W. Sampson

Superconducting Properties of Multifilamentary Nb3Sn Made by a New Process

A new processing method for producing multifilamentary A‐15 superconducting composite wires in a ductile matrix is described. Nb3Sn made in this way was found to have a critical temperature of 17.5 K and a critical current density of 7.5×105 A/cm2 at 40 kG when suitably heat treated. The composite conductor could be bent with a radius of 2 cm or greater without appreciable degradation of its current‐carrying capacity.

SUPERCONDUCTING PROPERTIES OF MULTIFILAMENTARY V3Ga WIRES

Multifilamentary superconducting V3Ga wires in a Cu–Ca solid‐solution matrix have been prepared. The superconducting critical temperature Tc and the critical current density Jc(H) are presented for wires with various heat treatments.

The effect of self field on the critical current determination of multifilamentary superconductors

In determining the short sample critical current of conductors of large cross section or high current density, the self-field produced by the transport current must be taken into account to obtain a true value for the critical current. A simple model calculation for determining this effect is described. Measurements on wires, cables, and monoliths show the validity and self-consistency of the procedures. >

High Field HTS R&D Solenoid for Muon Collider

This paper presents the goal and status of the high field High Temperature Superconductor (HTS) solenoid program funded through a series of SBIRs. The target of this R&D program is to build HTS coils that are capable of producing fields greater than 20 T when tested alone and approaching 40 T when tested in a background field magnet. The solenoid will be made with second generation (2G) high engineering current density HTS tape. To date, 17 HTS pancake coils have been built and tested in the temperature range from 20 K to 80 K. Quench protection, high stresses and minimization of degradation of conductor are some of the major challenges associated with this program.

Fabrication techniques and properties of multifilamentary Nb 3 Sn conductors

Various processing techniques for multifilamentary Nb 3 Sn and V 3 Ga are reviewed. The critical current of commercially produced Nb 3 Sn wires manufactured by both the bronze and external diffusion techniques are compared. Critical currents for in situ and powder processed Nb 3 Sn are also included. New developments which promise improvements in J c are discussed.

Second Generation HTS Quadrupole for FRIB

Quadrupoles in the fragment separator region of the Facility for Rare Isotope Beams (FRIB) will be subjected to very large heat loads (over 200 Watts) and an intense level of radiation (~10 MGy per year) into the coils of just the first magnet. Magnets made with High Temperature Superconductors (HTS) are advantageous over conventional superconducting magnets since they can remove these heat loads more efficiently at higher temperatures. The proposed design is based on second generation (2G) HTS which allows operation at ~50 K. 2G has been found to be highly radiation tolerant. The latest test results are summarized. The goal of this R&D program is to evaluate the viability of HTS in a real machine with magnets in a challenging environment where HTS offers a unique solution.

The effect of magnetic impurities and barriers on the magnetization and critical current of fine filament NbTi composites

It is known that the highest critical currents in fine-filament NbTi conductors are obtained when the filaments are closely spaced. However, the filaments in a composite with a high-parity copper matrix tend to be coupled via the proximity effect as the filament spacing is reduced leading to large magnetization at low fields. To reduce the proximity coupling, trial billets of NbTi were fabricated with Cu-30% Ni matrix, Cu-0.5% Mn matrix and one with a Ni barrier around the filaments. Wires drawn from these billets have shown that this interfilament coupling can be suppressed for very-small filament separations. A full-sized commercial billet with Cu-0.5% Mn matrix demonstrated that high-critical-current-density conductors with filament size approximately 1-5 mu m can be fabricated which show no interfilament coupling at low fields. >

Importance of spacing in the development of high current densities in multifilamentary superconductors

Abstract It has been shown that by reducing the spacing between the filaments and keeping all the other factors the same, significant increases in current density can be achieved in conventional multifilamentary NbTi superconductors of the type used in the Colliding Beam Accelerator and Tevatron dipole magnet designs.

Critical current density of a superconducting copper‐base alloy containing Nb3Sn filaments

The critical current density Jc of 0.25‐mm Cu88.5Nb10.0Sn1.5 and Cu83.5Nb15.0Sn1.5 wires has been measured at 4.2 °K as a function of magnetic field H up to 100 kG. A typical value of Jc at H = 0 is ∼105 A/cm2 indicating that the critical current density of the Nb3Sn filaments is probably of the order of 106 A/cm2. Mechanical deformation such as bending some of the wire samples around a 1/2‐in.‐diam mandrel does not produce any significant degradation of Jc at H =40 kOe.

Nb 3 Sn dipole magnets

Multifilamentary Nb 3 Sn conductors suitable for use in accelerator magnets have been under development at BNL for a number of years. To date three one meter long dipole magnets have been constructed from braided conductor which had been reacted prior to winding. The first of these dipoles and the method of construction has been described in an earlier paper. The most recent magnet in this series was tested over the temperature range 4.2 K to 15 K using high pressure gas cooling. The maximum field 4.8 T, was achieved at 4.2 K. At higher temperatures the field decreased approximately linearly with temperature passing through 4.0 T at just under 8 K.