Design of a 10 picosecond Time of Flight Detector using Avalanche Photodiodes

We describe a detector for measuring the time of flight of forward protons at the Large Hadron Collider (LHC) up to and beyond the full instantaneous design luminosity of 1034 cm-2 s-1. Our design is based on deep diffused, high gain avalanche photodiodes (APDs) which give a signal of ~6000 e when traversed by 7 Teravolt protons. We observe pulse risetimes of 650 psec and a pulse width of 5 nsec and calculate a time resolution of ~10 psec and a maximum count rate of >100 Mhz.