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The Reduction of the Critical Currents in Nb3Sn Cables under Transverse Loads

Description: The degradation of the critical current of impregnated Rutherford type Nb{sub 3}Sn cables is investigated as a function of the applied transverse load and magnetic field. The cable is made of TWCA modified jelly-roll type strand material and has a keystone angle of 1.0 degree. The voltage-current characteristics are determined for the magnetic field ranging from 2 to 11 tesla and transverse pressure up to 250 MPa on the cable surface. It is found that the 48-strand cable, made of strands with 6 elements in the matrix, shows a larger critical current degradation than the 26-strand cable with 36 elements per strand. The global degradation of the 48-strand cable is 63% at 150 MPa, and 40% at 150 MPa for the 26-strand cable. Micro-analysis of the cross-section shows permanent damage to the sharp edge of the cable. The influence of the keystone angle on the critical-current degradation is currently under investigation.
Date: August 1, 1992
Creator: Van Oort, J.M.; Scanlan, R.M.; Weijers, H.W.; Wessel, S. & Ten Kate, H.H.J.
Partner: UNT Libraries Government Documents Department

A general scaling relation for the critical current density inNb3Sn

Description: We review the scaling relations for the critical currentdensity (Jc) in Nb3Sn wires and include recent findings on the variationof the upper critical field (Hc2) with temperature (T) and A15composition. Measurements of Hc2(T) in inevitably inhomogeneous wires, aswell as analysis of literature results, have shown that all availableHc2(T) data can be accurately described by a single relation from themicroscopic theory. This relation also holds for inhomogeneity averaged,effective, Hc2*(T) results and can be approximated by Hc2(t)=Hc2(0) =1-t1.52, with t = T=Tc.Knowing Hc2*(T) implies that also Jc(T) is known.We highlight deficiencies in the Summers/Ekin relations, which are notable to account for the correct Jc(T) dependence. Available Jc(H) resultsindicate that the magnetic field dependence for all wires from mu0H = 1 Tup to about 80 percent of the maximum Hc2 can be described with Kramer'sflux shear model, if non-linearities in Kramer plots when approaching themaximum Hc2 are attributed to A15 inhomogeneities. The strain (e)dependence is introduced through a temperature and strain dependentHc2*(T,e) and Ginzburg-Landau parameter kappa1(T,e) and a straindependent critical temperature Tc(e). This is more consistent than theusual Ekin unification of strain and temperature dependence, which usestwo separate and different dependencies on Hc2*(T) and Hc2*(e). Using acorrect temperature dependence and accounting for the A15 inhomogeneitiesleads to the remarkable simple relation Jc(H,T,e)=(C/mu0H)s(e)(1-t1.52)(1-t2)h0.5(1-h)2, where C is a constant, s(e)represents the normalized strain dependence of Hc2*(0) andh =H/Hc2*(T,e). Finally, a new relation for s(e) is proposed, which is anasymmetric version of our earlier deviatoric strain model and based onthe first, second and third strain invariants. The new scaling relationsolves a number of much debated issues withrespect to Jc scaling in Nb3Snand is therefore of importance to the applied community, who use scalingrelations to analyze magnet performance from wire results.
Date: May 8, 2006
Creator: Godeke, A.; Haken, B. ten; Kate, H.H.J. ten & Larbalestier, D.C.
Partner: UNT Libraries Government Documents Department

A general scaling relation for the critical current density inNb3Sn

Description: We review the scaling relations for the critical currentdensity (Jc) in Nb3Sn wires and include recent findings on the variationof the upper critical field (Hc2) with temperature (T) and A15composition. Measurements of Hc2(T) in inevitably inhomogeneous wires, aswell as analysis of literature results, have shown that all availableHc2(T) data can be accurately described by a single relation from themicroscopic theory. This relation also holds for inhomogeneity averaged,effective, Hc2*(T) results and can be approximated by Hc2(t)=Hc2(0) =1-t1.52, with t = T=Tc.Knowing Hc2*(T) implies that also Jc(T) is known.We highlight deficiencies in the Summers/Ekin relations, which are notable to account for the correct Jc(T) dependence. Available Jc(H) resultsindicate that the magnetic field dependence for all wires from mu0H = 1 Tup to about 80 percent of the maximum Hc2 can be described with Kramer'sflux shear model, if non-linearities in Kramer plots when approaching themaximum Hc2 are attributed to A15 inhomogeneities. The strain (e)dependence is introduced through a temperature and strain dependentHc2*(T,e) and Ginzburg-Landau parameter kappa1(T,e) and a straindependent critical temperature Tc(e). This is more consistent than theusual Ekin unification of strain and temperature dependence, which usestwo separate and different dependencies on Hc2*(T) and Hc2*(e). Using acorrect temperature dependence and accounting for the A15 inhomogeneitiesleads to the remarkable simple relation Jc(H,T,e)=(C/mu0H)s(e)(1-t1.52)(1-t2)h0.5(1-h)2, where C is a constant, s(e)represents the normalized strain dependence of Hc2*(0) andh =H/Hc2*(T,e). Finally, a new relation for s(e) is proposed, which is anasymmetric version of our earlier deviatoric strain model and based onthe first, second and third strain invariants. The new scaling relationsolves a number of much debated issues withrespect to Jc scaling in Nb3Snand is therefore of importance to the applied community, who use scalingrelations to analyze magnet performance from wire results.
Date: May 8, 2006
Creator: Godeke, A.; Haken, B. ten; Kate, H.H.J. ten & Larbalestier, D.C.
Partner: UNT Libraries Government Documents Department

A Numerical Treatment of the Rf SQUID: II. Noise Temperature

Description: We investigate rf SQUIDs (Superconducting QUantum Interference Devices), coupled to a resonant input circuit, a readout tank circuit and a preamplifier, by numerically solving the corresponding Langevin equations and optimizing model parameters with respect to noise temperature. We also give approximate analytic solutions for the noise temperature, which we reduce to parameters of the SQUID and the tank circuit in the absence of the input circuit. The analytic solutions agree with numerical simulations of the full circuit to within 10%, and are similar to expressions used to calculate the noise temperature of dc SQUIDs. The best device performance is obtained when {beta}{sub L}{prime} {triple_bond} 2{pi}LI{sub 0}/{Phi}{sub 0} is 0.6-0.8; L is the SQUID inductance, I{sub 0} the junction critical current and F{sub 0} the flux quantum. For a tuned input circuit we find an optimal noise temperature T{sub N,opt} {approx} 3Tf/f{sub c}, where T, f and f{sub c} denote temperature, signal frequency and junction characteristic frequency, respectively. This value is only a factor of 2 larger than the optimal noise temperatures obtained by approximate analytic theories carried out previously in the limit {beta}{sub L}{prime} << 1. We study the dependence of the noise temperature on various model parameters, and give examples using realistic device parameters of the extent to which the intrinsic noise temperature can be realized experimentally.
Date: January 15, 2007
Creator: Kleiner, Reinhold; Koelle, Dieter & Clarke, John
Partner: UNT Libraries Government Documents Department

Characterizations of a CERN NbTi Reference Wire at LBNL

Description: We report on the measurement of two NbTi reference samples,obtained from CERN through BNL, wire number02R00056A01UX.265. The purposeof these characterizations is two-fold: 1) To establish aninter-laboratory comparisonof short sample tests and analysis betweenLBNL, BNL and Fermilab within the LARP collaboration. Due to differencesin reaction and mounting procedures and their resulting straindifferences, Nb3Sn is not suited for this purpose. 2) To determine theaccuracy of LBNL's system with regard to magnetic field, temperature andcurrent after a major system overhaul. The results show that at mu0H = 8T, the critical current result falls within the standard deviation of theCERN database, whereas at mu0H = 5 T, it falls outside the CERN standarddeviation, but within the range of critical current values that arereported by CERN for this wire. It is concluded that the LBNL resultsfall within the characterization variance as reported in the CERNdatabase.
Date: February 1, 2007
Creator: Godeke, A.; Dietderich, D.R.; Higley, H.C. & Liggins, N.L.
Partner: UNT Libraries Government Documents Department

Characterization and Coil Test Results for a Multifilamentary NbTi Conductor Utilizing Artificial Pinning Center Technology

Description: The introduction of pinning centers via the controlled addition of a second phase, with the correct size and spacing, has been proposed as a method for producing a material with optimum flux pinning and hence a higher critical current density in practical superconductors. The demonstration of such artificial pinning center (APC) materials has been the aim of recent collaborative efforts with several U.S. manufacturers. This paper reports the coil test results for a multifilamentary NbTi conductor fabricated using an APC technique. The conductor showed improved performance compared to earlier APC conductors, and its performance is comparable to that found in conventional multifilamentary NbTi conductors. In addition to coil test results, the paper will report on the low field magnetization, SEM, and TEM studies, and the results will be compared with similar results on conventional NbTi.
Date: August 1, 1992
Creator: Scanlan, R.M.; Dietderich, D.; Ghiorso, W. & McManaman, P.
Partner: UNT Libraries Government Documents Department

High Critical Current Densities in Nb3Sn Films with Engineered Microstructures--Artifical Pinning Microstructures

Description: Films with layers of Nb, Cu, and Sn have been fabricated to simulate a Nb{sub 3}Sn bronze-type process. These Nb{sub 3}Sn films have produced critical current densities greater than 1 x 10{sup 6} A/cm{sup 2} at 4.2 K and 7.5 T. Niobium films doped with Y, Sc, Dy, Al{sub 2}O{sub 3}, and Ti have been deposited with e-beam co-evaporation onto 75 mm diameter Si wafers with a 100 nm SiO{sub 2} buffer layer. The Nb layer was followed by a layer of Cu and a layer of Sn to complete the bronze-type process. The films with the highest J{sub c} had about 8 vol. % Sc and about 18 vol. % Al{sub 2}O{sub 3}. Characterization of the microstructure by TEM shows that these high J{sub c} films contained high density of inclusions about 5 nm in size and that the grain size of the Nb{sub 3}Sn is about 20-25 nm for samples heat treated at 700 C for up to eight hours.
Date: July 1, 1997
Creator: Dietderich, D.R.; Kelman, M.; Litty, J.R. & Scanlan, R.M.
Partner: UNT Libraries Government Documents Department

Advances in Nb3Sn Performance

Description: Nb{sub 3}Sn wires with non-Cu critical current densities (J{sub c}) that surpass 3 kAmm{sup -2} at 12 T and 4.2 K are commercially available in piece lengths longer than 10 km. Accelerator-type magnets that utilize these conductors have achieved record magnetic fields. This article summarizes key developments in the last decade that have led to these significant improvements in the performance of Nb{sub 3}Sn wires.
Date: May 19, 2008
Creator: Godeke, Arno
Partner: UNT Libraries Government Documents Department

An Improved model for the strain dependence of the superconducting properties of Nb3Sn

Description: We propose an improved model for the strain dependence of the superconducting properties of Nb{sub 3}Sn. The model is based on the three dimensional strain tensor and derived in terms of the first, second and third invariants, and improves an existing model that only includes the second invariant. The axial form of the new model accurately accounts for the experimentally observed dependence of the effective upper critical magnetic field (H*{sub c2}) on axial strain, i.e. a quasi-parabolic strain dependence, asymmetry, and an upturn at large compressive axial strain. An accurate model that accounts for the three dimensional nature of strain is important for scaling relations for the critical current that are used to model magnet performance based on wire measurements.
Date: May 1, 2008
Creator: Arbelaez, D.; Godeke, A. & Prestemon, S. O.
Partner: UNT Libraries Government Documents Department

Interlaboratory Comparisons of NbTi Critical Current Measurements

Description: We report on a multi-institute comparison of critical current data measured on a modern NbTi wire for the Large Hadron Collider (LHC), which has shown a standard deviation below 1% in critical current density spread in more than 1500 measurements. Interlaboratory comparisons on Nb{sub 3}Sn wires have shown ambiguities that could be attributable to strain related differences in critical current density, originating from differences in sample handling, reaction, and mounting techniques, or also to differences in the magnetic field and current calibrations between the institutes. A round robin test of a well characterized NbTi wire provides a baseline variance in critical current results that is presumed to be attributable only to differences in the characterization systems. Systematic differences on the order of 3.5% are found in the comparison. The most likely cause for the observed differences is a small diameter holder that brings the wire into a strain regime in which strain effects can no longer be ignored. A NbTi round robin test, when performed properly, will separate system differences from sample specific differences and provide laboratories with an opportunity to calibrate equipment against a standard measurement.
Date: August 16, 2009
Creator: Godeke, A.; Turrioni, D.; Boutboul, T.; Cheggour, N.; Goodrich, L.F.; Ghosh, A. et al.
Partner: UNT Libraries Government Documents Department

Characterization of Nb3Sn Strand for ITER

Description: We have an ongoing research program for characterization of superconductor composite strands, the principal output of which is sensitive measurements of critical current Ic over a broad range of the essential parameters: longitudinal strain ε, temperature T, and magnetic field B. This features a new apparatus for integrated measurement of Ic(ε,T,B) on the same, long-conductor sample without remounting.
Date: May 3, 2012
Creator: Cheggour, Najib & Goodrich, Loren F.
Partner: UNT Libraries Government Documents Department

Variable-Temperature Critical-Current Measurements

Description: This is the final report of a three year contract that covered 09/19/2005 to 07/14/2008. We requested and received a no cost time extension for the third year, 07/15/2007 to 07/14/2008, to allow DoE to send us funds if they became available during that year. It turned out that we did not receive any funding for the third year. The following paper covers our variable-temperature critical-current measurements. We made transport critical-current (Ic) measurements on commercial multifilamentary Nb3Sn strands at temperatures (T) from 4 to 17 K and magnetic fields (H) from 0 to 14 T. One of the unique features of our measurements is that we can cover a wide range of critical currents from less than 0.1 A to over 700 A.
Date: May 19, 2009
Creator: Goodrich, L. F. & Stauffer, T. C.
Partner: UNT Libraries Government Documents Department

Supercurrents in HgBa{sub 2}CaCu{sub 2}O{sub 6+{delta}} and TlBa{sub 2}CaCu{sub 2}O{sub 7} Epitaxial Thin Films

Description: The availability of high-quality epitaxial thin films of HgBa{sub 2}CaCu{sub 2}O{sub 6+{delta}} (Hg-1212) and TlBa{sub 2}CaCu{sub 2}O{sub 7} (Tl-1212) with high critical current densities (J{sub c}) has made it possible to examine and compare the J{sub c} of these species. Results reveal that the J{sub c} of 1212 species have very similar temperature behavior at low fields, strongly suggesting that the 30-K shift in critical temperature (T{sub c}) induced by the exchange of Hg and Tl in the 1212 structure is due largely to a change in charge carrier density.
Date: August 23, 1999
Creator: Gapud, A.A.; Wu, J.Z.; Fang, L.; Yan, S.L.; Xie, Y.Y.; Siegal, M.P. et al.
Partner: UNT Libraries Government Documents Department

Fault Current Tests of a 5-m HTS Cable

Description: The first industrial demonstration of a three-phase high-temperature superconducting transmission power cable at the Southwire manufacturing complex is in progress. One crucial issue during operation of the 30-m HTS cables is whether they could survive the fault current (which can be over an order of magnitude higher than the operating current) in the event of a short-circuit fault and how HTS cables and the cryogenic system would respond. Simulated fault-current tests were performed at ORNL on a 5-m cable. This single-phase cable was constructed in the same way as the 30-m cables and is also rated for 1250 A at 7.2 kV ac line-to-ground voltage. Tests were performed with fault-current pulses of up to 15 kA (for 0.5 s) with pulse lengths of up to 5 s (at 6.8 kA). Although a large voltage drop was produced across the HTS cable during the fault-current pulse, no significant changes in the coolant temperature, pressure, or joint resistance were observed. The cable survived 15 simulated fault-current shots without any degradation in its V-I characteristics.
Date: February 19, 2001
Creator: Lue, J.W.
Partner: UNT Libraries Government Documents Department

Design of a Probe for Strain Sensitivity Studies of Critical Current Densities in SC Wires and Tapes

Description: The design of a variable-temperature probe used to perform strain sensitivity measurements on LTS wires and HTS wires and tapes is described. The measurements are intended to be performed at liquid helium temperatures (4.2 K). The wire or tape to be measured is wound and soldered on to a helical spring device, which is fixed at one end and subjected to a torque at the free end. The design goal is to be able to achieve {+-} 0.8 % strain in the wire and tape. The probe is designed to carry a current of 2000A.
Date: July 1, 2011
Creator: Dhanaraj, N.; Barzi, E.; Turrioni, D.; Rusy, A.; Lombardo, V. & /Fermilab
Partner: UNT Libraries Government Documents Department

Transport and Magnetization Properties of rolled RRP Nb3Sn Strands.

Description: Restack Rod Process (RRP) strands with 54 and 108 sub-elements were rolled from 0.7 mm diameter to 0.45 mm thickness to simulate the deformation of strands at the edges of Rutherford cables. Various diagnoses were then applied to assess performance and stability. Transport measurements were used to assess the effect of rolling on the critical current. Magnetization measurements were used to probe superconducting pathway bridging between deformed sub-elements. The copper residual resistivity ratio RRR was also measured to assess tin contamination due to thinned or ruptured diffusion barriers. While systematic changes were observed in all three measurements with increasing deformation, RRR showed the strongest changes. The implications of these measurements for cable stability, and their relationship to observations of the strand cross-section by light microscopy, are discussed.
Date: August 27, 2007
Creator: Ghosh,A.K.; Cooley, L.D.; Dietderich, D.R. & Sun, L.
Partner: UNT Libraries Government Documents Department

A Numerical Treatment of the Rf SQUID: I. General Properties andNoise Energy

Description: We investigate the characteristics and noise performance of rf Superconducting Quantum Interference Devices (SQUIDs) by solving the corresponding Langevin equations numerically and optimizing the model parameters with respect to noise energy. After introducing the basic concepts of the numerical simulations, we give a detailed discussion of the performance of the SQUID as a function of all relevant parameters. The best performance is obtained in the crossover region between the dispersive and dissipative regimes, characterized by an inductance parameter {beta}{prime}{sub L} {triple_bond} 2{pi}LI{sub 0}/{Phi}{sub 0} {approx} 1; L is the loop inductance, I{sub 0} the critical current of the Josephson junction, and {phi}{sub 0} the flux quantum. In this regime, which is not well explored by previous analytical approaches, the lowest (intrinsic) values of noise energy are a factor of about 2 above previous estimates based on analytical approaches. However, several other analytical predictions, such as the inverse proportionality of the noise energy on the tank circuit quality factor and the square of the coupling coefficient between the tank circuit and the SQUID loop, could not be well reproduced. The optimized intrinsic noise energy of the rf SQUID is superior to that of the dc SQUID at all temperatures. Although for technologically achievable parameters this advantage shrinks, particularly at low thermal fluctuation levels, we give an example for realistic parameters that leads to a noise energy comparable to that of the dc SQUID even in this regime.
Date: January 15, 2007
Creator: Kleiner, Reinhold; Koelle, Dieter & Clarke, John
Partner: UNT Libraries Government Documents Department

Operational Characteristics, parameters, and history of a 13T Nb3Sn dipole

Description: The early design and test results have been previously reported. During the subsequent operation of 'D20' the accelerator prototype dipole has provided both additional and more detailed data as to its characteristics and performance. D20's use as a test facility for high field critical current measurements has provided operational experience and history pertammg to accelerator required characteristics. There has been recently obtained data related to field quality, operational reproducibility and reliability, which will be presented. This prototype 'D20' has attained the highest magnetic field of any accelerator prototype dipole constructed and tested to date. The magnet has continued to operate routinely.
Date: March 18, 1999
Creator: Benjegerdes, R.; Bish, P.; Caspi, S.; Chow, K.; Dietderich, D.; Hannaford, R. et al.
Partner: UNT Libraries Government Documents Department

Nb3Sn Artificial Pinning Microstructures

Description: Extension of the APC approach to Nb{sub 3}Sn requires that a second phae be incorporated into the Nb{sub 3}Sn layer. The second phase would increase pinning strength by either reducing the grain size or by the second phase pinning the flux itwelf. The following criteria for elements to be candidates for the APC approach are: (1) they must form intermetallic compounds with Cu or Sn and (2) they must have negligible solubility in Cu and Nb or they must be strong oxide formers. many of the rare earth elements satisfy these criteria. To circumvent the large strains required to produce wires with a fine distribution of the second phase, film deposition techniques have been used. Critical current densities for Nb films doped with Ti and Y are about 4,000 A/mm{sup 2} at 6T and 4.2 K.
Date: December 12, 1996
Creator: Dietderich, D.R. & Scanlan, R.M.
Partner: UNT Libraries Government Documents Department

Development of Superconducting Strang and Cable with Improved Properties for Use in SSC Magnets

Description: The critical current requirement for the NbTi superconductor strand was set at 2750 A/mm{sup 2} (5 T, 4.2 K) in the SSC Conceptual Design, compared with a value of 1800 A/mm{sup 2} which was specified for the strand used in the Tevatron dipoles. In addition, a filament diameter of 5 {micro}m, instead of the 9 {micro}m diameter used in the Tevatron. was chosen to reduce field distonion at injection. In order to meet the requirements for field homogeneity, the dimensional requirements for both strand and cable were also tightened. The technical solutions employed to achieve these improved properties and the resulting specifications will be discussed.
Date: February 1, 1989
Creator: Scanlan, R. M.
Partner: UNT Libraries Government Documents Department

Fabrication and Test Results for Rutherford-Type Cables Made from BSCCO Strands

Description: Wires based on the Bi-2212 HTS superconductor are becoming available commercially, with current densities that are attractive for some applications. We report here on our success in using these Bi-2212 wires to fabricate multistrand, kiloamp conductors that can be used to construct dipole and quadrupole magnets for particle accelerator applications. Multistrand cables have been made from several types of Bi-2212 wire supplied by two manufacturers. These cables were made with cores of various compositions and dimensions in order to optimize the fabrication process. In addition, cables have been made from aspected strands as well as round strands. Cable critical currents will be reported and compared for the various cable parameters investigated in this study.
Date: September 1, 1998
Creator: Scanlan, R.M.; Dietderich, D.R.; Higley, H.C.; Marken, K.R.; Motowidlo, L.R.; Solokowski, R. et al.
Partner: UNT Libraries Government Documents Department

Fabrication and testing of Rutherford-type cables for react and wind accelerator magnets

Description: A common coil design for a high-field accelerator dipole magnet using a Nb{sub 3}Sn cable with the React-and-Wind approach is pursued by a collaboration between Fermilab and LBNL. The design requirements for the cable include a high operating current so that a field of 10-11 T can be produced, together with a low critical current degradation due to bending around a 90 mm radius. A program, using ITER strands of the internal tin type, was launched to develop the optimal cable design for React-and-Wind common coil magnets. Three prototype cable designs, all 15 mill wide, were fabricated: a 41-strand cable with 0.7 mm diameter strands; a 57-strand cable with 0.5 mm diameter strands; and a 259 strand multi-level cable with a 6-around-1 sub-element using 0.3 mm diameter wire. Two versions of these cables were fabricated: one with no core and one with a stainless steel core. Additionally, the possibility of a wide (22 mm) cable made from 0.7 mm strand was explored. This paper describes the first results of the cable program including reports on cable fabrication and reaction, first winding tests and first results of the measurement of the critical current degradation due to cabling and bending.
Date: September 11, 2000
Creator: Bauer, P.; Ambrosio, G.; Andreev, N.; Barzi, E.; Dietderich, D.; Ewald, K. et al.
Partner: UNT Libraries Government Documents Department

Critical Current of Superconducting Rutherford Cable in High Magnetic Fields with Transverse Pressure

Description: For high energy physics applications superconducting cables are subjected to large stresses and high magnetic fields during service. It is essential to know how these cables perform in these operating conditions. A loading fixture capable of applying loads of up to 700 kN has been developed by NHMFL for LBNL. This fixture permits uniform loading of straight cables over a 122 mm length in a split-pair solenoid in fields up to 12 T at 4.2 K. The first results from this system for Rutherford cables of internal-tin and modified jelly roll strand of Nb{sub 3}Sn produced by IGC and TWC showed that little permanent degradation occurs up to 210 MPa. However, the cable made from internal-tin strand showed a 40% reduction in K{sub c} at 11T and 210 MPa while a dable made from modified jelly roll material showed only a 15% reduction in I{sub c} at 11T and 185 MPa.
Date: September 1, 1998
Creator: Dietderich, D.R.; Scanlan, R.M.; Walsh, R.P. & Miller, J.R.
Partner: UNT Libraries Government Documents Department