BNL Irradiation Damage Studies of the Metal Matrix Composite Mo-GR Considered for High Luminosity LHC Collimator Upgrade

A comprehensive experimental/analytical effort on the resilience of Mo-GR metal matrix composite to high energy proton beam irradiation combined with elevated temperatures has been undertaken at BNL on behalf of the CERN LHC Collimation effort as part of an effort to identify novel materials that will exhibit optimal performance in the high luminosity LHC upgrade. While the Mo-Gr composite was one of the four (4) different materials or composites (Mo, Glidcop, Cu-CD and Mo-Gr) that constituted the High Luminosity LHC collimation material campaign, this report focuses solely on Mo-GR with some reference to its constituents Mo and graphite (graphite studied in previous research or irradiation campaigns along with the carbonfiber composites). The multi-faceted study on Mo-GR (one of several different alloys and matrices) performed at BNL included the following stages: Irradiation damage phase using the 200 MeV proton beams of the BNL Linac and the BLIP target beamline. Specifically, Mo-GR samples encapsulated under vacuum in special capsules were exposed to direct protons as part of a multi-capsule, multi-material irradiation array. The long-term irradiation of ~8 weeks resulted in an accumulated fluence at the Mo-GR of ~10²¹ p/cm². The irradiation was conducted in two sessions (RUN 2013 and RUN 2014 of the BLIP operations in tandem with isotope production). Irradiation damage experiments using spallation neutrons at the BLIP beamline generated by 118 MeV protons that interact with and are stopped by an array of isotope producing targets. The Mo-GR capsule combined the effects of short-term proton irradiation and the effects of the mixed irradiating spectrum. Spallation-induced irradiation of Mo-GR at sub-zero temperatures utilizing the mixed field generated by spallation of 28 MeV protons of the BN Tandem on Mo targets Gamma spectrum analysis of the heavily irradiated Mo-Gr to enable the correlation of predicted isotope profile from Mo-Gr by transport codes and therefore the utilization of the validated transport code in other aspects of the damage induced on Mo-Gr by irradiation.