The application of high temperature superconductors to Maglev magnets

Abstract

Abstract The application of High Temperature Superconducting (HTS) coils is being considered for a Grumman designed iron-core magnets for a Maglev system based on the Electromagnetic Suspension (EMS) concept. The basic magnet unit consists of a U-shaped iron-core carrying a Superconducting (SC) coil around its back leg and a normal conducting (NC) control coil around each pole. The open side of the U-core is bridged by an iron rail with a large airgap between the poles and the rail. Grumman has designed, fabricated and is presently testing such an electromagnet utilizing a Low Temperature Superconducting (LTS) coil. An iron core magnet requires fewer ampere-turns than an equivalent air core magnet. Since most of the flux remains constrained in the iron core, the field experienced by the superconducting winding is approximately one-tenth of the field experienced by the windings of an air-core magnet. These two characteristics make the iron core magnet an ideal candidate for employing HTS coils. Our preliminary analysis has suggested that a functional Maglev magnet could be successfully built using currently available HTS conductors (Bi2212 or Bi2223). The HTS coil will be conductively cooled with a cryocooler and could be tested at temperatures of 10 K and higher. Our current test magnet is a 2 3 scale model of the magnet specified in Grumman's 1992 Concept Definition Study for the National Maglev Initiative. The magnet employs an LTS coil which operates in quasi-steady-state mode, i.e. the current changes in the SC coil are limited to less than 1 Hz rate. The NC control coils respond to faster changes occurring up to ~10 Hz. The HTS coils are likely to be more tolerant of a.c. heating due to their higher operating temperature and more favorable material thermal properties at these temperatures. These considerations led us to believe that a HTS coil could be designed to operate with 10 Hz current oscillations. If this could be confirmed by the planned tests then it might eliminate the NC control coils in the magnet. The cost and complexity of the EMS magnet system will be significantly reduced. This paper describes design of HTS magnets and discusses tests to be performed on them. Some of this testing will be completed before the end of 1994.