Autopsy results of failed lithium collection lenses at the FNAL antiproton source

A lithium lens focusing device is used at the FNAL antiproton source to collect antiprotons immediately downstream of the production target. Recently developed methods of removing lithium from old collection lens devices have enabled the dissection and autopsy of several failed lenses. Examination reveals longitudinal fatigue cracks in the titanium alloy (6Al-4V) cooling jackets. A finite element analysis to estimate stress intensity factors expected in the cooling jackets is presented and compared to the crack propagation and fracture toughness thresholds for Ti 6Al-4V. Results presented indicate that crack initiation and propagation at the currently estimated service loads are unlikely without additional material degradation mechanisms at work.