Comparison and Analysis of Twist Pitch Length Test Methods for ITER Nb3Sn and NbTi Strands

TL;DR

This paper compares various test methods for measuring the twist pitch length and direction of Nb3Sn and NbTi strands used in ITER magnets, analyzing their accuracy and recommending suitable techniques for verification.

Contribution

It introduces a comprehensive comparison of twist pitch measurement methods, proposing optimized techniques for ITER strand verification.

Findings

Several test methods are described and compared.

Accuracy and uncertainty of each method are analyzed.

Recommended measurement methods are proposed for ITER strands.

Abstract

A twisted multifilamentary structure is needed for Nb3Sn and NbTi strands to be used in the International Thermonuclear Experimental Reactor (ITER) magnets. As important parameters for the superconducting strands design and production, the twist pitch length and direction of strands must meet the requirements according to ITER Procurement Arrangement (PA) and this must be verified. The technical requirements are 15mm+/-2mm for twist pitch length and right hand twist for direction. The strand twist pitch and the twist direction can be measured on straight sections of strand, which is recognized by the repetition of filament bundles or by the angle of the filaments. Several test methods and results are described and compared in this paper. The accuracy, uncertainty and feasibility of different methods are analyzed and recommended measurement methods are proposed for ITER strands verification.