Transport Current Measurement of I_c(T, B, ?) and n(T, B, ?) for a Bulk REBCO Superconductor

Bulk rare-earth barium cuprate (REBCO) high temperature superconductors are attractive for many electromagnetic applications due to their ability to support large current densities and trap large magnetic fields. At present, magnetisation techniques are the predominant method of measuring the critical current density, Jc, for bulk superconductors, due to the abundance of measurement devices and ease of sample preparation and measurement. However, this approach does not provide direct access to measurements of magneto-angular anisotropy of Jc nor n-value. By contrast, transport current techniques allow direct measurement of the full thermo-magneto-angular dependence of both Ic and n, but limited data is available for REBCO bulks, due to the difficulties of sample preparation and measurement. This work introduces a reproducible method to prepare a single-grain bulk GdBCO-Ag superconductor for transport current characterisation, and presents measured data for both Ic and n that has been obtained over a broad parameter-space. The measured n-values are lower than is commonly assumed, with typical n-values at 77 K being in the range of 10 to 14. An accurate value of n is required when computationally modelling transient effects.