Saturday, 3F-01, 8:30-8:40

Losses in YBCO Strands and Quench in YBCO Coils

Michael Sumption

M. Majoros, and E. W. Collings

LASM, MSE, The Ohio State University, Columbus, OH 43210, USA

Transport and external field losses were measured for YBCO strands. Various kinds of IBAD YBCO coated conductors with Cu stabilizing layer of different thickness added either on one side only, or on both sides as well as at the edges have been measured in an applied magnetic field up to 140 mT (peak) in frequency range of 50 - 200 Hz. Measurements of striped conductors are also shown for conductors striped along 30 cm segments placed in uniform external fields. Computationally, different configurations of multifilament geometry with filaments embedded in ferromagnetic materials of different thickness and different magnetic permeability have been modelled in the past and a reduction of transport ac loss predicted by FEM calculations. In the present work we propose a much simpler and more practical method for magnetic decoupling of the strands in YBCO coated conductors. This method consists in filling just the inter-filamentary space between the filaments by a ferromagnetic material, rather than embedding the filaments completely. Calculations of transport ac loss reduction were performed using a finite element method where it was seen that the present method gives almost the same transport ac loss reduction as completely embedding the filaments in a ferromagnetic material. In the area of thermal propagation and quench, a series of small solenoidal YBCO coils have been made and measured for thermal conductivity and for quench propagation both along the tape length as well as in the radial direction. Results for mylar insulation are compared to those from a very thin ZnO insulation. Radial thermal conductivities, in the neighborhood of 2-3 W/m^-1K^-1, were somewhat higher with the ZnO insulation, mostly because of its reduced thickness, while winding J_e for these coils was increased significantly with the ZnO insulation. It was found for the given coil geometry, the large aspect ratio of the YBCO coated conductors caused the quench to propagate predominantly in a radial direction, in the sense that the heat quenching a given layer of conductor came from the winding directly under it, even though the radial NZP was less than the longitudinal NZP.

Back to the Saturday Schedule.