IEC 61788-4-2020 pdf download.Superconductivity – Part 4: Residual resistance ratio measurement – Residual resistance ratio of Nb‑Ti and Nb 3 Sn composite superconductors.
This part of IEC 61 788 specifies a test method for the determination of the residual resistance ratio (RRR) of Nb-Ti and Nb 3 Sn composite superconductors with Cu, Cu-Ni, Cu/Cu-Ni and Al matrix in a strain-free condition and zero external magnetic field. This method is intended for use with superconductor specimens that have a monolithic structure with rectangular or round cross-section, RRR value less than 350, and cross-sectional area less than 3 mm 2 . In the case of Nb 3 Sn, the specimens have received a reaction heat-treatment.
2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60050-81 5, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity (available at: www.electropedia.org)
3 Terms and definitions For the purposes of this document, the terms and definitions given in IEC 60050-81 5 and the following apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 residual resistance ratio
RRR ratio of resistance at room temperature to the resistance just above the superconducting transition
Note 1 to entry: This note applies to the French language only.
Note 2 to entry: In this document for Nb-Ti and Nb 3 Sn composite superconductors, the room temperature is defined
as 293 K (20 °C), and the residual resistance ratio is obtained in Formula (1 ), where the resistance (
1 R ) at 293 K is divided by the resistance
2 R ) just above the superconducting transition.
4 Principle The resistance measurement both at room and cryogenic temperatures shall be performed with the four-terminal technique. All measurements are done without an applied magnetic field. The target relative combined standard uncertainty of this method is defined as an expanded uncertainty ( 2 = k ) not to exceed 5 %. The maximum bending strain induced during mounting and cooling the Nb-Ti specimen shall not exceed 2 %. The measurement shall be conducted in a strain-free condition or in a condition with allowable thermal strain for the Nb 3 Sn specimen.
5 Apparatus
5.1 Material of measurement mandrel or of measurement base plate Material of the measurement mandrel for a coiled Nb-Ti specimen or of the measurement base plate for a straight Nb-Ti or Nb 3 Sn specimen shall be copper, aluminium, silver, or the like whose thermal conductivity is equal to or better than 1 00 W/(m·K) at liquid helium temperature (4,2 K). The surface of the material shall be covered with an insulating layer (tape or a layer made of polyethylene terephthalate, polyester, polytetrafluoroethylene, etc.) whose thickness is 0,1 mm or less.IEC 61788-4 pdf download.