The development of vacuum phototriodes for the CMS electromagnetic calorimeter

A new generation of vacuum phototriodes (VPTs) has been developed for application in the end-cap sub-system of the crystal electromagnetic calorimeter (ECAL) for the CMS experiment at the CERN Large Hadron Collider (LHC). These VPTs must operate with high reliability for at least 10 years in an extremely hostile environment. Results are presented from an extensive programme of tests, demonstrating that the required properties of significant gain in a 4 T magnetic field, resistance to ionising radiation, and stable operation with large photocurrents can all be satisfied in a robust, compact, inexpensive device.