Magnetic properties of cerium doped oxide glasses below 1 K

Temperature dependences of the magnetic susceptibilities from 1 K >T > 0.015 K have been determined as functions of cerium concentration for a number of cerium doped borate and silicate glasses. The magnetic susceptibility of all glasses was found to obey a Curie-Weiss Law in the temperature range studied and the Curie and Curie-Weiss constants, λ and θ respectively, were found to scale linearly with cerium composition independent of the glass type. Magnetic ordering temperatures were estimated from magnetic cooling studies. Contrary to the similarity in the glasses above 0.015 K, it was observed that borate glasses order systematically lower in temperature than silicate glasses for given cerium concentrations.     

Navy Programs in Superconducting Technology

A review of U.S. Navy efforts in superconducting technology is given. Programs include development of superconducting magnets for motors in ship propulsion systems and to generate magnetic moments in mine sweeping systems. A program to develop superconducting quantum interference devices (SQUIDs) for detection of mines and buried ordnance has successfully been demonstrated. In electronic applications, superconducting filters, resonators, and antennae are being developed for radar, communication, and space systems. Concurrent with these superconductivity programs are efforts to improve the efficiency, reliability, and affordability of refrigeration systems.     

High temperature superconductivity: Magnets and applications of naval interest

The Navy has had a long standing interest in power applications of superconductivity. Recent advances in high temperature superconducting (HTS) materials have caused the Navy science and technology community to assess the potential of HTS magnets for Naval applications. A program has begun to test HTS conductors and magnets in order to determine realistic performance expectations from which to determine proper systems integration. This paper presents some early results of industrially produced HTS magnets and discusses possible Naval applications. Speculative application toward magneto-hydrodynamic (MHD) propulsion is also discussed-specifically with respect to HTS materials.     

Magnetohydrodynamic ship propulsion with superconducting magnets

The feasibility of magnetohydrodynamic (MHD) ship propulsion using superconducting magnets is reviewed in light of recent advances in high-temperature superconductivity. The scaling relations for the electrical and hydraulic efficiencies of MHD pump-jets show that overall efficiencies >50% are feasible at speeds of 40 knots and higher provided that magnetic fields >5T can be maintained over volumes of the order of 100 m³. The development of large-scale electrical machinery and magnets using the high-temperature superconductors now under development could make it practical to construct submersibles for high-speed and silent operation. Low-speed tankers for movement of bulk cargo would be efficient with even lower fields.