W. Hassenzahl

The critical current density and microstructural state of an internal tin multifilamentary superconducting wire

The critical current density (J c ) of internal tin wires is increased when low-temperature diffusion heat treatments are performed prior to a high temperature reaction. To determine the variation of J c with pre-reaction heat treatments a copper-stabilized IGC internal tin wire with an outside diameter of 0.267mm was studied. The wire has 2 to 2.5 μm diameter filaments, and within the Ta barrier, the area ratio of the copper matrix and Sn core to Nb is about 2.2. Due to the character of the Cu-Sn phase diagram, heat treatments at a series of temperatures below the Nb 3 Sn reaction temperature affect the local Sn concentration in the matrix about the Nb filaments. The variation in J c resulting from these heat treatments is a consequence of the microstructural state of the conductor and the morphology of the Nb 3 Sn layer produced. The results of this work show that the internal tin and bronze-processed wires have different J c (H) characteristics. The two processes have comparable critical currents at high fields, suggesting the same H c2 , while at low fields the internal tin wire is superior, suggesting a better grain morphology.

The influence of magnesium addition to the bronze on the critical current of bronze-processed multifilamentary Nb 3 Sn

Results show that Mg may be used to improve J/sub c/ in multifilamentary wire, and that the increase is large (60 to 100%). Chemical analysis reveals that the Mg segregates to the reacted layer, and resides principally in the bulk Nb/sub 3/Sn. The microstructural analyses suggest that its principal effect is to suppress coarsening of the Nb/sub 3/Sn grains and establish a uniformly grained layer. Preliminary data also suggests that Mg decreases the minimum Nb/sub 3/Sn grainsize and improves the overall stoichiometry of the reacted layer. The samples used had very high bronze to Nb ratios (R). Since the increase in J/sub c/ apparently depends on the concentration of Mg in the reacted layer, and since virtually all the Mg accumulates there, it may prove difficult to achieve comparable results at lower R values without substantially raising the Mg content of the bronze, or changing to an external bronze process. 6 figures.

Full length prototype SSC dipole test results

Results are presented from tests of the first full length prototype SSC dipole magnet. The cryogenic behavior of the magnet during a slow cooldown to 4.5K and a slow warmup to room temperature has been measured. Magnetic field quality was measured at currents up to 2000 A. Averaged over the body field all harmonics with the exception of b 2 and b 8 are at or within the tolerances specified by the SSC Central Design Group. (The values of b 2 and b 8 result from known design and construction defects which will be corrected in later magnets.) Using an NMR probe the average body field strength is measured to be 10.283 G/A with point to point variations on the order of one part in 1000. Data are presented on quench behavior of the magnet up to 3500 A (approximately 55% of full field) including longitudinal and transverse velocities for the first 250 msec of the quench.

Design of epoxy-free superconducting dipole magnets and performance in both Helium I and pressurized Helium II

LBL-12455 | H 1 Lawrence Berkeley Laboratory K J UNIVERSITY OF CALIFORNIA Accelerator & Fusion Research Division P r e s e n t e d a t t h e V l l t h I n t e r n a t i o n a l Conference on Magnet Technology, K a r l s r u h e , Germany, March 3 0 - A p r l l 3 , 1981 DESIGN OF EPOXY-FREE SUPERCONDUCTING DIPOLE MAGNETS AND PERFORMANCE IN BOTH HELIUM I AND PRESSURIZED HELIUM II C. Taylor, R. Althaus, S. Caspi, W. Gilbert, W. Hassenzahl, R. Meuser, J. Rechen, and R. Warren March 1S81 H T B n W O T I M » K T IS UIUMIIHI S m i a F H S Prepared for the U.S. Department ot Energy under Contract W-7405-ENG-48

LARGE SCALE SUPERFLUID PRACTICE

Since 1979 Lawrence Berkeley Laboratory has been testing superconducting magnets in He II. The 1 atm pressure, 1.8 K, He II, test facility, is an integral part of the LBL Research and Development program on high field superconducting dipole magnets for particle accelerators. Some of the experience gained in this facility and the details of its operation are reported.

Design of a 10-T superconducting dipole magnet using niobium-tin conductor

LBL-14434 Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA I • Accelerator & Fusion Research Division Presented at the 1982 Applied Superconductivity Conference, Knoxville, TN, November 28-December 3, 1982; and to be published in the Proceedings DESIGN OF A 10-T SUPERCONDUCTING DIPOLE MAGNET USING NIOBIUM-TIN CONDUCTOR C. Taylor, R. Meuser, S. Caspi, W. Gilbert, W. Hassenzahl, C. Peters, R. Schafer, and R. Wolgast November 1982 Prepared for the U.S. Department of Energy under Contract DE-AC03-76SF00098

Multifilamentary Nb-Nb 3 Sn composite by liquid infiltration method: Superconducting, metallurgical, and mechanical properties

A rapid solid-liquid reaction mechanism has been used to form A15 Nb 3 Sn in the liquid-infiltration processed Nb-Sn wire. Small, equiaxed A15 grains across the fine reacted filaments of 0.2-1.0 μm thickness were revealed with the transmission electron microscopy studies. A uniform Sn concentration near the stoichiometry was found in the A15 region. High inductive T c s of 17.9K with sharp transition widths ( c s of 104A/cm2at 19T and 4.2K were achieved. Mechanical properties of the reacted wire are no worse than those of typical commercial bronze-process Nb 3 Sn conductors, and e irrev is slightly higher.

Superconducting sextupole correction coil operating in persistent mode

LBL-17634 Lawrence Berkeley Laboratory UNIVERSITY OF CALIFORNIA Accelerator & Fusion Research Division Presented at the Applied Superconductivity Conference, San Diego, CA, September 9-13, 1984 SUPERCONDUCTING SEXTUPOLE CORRECTION COIL OPERATING IN PERSISTENT MODE W. Gilbert, A. Borden, W. Hassenzah1, G. Mortiz, and C. Taylor September 1984 Prepared for the U.S. Department of Energy under Contract DE-AC03-76SF00098

A 6.4 Tesla Dipole Magnet For the SSC

A design is presented for a dipole magnet suitable for the proposed SSC facility. Test results are given for model magnets of this design 1 m long and 4.5 m long. Flattened wedge-shaped cables (“keystoned”) are used in a graded, two-layer “cos θ” configuration with three wedges to provide sufficient field uniformity and mechanical rigidity. Stainless steel collars 15 mm in radial depth, fastened with rectangular keys, provide structural support, and there is a “cold” iron flux return. The outer-layer cable has 30 strands of 0.648 mm diameter NbTi multifilamentary wire with Cu/S.C. = 1.8, and the inner has 23 strands of 0.808 mm diameter wire with Cu/S.C. = 1.3. Performance data is given including training behavior, winding stresses, collar deformation, and field uniformity.

The Effect of High Compressive Stress on the Critical Current in Multistrand Nb3Sn Conductors

The materials in superconducting accelerator magnets are subjected to high local stresses even though the coils are relatively small. A cross section of the 4.2-T Fermilab doubler dipole is shown in Fig. 1. The maximum compressive stress due to Lorentz forces is 9300 psi (64 MPa). Because the coils are precompressed during fabrication, the maximum stress in the windings is increased to about 12,000 psi (83 MPa) or higher. The NbTi conductors used today withstand this force with no apparent degradation.