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The US LHC Accelerator Research Program is constructing prototype interaction region quadrupoles as part of the US in-kind contribution to the Hi-Lumi LHC project. The low-beta MQXFA Q1/Q3 coils have a 4-m length and a 150 mm bore. The design was previously validated on short, one meter models (MQXFS) developed as part of the longstanding Nb3Sn quadrupole R&D by LARP in collaboration with CERN. In parallel, facilities and tooling are being developed and refined at BNL, LBNL, and FNAL to enable long coil production, assembly, and cold testing. Long length scale-up is based on the experience from the LARP 90-mm aperture (TQ-LQ) and 120-mm aperture (HQ and Long HQ) programs. A 4-m long MQXF practice coil was fabricated to verify procedures, parts, and tooling. In parallel, the first complete prototype coil (QXFP01a) was fabricated and assembled in a long magnetic mirror, MQXFPM1, to provide early feedback on coil design and fabrication following the successful experience of previous LARP mirror tests. [ABSTRACT FROM PUBLISHER]

We analyzed the ITER TFEU5 cable-in-conduit conductor (CICC) after the full SULTAN conductor qualification test in order to explore whether Lorentz force induced strand movement inside the CICC produces any fracture of the brittle Nb3Sn filaments. Metallographic image analysis was used to quantify the change in void fraction of each sub-cable (petal); strands move in the direction of the Lorentz force, increasing the void space on the low force side of the CICC and producing a densification on the high force side. Adjacent strand counting shows that local increases in void space result in lower local strand-strand support. Extensive metallographic sampling unambiguously confirms that Nb3Sn filament fracture occurred in the TFEU5 CICC, but the filament fracture was highly localized to strand sections with high local curvature (likely produced during cabling, where strands are pivoted around each other). More than 95% of the straighter strand sections were free of filament cracks, while less than 60% of the bent strand sections were crack free. The high concentration of filament fractures on the tensile side of the strand-strand pivot points indicates that these pivot points are responsible for the vast majority of filament fracture. Much lower crack densities were observed in CICC sections extracted from a lower, gradient-field region of the SULTAN-tested cable. We conclude that localized filament fracture is induced by high Lorentz forces during SULTAN testing of this prototype toroidal field CICC and that the strand sections with the most damage are located at the petal corners of the high field zone. [ABSTRACT FROM AUTHOR]

NbTi strands to be used in four of the six ITER poloidal field (PF) coils, all the correction coils (CC) and all the superconducting feeder busbars are being produced in China. Short full-size qualification conductor (cabled and jacketed) samples have been developed at ASIPP and tested at CRPP. Single pinning mechanism parametrization for this Chinese strand (type S2) has been obtained using the Bottura scaling law. The determination of the scaling parameters using a Kramer-type regression method will be described. A comparison between the critical temperature at the operating current and field of a single strand as determined by the parametrization and the current sharing temperature (TCS) of a few conductor samples tested at the SULTAN facility will be made. The validity and limitation of the estimation will be discussed. The estimated TCS dependence on various (superconducting critical as well as geometric and volumetric) parameters will be assessed using the modelled critical surface. Errors propagated from critical current (Ic) measurements of the strands and parameter fitting, and other uncertainties, will be quantified. [ABSTRACT FROM AUTHOR]

The longitudinal and transverse cross-sectional microstructures of several internal tin Nb3Sn strands have been systematically investigated. The critical current densities of these strands were then correlated with their design parameters. It is observed that the occurrence of certain coarse grain structures is related to the location of the filaments with respect to the subelements as well as to the strand. Experimental evidence suggests that the existence of these coarse grains is related to Sn distribution during the early stages of the heat treatment. It is also noticed that some coarse grains have high aspect ratio features, confirming the need to study the longitudinal fracture surface. We report in this paper the observation of some unusual grain sizes and morphologies. It appears that, of the high-Sn content Nb3Sn conductors investigated in this paper, a strand's global composition has a weaker influence on the critical current density (Jc) than local and structural factors, such as the local Cu:Nb area ratio (LAR) and filament layout. [ABSTRACT FROM AUTHOR]

The bronze phase transformations during the heat treatment of two multifilamentary internal tin Nb3Sn wires for high field applications made by Luvata are investigated and compared with some model single core wires. Non-uniform bronze profiles, non-uniform Sn distributions in different bundles, and Sn concentration gradient inversion were observed. Their possible formation mechanisms and consequences are discussed in relation to crystal orientation, Ti addition and microstructure. Wire manufacturing processes such as wire drawing impart preferred orientations on the components. The effect of wire texture on Cu-Sn interdiffusion and non-uniform bronze formation was investigated and believed not to be the cause of the non-uniform bronze profiles. 3-dimensional X-ray microtomography is applied to explain the non-uniformity in different bundles by analyzing the porosity formed during reactive diffusion of the low-melting phases. Ti is often added as a ternary addition, either in the Sn core or as Nb-Ti. In the Luvata wires investigated, Ti is present in Sn as the intermetallic compound Ti6Sn5. Its dissolution through a ternary CuSnTi phase, possibly via reaction with Cu3Sn, has been observed. EDS mapping of the Ti distribution suggests that it is likely to be responsible for the inversion of the Sn concentration gradient. The potential advantage of adding Ti in Sn over using Nb-Ti alloy is discussed. Critical temperature measurements were performed to relate superconducting properties to the phase transformations, composition changes and non-uniform bronze formation. [ABSTRACT FROM AUTHOR]