AC Losses in Multifilamentary Superconducting Composites for Levitated Trains Under AC and DC Magnetic Fields

Abstract

High-speed trains using superconducting magnets for levitation are presently in the planning and developmental stages in several countries. The superconductor used in such magnets is a composite consisting of normal metal matrix such as copper or aluminum with many superconducting filaments embedded in the matrix. The superconducting composite is influenced not only by a relatively strong dc magnetic field, but also by an ac field resulting from irregularities in the tracks or “heaving motions” of the train. The ac field produced in this manner has amplitudes below several hundred Oe and frequencies from a few Hz to several hundred Hz. To date, there have been several studies which have investigated the ac losses in superconducting composites under ac fields of relatively large amplitudes suitable for superconducting accelerators, but few reports have been presented covering the ac losses in the range mentioned above. This presentation reports on the ac loss measurements and the theoretical investigations which have been made on twisted and untwisted superconducting composites for use in levitated trains.