Magnet Replica by High Tc Superconductors
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MAGNET REPLICA BY HIGH Tc SUPERCONDUCTORS R. WEINSTEIN, IN-GANN CHEN, J. LIU, AND D. PARKS, Institute for Beam Particle Dynamics and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204-5506 ABSTRACT A study of magnetic field trapping phenomenon in oriented grain YBa 2 Cu 3 07_x samples produced by liquid phase processing has been conducted. The magnetic field reproduced from the parent magnetic field allows the production of "magnet replicas", which can be used in various instruments when large magnetic field is needed constant in time. This paper reports the magnetic field trapping capability and uniformity observed in these oriented grain samples. The feasibility of building large and uniform magnetic field by assembling small SC specimens has also been explored. INTRODUCTION When a type II superconductor (SC) is magnetized, the magnetic field may be trapped as the external field source is removed. This "incomplete Meissner Effect" associated with the type II SCs allows the production of magnet replicas, which are bulk SC with persistent magnetic field reproduced from the parent magnetic field. The field remains in place due to pinning and is an excellent copy of the parent field. This "magnet replica" concept has been demonstrated on low Tc SCs with transverse dipole field up to 2.2 T at 4 K by a group at SLAC in the 70's [1-3]. The application of high Tc SCs on magnet replicas has several advantages including low cost, low weight, interchangeability, etc [4]. Due to fact that no external current is required to maintain the trapped persistent field, magnetic replica devices can be assembled from separate small and simple geometric specimens. No SC wire or tape fabrication is needed to make magnetic replica devices. In addition, the extremely large Hc2 of high Tc SCs extends the theoretical limitation on the maximum field to very high values. Previous studies have shown that significantly higher critical current density can be obtained in YBa2Cu3O7-x samples with large grain, well aligned crystalline structures [5,6]. Intragranular Jc in the range of 104 Amp/cm 2 at 77 K and low field have been reported [5-7]. The magnetic field trapping capability and uniformity are two important parameters in judging the feasibility of the SC samples toward this application. The effect of assembling more than one sample together, in "lamination" and "mosaic" patterns on the field trapping capability is studied. In this report grain-oriented YBa2Cu3O7-x samples in disc shapes are used with dimensions in the range about 10 mm x 15 mm x 3 mm. These samples were produced by Salama et al [6] via liquid phase process method. EXPERIMENTAL PROCEDURE The SC sample is placed in a magnetic field, Bo, followed by cooling to 77 K (field cool). After the external field is removed, a portion of the magnetic field is trapped in the SC. The trapped field, BT, is measured by a near-by Hall effect probe (F.W. Bell 921-A & 921-T Hall generators with active area 0.2
Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials R
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