Superconductor Science and Technology, Jan 3, 2019
In this letter we demonstrate the development of ternary Nb3Sn multifilamentary conductors with a... more In this letter we demonstrate the development of ternary Nb3Sn multifilamentary conductors with artificial pinning centers (APC) which achieve high critical fields. These recently-developed conductors were tested in a 31 T magnet, and the results showed that their upper critical field (Bc2) values at 4.2 K are 27-28 T, and irreversible field (Birr) values are above 26 T, values similar to or higher than those of best RRP conductors. The non-Cu Jc has been brought to nearly 1200 A/mm 2 at 16 T and 4.2 K, comparable to RRP, in spite of the fact that the fine-grain Nb3Sn fractions in filaments are still low (20-30%) and the grain sizes are still not fully refined (70-80 nm) due to conductor designs and heat treatments that are not yet optimized. The Nb3Sn layer Jc at 4.2 K, 16 T is 4710 A/mm 2 for the APC wire with 1%Zr, about 2.5 times higher than RRP conductors, in spite of the fact that its grain size is not yet fully refined due to insufficient oxygen and unoptimized heat treatment. An analysis is presented about the non-Cu Jc that can be achieved by further optimizing the APC conductors and their heat treatments.
IEEE Transactions on Applied Superconductivity, Aug 1, 2021
Internally oxidized Nb3Sn wires with artificial pinning centers (APC) have been developed by manu... more Internally oxidized Nb3Sn wires with artificial pinning centers (APC) have been developed by manufacturing a multifilament PIT-style wire, each filament consisting of a Nb-Ta-Zr alloy tube filled with a mixture of Sn, Cu, and oxide powders. During heat treatment, the oxide decomposes, and the oxygen goes into solid solution in the Nb alloy. Upon Sn diffusion into the Nb alloy, ZrO2 nanoprecipitates form which serve both to inhibit grain coarsening and directly pin magnetic flux. The finer grain structure and high concentration of non-superconducting precipitates serve as flux pinning sites and enhance high-field Jc; direct pinning by the precipitates also shifts the maximum pinning force to higher fields. To distinguish these two effects, an APC wire with a high heat treatment temperature (700 °C) was compared to a conventional PIT wire with very low heat treatment temperature (600 °C), resulting in similar grain size in both samples. The pinning force vs applied field (Fp-B) curve was deconvoluted into grain boundary and point pinning components. It was found that the grain boundary component of the APC wire was very close to the Fp-B curve for the PIT wire, demonstrating that the two pinning components in an APC wire are directly additive. It was then possible to show that, in the 15-20 T regime, direct pinning contributed 45-50% of the total pinning.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Nb 3 Sn superconducting strands are the most practical conductors to generate high magnetic field... more Nb 3 Sn superconducting strands are the most practical conductors to generate high magnetic fields (12-16 T), and thus have significant applications in nuclear magnetic resonance (NMR), and great potential for fusion reactors and particle accelerator magnets. High critical current density (J c ) is a key parameter for such applications. Significant efforts towards optimization of various factors led to an 80% improvement in J c from the early 1990s to 2003, when the 4.2 K, 12 T non-matrix J c reached 3000 A/mm 2 (corresponding to 5000 A/mm 2 in Nb 3 Sn layer J c ). [1, However, further efforts over the past decade have failed to bring about further increase beyond this level, leading some researchers to conclude that the J c of conventional Nb 3 Sn strands had reached its maximum. Here, however, by applying an internal oxidation method, we reduce the grain size by a factor of three and nearly double the 12 T J c . In this method, a Nb 3 Sn strand is fabricated with Nb-Zr alloy as starting material; with oxygen supplied properly via an oxide powder, the Zr atoms in the Nb-Zr alloy are internally oxidized, forming fine intra-granular and inter-granular ZrO 2 particles in Nb 3 Sn layer, which effectively refine Nb 3 Sn grain size. At a reaction temperature of 625 °C, grain size down to 20-50 nm (36 nm on average) has been achieved. For this sample the 4.2 K, 12 T Nb 3 Sn layer J c reached 9600 A/mm 2 . Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))
ABSTRACT Several different Nb3Sn strand types have been investigated with a focus on relating the... more ABSTRACT Several different Nb3Sn strand types have been investigated with a focus on relating their microstructure and superconducting properties. Two types of strand were studied: (1) a standard internal-Sn-type rod-in-tube (RIT) conductor and (2) a so-called ``tube-type'' conductor comparable in structure to the above except that the annulus of Cu-clad Nb rods was replaced by a Cu-lined Nb tube. One member of each type was doped with Ti, initially present either in the filamentary array or in the Sn core. After full reaction, the Nb3Sn filaments and their grain structure were observed using high resolution scanning electron microscopy (SEM), and their grain sizes characterized. Subsequently, Energy Dispersive Spectroscopy (EDS) was used to obtain the composition of the filaments. Superconducting properties, with a focus on Jc, were measured and correlated to these factors. The effect of Ta and Ti on the composition distribution and grain morphology, and the relationship between the local composition and morphology with the Jc value are then discussed.
Magnetization, AC loss, v DC and d eff were measured for several designs of rod-in-tube based int... more Magnetization, AC loss, v DC and d eff were measured for several designs of rod-in-tube based internal-Sn Nb 3 Sn type superconducting multifilamentary strands. Two kinds of subelement geometries were used in strand construction. The first had the standard annular Nb/Cu ring surrounding a Sn source; the second was similar but included an internal split intended to reduce magnetization and loss. Strands with 18 and 36 subelements were measured, at strand diameters of 0.5-0.8 mm. Optical, SEM, and EDS measurements were performed on these samples; average radii are reported and physical barrier integrity is found to be good. The magnetizations of these structures were analyzed in terms of a d eff parameter, in this case calculated for annular structures. Analytical and numerical results of these calculations are presented. It was found that in general annular structures should be expected to have d eff values somewhat larger than the subelement diameter; the value of this enhancement is reported. Also, the effect of subelement splitting on d eff and magnetization was calculated. The results of these calculations are compared to the experimentally measured results. Reductions in d eff due to subelement splitting are compared to direct, low-field susceptibility measurements. Magnetization values are seen to be nearly uniformly lower in the split subelement strands, and this leads in some but not all cases to significantly lower d eff values. Possible reasons for these discrepancies are discussed.
Various types of internal-Sn multifilamentary strand were studied in an attempt to correlate frac... more Various types of internal-Sn multifilamentary strand were studied in an attempt to correlate fracture, subelement hardness, and interfacial conditions. Wire fracture (one of the main factors limiting the piece-length of multifilamentary precursor wires) is empirically known to increase with strand complexity. In an attempt to quantify this, a number of internal-tin multifilamentary precursor wires exhibiting various levels of drawability were
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
IEEE Transactions on Applied Superconductivity, Jun 1, 2009
AbstractThe tubular technique for economical production of Nb3Sn material with large numbers of ... more AbstractThe tubular technique for economical production of Nb3Sn material with large numbers of subelements is being ex-plored further by Supergenics I LLC and Hyper Tech Research Inc. The number of subelements has been raised to 271 (246+25) by increasing the size ...
Superconductor Science and Technology, May 28, 2013
In this work, the transport and magnetization properties of distributed-barrier Rod-in-Tube (RIT)... more In this work, the transport and magnetization properties of distributed-barrier Rod-in-Tube (RIT) strands and Tube Type strands are studied. While Tube Type strands had smaller magnetizations and thus better stabilities in the low field region, their 12 T non-Cu J c s were somewhat smaller than those of the RIT strands. Microstructures were investigated in order to find out the reasons for the difference in non-Cu J c values. Their grain size and stoichiometry were found to be comparable, leading to similar layer J c s. Accordingly it was determined that the lower A15 area fraction rather than the quality of A15 layer was the cause of the discrepancy in non-Cu J c . Subsequently, the area utilizations of subelements were investigated. While for a RIT strand the fine grain (FG) A15 area occupies ~60% of a subelement, for a Tube Type strand it is no more than 40%. Further analysis indicates that the low FG area fraction in a Tube Type strand is attributed to its much larger unreacted Nb area fraction. Finally, a simple change in strand architecture is proposed to reduce the unreacted Nb area fraction.
Transport current values of 7.5 x 10 4 A/cm 2 at 4.2 K and self-field are reported for MbB 2 -bas... more Transport current values of 7.5 x 10 4 A/cm 2 at 4.2 K and self-field are reported for MbB 2 -based tapes. MgB 2 strands were formed by directly filling commercially available MgB 2 powder into Nb-lined, monel tubes and then wire drawing. The wires were then rolled into tapes 2.56 x 0.32 mm 2 , with a total superconducting cross section of 0.2319 mm 2 . Transport measurements were performed using a standard four-point technique at T = 4.2 K (in liquid helium) and at self field. Three samples were prepared, with heat treatments of 900GC for 1, 2, and 3 h under 1/3 at Ar. Measured values of transport current were 4.7, 7.5, and 1.1 x 10 4 A/cm 2 , respectively, at 4.2 K and self field. M-H loops taken on the sample HT for 1 h showed magnetic J c s of 4.2 x 10 4 A/cm 2 at 4.2 K and 1 T, indicating that the material had reasonably well connected grains.
IOP Conference Series: Materials Science and Engineering, 2017
Use of superconducting coils for wind turbines and electric aircraft is of interest because of th... more Use of superconducting coils for wind turbines and electric aircraft is of interest because of the potential for high power density and weight reduction. Here we test a racetrack coil developed as a proof-of-concept for cryogen-free superconducting motors and generators. The coil was wound with 1209 m of 0.7-mm-diameter insulated tube-type Nb 3 Sn wire. The coil was epoxy-impregnated, instrumented, covered with numerous layers of aluminized mylar insulation, and inserted vertically into a dewar. The system was cooled to 4.2 K, and a few inches of liquid helium was allowed to collect at the bottom of the dewar but below the coil. The coil was cooled by conduction via copper cooling bars were attached to the coil but also were immersed in the liquid helium at their lower ends. Several current tests were performed on the coil, initially in voltage mode, and one run in current mode. The maximum coil I c at 4.2 K was 480 A, generating 3.06 T at the surface of the coil. The coil met the design targets with a noticeable margin.
Superconductor Science and Technology, Jan 3, 2019
In this letter we demonstrate the development of ternary Nb3Sn multifilamentary conductors with a... more In this letter we demonstrate the development of ternary Nb3Sn multifilamentary conductors with artificial pinning centers (APC) which achieve high critical fields. These recently-developed conductors were tested in a 31 T magnet, and the results showed that their upper critical field (Bc2) values at 4.2 K are 27-28 T, and irreversible field (Birr) values are above 26 T, values similar to or higher than those of best RRP conductors. The non-Cu Jc has been brought to nearly 1200 A/mm 2 at 16 T and 4.2 K, comparable to RRP, in spite of the fact that the fine-grain Nb3Sn fractions in filaments are still low (20-30%) and the grain sizes are still not fully refined (70-80 nm) due to conductor designs and heat treatments that are not yet optimized. The Nb3Sn layer Jc at 4.2 K, 16 T is 4710 A/mm 2 for the APC wire with 1%Zr, about 2.5 times higher than RRP conductors, in spite of the fact that its grain size is not yet fully refined due to insufficient oxygen and unoptimized heat treatment. An analysis is presented about the non-Cu Jc that can be achieved by further optimizing the APC conductors and their heat treatments.
IEEE Transactions on Applied Superconductivity, Aug 1, 2021
Internally oxidized Nb3Sn wires with artificial pinning centers (APC) have been developed by manu... more Internally oxidized Nb3Sn wires with artificial pinning centers (APC) have been developed by manufacturing a multifilament PIT-style wire, each filament consisting of a Nb-Ta-Zr alloy tube filled with a mixture of Sn, Cu, and oxide powders. During heat treatment, the oxide decomposes, and the oxygen goes into solid solution in the Nb alloy. Upon Sn diffusion into the Nb alloy, ZrO2 nanoprecipitates form which serve both to inhibit grain coarsening and directly pin magnetic flux. The finer grain structure and high concentration of non-superconducting precipitates serve as flux pinning sites and enhance high-field Jc; direct pinning by the precipitates also shifts the maximum pinning force to higher fields. To distinguish these two effects, an APC wire with a high heat treatment temperature (700 °C) was compared to a conventional PIT wire with very low heat treatment temperature (600 °C), resulting in similar grain size in both samples. The pinning force vs applied field (Fp-B) curve was deconvoluted into grain boundary and point pinning components. It was found that the grain boundary component of the APC wire was very close to the Fp-B curve for the PIT wire, demonstrating that the two pinning components in an APC wire are directly additive. It was then possible to show that, in the 15-20 T regime, direct pinning contributed 45-50% of the total pinning.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Nb 3 Sn superconducting strands are the most practical conductors to generate high magnetic field... more Nb 3 Sn superconducting strands are the most practical conductors to generate high magnetic fields (12-16 T), and thus have significant applications in nuclear magnetic resonance (NMR), and great potential for fusion reactors and particle accelerator magnets. High critical current density (J c ) is a key parameter for such applications. Significant efforts towards optimization of various factors led to an 80% improvement in J c from the early 1990s to 2003, when the 4.2 K, 12 T non-matrix J c reached 3000 A/mm 2 (corresponding to 5000 A/mm 2 in Nb 3 Sn layer J c ). [1, However, further efforts over the past decade have failed to bring about further increase beyond this level, leading some researchers to conclude that the J c of conventional Nb 3 Sn strands had reached its maximum. Here, however, by applying an internal oxidation method, we reduce the grain size by a factor of three and nearly double the 12 T J c . In this method, a Nb 3 Sn strand is fabricated with Nb-Zr alloy as starting material; with oxygen supplied properly via an oxide powder, the Zr atoms in the Nb-Zr alloy are internally oxidized, forming fine intra-granular and inter-granular ZrO 2 particles in Nb 3 Sn layer, which effectively refine Nb 3 Sn grain size. At a reaction temperature of 625 °C, grain size down to 20-50 nm (36 nm on average) has been achieved. For this sample the 4.2 K, 12 T Nb 3 Sn layer J c reached 9600 A/mm 2 . Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))
ABSTRACT Several different Nb3Sn strand types have been investigated with a focus on relating the... more ABSTRACT Several different Nb3Sn strand types have been investigated with a focus on relating their microstructure and superconducting properties. Two types of strand were studied: (1) a standard internal-Sn-type rod-in-tube (RIT) conductor and (2) a so-called ``tube-type'' conductor comparable in structure to the above except that the annulus of Cu-clad Nb rods was replaced by a Cu-lined Nb tube. One member of each type was doped with Ti, initially present either in the filamentary array or in the Sn core. After full reaction, the Nb3Sn filaments and their grain structure were observed using high resolution scanning electron microscopy (SEM), and their grain sizes characterized. Subsequently, Energy Dispersive Spectroscopy (EDS) was used to obtain the composition of the filaments. Superconducting properties, with a focus on Jc, were measured and correlated to these factors. The effect of Ta and Ti on the composition distribution and grain morphology, and the relationship between the local composition and morphology with the Jc value are then discussed.
Magnetization, AC loss, v DC and d eff were measured for several designs of rod-in-tube based int... more Magnetization, AC loss, v DC and d eff were measured for several designs of rod-in-tube based internal-Sn Nb 3 Sn type superconducting multifilamentary strands. Two kinds of subelement geometries were used in strand construction. The first had the standard annular Nb/Cu ring surrounding a Sn source; the second was similar but included an internal split intended to reduce magnetization and loss. Strands with 18 and 36 subelements were measured, at strand diameters of 0.5-0.8 mm. Optical, SEM, and EDS measurements were performed on these samples; average radii are reported and physical barrier integrity is found to be good. The magnetizations of these structures were analyzed in terms of a d eff parameter, in this case calculated for annular structures. Analytical and numerical results of these calculations are presented. It was found that in general annular structures should be expected to have d eff values somewhat larger than the subelement diameter; the value of this enhancement is reported. Also, the effect of subelement splitting on d eff and magnetization was calculated. The results of these calculations are compared to the experimentally measured results. Reductions in d eff due to subelement splitting are compared to direct, low-field susceptibility measurements. Magnetization values are seen to be nearly uniformly lower in the split subelement strands, and this leads in some but not all cases to significantly lower d eff values. Possible reasons for these discrepancies are discussed.
Various types of internal-Sn multifilamentary strand were studied in an attempt to correlate frac... more Various types of internal-Sn multifilamentary strand were studied in an attempt to correlate fracture, subelement hardness, and interfacial conditions. Wire fracture (one of the main factors limiting the piece-length of multifilamentary precursor wires) is empirically known to increase with strand complexity. In an attempt to quantify this, a number of internal-tin multifilamentary precursor wires exhibiting various levels of drawability were
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
IEEE Transactions on Applied Superconductivity, Jun 1, 2009
AbstractThe tubular technique for economical production of Nb3Sn material with large numbers of ... more AbstractThe tubular technique for economical production of Nb3Sn material with large numbers of subelements is being ex-plored further by Supergenics I LLC and Hyper Tech Research Inc. The number of subelements has been raised to 271 (246+25) by increasing the size ...
Superconductor Science and Technology, May 28, 2013
In this work, the transport and magnetization properties of distributed-barrier Rod-in-Tube (RIT)... more In this work, the transport and magnetization properties of distributed-barrier Rod-in-Tube (RIT) strands and Tube Type strands are studied. While Tube Type strands had smaller magnetizations and thus better stabilities in the low field region, their 12 T non-Cu J c s were somewhat smaller than those of the RIT strands. Microstructures were investigated in order to find out the reasons for the difference in non-Cu J c values. Their grain size and stoichiometry were found to be comparable, leading to similar layer J c s. Accordingly it was determined that the lower A15 area fraction rather than the quality of A15 layer was the cause of the discrepancy in non-Cu J c . Subsequently, the area utilizations of subelements were investigated. While for a RIT strand the fine grain (FG) A15 area occupies ~60% of a subelement, for a Tube Type strand it is no more than 40%. Further analysis indicates that the low FG area fraction in a Tube Type strand is attributed to its much larger unreacted Nb area fraction. Finally, a simple change in strand architecture is proposed to reduce the unreacted Nb area fraction.
Transport current values of 7.5 x 10 4 A/cm 2 at 4.2 K and self-field are reported for MbB 2 -bas... more Transport current values of 7.5 x 10 4 A/cm 2 at 4.2 K and self-field are reported for MbB 2 -based tapes. MgB 2 strands were formed by directly filling commercially available MgB 2 powder into Nb-lined, monel tubes and then wire drawing. The wires were then rolled into tapes 2.56 x 0.32 mm 2 , with a total superconducting cross section of 0.2319 mm 2 . Transport measurements were performed using a standard four-point technique at T = 4.2 K (in liquid helium) and at self field. Three samples were prepared, with heat treatments of 900GC for 1, 2, and 3 h under 1/3 at Ar. Measured values of transport current were 4.7, 7.5, and 1.1 x 10 4 A/cm 2 , respectively, at 4.2 K and self field. M-H loops taken on the sample HT for 1 h showed magnetic J c s of 4.2 x 10 4 A/cm 2 at 4.2 K and 1 T, indicating that the material had reasonably well connected grains.
IOP Conference Series: Materials Science and Engineering, 2017
Use of superconducting coils for wind turbines and electric aircraft is of interest because of th... more Use of superconducting coils for wind turbines and electric aircraft is of interest because of the potential for high power density and weight reduction. Here we test a racetrack coil developed as a proof-of-concept for cryogen-free superconducting motors and generators. The coil was wound with 1209 m of 0.7-mm-diameter insulated tube-type Nb 3 Sn wire. The coil was epoxy-impregnated, instrumented, covered with numerous layers of aluminized mylar insulation, and inserted vertically into a dewar. The system was cooled to 4.2 K, and a few inches of liquid helium was allowed to collect at the bottom of the dewar but below the coil. The coil was cooled by conduction via copper cooling bars were attached to the coil but also were immersed in the liquid helium at their lower ends. Several current tests were performed on the coil, initially in voltage mode, and one run in current mode. The maximum coil I c at 4.2 K was 480 A, generating 3.06 T at the surface of the coil. The coil met the design targets with a noticeable margin.
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