IEC 61788-4:2011 covers a test method for the determination of the residual resistance ratio (RRR) of composite superconductors comprised of Nb-Ti filaments and Cu, Cu-Ni or Cu/Cu-Ni matrix. This method is intended for use with superconductors that have a monolithic structure with rectangular or round cross-section, RRR less than 350, and cross-sectional area less than 3 mm2. All measurements are done without an applied magnetic field. The method described in the body of this standard is the "reference" method and optional acquisition methods are outlined in Clause A.3. This third edition constitutes a technical revision which adds two new annexes: "Uncertainty considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for NbTi" (Annex C). Copper is used as a matrix material in multifilamentary superconductors and works as an electrical shunt when the superconductivity is interrupted. It also contributes to recovery of the superconductivity by conducting heat generated in the superconductor to the surrounding coolant. The cryogenic-temperature resistivity of copper is an important quantity, which influences the stability of the superconductor. The residual resistance ratio is defined as a ratio of the resistance of the superconductor at room temperature to that just above the superconducting transition.
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