a b s t r a c tThe anticipated performance of calorimeter crystals in the environment expected after the planned High-Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN has to be well understood, before informed decisions can be made on the need for detector upgrades. Throughout the years of running at the HL-LHC, the detectors will be exposed to considerable fluences of fast hadrons that have been shown to cause cumulative transparency losses in Lead Tungstate scintillating crystals. In this study, we present direct evidence of the main underlying damage mechanism. Results are shown from a test that yields a direct insight into the nature of the hadron-specific damage in Lead Tungstate calorimeter crystals exposed to 24 GeV/c protons.

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Abstract-The phase transformations that occur during the reaction heat treatment (HT) of Nb 3 Sn superconductors depend on the overall elemental composition of the strand subelements. In the case of modern high strands with a relatively low Cu content, liquid phases are present during large temperature intervals and phases that can be detrimental for the microstructural and microchemical homogeneity of the fully reacted strand are formed. We report synchrotron X-ray diffraction measurements during in-situ reaction HT of a state-of-the-art high Nb 3 Sn internal tin strand. In this strand, Cu 3 Sn is formed upon Cu 6 Sn 5 decomposition at 415 C, a Sn-rich ternary Cu-Nb-Sn phase is detected in the approximate temperature interval 345 C-575 C, and NbSn 2 is present in the temperature interval 545 C-630 C. The formation of voids in the strand subelements has been monitored by synchrotron microtomography during in-situ reaction HT.

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