Previously reported temperature increases above 4.2 K in an immersion geometry in liquid 4He at fields >19 T have been verified and examined. Magnetic forces (B dB/dx) above a threshold level of ∼21 T2/cm were found to trap 4He bubbles near the center of the field. Significant heat input to the region (from conduction, radiation, etc.) can then raise the temperature by as much as several kelvins. Thus, measurements at very high B dB/dx should not depend on vapor pressure thermometry. To assure temperature accuracy and stability, the temperature should be measured directly at the sample position.

Temperature anomalies observed in liquid 4He columns in magnetic fields with field–field‐gradient products >21 T2/cm

Far from being scarce, the rare earth elements are prevalent in the earth’s crust and common in diverse industrial applications. From their humble beginnings as lighter flints, lanthanide metals have progressed to leading-edge applications in super-conductors and hydrogen storage alloys. They are widely used in iron and steel production, and their physical properties are being exploited in high-strength permanent magnets and magneto-optic data recording.

Metallurgical Applications of Yttrium and the Lanthanides

This paper gives a brief historical review of the development of high magnetic fields and high field superconductors including brief summaries of the early developments of high magnetic fields and the Francis Bitter National Magnet Laboratory (FBNML). The start of the first revolution (when large critical currents in Nb/sub 3/Sn were observed in high magnetic fields) and the development of practical superconductors are outlined in parallel with selected applications developed at Lincoln Laboratory, FBNML, and other departments at MIT. Many large scale superconductor applications, supported by governments, are reviewed briefly; although many models and preliminary designs were completed, a number of US initiatives for large superconducting systems were discontinued. This summary of high-field superconducting applications is followed by an outline of the development of the highest field superconducting materials, comments on the false reports of high T/sub c/ superconductors which appeared throughout the 1970s, and the start of the second revolution (when the high T/sub c/ oxides were reported). >

High-field magnets and high-field superconductors

Alternative approaches for producing stationary (nondestructive) pulsed fields above available dc fields are considered. Multilayer, high strength, wire-wound, steel reinforced, Cu/Nb metal-matrix microcomposite pulsed magnets achieving up to 68.4 T for a 5.6 ms half-period were developed. Such magnets are the preferred technology for further development. Operation for experiments in a user mode is reviewed. Higher fields and longer pulse times can be achieved as the microcomposite is developed. These new materials will advance dc and pulsed field technology which are materials-limited and have relevance to many other applications requiring high strength, and high electrical and/or thermal conductivity.

Experiments with strong pulsed magnetic fields produced by Cu/Nb microcomposite wire-wound magnets

Ferromagnetic polycrystalline dysprosium cores made from a rod-billet by hydropressing were used in concentrators to contribute up to 7.6 T in the gap between two conical end pieces. In each end piece the plane of easy magnetization is inclined at an angle to the central axis of the concentrator. Because of its magnetic characteristics a concentrator with textured dysprosium exceeds the known concentrators made from rare-earth materials. With this concentrator in a superconducting solenoid a total field of 21.2+or-0.2 T was obtained. >

A magnetic concentrator, made from textured dysprosium, contributed up to 7.6 T

A dc magnetic field of 33.6±0.3 T was produced in a hybrid magnet whose central field was enhanced by a 3.5 T contribution from holmium pole pieces. The working (sample) volume was a 2‐mm gap between the 19‐mm‐diam×32‐mm‐long pole pieces tapered to 12‐mm‐diam faces. The magnetic field was measured with high‐field/low‐temperature Hall‐effect sensors whose reproducibility and linearity made practical an extrapolation technique for fields above 30 T. Three superconducting samples with previously measured upper critical fields were used as calibration check points.

L. G. Rubin

Papers

33.6 T dc magnetic field produced in a hybrid magnet with Ho pole pieces