MODELLING AC LOSSES IN HIGH‐TEMPERATURE SUPERCONDUCTORS AS A NONLINEAR DIFFUSION PROCESS

Abstract

Ceramic superconductors experience losses when carrying alternating currents. A first step in an attempt to macroscopically model the loss mechanism is to consider the ac transport current in a ribbon that has a cross‐section of width much greater than thickness. To some extent high‐temperature superconductors behave in a way similar to type II superconductors in which the loss mechanism is described by the critical state model, where the current is assumed to flow with a constant critical density Jc and is independent of the magnetic flux density B and ∂B/∂t. The dominant mechanism is the irreversible motion of fluxoids due to their interaction with the pinning sites, resulting in a form of hysteretic loss that can be represented in macroscopic terms (in a system with only one component of magnetic field) as proportional to ∫HsdBa/T over a complete cycle of period T, where Hs is the surface magnetic field strength and Ba is the space average value of flux density. However, it is found that the high‐temperature materials exhibit strong flux creep effects, and so the critical state model may not provide a sufficient description. To find an alternative formulation it is necessary to consider the flux creep E‐J characteristic of the ceramic material. If a highly nonlinear expression for the resistivity ? can be found, it may be possible to model the flux and current behaviour as a diffusion process.

Citation

Stoll, R.L., Mahdi, A.E. and Sykulski, J.K. (1995), "MODELLING AC LOSSES IN HIGH‐TEMPERATURE SUPERCONDUCTORS AS A NONLINEAR DIFFUSION PROCESS", COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, Vol. 14 No. 4, pp. 269-273. https://doi.org/10.1108/eb051955