IEC 61788-4-2020 pdf free download – Superconductivity – Part 4: Residual resistance ratio measurement – Residual resistance ratio of Nb‑Ti and Nb 3 Sn composite superconductors.
This part of lEC 61788 specifies a test method for the determination of the residual resistance
ratio (RRR) of Nb-Ti and Nb 3Sn composite superconductors with Cu，Cu-Ni,Cu/Cu-Ni and Almatrix in a strain-free condition and zero external magnetic field.This method is intended foruse 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 caseof Nb 3Sn, the specimens have received a reaction heat-treatment.
2Normative references
The following documents are referred to in the text in such a way that some or all of their contentconstitutes requirements of this document. For dated references, only the edition cited applies.
For undated’ references,the latestedition of the referenced document(including anyamendments) applies.
IEC 60050-815,International Electrotechnical Vocabulary (IEV) – Part 815:Superconductivity(available at: www.electropedia.org)
3Terms and definitions
For the purposes of this document, the terms and
definitions given in lEC 60050-815 and the
following apply.
ISO and lEC maintain terminological databases for use in standardization at the followingaddresses:
.IEC Electropedia: available at http://www.electropedia.orgl
-Iso Online browsing platform: available at http://www.iso.orglobp
3.1
residual resistance ratioRRR
ratio of resistance at room temperature to the resistance just above the superconductingtransition
Note 1 to entry: This note applies to the French language only.
Note 2 to entry: In this document for Nb-Ti and NbsSn composite superconductors，the room temperature is definedas 293 K (20 C), and the residual resistance ratio is obtained in Formula (1), where the resistance ( Ri) at 293 Kisdivided by the resistance ( R2 ) just above the superconducting transition.
4Principle
The resistance measurement both at room and cryogenic temperatures shall be performed withthe 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 expandeduncertainty ( k = 2 ) not to exceed 5 %.
The maximum bending strain induced during mounting and cooling the Nb-Ti specimen shallnot exceed 2 %.The measurement shall be conducted in a strain-free condition or in a condition
with allowable thermal strain for the Nb3Sn specimen.
5Apparatus
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 Nb3Sn specimen shall be copper,aluminium，silver，or the likewhose thermal conductivity is equal to or better than 100 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 layermade of polyethylene terephthalate，polyester，polytetrafluoroethylene,etc.) whose thicknessis 0,1 mm or less.
5.2 Diameter of the measurement mandrel and length of the measurement base plate The diameter of the measurement mandrel shall be large enough to keep the bending strain of the specimen less than or equal to 2 % for the Nb-Ti specimen. The Nb 3 Sn specimen on a base plate shall be measured in a strain-free condition or a condition with allowable thermal strain.
The measurement base plate shall be at least 30 mm long in one dimension.
5.3 Cryostat for the resistance ( R 2 ) measurement
The cryostat shall include a specimen support structure and a liquid helium reservoir for measurement of the resistance R 2 . The specimen support structure shall allow the specimen, which is mounted on a measurement mandrel or a measurement base plate, to be lowered into and raised out of a liquid helium bath. In addition, the specimen support structure shall be made so that a current can flow through the specimen and the resulting voltage generated along the specimen can be measured.IEC 61788-4 pdf download