Nb3Sn research and development in the USA – Wires and cables

We have developed HTS cables using Bi-2212 round wires, which have high mechanical strength and an average J/sub c/ of 200 kA/cm/sup 2/ at 4.2 K in self-field. Four designs of cables were fabricated in this work and those tables could carry I/sub c/ values from 1 kA to 10 kA at 4.2 K and self-field depending on the number of strands. A 70m-long 20-strand Rutherford cable was successfully manufactured. Optimization of heat treatment conditions was effective to reduce I/sub c/ degradation observed in the case of heat treatment with a long length. I/sub c/ values of a Rutherford cable were measured under loading at 4.2 K in 4 T. The critical values of the stress on face loading and edge loading were 60 MPa and 100 MPa, respectively. We successfully obtained high J/sub c/ value of 500 kA/cm/sup 2/, which was almost double that of the conventional wires capitalize "Rutherford".

Improvement of superconducting properties of Bi-2212 round wire and primary test results of large capacity Rutherford cable

https://escholarship.org/content/qt0x94t5jb/qt0x94t5jb.pdf

State of the art powder-in-tube niobium–tin superconductors

In order to provide a cost effective high field magnet option for the next generation HEP accelerator, higher performance Nb/sub 3/Sn superconductor is required. These requirements have been recognized by the DOE, and a conductor development program has been initiated. The goal is to produce cost-effective conductor with a Jc (noncopper, 12 T, 4.2 K) exceeding 3000 A/mm/sup 2/ and an effective filament size of less than 40 micrometers. Although the Nb/sub 3/Sn conductors manufactured at present have produced Jc values in excess of 2200 A/mm/sup 2/, no conductor being manufactured at present can achieve both the aggressive Jc and effective filament size goals. The first phase of the present program is underway, and is focused on improving the understanding of the factors that control Jc. Samples are being manufactured by industry and are being characterized with respect to Jc and magnetization as a function of composition and heat treatment condition. Using this new knowledge as a base, the program will move into a fabrication scale-up phase where the performance and cost-effectiveness can be demonstrated on production size quantities. The status and accomplishments of this program are reviewed, and the plans for the scale-up program are presented.

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Conductor development for high energy physics-plans and status of the US program

The Superconducting Magnet Group at Lawrence Berkeley National Laboratory has been developing the technology for using brittle superconductor in high-field accelerator magnets. HD1, the latest in a series of magnets, contains two, double-layer Nb/sub 3/Sn flat racetrack coils. This single-bore dipole configuration, using the highest performance conductor available, was designed and assembled for a 16 tesla conductor/structure/pre-stress proof-of-principle. With the combination of brittle conductor and high Lorentz stress, considerable care was taken to predict the magnet's mechanical responses to pre-stress, cool-down, and excitation. Subsequent cold testing satisfied expectations: Training started at 13.6 T, 83% of "short-sample", achieved 90% in 10 quenches, and reached its peak bore field (16 T) after 19 quenches. The average plateau,/spl sim/92% of "short-sample", appeared to be limited by "stick-slip" conductor motions, consistent with the 16.2 T conductor "lift-off" pre-stress that was chosen for this first test. Some lessons learned and some implications for future conductor and magnet technology development are presented and discussed.

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Test results for HD1, a 16 tesla Nb/sub 3/Sn dipole magnet

ASC'98 Palm September 14- 18, 1998 D~~!i11JG L8/11- Jt: fj.:2/hF be:;}'! Critical Current of Superconducting Rutherford Cable in High Magnetic Fields with Transverse Pressure Daniel R. Dietderich and Ronald M. Scanlan, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Robert P. Walsh and John R. Miller National High Magneti c Field Laboratory, Tallahassee, FL 32706 Abstract-For high energy physics appli cations supereon· dueting 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 700kN has been developed by NHMFL for LBNL. This fixture permits uniform loading of straight cables over a 122 nun length in a split-pair solenoid in field s 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,Sn produced by IGC and TWC showed that lillie permanent degradation occurs up to 210 MPa. However, the cable made from internal· tin s't rand showed a 40 % reduction in at lIT and 210 MPa while a cable made from modified jelly roll material showed onJy a 15 % reduction in Ie at liT and 185 MP•. I. INTRODUCTION Large forces are produced when superconducting magnets are ene rgized . Therefore, it is necessary to support the conductor to prevent large displacements that can strain the conductor beyond its elastic limit. These same forces also reduce the critical current of the conductor before the elastic limit is reached. To produce an optimum magnet design which best utilizes the superconductor material and maximizes the field the critical current variation with pressure is required. For a cosine 0 magnet design large pressures are produced at the mid-plane of the magnet on the large face of the Rutherford cable. The magnets (i.e. common coil) presently being designed and built in the Superconducting Magnet Group (SMG) of Lawrence Berkeley National Laboratory such that the cable will be bi-axially loaded on both the face and the edge with the edge loading being about twice that applied to the face. Therefore information for loading in both orientations is required. The results presented here are the first measurements performed at the National High Magnetic Field Laboratory (NHMFL) in a system designed for the SMG. These tests were performed on cable designed for and used in the inner coi ls ofthc world record dipole magnet D20 [I]. Manu sc ript received September 14, 1998. Thi s work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, High Energy Physics Division, U. S. Department of Energy, under Contrac t No. DE-AC03-6SFOOO98 . These cables were fabricated in our Group from modified jelly roll wire produced by Teledyne Wah Chang (TWC) and from internal tin wire manufactured by Intermagnetics General Corporation (IGC). The results for both cables showed that very little if any permanent degradation occurred for transverse loads up to 185 to 210 MPa. However, the critical current of the cable with IGC strand was reduced by 40 % with a transverse pressure of 210 MPa at II T. ·The I, of the cable with TWC strand was only reduced by 15 % at II T and 185 MPa. The behavior of both cables with loading was also different. The TWC strand showed a quadratic behavior with increasing press ure while the IGC strand showed a linear behavior. These results have important ramifications for high field magnet designs beyond the 13.5 T of D20. Not only must the strain level be controlled to prevent irreversible damage at these hi gher field s but the reduction in critical current due to the lower T, and B with high pressure must be controlled. II. MATERIALS AN D TEST SYSTEM A. Strand and Cable Characteristics Two strands made by two manufacturers were used jn the Rutherford cables of this study. Cable 523 was made from IGC strand while cable 522 was made from TWC strand. Each cable was rectangular and contained 37 strands. The cabling parameters are listed in Table I. Strand specifications are given in Table II. The two strands had very different internal geometries. The TWC strand had more Cu stabili zer and each of its 120 sub·e1ements had its own diffusion barrier. (Fig. I (a» The IGC strand had less Cu stabilizer and a diffusion barrier around all of its 19 sub· elements (Fig. I (b». Both cables were hea t treated at the same time and received the following schedule: 210 °C for 121 h, 340 °C for 60 h, and 660 °C for 259 h. For heat treatment the samples were sealed in a stainless steel retort that was continuously purged with fl owing argon. The data has not been corrected for self· field but due to the bifilar nature of the test arrangement the correction s h o ~ld be small.

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D.R. Dietderich

Papers

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