an optional electrical stabilizer layer overlying the capping layer or around the entire structure. However, to date, numerous engineering and manufacturing challenges remain prior to full commercialization of such second generation-tapes and devices incorporating such tapes.
With the advent of a new technology comes new problems, and in the realm of HTS tapes, reducing the alternating current (AC) losses and while maintaining the current carrying capacity is particularly troublesome. AC losses reduce the effectiveness of the conductor and are caused by magnetic fields that are generated by running a current through the superconducting article. While some superconductor designs have been suggested to mitigate the AC losses, the formation and utilization of these articles poses unique obstacles given the complex multilayered structure of second generation HTS tapes. In particular, the formation of such structures into commercially viable, long-length conductors remains a major obstacle given than such articles are expected have the capacity to handle the increasing power demands with enhanced performance and durability.
According to one aspect, a superconducting article comprising a multifilamentary superconducting tape segment is disclosed that includes a substrate tape, a buffer layer overlying the substrate, and filaments comprising a high temperature superconducting (HTS) material overlying the buffer layer. The filaments extend along a length of the substrate, laterally spaced apart from an adjacent filament by a space, and longitudinally spaced apart by a gap. The multifilamentary superconducting tape segment has a lateral inter-filament misalignment of not greater than about 100 microns.
According to another aspect, a superconducting article is disclosed that includes multifilamentary superconducting tape segment having a substrate tape, a buffer layer overlying the substrate, and filaments comprising a high temperature superconducting (HTS) material overlying the buffer layer. The filaments extend along a length of the substrate and are laterally spaced apart from adjacent filaments by a space. Also, the multifilamentary superconducting tape segment comprises a critical current retention ratio of at least about 0.6.
According to a third aspect, a method of forming a multifilamentary superconducting tape is provided that includes translating a superconducting tape on a reel-to-reel process, wherein the superconducting tape includes a substrate, a buffer layer overlying the substrate, and a HTS layer overlying the buffer layer. The method further includes forming a mask overlying the superconducting tape, and removing portions of the mask and portions of the HTS layer using abrasive particles to form a multifilamentary superconducting tape having filaments comprising the HTS material and extending along a length of the superconducting tape and laterally spaced apart from adjacent filaments by spaces.
The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.
The use of the same reference symbols in different drawings indicates similar or identical items.
Turning to
The substrate 10 is generally metal-based, and typically, an alloy of at least two metallic elements. Particularly suitable substrate materials include nickel-based metal alloys such as the known Hastelloy® or Inconel® group of alloys. These alloys tend to have desirable creep, chemical and mechanical properties, including coefficient of expansion, tensile strength, yield strength, and elongation. These metals are generally commercially available in the form of spooled tapes, particularly suitable for superconducting tape fabrication, which typically will utilize reel-to-reel tape handling.
The substrate 10 is typically in a tape-like configuration, having a high dimension ratio. As used herein, the term ‘dimension ratio’ is used to denote the ratio of the length of the substrate or tape to the next longest dimension, the width of the substrate or tape. For example, the width of the tape is generally on the order of about 0.1 to about 10 cm, and the length of the tape is typically at least about 0.1 m, most typically greater than about 5 m. Indeed, superconducting tapes that include substrate 10 may have a length on the order of 100 m or above. Accordingly, the substrate may have a dimension ratio which is fairly high, on the order of not less than 10, not less than about 102, or even not less than about 103. Certain embodiments are longer, having a dimension ratio of 104 and higher.
In one embodiment, the substrate is treated so as to have desirable surface properties for subsequent deposition of the constituent layers of the superconducting tape. For example, the surface may be polished to a desired flatness and surface roughness. Additionally, the substrate may be treated to be biaxially textured as is understood in the art, such as by the known RABiTS (roll assisted biaxially textured substrate) technique, although embodiments herein typically utilize a non-textured, polycrystalline substrate, such as commercially available nickel-based tapes noted above.
Turning to the buffer layer 12, the buffer layer may be a single layer, or more commonly, be made up of several films. Most typically, the buffer layer includes a biaxially textured film, having a crystalline texture that is generally aligned along crystal axes both in-plane and out-of-plane of the film. Such biaxial texturing may be accomplished by IBAD. As is understood in the art, IBAD is acronym that stands for ion beam assisted deposition, a technique that may be advantageously utilized to form a suitably textured buffer layer for subsequent formation of a superconducting layer having desirable crystallographic orientation for superior superconducting properties. Magnesium oxide is a typical material of choice for the IBAD film, and may be on the order of about 1 to about 500 nanometers, such as about 5 to about 50 nanometers. Generally, the IBAD film has a rock-salt like crystal structure, as defined and described in U.S. Pat. No. 6,190,752, incorporated herein by reference.
The buffer layer may include additional films, such as a barrier film provided to directly contact and be placed in between an IBAD film and the substrate. In this regard, the barrier film may advantageously be formed of an oxide, such as yttria, and functions to isolate the substrate from the IBAD film. A barrier film may also be formed of non-oxides such as silicon nitride. Suitable techniques for deposition of a barrier film include chemical vapor deposition and physical vapor deposition including sputtering. Typical thicknesses of the barrier film may be within a range of about 1 to about 200 nanometers. Still further, the buffer layer may also include an epitaxially grown film(s), formed over the IBAD film. In this context, the epitaxially grown film is effective to increase the thickness of the IBAD film, and may desirably be made principally of the same material utilized for the IBAD layer such as MgO or other compatible materials.
In embodiments utilizing an MgO-based IBAD film and/or epitaxial film, a lattice mismatch between the MgO material and the material of the superconducting layer exists. Accordingly, the buffer layer may further include another buffer film, this one in particular implemented to reduce a mismatch in lattice constants between the superconducting layer and the underlying IBAD film and/or epitaxial film. This buffer film may be formed of materials such as YSZ (yttria-stabilized zirconia) strontium ruthenate, lanthanum manganate, and generally, perovskite-structured ceramic materials. The buffer film may be deposited by various physical vapor deposition techniques.
While the foregoing has principally focused on implementation of a biaxially textured film in the buffer stack (layer) by a texturing process such as IBAD, alternatively, the substrate surface itself may be biaxially textured. In this case, the buffer layer is generally epitaxially grown on the textured substrate so as to preserve biaxial texturing in the buffer layer. One process for forming a biaxially textured substrate is the process known in the art as RABiTS (roll assisted biaxially textured substrates), generally understood in the art.
The superconducting layer 14 is generally in the form of a high-temperature superconductor (HTS) layer. HTS materials are typically chosen from any of the high-temperature superconducting materials that exhibit superconducting properties above the temperature of liquid nitrogen, 77K. Such materials may include, for example, YBa2Cu3O7-x, Bi2Sr2CaCu2Oz, Bi2Sr2Ca2Cu3O10+y, Tl2Ba2Ca2Cu3O10+y, and HgBa2Ca2Cu3O8+y. One class of materials includes REBa2Cu3O7-x, wherein RE is a rare earth or combination of rare earth elements. Of the foregoing, YBa2Cu3O7-x, also generally referred to as YBCO, may be advantageously utilized. YBCO may be used with or without the addition of dopants, such as rare earth materials, for example samarium. The superconducting layer 14 may be formed by any one of various techniques, including thick and thin film forming techniques. Preferably, a thin film physical vapor deposition technique such as pulsed laser deposition (PLD) can be used for a high deposition rates, or a chemical vapor deposition technique can be used for lower cost and larger surface area treatment. Typically, the superconducting layer has a thickness on the order of about 0.1 to about 30 microns, most typically about 0.5 to about 20 microns, such as about 1 to about 5 microns, in order to get desirable amperage ratings associated with the superconducting layer 14.
The superconducting article may also include a capping layer 16 and a stabilizer layer 18, which are generally implemented to provide a low resistance interface and for electrical stabilization to aid in prevention of superconductor burnout in practical use. More particularly, layers 16 and 18 aid in continued flow of electrical charges along the superconductor in cases where cooling fails or the critical current density is exceeded, and the superconducting layer moves from the superconducting state and becomes resistive. Typically, a noble metal is utilized for capping layer 16 to prevent unwanted interaction between the stabilizer layer(s) and the superconducting layer 14. Typical noble metals include gold, silver, platinum, and palladium. Silver is typically used due to its cost and general accessibility. The capping layer 16 is typically made to be thick enough to prevent unwanted diffusion of the components from the stabilizer layer 18 into the superconducting layer 14, but is made to be generally thin for cost reasons (raw material and processing costs). Various techniques may be used for deposition of the capping layer 16, including physical vapor deposition, such as DC magnetron sputtering.
The stabilizer layer 18 is generally incorporated to overlie the superconducting layer 14, and in particular, overlie and directly contact the capping layer 16 in the particular embodiment shown in
Referring to
The formation of a multifilamentary superconducting article having discrete filaments facilitates the formation of a low AC loss superconducting article. The formation of discrete filaments along the length of a superconducting tape segment facilitates the reduction of magnetic interferences caused by the current flowing through the HTS layer. Accordingly, the formation of a superconducting article having filaments comprising the HTS material can facilitate the formation of an efficient and low AC loss superconducting article.
While
Referring to
As illustrated, the filaments 203-210 extend along the length of the multifilamentary superconducting article. Generally, the filaments 203-210 have a continuous length 217 of at least about 100 microns. In another embodiment, the filaments 203-210 can have a greater length, such as at least about 200 microns, or at least about 400 microns or even at least about 1000 microns. In one particular embodiment, the filaments 203-210 have a continuous length that extends along essentially the entire length of the tape segment. As previously described, such lengths can be far greater than micron size, since the multifilamentary superconducting tape segment can have lengths of at least about 5 m, and more typically on the order of at least about 10 m or even at least about 100 m. In one particular embodiment, the multifilamentary superconducting articles herein have a length within a range between about 1 m and about 1 km, such as within a range between about 5 m and about 100 m.
The filaments 203-210 can be laterally spaced apart by a spacing distance illustrated by the arrow 213. Generally, the spacing distance 213 separating adjacent filaments is not greater than about 1 mm. In other embodiments, the space 213 can be less, such as not greater than approximately 0.5 mm, not greater than about 0.25 mm or even not greater than about 0.1 mm. In one particular embodiment, the spacing distance 213 separating adjacent filaments is within a range between about 0.05 mm and about 1 mm, and more particularly within a range between about 0.1 mm and about 0.5 mm.
According to one embodiment, the filaments 203-210 can be longitudinally separated by gaps, illustrated as arrow 215, extending along the length of the tape segment. Generally, such gaps have a length that is less than the length of the filaments 203-210. According one embodiment, the gap is not greater than about 3 mm, such as not greater than about 1 mm, and in particular instances can be less. For example, in one embodiment, the gap 215 is not greater than about 100 microns, 75 microns, 50 microns, or even not greater than about 20 microns. Still, in one particular embodiment, the gap is within a range between 100 microns and about 400 microns. In one particular embodiment, the filaments 203-210 can extend for essentially the entire length of the substrate tape, and accordingly no substantial gaps are present.
The process further includes translating a mask tape from a feed reel at step 403. In particular, the mask tape can be a long length of material in the form of a tape. According to one embodiment, the mask tape has dimensions similar to that of the superconducting tape. As such, in one embodiment, the mask tape has a dimension ratio that is at least about 10:1. In another embodiment, the mask tape has a dimension ratio of at least about 100:1 or even at least about 1000:1.
In particular reference to certain dimensions, in one embodiment, the mask tape has an average width that is generally the same as the superconducting tape segment. In one embodiment, the mask tape has an average width of not greater than about 10 cm. In another embodiment, the average width of the mask tape is not greater than about 5 cm, such as not greater than about 1 cm. In one particular embodiment, the mask tape has an average width within a range between about 1 mm and about 1 cm.
In another embodiment, the mask tape has an average thickness than is not greater than about 5 mm. Still, according to another embodiment, the mask tape has an average thickness that is not greater than about 2 mm, such as not greater than about 1 mm, or even not greater than about 0.5 mm. In certain embodiments, it is desirable that the mask tape be particularly thin, having an average thickness within a range between about 0.05 mm and about 0.25 mm.
According to one embodiment the mask tape can be a radiation-sensitive material. Including for example, a photolithography material or resist material used in the electronics industry. In one embodiment, the mask tape can include an organic material, such as a resin.
While translating the superconducting tape and the mask tape from a feed reel as provided in the steps 401 and 403 respectively, the process can continue at step 405 by forming the mask tape over the superconducting tape to form a masked superconducting tape. The process of forming the mask tape over the superconducting tape can include combining the two tapes such that the mask tape is overlying the HTS layer of the superconducting tape. According to one embodiment, the process of forming the mask tape over the superconducting tape includes laminating the mask tape over the superconducting tape by aligning the tapes laterally and pressing the two tapes together. In one particular embodiment, the process of laminating the mask tape over the superconducting tape includes translating the masked tape and superconducting tape together through a substrate holder and applying pressure to the tapes. For example, the mask tape and the superconducting tape can be translated through a substrate holder and pressure is applied to the tapes via a roller. In a more particular embodiment, the process of forming the mask tape over the superconducting tape can further include heating the mask tape and superconducting tape to facilitate suitable lamination. The heat can be applied locally to the tapes to facilitate lamination. In one embodiment, a combination of heat and pressure can be applied to complete lamination. In certain embodiments using heat, the temperature may be greater than approximately 50° F., such as greater than about 75° F. Typically, the temperature provided locally to the tapes during lamination is not greater than approximately 150° F.
During the lamination process, a moistening agent may be applied to the masked tape or superconducting tape or both tapes. The addition of a moistening agent be provided in the form of an aerosol or spray, which can be applied to the surfaces of the respective tapes to be joined in contact. Typically, the material applied to the superconducting tape and mask tape for purposes of moisture is a material that will not contaminate the constituent layers of the superconducting tape or mask tape. As such, in one embodiment, the moistening agent includes an aqueous-based solution. In a particular embodiment, the moistening agent can consist essentially of de-ionized water.
After combining the mask tape over the superconducting tape to form a masked superconducting tape as provided in step 405, the process can continue by translating the masked superconducting tape through a substrate holder having a first registration mark and under a reticle having a second registration mark as provided in step 407.
Referring briefly to
Moreover, methods and devices use for aligning the registration marks can include mechanical, electrical, or optical methods. For example, in one particular embodiment, optical methods of alignment can include a laser and a sensor to align the registration marks. Mechanical methods can include registration marks that protrude from their respective surfaces and trip a switch.
After translating the masked superconducting tape through the substrate holder and under the reticle as provided in step 407, the process continues at step 409 by exposing the masked superconducting tape to radiation directed through the reticle to form a patterned superconducting tape. According to a particular embodiment, radiation can be directed through a pattern within the reticle such that portions of the masked superconducting tape are exposed to the radiation and other portions of the masked superconducting tape are not exposed to the radiation. Such a process facilitates changing the hardness of the masked tape portions exposed to the radiation, such as making them softer as compared to portions not exposed to the radiation.
Generally, the radiation directed through the reticle is of a particular wavelength. Suitable wavelengths generally include wavelengths of radiation less than approximately 500 nanometers. In one embodiment, the radiation has a shorter wavelength, such that it is typically referred to as an ultraviolet or deep ultraviolet wavelength, including those wavelengths less than approximately 400 nanometers, or even less than approximately 350 nanometers.
Referring again briefly to
Returning to the process provided in
The abrasive particles can include an inorganic material, such as an oxide, carbide, nitride, boride, or any combination thereof. In one particular embodiment, suitable abrasive particles can include silica, alumina, silicon carbide, diamond, cubic boron nitride, or any combination thereof. In one particular embodiment the abrasive particles include silica or alumina.
The average particle size is suitable to facilitate patterning of filaments using a reel-to-reel process. Accordingly, in one embodiment, the abrasive particles have an average particle size of not greater than 100 microns. In another embodiment, the abrasive particles are smaller, such as not greater than about 75 microns, not greater than about 50 microns, not greater than about 25 microns, or even not greater than about 10 microns. According to a particular embodiment, the particle size of the abrasive particles is within a range between about 1 micron and about 75 microns, and more particularly within a range between about 5 microns and about 50 microns.
After removing portions of the mask tape and portions of the HTS tape using abrasive particles to form a multifilamentary superconducting tape having discrete filaments, portions of the mask tape can still overlie portions of the tape that were not removed by the abrasive particles. Accordingly, the process can further include removing those portions of the mask tape by exposing them to a cleaning agent. Suitable cleaning agents can include inorganic or organic material. In one particular embodiment, the cleaning agent is an aqueous-based solution. In a more particular embodiment, the cleaning agent can include de-ionized water. In one particular embodiment, the process of cleaning the multifilamentary superconducting tape can include translating the multifilamentary superconducting tape through a bath on a reel-to-reel process. Such a bath can include exposing the multifilamentary superconducting tape to heat to remove those portions of the mask tape overlying the mask tape overlying the HTS filaments. In another embodiment, the process of cleaning the multifilamentary superconducting tape can further include spraying the top surface of the multifilamentary superconducting tape with a cleaning agent and may also include agitation of the multifilamentary superconducting tape, such as by ultra-sonication.
Referring briefly to
As further illustrated in
Referring still to
Referring again to
As the printable tape material can be translated in a reel-to-reel process, the printable tape material generally has those dimensions similar to the superconducting tape material. According to one embodiment, the printable tape material has a dimension ratio of not less than about 10:1. In another embodiment, the printable tape material has a dimension ratio of not less than 100:1 or even not less than about 1000:1.
As provided above, the printable tape material can be substantially transparent to certain wavelengths of radiation. In one particular embodiment, the printable tape material is transparent to ultraviolet radiation, that is radiation having a wavelength less than approximately 500 nm, and more particularly less than approximately 400 nm. Moreover, the printable tape material has an average thickness that is suitable for allowing radiation to transmit through its thickness. In one particular embodiment the printable tape material has an average thickness that is not greater than approximately 5 mm. In other embodiments, the printable tape material is thinner, such that the average thickness is not greater than approximately 3 mm, or even not greater than approximately 1 mm. In one particular embodiment, the printable tape material has an average thickness that is within a range between about 0.05 mm and about 0.25 mm.
In reference to the process of printing a pattern on the surface of the printable tape material, generally the printable tape material is translated in a reel-to-reel process through the printer to form the printed tape. The pattern on the surface can be representative of the filaments to be formed on the final multifilamentary superconducting tape. That is, the pattern can include images of filaments having discrete images resembling filaments spaced apart from each other and including gaps between groups of filaments.
After forming the printed tape in step 601 the process continues at step 603 by combining the printed tape with a radiation-sensitive tape material to form a printed mask tape in a reel-to-reel process. The printed tape can be unwound from a first feed reel and the radiation-sensitive material can be unwound from a second reel and the two tapes can be combined and gathered on a single take-up reel. Generally, the radiation-sensitive tape material used in this embodiment is the same material used in embodiments described in
The process of combining the printed tape with the radiation-sensitive tape material can include a lamination process. The lamination process can include a process similar to that described previously in accordance with
In one particular embodiment, the printed tape can be combined with the radiation-sensitive tape material such that the pattern on the surface of the printed tape is not in contact with a surface of the radiation-sensitive tape material. Alternatively, in another embodiment, the printed tape is combined with the radiation-sensitive tape material such that the pattern on the surface of the printed tape is in contact with a major surface of the radiation-sensitive tape material.
After forming the printed mask tape at step 603, the process continues at step 605 by translating the printed mask tape through a radiation zone and exposing portions of the printed mask tape to radiation to form a patterned mask tape. Accordingly, the pattern on the printed mask tape, particularly darker portions of the pattern, can block the radiation while unprinted portions can allow the radiation through to develop the underlying radiation-sensitive tape material. As previously described, portions of the printed masked tape exposed to the radiation, particularly those portions of the printed mask tape comprising the radiation-sensitive tape material can become softer due to the exposure to the radiation.
After forming the patterned masked tape at step 605, the process continues at step 607 by removing the printed tape from the patterned masked tape. In one particular embodiment, after exposing portions of the printed masked tape to radiation, the printed tape can be separated from the radiation-sensitive tape material. In one embodiment, removing the printed tape from the pattern masked tape can be completed using an interleaf stripper.
After removing the printed tape from the patterned masked tape at 607, the process can continue at step 609 which includes combining the patterned masked tape with a superconducting masked tape on a reel-to-reel process. Generally, the superconducting tape includes a substrate, a buffer layer overlying the substrate, and a conformal HTS layer overlying the buffer layer. In one embodiment, the superconducting tape can also include a capping layer or stabilizer layer, or both. Combining the patterned masked tape with the superconducting tape can include a lamination process as described herein.
After combining the patterned masked tape with the superconducting tape in step 609, the process can continue at step 611 by removing portions of the patterned masked tape and portions of the HTS layer using abrasive particles to form a multi-filamentary superconducting tape, as described previously in accordance with
After combining the printed tape 1002 with the radiation-sensitive tape material 1004 to form the printed masked tape, the process continues at step 1003 wherein the printed masked tape 1006 is translated through a radiation zone 1008, wherein radiation is direct at the surface of the printed masked tape 1006 to expose portions of the radiation-sensitive tape material 1004. As described herein, such a process facilitates softening of those portions of the radiation-sensitive tape material 1004 that are exposed to the radiation.
After exposing portions of the printed masked tape 1006 to radiation at step 1003 the process continues at step 1005 wherein the patterned masked tape 1010 is combined with a superconducting tape 1012. As described herein, after exposing the tape to radiation, the overlying printed tape 1002 can be removed, leaving behind the patterned masked tape 1010 (i.e., the radiation-sensitive tape material) including portions 1020 which can be harder in comparison to softer portions 1022. The superconducting tape 1012 can include a substrate 1018, a buffer layer 1016 overlying the substrate, and a HTS layer 1014 overlying the buffer layer. According to one embodiment, the superconducting tape 1012 further includes a capping layer overlying the HTS layer 1014. In another embodiment, the superconducting tape 1012 further includes a stabilizer layer overlying the HTS layer 1014.
After combining the patterned masked tape 1010 with the superconducting tape 1012 at step 1005, the process continues at step 1007 wherein portions of the patterned masked tape 1010 and HTS layer 1012 are removed using abrasive particles. The superconducting tape 1012 with the overlying patterned masked tape 1010 can be translated through a blasting zone 1024 which directs abrasive particles 1026 under pressure toward the surface of the patterned masked tape 1010. Such a process facilitates removal of certain portions of the patterned masked tape 1010 as well as the portions of the HTS layer 1014 underlying softer portions 1022 of the patterned masked tape 1010. Accordingly, after translating the tape through the blasting region 1024, portions of the HTS layer 1014 and portions 1020 of the pattern masked tape still remain and resemble filaments.
The process continues at step 1009, wherein after removing portions of the patterned masked tape 1010 to form filaments 1028 overlying the buffer layer 1016, portions 1020 of the patterned masked tape remaining can be removed. Accordingly, such a process for removing portions of the patterned masked tape 1020 overlying the filaments 1028 can include a rinse as described herein in accordance with
As such, formation of a multifilamentary superconducting article according to embodiments herein facilitates the formation of a superconducting article having improved current capacity. As will be illustrated herein, the multifilamentary superconducting articles formed herein have a critical current retention ratio of at least about 0.6. In certain embodiments, this ratio is greater, such as at least about 0.65, at least about 0.70, or even at least about 0.75. In one particular embodiment, the critical current retention ratio is within a range between 0.60 and about 0.90.
Referring to
In one embodiment, the multifilamentary superconducting tape segment 1101 is suspended above a base 1102 and wrapping around contacts 1103, 1104, 1105, 1106, 1107, 1108, 1109, 1110, 1111 (1103-1111) such that the path the multifilamentary superconducting tape segment 1101 is substantially non-inductive. Generally, the multifilamentary superconducting tape segment 1101 can be suspended between the contacts 1103-1111 to facilitate exposure to a cooling medium. Accordingly, in one embodiment, not less than about 50% of the total external surface area of the multifilamentary superconducting tape segment 1101 is exposed to the cooling medium. In another embodiment, not less than about 75%, such as not less than about 90%, or even not less than about 98% of the total external surface area of the superconducting tape is exposed to the cooling medium.
In the particular illustrated embodiment, the multifilamentary superconducting tape segment 1101 is suspended between contacts over the base 1102. According to a particular embodiment, the multifilamentary superconducting tape segment 1101 is suspended over the base 1102 on its side, such that planes tangential to the top and bottom surfaces of the tape segment are perpendicular or substantially perpendicular to the major plane of the base 1102. According to one embodiment, not less than about 75% of the total length of the multifilamentary superconducting tape segment 1101 is suspended above the base 1102. In another embodiment, not less than about 90% of the total length of the tape segment is suspended, still, in other embodiments, essentially the entire length of the multifilamentary superconducting tape segment 1101 is suspended above the base 11102.
The multifilamentary superconducting tape 1101 can be electrically coupled to a shunting circuit 1121. Accordingly, the FCL device can include a single or a plurality of shunting circuits spanning the entire distance of the meandering path. As illustrated in
Generally, the impedance elements are selected to have a particular impedance based upon the length of multifilamentary superconducting tape segment that the shunting circuit spans, such that each impedance element protects a certain length of the multifilamentary superconducting tape segment. In one embodiment, the shunting circuit includes impedance elements having an impedance of not less than about 0.1 milliOhms per meter of tape protected. Other embodiments utilize a greater impedance per length of tape protected, such that the impedance elements have a value of not less than about 1 milliOhms per meter of tape protected, or not less than about 5 milliOhms per meter of tape protected, or even not less than about 10 milliOhms per meter of tape protected, and even up to about 1.0 Ohm per meter of tape protected.
According to one particular embodiment, the multifilamentary superconducting tape segment 1102 includes rotation regions 1117 and 1119 where the multifilamentary superconducting tape segment 1101 is tilted or rotated. According to the illustrated embodiment, the rotation regions 1117 and 1119 are particularly localized along straight portions of the superconducting tape segment 401. Such rotation regions 1117 and 1119 facilitate coupling of the superconducting tape segment 401 to electrical contacts 1113 and 1115, which in turn couple the superconducting tape segment 1101 to a shunting circuit 1121. Notably, within the rotation regions 1117 and 1119 the multifilamentary superconducting tape segment 1101 is rotated such that at least a portion of the superconducting tape segment 401 is parallel to the base 1102 and lies flat against a contact surface of the electrical contacts 1113 and 1115. It will be appreciated that such FCL devices can include a plurality of multifilamentary superconducting articles that can be joined and operate in series, or alternatively operate in parallel configurations.
Referring to Table 1 below, comparative data is provided that illustrates improved current retention capabilities of multifilamentary superconducting tape segments formed according to embodiments provided herein as compared to conventional multifilamentary superconducting tape segments formed using a chemical etch process. Samples 1-6 include samples formed via the processes described herein, including a masking, patterning, and abrasive removal technique. The Samples 1-5 are multifilamentary superconducting articles including filaments made of a HTS layer and a stabilizer material overlying an Inconel substrate and biaxially-textured buffer layer including MgO.
The Standard Samples 1-3 were formed using a standard chemical etching process including the use of 0.5 M citric acid. Standard Samples 1-3 include an Inconel substrate, an overlying conformal biaxially-textured buffer layer, and a HTS layer and stabilizer layer patterned to form filaments. In each of the samples provided in Table 1, the filaments were formed having a length of 33 cm a width of 600 microns and laterally separated by a space width of 400 microns. The gap length was 2.5 mm. The tape segments for all of the samples were 1 m long and 4 mm wide.
Table 1 provides critical current (Ic) values for the tape segments before the formation of filaments (Ic Before) and after the formation of the filaments (Ic After). The critical current (Ic) is a measure of the current carrying capabilities of an HTS tape, a significant characteristic of a superconducting article. More particularly, Table 1 provides data on the critical current retention ratio, which illustrates the percentage of lost current carrying capabilities attributed to forming the multifilamentary structure. As illustrated in Table 1, each of the Samples 1-5 formed according to embodiments described herein, demonstrated a greater critical current retention ratio as opposed to the Standard Samples (i.e., Std. 1-3) formed using a chemical etching process.
More particularly, each of the Samples 1-5 demonstrated a critical current retention ratio of at least 0.60 (i.e., 40%), which is about 30% greater than the best multifilament HTS samples formed via a chemical etching process (i.e., sample Std. 1) and thus are multifilament superconducting tapes capable of handling at least about 30% more current. All of the Samples 1-6 demonstrate a critical current retention ratio of at least 0.60, if not at least 0.65.
Moreover, each of the Standard Samples 1-5 demonstrated a greater absolute current carrying capability after the formation of the filaments. The greatest current value for the Standard Samples after formation of the filaments was 62 A, while the lowest current value for the Samples 1-5 was Sample 2 with a current of 88 A. Accordingly, Samples 1-5 demonstrate an improved absolute current capacity value after the forming process as compared to all of the Standard Samples.
Each of the Standard Samples were purposefully compared to Samples 1-5 because all of the samples demonstrated nearly the same degree of AC loss reduction. AC loss reduction is desirable in long-length conductors to minimize the power lost due to interfering magnetic fields generated from the movement of charges (i.e., a current). As such, Samples 1-5 demonstrate a greater current carrying capacity after patterning with the same degree of AC loss reduction, while the Standard Samples demonstrate a lesser current carrying capacity
Moreover, Samples 1-5 have a greater AC loss reduction than unpatterned superconducting articles. Referring to
The information provided above in Table 1 and
Additionally, the incorporation of the presently disclosed multifilamentary superconducting articles within FCL devices results in improved FCL characteristics.
During tests conducted in a liquid nitrogen bath at 77 K, the conventional sample of
Referring to
Accordingly, the multifilamentary superconducting articles, devices, and process disclosed herein demonstrate a departure from the state of the art. The embodiments herein describe a combination of elements including a process of forming multifilamentary superconducting articles using a reel-to-reel process, multiple tapes, masking processes, patterning processes, exposure techniques, and particular blasting techniques suitable for forming improved, long-length multifilamentary superconducting articles. Such processes are further enhanced by the use of particular devices, including a substrate holder, a reticle, combined with the features of registration marks. The combination of such processes and devices facilitate the formation of multifilamentary superconducting articles having precisely aligned filaments with low lateral inter-filamentary misalignment, improved AC loss reduction, and improved current carrying capacity. Moreover, the processes provided herein remove the need for multiple chemical etches and/or different chemical etches to form multifilamentary superconducting articles having filaments including different layers of material. Any one of the same forming processes disclosed herein can be used to form multifilamentary superconducting articles having filaments incorporating different layers of materials.
While certain references, for example U.S. 2007/0197395 and U.S. 2006/0040830, broadly recognize the possibility of patterning superconducting oxide films using abrasive milling or sandblasting, such references are particularly directed to chemical patterning techniques. And in fact, patterning an intermediate film before converting the intermediate film to an oxide superconductor. Moreover, such references, particularly U.S. 2007/0197395, explicitly disclose that the HTS material may harder to remove by abrasive techniques as compared to a softer chemical intermediate film, or may be damage after forming the HTS material, as it is generally a brittle oxide layer. Additionally, while general passing references are made to use of abrasives, none of these references discloses the combination of features including a reel-to-reel process, devices for facilitating the reel-to-reel operation, particular masking techniques, or the abrasive blasting technique disclosed herein. Much less, none of the references demonstrate the formation of long-length multifilamentary superconducting articles having improved critical current retention or AC loss reduction, not to mention improvement of response times when used in FCL articles.
While the invention has been illustrated and described in the context of specific embodiments, it is not intended to be limited to the details shown, since various modifications and substitutions can be made without departing in any way from the scope of the present invention. For example, additional or equivalent substitutes can be provided and additional or equivalent production steps can be employed. As such, further modifications and equivalents of the invention herein disclosed may occur to persons skilled in the art using no more than routine experimentation, and all such modifications and equivalents are believed to be within the scope of the invention as defined by the following claims.
