Patent Document

FIELD OF THE INVENTION 
     The present invention relates to coated conductor high temperature superconductor (HTS) conductors having high in-field current and current carrying capacity. More particularly, the coated conductors are formed as wires. 
     RELATED CASE INFORMATION 
     While no claims of priority are being made, the following cases include relevant subject matter: Ruby, et al., “High-Throughput Deposition System for Oxide Thin Film Growth By Reactive Coevaporation”, now published as US Published Application 2007/0125303 and Moeckly et al., “RF-Properties Optimized Compositions of (RE)Ba 2 Cu 3 O 7-δ , Thin Film Superconductors”, now issued as U.S. Pat. No. 7,867,950. Each of these is incorporated herein by reference as if fully set forth herein in their entirety. 
     BACKGROUND OF THE INVENTION 
     The last 25 years have shown significant advancements in the performance properties of high temperature superconductors. With those improving performance properties has come the desire to utilize HTS for the practical application of loss-free electrical power transmission and other energy saving applications in the development of the smart grid and other energy 
     RELATED APPLICATIONS 
     Early efforts, sometimes termed the first generation (1G) HTS, to form wires did not yield technically or commercially acceptable solutions. The superconductors typically used wire drawing technology, often using variations on Bi 2 Si 2 Ca 2 O 7 . Unfortunately, the HTS was too brittle and costly due to high silver content for the intended applications. 
     Efforts in the so-called second generation (2G) HTS have focused on using a thin layer of high quality HTS usually (RE)BaCuO (also known as (RE)BCO, and where (RE) is a rare earth such as yttrium, samarium, gadolinium, neodymium, dysprosium, etc.) usually on a flexible metal substrate. Such 2G HTS is capable of maintaining a dissipation free state while still carrying large electrical currents even in the presence of a large magnetic field such as is found in motor and generator applications. Most proposed solutions adopt the addition of materials beyond the basic components of the HTS in order to provide extrinsic pinning centers. For example, prior art focuses on adding extra pinning centers by incorporating extra elements during film growth, e.g. Zr, Ta, Nb, Sn. Adding these extrinsic elements to (RE)BCO makes the process more complicated and also raises cost. Despite these clear drawbacks, the field relatively uniformly follows this approach. See, e.g., Foltyn et al., “Materials Science Challenges for High-Temperature Superconducting Wire”, Nature Materials, Vol. 6, September 2007, pp. 631-641, Maiorov, et al., “Synergetic Combination of Different Types of Defect to Optimize Pinning Landscape Using BaZrO 3 -doped YBa 2 Cu 3 O 7″ , Nature Materials, Vol. 8, May 2009, pp. 398-404, Zhou, et al., “Thickness Dependence of Critical Current Density in YBa 2 Cu 3 O 7 -δ Films with BaZrO 3  and Y 2 O 3  Addition, “Supercond. Sci. Technol. 22 (2009), pp. 1-5, Sung Hun Wee, Amit Goyal, and Yuri L. Zuev, “Growth of thick BaZrO 3 -doped YBa 2 Cu 3 O 7-δ  films with high critical currents in high applied magnetic fields”, IEEE Transactions on Applied Superconductivity, Volume 19, Number 3, June 2009, pp. 3266-3269, Amit Goyal, M. Parans Paranthaman, and U. Schoop, “The RABiTS Approach: Using Rolling-Assisted Biaxially Textured Substrates for high-performance YBCO superconductors”, MRS Bulletin, August 2004, pp. 552-561, T Aytug, M Paranthaman, E D Specht, Y Zhang, K Kim, Y L Zuev, C Cantoni, A Goyal, D K Christen, V A Maroni, Y Chen, and V Selvamanickam, “Enhanced flux pinning in MOCVD-YBCO films through Zr additions: systematic feasibility studies”, Superconductor Science and Technology Volume 23 (2010), Sung Hun Wee, Amit Goyal, Eliot D. Specht, Claudia Cantoni, Yuri L. Zuev, V. Selvamanickam, and Sy Cook, “Enhanced flux pinning and critical current density via incorporation of self-assembled rare-earth barium tantalate nanocolumns within YBa 2 Cu 3 O 7-δ  films”, Rapid Communications, Physical Review B Volume 81 (2010), Amit Goyal, Claudia Cantoni, Eliot Specht, Sung-Hun Wee, “Critical current density enhancement via incorporation of nanoscale Ba 2 (Y,Re)TaO 6  in REBCO films”, US Patent Application publication US2011/0034338A1, Feb. 10, 2011. 
     Another approach which has proved less promising to date is introducing microstructural defects into the HTS. See, for example, Selvamanickam published US Application 2011/0028328 which suggests use of a complex surface treatment including the formation of nanorods grown on an array of nanodots, Foltyn et al, where multiple interlayers of CeO2 are grown within the (RE)BCO film to introduce structural defects, and H. Wang et al. U.S. Pat. No. 7,642,222, issued Jan. 5, 2010, where SrTiO 3  layers with varied microstructure are used as the seed layer for growth of the (RE)BCO film. 
     Other investigators have reported on process dependent limitations, such as critical current saturation as a function of film thickness, for coated conductors formed via pulsed laser deposition. See, e.g., Inoue, “In-Field Current Transport Properties of 600 A-Class GdBa 2 Cu 3 O 7-δ  Coated Conductor Utilizing IBAD Template”, IEEE Transactions on Applied Superconductivity, Vol. 21, No. 3, June 2011. A 2.5 μm thick GdBCO film was made by pulsed laser deposition on a Hastelloy substrate, with a 1.1 μm thick GdZrO 7  layer made by ion-beam assisted deposition (IBAD), and a 0.5 μm thick CeO 2  layer formed by pulsed laser deposition. A silver protection layer was provided. The measured sample was formed from a 1 cm long piece, formed into a microbriadge 70 μm width by 500 μm length. Critical current at 77K and self-field were 600 A/cm-w, and critical temperature was 93 K. 
     Despite the clear desirability of a coated conductor achieving these objects, the need remains for a comprehensive and effective solution having high yield and low cost in commercially useable lengths. 
     SUMMARY OF THE INVENTION 
     A 2 nd  generation HTS coated conductor is provided having a substrate and a (RE)BCO superconductor supported by the substrate. The superconductor is adapted to carry current in a superconducting state, with the superconductor having a current (I) carrying capacity of at least 250 A/cm width, in a field of 3 Tesla (T), at 65 Kelvin (K), at all angles relative to the coated conductor. More preferably, the current carrying capacity extends through the range of substantially 250 A/cm to 500 A/cm. Preferably, the coated conductor has a critical current (I c ) carrying capacity of at least 250 A/cm width, in a field of 3 T, at 65 K, at all angles relative to the coated conductor. Preferably, the coated conductor has a critical current density (J c ) carrying capacity of at least 0.5, and more preferably, at least 0.55, MA/cm 2 , in a field of 3 T, at 65 K, at all angles relative to the coated conductor. 
     In yet another aspect of the invention, a multilayer structure is provided, having at least a substrate and (RE)BCO superconductor having the properties stated, above. The substrate may be non-flexible, such as a crystal substrate, preferably an MgO crystal substrate. Alternately, the substrate may be flexible, such as a flexible metal tape, preferably made of non-magnetic alloy, such as Hastelloy or stainless steel. Optionally, the substrate is subject to a planarization process, preferably a solution deposition planarization process. Preferably, the planarization process provides a Y 2 O 3  or other metal oxide solution deposition planarization layer. An optional intermediate layer may be formed between the substrate, or planarization layer if present, and the superconductor layer. Preferably, the intermediate layer is formed by ion beam assisted deposition (IBAD) to form a highly oriented crystalline layer, more preferably an MgO IBAD crystalline layer, followed by an epitaxial MgO layer, more preferably formed by evaporation or sputtering. The (RE)BCO layer is preferably formed via a reactive co-evaporation—cyclic deposition and reaction (RCE-CDR) process. Optional buffer layers and capping layers may be provided. 
     In yet another aspect, a multi-layer coated conductor is formed having a substrate and a (RE)BCO superconductor supported by the substrate, the superconductor adapted to carry current in a superconducting state, where that structure is formed by the process and method steps of, first, providing a first substrate having a first face, second, planarizing at least the first face of the substrate to form a planarized surface, third, forming an ion beam assisted deposition epitaxial layer on the planarized surface, and lastly forming the (RE)BCO superconductor in a layer supported by the epitaxial layer. Additional optional layers may be formed between or on those layers mentioned. Preferably, the planarizing is performed via solution deposition planarization. Also preferably, the ion beam assisted deposition epitaxial layer is an MgO layer. 
     In yet another aspect of the invention, a multi-layer coated conductor has a substrate having a first face, the substrate having a length dimension of at least one meter, an epitaxial layer supported by the substrate, and a (RE)BCO superconductor layer supported by the epitaxial layer, the layer having a thickness of at least 2 microns and a length of at least one meter, the superconductor adapted to carry current in a superconducting state, having an critical current (I c ) of at least 100 A/cm width at a temperature of 65 K in a field of 3 Tesla at all angles. More preferably, the conductor has a critical current of at least 200 A/cm width at a temperature of 65 K in a field of 3 Tesla at all angles. Most preferably, the conductor has a critical current of at least 200 A/cm width at a temperature of 65 K in a field of 3 Tesla at all angles. 
     In yet another aspect of these inventions, a multi-layer coated conductor has a substrate having a first face, a planarization layer disposed adjacent the first face of the substrate, a ion beam assisted deposition epitaxial layer supported by the planarization layer, and a (RE)BCO superconductor supported by the epitaxial layer, the superconductor adapted to carry current in a superconducting state, having an critical current (I c ) of at least 50 A/cm, more preferably 100 A/cm, and most preferably 200 A/cm, at a temperature of 77 K and no external magnetic field (self field). 
     One object of this invention is to produce HTS material with intrinsic pinning centers on an industrial scale and at a low cost. This invention preferably avoids additional elements in order to maintain high critical current density under high DC magnetic field. This invention utilizes intrinsic pinning centers that maintain high critical current in high fields at high temperatures. The key steps in the processes are all inherently scalable to large area, long length and high throughput, making them ideal for industrial applications. Also this approach makes it possible to reduce the number of process steps, therefore, lowering the overall cost for the final product by reducing the raw material used and also saving capital equipment expenditure. Additionally the high throughput and modest capital expenditure of these processes means that the cost of capital is low. Finally, since the HTS is grown on layers built on low cost flexible metal tape, the raw material cost is low. 
     Yet other objects of the inventions are to provide for an inherently scalable process, having reduced number of process steps per layer, with high throughput. This should result in a large HTS growth area. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a coated conductor. 
         FIG. 2  is a perspective drawing of the solution deposition planarization (SDP) equipment and method. 
         FIG. 3  is an exploded cross-sectional view of a substrate and planarization layer after the solution deposition planarization process. 
         FIG. 4  is a perspective drawing of the ion beam assisted deposition equipment and method. 
         FIG. 5  is a perspective drawing of the reactive co-evaporation, cyclic deposition and reaction (RCE-CDR) equipment and method. 
         FIG. 6  is a plot of the critical current (I c ) (left vertical axis) and critical current density (J c ) (right vertical axis) as a function of magnetic field strength applied parallel to the sample, for two different temperatures. 
         FIG. 7  is a plot of the critical current (I c ) (left vertical axis) and critical current density (J c ) (right vertical axis) as a function of the angle from the c-axis applied to the sample. 
         FIG. 8  is a plot of the critical current (I c ) (left vertical axis) and critical current density (J c ) (right vertical axis) as a function of the angle of the magnetic field from the c-axis. 
         FIG. 9  is a plot of the critical current (I c ) (left vertical axis) and critical current density (J c ) (right vertical axis) as a function of magnetic field strength applied parallel to the sample, at two different temperatures. 
         FIG. 10  is a plot of the critical current density (J c ) (left vertical axis) and critical current (I c ) (right vertical axis) as a function the angle of the magnetic field from the c-axis. 
         FIG. 11  is a plot of the critical current density (J c ) as a function of the angle of the magnetic field from the c-axis for three differently prepared samples of NdBCO 
         FIG. 12  is a plot of the critical current density (J c ) as a function of the angle of the magnetic field from the c-axis for three differently prepared samples of SmBCO and one sample of NdBCO. 
         FIG. 13  is a plot of the critical current density (J c ) as a function of the angle of the magnetic field from the c-axis 
         FIGS. 14  A and B show X-ray diffraction scan showing 2θ-ω and co scans for:  FIG. 14A  YBCO on MgO single crystal and  FIG. 14B  YBCO on IBAD/epi MgO on SDP Hastelloy. 
         FIG. 15  is a X-ray diffraction 2θ-ω scan showing SmBCO on IBAD MgO and SDP on Hastelloy. 
         FIG. 16  is a X-ray diffraction pole figure of (RE)BCO ( 103 ) peak. 
         FIG. 17  is an atomic force microscope (AFM) image of (RE)BCO grown on a metal substrate, and then capped with silver. 
         FIG. 18  is a graph of resistivity as a function of temperature of a sample of SmBCO grown on single crystal MgO. 
         FIGS. 19  A, B and C are graphs of critical current (I c ) under magnetic field of 0.66 T as a function of position along a tape for a 70 cm long tape ( FIG. 19A ), a 120 cm long tape ( FIG. 19B ) and a 24 cm long tape ( FIG. 19C ), for self-field at 77 K. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions: 
     “ReBaCuO superconductor” means rare earth (Re), barium (Ba), copper (Cu) and oxygen (O) containing compositions that constitute superconductors at cryogenic temperatures. 
     “Substantially pure ReBaCuO superconductor” means a ReBaCuO superconductor that contains less than 2%, preferably less than 1%, most preferably less than 0.5% by weight of materials other than Re, Ba, Cu and O. 
     Structure and Process: 
       FIG. 1  shows a cross-section of one embodiment of the coated conductor  10 . At least a substrate  12  and (RE)BCO layer  14  are provided. The substrate  12  supports, either directly or through the presence of one or more intermediate layers, the (RE)BCO(RE)BCO layer  14 . Optionally, a solution deposition planarization layer  16  is formed at the surface of the substrate  12 . The solution deposition planarization layer  16  may then directly support the (RE)BCO layer  14 , or may interface with an intermediate layer  18 . In one implementation, the intermediate layer  18  may be an IBAD epitaxial layer, such as an IBAD epi MgO layer. The intermediate layer  18  may directly support the (RE)BCO layer  14 , or may interface with a optional buffer layer  20 , which in turn can support the (RE)BCO layer  14 . 
     The substrate may be either non-flexible or flexible. If non-flexible, it may be a crystal substrate, such as an MgO substrate. If the substrate is flexible, it may be for example a flexible metal tape. In one implementation, substrate  10  is a flexible metal substrate that can for example be stainless steel or Hastelloy. The thickness of the substrate is often in the range of 0.002 to 0.004 inch. The substrate material must meet certain selection criteria: it must be mechanically and chemically stable at the growth temperature of the superconductor (˜800 C), it must have a thermal expansion coefficient similar to the superconductor (˜12-13), a high yield strength, and be non-magnetic. 
     With reference to  FIGS. 2 and 3 , an optional planarization step is performed. The planarization provides an amorphous metal oxide layer that is solution deposited preferably using a solution deposition planarization (SDP) process on the substrate. This one layer provides a diffusion barrier, planarizes the rough metal surface, is chemically stable and provides an amorphous surface suitable for the growth of subsequent layers. Often to otherwise accomplish all of these features several separate steps including electropolishing, the addition of a diffusion barrier and a amorphous bed layer for ion beam assisted deposition (IBAD), would be required. Substrate tape stock  24  may be fed from a spool into a bath  26  containing the planarization solution. The coated conductor passes through dryer  28  onto a take up spool having the now planarization layer coated substrate  30 .  FIG. 3  shows an exploded view of the substrate  12  and the solution deposition planarization layer  16 . 
     The solution deposition planarization (SDP) process uses metal organic precursor dissolved in solvent. This solution can be applied to the metal substrate utilizing techniques such as dip coating, spray coating, meniscus coating or slot die coating. The solution deposited on the metal substrate travels into a heater where the solvent is evaporated out, and the organic carrier is volatilized leaving behind only the dense, amorphous, metal oxide film. Multiple coatings deposited by sequentially repeating this process creates a smooth (roughness ˜1 nm), planarized, chemically stable, and amorphous surface. 
     With reference to  FIG. 4 , the optional next layer is deposited using an ion beam assisted deposition (IBAD) technique. A metal oxide having a rock-salt-like crystal structure, usually MgO, is deposited with the assistance of an ion beam (see, e.g., Do et al., U.S. Pat. No. 6,190,752 entitled “Thin Films Having Rock-Salk-Like Structure Deposited on Amorphous Surfaces”, see also Wang, et al., “Deposition of in-plane textured MgO on amorphous Si 3 N 4  substrates by ion-beam-assisted deposition and comparisons with ion-beam-assisted deposited yttria-stabilized-zirconia” Appl. Phys. Lett. 71 (20), pp. 2955-2957, 17 Nov. 1997 and Iijima et al, “Research and Development of Biaxially Textured IBAD-GZO Templates for Coated Superconductors”, MRS Bulletin, August 2004 pp. 564-571, all incorporated herein as if fully set forth herein) to permit the formation of a 3-dimensionally ordered, crystalline thin film. Optionally a thicker layer of the metal oxide can be grown epitaxially to increase thickness and improve crystallinity. Ion beam assisted deposition (IBAD) is typically done by vacuum evaporating magnesium oxide (MgO) (source  32 ) while directing an ion beam  34  at an angle to the substrate  12 . When the ion beam is set to the correct energy and density, it gives bi-axially textured orientation to the MgO. This IBAD textured layer then provides a seed layer for the epitaxial growth of (RE)BCO material. 
     Next an optional buffer layer  20  ( FIG. 1 ) is grown on the IBAD layer to improve the lattice match to the (RE)BCO film. The epitaxial HTS layer is next grown, preferably using a reactive co-evaporation cyclic deposition and reaction (RCE-CDR), described in more detail, below. Lastly an optional cap layer  22  of metal, preferably silver is deposited on the HTS to provide electrical contact to the superconducting film and physical protection. 
     With reference to  FIG. 5 , the RCE-CDR uses high purity metal targets  36  of one or more of the following rare earths (Yttrium, Samarium, Gadolinium, Neodymium, Dysprosium, etc.), barium and copper in an oxygen background environment of 10 −5  Torr. The film growth occurs when it passes through the oxygen pocket where the pressure is maintained at 10-30 mTorr. This deposition and film growth cycle is done at 5-10 Hz by rotating the sample holder. Heater  38  heats the substrate. After the film is fully grown it is cooled down in oxygen pressure of 600 Torr. Techniques for RCE-CDR are now known to those skilled in the art, see, e.g., Ruby et al, “High-Throughput Deposition System for Oxide Thin Film Growth By Reactive Coevaporation”, now published as US Published Application 2007/0125303, which is incorporated herein by reference for the teaching of RCE-CDR, as if fully set forth herein. 
       FIG. 6  is a plot of the critical current (I c ) (left vertical axis) and critical current density (J c ) (right vertical axis) as a function of magnetic field strength applied parallel to the sample, for two different temperatures. The graph shows the critical current of (RE)BCO grown on flexible metal tape measured in magnetic field at different temperatures. As the magnetic field increases the critical current decreases. At a field of 3 T, with the magnetic field parallel to the film, the I c  is approximately 290 A/cm-width, and J c  is approximately 0.66 MA/cm 2 . The upper data set is at 65 K and the lower data set is at 75 K. 
       FIG. 7  is a plot of the critical current (I c ) (left vertical axis) and critical current density (J c ) (right vertical axis) as a function of the angle from the c-axis applied to the sample.  FIG. 7  shows the critical current of the same sample as in  FIG. 6  measured at 75 K as a function of the angle of the applied magnetic filed. It shows a very strong peak when the magnetic filed is perpendicular to the film normal. The upper data set is at 75 K in a 3 T field, and the lower data set is at 75 K in a 5 T field. 
       FIG. 8  is a plot of the critical current (I c ) (left vertical axis) and critical current density (J c ) (right vertical axis) as a function of magnetic field strength applied parallel to the sample.  FIG. 8  is the same type of measurement as  FIG. 7  but done at a lower temperature of 65 K. The critical current increases significantly when cooled from 75 K. At 65 K and 3 T the minimum critical current is 250 A. The upper data set is at 65 K in a 3 T field, and the lower data set is at 55 K in a 5 T field. 
       FIG. 9  is a plot of the critical current (I c ) (left vertical axis) and critical current density (J c ) (right vertical axis) as a function of magnetic field strength applied parallel to the sample, at two different temperatures. It shows the critical current of the same (RE)BCO deposited on single crystal MgO instead of the metal tape. This was measured in magnetic field at different temperatures under the same condition as  FIG. 6 . The minimum critical current improves roughly 50% when (RE)BCO is grown on single crystal. The upper data set is at 65 K and the lower data set is at 75 K. 
       FIG. 10  is a plot of the critical current density (J c ) (left vertical axis) and critical current (I c ) (right vertical axis) as a function of magnetic field strength applied parallel to the sample.  FIG. 10  shows the critical current of the sample grown on single crystal MgO measured at 65 K as a function of the angle of the applied magnetic field. Comparing  FIG. 8  to  FIG. 10  shows a minimum critical current improvement of 80%. The uppermost data set is at 3 T, the middle data set is at 5 T and the bottom data set is at 7 T. 
       FIG. 11  is a plot of the critical current density (J c ) as a function of the angle from the c-axis of the magnetic field applied to a three different NdBCO samples. The field is 1 T, at 75.5 K. At angle  0 , the uppermost data set is for a field of 1 T, with NdBCO of thickness 0.7 μm, the middle data set is for a field of 0.9 T, for Nd 1.11 BCO of thickness 0.7 and the bottom data set is for a field of 1 T for NdBCO of thickness 1.4 μm. The off-stoichiometry for Nd rich films significantly enhanced the minimum J c  values, by approximately a factor of 4. 
       FIG. 12  is a plot of the critical current density (J c ) as a function of the angle from the c-axis of the magnetic field applied to a three different SmBCO samples and one NdBCO sample.  FIG. 12  may be compared to  FIG. 11  for the difference between the two rare earths (Nd and Sm). At angle  0 , the uppermost data set is for a field of 0.9 T, with SmBCO of thickness 0.7 μm, the second data set is for a field of 0.9 T, for Sm 1.1 BCO of thickness 0.8 μm, the third data set is for a field of 0.9 T, for Sm 1.2 BCO of thickness 0.86 μm, and the bottom data set is for a field of 0.9 T for NdBCO of thickness 0.7 μm. The off-stoichiometry for Sm rich films significantly enhanced the minimum J c  values, especially those having a Sm enhancement of substantially 1.1, or 10%. 
       FIG. 13  is a plot of the critical current density (J c ) as a function of the angle from the c-axis of the magnetic field applied to a series of SmBCO samples having various thicknesses. At angle  0  the upper most data are for the 0.7 μm film, the 1.6 μm film, then the 4.4 μm film, then the 3.3 μm film, with the 2.2 μm film showing at angle  0  as the lowest datapoint. For films less than 1.6 μm, and particularly for films at substantially 2.2 μm and thicker, the angular dependence of the J c  is essentially flat. 
       FIGS. 14  A and B show X-ray diffraction patterns showing 2θ-ω and ω scans for:  FIG. 14A  YBCO on MgO single crystal and  FIG. 14B  YBCO on IBAD/epi MgO on SDP Hastelloy. The Δ2θ is preferably less than 0.2, more preferably less than 0.1, and most preferably less than 0.050. The Δω is preferably less than 0.5, more preferably less than 0.36, and most preferably less than 0.15. These results establish that the films are of very high crystal quality. 
       FIG. 15  shows the X-ray diffraction pattern of (RE)BCO grown on metal tape substrate. (001) peaks are well defined and it is a clear indication that the HTS is growing c-axis orientated. There are no signs of polycrystalline material nor evidence of a, b oriented growth. 
       FIG. 16  is a X-ray diffraction pole of (RE)BCO ( 103 ) peak which shows that in-plane texture is well defined having four strong peaks. 
       FIG. 17  is an Atomic Force Microscopy (AFM) image showing the surface image of a thin layer of silver deposited on (RE)BCO grown on metal substrate. The large particles are copper oxide covered by silver and the short needle-like microstructure comes from the silver grains grown on top of (RE)BCO. 
       FIG. 18  is a resistivity vs. temperature curve of (RE)BCO grown on MgO single crystal substrate. The single crystal was inserted next to the metal substrate as a process monitor. This particular sample had a critical temperature of 93.7 Kelvin. 
       FIGS. 19  A, B and C are graphs of critical current (I c ) under magnetic field of 0.66 T as a function of position along a tape for a 70 cm long tape ( FIG. 19A ), a 120 cm long tape ( FIG. 19B ) and a 24 cm long tape ( FIG. 19C ), for self-field at 77 K. 
     Experimental 
     High temperature superconductor (RE)BCO is deposited on 2 different types of substrates: flexible metal substrate and single crystal magnesium oxide. The dimension of the metal tape is 4 cm long, 1 cm wide and 0.004 inch thick. Solution deposition layer of metal oxide is deposited on the metal substrate followed by ion beam assisted deposition of magnesium oxide. Single crystal magnesium oxide substrate is cut into 1 cm length, 1 cm width and 0.02 inch thick piece and crystal orientation is (100). 
     The method of deposition is reactive co-evaporation. High purity metal targets of rare earths (yttrium, samarium, gadolinium, neodymium, dysprosium, etc.), barium and copper are used for evaporation. Barium and copper can be evaporated with a thermal source, whereas most of the rare earths require electron beam source because of their high melting temperature. Samarium is an exception due to its nature to sublimate. It is easily deposited with special thermal source with baffles. The evaporation rate is monitored and controlled by quartz crystal monitors (QCM). Each elemental source has its own QCM directed line-of-sight through multiple collimators. The oxygen is directly supplied through the heater and its flow is controlled by a mass flow controller. The overall background oxygen pressure is monitored by a hot cathode ion gauge. Typical background pressure during deposition is in the range of 10 −5  Torr. This deposition and film growth cycle is done at 5/10 Hz by rotating the sample holder attached to the heater. The film growth occurs when the sample passes through the oxygen pocket where the pressure is maintained at 10/30 mTorr. Heater temperature ranges between 750-800° C. After the film is fully grown it is cooled down in oxygen pressure of 600 Torr. 
     These inventions provide cutting edge high-magnetic-field test results for second generation (2G) HTS wire. This demonstrates exceptional in-field critical current values. This world-class current-carrying capability in high magnetic field demonstrates the effectiveness of the disclosed HTS fabrication process at producing 2G HTS wire for demanding applications such as superconducting fault current limiters and high-power wind turbine generators. 
     The 2G HTS coated conductor sample on a template that exhibits a minimum critical current of 228 amperes (A) at a temperature of 65 Kelvin (K) in an applied magnetic field of 3 Tesla (T), corresponding to 256 A/centimeter (cm)-width. This critical current is the minimum value as a function of magnetic field angle. The maximum critical current of this sample at 65 K exceeded 404 A/cm-width for a 3-T magnetic field oriented parallel to the coated conductor surface; this latter current value was limited by the amount of current supplied by the measurement apparatus. In a ST field at 65 K, the coated conductor exhibited a minimum critical current of 143 A/cm-width and a maximum critical current of 322 A/cm-width. 
     This sample was fabricated using a straightforward HTS structure and did not need to add additional elements or so-called artificial pinning centers to the coated conductor to obtain this result. 
     These 2G HTS wires utilize HTS material deposition processes and volume manufacturing to produce energy-efficient, cost-effective, and high-performance 2G HTS wire for next generation power applications. 2G HTS wire is fabricated using its deposition technology known as reactive coevaporation with cyclic deposition and reaction (RCE-CDR). This specific sample of 2G HTS wire is 8.9 millimeters wide×4.4 microns thick and was grown on a 1-cm-wide×4-cm-long template. This simplified template contained a reduced number of layers compared to competing 2G HTS wire technologies. The template consisted of a non-magnetic nickel-alloy substrate followed by layers of only two materials: a solution-deposition planarization (SDP) layer and an ion-beam assisted deposition (IBAD) layer. An advantage of the RCE-CDR technology is that it allows high-performance 2G HTS wire to be grown on these simplified templates. This simplified template platform combined with the RCE-CDR process results in a superior high-yield, low-cost 2G HTS wire technology. 
     Applications 
     Coated conductors are useful in a wide variety of applications including but not limited to high power transmission cables (AC), superconducting fault current limiters, wind turbine (generator), industrial motors and generators, and magnetic resonance imaging machines. 
     All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity and understanding, it may be readily apparent to those of ordinary skill in the at in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the following claims.

Technology Category: 5