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Characterization of superconductors with artificial pinning microstructures

Description: Extension of the APC approach to Nb{sub 3}Sn requires that a second phase be introduced into the Nb{sub 3}S reaction layer with the intent of increasing the volume pinning strength. This can be achieved by either the refinement of the Nb{sub 3}S grains due to the presence of a second phase or by the second phase itself pinning flux. If a bronze-type process is to be used a different addition than Zr is required since internal oxidation of Nb is not possible. The criteria for elements to be candidates for the APC approach are discussed. The results for one of the candidates (Ag) show that it is not incorporated into the Nb{sub 3}S, however, its addition did increase the growth rate.
Date: October 1, 1994
Creator: Dietderich, D.R. & Scanlan, R.M.
Partner: UNT Libraries Government Documents Department

Characterization of Nb-Ti superconductors with artificial pinning structures

Description: A series of multifilamentary APC Nb-Ti superconductors have been made with Nb added as a normal second phase to provide flux pinning centers. Two compositions, 12.5% vol % and 25 vol % Nb in Nb-Ti, have fabricated into multifilamentary composites using two different fabrication methods. One method used hot isostatic compaction and hot extrusion thoughout the processing. The other method (bundle-and-draw process) discontinued all hot processing at an intermediate level. While the J{sub c} values of the bundle-and-draw wires are quite promising, the critical current of the extruded wires appears to be limited by poor uniformity of the filament cross-sectional area along the conductor length. The large values of the index of the resistive transition and small filament standard-deviation-to-average area ratios observed in the wires produced by the bundle-and-draw process suggest extrinsic factors have little effect on J{sub c}. The variation in J{sub c} as the wire diameter is reduced appears to be most strongly affected by intrinsic factors: Nb distribution and pinning strength. The final filament microstructure and Nb spacing are shown to be difficult to calculate, e.g., the mean Nb spacing near the final wire size may be {1/2} to 1/3 that of the calculated value. 5 refs., 5 figs.
Date: June 1, 1990
Creator: Dietderich, D.R. & Scanlan, R.M.
Partner: UNT Libraries Government Documents Department

Research on the monolithic process of making A-15 superconducting materials

Description: It is possible to produce high T/sub c/ wires or tapes from the V-Ga system by a monolithic process in which an ingot is cast as a supersaturated solution of V and Ga, homogenized at elevated temperature, quenched to preserve the supersaturation, formed into a wire or tape, and finally heat treated at a relatively low temperature to precipitate the superconducting phase. To achieve exceptionally high critical temperatures, the precipitation reaction must be carried out at temperatures below approximately 750/sup 0/C. The measured critical temperature then becomes a function of the aging time, and reaches a maximum value as high as 14.8/sup 0/K in alloys containing 17 to 19 at. % Ga. The reason for the exceptionally high critical temperature when the precipitation is carried out at lower aging temperatures is not established, but may be plausibly interpreted as due to a thermodynamic tendency for small precipitates formed from highly supersaturated solid solutions to be rich in solute content.
Date: August 1, 1979
Creator: Hong, M.; Dietderich, D. & Morris, J.W. Jr.
Partner: UNT Libraries Government Documents Department

A new generation Nb3Sn wire, and the prospects for its use inparticle accelerators

Description: The US DOE has initiated a Conductor Development Program aimed at demonstrating a high current density, cost effective Nb3Sn conductor for use in accelerator magnets. The first goal, an increase in current density by 50%, has been achieved in a practical conductor. The program is focused at present on achieving the second goal of reduced losses. The different approaches for achieving these goals will be discussed, and the status will be presented. Magnet technology R&D has been proceeding in parallel with the conductor development efforts, and these two technologies are reaching the level required for the next step--introduction into operating accelerator magnets. An obvious point for introducing this technology is the LHC interaction region magnets, which require large apertures and high fields (or high field gradients). By upgrading the interaction region magnets, machine performance can be enhanced significantly without replacing the arc magnets, which represent most of the cost of an accelerator. Design requirements generated by recent studies and workshops will be reviewed, and a roadmap for the development of the next-generation interaction region magnets will be presented.
Date: September 30, 2003
Creator: Scanlan, R.M.; Dietderich, D.R. & Gourlay, S.A.
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

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

Conductor Development for High Field Dipole Magnets

Description: Historically, improvements in dipole magnet performance have been paced by improvements in the superconductor available for use in these magnets. The critical conductor performance parameters for dipole magnets include current density, piece length, effective filament size, and cost. Each of these parameters is important for efficient, cost effective dipoles, with critical current density being perhaps the most important. Several promising magnet designs for the next hadron collider or a muon collider require fields of 12 T or higber, i.e. beyond the reach of NbTi. The conductor options include Nb{sub 3}Sn, Nb{sub 3}Al, or the high temperature superconductors. Although these conductors have the potential to provide the combination of performance and cost required, none of them have been developed sufficiently at this point to satisfy all the requirements. This paper will review the status of each class of advanced conductor and discuss the remaining problems that require solutions before these new conductors can be considered as practical. In particular, the plans for a new program to develop Nb{sub 3}Sn and Nb{sub 3}Al conductors for high energy physics applications will be presented. Also, the development of a multikiloamp Bi-2212 cable for dipole magnet applications will be reported.
Date: March 1, 2000
Creator: Scanlan, R.M.; Dietderich, D.R. & Higley, H.C.
Partner: UNT Libraries Government Documents Department

Development of cost-effective Nb3Sn conductors for the next generation hadron colliders

Description: Significant progress has been made in demonstrating that reliable, efficient high field dipole magnets can be made with Nb{sub 3}Sn superconductors. A key factor in determining whether these magnets will be a cost-effective solution for the next generation hadron collider is the conductor cost. Consequently, DOE initiated a conductor development program to demonstrate that Nb{sub 3}Sn can be improved to reach a cost/performance value of $1.50/kA-m at 12T, 4.2K. The first phase of this program was initiated in Jan 2000, with the goal of improving the key properties of interest for accelerator dipole magnets--high critical current density and low magnetization. New world record critical current densities have been reported recently, and it appears that significant potential exists for further improvement. Although new techniques for compensating for magnetization effects have reduced the requirements somewhat, techniques for lowering the effective filament size while maintaining these high Jc values are a program priority. The next phase of this program is focused on reducing the conductor cost through substitution of lower cost raw materials and through process improvements. The cost drivers for materials and fabrication have been identified, and projects are being initiated to demonstrate cost reductions.
Date: April 12, 2001
Creator: Scanlan, R.M.; Dietderich, D.R. & Zeitlin, B.A.
Partner: UNT Libraries Government Documents Department

Influence of microstructure on the properties of bronze-processed multifilamentary wire

Description: The A15 layer of a commercial Airco wire containing 2869 Nb filaments was analyzed as a function of heat treatment. Its microstructure is composed of three morphologically concentric shells. The central shell consists of fine equiaxed grains and has a nearly stoichiometric Sn concentration. High resolution electron microscopic analysis suggests that the fine grains are formed through the polygonization of dislocations. The homogeneous composition through the fine-grained layer is a probable consequence of the small grain size, which permits relatively rapid chemical redistributions through grain boundary diffusion. In contrast, the chemical gradient in the large-grained inner and outer sheels is steep. The microstructure is established by the reaction heat treatment, and determines the critical current. The best combination of grain size, composition, and volume of the fine-grained shell is obtained with an intermediate reaction temperature (700 to 730/sup 0/C); this temperature range also yields the best values of J/sub c/. Various two-step heat treatments were studied and compared to isothermal aging. The best microstructure and, hence, the best critical current characteristic was obtained by aging the specimen at 700/sup 0/C for 4 days followed by 730/sup 0/ for 2 days.
Date: May 1, 1983
Creator: Wu, I.W.; Dietderich, D.R.; Hassenzahl, W.V. & Morris, J.W. Jr.
Partner: UNT Libraries Government Documents Department

Microstructure and properties of A15 superconductors formed by direct precipitation

Description: Superconducting materials were made by quenching supersaturated solutions of V-Ga and Nb-Al, deforming the quenched specimens, and then precipitating the A15 phase by aging at intermediate temperature. The critical current characteristics of the product materials depend both on the inherent properties of the A15 phase, which presumably reflect its composition, and on the details of the precipitation process, which determine the grain size, continuity, and volume fraction of the A15. These features of the precipitation process differ qualitatively between V-Ga and Nb-Al. They are described and used to interpret the critical current characteristics.
Date: September 1, 1980
Creator: Hong, M.; Dietderich, D.R.; Wu, I.W. & Morris, J.W. Jr.
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

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

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

Design issues for cryogenic cooling of short periodsuperconducting undulators

Description: Superconducting insertion devices, which produce periodic magnetic fields, have been built and installed in a number of synchrotron-light source storage-rings. For the most part, these devices have been wigglers, which have relatively long period lengths. This report concerns itself with the special cryogenic issues associated with short period undulators. The motivation for considering the incorporation of superconducting technology in insertion device designs is to achieve higher magnetic fields than can be achieved with more conventional permanent magnet technology. Since the peak field decreases sharply with increased magnet gap to period ratio, the cryogenic design of the magnet system is crucial. In particular, the insulation required for a warm vacuum bore device is impractical for short period undulators. This report describes the issues that are related to a cold bore ({approx}4 K) and an intermediate temperature bore (30 to 70 K) designs. The criteria for the use of small cryocoolers for cooling a short period undulator are presented. The problems associated with connecting small coolers to an undulator at 4.2 K are discussed.
Date: September 15, 2003
Creator: Green, M.A.; Dietderich, D.R.; Marks, S.; Prestemon, S.O. & Schlueter, R.D.
Partner: UNT Libraries Government Documents Department

Characterization of High Current RRP(R) Wires as a Function of Magnetic Field, Temperature and Strain

Description: A new instrument for the characterization of superconducting materials as a function of Magnetic Field, Temperature and Strain, was designed, constructed and tested at Lawrence Berkeley National Laboratory (LBNL). A U-shaped bending spring was selected, since that design has proven to enable accurate characterizations of a multitude of superconducting materials for more than a decade. The new device is validated though measurements on very high current Rod Restack Processed (RRP) Internal-Tin (IT) wires, for which we will present initial results, including parameterizations of the superconducting phase boundaries and comparisons with other wire types. Accurate parametrization of modern high magnetic field conductors is important for the analysis of the performance of magnet systems.
Date: August 16, 2009
Creator: Godeke, A.; Mentink, M.G.T.; Dietderich, D. R. & den Ouden, A.
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

Limits of NbTi and Nb3Sn, and Development of W&R Bi-2212 HighField Accelerator Magnets

Description: NbTi accelerator dipoles are limited to magnetic fields (H)of about 10 T, due to an intrinsic upper critical field(Hc2) limitationof 14 T. To surpass this restriction, prototype Nb3Sn magnets are beingdeveloped which have reached 16 T. We show that Nb3Sn dipole technologyis practically limited to 17 to 18 T due to insufficient high fieldpinning, and intrinsically to 20 to 22 T due to Hc2 limitations.Therefore, to obtain magnetic fields approaching 20 T and higher, amaterial is required with a higher Hc2 and sufficient high field pinningcapacity. A realistic candidate for this purpose is Bi-2212, which isavailable in roundwires and sufficient lengths for the fabrication ofcoils based on Rutherford-type cables. We initiated a program to developthe required technology to construct accelerator magnets from'windand-react' (W&R) Bi-2212 coils. We outline the complicationsthat arise through the use of Bi-2212, describe the development paths toaddress these issues, and conclude with the design of W&R Bi-2212sub-scale magnets.
Date: December 1, 2006
Creator: Godeke, A.; Cheng, D.; Dietderich, D.R.; Ferracin, P.; Prestemon,S.O.; Sabbi, G. et al.
Partner: UNT Libraries Government Documents Department

Limits of NbTi and Nb3Sn, and Development of W&R Bi-2212 HighField Accelerator Magnets

Description: NbTi accelerator dipoles are limited to magneticfields (H)of about 10 T, due to an intrinsic upper critical field (Hc2) limitationof 14 T. To surpass this restriction, prototype Nb3Sn magnets are beingdeveloped which have reached 16 T. We show that Nb3Sn dipole technologyis practically limited to 17 to 18 T due to insufficient high fieldpinning, and intrinsically to 20 to 22 T due to Hc2 limitations.Therefore, to obtain magnetic fields approaching 20 T and higher, amaterial is required with a higher Hc2 and sufficient high field pinningcapacity. A realistic candidate for this purpose is Bi-2212, which isavailable in roundwires and sufficient lengths for the fabrication ofcoils based on Rutherford-type cables. We initiated a program to developthe required technology to construct accelerator magnets from'windand-react' (W&R) Bi-2212 coils. We outline the complicationsthat arise through the use of Bi-2212, describe the development paths toaddress these issues, and conclude with the design of W&R Bi-2212sub-scale magnets.
Date: September 1, 2006
Creator: Godeke, A.; Cheng, D.; Dietderich, D.R.; Ferracin, P.; Prestemon,S.O.; Sa bbi, G. et al.
Partner: UNT Libraries Government Documents Department

A High Field Magnet Design for A Future Hadron Collider

Description: US high energy physics community is exploring the possibilities of building a Very Large Hadron Collider (VLHC) after the completion of LHC. This paper presents a high field magnet design option based on Nb{sub 3}Sn technology. A preliminary magnetic and mechanical design of a 14-16 T, 2-in-1 dipole based on the 'common coil design' approach is presented. The computer code ROXIE has been upgraded to perform the field quality optimization of magnets based on the racetrack coil geometry. A magnet R&D program to investigate the issues related to high field magnet designs is also outlined.
Date: September 1, 1998
Creator: Gupta, R.; Chow, K.; Dietderich, D.; Gourlay, S.; Millos, G.; McInturff, A. et al.
Partner: UNT Libraries Government Documents Department

Test of a NbTi Superconducting Quadrupole Magnet Based on Alternating Helical Windings

Description: It has been shown that by superposing two solenoid-like thin windings, that are oppositely skewed (tilted) with respect to the bore axis, the combined current density on the surface is cos({theta})-like and the resulting magnetic field in the bore is a pure dipole field. Following a previous test of such a superconducting dipole magnet, a quadrupole magnet was designed and built using similar principles. This paper describes the design, construction and test of a 75 mm bore 600 mm long superconducting quadrupole made with NbTi wire. The simplicity of the design, void of typical wedges, end-spacers and coil assembly, is especially suitable for future high field insert coils using Nb{sub 3}Sn as well as HTS wires. The 3 mm thick coil reached 46 T/m but did not achieve its current plateau.
Date: August 16, 2009
Creator: Caspi, S.; Trillaud, F.; Godeke, A.; Dietderich, D.; Ferracin, P.; Sabbi, G. et al.
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

Numerical Investigation of the Quench Behavior of Bi2Sr2CaCu2Ox Wire

Description: The quench behavior of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi2212) wire is investigated through numerical simulations. This work is part of the U.S. Very High Field Superconducting Magnet Collaboration (VHFSMC). Numerical simulations are carried out using a one-dimensional computational model of thermal transport in Bi2212 composite wires. A quench is simulated by introducing heat in a section of the wire, and the voltage and temperature are monitored as function of time and position. The quench energy, normal zone propagation velocity, and spatial distribution of temperature are calculated for varying transport current and applied magnetic field. The relevance of these simulations in defining criteria for experimental measurements is discussed.
Date: August 1, 2010
Creator: Arbelaez, D.; Prestemon, S. O.; Dietderich, D. R.; Godeke, A.; Ye, L.; Hunte, F. et al.
Partner: UNT Libraries Government Documents Department

Introduction of Nonlinear Properties Into Hierachical Models of Nb3Sn Strands

Description: The development of computational models representing Rutherford cable formation and deformation is necessary to investigate the strain state in the superconducting filaments in Nb{sub 3}Sn magnets. The wide variety of length scales within accelerator magnets suggests usage of a hierarchical structure within the model. As part of an ongoing investigation at LBNL, a three-dimensional simplified nonlinear multiscale model is developed as a way to extend previous linear elastic versions. The inclusion of plasticity models into the problem formulation allows an improved representation of strand behavior compared to the linear elastic model. This formulation is applied to a single Nb{sub 3}Sn strand to find its effective properties as well as the strain state in the conductor under loading.
Date: August 1, 2010
Creator: Collins, B.; Krishnan, J.; Arbelaez, D.; Ferracin, P.; Prestemon, S. O.; Godeke, A. et al.
Partner: UNT Libraries Government Documents Department

Mechanical design of a high field common coil magnet

Description: A common coil design for high field 2-in-1 accelerator magnets has been previously presented as a 'conductor-friendly' option for high field magnets applicable for a Very Large Hadron Collider. This paper presents the mechanical design for a 14 tesla 2-in-1 dipole based on the common coil design approach. The magnet will use a high current density Nb{sub 3}Sn conductor. The design addresses mechanical issues particular to the common coil geometry: horizontal support against coil edges, vertical preload on coil faces, end loading and support, and coil stresses and strains. The magnet is the second in a series of racetrack coil magnets that will provide experimental verification of the common coil design approach.
Date: March 18, 1999
Creator: Caspi, S.; Chow, K.; Dietderich, D.; Gourlay, S.; Gupta, R.; McInturff, A. et al.
Partner: UNT Libraries Government Documents Department