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

摘要

A twisted multifilamentary structure is needed for Nb3Sn and NbTi strands tobe 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 requirementsaccording to ITER Procurement Arrangement (PA) and this must be verified. Thetechnical requirements are 15mm+/-2mm for twist pitch length and right handtwist for direction. The strand twist pitch and the twist direction can bemeasured on straight sections of strand, which is recognized by the repetitionof filament bundles or by the angle of the filaments. Several test methods andresults are described and compared in this paper. The accuracy, uncertainty andfeasibility of different methods are analyzed and recommended measurementmethods are proposed for ITER strands verification.