Diameter Quality Control of Nb ₃Sn Wires for MQXF Cables in the USA

During this project, the 0.850 ± 0.003 mm Nb₃Sn wires for the low-beta quadrupole magnets 'MQXFA' procured for the U.S. LHC Accelerator R&D Program (LARP) and the U.S. High Luminosity LHC Accelerator Upgrade Project (US HL-LHC AUP, or simply AUP) are received at Lawrence Berkeley National Laboratory (LBNL). There, the wires are respooled and then fabricated into Rutherford cables for winding coils. As part of the quality control program, AUP obtains from the wire manufacturer values of the maximum, average, minimum, and standard deviation of the two orthogonal axes, which are assessed prior to shipment approval. At LBNL, a dual-axis optical micrometer is used to measure the wire diameter of each spool every ~30 cm prior to cabling. This helps decide whether wire pieces with abnormal diameters should be distributed across the cable cross section, in order to improve cable parameter quality and mechanical stability consistency. This paper presents: 1) diameter data of LARP cables and of the first AUP cables made using wires acquired under LARP; 2) our deviation acceptance/rejection justification; and 3) the impact of wire diameter statistics on cable fabrication.