BS EN IEC 61788-27:2025

1   Scope

  This part of [IEC 61788](/search?q=IEC%C2%A061788)
   specifies a test method for the  twist  pitch measurement of Nb-Ti/Cu and Nb-Sn/Cu composite superconductors by an untwisting
  method. 
The test method is applicable to Nb-Ti/Cu and Nb-Sn/Cu composite superconducting wires
  with monolithic structures, which have either a round cross section with a diameter
  ranging from 0,2 mm to 2 mm or a rectangular cross section that is equivalent in area
  to the round cross-sectional wires. These wires possess a filament diameter ranging
  from 6 µm to 200 µm, a  twist  pitch between 5 mm and 50 mm, and a matrix of copper or copper alloy. This document
  uses nitric acid to remove the matrix (copper or copper alloy), so the surface of
  the composite superconducting wire can be plated with a material that is dissolvable
  by nitric acid. 
Though uncertainty can increase, the method can apply to Nb-Ti/Cu or Nb-Sn/Cu composite
  superconducting wires when the parameters of cross-sectional area, filament diameter
  and  twist  pitch are out of the limit. 
The test method specified in this document is expected to apply to other types of
  composite superconducting wires after some appropriate modifications.